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87-9(MAY) (2000), 770-772
Multilayer assemblies incorporating the J-aggregate of 3,3'- disulfopropyl-5,5'-dichloro-thiacyanine dye were fabricated up to 50 layers by the alternate adsorption technique to examine their luminescence properties. Fluorescence spectra as well as fluorescence lifetime of multilayer assemblies remarkably depend on the number of layers. The result is interpreted in terms of the interaction between dye lavers within a limited distance, as well as the luminescence reabsorption effect. (C) 2000 Elsevier Science B.V. All rights reserved.

[81] Multilayered Supermolecular Structures Self-Assembled from Polyelectrolytes and Cyclodextrin Host-Guest Complexes

M. Dreja, I. T. Kim, Y. D. Yin and Y. N. Xia

J. Mater. Chem. 10(3) (2000), 603-605

Supermolecular multilayers with high levels of compositional and structural complexities have been fabricated with an example that involves formation of stable host-guest complexes from bolaamphiphiles and cyclodextrins, followed by sequential build-up of multilayered films by these complexes in combination with anionic polystyrene sulfonate polymer chains.

[82] Oriented Polyoxometalate-Polycation Multilayers on a Carbon Substrate

S. Q. Liu, Z. Tang, Z. X. Wang, Z. Q. Peng, E. K. Wang and S. J. Dong

J. Mater. Chem. 10(12) (2000), 2727-2733

In this paper, a new method of fabricating multilayers on a carbon substrate is presented. First, a uniformly charged carbon surface was prepared through molecular design. Then an ultrathin film consisting of layer-pairs of oppositely charged polymeric cationic poly(diallyldimethylammonium chloride) (PDDA) and silicotungstate, SiW12O404- (SiW12), was grown layer- by-layer onto the grafted carbon substrate using a molecular self-assembly technique and an electrochemical method. The technique allows one to prepare highly adherent, dense and smooth films of polyoxometalates with special properties. By combining cyclic voltammetry (CV) and X-ray (XR) reflectometry, it was determined that the average surface density of SiW12 was 2.10 x 10(-10) mol cm(-2), and the thickness increase per adsorption of PDDA-SiW12 was 1.7 +/- 0.2 nm, indicating that the amount of SiW12 anion per one layer adsorption corresponded to a monolayer coverage. Atomic force microscopy (AFM) was also used to examine the surface morphology and determine the grain size distribution and roughness for multilayer films. An increase in root-mean-square (RMS) surface roughness from 7 to 9 Angstrom was observed as the number of layer-pairs in the film increased from 2 to 6. FTIR results showed that the good stability of the multilayer films was due to Coulomb interactions between the SiW12 anion and the polymeric cations PDDA. Moreover, the multilayer films, in acidic aqueous solution, showed good electrocatalytic activity toward the reduction of NO2-, and the catalytic currents increased with increasing the layer numbers of SiW12 adsorption. These characteristics of the multilayer films might find potential applications in the field of sensors and microelectronics devices.

[83] Microencapsulation by Means of Step-Wise Adsorption of Polyelectrolytes

G. B. Sukhorukov, E. Donath, S. Moya, A. S. Susha, A. Voigt, J. Hartmann and H. Möhwald

J. Microencapsul. 17(2) (2000), 177-185

Step-wise adsorption of polyelectrolytes is used for the fabrication of micro- and nanocapsules with determined size, capsule wall composition and thickness. The capsule walls made of polyelectrolyte multilayers exclude high molecular weight compounds. Assembling of lipid layers onto these polyelectrolyte capsules prevents the permeation of small dyes. Encapsulation of magnetite nanoparticles is demonstrated and the features of these novel capsules are discussed.

[84] Plastic Behavior of Polyelectrolyte Microcapsules Derived from Colloid Templates

H. Baumler, G. Artmann, A. Voigt, R. Mitlohner, B. Neu and H. Kiesewetter

J. Microencapsul. 17(5) (2000), 651-655

The deformability and osmotic properties of hollow microcapsules were studied by means of the micropipette video microscopic technique. The microcapsules were prepared by consecutive multiple adsorption of the polyanion, poly (styrene sulphonate), and the polycation, poly( allylamine hydrochloride), onto melamine formaldehyde resin latex of 5 mu m diameter, which was decomposed after completing the coating by transferring to hydrochloric acid of pH 1.1. The polyelectrolyte microcapsules reacted to micropipette suction with plastic deformation. If lipids are added to the polyelectrolyte layers, the capsules cannot be visibly deformed by micropipette suction up to 10(4) N/m(2). However, plastic shrinking was observed if the stress was generated by the osmotic pressure of a sucrose solution of 10(6) N/m(2).

[85] Structural and Photophysical Properties of a Water-Soluble Porphyrin Associated with Polycations in Solution and Electrostatically-Assembled Ultrathin Films

P. G. Vanpatten, A. P. Shreve and R. J. Donohoe

J. Phys. Chem. B 104(25) (2000), 5986-5992

A water-soluble porphyrin, meso-tetra(4- sulfonatophenyl)porphyrin (TSPP), has been associated with two different polycations, poly(diallyldimethylammonium chloride) (PDDA) and poly(ethyleneimine) (PEI), to investigate the effects of polymer binding upon the TSPP structure and excited- state dynamics both in solution and in ultrathin (similar to 10- 30 Angstrom) films deposited on glass slides by electrostatic assembly. Association of the porphyrin with PEI intrinsically quenches the singlet state dynamics of TSPP, both in solution and in films, while quenching is observed upon association with PDDA only for high concentrations of porphyrins or in films where TSPP aggregates are observed. For PDDA:TSPP films without significant aggregate content, the fluorescence decay time (tau(1/e) similar to 5-6 ns) approaches that observed for monomeric or polymer-bound porphyrins in dilute solution (tau(1/ e) = 10.2 and 11.3 ns, respectively). However, rapid (< 1 ns) deactivation of the singlet states can be observed whenever appreciable aggregates are present, indicating that efficient energy transfer between the porphyrins leads to quenching at aggregate sites. A number of phenomenological observations regarding the presence of aggregates are presented. In particular, the extent of aggregation in the films depends on the concentration, pH, and temperature of the deposition solutions and also the age of the films, with older samples exhibiting reduced effects due to aggregation.

[86] Surface Texture of Poly(Styrenesulfonate Sodium-Salt) and Poly(Diallyldimethylammonium Chloride) Micron-Sized Multilayer Capsules - A Scanning Force and Confocal Microscopy Study

C. Y. Gao, S. Leporatti, E. Donath and H. Möhwald

J. Phys. Chem. B 104(30) (2000), 7144-7149

Ultrathin polyelectrolyte capsules fabricated by stepwise assembly of poly(styrenesulfonate Sodium salt) and poly(diallyldimethylammonium chloride) are examined by confocal laser scanning microscopy and scanning force microscopy. The capsule surface is composed of grains of 124 +/- 10 nm in diameter with a roughness of similar to 13 nm. These grains are formed by laterally segregated polyelectrolyte complexes. Osmotically and annealing-induced capsule swelling facilitated further grain segregation together with a capsule surface area increase. Incubation in salt solution induced capsule shrinking and grain aggregation.

[87] Luminescence Properties of the Mixed J-Aggregate of 2 Kinds of Cyanine Dyes in Layer-by-Layer Alternate Assemblies

N. Kometani, H. Nakajima, K. Asami, Y. Yonezawa and O. Kajimoto

J. Phys. Chem. B 104(41) (2000), 9630-9637

The layer-by-layer alternate assemblies incorporating two kinds of cyanine dyes have been fabricated by alternately adsorbing a cationic polyelectrolyte and anionic cyanine dyes on the quartz plate. A thiacyanine dye (dye I) was employed as the donor and two kinds of thiacarbocyanine dye having a meso-alkyl group-m- ethyl (dye II), in-methyl (dye III)-as the acceptor. The mole fraction of the acceptor in the mixed J-aggregate, chi, was varied from 0 to 1. It is confirmed that these dye combinations form the mixed J-aggregate in the alternate assemblies. From steady-state fluorescence spectra of the molecular assemblies, excitation energy transfer from the donor J-aggregate to the acceptor J-aggregate is observed, whose kinetics obeys the Stern-Volmer relationship. The experimentally determined rate constant of energy transfer, k(ET), is fairly large, indicating efficient energy transfer due to exciton migration through the donor J-aggregate. The relative fluorescence quantum yield and the fluorescence lifetime of the acceptor aggregate decrease with increasing chi, implying the considerable self-quenching of acceptor fluorescence. The relative change of the coherent size of the dye II aggregate has been estimated from the J-band line width and the radiative decay rate constant. It is found that the coherent size of the dye II aggregate is increased by a factor of 4-5 with increasing chi from 0.008 to 1.

[88] Photochemical Behavior and Formation of Surface-Relief Grating on Self-Assembled Polyion/Dye Composite Film

J. A. He, S. P. Bian, L. Li, J. Kumar, S. K. Tripathy and L. A. Samuelson

J. Phys. Chem. B 104(45) (2000), 10513-10521

Holographic surface relief gratings (SRGs) were fabricated on composite films assembled by electrostatic layer-by-layer (ELBL) deposition of a polyelectrolyte, poly(dimethyl diallylammonium chloride) (PDAC), and an azo dye, Congo Red (CR). Surface modulation and first-order diffraction efficiency of the SRG were found to increase with the thickness of the PDAC/CR films. Polarized absorption spectra indicated an oriented growth of CR on the PDAC film. Analysis of the film thickness, FTIR, and FT-Raman results confirmed that the electrostatic attraction between CR and PDAC, as well as the pi- pi interaction between CR chromophores resulting in the formation of J aggregates, lead to formation of PDAC/CR composite films. Photochemical changes of the PDAC/CR films after irradiation were investigated by W-vis absorption, FTIR, and FT-Raman spectroscopy. The results indicate that in addition to trans double left right arrow cis photoisomerization of CR in the composite film, an irreversible photochemical degradation of CR also simultaneously occurs. Recording SRG on PDAC/CR films by s- and p-polarized beams show different behavior compared to spin-coated films of polymers containing functionalized azo chromophores. Our results indicate that the volume collapse due to the photodegradation of CR in the polymeric matrix, as well as gradient force- induced migration due to trans double left right arrow cis isomerization cycling of CR contribute to the formation of SRG on the composite films. This approach provides a methodology to fabricate SRGs for optical information storage applications by using the facile ELBL technique to assemble commercially available azo dyes and polyelectrolytes.

[89] Surface Electronic-Properties of Self-Assembled, Oppositely Charged Macrocycle and Polymer Multilayers on Conductive Oxides

L. S. Li, R. Wang, M. Fitzsimmons and D. Q. Li

J. Phys. Chem. B 104(47) (2000), 11195-11201

Using the layer-by-layer self-assembly technique, we have deposited multilayer thin films on conductive indium tin oxide (ITO) surfaces by alternatively dipping ITO substrates in a polymer PDDA or poly(diallydimethylammonium) chloride solution and a macrocyle NiPc or nickel phthalocyanine solution. In addition to characterizing PDDA-NiPc systems with X-ray reflectometry and cyclic voltammetry, we monitored the growth of PDDA/NiPc multilayers on conductive oxides with Fourier transform infrared (IR) spectroscopy at an external grazing- angle reflection configuration. IR spectra with polarization perpendicular to the conductive ITO surfaces revealed vibration bands at 1227 and 1200 cm(-1) corresponding to salt bridges of - SO3-. . . Me2N+ = binding between PDDA and NiPc. An oscillation of the surface electronic potential was observed with a Kelvin Probe as the surface layer alternated between PDDA and NiPc. The average gap of the surface potential difference between NiPc and PDDA monolayers is about 400 mV. Oscillation of surface potential or work function is caused by the modulation in electron affinity of ITO due to the dipolar effect, generated by the highly charged layers of PDDA or NiPc.

[90] Reversal of Interfacial Dipole Orientation in Polyelectrolyte Superlattices Due to Polycationic Layers

J. L. Casson, D. W. Mcbranch, J. M. Robinson, H. L. Wang, J. B. Roberts, P. A. Chiarelli and M. S. Johal

J. Phys. Chem. B 104(50) (2000), 11996-12001

Repeated bilayers of a polycation and a polyanion were assembled by adsorption from their aqueous solutions. The polycations used were PEI (poly(ethylenimine)), PAH (poly(allylamine hydrochloride)), and generation 3.0 dendrimer (poly(propylenimine)). The polyanion was PAZO (poly[1-[4-(3- carboxy-4-hydroxyphenylazo)-benzenesulfonamido]-1,2-ethanediyl, sodium salt]). Second harmonic generation (SHG) and UV-vis spectroscopy were used to study the structure and formation of the superlattices. The linear increase in absorbance versus the number of bilayers suggested that a uniform and consistent amount of polymer adsorbed during each deposition cycle. The observation of a second harmonic (SH) signal from the film showed that the conjugated chromophores in the PAZO polymer were aligned with a net dipole. However, the SHG signal did not continue to increase as the number of bilayers was increased. On the basis of thorough studies of the UV and SH properties for each bilayer for 10 total bilayers, we propose that the asymptotic nonlinear optical response is due to loss of charge density on the polycation. The SH signal from multilayers terminated with the polycation is smaller than when PAZO is the terminal layer. We attribute this to a change in orientation of the dipole of the outermost PAZO chromophores at the interface of the PAZO and the terminal polycation layer. We also propose multilayer assemblies that will lead to self-assembled polyelectrolyte superlattices with a high nonlinear optical susceptibility.

[91] Adsorption of Charged Polymers

J. F. Joanny, M. Castelnovo and R. Netz

J. Phys. Condens. Matter 12(8A) (2000), A1-A7

We review some of the theoretical results that we have obtained recently on the adsorption of polyelectrolytes on surfaces of opposite charge. We consider two problems, the formation of polyelectrolyte multilayers and the formation of complexes between rigid polyelectrolytes and small spheres. For polyelectrolyte multilayers, the overcompensation of the adsorbing surface charge and the anchoring between consecutive layers are studied. For polyelectrolyte-sphere complexes, the wrapping of the polymer on the sphere is shown to occur continuously at low ionic strength and discontinuously at high ionic strength. The findings of some recent experiments are briefly compared with our results.

[92] Optical and Electrical Characterizations of Ultrathin Films Self-Assembled from 11-Aminoundecanoic Acid Capped TiO2 Nanoparticles and Polyallylamine Hydrochloride

T. Cassagneau, J. H. Fendler and T. E. Mallouk

Langmuir 16(1) (2000), 241-246

11-Aminoundecanoic acid capped titanium dioxide (capped-TiO2) nanoparticles (63 +/- 2 Angstrom total diameter and 20 - 24 Angstrom core diameter) and polyallylamine hydrochloride, PAK, have been layer-by-layer self-assembled onto precoated (by poly(diallyldimethylammonium chloride), PDDA, or PAH) substrates. The ultrathin S-PDDA(capped-TiO2/PAH)(n) (n = 5, 10, 15) films have been characterized by absorption and surface plasmon spectroscopies, cyclic voltammetry, and scanning force microscopy. AS-PDDA(capped-TiO2/PAH)(10) film coated by a layer of gold has been shown to function as a Schottky diode.

[93] Selective Ion-Transport Across Self-Assembled Alternating Multilayers of Cationic and Anionic Polyelectrolytes

L. Krasemann and B. Tieke

Langmuir 16(2) (2000), 287-290

Ultrathin membranes consisting of an alternating sequence of cationic and anionic polyelectrolytes were prepared by means of electrostatic layer-by-layer adsorption and investigated on their permeability for NaCl, Na2SO4, and MgCl2 in aqueous solution. It is demonstrated that the multi-bipolar structure of the polyelectrolyte membranes favors the separation of mono- and divalent ions by Donnan exclusion of the divalent ions. Various effects on the rate of ion permeation and the selectivity were investigated. Addition of salt to the polyelectrolyte solutions used for membrane preparation led to improved ion separation, while an increase of the pH had the opposite effect. Use of polyelectrolytes with high charge density also improved the ion separation. Especially good results were obtained if membranes containing polyallylamine (PAH) as the cationic polyelectrolyte were used. For 60 layer pairs of PAH/polystyrenesulfonate, for example, a separation factor a for Na+/Mg2+ up to 112.5 and for Cl-/SO42- up to 45.0 was found. The origins of the various effects are discussed in terms of different charge density and concentration of excess charges in the polyelectrolyte membrane.

[94] Fabrication of Photochromic WO3/4,4'-Bambp Superlattice Films

Z. H. Chen, Y. A. Yang, J. B. Qiu and J. N. Yao

Langmuir 16(2) (2000), 722-725

A layered superlattice WO3/4,4'-BAMBp self-assembled multilayer film has been fabricated onto aminopropylsilanated quartz or silicon substrate from transition-metal W compound and 4,4'- BAMBp solution using a polyelectrolyte approach. The superlattice film showed good photochromic properties. UV- visible spectra were employed to study the growth process and the aggregation of organic molecules. A well-ordered superlattice structure was identified by X-ray diffraction. A possible structural model was proposed according to UV-visible, XRD, and XPS spectra.

[95] In-Situ Determination of the Structural-Properties of Initially Deposited Polyelectrolyte Multilayers

G. Ladam, P. Schaad, J. C. Voegel, P. Schaaf, G. Decher and F. Cuisinier

Langmuir 16(3) (2000), 1249-1255

The buildup of the first layers of polystyrenesulfonate (PSS)/ polyallylamine (PAH) multilayer is studied in situ by means of streaming potential measurements (SPM) and by scanning angle reflectometry (SAR). The results are discussed in the framework of a schematic representation of the multilayer in three zones: a precursor zone (I), a core zone (II), and an outer zone (III). This view seems to be supported by our experimental findings. The zeta potential of the multilayer determined by the SPM shows a symmetrical and constant charge inversion during the multilayer buildup. This seems to indicate an exact charge compensation in zone II and an excess charge that is entirely located in the outer zone III. It is also shown by SAR that a regular buildup regime, in which the thickness increment per layer is constant, is reached after the deposition of the first six polyelectrolyte layers, which gives an indication of the extension of zone I. The influence of the salt concentration C-NaCl present in the polyelectrolyte solutions during multilayer buildup is also investigated. It is found that an increase of the salt concentration in the polyelectrolyte solutions leads to larger amounts of deposited polyelectrolytes and to thicker multilayers. The amount deposited per polyelectrolyte layer delta Q (PSS or PAH) is correctly predicted by the law delta Q = a.C-Nacl(a) + b where a lies between 0.05 and 0.15. In addition, when a multilayer built up in salty solutions is brought in contact with pure water, it expands, indicating that the rinsing step mainly affects zone III of the multilayer, which appears thus to behave like a polyion layer. The structural changes of the multilayer consecutive to the replacement of the salt solution by pure water occur with characteristic times ranging from a few tens of minutes to several hours depending on the initial salt concentration. Finally, it is also found that the structural modifications of the film are fully reversible so that the initial multilayer structure is recovered when water is replaced again by the initial salt solution.

[96] Enzyme Encapsulation in Layer-by-Layer Engineered Polymer Multilayer Capsules

F. Caruso, D. Trau, H. Möhwald and R. Renneberg

Langmuir 16(4) (2000), 1485-1488

We report on the encapsulation of enzyme (catalase) by the controlled polymer multilayer coating of biocrystals, achieved by the sequential adsorption of oppositely charged polyelectrolytes onto enzyme crystal templates. An extremely high enzyme loading in each polymer capsule is obtained, and the activity of the encapsulated enzyme is preserved. The polymer-encapsulated enzyme is stable against protease degradation: The polymer-coated enzyme retains 100% of its activity after incubation for 100 min with protease, whereas uncoated, solubilized catalase loses more than 90% of its initial activity within 100 min under the same conditions. This simple, general, and versatile approach can potentially be applied for the encapsulation of various crystallized substances for catalysis and drug delivery applications.

[97] Electrochemical and in-Situ Ellipsometric Investigation of the Permeability and Stability of Layered Polyelectrolyte Films

J. J. Harris and M. L. Bruening

Langmuir 16(4) (2000), 2006-2013

Utilization of layered polyelectrolyte films as sensor or ion- separation materials will depend critically on their stability and ion permeability in aqueous solution. We report electrochemical and in situ ellipsometric studies on the permeability and stability of poly(allylamine hydrochloride)/ poly(styrenesulfonate) (PAH/ PSS) and PAH/poly(acrylic acid) (PAA) films. The permeability of these layered polyelectrolyte films to Fe(CN)(6)(3-) and Ru(NH3)(6)(3+) depends on the solution pH, the number of bilayers in the film, whether supporting electrolyte is present during film deposition, and the nature of constituent polycations and polyanions. Cyclic voltammetry and impedance spectroscopy show that film permeability is similar in pH 3.2- and pH 6.3-buffered solutions but increases dramatically in alkaline solutions. In situ ellipsometry helps to explain these results. Upon immersion in pH 3.2- and pH 6.3-buffered solutions, the thickness of PAH/PSS films increases by 40%, but swelling is constant over time. At pH 10, these films initially swell by 40% but then continue to swell for several minutes before delaminating. The onset of increased swelling corresponds with dramatic increases in film permeability. Both peak current (cyclic voltammetry) and charge-transfer resistance (ac impedance) depend nonlinearly on the number of polyelectrolyte bilayers. The structure of the first two bilayers is more porous than that of later bilayers. Adding supporting electrolyte to deposition solutions results in thicker bilayers and changes film permeability. For PAH/PSS films, the use of supporting electrolyte during film formation results in a much less permeable film (comparing films of similar thickness). In PAH/PAA films, however, the use of supporting salt results in highly permeable films (even with thicknesses as high as 44 nm). Thus proper choice of constituent polyelectrolytes and deposition conditions permits control over the permeability of layered polyelectrolyte films.

[98] One-Pot Synthesis of Ag-at-TiO2 Core-Shell Nanoparticles and Their Layer-by-Layer Assembly

I. Pastorizasantos, D. S. Koktysh, A. A. Mamedov, M. Giersig, N. A. Kotov and L. M. Lizmarzan

Langmuir 16(6) (2000), 2731-2735

Silver nanoparticles coated with a uniform, thin shell of titanium dioxide are synthesized via a remarkably simple one- pot route, where the reduction of Ag+ to Ag-0 and the controlled polymerization of TiO2 on the surface of silver crystallites take place simultaneously. The prepared dispersions of coated nanoparticles display a surface plasmon band, which is significantly red-shifted with respect to that of bare AK. High quality ultrathin films of the core-shell clusters are prepared via layer-by-layer assembly. The nanoparticles are arranged in closely packed layers interlaced with polyelectrolyte producing a stratified core-shell hybrid material with unique structure and catalytic and electron- transport properties.

[99] Energies of Adsorption of Poly(O-Methoxyaniline) Layer-by-Layer Films

M. Raposo and O. N. Oliveira

Langmuir 16(6) (2000), 2839-2844

The adsorption mechanisms in layer-by-layer films of poly(o- methoxyaniline) (POMA) alternated with poly(ethene sulfonic acid) (PVS) are controlled by H-bonding, even for charged POMA where electrostatic interactions were expected to predominate. This is shown here by analyzing adsorption isotherms using three analytical models for adsorption, namely, Langmuir, Frumkin, and Fillippova models, and thermally stimulated desorption results, from which energies of interaction were estimated. The adsorption free energy is ca. -35 kJ/mol, whereas the activation energy for desorption obtained from thermally stimulated desorption was +75 kJ/mol. According to the three models, adsorption is favored when the number of POMA/ PVS bilayers increases, consistent with the increase in the amount of adsorbed material and film roughness. The importance of H-bonding was confirmed by FTIR measurements and adsorption experiments at high pHs where POMA is no longer doped.

[100] Construction of Multilayer Thin-Films of Enzymes by Means of Sugar-Lectin Interactions

J. Anzai and Y. Kobayashi

Langmuir 16(6) (2000), 2851-2856

A layer-by-layer deposition of concanavalin A (Con A) and glycoproteins such as glucose oxidase (GOx) and horseradish peroxidase (HRP) afforded multilayer thin films on the surfaces of a quartz slide and a platinum electrode, through biospecific complexation of Con A and sugar residues in the glycoenzymes. Lactate oxidase (LOx), which contains intrinsically no sugar chain, was also built into a multilayer assembly by being modified extrinsically with mannose residues. The enzymes formed monomolecular or sub-monomolecular layers in each layer of the multilayer films. Electrochemical measurements using Con A-enzyme multilayer-modified electrodes revealed that the enzymes are catalytically active in the multilayer films. The Con A-enzyme multilayer films are relatively stable against low concentrations of mannose and urea, although the films destructed gradually in high concentrations of urea solutions (>3 M).

[101] Stratified Assemblies of Magnetite Nanoparticles and Montmorillonite Prepared by the Layer-by-Layer Assembly

A. Mamedov, J. Ostrander, F. Aliev and N. A. Kotov

Langmuir 16(8) (2000), 3941-3949

Hybrid thin films are prepared from 8 to 10 nm Fe3O4 nanoparticles and exfoliated montmorillonite clay by using layer-by-layer assembly on poly(diallyldimethylammonium bromide), PDDA. Distinct stratification of the Fe3O4/PDDA/clay films is obtained due to the sheetlike structure of the clay particles. This feature distinguishes these assemblies from their polyelectrolyte-polyelectrolyte analogues, where the layers of individual polyelectrolytes are strongly interdigitated. Being adsorbed on PDDA strictly parallel to the substrate surface, montmorillonite produces a dense layer of overlapping alumosilicate sheets, which virtually flawlessly separates one magnetite layer from another. The difference in magnetic properties between assemblies of various architectures is attributed to the insulation effect of clay layers inserted between magnetic layers. The montmorillonite sheets disrupt the electron exchange interactions between the magnetite nanoparticles in adjacent layers, thereby limiting the magnetization reversal to two dimensions. Some optical properties of Fe3O4/PDDA films are investigated as well. When they are deposited on thin plastic substrate, oscillations of optical density were observed in the red part of the UV-vis spectrum. This effect, which was never been observed for conventional, thick substrates such as glass slides, stems from the interference of the light beams passed through and reflected off of the assembled film.

[102] Scanning Force Microscopy Investigation of Polyelectrolyte Nanocapsule and Microcapsule Wall Texture

S. Leporatti, A. Voigt, R. Mitlohner, G. Sukhorukov, E. Donath and H. Möhwald

Langmuir 16(9) (2000), 4059-4063

Ultrathin polymer capsules prepared by stepwise deposition of oppositely charged polyelectrolytes onto melamine formaldehyde latex particles and biological cells with subsequent dissolution of the core have been examined by scanning force microscopy (SFM) in the dried state. Folds generated during the drying induced collapse of the shells are observed. The thickness of a single polyelectrolyte layer in the dried state was determined as 1.3 +/- 0.3 nm. Imaging at high resolution revealed the existence of domains and invaginations. This typical lateral pattern has been quantified by means of an autocorrelation analysis of the SFM images. A characteristic domain size of 50-100 nm is found. If the polyelectrolytes have been cross-linked prior to the core decomposition, a surface separation into defined domains is not observed. The nature and size of the domains are discussed in relation to the drying and the molecular parameters of the layer constituents.

[103] 2-Dimensional Auto-Organized Nanostructure Formation of Hyaluronate on Bovine Serum-Albumin Monolayer and Its Surface- Tension

T. Nonogaki, S. H. Xu, S. Kugimiya, S. Sato, I. Miyata and M. Yonese

Langmuir 16(9) (2000), 4272-4278

The layer-by-layer interaction between bovine serum albumin BSA and sodium hyaluronate NaHA was studied by a quartz crystal microbalance QCM method. The surface structures of the BSX layer and the NaHA layer and their surface tensions were investigated using atomic force microscopy AFM. BSA showed Langmuir type adsorption on poly(gamma-methyl-L-glutamate) PMLG thin film and were found to be a monolayer in the saturated adsorption state. The adsorption of NaHA on the BSA monolayer was also the Langmuir type. From their linear reciprocal plots, adsorption constants K and saturated adsorption masses Gamma(infinity) were determined. The BSA molecules on the PMLG film surface could be imaged using AFM in the monolayer state. Furthermore. the surface structure of NaHA adsorbed on the BSA monolayer was found to form hexagonal-like networks. From the adhesion force F-ad between the AFM tip and the surfaces of the BSA layers or the NaHA layers, their surface tensions gamma(s) were estimated. The surface tension of the PMLG films increased with increasing the adsorption of BSA but the surface tension of the saturated adsorption BSA layer was found to decrease with increasing the adsorption of NaHA.

[104] Characterization of Flexibility of Ultrathin Protein Films by Optical Sensing

E. Brynda, M. Houska, A. Wikerstal, Z. Pientka, J. E. Dyr and A. Brandenburg

Langmuir 16(9) (2000), 4352-4357

Films consisting of three cross-linked molecular layers of human serum albumin (HSA) or three HSA layers alternating with three heparin layers were immobilized on surfaces of grating coupler sensors and hydrophobized glass. Optical responses of the coated sensors to pH changes were observed. A decrease in the effective refractive index, Delta N-eff, measured by a grating coupler was observed when the pH of buffers contacting the films was increased. The process was quite reversible, which indicated that the mass of the film remained constant when the buffers were repeatedly exchanged. Theoretical treatment of the grating coupler optics related the decrease in Delta N-eff to expansion of the films. The interpretation of sensor measurements was confirmed by atomic force microscopy which revealed reversible changes in the thickness of NSA/ heparin film induced by pH changes of the buffers.

[105] Influence of a Base Electrolyte on the Adsorption Behavior of an Anionic Surfactant as Observed by 2nd-Harmonic Generation

G. Moller, S. Schrader, H. Motschmann and D. Prescher

Langmuir 16(10) (2000), 4594-4598

The adsorption process of sodium-[4-(4'- trifluormethylphenylazo)phenyl-1-oxyethylsulfonate] (NaTAPOS) at the water/1,2-dichlorethane interface was investigated by second harmonic generation and ellipsometry. The combination of both techniques yields the surface excess and the orientation of the amphiphiles within the adsorption layer. These data were used for an investigation of equilibrium properties of the system. The average tilt angle of the chromophore within the adsorption layer remains constant in the whole concentration range. The mean tilt angle was found to be 39 +/- 3 degrees and the area per molecule at maximum surface coverage is 45.2 +/- 6 Angstrom(2). The present study focuses on the impact of a base electrolyte on the adsorption process. Neither the limiting area per molecule nor the orientational order was changed by base electrolyte dissolved in the aqueous phase. The maximum surface coverage with and without base electrolyte is achieved at the same bulk concentration and is within the error limit identical; however, at lower concentrations a significantly higher surface excess is observed in the absence of base electrolyte. This is counterintuitive since one might expect an electrostatic shielding of the prevailing interaction. The adsorption isotherms with and in absence of base electrolyte can be described by Frumkin's equation of state. This model accounts for regular surface behavior and takes into account the lateral interaction of the absorbed species. The model fit yields two quantities: the free enthalpy of adsorption and the interaction parameter. Only slight changes of the free enthalpy of adsorption were observed by the presence of base electrolyte; however, a significant increase of the corresponding interaction parameter was observed. These findings are in contradiction to the Debye-Huckel theory and are explained by a model in analogy to the polyelectrolyte layer-by-layer adsorption.

[106] Covalently Attached Multilayer Assemblies by Sequential Adsorption of Polycationic Diazo-Resins and Polyanionic Poly(Acrylic Acid)

J. Q. Sun, T. Wu, F. Liu, Z. Q. Wang, X. Zhang and J. C. Shen

Langmuir 16(10) (2000), 4620-4624

Diazo-resins (DAR) as polycation and poly(acrylic acid) (PAA) as polyanion were alternately assembled into a multilayer structure by using the layer-by-layer self-assembly technique. PAA as a weak polyelectrolyte was very sensitive to the pH value of the solution, and that pH could be used to tune the thickness of the PAA layer. Upon UV irradiation, a fraction of the carboxylate groups reacted with diazonium groups at the adjacent interfaces of the multilayer, so partially covalently attached multilayer assemblies could be formed. Their stability improved greatly compared with the fraction that was not UV- irradiated. The photoreaction occurring between the layers was confirmed by means of UV-visible and Fourier transform infrared spectroscopy. The thickness of the W-irradiated films was characterized with X-ray diffraction, results from which showed that the thickness of the films can be adjusted in nanometer scale by simply changing the pH value of the solutions.

[107] Electroactive Myoglobin Films Grown Layer-by-Layer with Poly(Styrenesulfonate) on Pyrolytic-Graphite Electrodes

H. Y. Ma, N. F. Hu and J. F. Rusling

Langmuir 16(11) (2000), 4969-4975

Stable multilayer electroactive films were grown on rough pyrolytic graphite (PG) electrodes by alternate adsorption of layers of polyanion poly(styrenesulfonate) (PSS) and positively charged myoglobin (Mb) from their aqueous solutions. Incorporation of large amounts of electroactive Mb was facilitated by high electrode surface areas and by adsorbing coiled PSS from 0.5 M NaCl solutions. Cyclic voltammetry of {PSS/Mb}(n), films showed a pair of well-defined, chemically reversible peaks at about -0.25 V vs SCE at pH 5.5, characteristic of the Mb heme Fe-III/Fe-II redox couple. Electroactivity was extended to 7 {PSS/Mb} bilayers on rough PG surfaces, in comparison to 2 electroactive layers on smooth gold coated with mercaptopropanesulfonic acid. Square wave voltammograms of {PSS/Mb}, films gave good fits by nonlinear regression analysis to a model featuring dispersion of formal potentials, providing average formal potentials and an apparent rate constant. Oxygen and trichloroacetic acid were catalytically reduced by Mb in {PSS/Mb}(n) films with significant decreases in the electrode potential required. Making such films on PG rather than on gold provides a larger number of electroactive layers with no need for chemical pretreatment of the electrode.

[108] Fabrication of Microporous Thin-Films from Polyelectrolyte Multilayers

J. D. Mendelsohn, C. J. Barrett, V. V. Chan, A. J. Pal, A. M. Mayes and M. F. Rubner

Langmuir 16(11) (2000), 5017-5023

A simple process has been developed to create large area, highly uniform microporous thin films. Multilayers of weak polyelectrolytes were assembled onto silicon substrates by the sequential adsorption of poly(acrylic acid) and poly(allylamine) from aqueous solution. These multilayers were then immersed briefly into acidic solution (pH approximate to 2.4) to effect a substantial and irreversible transformation of the film morphology. The resulting microporous structures are 2- 3 times the thickness of the original films, possess a correspondingly reduced relative density of 1/2 to 1/3, and are stable against further rearrangement under ambient; conditions. In addition, the microporous films may undergo a secondary reorganization in neutral water, leading to a morphology with more discrete throughpores. A mechanism is proposed for these transformations based on interchain ionic bond breakage and reformation in this highly protonating environment;, leading to an insoluble precipitate on the substrate which undergoes spinodal decomposition with the solvent. FTIR (Fourier transform infrared spectroscopy) analysis supports the underlying chemical basis of this pH-induced phase separation, and AFM (atomic force microscopy), in situ ellipsometry, and SEM (scanning electron microscopy) have been used to monitor the morphological changes. The unique combination of properties exhibited by these microporous films makes them potential candidates for microelectronic and biomaterial applications.

[109] Mobile Phospholipid-Bilayers on a Polyion/Alkylthiol Layer Pair

L. Q. Zhang, M. L. Longo and P. Stroeve

Langmuir 16(11) (2000), 5093-5099

The formation of phospholipid bilayers on a polymer/alkylthiol layer pair was investigated by surface plasmon resonance (SPR). The organic layer pair between the lipid membrane and the solid gold surface consisted of a self-assembled monolayer of 11- mercaptoundecanoic acid (MUA) on a gold surface followed by a thin layer of hydrated cationic poly(diallyldimethylammonium chloride) (PDDA). The lipid layers were formed by vesicular fusion of small unilamellar vesicles of an anionic lipid 1- stearoyl-2-oleoyl-phosphatidylserine (SOPS), a zwitterionic lipid 1-palmitoyl-2-oleoylphosphatidylcholine (POPC), and mixtures of these two lipids with different compositions. In the case of pure SOPS and lipid mixtures with a POPC composition below 25%, the lipid layer thickness was approximately that of a single bilayer, while multilayers tended to build up with higher concentrations of POPC. The electrostatic interaction of the cationic PDDA with the negatively charged lipid membrane is most probably the driving force for the adsorption of a single bilayer. Fluorescence recovery after photobleaching (FRAP) experiments showed that single bilayers supported on the PDDA/alkylthiol layer pair were mobile at room temperature with lateral diffusivities of approximately (1-2) x 10(-9) cm(2)/s. A membrane fusion peptide wt-20 of the influenza virus was bound to the supported bilayers as detected by SPR. This suggests the potential of this model membrane system for use as a biosensor.

[110] Self-Assembled Monolayers and Multilayered Stacks of Lyotropic Chromonic Liquid-Crystalline Dyes with Inplane Orientational Order

T. Schneider and O. D. Lavrentovich

Langmuir 16(12) (2000), 5227-5230

A simple method to create large areas of in-plane oriented molecular mono- and multilayers is presented. The method is based on layer-by-layer adsorption of polyions and a lyotropic chromonic (nonamphiphilic) liquid crystal, which allows one to orient the molecules uniformly in the plane of deposition. The long-range in-plane orientation of the chromonic molecules determines the unique structural and optical properties of the films. Control of the orientational order allows one to use the films as polarizers, alignment layers, optical compensators, retarders, filters, etc.

[111] Freestanding Layer-by-Layer Assembled Films of Magnetite Nanoparticles

A. A. Mamedov and N. A. Kotov

Langmuir 16(13) (2000), 5530-5533

A new technique for preparation of free-standing ultrathin films is presented. These films were made by layer-by-layer (LBL) deposition process, which is utilized for coatings on solid substrates and colloids. A film composed of alternating layers of magnetite nanoparticles and poly(diallyldimethylammonium bromide) was assembled on cellulose acetate, which was subsequently dissolved in acetone. From the suspended state, the LBL film can be transferred onto any solid or porous support. The strength of the film was observed to significantly increase when every other layer of magnetite was replaced with a layer of alumosilicate sheets serving as a molecular framework for the assembly.

[112] Imaging Nanoscale Patterns on Biologically Derived Microstructures

Y. M. Lvov, R. R. Price, J. V. Selinger, A. Singh, M. S. Spector and J. M. Schnur

Langmuir 16(14) (2000), 5932-5935

We have demonstrated a new approach for imaging nanoscale patterns on three-dimensional submicrometer structures using charged particles. Nanoparticle structures were assembled onto lipid tubules through the sequential adsorption of oppositely charged polymers and silica spheres. For tubules of the zwitterionic lipid DCB8,11PC, this process leads to the formation of caps on the ends of the tubules, with 50-100 silica spheres in each cap. For tubules of DC8,11PC mixed with 2% of the charged lipid DC8,9PEOH, the sequential adsorption leads to both end caps and helices of nanoparticles winding around the interior of the tubules. These results give new insight into the pattern of charge in lipid tubules.

[113] Construction of Multilayer Thin-Films Containing Avidin by a Layer-by-Layer Deposition of Avidin and Poly(Anion)S

J. Anzai, T. Hoshi and N. Nakamura

Langmuir 16(15) (2000), 6306-6311

A layer-by layer deposition of avidin and poly(anion)s including poly(styrenesulfonate) (PSS), poly(vinyl sulfate) (PVS), and dextransulfate (DS) afforded multilayer thin films on the surface of a quartz slide, through electrostatic force of attraction between positive charges on the avidin molecule and negative charges on the polymer chains. It was possible to regulate the thickness of the films arbitrarily by changing the number of depositions. The loading of avidin in the multilayer thin films depended on the concentration of avidin and poly(anion)s in the bathing solutions from which the films were deposited. In the PVS- and PSS-based multilayer films, a large amount of avidin was immobilized in each deposition, depending on the concentrations of avidin and poly(anion) in the bathing solutions. In contrast, nearly a monomolecular layer was formed in each layer in the avidin-DS films independent of the concentration of bathing solutions. Avidin molecules assembled into the thin film retained its binding activity to biotin and analogues. The binding properties of avidin in the multilayer films were nearly comparable to those in solution; the films bound biotin, desthiobiotin, iminobiotin, and 2-(4'- hydroxyphenyl azo)benzoic acid effectively.

[114] Sequential Electrostatic Assembly of Amine-Derivatized Gold and Carboxylic Acid-Derivatized Silver Colloidal Particles on Glass Substrates

A. Kumar, A. B. Mandale and M. Sastry

Langmuir 16(17) (2000), 6921-6926

The formation of alternating layers of positively charged gold and negatively charged silver colloidal particles on glass substrates via electrostatic interaction is described. The charging of the gold and silver colloidal particles is accomplished by self-assembly of 4-aminothiophenol (4-ATP) and 4-carboxythiophenol (4-CTP) monolayers on the colloidal particles respectively and subsequent ionization of the functional groups at appropriate pH values of the colloidal solution. Glass substrates, which are negatively charged at pH > 3, are immersed first in the positively charged amine- derivatized gold solution leading to the formation of a monolayer of the gold particles and charge reversal of the glass surface. Thereafter, the gold particle covered glass surface is immersed in the negatively charged carboxylic acid- derivatized colloidal silver solution and the silver particles electrostatically self-assembled on the glass surface. This process map be continued to yield multilayer structures of the colloidal particles. The kinetics of electrostatic self- assembly of the colloidal particles on glass, the formation of the multilayer films, and their thermal stability have been followed with UV-vis spectroscopy, X-ray diffraction, ellipsometry, and X-ray photoemission spectroscopy measurements.

[115] Conductance and Capacitance of Polyelectrolyte and Lipid- Polyelectrolyte Composite Capsules as Measured by Electrorotation

R. Georgieva, S. Moya, S. Leporatti, B. Neu, H. Baumler, C. Reichle, E. Donath and H. Möhwald

Langmuir 16(17) (2000), 7075-7081

Polyelectrolyte capsules were fabricated in aqueous media by stepwise adsorption of polyelectrolytes onto fixed erythrocytes and subsequent template dissolution. Lipid polyelectrolyte composite capsules were prepared assembling lipid layers on these polyelectrolyte capsules. Dipalmitoyl phosphatidyl acid (DPPA), dipalmitoyl phosphatidyl choline (DPPC), and a mixture of both were used. Confocal laser scanning microscopy showed that the Lipids form a homogeneous coverage on the capsule surface. An electrorotation technique was used to study the electrical properties of polyelectrolyte and lipid- polyelectrolyte composite capsules. A conductivity of 1 S/m for polyelectrolyte capsule walls was found. Lipid-polyelectrolyte composite capsules yielded conductivities in the range from 10(- 4) to 10(-1) mS/m and capacities of 2.7 mu F/cm(2) for DPPA and 0.5 mu F/cm(2) for DPPC. These conductivities of lipid- polyelectrolyte composite capsules were much higher than for black lipid membranes. They increased with the bulk electrolyte concentration, which was attributed to the presence of pores or defects in the lipid structures. The effective area of pores was estimated as 0.01% of the total capsule surface.

[116] Nucleation and Growth of Cobalt Hydroxide Crystallites in Organized Polymeric Multilayers

L. Q. Zhang, A. K. Dutta, G. Jarero and P. Stroeve

Langmuir 16(17) (2000), 7095-7100

In this paper, we report the hydrolysis of Co2+ ions absorbed in organized, multilayered polymer films to form cobalt hydroxide nanocrystals. Polymer films were prepared using the layer-by-layer deposition technique that consists of adsorbing polycations and polyanions alternately on a quartz substrate. By monitoring the UV-vis absorbance of the polymer films as a function of the number of absorption-hydrolysis cycles, it was shown that the crystals continued to grow with additional cycles. It is also found in this study that using more polymer layer pairs results in more crystal growth. Hydrolysis of the Co2+ ions in a nitrogen-rich environment gives rise to mainly needlelike crystallites of alpha-Co(OH)(2) that are initially about 100 nm in length and th en increase in size with the number of absorption-hydrolysis cycles. However, in an oxygen- rich microenvironment, hexagonal crystallites were found to be predominant. X-ray diffraction and transmission electronmicroscopic studies revealed that these hexagonal crystallites mainly consist of beta-Co(OH)(2) with a contribution of CoOOH. Our studies suggest that by varying the nitrogen-to-oxygen ratio the formation of alpha-Co(OH)(2) and beta-Co(OH)(2) can be controlled.

[117] Stepwise Assembly of Isotactic Poly(Methyl Methacrylate) and Syndiotactic Poly(Methacrylic Acid) on a Substrate

T. Serizawa, K. Hamada, T. Kitayama, K. Katsukawa, K. Hatada and M. Akashi

Langmuir 16(18) (2000), 7112-7115

Stepwise assembly of isotactic poly(methyl methacrylate) and syndiotactic poly(methacrylic acid) from acetonitrile and mixed acetonitrile/water solutions, respectively, onto a gold substrate was studied. Quantitative quartz crystal microbalance analysis of the molar ratio (monomer unit) between assembled polymers suggested Stepwise stereocomplex formation. The assembled amount and the assembly ratio between PMAA and PMAA were dependent on the acetonitrile content of the poly(methacrylic acid) solution. Infrared spectra of the assembly and cast films of each polymer also showed stereocomplex formation in the assembly. Atomic force microscopic observation showed the assembled polymer to have a molecularly smooth surface. The solvent species used was an important factor in stereocomplex formation at the liquid- polymer film interface.

[118] Preparation and Characterization of Ultrathin Films Layer-by- Layer Self-Assembled from Graphite Oxide Nanoplatelets and Polymers

T. Cassagneau, F. Guerin and J. H. Fendler

Langmuir 16(18) (2000), 7318-7324

Graphite, oxidized by HNO3 and NaClO3 to 25% (GO-25), 42% (GO- 42), and 33% (GO-33), has been dispersed to partially exfoliated nanoplatelets and, along with poly(diallyldimethylammonium chloride) (PDDA) and poly(ethylene oxide) (PEO), layer-by-layer self-assembled to ultrathin S- (PDDA/GO)(10), S-PDDA/(GO/PEO)(10), and S-(PDDA/GO/PEO)(10) films (where S is the indium tin oxide- or chromium/gold-coated glass or quartz substrate and GO refers to platelets of oxidized graphite). The GO powders have been characterized by X- ray diffraction prior and by transmission electron microscopy after their dispersions. Thicknesses of each of the successively adsorbed layers were comparatively determined by absorption spectrophotometry, surface plasmon resonance spectroscopy, quartz crystal microbalance, and scanning force microscopy. Good agreements were obtained by these three different techniques.

[119] Formation of Polyelectrolyte Multilayers

M. Castelnovo and J. F. Joanny

Langmuir 16(19) (2000), 7524-7532

A mechanism for the formation of polyelectrolyte multilayers is proposed. All of the experiments on such systems show that there is strong interpenetration of consecutive layers. We explain the very strong stability of the multilayers by the complexation between polyelectrolytes of opposite signs. Scaling laws on bulk polyelectrolyte complexation and their applications to the case of multilayers are derived in analogy with the description of neutral polymers under poor solvent conditions. Qualitative agreement is reached with some recent experiments.

[120] Nanocomposites by Electrostatic Interactions - 1 - Impact of Sublayer Quality on the Organization of Functionalized Nanoparticles on Charged Self-Assembled Layers

F. Auer, M. Scotti, A. Ulman, R. Jordan, B. Sellergren, J. Garno and G. Y. Liu

Langmuir 16(20) (2000), 7554-7557

Bis-benzamidines were studied as linkers for the formation of gold nanoparticle assemblies on planar gold surfaces modified with omega-mercaptohexadecanoic acid. In situ ellipsometry, external reflection Fourier transform spectroscopy, and atomic force microscopy showed that the packing density and order of the bis-benzamidine layer exerted a pronounced influence on the thickness and density of the nanoparticle layers. These layers exhibited optical properties similar to those of solid gold.

[121] Selective Self-Organization of Colloids on Patterned Polyelectrolyte Templates

K. M. Chen, X. P. Jiang, L. C. Kimerling and P. T. Hammond

Langmuir 16(20) (2000), 7825-7834

Submicron-sized colloidal particles have been self-organized into patterned arrangements on a substrate using a novel technique. At the substrate, a polyelectrolyte multilayer film has been deposited onto a chemically patterned surface; subsequently, the polyelectrolyte surface is immersed in an aqueous colloidal suspension of bare SiO2 microspheres or functionalized polystyrene latex particles. The colloids self- organize at the surface, driven by the spatially varied electrostatic and secondary interactions between the colloid and the substrate. The polyelectrolyte platform provides a strong bond to the colloids, imparting mechanical robustness which enables postprocessing of the patterned assemblies. An important advantage to this approach is that the use of a polyelectrolyte multilayer platform opens up the possibility of introducing functionality into the underlying layers. We have demonstrated control over the density and selectivity of particle adsorption. Three mechanisms have been used to control adsorption: (i) pH of the colloid suspension, which determines the ionization of the uppermost surface of the polyelectrolyte multilayer; (ii) ionic strength of the suspension, which determines the extent of charge screening about the colloid and polyelectrolyte; and (iii) concentration of added surfactant, which causes charge screening and introduces hydrophobic interactions between the surfactant and polyelectrolyte. Finally, an energy adsorption model is presented.

[122] Layer-by-Layer Assembly of CdSe Nanoparticles Based on Hydrogen- Bonding

E. C. Hao and T. Q. Lian

Langmuir 16(21) (2000), 7879-7881

We report the synthesis of nonaqueous dispersion of CdSe nanoparticles and the layer-by-layer assembly of hybrid poly(vinylpyridine) (PVP)/CdSe multilayer thin films based on hydrogen bonding. The multilayer buildup is monitored by W-vis spectra, which showed a linear increase of the film absorbance with the number of adsorbed CdSe layers. The resulted films have a high degree of flatness and smoothness as indicated by small-angle X-ray diffraction. Hydrogen bond interaction, the driving force for the formation of PVP/CdSe multilayer thin film, between the pyridine group of PVP and the carboxylic acid group on CdSe was verified by FTIR spectroscopy.

[123] Selective Deposition in Layer-by-Layer Assembly - Functional Graft-Copolymers as Molecular Templates

X. P. Jiang and P. T. Hammond

Langmuir 16(22) (2000), 8501-8509

A new approach to creating patterned composite structures with layer-by-layer assembled thin films is introduced. In this approach, the top surfaces of layer-by-layer films are chemically patterned by the direct stamping of functional polymers on the surface. The resulting pattern is then used as a template for the further deposition of materials on the surface. This paper illustrates this concept through the patterning of an oligoethylene glycol resist atop a polyelectrolyte multilayer surface. The resist layer is created by stamping an oligoethylene oxide-maleic anhydride graft copolymer onto the top polyamine surface. Further deposition of polyions results in the formation of a patterned polymer film atop the original multilayer thin film. When a patterned polyelectrolyte film is used as the base layer or substrate in this process, a second pattern can be stamped atop the original patterned array. Subsequent selective adsorption of polymers yields a second level of microstructures, illustrating the concept of multiple level patterning for layer-by-layer thin films; this concept can be broadened to include selective deposition of numerous materials on top of multilayer polymer systems.

[124] Design and Demonstration of Hybrid Multilayer Structures - Layer-by-Layer Mixed Covalent and Ionic Interlayer Linking Chemistry

P. Kohli and G. J. Blanchard

Langmuir 16(22) (2000), 8518-8524

We report on the growth of layered molecular assemblies where the interlayer attachment chemistry is controlled layer-by- layer. We demonstrate the compatibility of chemistry where the layers are connected by ionic coordination chemistry [ROPO32-- Zr4+--O2CR]+OH- and by the formation of covalent urea moieties. A maleimide-vinyl ether (MVE) copolymer containing pendant benzoic acid and butyl alcohol functionalities is used for ionic layer growth. Coupling of covalently bonded adlayers to the MVE polymer is achieved by the attachment of poly(ethylene imine), PEI, to the MVE surface. Subsequent reaction of the PEI surface with diisocyanates and diamines produces urea-linked covalent multilayers. The covalent multilayers can be converted to ionic growth chemistry by treatment of the aminated terminal surface with POCl3 and water followed by further reaction with MVE polymer and Zr4+ ions. We report the reaction schemes for these hybrid layer structures and the characterization of these novel materials by optical ellipsometry, FTIR and UV-vis spectroscopy, XPS, and X-ray diffraction. The data show the formation of robust multilayer assemblies characterized by limited order within each layer.

[125] Films of Manganese Oxide Nanoparticles with Polycations or Myoglobin from Alternate-Layer Adsorption

Y. Lvov, B. Munge, O. Giraldo, I. Ichinose, S. L. Suib and J. F. Rusling

Langmuir 16(23) (2000), 8850-8857

Alternate adsorption of manganese oxide nanoparticles with polycations poly(dimethyldiallyl-ammonium) (PDDA) or myoglobin (Mb) onto silver, quartz, and rough pyrolytic graphite gave stable, porous, ultrathin films. Quartz crystal microbalance (QCM) and UV- vis absorbance revealed regular film growth at each adsorption step for MnO2 and PDDA and for SiO2 nanoparticles and Mb. Scanning electron microscopy of MnO2/PDDA films showed smooth surfaces on the 20 nm scale and cross sections consistent with individual nanoparticles. QCM during growth of films of Mb and MnO2 reflected a competition for adsorption of the protein by the film surface and dispersed MnO2 nanoparticles. Nevertheless, films of Mb and MnO2 up to 30 nm thick on rough pyrolytic graphite electrodes could be constructed These novel films featured reversible interconversion of the protein's heme Fe-III/Fe-II redox couple with 10 electroactive layers of protein, considerably more than for polyion-Mb films on smooth gold (ca. 1.3 electroactive layers), and coiled PSS/Mb, films on rough graphite (7 electroactive layers). Shifts in redox potential caused by CO complexation of the heme Fen, BET specific areas, and electrochemically driven catalytic reduction of oxygen suggest that the Mb/MnO2 films are highly porous to gas molecules. To our knowledge, these films represent the first nanofabrication of inorganic particles with functional proteins by the layer-by- layer method.

[126] Steady-State and Time-Resolved Spectroscopy of a Self-Assembled Cyanine Dye Multilayer

E. Rousseau, M. Vanderauweraer and F. C. Deschryver

Langmuir 16(23) (2000), 8865-8870

Ultrathin organic multilayers, consisting of polyelectrolytes and J-aggregates of a cyanine dye, were obtained using the layer by layer alternate adsorption technique. Buildup of the multilayer is followed by UV-vis absorption spectroscopy. The fluorescence properties of the J-aggregates are studied by steady-state fluorescence spectroscopy and picosecond fluorescence decay measurements. Fluorescence of the cyanine dye, when adsorbed on the substrate, results in a narrow emission band with a small Stokes shift which is characteristic for J-aggregate emission. Time-resolved fluorescence measurements yield a very short average decay time, which can be attributed to the J-aggregates. These results describing the fluorescence properties of multilayer assemblies containing J- aggregates allow on to compare them to those of J-aggregates of the cyanine dye in solution.

[127] Polyelectrolytes I - Polyanion/Polycation Multilayers at the Air/Monolayer/Water Interface as Elements for Quantitative Polymer Adsorption Studies and Preparation of Hetero- Superlattices on Solid-Surfaces

J. Ruths, F. Essler, G. Decher and H. Riegler

Langmuir 16(23) (2000), 8871-8878

Polyanion/polycation multilayers floating at the air/water interface were prepared by consecutive adsorption of polyelectrolyte layers onto a Langmuir monolayer from aqueous polyelectrolyte subphase solutions. With the positively charged Langmuir monolayer headgroups of the lipid dimethyldioctadecylammonium bromide, the layer sequence starts with the negatively charged polyelectrolyte polystyrene sulfonate. With the negatively charged monolayer dimyristoylphosphatidic acid, it starts with the positively charged polyallylamine. Equally charged monolayer headgroups and polyelectrolytes do not bind to each other. Consecutive subphase exchange cycles of polyelectrolyte solutions with alternating charges and pure solvent in between lead to the formation of floating multilayers consisting of an alternating polyelectrolyte sequence. Ellipsometric measurements show that the thickness (adsorbed amount per unit area) of the multilayer film at the air/water interface grows in proportion to the number of adsorbed polyelectrolyte layers. The thickness of individual layers increases with increasing polyelectrolyte and/ or ion subphase concentration, respectively. The floating multilayers can be deposited as a sequence of layers of monomeric lipid and polyelectrolytes (hetero-superlattices) onto solid substrates via Langmuir-Blodgett transfer. UV- absorbance studies corroborate the quantitative interpretation of the ellipsometric data in terms of the polymer concentration in the layers, the individual layer thicknesses, and the adsorbed amounts per unit area.

[128] Microencapsulation of Uncharged Low-Molecular-Weight Organic Materials by Polyelectrolyte Multilayer Self-Assembly

F. Caruso, W. J. Yang, D. Trau and R. Renneberg

Langmuir 16(23) (2000), 8932-8936

Two uncharged microcrystalline substances, pyrene (PYR) and fluorescein diacetate (FDA), were rendered water dispersible by treatment with various amphiphilic substances and subsequently encapsulated by exposure to an alternating sequence of cationic and anionic polyelectrolytes. The amphiphilic compounds employed to charge the microcrystals were ionic surfactants, phospholipids, and polyelectrolytes with an amphiphilic nature. Polyelectrolyte layers were self-assembled onto the pre-charged microcrystalline templates by means of electrostatic layer-by- layer deposition, thus forming a multilayered polymeric shell around the crystalline cores. The semipermeable nature of the polymer multilayer shell was thereafter exploited to remove the templated core by exposure to a mild organic solvent. The release behavior of solubilized PYR and FDA from the crystalline core was examined by monitoring their fluorescence after dissolution with ethanol. Complete removal of the core yielded hollow polymer capsules of micrometer dimensions. The capsule porosity was found to be influenced by the amphiphile used to pre-charge the microcrystal surface. The strategy presented is expected to be a general approach for the encapsulation of hydrophobic, low molecular weight compounds such as drugs, as well as providing a novel and facile pathway to the fabrication of polymer multilayered microcapsules with controlled release properties for drug delivery.

[129] Adsorption-Induced 2nd-Harmonic Generation from the Layer-by- Layer Deposited Ultrathin-Film Based on the Charge-Transfer Interaction

Y. Shimazaki, S. Ito and N. Tsutsumi

Langmuir 16(24) (2000), 9478-9482

This paper is concerned with the second harmonic generation (SHG) from as deposited layer-by-layer adsorbed films. A nanolayered film was fabricated through the intermolecular charge-transfer interaction between the electron-donating carbazole (Cz) group and electron-accepting 3,5-dinitrobenzoyl group in the side chains of methacrylate-based polymers. A nonlinear optical dye was introduced in the film by using the copolymer in which Cz and disperse red 1 (DR1) groups were attached to the side chains. The DR1 moiety was highly oriented through the adsorption of PCzEMA-DR1, and the orientation was relaxed by additional adsorption of the polymers onto the DR1- containing layer, The second harmonic (SH! intensity of the multilayered film remained almost constant for the layers of even and odd numbers. This behavior could be explained by considering the change in the nonlinear susceptibility of the succeeding DR1-containing layer. The SH intensity kept constant up to 120 degreesC for thermal stability.

[130] Enzyme Multilayers on Colloid Particles - Assembly, Stability, and Enzymatic-Activity

F. Caruso and C. Schuler

Langmuir 16(24) (2000), 9595-9603

Colloidal biocatalysts, comprising polystyrene (PS) carrier particles coated with enzyme multilayers, were fabricated via the layer-by-layer self-assembly method. Glucose oxidase (GOD), horseradish peroxidase (POD), or preformed enzyme- polyelectrolyte complexes were assembled in alternation with oppositely charged polyelectrolytes onto PS particles. Microelectrophoresis, single-particle light scattering, and transmission electron microscopy confirmed stepwise growth of the multilayer films on the colloid particles. The high surface area Enzyme multilayer-coated particles were successfully employed as specific enzyme reactors (i.e., as catalysts). Whereas no loss in activity was observed for the enzymes immobilized directly onto particle surfaces, precomplexing the enzymes with polymer in solution drastically reduced their activity (by up to 70%). The enzymatic activity (per particle) was found to increase with the number of enzyme layers immobilized, irrespective of whether the enzyme was precomplexed. However, particles coated with preformed enzyme- polyelectrolyte complexes displayed a significantly lower enzymatic activity than those fabricated by the direct adsorption of free enzyme. Multicomponent films of GOD and POD on colloid particles were also prepared, and sequential enzymatic catalysis was demonstrated. Furthermore, experiments were conducted with particles exhibiting both magnetic and catalytic functions. These particles, premodified with a layer of magnetic nanoparticles to impart a magnetic property and subsequently coated with enzyme multilayers, were repeatedly used as catalysts following their rapid and easy separation with a magnet. Such biocolloids are expected to find applications in biotechnology.

[131] Layer-by-Layer Self-Assembly of Organic-Organometallic Polymer Electrostatic Superlattices Using Poly(Ferrocenylsilanes)

M. Ginzburg, J. Galloro, F. Jakle, K. N. Powerbillard, S. M. Yang, I. Sokolov, C. N. C. Lam, A. W. Neumann, I. Manners and G. A. Ozin

Langmuir 16(24) (2000), 9609-9614

Water-soluble poly(ferrocenylsilane) (PFS) and poly(styrenesulfonate) (PSS) of alternating charge are shown to self-assemble in a layer-by-layer fashion on primed Au, Si, and quartz substrates to create the first examples of organic- organometallic electrostatic superlattices from polymers with ferrocene units in the backbone. The layer-by-layer assembly of these electrostatic superlattices has been monitored through frequency changes with layer deposition using a quartz-crystal microbalance (QCM), a regular film thickness increase observed using ellipsometry, and step-wise absorbance increases observed using ultraviolet-visible (UV-vis) spectroscopy. As well, structural information was obtained using X-ray photoelectron spectroscopy (XPS), water contact angle measurements, and atomic force microscopy (AFM). These superlattices are of interest as possible precursors to patterned magnetic and redox active multilayers.

[132] Amphoterization of Colloidal Gold Particles by Capping with Valine Molecules and Their Phase-Transfer from Water to Toluene by Electrostatic Coordination with Fatty Amine Molecules

A. Kumar, P. Mukherjee, A. Guha, S. D. Adyantaya, A. B. Mandale, R. Kumar and M. Sastry

Langmuir 16(25) (2000), 9775-9783

The surface modification of colloidal gold particles with the amino acid valine is demonstrated. Self-assembly of valine on the gold particles is accomplished in the aqueous phase, linkage with the gold particles possibly occurring through covalent interaction of the amine group with the surface gold atoms. Derivatization with the amino acid in this manner imparts amphotericity to the gold particles, the particles being negatively charged at pH values greater than 6 (the isoelectric point of valine) and positively charged below this pH. The charge reversal on the gold particles is demonstrated by electrostatic self-assembly of the colloidal gold particles on glass (which is negatively charged at pH > 3) by immersion of the substrate alternately into the valine-capped gold solutions maintained at pH = 3.5 and 8.5. The phase transfer of the aqueous valine-capped gold colloidal particles by electrostatic linkage with fatty amine molecules present in toluene is also described. The two-phase method described herein is extremely simple and results in hydrophobic gold particles which may be precipitated out of solution and redissolved in different nonpolar organic solvents without significant variation in the particle size distribution. The electrostatically driven multilayer assembly of the valine- derivatized gold particles on glass substrates, the phase transfer process, and the stability of the hydrophobized gold particles have been investigated with a variety of techniques such as UV-vis, infrared and X-ray photoemission spectroscopies, ellipsometry, and thermogravimetry/differential thermal analyses.

[133] Modeling of the Salt Permeability in Fixed Charge Multilayer Membranes

K. Lebedev, P. Ramirez, S. Mafe and J. Pellicer

Langmuir 16(25) (2000), 9941-9943

[134] Sprayed Polyelectrolyte Multilayers

J. B. Schlenoff, S. T. Dubas and T. Farhat

Langmuir 16(26) (2000), 9968-9969
Polyelectrolyte multilayers deposited by sequential spraying of poly(styrenesulfonate) and poly(diallyldimethylammonium) solutions are described. A highly uniform thin film is rapidly obtained over a large area. The morphology, uniformity, and chemical composition of sprayed multilayers, as well as the selective membrane properties, are found to be virtually identical to those prepared by dip-immersion.

[135] The Role of Secondary Interactions in Selective Electrostatic Multilayer Deposition

S. L. Clark and P. T. Hammond

Langmuir 16(26) (2000), 10206-10214

Electrostatic layer-by-layer thin films maybe directed to specific regions of a surface based on electrostatics, secondary interactions, and steric repulsion. In this study, a series of polyamines ranging from hydrophobic polyallylammonium hydrochloride (PAH) to hydrophilic linear polyethyleneimine (LPEI) were coadsorbed with poly(acrylic acid) (PAA) onto patterned self-assembled monolayer (SAM) surfaces. When an acid (COOH) and oligoethylene glycol (EG) SAMs are used as the surface template, it was found that the region of preferred deposition for the more hydrophobic polyamine species was generally the EG region at pH 4.8, rather than the partially charged COOH region. The more hydrophilic LPEI species preferred adsorption on the COOH surface. It is proposed that PAH undergoes complexation with the EG surface based on hydrophobic and hydrogen bonding interactions at moderate pH. On the other hand, the LPEI backbone is hydrated and is thought to undergo large steric repulsion with the EG surface, thus resulting in deposition only on the COOH surface. The region of preferred adsorption also varied with pH, as the hydrogen- bonding interaction of PAA became important at low pH, and electrostatic interactions became the controlling element for selectivity at high pH, when all systems were highly charged. By tuning polyion-surface interactions, the region of polyion deposition can be carefully controlled on patterned chemical surfaces.

[136] Ultrathin-Film Self-Assembly of Hybrid Organic-Inorganic Metal Coordination Polymers

H. Byrd, C. E. Holloway, J. Pogue, S. Kircus, R. C. Advincula and W. Knoll

Langmuir 16(26) (2000), 10322-10328

We have investigated the self-assembly of ultrathin zirconium coordination monomer and polymer films using a layer-by-layer approach. These materials are of great interest for incorporating metal ion (inorganic) moieties in organic (polymer) films with applications ranging from conductors to catalytic materials. The differences between the polymer and monomer assembly from solution are described. These differences were investigated using UV-vis spectroscopy, AFM, and surface plasmon spectroscopy. The differences in orientation, morphology, roughness, and linearity of deposition reflect the conformational limitations of the polymer toward self-assembly. On the other hand, the sequential assembly of the monomer and Zr metal ion indicates the strong coordination between the metal and the organic ligands, resulting in robust homogeneous films.

[137] Thin-Film Optical Sensors Employing Polyelectrolyte Assembly

S. H. Lee, J. Kumar and S. K. Tripathy

Langmuir 16(26) (2000), 10482-10489

This work describes the development of thin film optical sensors for pH, metal ions (ferric and mercury), and 2,4- dinitrotoluene detection. To fabricate the pH sensor, a fluorescent molecule, 1-hydroxypyren-3,6,8-trisulfonate, was assembled with a polycation by an electrostatic layer-by-layer assembly technique. The fluorescent indicator molecule exhibits distinct and well-defined emission peaks for protonated and deprotonated forms. The relative peak positions and intensity of fluorescence of the protonated and deprotonated forms change in response to pH variations. For metal ion (ferric and mercury) and 2,4-dinitrotoluene sensing, the indicator molecules were covalently incorporated into poly(acrylic acid) and subsequently assembled with a polycation employing electrostatic layer-by-layer assembly. The sensor is based on the fluorescence quenching of indicator molecules by electron transfer from indicator to electron-deficient analytes such as ferric ions, mercury, and 2,4-dinitrotoluene. Fluorescence intensities decreased with increasing concentration of analytes, Quenching behavior follows Stern-Volmer bimolecular quenching kinetics. Linear increase in absorbance, film thickness, and emission intensity was observed as a function of number of bilayers deposited in all these films.

[138] Multilayer Assemblies of Copolymer Psoh and PVP on the Basis of Hydrogen-Bonding

L. Y. Wang, S. X. Cui, Z. Q. Wang, X. Zhang, M. Jiang, L. F. Chi and H. Fuchs

Langmuir 16(26) (2000), 10490-10494

An alternating deposition film of a copolymer of p-(hexaflouro- 2-hydroxylisopropyl)-alpha -methylstyrene and styrene (PSOH) and poly(4-vinylpyridine) (PVP) was fabricated on the basis of hydrogen bonding between hydroxyl and a pyridine ring in chloroform. It is found that the selection of solvent is very important for successful preparation of a multilayer film on the basis of hydrogen bonding. A series of PSOHs with different contents of hydrogen-bonding donors were used to fabricate multilayer assemblies. The driving force for multilayer assemblies was identified by FTIR. Several factors, such as solvents, concentration, and content of hydrogen-bonding donors, were discussed, which influence greatly the deposition process and layered architectures.

[139] Preparation of Microcapsules of Strong Polyelectrolyte Couples by One-Step Complex Surface Precipitation

A. Voigt, E. Donath and H. Möhwald

MACROMOL MATER ENG 282(9) (2000), 13-16

Full Paper: Polyelectrolyte microcapsules are fabricated by a one-step surface precipitation and by a layer-by-layer technique an decomposable colloids. The ternary solvent water/ acetone/sodium bromide is adjusted properly keeping dissolved simultaneously the strong polyelectrolytes sodium poly(styrene sulfonate) and poly(vinyl benzyl trimethylammonium chloride). Microcapsules are characterized by confocal laser scanning microscopy and scanning force microscopy. The capsules are dissolvable in the ternary solvent. Other dissolved strong polyelectrolyte couples and template-free preparation pathways are suggested.

[140] Self-Assembly of Mono-Layer and Multilayer of Polyconjugated Conducting Polymers

A. Berlin and G. Zotti

MACROMOL RAPID COMMUN 21(7) (2000), 301-318

To obtain organised mono- and multilayers of policonjugated polymers or oligomers by self assembly techniques has recently attracted much attention. This is due to the simplicity of the method and to the fact that no sophisticated apparatus is required. In the present feature the state of the art in this field is discussed including our own research results. A survey on self assembly of thiols, disulfides, and alkylsilanes on gold or glass surfaces is presented as well as self assembly of ferrocenylalkyl-substituted heterocycle adsorbates on ITO surfaces. Carboxyalkyl bithiophenes and terthiophenes, in which the oligothiophene tail is either perpendicularly or linearly linked to the tethering carboxyalkyl chain form stable monolayers on ITO electrodes and are anodically oxidised to produce polymer layers or to couple with oligothiophenes in solution, depending on the structure. As for multilayers, an introductory survey on the self assembly technique usually employed is given. Several examples of multilayers constituted of electroconductive polymers are discussed. Finally our recent results concerning different multilayers from polythiophenes bearing anionic and cationic moieties are discussed.

[141] Ultrathin Polymer-Coatings by Complexation of Polyelectrolytes at Interfaces - Suitable Materials, Structure and Properties

P. Bertrand, A. Jonas, A. Laschewsky and R. Legras

MACROMOL RAPID COMMUN 21(7) (2000), 319-348

The article presents the state-of-the-art of alternating physisorption of oppositely charged polyelectrolytes, the so- called ''layer-by-layer'' method or ''electrostatic self- assembly'' (ESA), for the preparation of thin polymer coatings. In comparison to other, more established self-organization techniques, this recent method is distinguished by its simplicity, versatility, and speed. In particular, the tendency for self-healing is unique. Emphasis is given to the role of the molecular structure of the polyelectrolytes, and to the nature of the support. Also, various parameters for the preparation of multilayer films are highlighted, which are very important due to the kinetic control of the build-up process. The structure of the resulting coatings, their quality and stability, chemical reactions in the films, and potential applications are discussed.

[142] Preparation of Enzyme Multilayers on Colloids for Biocatalysis

C. Schuler and F. Caruso

MACROMOL RAPID COMMUN 21(11) (2000), 750-753

Communication: The construction of enzyme multilayer films on colloidal particles for biocatalysis is described. The enzyme multilayers were assembled on submicrometer-sized polystyrene spheres via the alternate adsorption of poly(ethyleneimine) and glucose oxidase using a layer-by-layer approach. Microelectrophoresis and single particle light scattering measurements revealed regular and step-wise assembly of the multilayers on the colloids. The high surface area bio- multilayer coated particles formed were subsequently utilized in enzymatic catalysis.

[143] Synthesis and Electrostatic Multilayer Assembly of an Acridine- Containing Polymer with Properties of an Optical Sensor

T. S. Lee, C. D. Yang and W. H. Park

MACROMOL RAPID COMMUN 21(14) (2000), 951-955

We have synthesized an acridine-containing polymer linked with alkyl amide via simple polycondensation reaction. It was found that the polymer exhibits high selectivity and sensitivity toward ferric ions indicating that this polymeric material would be an efficient fluorescence sensor for ferric ions. The formation of self-assembled multilayers was carried out via layer-by-layer deposition technique between the acridine- containing polymer and poly(sodium-4-styrenesulfonate).

[144] Layer-by-Layer Adsorption of Identically Charged Polyelectrolytes

P. Fischer and A. Laschewsky

Macromolecules 33(3) (2000), 1100-1102

[145] PH-Dependent Thickness Behavior of Sequentially Adsorbed Layers of Weak Polyelectrolytes

S. S. Shiratori and M. F. Rubner

Macromolecules 33(11) (2000), 4213-4219
A detailed study of the role that solution pH plays in the layer-by-layer processing of the weak polyelectrolytes poly(acrylic acid) and poly(allylamine hydrochoride) was carried out. It was found that dramatically different polymer adsorption behavior is observed as one systematically increases (or decreases) the charge density of a weak polyelectrolyte including transitions from very thick adsorbed layers (ca. 80 Angstrom) to very thin adsorbed layers (ca. 4 Angstrom) over a very narrow pH range. By controlling pH, it is possible to vary the thickness of an adsorbed polycation or polyanion layer from 5 to 80 Angstrom. In addition, control over the bulk and surface composition of the resultant multilayer thin films is readily achieved via simple pH adjustments. These studies have provided new insights into the polyelectrolyte sequential adsorption process and have already opened up some interesting technological applications.

[146] Lipid Coating on Polyelectrolyte Surface-Modified Colloidal Particles and Polyelectrolyte Capsules

S. Moya, E. Donath, G. B. Sukhorukov, M. Auch, H. Baumler, H. Lichtenfeld and H. Möhwald

Macromolecules 33(12) (2000), 4538-4544

Dipalmitoyldiphosphatidic acid (DPPA), dipalmitoyldiphosphatidylcholine (DPPC), and sphingosine were adsorbed onto polyelectrolyte coated colloids and capsules forming composite lipid-polyelectrolyte layers. The stepwise coating was performed either by adsorption of preformed vesicles onto the capsule surface or by a solvent exchange protocol. The lipid assembly was monitored by zeta-potential measurements. Single particle light scattering, flow cytometry, and fluorescence studies of Forster energy transfer have been used to quantify the lipid coating. Confocal microscopy images of capsules coated with fluorescent lipids demonstrated a homogeneous coverage of the capsule surface. Differential scanning calorimetry shows a phase transition temperature characteristic for lipid layer structures. It was concluded that the adsorbed DPPA form bilayers while DPPC may form multilayers. It was further shown that on top of the lipid layers further polyelectrolyte layers could be assembled. The permeability of B-carboxyfluorescein (6-CF) through the composite layer structure was studied by means of confocal laser scanning microscopy. The permeation time through the composite layer was of the order of 10(1)-10(2) min, while in the absence of lipids 6-CF equilibrated faster than the time resolution of the technique.

[147] Azo Polymer Multilayer Films by Electrostatic Self-Assembly and Layer-by-Layer Post Azo Functionalization

S. H. Lee, S. Balasubramanian, D. Y. Kim, N. K. Viswanathan, S. Bian, J. Kumar and S. K. Tripathy

Macromolecules 33(17) (2000), 6534-6540

This work focuses on the development of a novel method for molecular level assembly and processing of multilayer azo polymer films. Poly(acrylic acid)-based precursor anilino- functional polymer was first synthesized and used as a polyanion. This polymer was assembled into mono- and multilayer thin films by an electrostatic layer-by-layer deposition technique in conjunction with a polycation. The aniline group in the assembled polymer layer was subsequently converted to an azobenzene chromophore by post azo coupling reaction with appropriate diazonium salts. This method provides easy control of film thickness and well-ordered chromophore structure in the multilayer. Second harmonic generation was observed in all multilayer films, indicating acentric organization of the chromophores synthesized in the multilayered films. The second harmonic intensity and film thickness are dependent on the assembly conditions (pH, etc.) of the polyions. The post- functionalized azo polymer layers were further modulated by Light-driven mass transport.

[148] Effects of Spacer Chain Lengths on Layered Nanostructures Assembled with Main-Chain Azobenzene Ionenes and Polyelectrolytes

J. D. Hong, B. D. Jung, C. H. Kim and K. Kim

Macromolecules 33(21) (2000), 7905-7911

With the aim of fabricating internally ordered multilayer assemblies using the layer-by-layer electrostatic deposition method, we have prepared polyelectrolytes called ionenes that contain rigid azobenzene chromophores separated by flexible spacer chains, i.e., poly ((4,4'-bis(6- dimethylammonio)hexyl)oxy)azobenzene bromide), PAZ-B, poly ((4,4'-bis(10-dimethylammonio)decyl)oxy)azobenzene bromide), PAZ-10, and poly ((4,4'-bis(12- dimethylammonio)dodececyl)oxy)azobenzene bromide), PAZ-12. UV/ vis spectroscopy of solutions shows that PAZ-10 and PAZ-12 form robust lamellar aggregates that could be successfully transferred onto a solid substrate by forming multilayer assemblies with oppositely charged polyelectrolytes, From FTIR spectra of the resulting multilayer assemblies, the alkyl chains appeared to be highly ordered, especially in the case of longer spacer chain. The thicknesses of the PAZ monolayers measured atomic force microscopy were overall consistent with the theoretical values (2.61 and 3.23 nn) determined by a model calculation, based on the tilt angle measurement of chromophore and the molecular length of the repeat unit of the ionenes.

[149] Orientation of Nonlinear-Optical Active Dyes in Electrostatically Self-Assembled Polymer-Films Containing Cyclodextrins

P. Fischer, M. Koetse, A. Laschewsky, E. Wischerhoff, L. Jullien, A. Persoons and T. Verbiest

Macromolecules 33(26) (2000), 9471-9473

[150] Ultrathin-Film Fabricated from Pddac/DSB and Ndr/DSB

J. Y. Chen, G. B. Luo, R. X. Wang, X. S. Zhao and W. X. Cao

MATER RES BULL 35(12) (2000), 1945-1954
Two kinds of ultrathin films were successfully fabricated by the self-assembly deposition technique from poly(diallyldimethylammonium chloride) (PDDAC) or nitro- containing diazoresin (NDR) as the polycation and 4,4'- di(sodium styryl-2-sulfonate) biphenyl (DSB) as the dianion. This stepwise fabrication process was monitored by UV-vis spectrometry. The regularity of the film and the morphology of the film surface were examined by X-ray diffraction (XRD) and atom force microscopy (AFM), respectively. The results show that these kinds of films are composed of well arranged molecules, and have a very flat surface. Among them, the PDDAC/ DSB film emits fluorescence when excited with UV light at 354 nm. The NDR/DSB film does not emit fluorescence, because the NDR quenches the fluorescence of DSB; however, the NDR/DSB film possesses more stability against solvent etching (such as DMF), compared with the PDDAC/DSB film. (C) 2001 Elsevier Science Ltd. All rights reserved.

[151] Ultrathin Nanoparticle ZnS and ZnS Mn Films - Surface Sol-Gel Synthesis, Morphology, Photophysical Properties

N. I. Kovtyukhova, E. V. Buzaneva, C. C. Waraksa and T. E. Mallouk

MATER SCI ENG B SOLID STATE M 69(NSI) (2000), 411-417

Ultrathin films of ZnS and Mn-doped ZnS were grown on silicon substrates using surface sol-gel reactions, and the film growth process was characterized by ellipsometry, atomic force microscopy, X-ray photoelectron spectroscopy, UV-visible absorbance and photoluminescence (PL) spectroscopy. The Si substrates were pre-treated by chemical oxidation. On the oxidized Si/SiOx surface, nanoparticulate films of ZnS and Mn- doped ZnS were grown by sequential immersion in aqueous metal acetate and sodium sulfide solutions. During the first four adsorption cycles, there was little film growth, but thereafter the amount of material deposited was linear with the number of adsorption cycles. This behavior is consistent with the formation of ZnS nuclei at low coverage, followed by particle growth in subsequent cycles. PL spectra are consistent with incorporation of Mn2+ into the ZnS nanoparticles. (C) 2000 Elsevier Science S.A. All rights reserved.

[152] Self-Assembly of Nanostructured Composite ZnO/Polyaniline Films

N. I. Kovtyukhova, A. D. Gorchinskiy and C. Waraksa

MATER SCI ENG B SOLID STATE M 69(NSI) (2000), 424-430

Ultrathin composite ZnO/polyaniline (PAN) films were deposited from organic solutions on silicon and ITO substrates using wet layer-by-layer self-assembly technique. The film growth process was characterized by transmission electron microscopy, ellipsometry, atomic force microscopy, IR and UV-visible absorbance and photoluminescence spectroscopy, and electrical measurements. The Si substrates were pre-treated by chemical oxidation. Multilayer films were grown by sequential immersion of the substrate in an ethanolic ZnO sol and PAN solution in dimethyl formamide. The first adsorption cycle resulted in well- packed monoparticulate ZnO layer almost completely covering the substrate, which predetermined the regular growth of densely packed and quite smooth ten-layer ZnO/PAN film. Photoluminescence and IR data assumed chemical interaction between the components in neighbouring layers. The multilayer (ZnO/PAN)(9)ZnO film sandwiched between ITO and Pr electrodes exhibited strong photoelectrical response while both the components were photoelectrically inactive in our experimental conditions. The reversible conversion from insulating to conducting state was observed under irradiation by light with a wavelength below 350 nm. (C) 2000 Elsevier Science S.A. All rights reserved.

[153] Photoinduced Alignments of Liquid-Crystal Molecules on Alternate Self-Assembly Films Evaluated by the Attenuated Total- Reflection Measurement

A. Baba, F. Kaneko, K. Shinbo, K. Kato, S. Kobayashi and R. C. Advincula

MOL CRYST LIQUID CRYST 347 (2000), 259-268

Photo-induced in-plane alignments of nematic liquid crystal (LC) molecules, 5CB, have been investigated in the cell with alternate self-assembly films of polyelectrolyte and low- molecular weight dyes on the gold electrodes using the attenuated total reflection (ATR) measurement method. Reflectivities due to the excitations of the surface plasmon polariton (SPP) were observed in the ATR properties of the LC cell. In-plane switching of LC molecules adjacent to the aligning layer was evaluated from the ATR curves by means of irradiation of the linearly polarized visible light to the LC cell. It was also estimated that the re-orientation of the LC molecules occurred within about 130 nm from the surface of the aligning layer on the prism by the irradiation of the polarized light.

[154] Rectifying Self-Assembled Ultrathin Films

T. P. Cassagneau, B. Swerydakrawiec and J. H. Fendler

MRS BULL 25(9) (2000), 40-46

[155] Nanoassemblies of Sulfonated Polyaniline Multilayers

N. Sarkar, M. K. Ram, A. Sarkar, R. Narizzano, S. Paddeu and C. Nicolini

NANOTECHNOL 11(1) (2000), 30-36
A self-assembly layer-by-layer (LBL) technique was used for the sequential adsorption of polycation, poly(diallyldimethylammonium chloride) (PDDA) and polyanion, sulfonated polyaniline (SPANI) on glass. indium-tin-oxide (ITO) coated grass plates, polystyrene sulfonate (PSS)/glass and PSS/ ITO surfaces, respectively The building up of such multilayers was characterized by the increment of the: adsorbed amount through UV-visible spectroscopy and cyclic voltammetry The atomic force microscopic study showed the granular surface topology of such self-assembled films of sulfonated polyaniline. PDDA/SPANI LBL films were electrically active and detailed electrochemical parameters were investigated.

[156] Nano-Assembly of Glucose-Oxidase on the in-Situ Self-Assembled Films of Polypyrrole and Its Optical, Surface and Electrochemical Characterizations

M. K. Ram, M. Adami, S. Paddeu and C. Nicolini

NANOTECHNOL 11(2) (2000), 112-119

An in situ self-assembly technique with nanometre control over thicknesses and multilayered structures was used to manufacture the ultrathin films of polypyrrole (PPY). The PPY film was deposited on a polyanion, poly(styrene sulfonate) (PSS) modified surface as a Function of time, previously PSS had been deposited on various substrates (glass, mica, indium-tin-oxide coated glass plates). Later, alternate PPY and PSS films were fabricated on such substrates using a layer-by-layer (LBL) technique. The glucose oxidase (GOD) molecules were also deposited on such self-assembled PPY films by the LBL technique. The PSS/PPY/GOD, PPY/PPY/GOD/poly(ethylene imine) (PEI)/GOD etc, film configurations were fabricated. and functionally as well as structurally characterized by UV- visible, electrochemical and scanning probe microscopy techniques, respectively. The results of a scanning probe microscopic study on the films were analysed to understand the molecular orientation of GOD on the PPY surface, and the dependence of the enzyme concentration for the depositing solutions. Moreover, the electrochemical studies performed provided information with respect to the electron transfer processes on the spatial arrangement of GOD molecules on the PPY surfaces. The immobilization of GOD on a conductive PPY represented a crucial and important step, and allowed us to construct the glucose-responsive biosensors.

[157] Molecular-Scale Interface Engineering for Polymer Light- Emitting-Diodes

P. K. H. Ho, J. S. Kim, J. H. Burroughes, H. Becker, S. F. Y. Li, T. M. Brown, F. Cacialli and R. H. Friend

Nature