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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