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12(11) (2000), 3392-3396
We report two new hydrogen-bonding-based routes for layer-by- layer fabrication of polymer/Au nanoparticle multilayer thin films. Two types of Au nanoparticles surface-modified with carboxyl groups or pyridine groups were prepared in nonaqueous solvents. In the first assembly route, we consecutively adsorbed poly(4-vinylpyridine) (PVP) and Au nanoparticles with carboxyl group tailored surfaces. In the second route, we alternatively deposited poly(acrylic acid) (PAA) and Au nanoparticles with pyridine group tailored surfaces. The multilayer buildup was monitored by UV-vis spectroscopy, which showed a linear increase of the film absorbance with the number of adsorbed Au layers. FTIR spectroscopy was used to verify hydrogen bonding between the pyridine and carboxyl groups, which is believed to be the driving force for the formation of polymer/Au multilayer thin films.

[49] Electron-Transfer Between Adjacent Layers in Self-Assembled Films

V. B. P. Leite, M. Ferreira and O. N. Oliveira

Chem. Phys. Lett. 316(5-6) (2000), 343-348

A simple model of electron transfer is adapted to explain fluorescence quenching in self-assembled films of poly( p- phenylene vinylene) (PPV) alternating with poly(thiophene acetic acid) (PTAA). Quenching is caused by a photo-induced electron transfer between the excited PPV (donor, D) and the PTAA (acceptor, A). The electron-transfer process can be mediated by insertion of electronically inert spacing bilayers between the D and A layers, As the number of bilayers is increased, the fluorescence is gradually recovered which is explained theoretically by assuming that the electron-transfer rate can be described as k = Z exp(- beta r) where r is the distance between D and A. (C) 2000 Elsevier Science B.V. All rights reserved.

[50] Controlled Synthesis of Stable Poly(Vinyl Formamide-Co-Vinyl Amine)/Silica Hybrid Particles by Interfacial Post-Cross- Linking Reactions

I. Voigt, F. Simon, H. Komber, H. J. Jacobasch and S. Spange

Colloid Polym. Sci. 278(1) (2000), 48-56

The chemical synthesis and the physicochemical properties of stable poly(vinyl formamide-co-vinyl amine)/silica hybrid particles are presented. Copolymers of poly(vinyl formamide) (PVFA) and poly(vinyl amine) (PVAm) and their protonated forms were adsorbed onto silica from aqueous solutions. The influences of the pH strength and the ion concentration of the aqueous solution as well as the copolymer composition (degree of hydrolyzation of PVFA). and the molecular mass on the adsorption process were investigated by electrokinetic measurements, potentiometric titration, and quantitative elemental analyses. Silica surface-charge neutralization is achieved at a pH strength above 10 for highly hydrolyzed (95%) PVFA polymers. Decreasing the amino content in the PVAm chain shifts successively both the point of zero charge and the isoelectric point to lower pH values. PVFA-co-PVAm layers onto silica are adsorbed weakly. To fix these layers irreversibly, cross-linking reactions with (4,4'-diisocyanate)diphenyl methane were carried out on the surface of solid PVFA-co-PVAm/ silica hybrid particles suspended in acetone. The cross-linking reaction, which is connected with the conversion of amino groups, is also a tool to control the surface charge of the PVFA-co-PVAm/silica hybrids. X-ray photoelectron spectroscopy and solid-state C-13 cross-polarization magic-angle spinning NMR spectroscopy were used to obtain information on the number of and the structure of the functionalized polyelectrolyte layers on silica. The success of cross-linking was also shown by the results of these spectroscopic methods.

[51] Synchronous Alternate Multilayered Adsorption of Poly(4-Vinyl-N- N-Butylpyridinium) Cations and Poly(Styrene Sulfonate) Anions on Polystyrene Colloidal Spheres

T. Okubo and M. Suda

Colloid Polym. Sci. 278(4) (2000), 380-384

Alternate multiple adsorbed layers of up to six macrocations [poly(4-vinyl-N-n-butylpyridinium bromide)] and macroanions [sodium poly(styrene sulfonate)] are formed on monodispersed polystyrene colloidal spheres above the critical concentration of the macroions, m*. The m* value is the minimum number of macroions needed to reverse the sign of the zeta potential of the spheres in the first adsorption step. Alternate sign reversal in the zeta potential and expansive-contractive thickness changes are observed on the repeated and alternate addition of macrocations first and macroanions next. When the macroanions are added first, sign reversal in the zeta potential and reversible expansion and contraction do not occur. Breaking of the alternate multiple-type adsorption also occurs when equivalency in the number of dissociative groups of macrocations and macroanions is broken. Synchronous conformational changes of macrocations and macroanions in the multiple-adsorbed layers occurs only when the conformational rigidities with the multiple electrostatic and hydrophobic attraction and/or repulsion between macrocations and macroanions are delicately balanced.

[52] From Langmuir Monolayers to Nanocapsules

H. Möhwald

Colloid Surf. A 171(1-3) (2000), 25-31

This report intends to draw a line from the controlled preparation and understanding of Langmuir monolayers to the fabrication of hollow capsules with exciting perspectives for basic science and applications. It is shown that methods used to characterize structure and transport properties of Langmuir and Langmuir-Blodgett films could be used to study polymeric ultrathin films. Since the latter are permeable to small molecules they could be used to prepare capsules after coating depolymerizable colloids. The inside of the capsule can be designed such that it is distinguished by inner walls and pH in the interior to perform a specific chemistry. As an application example selective precipitation of a dye molecule as a model for drug loading is presented. (C) 2000 Elsevier Science B.V. All rights reserved.

[53] Formation of Luminescent Spherical Core-Shell Particles by the Consecutive Adsorption of Polyelectrolyte and CdTe(S) Nanocrystals on Latex Colloids

A. S. Susha, F. Caruso, A. L. Rogach, G. B. Sukhorukov, A. Kornowski, H. Möhwald, M. Giersig, A. Eychmuller and H. Weller

Colloid Surf. A 163(1) (2000), 39-44

Functional core-shell particles were prepared by assembling a composite multilayer shell of charged polyelectrolytes and luminescent CdTe(S) nanocrystals (cadmium telluride with a certain content of sulfide) via their consecutive electrostatic adsorption from solution onto micron-sized latex particles. The formation of the composite shell has been confirmed by optical spectroscopy, confocal microscopy and high-resolution transmission electron microscopy. Variation of the size and surface chemistry of the semiconductor nanoparticles, the size and shape of the colloid templates, and the nature of the polyelectrolyte opens new avenues for the production of a variety of novel core-shell materials. (C) 2000 Elsevier Science B.V. All rights reserved.

[54] Lateral Lipid Diffusion in Phospholipid Monolayers Coupled to Polyelectrolyte Films

M. Auch, B. Fischer and H. Möhwald

Colloid Surf. A 164(1) (2000), 39-45

The lateral diffusion of lipid probes in lipid monolayers on polyelectrolyte support in different solvent environment was studied by a fringe pattern photobleaching experiment that enabled to measure diffusion coefficients D of over six orders of magnitude, In nonpolar solvents, as well as in air, electrostatic binding of ionic and also of zwitterionic lipids is so strong, that D < 10(-12) cm(2) s(-1) was observed. In polar solvents (e.g. methanol), the interaction is reduced for zwitterionic lipids, enabling D > 10(-7) cm(2) s(-1). In water, the coupling is similarly reduced for zwitterionic, not for ionic lipids. In the case of a weak interaction with the polymer, one encounters a temperature dependence for the monolayer of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) as expected for a system with a fluid/gel phase transition. (C) 2000 Elsevier Science B.V. All rights reserved.

[55] Polyelectrolyte Adsorption Processes Characterized in-Situ Using the Quartz-Crystal Microbalance Technique - Alternate Adsorption Properties in Ultrathin Polymer-Films

A. Baba, F. Kaneko and R. C. Advincula

Colloid Surf. A 173(1-3) (2000), 39-49

The alternate adsorption processes of polyelectrolytes from solution have been investigated in situ using a functionalized (gold electrode) quartz substrate via the quartz crystal microbalance (QCM) technique. The deposition process involved the alternate layer by layer electrostatic (Coulombic) interaction between oppositely charged adsorbing polyelectrolytes resulting in ultrathin multilayer films. Three kinds of polyelectrolyte combinations were used: poly(diallyldimethylammonium chloride) (PDADMAC), poly(ethylenimine) (PEI) and poly(allylamine hydrochloride) (PAH) as the cationic polymers and poly(sodium-4- styrensulfonate) (PSS) as the anionic polymer for polycation/ polyanion combinations. The electrical behavior of the piezoelectric 'quartz crystal' was sensitive to the adsorption properties of the polyelectrolytes, thus allowing dose observation of the time-dependent adsorption processes. The adsorption relationship was explored for different polyelectrolyte pair-combinations, alternate solution concentration and the presence of rinsing and drying steps. The results showed that the amount of frequency change is mostly dependent on the immediate subphase environment of the crystal surface, i.e. aqueous environment versus air in relation to the classic Sauerbrey equation. (C) 2000 Elsevier Science B.V. All rights reserved.

[56] Influence of the Ionic-Strength on the Structure of Polyelectrolyte Films at the Solid/Liquid Interface

R. Steitz, V. Leiner, R. Siebrecht and R. Vonklitzing

Colloid Surf. A 163(1) (2000), 63-70

The structure of polyelectrolyte multilayers built up by alternate adsorption of polyanions and polycations is investigated by X-ray reflectivity at the solid/air and neutron reflectivity at the solid/liquid interface. The experiments provide detailed information about the density gradient of polyelectrolyte chains across the film and show the influence of the water content of the film on the internal structure. The polyelectrolyte density is determined by the adsorption conditions (e.g. amount of NaCl) and cannot be changed by addition of salt after adsorption. After drying the film thickness is reduced by 30%. (C) 2000 Elsevier Science B.V. All rights reserved.

[57] Electrostatic Adsorption of Polystyrene Particles with Different Surface-Charges Onto the Surface of an Ultrathin Polymer Film

T. Serizawa, S. Kamimura and M. Akashi

Colloid Surf. A 164(2-3) (2000), 237-245

The adsorption of polystyrene particles with different surface charges from aqueous dispersions onto the surfaces of cationic ultrathin polymer films was quantified using a quartz crystal microbalance (QCM) technique. The polymer films were prepared by the alternate adsorption technique from poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) in the presence or absence of NaCl onto the QCM substrate. Particle adsorption, as a result of electrostatic interaction, onto the outermost PAH surface was observed by QCM. The adsorption behavior of two differently charged particles was examined and revealed greater adsorption of particles with a relatively larger surface charge. The dependence of adsorption of all the particles against an outermost PAH thickness in a polymer precursor film was described by a sigmoid curve, indicating that a critical charge on/in the him is required for adsorption. SEM observations showed monolayer adsorption without three-dimensional aggregation. (C) 2000 Elsevier Science B.V. All rights reserved.

[58] Assembly of Beta-Glucosidase Multilayers on Spherical Colloidal Particles and Their Use as Active Catalysts

F. Caruso, H. Fiedler and K. Haage

Colloid Surf. A 169(1-3) (2000), 287-293

beta-glucosidase (beta-GLS) layers of the enzyme, each separated by oppositely charged polyelectrolyte (poly(styrenesulfonate), PSS), were deposited onto polystyrene (PS) latex particles using the layer-by-layer adsorption technique. Electrophoretic mobility (EPM) and single-particle light scattering (SPLS) measurements revealed regular and step- wise assembly of beta-GLS/PSS multilayers on the colloidal particles. Alternating positive and negative zeta-potentials were observed for beta-GLS and PSS deposition, respectively. An average thickness of 3.5 +/- 0.6 nm was calculated for each beta-GLS/PSS layer pair from SPLS data. The immobilized catalyst (in the form of an enzyme multilayer film on particles) proved to be active in the glucosidation of dodecanol, yielding dodecyl-beta-D-glucopyranoside. The product yield increased with increasing enzyme layer number for beta- GLS multilayer-coated PS particles when the outermost layer was polyelectrolyte. (C) 2000 Elsevier Science B.V. All rights reserved.

[59] Assembly and Structural Study of the Films of Immunoglobulin-M on Solid Substrates

R. L. Kayushina, A. L. Tolstikhina, N. D. Stepina, V. V. Belyaev, V. A. Lapuk and E. Y. Varlamova

Crystallogr. Rep. 45(6) (2000), 1001-1006

Immunoglobulin M (IgM) was immobilized from a solution by the method of charge self-assembly on solid substrates (ordered polyelectrolytes and as-cleaved mica). The process of film formation and the structural organization was controlled and studied by the methods of atomic-force microscopy and X-ray reflectometry. It was shown that adsorption from rather concentrated (0.680-0.068 mg/ml) IgM solutions gave rise to formation of 100- to 150-Angstrom -thick continuous protein layers. At lower concentrations (0.006 mg/ml), no continuous protein films were formed. The substrates of mica-type atomically smooth surfaces provide a higher image resolution, which, in turn, allows the observation of isolated IgM molecules and their aggregates. In the image plane, the molecules have rounded contours 300-500 Angstrom in diameter and 40-60 Angstrom in height. (C) 2000 MAIK ''Nauka/ Interperiodica''.

[60] Layer-by-Layer Electrostatic Deposition of Biomolecules on Surfaces for Molecular Recognition, Redox Mediation and Signal Generation

E. J. Calvo, F. Battaglini, C. Danilowicz, A. Wolosiuk and M. Otero

FARADAY DISCUSS Iss 116 (2000), 47-65

Layer-by-layer supramolecular structures composed of alternate layers of negatively charged enzymes and cationic redox polyelectrolyte have been assembled. Glucose oxidase (GOx), lactate oxidase (LOx) and soybean peroxidase (SBP) have been electrically wired to the underlying electrode by means of poly(allylamine) with [Os(bpy)(2)ClPyCOH](+) covalently attached (PAA-Os) in organized structures with high spatial resolution. Biotinylated glucose oxidase has also been used to assemble step-by-step on antibiotin goat immunoglobulin (IgG) layers and the enzyme was electrically wired by PAA-Os. These spatially organized multilayers with mono- and bienzymatic schemes can work efficiently in molecular recognition, redox mediation and generation of an electrical signal. The concentration of redox mediator integrated into the multilayers, obtained from the voltammetric charge and an estimation of the layer thickness, exceeds by 100-fold the amount of deposited enzyme assessed by quartz crystal microbalance. Differences in GOx electrical wiring efficiency have been detected with the different assembling strategies. The surface concentration of electrically wired enzyme represents a small proportion of all the enzyme molecules present in the multilayers which can be oxidized by the soluble mediator [Os(bpy)(2)Cl PyCOOH]Cl. This proportion, as well as the rate of FADH(2) oxidation by PAA-Os, increases with the number of electrically wired enzyme layers and with the spatial accessibility of the Os moiety to the enzyme active center.

[61] Applications of Polyion Films Containing Biomolecules to Sensing Toxicity

J. F. Rusling, L. P. Zhou, B. Munge, J. Yang, C. Estavillo and J. B. Schenkman

FARADAY DISCUSS Iss 116 (2000), 77-87

This paper describes several applications of polyion- biomolecule films on electrodes related to future development of in vitro chemical toxicity sensors. In the first example, composite films of DNA and ionomers cast onto pyrolytic graphite (PG) electrodes are shown to be useful for detecting DNA damage during incubation with the carcinogen styrene oxide at pH 5.5. Single electrodes can be used to estimate relative damage rates by derivative square wave voltammetry. Films containing the ionomer Nafion gave better reproducibility than another ionomer, Eastman AQ38. In the second example, films containing redox proteins myoglobin (Mb) and cytochrome (cyt) P450(cam) were constructed in alternate layers with polyions including DNA on rough PG electrodes. Films with reversible protein Fe-III/Fe-II electrochemistry with up to 7 electroactive layers were made. Amounts of electroactive protein on rough PG that were 7 to 17-fold larger than in similar films on smooth gold were achieved because many more layers were electroactive. Films of Mb/DNA also showed oxidation peaks after short incubations with styrene oxide that may be attributable to DNA damage. Results are relevant to the future design of enzyme-DNA films which convert pollutants and drugs to reactive metabolites, followed by electrochemical detection of the resulting DNA damage.

[62] Ultrathin, Layered Polyamide and Polyimide Coatings on Aluminum

J. H. Dai, D. M. Sullivan and M. L. Bruening

IND ENG CHEM RES 39(10) (2000), 3528-3535

Ultrathin, passivating films are attractive for protecting metal surfaces without completely masking substrate properties. Alternating polyelectrolyte deposition of layered poly(acrylic acid)/ poly(allylamine hydrochloride) (PAA/PAH) films on Al produces ultrathin coatings that protect Al from Cl--induced corrosion. Although the resistance of these films is minimal, they form a passivating layer on the surface oxide and increase oxide resistance by 2-3 orders of magnitude. Heating of PAA/PAH yields cross-linked polyamides that have film resistances of about 5 M Omega cm(2), even when the film is only 10-nm thick. Although the resistance of these films is high, reductions in corrosion current due to cross-linked films are still primarily due to passivation of the surface oxide as oxide resistance is larger than film resistance. Layer-by-layer covalent deposition of Gantrez/poly(allylamine) films yields ultrathin amic acid- linked layers that can be imidized by heating. Impedances of Al electrodes coated with Gantrez/poly(allylamine) films depend on the number of deposited bilayers and increase by an order of magnitude after imidization. These results suggest that increases in film resistance play a role in oxide passivation by this system.

[63] Layer-by-Layer Deposition of J-Aggregates and Polyelectrolytes for Electroluminescence Applications - A Spectroscopic Study

S. Kirstein, S. Bourbon, M. Y. Gao and U. Derossi

Isr. J. Chem. 40(2) (2000), 129-138

The self-assembly method of layer-by-layer deposition of oppositely charged polyelectrolytes is used to insert J- aggregates of the dye tetrachloro-diethyl-disulfobutyl- benzimido-carbocyanine (TDBC) into thin polymeric films. The J- aggregates are characterized by a narrow absorption- and fluorescence band with its maximum at 590 nm, which is red- shifted with respect to the monomeric transition at 515 nm. The dyes are either coadsorbed with the polyelectrolytes poly(allylamine hydrochloride (PAH) and poly(styrene sulfonate) (PSS), or alternately deposited with the precursor of poly(phenylene vinylene) (pre-PPV). The optical properties of the aggregates are nor changed significantly by the deposition process. The pre-PPV/TDBC films are heated under vacuum to convert the PPV to its conjugated form. The resulting films can be used fur the fabrication of light-emitting devices. The optical properties such as fluorescence and electroluminescence are dominated by the J-aggregates. The excitation energy of PPV is transferred to the dye aggregates with an efficiency of 100%. The electroluminescence is not very stable and shows a very slow turn-on time. However, the combination of self- assembled PPV/TDBC layers with a spin-coated film of PPV results in stable electroluminescence emission under ambient conditions. In this case, light is emitted from both species, the PPV and the J-aggregates, whereas the ratio of the two intensities strongly depends on temperature.

[64] Stepwise Stereocomplex Assembly of Stereoregular Poly(Methyl Methacrylate)S on a Substrate

T. Serizawa, K. Hamada, T. Kitayama, N. Fujimoto, K. Hatada and M. Akashi

J. Am. Chem. Soc. 122(9) (2000), 1891-1899

Isotactic (it-) and syndiotactic (st-) poly(methyl methacrylate)s (PMMAs) were synthesized by anionic polymerization in toluene at -78 degrees C with t-C4H9MgBr and t-C4H9Li/(C2H5)3Al, respectively, as initiators. Polymers were assembled by the stepwise immersion of a 9-MHz quartz-crystal microbalance (QCM) as a substrate into organic solutions at ambient temperature. Quantitative QCM analysis revealed that acetonitrile was the best solvent for assembly on the substrate compared to acetone and N,N-dimethylformamide (DMF). The analysis also showed linear growth of the assembly except during the initial two steps (possibly due to direct influence of the gold QCM substrate), indicating that the amount of assembly can be easily regulated at each step. A 5 min immersion of the QCM into each PMMA solution was enough to obtain stepwise assembly. The ratios of st-/it-PMMA assembled, the static contact angle of the assembly at each step, and its reflection absorption spectrum (RAS) strongly implied the stepwise formation of a stereocomplex between it- and st-PMMAs in the assembly. The amount of stereocomplex assembled was significantly affected by the addition of water to the organic solutions, the PMMA concentration, and its molecular weight, as well as the solvent species. Atomic force microscopic (AFM) examination of the assembly revealed a smooth surface. The assembly was formed at the step from the physically adsorbed it- PMMA to st-PMMA. A possible assembling mechanism was also proposed.

[65] Adsorption and Desorption Behavior of an Anionic Pyrene Chromophore in Sequentially Deposited Polyelectrolyte-Dye Thin- Films

C. Tedeschi, F. Caruso, H. Möhwald and S. Kirstein

J. Am. Chem. Soc. 122(24) (2000), 5841-5848

Alternating thin films of the anionic dye pyrenetetrasulfonic acid (4-PSA) and poly(allylamine hydrochloride) (PAH) were formed by the sequential deposition of 4-PSA and PAH from aqueous solution onto solid substrates. Film growth was followed by absorption spectroscopy, and the resulting polyelectrolyte dye multilayer assemblies were characterized by using fluorescence spectroscopy, X-ray reflectivity, and atomic force microscopy (AFM) measurements. 4-PSA was successfully deposited in alternation with PAH when the ionic strength of the BAH solution was greater than 0.1 M. At each PAH adsorption step a given amount of previously adsorbed 4-PSA was extracted. The amount of dye released depended on the film thickness and the salt concentration in the PAH solution from which PAH was subsequently adsorbed. However, the total amount of dye remaining in the film after PAH deposition was essentially independent of the salt content in the PAH solution. Both X-ray reflectivity and AFM measurements revealed a high roughness of the 4-PSA/PAH multilayer films (ca. 20 Angstrom). To gain a better understanding of the parameters that control dye adsorption and extraction, dye adsorption was also investigated by immersion of preformed PAH and poly(styrene sulfonate) (PSS) multilayer films of various thickness into 4-PSA solutions. The amount of 4-PSA absorbed by the films increased with film thickness, and saturated at a thickness above about 20 nm. For these films, subsequent adsorption of a PAH layer extracted most of the dye, except for a small amount approximately equal to that present in one 4-PSA/PAH bilayer prepared by the alternate adsorption process. These observations indicate that the dye molecules are adsorbed to a finite depth of about 20 nm, and after deposition of the oppositely charged PAH, a small amount that is independent of film thickness remains. The presence of this remaining 4-PSA is necessary to complex and bind the next PAH layer, hence allowing continued multilayer film growth. It was also found that the 4-PSA adsorption/ desorption process depended on the drying process that was employed during the formation of the PSS/PAH multilayer films. The amount of dye as well as the penetration depth was reduced when the film was dried between deposition of each layer, and minor changes in the film structure were observed by X-ray reflectivity measurements.

[66] Influence of Polyelectrolyte Multilayer Films on Calcium- Phosphate Nucleation

P. A. Ngankam, P. Lavalle, J. C. Voegel, L. Szyk, G. Decher, P. Schaaf and F. J. G. Cuisinier

J. Am. Chem. Soc.