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Polyelectrolyte multilayer (PEM) capsules are introduced as versatile magnetic carrier systems. Superparamagnetic magnetite is mounted to the multilayer shell itself or is a component of the capsule interior. The PEM is formed at different (decomposable) colloidal templates, e.g. melamine formaldehyde resin, glutaraldehyde fixed red blood cells, emulsion oil droplets. The results are illustrated by transmission electron microscopy and confocal laser scanning microscopy. (C) 2001 Elsevier Science B.V. All rights reserved. [208] Self-Assembly Films from Diazoresin and Carboxy-Containing Polyelectrolytes H. Luo, J. Y. Chen, G. B. Luo, Y. N. Chen and W. X. Cao J. Mater. Chem. 11(2) (2001), 419-422 Multilayer films from diazoresin (I) and poly(sodium acrylate) (II) or a hydrolyzed maleic anhydride-styrene copolymer (III) have been fabricated on mica. During the fabrication process the absorbance of the film at 380 epsilon nm, which is the characteristic absorption of the diphenylamine 4-diazonium group of I, increases about 0.033 for each fabrication cycle. This means that the thickness of the film increases regularly. Under irradiation with UV light or heating, following the decomposition of the diazonium group, the ionic bond in the film structure converts to a covalent bond; this conversion was preliminarily verified by FTIR spectrum analysis. The stability of the different films (irradiated or unirradiated) was determined by UV-vis spectroscopy and the results show that the resistance of the film to etching by polar solvents increases significantly after bond conversion. [209] Precipitation of Multilayered Core-Shell TiO2 Composite Nanoparticles Onto Polymer Layers M. T. Wang and L. D. Zhang J. Mater. Res. 16(3) (2001), 765-773 A composite film of titanium dioxide (TiO2) nanoparticles and hydrolyzed styrene-maleic anhydride alternating copolymer (HSMA) was obtained on a substrate when a TiCl4 solution was heated at 80 degreesC with a spin-cast thin HSMA film present in the solution. The composite film was characterized with x- ray photoelectron spectroscopy and transmission electron microscopy. Results revealed that TiO2 nanoparticles discretely dispersed on the poly-mer layer, and they were dominantly rutile phase, of a spherical shape and 18-20 nm in diameter. In contrast, mainly amorphous TiO2 powders were obtained from the identical TiCl4 solution by drying the solution with the absence of the HSMA film. The TiO2 nanoparticles deposited on the polymer layer were regarded to contain polymer chains, rind a multilayered core-shell model was suggested for the formation of these composite nanoparticles. It is regarded that the core of a composite particle consisted of an anatase-phase TiO2 colloidal nanoparticle, while the shell layer was made of rutile-phase TiO2/polymer multilayers; the composite particles formed by a layer-by-layer self-assembly of TiO2 and polymer layers analogous to biomineralization, where the polymer promoted the crystallization of rutile-phase TiO2 when TiO2 deposited from solution. [210] Fabrication of Polyaniline/Phthalocyanine Hybrid Ultrathin Films via Electrostatic Attraction and Doping Reaction D. Li, Y. D. Jiang, Y. R. Li, X. J. Yang, L. D. Lu and X. Wang J. Mater. Sci. Lett. 20(3) (2001), 233-235 [211] Self-Assembled Polyelectrolyte Multilayer Membranes with Highly Improved Pervaporation Separation of Ethanol/Water Mixtures L. Krasemann, A. Toutianoush and B. Tieke J. Membrane Sci. 181(2) (2001), 221-228
[212] Pervaporation Separation of Water/Alcohol Mixtures Using Composite Membranes Based on Polyelectrolyte Multilayer Assemblies J. Meierhaack, W. Lenk, D. Lehmann and K. Lunkwitz J. Membrane Sci. 184(2) (2001), 233-243 Composite pervaporation membranes composed of an asymmetric polyamide-6 membrane and an ultrathin self-assembled polyelectrolyte separating layer are described. The supporting membrane was prepared from both an unmodified polyamide-6 and a comb-like polymer with carboxyl terminated polyamide-6 side chains. A high end group concentration was found to be advantageous for sufficient adhesion of the multilayer systems on the supports. Up to 20 layers were deposited onto the membrane surface by dipping the membranes in aqueous solutions containing oppositely charged polyelectrolytes. The polyanions used were poly(acrylic acid), poly(styrene sulfonic acid) and alginic acid. The polycations used were poly(diallyldimethylammoniumchloride), chitosan and poly(ethylenimine). Performance of these membranes depends strongly on the layer number and on the type of polyelectrolytes. In general, membranes modified with two weak polyelectrolytes of high charge density gave the best separation properties while those modified with strong polyelectrolytes of low charge density led to poorer separation properties. However, the highest separation factor (greater than or equal to 10,000) for a water/2-propanol mixture (12/88 w/w) at permeate flux of 300 g/m(2)h was obtained with six double layers consisting of poly(ethylenimine) and alginic acid. These composite membranes were stable over an operating period of at least 400 h. (C) 2001 Elsevier Science B.V. All rights reserved. [213] Biological Cells as Templates for Hollow Microcapsules B. Neu, A. Voigt, R. Mitlohner, S. Leporatti, C. Y. Gao, E. Donath, H. Kiesewetter, H. Möhwald, H. J. Meiselman and H. Baumler J. Microencapsul. 18(3) (2001), 385-395 Microcapsules in the micrometer size range with walls of nanometer thickness are of both scientific and technological interest, since they can be employed as micro- and nano- containers. Liposomes represent one example, yet their general use is hampered due to limited stability and a low permeability for polar molecules. Microcapsules formed from polyelectrolytes offer some improvement, since they are permeable to small polar molecules and resistant to chemical and physical influences. Both types of closed films are, however, limited by their spherical shape which precludes producing capsules with anisotropic properties. Biological cells possess a wide variety of shapes and sizes, and, thus, using them as templates would allow the production of capsules with a wide range of morphologies. In the present study, human red blood cells (RBC) as well as Escherichia coli bacteria were used; these cells were fixed by glutardialdehyde prior to layer-by-layer (LbL) adsorption of polyelectrolytes. The growth of the layers was verified by electrophoresis and flow cytometry, with morphology investigated by atomic force and electron microscopy; the dissolution process of the biological template was followed by confocal laser scanning microscopy. The resulting microcapsules are exact copies of the biological template, exhibit elastic properties, and have permeabilities which can be controlled by experimental parameters; this method for microcapsule fabrication, thus, offers an important new approach for this area of biotechnology. [214] Sustained-Release Properties of Polyelectrolyte Multilayer Capsules A. A. Antipov, G. B. Sukhorukov, E. Donath and H. Möhwald J. Phys. Chem. B 105(12) (2001), 2281-2284 Layer-by-layer (LbL) assembly of oppositely charged polyelectrolytes was used to coat fluorescein particles. These particles, with a size of 4-9 mum, were prepared by precipitation of fluorescein at pH 2. Polystyrensulfonate (PSS) and polyallylamine (PAH) were used to form a polyelectrolyte shell on the fluorescein core. The permeation of fluorescein molecules through the polyelectrolyte shell during core dissolution was monitored at pH 8 by the increasing fluorescence intensity as a result of dequenching. The number of polyelectrolyte layers sufficient to sustain fluorescein release was found to be 8-10. Increasing the number of layers prolonged the core dissolution time for minutes. The permeability of polyelectrolyte multilayers of the thickness of 20 nm for fluorescein is about 10(-9) m/s. The features of the release profile and possible applications of the LbL method for shell formation in order to control release properties for entrapped materials are outlined. [215] Optical-Properties of Thin-Films of Au-at-SiO2 Particles T. Ung, L. M. Lizmarzan and P. Mulvaney J. Phys. Chem. B 105(17) (2001), 3441-3452 Homogeneous films of Au@SiO2 particles have been deposited on glass as a prototype 3D ''artificial solid'' using the LBL method. The film thickness is controlled by the number of dipping cycles and is measured by AFM. Each cycle results in approximately one monolayer of particles being deposited. The particle films are dense, but disordered. The optical properties of the resulting thin films have been analyzed as a function of the particle volume fraction, which is controlled through the silica shell thickness. We find that the surface plasmon peak position in films with volume fractions up to phi > 0.5 is accurately predicted by the Maxwell-Garnett model. The films exhibit remarkably uniform, transmitted colors and display metallic reflection at low angles of incidence, even at low volume fractions. The films can be annealed at T > 500 K to provide extremely stable, optical films. [216] Metal-Ion Sensing Using Ultrathin Organic Films Prepared by the Layer-by-Layer Adsorption Technique C. Pearson, J. Nagel and M. C. Petty J. Phys. D, Appl. Phys. 34(3) (2001), 285-291 Bilayer films of poly(ethyleneimine) and poly(ethylene-co- maleic acid) have been prepared using the layer-by-layer assembly technique. These films have been characterized using surface plasmon resonance (SPR). Exposure to aqueous solutions of metal acetate (metal = copper, nickel) resulted in a shift in the position of the SPR curve. This shift could be monitored by observing the intensity of the reflected laser beam at fixed angle and concentrations of copper acetate down to at least 10(- 6) M could be detected. [217] Protein Adsorption Onto Auto-Assembled Polyelectrolyte Films G. Ladam, P. Schaaf, F. J. G. Cuisinier, G. Decher and J. C. Voegel Langmuir 17(3) (2001), 878-882 We investigate the adsorption processes of a series of positively and negatively charged proteins onto the surface of polyelectrolyte multilayers. We find that proteins strongly interact with the polyelectrolyte film whatever the sign of the charge of both the multilayer and the protein. When the charges of the multilayer and the protein are similar, one usually observes the formation of protein monolayers which can become dense. We also show that when the protein and the multilayer become oppositely charged, the adsorbed amounts are usually larger and the formation of thick protein layers extending up to several times the largest dimension of the protein can be observed. Finally, we find that proteins are mainly adsorbed in a strong way on polyelectrolyte multilayers and protein surface diffusion is strongly suggested. Our results confirm that electrostatic interactions play an important role in polyelectrolyte multilayer/protein interactions. [218] Controlling the Permeability of Multilayered Polyelectrolyte Films Through Derivatization, Cross-Linking, and Hydrolysis J. H. Dai, A. W. Jensen, D. K. Mohanty, J. Erndt and M. L. Bruening Langmuir 17(3) (2001), 931-937 Partial Fischer esterification of poly(acrylic acid) allows tailoring of the hydrophobicity and charge density of multilayered films containing poly(allylamine hydrochloride) (PAH) and derivatized poly(acrylic acid) (d-PAA). As hydrophobicity and charge density strongly affect film permeability, control over these properties is vital for possible applications of PAH/d-PAA films as ion-separation membranes and sensors. The hydrophobicity of these films depends on both the extent of esterification and the nature of the derivatizing alcohol. Even though PAH/d-PAA films are composed of polyelectrolytes, the presence of hydrophobic ester groups results in advancing water contact angles as high as 101 degrees. The hydrophobicity of these coatings allows them to effectively passivate underlying electrodes as shown by minimal peak currents in cyclic voltammograms (CVs) of RU(NH3)(6)(3+) and Fe(CN)(6)(3-). Cross-linking of hydrophobic PAH/ d-PAA films via heat-induced amidation stabilizes coatings over a wide pH range but does not significantly decrease the already low film permeability to Ru(NH3)(6)(3+) and Fe(CN)(6)(3-). Stabilization due to cross-linking does, however, allow base- promoted hydrolysis of the ester groups of PAH/d-PAA coatings. After hydrolysis, films are extremely hydrophilic and selectively permeable to Ru(NH3)(6)(3+) over Fe(CN)(6)(3-) due to,the high density of newly formed -COO- groups. In the case of some hydrolyzed films, the presence of small concentrations of Ca2+ results in dramatic current decreases in CVs of RU(NH3)(6)(3+), suggesting possible use of these films in sensing applications. [219] Molecular-Weight Dependence of Alternate Adsorption Through Charge-Transfer Interaction Y. Shimazaki, R. Nakamura, S. Ito and M. Yamamoto Langmuir 17(3) (2001), 953-956 [220] Layered Polyelectrolyte Films on Au Electrodes - Characterization of Electron-Transfer Features at the Charged Polymer Interface and Application for Selective Redox Reactions V. Pardoyissar, E. Katz, O. Lioubashevski and I. Willner Langmuir 17(4) (2001), 1110-1118
[221] Ion-Transport and Equilibria in Polyelectrolyte Multilayers T. R. Farhat and J. B. Schlenoff Langmuir 17(4) (2001), 1184-1192 Transport of redox-active probe ions through multilayers made from highly charged polyelectrolytes is described. Because of intrinsic charge balance between polyelectrolyte segment ion pairs, there are no sites for the exchange of small ions within the bulk of as-made multilayers. In the presence of salt in the external bathing solution, sites for small ion exchange are forced into these ''reluctant'' amphoteric exchangers. Equilibrium considerations lead to the conclusion that, under conditions of high salt concentration and strong polymer ion pairing, the exchanger site concentration is proportional to the solution salt concentration, while the population of redox ions within the multilayer remains constant. Rotating disk electrodes coated with multilayers yield cyclic voltammograms which retain their classical sigmoidal shape, indicating well- behaved membrane transport. Limiting currents are strongly attenuated by membranes of thickness on the order of a few hundred angstroms. Layer-by-layer buildup reveals enhanced transport of negative ions through multilayers bearing a positive surface charge, attributed to Donnan-enhanced membrane inclusion of negative ions. Good matching of internal charge, efficiently excluding ions, is a distinctic feature of membranes made from polyelectrolyte multilayers. The flux through membranes is a strongly nonlinear function of salt concentration for the multiply charged ferro- and ferricyanide ions. This leads to significant transport selectivity between ions, favoring species with lower charge. With the membrane concentration of redox ion, charge n, constant, membrane flux is proportional to membrane diffusion coefficient, (D) over bar, which depends on solution salt concentration in the manner (D) over bar similar to k [salt](n). The implications of this for membrane transport control of multiply charged biomolecules are discussed. [222] Fuzzy Assembly and 2nd-Harmonic Generation of Clay/Polymer/Dye Monolayer Films B. Vanduffel, T. Verbiest, S. Vanelshocht, A. Persoons, F. C. Deschryver and R. A. Schoonheydt Langmuir 17(4) (2001), 1243-1249 Fuzzy assembled multicompound films consisting of natural and synthetic colloidal clay particles, poly(diallyldimethylammonium chloride) (PDDA) and the dyes methylene blue (MB+) and 4-(4-[N-allyl-N-methylamino] phenylazo)benzenesulfonic acid, sodium salt (NAMO(-)) have been prepared. The organization of the clay particles was imaged by means of atomic force microscopy. Fuzzy assembled glass/clay/ methylene blue films have been investigated by visible spectroscopy, and the spectra were explained in terms of the substrate-clay interaction and clay particle overlap. Glass/ clay/PDDA/NAMO films were investigated by means of absorption spectroscopy, polarized absorption spectroscopy, and second harmonic generation. The nonlinear optical properties of the films were found to be determined by the adsorbed amount of NAMO and its noncentrosymmetric organization. These factors are in turn governed by the substrate type, the PDDA concentration, and the clay type. Optimized second harmonic generation for the glass/laponite/ PDDA/NAMO films was found in which the clay particles are deposited-onto a (3-aminopropyl)-trimethoxysilane modified glass surface and PDDA chains are adsorbed from a 0.1 M solution. [223] Release Behavior of Thin-Walled Microcapsules Composed of Polyelectrolyte Multilayers X. Y. Shi and F. Caruso Langmuir 17(6) (2001), 2036-2042 The release properties of the fluorescent probe pyrene, PYR, encapsulated in polyelectrolyte multilayer capsules were examined by fluorescence spectroscopy. PYR was encapsulated by the layer-by-layer deposition of oppositely charged polyelectrolytes onto PYR microcrystal templates, and its release was accomplished by exposing the polyelectrolyte-coated microcrystals to ethanol solutions. Solubilization of the hydrophobic probe by ethanol resulted in its expulsion from the core through th permeable polyelectrolyte: multilayer shells. The PYR release rate, quantified by following the monomer fluorescence of the solubilized PYR as a function of time, decreased with increasing number of polyelectrolyte layers deposited onto the microcrystal cores. In addition, two amphiphiles (sodium dodecyl sulfate and dipalmitoyl-(DL)-alpha - phosphatidylcholine) used to disperse the microcrystals in aqueous solution prior to coating with polyelectrolytes significantly influenced the PYR release rate. The maximum release time, defined as the time required to achieve saturation release, could be varied by a factor of 2-5 depending on the nature of the first adsorbed layer and the number of polyelectrolyte layers composing the shell wall. The influence of flow (i.e., centrifugation vs magnetic stirring) as well as solvent on the PYR release rate is also discussed. [224] Formation of Multilayer Composite-Particles Comprised of Silica/ Vesicle/Silica Particles by Heterocoagulation B. Yang, H. Matsumura, K. Katoh, H. Kise and K. Furusawa Langmuir 17(8) (2001), 2283-2286 The multilayer composite particles comprised of silica/PC (phosphatidylcholine) vesicle/silica particles have been prepared by using the heterocoagulation technique. The formation process is as follows: at first, large silica particles (2r = 1.5 mum) and PC vesicles (2r = 0.2 mum) were mixed at a definite particle number ratio in 10(-4) M LaCl3 aqueous solution. The PC vesicle/silica composites were spontaneously formed by mutual electrostatic attraction. After removal of the excess PC vesicles from the system, the small silica particle (2r = 0.5 mum) suspension was added into the PC vesicle/silica composite dispersions to form the multilayer composite particles composed of small silica, PC vesicle, and core silica particles. The formation of multilayer composite particles was confirmed by the electrophoresis, dynamic light scattering (DLS), and adsorption measurements of PC molecules. Finally, the existence of multilayers was confirmed directly using a special optical microscope. [225] Influence of Thickness on Catalytic Efficiency of Cobalt Corrin- Polyion Scaffolds on Electrodes in Microemulsions C. J. Campbell, C. K. Njue, B. Nuthakki and J. F. Rusling Langmuir 17(11) (2001), 3447-3453 Catalytic electrodes were prepared by covalently binding poly-L- lysine (PLL) onto oxidized carbon electrodes and then linking the cobalt corrin vitamin B-12 hexacarboxylic acid [B- 12(COOH)(6)] to this surface. Additional layers of PLL-B- 12(COOH)(6) were attached in a similar way. Quartz crystal microbalance studies showed regular and reproducible layer formation. Electrochemical and catalytic properties of the (CoL)-L-II/ (CoL)-L-I redox couple in these films were investigated using voltammetry and preparative electrolysis in an sodium dodecyl sulfate microemulsion. These films obeyed theoretical predictions of a maximum in voltammetric catalytic efficiency as thickness increased for the reduction of 1,2- dibromocyclohexane (DBCH) in a microemulsion. In films with less' than optimum thickness, kinetic control of the chemical reaction between (CoL)-L-I and DBCH predominated. As film thickness was increased beyond that found for maximum efficiency, electron and reactant mass transport within the films became limiting factors. Under synthetic electrolysis conditions, optimal turnover numbers were found for very thin films on porous electrodes, and best yields and current efficiencies were obtained with the relatively small catalyst coverage of about 2 nmol cm(-2). [226] Stability and Mechanical-Properties of Polyelectrolyte Capsules Obtained by Stepwise Assembly of Poly(Styrenesulfonate Sodium- Salt) and Poly(Diallyldimethyl Ammonium) Chloride Onto Melamine Resin Particles C. Y. Gao, S. Leporatti, S. Moya, E. Donath and H. Möhwald Langmuir 17(11) (2001), 3491-3495 Capsules composed of poly(styrene sulfonate, sodium salt) (PSS)/ poly(diallyldimethyl ammonium) chloride (PDADMAC) were prepared by layer-by-layer deposition of the polyelectrolytes on melamine formaldehyde colloidal templates followed by the decomposition of the cores by hydrochloride. A yield of more than 90% of intact capsules was achieved if (i) the core diameter was equal to or less than 3.8 mum and (ii) not more than five pairs of layers were adsorbed. When the cores were larger or the layers were thieber, the osmotic pressure difference caused by core dissolution led to an increased frequency of wall rupture. The elasticity modulus of a multilayer consisting of five pairs of PSS/PDADMAC was about 140 MPa as measured by osmotic pressure induced capsule deformation. [227] Ex-Situ SFM Study of 2-D Aggregate Geometry of Azobenzene Containing Bolaform Amphiphiles After Adsorption,at the Mica/ Aqueous Solution Interface B. Zou, L. Y. Wang, T. Wu, X. Y. Zhao, L. X. Wu, X. Zhang, S. Gao, M. Gleiche, L. F. Chi and H. Fuchs Langmuir 17(12) (2001), 3682-3688 Self-assembled nanometer-sized stripes are obtained spontaneously by electrostatic adsorption of bolaform amphiphiles bearing hydrophilic :pyridinium headgroups and rigid hydrophobic azobenzene onto mica sheets. The ordered stripes have a repeat spacing of 10 nm, and the ordered region can extend over: macroscopic areas. The formation of such nanostructures mainly depends on the concentration of the bolaform amphiphiles. The template effect of the mica sheet also plays a crucial role in the molecular organization at the Liquid solid interface. The degree of order of the stripes is influenced by adding electrolyte into the aqueous solution or upon irradiating the solution for physical adsorption under UV light. [228] Ionic Self-Assembly of Glucose-Oxidase with Polycation Bearing Os Complex J. Q. Sun, Y. P. Sun, Z. Q. Wang, C. Q. Sun, Y. Wang, X. Zhang and J. C. Shen MACROMOL CHEM PHYSICS 202(1) (2001), 111-116 Multilayer assemblies of glucose oxidase (GOD) and poly(4- vinylpyridine) complex of osmium were fabricated on a quartz slide or a gold electrode by ionic self-assembly technique. Cyclic voltammogram experiments showed that osmium transferred electrons successfully between the immobilized GOD and the electrode surface. Its application as a glucose sensor was greatly anticipated. [229] Investigation of the Covalently Attached Multilayer Architecture Based on Diazo-Resins and Poly(4-Styrene Sulfonate) J. Q. Sun, Z. Q. Wang, L. X. Wu, X. Zhang, J. C. Shen, S. Gao, L. F. Chi and H. Fuchs MACROMOL CHEM PHYSICS 202(7) (2001), 967-973 [230] Organometallic Polyelectrolytes - Synthesis, Characterization and Layer-by-Layer Deposition of Cationic Poly(Ferrocenyl(3- Ammoniumpropyl)Methylsilane) M. A. Hempenius, N. S. Robins, R. G. H. Lammertink and G. J. Vancso MACROMOL RAPID COMMUN 22(1) (2001), 30-33
[231] PH-Controlled Macromolecule Encapsulation in and Release from Polyelectrolyte Multilayer Nanocapsules G. B. Sukhorukov, A. A. Antipov, A. Voigt, E. Donath and H. Möhwald MACROMOL RAPID COMMUN 22(1) (2001), 44-46 Communication: pH-Controlled encapsulation in and release of macromolecules from polyelectrolyte capsules of a few microns in diameter is demonstrated. Capsules were prepared via alternating adsorption of the oppositely charged polymers poly(allylamine hydrochloride) and poly(styrene sulfonate) onto decomposable melamin formaldehyde cores. The capsules were open for macromolecules at pH values below 6 and closed at pH > 8. Permeation and encapsulation of FITC-dextran (MW 75 000) into polyelectrolyte multilayer capsules. Top: pH 10, center: pH 3, bottom: pH increased to 10 after the capsules were loaded with FITC-dextran at pH 3. The bulk FITC-dextran was removed by washings at pH 10. [232] Fabrication of a Stable Layer-by-Layer Thin-Film Based on Diazoresin and Phenolic Hydroxy-Containing Polymers via H- Bonding T. B. Cao, J. Y. Chen, C. H. Yang and W. X. Cao MACROMOL RAPID COMMUN 22(3) (2001), 181-184 Using the self assembly technique, a stable multilayer films was successfully fabricated from diazoresin (DR) and poly(styrene-co-(N-(p-hydroxyphenyl)maleimide)) (P(S-co-HPMI)) followed by UV irradiation. The driving force of the self- assembly was confirmed to be H-bonding attraction between the diazonium group (-N-2(+)) Of DR and the phenolic hydroxy group (-Ph-OH) of P(S-co-HPMI). A linkage conversion from H-bond to covalent bond takes place after decomposition of the -N-2(+) group using UV irradiation. As a result, the stability of the film towards polar solvents increases dramatically. [233] Fabrication of a Covalently Attached Multilayer Film via in- Situ Reaction J. Y. Chen, G. B. Luo and W. X. Cao MACROMOL RAPID COMMUN 22(5) (2001), 311-314 A covalently linked ultrathin multilayer film was fabricated from 2-nitro-N-methyl-diphenyl-amine-4-diazonium-formaldehyde resin (PR) in methanol in-situ. The UV-vis, XRD, AFM and FTIR show that his multilayer is of high regularity, smoothness and stability. [234] Selective Interaction Between Proteins and the Outermost Surface of Polyelectrolyte Multilayers - Influence of the Polyanion Type, pH and Salt M. Muller, T. Rieser, P. L. Dubin and K. Lunkwitz MACROMOL RAPID COMMUN 22(6) (2001), 390-395 Protein adsorption was studied by insitu ATR-FT-IR spectroscopy of consecutively deposited polyelectrolyte multilayer systems terminated either with poly(ethyleneimine) (PEI) or polyanions, such as poly(acrylic acid) (PAC), poly(maleic acid-co- propylene) (PMA-P) or poly(vinyl sulfate) (PVS). The influence of the polyanion type, pH and ionic strength was investigated. Negatively charged human serum albumin (HSA) was strongly repelled by multilayers terminated with weak polyanions (PAC, PMA-P), whereas moderate attraction was observed for those terminated with the strong polyanion PVS. Changing the pH from 7.4 to 5 resulted in enhanced HSA adsorption onto PAC- terminated multilayers. An increase in ionic strength diminished the attractive HSA adsorption onto PEI-terminated multilayers. For the PEI/PAC system, the biomedically relevant adsorption of human fibrinogen (FGN) is determined via its isoelectric point in accordance with three other proteins. [235] Mechanism of Polyelectrolyte Multilayer Growth - Charge Overcompensation and Distribution J. B. Schlenoff and S. T. Dubas Macromolecules 34(3) (2001), 592-598 A mechanism for distributing excess polymer surface charge is used to model the growth of multilayers of strongly charged polyelectrolytes. Two parameters are required for the semiempirical analysis: the surface, or unrestricted, charge overcompensation level, phi, which is assumed to decrease exponentially from the film surface to bulk, and the characteristic length for this decay, l(cp), which is termed the charge penetration length. Modeling of the data reveals that only modest levels of polymer charge overcompensation are required to account for large increments in polymer thickness, realized at high salt concentration, since the excess charge is distributed over several ''layers''. Experimentally, phi appears to be roughly independent of salt concentration. The thickness increment is primarily controlled by l(cp), which is about 2.5 nominal layers for the system studied. Whereas the growth conditions and polyelectrolyte type lead to the formation of intrinsically compensated multilayers in this work, conditions for obtaining extrinsic compensation are also discussed. Kinetic vs thermodynamic limitations for polymer addition during a deposition cycle are contrasted. [236] Stepwise Assembly of Enantiomeric Poly(Lactide)S on Surfaces T. Serizawa, H. Yamashita, T. Fujiwara, Y. Kimura and M. Akashi Macromolecules 34(6) (2001), 1996-2001 Enantiomeric poly(lactide)s were assembled on a quartz crystal microbalance (QCM) substrate, which detects the mass of the polymers from the frequency shift, following immersion of QCM into alternating acetonitrile solutions. A quantitative QCM analysis at each step and a differential scanning calorimetric study of the assembly showed racemic crystal (stereocomplex) formation on the substrate surface. Atomic force microscopic observation showed a dotted nanostructure of the assembly. The assembly amount was increased with increasing the PLA concentration and the immersion time, while that was decreased with increasing the assembly temperature. The heterogeneous assembly was also prepared by altering the immersion time. We found that racemic crystal formation was applied to the alternate deposition of certain structurally regulated polymers. [237] Coating of Colloidal Particles by Controlled Precipitation of Polymers V. Dudnik, G. B. Sukhorukov, I. L. Radtchenko and H. Möhwald Macromolecules 34(7) (2001), 2329-2334 A method is suggested for the coating of micron-sized particles by polymeric films based on surface-controlled precipitation. Polymer particles were coated by dextran and DNA in a water/ ethanol mixture containing multivalent cations. A theoretical model for depositing polymers on colloidal particles is presented using the Smoluchowski solution for diffusion- controlled irreversible coagulation. Theoretical estimations appear to provide the proper particle and polymer concentration ranges in order to achieve smooth coverage. The optimal concentration range also was determined experimentally and agrees with the theoretical calculations. The controlled precipitation method of assembling thin films on colloids is compared with the layer-by-layer adsorption approach. Advantages and drawbacks of both approaches are discussed. [238] Polyvalent Hydrogen-Bonding Functionalization of Ultrathin Hyperbranched Films on Polyethylene and Gold D. E. Bergbreiter, G. L. Tao, J. G. Franchina and L. Sussman Macromolecules 34(9) (2001), 3018-3023 Hyperbranched poly(acrylic acid) and poly(N- isopropylacrylamide) grafts on gold and polyethylene films are good substrates for a new, mild hydrogen-bond-based grafting method. In this chemistry, a hydrogen-bond-donating or - accepting hyperbranched graft couples to a polymeric acceptor or donor in ethanol solution through multiple hydrogen-bonds. In contrast to plain surface-functionalized polyethylene films or to functional monolayers on gold, hyperbranched grafts are more capacious and more tenacious in this hydrogen-bond graft chemistry. Substantial amounts of polyacrylamide or poly(acrylic acid) reversibly bind to the hyperbranched graft based on IR spectroscopy, fluorescence spectroscopy, and ellipsometry. Fluorescence studies using dansyl-labeled soluble polymers that were hydrogen-bonded to hyperbranched grafts show that these hydrogen-bond assemblies are stable to prolonged extraction with protic and aprotic solvents. These interfacial hydrogen-bonded assemblies do not readily disassemble unless the hydrogen-bond donor is deprotonated with base. [239] Ordered Polyelectrolyte Multilayers - 1 - Mechanisms of Growth and Structure Formation - A Comparison with Classical Fuzzy Multilayers X. Arys, A. Laschewsky and A. M. Jonas Macromolecules 34(10) (2001), 3318-3330 The growth and structuring of polyelectrolyte self-assemblies (so-called ''multilayers'') made from a lyotropic ionene and a strong polyelectrolyte are examined in depth using X-ray reflectometry among other techniques. We show that highly ordered polyelectrolyte films may be obtained, consisting of a regular lamellar nanostructure extending over considerable distances in the films, with preferential orientation of chain fragments occurring in the films. This is in marked contrast with classical, ''fuzzy'' multilayers, for which no internal structure was reported so far. From our set of results, including a comparison of the structures of ''multilayers'' and bulk complexes, we propose that three mechanisms govern film growth and structuring: adsorption of the polyelectrolyte (governed by electrostatic balance), diffusion of the polyelectrolyte into the previously adsorbed film (which is the blurring step), and surface-constrained complexation between the polyanion and the polycation resulting from the mixing due to diffusion. Depending on whether the polyelectrolytes are capable of forming structured complexes or not, the self- assembled film will present different levels of internal organization. These findings have important implications for the general understanding of electrostatic self-assembly and for possible applications therefrom. [240] Anomalous Adsorption of Polyelectrolyte Layers S. Y. Park, C. J. Barrett, M. F. Rubner and A. M. Mayes Macromolecules 34(10) (2001), 3384-3388 We study the adsorption of polyelectrolytes onto oppositely charged surfaces as the surface charge density is varied while keeping the polyelectrolyte charge density fixed. As observed previously from multilayer adsorption studies,(1,2) nonmonotonic adsorption behavior is obtained in the intermediate surface charge density regime, with anomalously thick ''supermonolayers'' transitioning to molecularly thin lavers over a small range of surface charge densities. A simple adsorption model is introduced to explain these findings, in which the surface is characterized by discrete and fully compensated adsorption sites. [241] Adsorption of Polyelectrolytes at Oppositely Charged Surfaces A. V. Dobrynin, A. Deshkovski and M. Rubinstein Macromolecules 34(10) (2001), 3421-3436 We have developed a scaling theory of polyelectrolyte adsorption at an oppositely charged surface. At low surface charge densities, we predict two-dimensional adsorbed layers with thickness determined by the balance between electrostatic attraction to the charged surface and chain entropy. At high surface charge densities, we expect a 3-dimensional layer with a density profile determined by the balance between electrostatic attraction and short-range monomer-monomer repulsion. These different stabilizing mechanisms result in a nonmonotonic dependence of the layer thickness on the surface charge density. For adsorption of polyelectrolyte chains from salt solutions, the screening of the electrostatic repulsion between adsorbed polyelectrolyte chains results in large overcompensation of the surface charge for two-dimensional adsorbed layers. At higher salt concentrations this overcompensation of the surface charge by the 2-d adsorbed layer is independent of the original surface charge and depends only on the fraction of the charged monomers on the polyelectrolyte chains and increases with ionic strength. The polyelectrolyte surface excess in 3-d adsorbed layers increases at low ionic strength and decreases at higher ionic strength. [242] Polyelectrolyte Multilayers Containing a Weak Polyacid - Construction and Deconstruction S. T. Dubas and J. B. Schlenoff Macromolecules 34(11) (2001), 3736-3740 The growth of multilayers made from a combination of a weak polyacid and a strongly dissociated polycation is studied as a function of salt concentration and molecular weight. Film thickness reaches a maximum at around 0.3 M salt and then decreases quickly. Preformed multilayers are shown to decompose rapidly and, for high molecular weights, completely when exposed to aqueous solutions of NaCl of concentration >0.6 M. The apparent dissociation of multilayer polyelectrolyte complexes is due to competition for polymer/polymer ion pairs by external salt ions. Similar experiments aimed at decomposing multilayers by protonating the weak acid, thus decreasing polymer/polymer interactions, lead to incomplete loss of polymer, probably due to additional hydrogen bonding from the protonated weak acid. A model based on ion exchange/swelling of multilayers is used to explain their stability and permeability as well as the dependence of film thickness on salt concentration and type. [243] Layer-by-Layer Preparation of Zeolite Coatings of Nanosized Crystals V. Valtchev and S. Mintova MICROPOROUS MESOPOROUS MAT 43(1) (2001), 41-49 In this contribution a new approach for preparation of zeolite films is described. Layer-by-layer self-assembly technique was employed for the preparation of zeolite coatings on negatively charged polystyrene beads, The procedure consists of two basic steps. In the first the beads were surface modified in order to facilitate adsorption of zeolite nanocrystals. A monolayer of crystals are then adsorbed on the bead surface, The number of deposition cycles control the thickness of zeolite coatings. Following this approach zeolite coatings of LTA, FAU, BEA and MFI type zeolites were prepared. Zeolite/polystyrene composites and the corresponding hollow zeolite spheres were characterized by SEM, TEM, X-ray diffraction, FTIR and thermogravimetric analyses. (C) 2001 Elsevier Science B.V. All rights reserved. [244] Tuning the Performance of Layer-by-Layer Assembled OLEDs by Controlling the Position of Isolating Clay Barrier Sheets M. Eckle and G. Decher Nanoletters 1 (2001), 45-49 We have fabricated organic light emitting diodes (OLEDs) based on poly(p-phenylenevinylene) (PPV) and poly(methacrylic acid) (PMA), including an isolating layer composed of montmorillonite. We show that the single clay layer influences the behavior of the devices, lowering current densities and increasing light output in comparison with pure polymer systems. The subnanometer positioning of this isolating barrier within the active medium with respect to both electrodes, which is easily controlled by the deposition sequence, plays a key role for the electrooptical properties of the diodes. [245] Self-Assembly of Small Molecules - An Approach Combining Electrostatic Self-Assembly Technology with Host-Guest Chemistry Y. J. Zhang and W. X. Cao New J. Chem. 25(3) (2001), 483-486 A fluorescence probe study, surface tension and dye solubilization tests indicate that the water-soluble calixarene, 5,11,17,23,29,35,41,47-octosulfonato- 49,50,51,52,53,54,55,56-octododecyloxycalix[8]arene (1(8)-C-12) acts as a ''unimolecular'' micelle in water. By forming guest- host-type complexes with 1(8)-C-12, lipophilic dyes, such as methyl yellow (MY), p-hydroxyazobenzene (HAB) and 1-(p- phenylazophenylazo)-2-naphthol (Sudan III), dissolve in aqueous solution. By dipping a charged substrate in the 1(8)-C-12-dye solution and a cationic polyelectrolyte solution alternately, these small molecular dyes were successfully self-assembled into multilayer films. [246] Fabrication of Microgratings on the Ends of Standard Optical Fibers by the Electrostatic Self-Assembly Monolayer Process F. J. Arregui, I. R. Matias, K. L. Cooper and R. O. Claus Optics Letters 26(3) (2001), 131-133 The electrostatic self-assembly monolayer process has been utilized for what is believed to be the first time to deposit quarter-wavelength stacks on the end faces of cleaved and polished optical fibers. Standard multimode optical fibers as well. as single-made optical fibers were used as substrates with different coating materials to fabricate broadband filters, and the experimentally measured spectral responses of these devices are shown. These optical filter structures were employed to develop chemical sensors that use an unperturbed reference wavelength to normalize the output signal. (C) 2001 Optical Society of America. [247] Effect of pH on the Preparation of Self-Assembled Films of Poly(O-Ethoxyaniline) and Sulfonated Lignin L. G. Paterno and L. H. C. Mattoso Polymer 42(12) (2001), 5239-5245 Self-assembled films of Poly(o-ethoxyaniline) (POEA) doped with HCl alternated with sulfonated lignin (SL) were successfully produced under different pHs and their kinetics of formation studied. The adsorption at lower pi-Is is faster due to the greater electrostatic attraction between the POEA and the SL covered substrate, but a lower amount of POEA is deposited due to ch;uge repulsion of additional POEA chains and conformational steric hindrance. At higher pHs the adsorption of POEA cakes longer but it is greater due to the contribution of hydrogen bonding interactions, lower charge repulsion between POEA chains and a more compact polymer conformation. Adsorption of POEA/SL multilayers could be carried out in different types of substrates. Atomic force microscopy (AFM) employed to investigate the morphology of the alternated layers showed that POEA layers exhibited a granular rough aspect, while SI, layers presented a much smoother surface. (C) 2001 Elsevier Science Ltd. All rights reserved. [248] Photovoltaic Cells Based on Ionically Self-Assembled Nanostructures T. Piok, C. Brands, P. J. Neyman, A. Erlacher, C. Soman, M. A. Murray, R. Schroeder, W. Graupner, J. R. Heflin, D. Marciu, A. Drake, M. B. Miller, H. Wang, H. Gibson, H. C. Dorn, G. Leising, M. Guzy and R. M. Davis Synthet. Metal Yüklə 0,52 Mb. Dostları ilə paylaş:
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