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| 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 116(1-3) (2001), 343-347 We use the technique of ionically self-assembled monolayers (ISAMs) to produce photovoltaic devices of well-controlled thickness and composition. The ISAM nanostructure fabrication method simply involves the alternate dipping of a charged substrate into aqueous cationic and anionic solutions at room temperature. We have employed several approaches to combine the tetrahydrothiophenium precursor of poly(para-phenylene- vinylene) (PPV) with fullerenes and other organic materials. We apply modulation spectroscopy for the electrooptical characterization of the ISAM-devices. The modulation frequency dependence of the photocurrent can be assigned to the influence of trapped charges taking Dart in the photovoltaic process. (C) 2001 Published by Elsevier Science B.V. [249] Electrostatic Self-Assembly as a Means to Create Organic Photovoltaic Devices M. F. Durstock, B. Taylor, R. J. Spry, L. Chiang, S. Reulbach, K. Heitfeld and J. W. Baur Synthet. Metal 116(1-3) (2001), 373-377 Recently, there has been a significant amount of work done on making photovoltaic devices (solar cells) from thin films of conjugated polymers and other organic systems. The advantages over conventional inorganic systems include the potential to create lightweight, flexible, and inexpensive structures. The challenge, however, has been to create more highly efficient devices. To date, the primary photovoltaic device mechanism that has been utilized is that of photoinduced charge transfer between an electron donor and acceptor. In this study, similar photovoltaic devices are fabricated using a water-based electrostatic self-assembly procedure, as opposed to the more conventional spin-coating and/or vacuum evaporation techniques. In this process, layers of oppositely charged species are sequentially adsorbed onto a substrate from an aqueous solution and a film is built up due to the electrostatic attraction between the layers. The technique affords molecular level control over the architecture and gives bilayer thickness values of the order of tens of angstroms. By repeating this process a desired number of times and utilizing different cations and anions, complex architectures can be created with very accurate control over the thickness and the interfaces. We have examined a number of systems built from a variety of components including a cationic PPV precursor, functionalized Co,, and numerous other polyelectrolytes. We report on the device characteristics of these films and on the overall applicability of this technique to the fabrication of photovoltaic devices. Published by Elsevier Science B.V. [250] Highly Efficient Energy and Charge-Transfer in Thin Self- Assembled Multilayered Polymer-Films H. L. Wang, D. W. Mcbranch, R. J. Donohoe, S. Xu, B. Kraabel, L. H. Chen, D. Whitten, R. Helgeson and F. Wudl Synthet. Metal Yüklə 0,52 Mb. Dostları ilə paylaş:
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