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| 122(37) (2000), 8998-9004
The nucleation of calcium phosphate crystals from a weakly supersaturated calcium phosphate solution on the surface of polyelectrolyte multilayers was investigated in dependence on the chemical nature of the outermost layer. Scanning angle reflectometry was used to follow in situ the initial stages of the nucleation kinetics. The multilayers were constructed by alternate adsorption of poly(styrene sulfonate) (PSS) and poly(allylamine) (PAH), leading to oppositely charged surfaces. It was verified that films terminating with either PSS or PAH exhibited a negative or positive 5-potential, respectively. Surprisingly, both types. of surface layers induced a nucleation process for supersaturations smaller than the one observed on the bare silica surface. According to the literature, such an effect should only be expected on a negatively charged surface. Infrared spectroscopy showed that the nucleated crystals are hydroxyapatite (OHAP) or octacalcium phosphate (OCP) but not dicalcium phosphate dihydrate (DCDP) which is found on bare silica surfaces. On both PSS and PAH surfaces, the nucleation processes started only after a given induction time. The evolution of the induction times with different supersaturations was analyzed within the framework of the classical nucleation theory. The effective surface free energies of the formed crystals were estimated to be on the order of 32 mJ.m(-2) on a multilayer terminating with PSS and to be about 37 mJ.m(-2) on a multilayer terminating with PAH. A mechanism for the enhanced nucleating effect of such polyelectrolyte surfaces is proposed. [67] Layered, Erasable, Ultrathin Polymer-Films S. A. Sukhishvili and S. Granick J. Am. Chem. Soc. 122(39) (2000), 9550-9551 [68] Photoelectrochemistry with Integrated Photosensitizer-Electron Acceptor and Au-Nanoparticle Arrays M. Lahav, V. Helegshabtai, J. Wasserman, E. Katz, I. Willner, H. Durr, Y. Z. Hu and S. H. Bossmann J. Am. Chem. Soc. 122(46) (2000), 11480-11487
[69] Electroluminescence of Different Colors from Polycation/CdTe Nanocrystal Self-Assembled Films M. Y. Gao, C. Lesser, S. Kirstein, H. Möhwald, A. L. Rogach and H. Weller J. Appl. Phys. 87(5) (2000), 2297-2302 Water soluble thiol capped CdTe nanocrystals are assembled into ultrathin films in combination with poly(diallyldimethylammonium chloride) (PDDA) by the self- assembly method of layer-by-layer adsorption of oppositely charged polyelectrolytes. Electroluminescent devices, which produce different color emissions, are fabricated by sandwiching CdTe/PDDA films between indium-tin-oxide (ITO) and aluminum electrodes using CdTe nanocrystals of different sizes. It is shown that the electroluminescence (EL) spectra of the CdTe/polymer films are nearly identical to the photoluminescence spectra of the corresponding CdTe nanocrystals in aqueous solutions. The devices produce room- light visible light output with an external quantum efficiency up to 0.1%. Light emission is observed at current densities of 10 mA/cm(2) and at low onset voltages of 2.5-3.5 V, which depends on the thickness of the film indicating field-dependent current injection. A variation of the EL efficiency with the size of the CdTe particles is observed and explained by the size dependent shift of the CdTe energy levels with respect to the work function of the electron injecting Al electrode. This is confirmed by the behavior of two-layer devices prepared from two differently sized CdTe particles being spatially separated, i.e., one size CdTe near ITO and the other size CdTe near Al by using the self-assembly method. (C) 2000 American Institute of Physics. [S0021-8979(00)06404-5]. [70] Self-Assembled Multilayer Films Based on Diazoresins Studied by Atomic-Force Microscopy/Friction Force Microscopy L. Huang, G. B. Luo, X. S. Zhao, J. Y. Chen and W. X. Cao J. Appl. Polym. Sci. 78(3) (2000), 631-638 The layer-by-layer self-assembled NDR-PSS (nitro-containing diazoresin-polysodium p-styrenesulfonate) films were fabricated. The crosslinking structure formed from the conversion of ionic bond to covalent bond after UV irradiation, confirmed by small angle X-ray diffraction. The roughness and microtribological properties of NDR-PSS films were investigated by atomic force microscopy/friction force microscopy. The ordered multilayer films after photoreaction are better in microtribological performance than that of the monolayer film. (C) 2000 John Wiley & Sons, Inc. [71] Probing Nanoscale Photooxidation in Organic Films Using Spatial Hole-Burning Near-Field Scanning Optical Microscopy G. M. Credo, G. M. Lowman, J. A. Dearo, P. J. Carson, D. L. Winn and S. K. Buratto J. Chem. Phys. 112(18) (2000), 7864-7872 Spatial hole burning near-field scanning optical microscopy (SHB-NSOM) is used to locally photopattern three species of organic thin films, poly(2-methoxy, 5-(2'-ethyl hexyloxy)-p- phenylene vinylene) (MEH-PPV), tris-8-hydroxyquinoline aluminum (Alq(3)) and dye-functionalized polyelectrolyte self-assembled layers, on a 100 nm length scale. In SHB-NSOM the film is illuminated with light from a stationary NSOM tip to induce photo-oxidation. The reduction in the fluorescence yield resulting from this exposure is then mapped using fluorescence NSOM (FL-NSOM). We have examined the localized photo-oxidation as a function of time, position, and environment free from the limits of far-field spatial averaging. In all of the thin film materials studied we find that the long-time diameter of the dark spot is much larger than the tip diameter and is a signature of energy migration. Characteristic lengths of the energy migration are extracted from this data by a simple diffusion model and are found to be of the order of a few hundred nanometers for each of the films studied. (C) 2000 American Institute of Physics. [S0021-9606(00)71116-0]. [72] Facile Construction of an Ultra-Thin (60)Fullerene Layer from (60)Fullerene-Homooxacalix(3)Arene Complexes on a Gold Surface T. Hatano, A. Ikeda, T. Akiyama, S. Yamada, M. Sano, Y. Kanekiyo and S. Shinkai J. Chem. Soc., Perkin Trans. 2 5(MAY) (2000), 909-912 A hexacationic homooxacalix[3]arene-[60]fullerene 2:1 complex can be deposited on an anion-coated gold surface as a monolayer (or at least as a monolayer-like ultra-thin film); as expected, this membrane efficiently shows a redox response in cyclic voltammetry and a photoelectrochemical response under visible light irradiation. [73] Investigation of Structure and Growth of Self-Assembled Polyelectrolyte Layers by X-Ray and Neutron-Scattering Under Grazing Angles A. Plech, T. Salditt, C. Munster and J. Peisl J. Colloid Interface Sci. 223(1) (2000), 74-82 The structure of self-assembled polyelectrolyte thin films on float glass has been investigated by interface sensitive X-ray and neutron scattering methods. Special emphazis was given to the adsorption process of poly (ethylene imine) and polystyrole sulfonate as an important model system which is often used as a basis for subsequent multilayer buildup. From complementary X- ray and neutron reflectivity data, the vertical film density profile was derived for various growth parameters, including kinetic effects of different adsorption times. In addition to specular reflectivity, we have for the first time employed nonspecular X-ray scattering to study lateral structure parameters in self-assembled polyelectrolyte films. Furthermore, the technique of time-resolved in situ X-ray reflectivity during film growth has been demonstrated and is discussed in view of its future potential. (C) 2000 Academic Press. [74] Phosphatidylserine/Cholesteral Bilayers Supported on a Polycation/Alkylthiol Layer Pair L. Q. Zhang, C. A. Booth and P. Stroeve J. Colloid Interface Sci. 228(1) (2000), 82-89 1-Stearoyl-2-oleoyl phosphatidylserine (SOPS)/cholesterol bilayers, supported on a polycation/alkylthiol layer pair on a gold surface, were investigated by surface plasmon resonance (SPR) and fluorescence recovery after photobleaching. The substrate was formed by electrostatic adsorbance of a hydrated poly(diallyldimethylammonium chloride) (PDDA) layer on the negatively charged surface of a self-assembled monolayer of 11- mercaptoundecanoic acid (MUA) on gold. Lipid membranes with different SOPS/cholesterol compositions were deposited on the PDDA/MUA layer pair by vesicle fusion. When the cholesterol content was below 20%, single bilayers were deposited. Fluorescence recovery after the bleaching experiments revealed that the SOPS/cholesterol bilayers were mobile at room temperature; lateral diffusion coefficients of a fluorescence probe were approximately 1 x 10(-9) cm(2)/s. The kinetics of the addition of the ion-channel-forming peptide gramicidin to the supported bilayers was detected by SPR. (C) 2000 Academic Press. [75] Electroactive Films of Alternately Layered Polycations and Iron- Sulfur Protein Putidaredoxin on Gold Z. Q. Lu, Y. Lvov, I. Jansson, J. B. Schenkman and J. F. Rusling J. Colloid Interface Sci. 224(1) (2000), 162-168 Layered, electrochemically active films of bacterial iron- sulfur protein putidaredoxin (Pdx) and poly(dimethyldiallyammonium) (PDDA) polycations were constructed on gold electrodes coated with mercaptopropane sulfonate (MPS) and on quartz slides. Second-derivative UV-vis spectra suggested similar structures of Pdx in films and solutions at pH 7. Direct electrochemistry was achieved between Pdx and gold electrodes in these films, with significantly better electrochemical reversibility than in cast Nafion-lipid- Pdx films. A formal potential dispersion model gave a good fit to square wave voltammograms by regression analysis and was used to estimate an average apparent rate constant of 4.5 s(- 1). Reduced Pdx in the polyion films did not react with its natural redox partner cytochrome P450(cam) because of unfavorable thermodynamics in the film environment. (C) 2000 Academic Press. [76] Assembly of Alternated Multivalent Ion/Polyelectrolyte Layers on Colloidal Particles - Stability of the Multilayers and Encapsulation of Macromolecules into Polyelectrolyte Capsules I. L. Radtchenko, G. B. Sukhorukov, S. Leporatti, G. B. Khomutov, E. Donath and H. Möhwald J. Colloid Interface Sci. 230(2) (2000), 272-280 Alternating adsorption of multivalent ions and oppositely charged polyelectrolytes on colloid particles has been investigated. Multilayer films composed of Tb3+/polysterene sulfonate (PSS) and 4-pyrene sulfate/polyallylamine (PAH) were successfully assembled on polysterene sulfonate (PS) and melamine formaldehyde (MF) latex particles. The amount of assembled material was estimated by fluorescence and the linear growth of the film versus the number of layers was demonstrated. These multilayers are not stable and can be decomposed by salt and temperature, Dissolution of MF particles leads to formation of hollow capsules consisting of multivalent ion/polyelectrolyte multilayers. Comparative analysis of the capsules was done by confocal and scanning force microscopy. Complex hollow spheres consisting of Tb3+/PSS or 4-PS/PAH as an inner shell and stable PSS/PAH as an outer shell were produced. Due to selective permeability of the outer shell after degradation of the inner shell the multivalent ions are released out of the capsule while the polyelectrolytes fill the capsule interior. This is indicative of swelling of the capsule by osmotic pressure. The filled capsules were studied by confocal and scanning electron microscopy. Possibilities of encapsulating macromolecules in defined amounts per capsule are discussed. (C) 2000 Academic Press. [77] Comparative-Studies on Electrochemical-Behavior and Electrocatalytic Properties of Heteropolyanion-Containing Multilayer Films Prepared by 2 Methods L. Cheng and S. Dong J. Electroanal. Chem. 481(2) (2000), 168-176 Two modification methods for multilayer formation, i.e. immersion growth and electrochemical growth, were studied comparatively for their influence on the electrochemical behavior and the electrocatalytic properties of the thus- fabricated SiMo11V-containing multilayer films. Electrochemical growth was proven to be a more suitable method than immersion growth in preparing uniform ultrathin multilayer self- assemblies with good functions. We investigated the effects of scan rate and pH on the electrochemical behavior of the monolayer and multilayer films. We also compared the electrocatalytic effects on the reduction of BrO3- and HNO2 by the multilayer films prepared by the two methods. Moreover, the influence of multilayer thickness and the identity of the outermost layer on the electrocatalytic properties were studied. Much higher catalytic currents appeared on the thicker multilayer films than those on the thinner ones. On the other hand, the catalytic currents became smaller when the multilayer films with SiMo11V as the outermost layer were covered with an additional quarternized poly(4-vinylpyridine) layer partially complexed with osmium bis(2,2'-bypyridine) chloride (QPVP-Os layer). These influences were believed to be due to the different quantities of electrocatalyst loaded in the multilayer films and the blocking effect of the QPVP-Os outermost layer. (C) 2000 Elsevier Science S.A. All rights reserved. [78] An Enlarged bis-Bipyridinium Cyclophane-Au Nanoparticle Superstructure for Selective Electrochemical Sensing Applications M. Lahav, A. N. Shipway, I. Willner, M. B. Nielsen and J. F. Stoddart J. Electroanal. Chem. 482(2) (2000), 217-221 Highly stable electrostatically-linked superstructures of 13 nn Au-colloids have been constructed by the use of the tetracationic cyclophanes cyclobis(paraquat-p-phenylene) and cyclobis(paraquat-p-biphenylene). These architectures have been characterized by optical and electrochemical means and exhibit sensing capabilities that are shown to depend on the crosslinking cyclophane. While superstructures linked by cyclobis(paraquat-p-phenylene) sense hydroquinone derivatives and not ferrocene derivatives, those linked by the larger receptor cyclobis(paraquat-p-biphenylene) sense only the ferrocene derivatives. This high degree of selectivity is based on the topological and supramolecular fit of the analyte in the cavity of the receptor. Arrays containing both cyclophanes are shown to exhibit sensing characteristics that are dependent on the position of each cyclophane in the superstructure, possibly as a consequence of the limited porosity of the composite. (C) 2000 Elsevier Science S.A. All rights reserved. [79] Electrochemical-Behavior and Electrocatalytic Properties of Ultrathin Films Containing Silicotungstic Heteropolyanion Siw12O404- L. Cheng and S. J. Dong J. Electrochem. Soc. 147(2) (2000), 606-612 We describe here a controlled fabrication of ultrathin monolayer and multilayer films consisting of silicotungstic heteropolyanion SiW12O404- and a cationic polymer of quaternized poly(4-vinylpyridine) partially complexed with osmium bis(2,2'-bipyridine) on Au electrodes previously self- assembled with cysteamine monolayers based on layer-by-layer electrostatic interaction. The thus-forming monolayer and multilayer chemically modified electrodes are investigated by cyclic voltammetry on their electrochemical behavior and electrocatalytic properties. The composite ultrathin films exhibit remarkable electrocatalytic effects on the reduction of BrO3-, H2O2, and HNO2. The electrocatalytic effects on HNO2 reduction are enhanced with increasing layer number from 1 to 3 but level off with much thicker multilayers. The stability of the monolayer and multilayer films is also examined. (C) 2000 The Electrochemical Society. S0013-4651(99)04-057-4. All rights reserved. [80] Luminescence Properties of the J-Aggregate of Cyanine Dyes in Multilayer Assemblies N. Kometani, H. Nakajima, K. Asami, Y. Yonezawa, I. G. Scheblykin and A. G. Vitukhnovsky J. Luminesc. 87-9(MAY) (2000), 770-772 Multilayer assemblies incorporating the J-aggregate of 3,3'- disulfopropyl-5,5'-dichloro-thiacyanine dye were fabricated up to 50 layers by the alternate adsorption technique to examine their luminescence properties. Fluorescence spectra as well as fluorescence lifetime of multilayer assemblies remarkably depend on the number of layers. The result is interpreted in terms of the interaction between dye lavers within a limited distance, as well as the luminescence reabsorption effect. (C) 2000 Elsevier Science B.V. All rights reserved. [81] Multilayered Supermolecular Structures Self-Assembled from Polyelectrolytes and Cyclodextrin Host-Guest Complexes M. Dreja, I. T. Kim, Y. D. Yin and Y. N. Xia J. Mater. Chem. 10(3) (2000), 603-605 Supermolecular multilayers with high levels of compositional and structural complexities have been fabricated with an example that involves formation of stable host-guest complexes from bolaamphiphiles and cyclodextrins, followed by sequential build-up of multilayered films by these complexes in combination with anionic polystyrene sulfonate polymer chains. [82] Oriented Polyoxometalate-Polycation Multilayers on a Carbon Substrate S. Q. Liu, Z. Tang, Z. X. Wang, Z. Q. Peng, E. K. Wang and S. J. Dong J. Mater. Chem. 10(12) (2000), 2727-2733 In this paper, a new method of fabricating multilayers on a carbon substrate is presented. First, a uniformly charged carbon surface was prepared through molecular design. Then an ultrathin film consisting of layer-pairs of oppositely charged polymeric cationic poly(diallyldimethylammonium chloride) (PDDA) and silicotungstate, SiW12O404- (SiW12), was grown layer- by-layer onto the grafted carbon substrate using a molecular self-assembly technique and an electrochemical method. The technique allows one to prepare highly adherent, dense and smooth films of polyoxometalates with special properties. By combining cyclic voltammetry (CV) and X-ray (XR) reflectometry, it was determined that the average surface density of SiW12 was 2.10 x 10(-10) mol cm(-2), and the thickness increase per adsorption of PDDA-SiW12 was 1.7 +/- 0.2 nm, indicating that the amount of SiW12 anion per one layer adsorption corresponded to a monolayer coverage. Atomic force microscopy (AFM) was also used to examine the surface morphology and determine the grain size distribution and roughness for multilayer films. An increase in root-mean-square (RMS) surface roughness from 7 to 9 Angstrom was observed as the number of layer-pairs in the film increased from 2 to 6. FTIR results showed that the good stability of the multilayer films was due to Coulomb interactions between the SiW12 anion and the polymeric cations PDDA. Moreover, the multilayer films, in acidic aqueous solution, showed good electrocatalytic activity toward the reduction of NO2-, and the catalytic currents increased with increasing the layer numbers of SiW12 adsorption. These characteristics of the multilayer films might find potential applications in the field of sensors and microelectronics devices. [83] Microencapsulation by Means of Step-Wise Adsorption of Polyelectrolytes G. B. Sukhorukov, E. Donath, S. Moya, A. S. Susha, A. Voigt, J. Hartmann and H. Möhwald J. Microencapsul. 17(2) (2000), 177-185 Step-wise adsorption of polyelectrolytes is used for the fabrication of micro- and nanocapsules with determined size, capsule wall composition and thickness. The capsule walls made of polyelectrolyte multilayers exclude high molecular weight compounds. Assembling of lipid layers onto these polyelectrolyte capsules prevents the permeation of small dyes. Encapsulation of magnetite nanoparticles is demonstrated and the features of these novel capsules are discussed. [84] Plastic Behavior of Polyelectrolyte Microcapsules Derived from Colloid Templates H. Baumler, G. Artmann, A. Voigt, R. Mitlohner, B. Neu and H. Kiesewetter J. Microencapsul. 17(5) (2000), 651-655 The deformability and osmotic properties of hollow microcapsules were studied by means of the micropipette video microscopic technique. The microcapsules were prepared by consecutive multiple adsorption of the polyanion, poly (styrene sulphonate), and the polycation, poly( allylamine hydrochloride), onto melamine formaldehyde resin latex of 5 mu m diameter, which was decomposed after completing the coating by transferring to hydrochloric acid of pH 1.1. The polyelectrolyte microcapsules reacted to micropipette suction with plastic deformation. If lipids are added to the polyelectrolyte layers, the capsules cannot be visibly deformed by micropipette suction up to 10(4) N/m(2). However, plastic shrinking was observed if the stress was generated by the osmotic pressure of a sucrose solution of 10(6) N/m(2). [85] Structural and Photophysical Properties of a Water-Soluble Porphyrin Associated with Polycations in Solution and Electrostatically-Assembled Ultrathin Films P. G. Vanpatten, A. P. Shreve and R. J. Donohoe J. Phys. Chem. B 104(25) (2000), 5986-5992 A water-soluble porphyrin, meso-tetra(4- sulfonatophenyl)porphyrin (TSPP), has been associated with two different polycations, poly(diallyldimethylammonium chloride) (PDDA) and poly(ethyleneimine) (PEI), to investigate the effects of polymer binding upon the TSPP structure and excited- state dynamics both in solution and in ultrathin (similar to 10- 30 Angstrom) films deposited on glass slides by electrostatic assembly. Association of the porphyrin with PEI intrinsically quenches the singlet state dynamics of TSPP, both in solution and in films, while quenching is observed upon association with PDDA only for high concentrations of porphyrins or in films where TSPP aggregates are observed. For PDDA:TSPP films without significant aggregate content, the fluorescence decay time (tau(1/e) similar to 5-6 ns) approaches that observed for monomeric or polymer-bound porphyrins in dilute solution (tau(1/ e) = 10.2 and 11.3 ns, respectively). However, rapid (< 1 ns) deactivation of the singlet states can be observed whenever appreciable aggregates are present, indicating that efficient energy transfer between the porphyrins leads to quenching at aggregate sites. A number of phenomenological observations regarding the presence of aggregates are presented. In particular, the extent of aggregation in the films depends on the concentration, pH, and temperature of the deposition solutions and also the age of the films, with older samples exhibiting reduced effects due to aggregation. [86] Surface Texture of Poly(Styrenesulfonate Sodium-Salt) and Poly(Diallyldimethylammonium Chloride) Micron-Sized Multilayer Capsules - A Scanning Force and Confocal Microscopy Study C. Y. Gao, S. Leporatti, E. Donath and H. Möhwald J. Phys. Chem. B Yüklə 0,52 Mb. Dostları ilə paylaş:
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