Polyhedral oligomeric silsesquioxane nanocomposite thin films via layer-by-layer electrostatic self-assembly

Fabrication of ultrathin polymer composite films with low dielectric constants has been demonstrated. Octa( aminophenyl) silsesquioxane (OAPS) was synthesized and assembled with poly( acrylic acid) (PAA) and poly( styrene sulfonate) (PSS) via a layer-by-layer electrostatic self-assembly technique to yield nanoporous ultrathin films. The OAPS was soluble in water at pH 3 or lower, and suitable pH conditions for the OAPS/PAA and OAPS/PSS assemblies were determined. The multilayer formation process was studied by contact angle analysis, X-ray photoelectron spectroscopy, atomic force microscopy, quartz crystal microgravimetry, UV-vis spectroscopy, and ellipsometry. The multilayer growth was found to be steady and uniform, and the analysis of the film surface revealed a rough topography due to OAPS aggregates. The incorporation of porous OAPS molecules into the thin films significantly lowered their dielectric constants. The OAPS/PAA multilayer thin film thus prepared exhibited a dielectric constant of 2.06 compared to 2.58 for pure PAA film. The OAPS/PAA multilayer film was heated to effect cross-linking between the OAPS and the PAA layers, and the transformation was verified by reflection-absorption Fourier transform infrared spectroscopy.

Chitosan mediated assembly of gold nanoparticles multilayer

We initiate a systematic exploration of a natural polymer, chitosan, as a structural material for designing functional layers on electrode surfaces in this work. Au colloid films are organized on chitosan layer by adsorption. We have successfully constructed a multilayer An nanoparticle assembly through electrostatic interactions on chitosan functionalized quartz substrates by the alternate treatment of the substrate with solution of citrate-stabilized gold nanoparticles (negatively charged) and chitosan solution (positively charged). The resulting substrates were characterized by UV-Vis spectrometry, atomic force microscopy (AFM), and electrochemical impedance spectroscopy (EIS) measurements. These assemblies of colloid An multilayer are highly stable, and can be kept for a long time in distilled water, only being removed by scratching or extreme electrochemical conditions.

A novel photochromic multilayer based on preyssler's cluster

A novel photochromic multilayer film containing polyoxometalates has been fabricated using layer-by-layer self-assembly.

Preparation and characterization of ordered yttrium arachidate multilayer

The behavior of arachidic acid on the surface of YCI3 aqueous subphase was studied by LB and Brewster angle microscopy techniques. The results showed that the pre-compressing time and the pH of the subphase played an important role in the forming of the monolayer. The monolayer on the subphase surface was irreversible. If the monolayer was compressed into wrinkles, the monolayer could not become uniform again. The optimum transferring conditions were selected and the ordered yttrium arachidate multilayer with a long spacing of 4.96 nm and a tilt angle of 28.5degrees of the three alkyl chains from the surface normal was fabricated and characterized.

Multilayer assembly of Bis-Keggin-type heteropoly compound on chemically modified glassy carbon electrode and its electrocatalysis

Through layer-by-layer assembly, the bis-Keggin-type heteropolyanion K10H3 [Nd(SiMo7W4O39)(2)] XH2O was successfully immobilized on a glassy carbon electrode surface grafted covalently by 4-aminobenzoic acid. The electrochemical behavior of the heteropolyanion was investigated. Cyclic voltammetry proved the uniform growth of the film. However, the characteristic redox peaks of the heteropolyanion in the film were deformed with increasing of the number of the multilayer film. The effect of pH on the redox behaviors of [Nd(SiMo7W4)(2)](13-) in the film was discussed. The multilayer film electrodes have excellent electrocatalytic activities to the reduction of BrO3-, HNO2 and H2O2.

Covalently attached multilayer assemblies containing photoreactive diazo-resins and conducting polyaniline

We reported on the multilayer architecture containing diazo-resins (DAR) as polycations and polyaniline poly(aniline-co-N-propanesulfonic acid aniline) (PAPSAH) as polyanions held together by electrostatic interaction. Upon UV irradiation, the adjacent interfaces of the multilayer reacted to form a covalently crosslinking structure which greatly improved the stability of the films as confirmed by solvent etching experiments. These changes were confirmed by UV-Vis and FTIR spectroscopy. The thickness of the covalently attached films were characterized with small angle X-ray diffraction (SAXD) and a value of 30.0 Angstrom per bilayer was obtained. This type of film was further characterized by cyclic voltammetry which showed that the electroactive property of PAPSAH was still kept in the films after photoreaction. (C) 2000 Elsevier Science B.V. All rights reserved.

Multilayer assembly of Mn-substituted Keggin-type [ZnW11O39Mn(H2O)](8-) on chemically modified glassy carbon electrode and its electrocatalytic properties

Through layer-by-layer assembly, undecatungstozincates monosubstituted by transition metals Mn, ZnW11 Mn (H2O) O-39(8-) was successfully immobilized on a glassy carbon electrode surface grafted covalently by 4-aminobenzoic acid. The electrochemical behavior of these polyoxometalates was investigated. Cyclic voltammetry proves the uniform growth of the film. They exhibit some special electrochemical properties in the films, different from those in homogeneous aqueous solution. The effect of pH on the redox behavior of ZnW11Mn(H2O)O-39(8-) in the film was discussed in detail. The multilayer film electrodes have an excellent electrocatalytic response to the reduction of H2O2 and BrO3-, and to the oxidation of ascorbic acid.

Mixed ion transfer analysis in redox processes of electroactive thin films

Electrochemical quartz crystal microbalance (EQCM) technique was used to measure the ion transfer in redox processes in electroactive organic thin films, such as self-assembled monolayer (SAM) (4-pyridyl hydroquinone, abbr. 4PHQ), multilayer based on SAM and conducting polymer film (here poly-(3,4-ethylenedioxythiophene), abbr. PEDOT). A mechanism of mixed ion transfer is developed and presented. Analysis of mixed ion transfer during redox processes successfully elucidates the deviation of oscillation frequency of the quartz crystal from theoretical expectation.

Preparation and characterization of DBSA doped polyaniline thin films

Stable monolayer of the polyaniline(PAn) doped with dodecyl benzenesulfonic acid(DBSA) can form on the pure water surface. The multilayer ultrathin film can be successfully deposited by Langmuir-Blodgett(LB) technique onto CaF2 substrate. The limiting mean molecular area and collapse pressure observed are 0.066 nm(2) and 35 mN m(-1), respectively. The multilayer LB film and casting film were all characterized by TR and UV-Vis-NIR spectroscopies.

Preparation and characterization of doped polyaniline films

Stable monolayer of the polyaniline doped with camphor sulfonic acid at the air-water interface has been obtained, of which multilayers have been successfully deposited by Langmuir-Blodgett technique onto CaF2 substrate. The limiting mean molecular area and collapse pressure are found to be 0.294 nm(2) and 41 mN/m, respectively. The multilayers were characterized by IR and W-Vis-NIR spectroscopies. X-ray small-angle diffraction data show that the multilayer was periodic layer structure with the layer spacing of 1.60 nm. The comparisons are also made with characterization of the casting film. (C) 1999 Elsevier Science S.A. All rights reserved.

Multilayer assemblies of colloidal ZnS doped with silver and polyelectrolytes based on electrostatic interaction

Multilayer assemblies of silver doped ZnS colloid and polycation were fabricated by a self-assembly technique exploiting electrostatic interaction. UV/Vis spectra showed the uniform deposition process and X-ray photoemission spectroscopy (XPS) confirmed the coexistence of silver. It was found that the emission spectra of the silver doped ZnS colloid red-shifted to 528 nm comparing with undoped ZnS colloid. However, the most important finding was that the luminescence intensity of doped ZnS assembled in films was much stronger than that of undoped ZnS in films and that of doped ZnS in the spin-casting film. The mechanism of the enhancement luminescence was discussed. (C) 1998 Elsevier Science S.A. All rights reserved.

Stability of Mo/Si multilayer structure used in Bragg-Fresnel optics

The thermal and chemical stabilities of Mo/Si multilayer structure used in Bragg-Fresnel optics were studied to get optimal technological parameters of pattern generation. Mo/Si multilayers were annealed at temperature ranging from 360 to 770 K, treated with acetone and 5 parts per thousand NaOH solution, and characterized by small-angle x-ray diffraction technique as well as x-ray photoelectron spectroscopy, and Olympus microscopy.

Photoluminescence study of Langmuir-Blodgett films of blend poly 3-(2-(5-chlorobenzotriazole)ethyl) thiophene

The multilayer Langmuir-Blodgett (LB) films of pr,ly 3-(2-(5-chlorobenzotriazole)ethyl) thiophene (PCBET) blended with amphibious arachidic acid (AA) were prepared and characterized. The photoluminescence intensity of the blend film was enhanced as the AA increased by a certain amount. The PCBET excimers were not formed in the blend LB films.

Study on Ordered Assembly of SnO2 Nonoparticles-Arachidic Acid Composite LB Films

The hydrosol of SnO2 nanoparticles (NP) have been prepared by colloid chemistry method. The composite LB monolayer and multilayer of SnO2 NP-AA have been obtained by LB technique at the gas-liquid interface of the hydrosol subphase. The structures of the monolayer and multilayer were characterized by IR, UV-Vis, small angle X-ray diffraction spectroscopy and TEM technique, The results indicate that the coverage of SnO2 NP at the composite monolayer's surface is high and the sites of SnO2 NP are similar. The multilayer has good periodic structure.

Study on the Films Forming Process of Nanosized SnO2 Colloid Particles at the Gas-Liquid Interface

The hydrosol of SnO2 nanoparticles are prepared by the method of colloid chemistry. The free piling up process of nanosized SnO2 colloid particles are investigated at the gas-liquid interface by LB and Brewster Angle Microscopy techniques. The result indicates that solid state monolayer and multilayer of SnO2 nanoparticles can be formed at the gas-liquid interface only by aging the sol in air or compressing it without amphiphiles surfactant.