Electrostatic Films Research Articles

Preparation of β-Phase Poly(vinylidene fluoride) Films on Aluminum Substrate with the Addition of Hydrated Metal Salts.

Poly(vinylidene fluoride) (PVDF) is one of the most studied polymers that exhibits piezoelectric and ferroelectric properties. PVDF crystallizes into four different forms, namely α, β, γ, and δ phases. Generally, the nonpolar α phase, as a replacement for the polar β phase with the most superior ferroelectric and piezoelectric properties, is formed from the precursor melt and solution. Here, we report a method for the preparation of β-phase-dominant PVDF thin films by doping PVDF solution with a metal hydrated salt, such as Co(NO₃)₂·6H₂O, without any stretching procedure. The crystal structure of the film was analyzed using X-ray diffraction -2 scanning and Fourier transform infrared spectroscopy. The morphology of the film was observed using a field emission-scanning electron microscope. To determine the frequency dependence of dielectric properties, an LCR meter was used in the range of 50 Hz to 1 MHz. The crystalline phase and morphology of the electrostatic spray-deposited PVDF films depended on the chemical additive. Our results show that the addition of a metal hydrated salt can induce an in situ poling effect, consequently facilitating the preferred dipole orientation in the electrostatically sprayed PVDF films.

Electrochemical characteristics of zinc oxide-polyethyleneglycol complex films using EQCM.

ZnO-PEG-ZnO complex film was fabricated by forming ZnO thin film on the Polyethyleneglycol (PEG) thin film. ZnO thin films were formed by an electrostatic method and ZnO-PEG complex films were fabricated by adsorbing PEG on the ZnO thin films surface with hydrogen bond. The electrochemical characteristic of the ZnO-PEG-ZnO film was analyzed by EQCM techniques. The resonance frequency, resistance and current changes were measured simultaneously with scan rate 100 mV/s, sweep range -1.4-1.2 V in 5 mM ZnCl2 aqueous solution. The electrochemical characteristic of the ZnO-PEG-ZnO complex film was compared with that of the ZnO thin film, and the possible electrode applications of ZnO-PEG-ZnO complex films were examined.

Preparation and Characterization of Ta2O5Films Surface Modified by Electrostatic Self-assembly Ultrathin Films

Ultrathin films of poly-diallyldimethylammonium chloride (PDDA)/polystyrene sulfonate (PSS) and PDDA/poly(3,4-ethylene dioxythiophene)-polystyrene sulfonate (PEDOT-PSS) were constructed on Ta2O5 films through layer-by-layer electrostatic self-assembly (ESA) method for a surface modification purpose. The self-assembly ability of PDDA/PSS and PDDA/PEDOT-PSS ultrathin films on Ta2O5 film was investigated. The results showed that the ESA ultrathin films can be constructed on Ta2O5 film surface with a layer-by-layer deposition method, and the Ta2O5 film covered with ESA film exhibited smoother surface roughness compared with Ta2O5 film without surface modification. Moreover, the electronic performance of Ta/Ta2O5/ESA films/polymer film capacitor structure was investigated. The results revealed that the capaci- tor composed of ultrathin ESA film exhibited better anti-voltage endurance ability and less leakage current, which resulted from the isolation of leakage current channel in Ta2O5 films because of surface coverage of ultrathin ESA film on Ta2O5. It also can be found that the thicker ultrathin ESA film for surface modification resulted in better anti-voltage endurance ability and higher equivalent series resistance (ESR) of Ta2O5 ca- pacitor. The further investigation confirmed that lower ESR of capacitor composed of PDDA/PEDOT-PSS ESA films because of high conductive ability of PEDOT-PSS. Keywords electrostatic self-assembly; Ta2O5; anti-voltage endurance ability; equivalent series resistor;

Electrochemical and Photoelectrochemical Investigation of New Electrostatic Self-Assembled Films Based on Prussian Blue and a Binuclear Ru(II) Complex

New hybrid multilayer films containing Prussian blue (PB) and a binuclear Ru(II) complex were successfully fabricated using the electrostatic layer-by-layer self-assembly technique. The process was carefully monitored by ultraviolet-visible (UV-vis) spectroscopy. A linear increase in the UV-vis absorbance with the number of deposited layers indicated that the film deposition was uniform and reproducible. The electrochemical and photoelectrochemical properties of these hybrid multilayer films were investigated in an aqueous Na2SO4 solution. PB and the binuclear Ru(II) complex assembled in the film were redox active with surface confined characteristics. The surface concentration and molecular area of RuL in the film were calculated according to a UV-vis absorption spectrum and cyclic voltammetry, respectively. The photocurrent generated by switching on the light irradiation of the film increased linearly as the deposited bilayers increased. The photocurrent action spectrum was in agreement with metal-to-ligand charge-transfer (MLCT) band of RuL in the absorption spectrum, which indicated that the photocurrent was generated based on MLCT excitation of the RuL in the (PB/RuL) film.

THE THIRD- AND FIFTH-ORDER NONLINEAR REFRACTION IN THE SINGLE- AND DOUBLE-SIDED TMAF/PSS ELECTROSTATIC SELF-ASSEMBLY FILMS

The nonlinear refraction in the single- and double-sided 40-bilayer TMAF/PSS electrostatic self-assembly films were measured by closed-aperture Z-scan technique with picosecond laser pulses (with duration of 40 ps at 532 nm). The materials contain a positively charged material trifluoroacetic acid (TFA) salt of amino-substitute methanofullerene derivative monoadduct fullerene (TMAF) and a negatively charged material ploy (sodium 4-styrenesulfon ate) (PSS). The experimental results show that under the conditions of the peak intensity I0 = 7.0 GW/cm2, both the single- and double-sided films demonstrate third- and fifth-order non-linearities, and the fifth-order non-linearity has greater contribution to the nonlinear refraction than the third-order nonlinearity. The theoretical fittings also prove that the nonlinear refraction coefficients both γ and η are almost the same for the same materials no matter what the measurements are from the single- or the double-sided films.

Investigating into a Ca2+-sensitive electrostatic self-assembly films to fabricate reproducible immunobeads for flow immunoassay

Abstract A novel strategy has been developed for fabricating reproducible bead-based flow immunoassay system by combining the merits of Ca 2+ -induced cross-linkage of sodium alginate with negative carboxyl groups of alginate. The sodium alginate was applied to modify the polyallyamine beads and render beads negative charge to immobilize antibodies via electrostatic/hydrogen bonding interaction between alginate and antibodies to realize the fabrication of immunobeads in buffer solution of 0.01 mol/l acetic-acetate (pH 7.5). The Ca 2+ -induced cross-linkage of alginate on the immunobeads can easily release antibodies from beads and regenerate a fresh alginate-modified beads for next fabrication of new immunobeads. The electrochemical flow immunoassay system based on the so-made immunobeads has been fabricated and the feasibility of the proposed strategy and qualities of so-fabricated flow immunoassay system was evaluated by applying to a competitive transferrin–transferrin antiserum immunoassay system.

Tuning of conductance switching by supramolecular structures

Conductance switching in layer-by-layer electrostatic films of Rose Bengal has been studied. High-conducting state appeared due to electroreduction and/or conformation change of such molecules. Conduction mechanisms of the two states have been studied and role of dielectric constant of the material and barrier height with the electrode have been focused. Conductivity of each of the two states, namely low- and high-conducting states, has been tuned individually by introducing supramolecular matrix. We showed that in supramolecular structures, Rose Bengal determined the low-state current, while the conduction process of the matrix controlled the high-state current.

Investigation of Interaction of Proflavine and Naphthol Red in Nucleic Acids by Light‐Absorption Spectrometry

The formation of the double electrostatic films in nucleic acid will cause the aggregation of small molecules on it by a non‐covalent bond. The interaction of the dyes: proflavine (PLV) and naphthol red (NR) with nucleic acids [calf thymus (ct) DNA and yeast (y)RNA] in acidic medium was investigated by the microsurface adsorption–spectral correction (MSASC) technique. Results showed that the aggregation of PLV and NR on DNA and RNA agrees with the Langmuir isothermal adsorption. The maximal binding numbers of PLV is 0.85 with ctDNA‐P and 0.50 with yRNA‐P and those of NR 0.12 with ctDNA‐P and 0.07 with yRNA‐P. Their binding constants K are 8.13 × 104, 2.15 × 105, 2.20 × 105, and 2.05 × 105, respectively. The effect of ionic strength and temperature on the aggregation was made. The aggregation of PLV and NR in nucleic acids has been tried to apply to the quantitative detection of nucleic acids.

Modulation of protein adsorption and cell adhesion by poly(allylamine hydrochloride) heparin films

Electrostatic layer-by-layer film assembly is an attractive way to non-covalently incorporate proteins and bioactive moieties into the surface of conventional biomaterials. Selection of polycationic and polyanionic components and deposition conditions can be used to control the interfacial properties, and through them protein adsorption, cell adhesion, and tissue development. In this study the polycation was poly(allylamine hydrochloride) (PAH), which is a weak base and consequently adsorbs at interfaces in a pH-dependent manner, and the polyanion was heparin, which is capable of interacting with many adhesion ligands and growth factors. PAH/heparin multilayer films were formed using PAH solutions of pH 6.4, 7.4, 8.4, and 9.4. Film thickness increased both with the number of PAH/heparin bilayers and the pH of the PAH solution. Films consisting of 10 bilayers with heparin topmost exhibited similar bulk atomic compositions and penetration of PAH into the heparin top layer. Finally, fibronectin adsorption and cell adhesion were maximal at an intermediate pH (pH 8.4>pH 9.4>pH 7.4). These results demonstrate that heparin-containing electrostatic films support cell adhesion and protein adsorption in a manner sensitive to film deposition conditions.

Ultra-water-repellent surface: fabrication of complicated structure of SiO2 nanoparticles by electrostatic self-assembled films

Ultra-water-repellent surface requires a high surface roughness and low surface energy. We designed surface complicated microstructure of SiO2 nanoparticles by using electrostatic self-assembly process. The films that were prepared by the alternate adsorption of poly(allylamine hydrochloride), SiO2 nanoparticles mixture solution and poly(acrylic acid) on the substrates were very complicated in surface structure. After surface hydrophobic treatment by dichlorodimethylsilane, the film surface showed a contact angle of larger than 160° for water droplets. The value was much larger compared with the contact angle on silicon wafer treated by dichlorodimethylsilane. The difference was strongly dependent on the surface structure. In this paper, we changed deposition conditions to fabricate the water-repellent surfaces with various surface structures by using three types of silica nanoparticles, and we found that the nanoscale structure was very important for the ultra-water-repellency.

Langmuir Aggregation of Thionin in Nucleic Acids and Its Application

AbstractThe microsurface adsorption‐spectral correction (MSASC) technique has been described. The formation of the double electrostatic films in nucleic acids causes the monolayer aggregation of stain molecules. The interaction of thionin (TN) with nucleic acids, ctD‐NA, sDNA and yRNA, has been investigated at pH 7.8. Results show that the binding ratios of TN to ctDNA‐P, sDNA‐P and yR‐NA‐P are 1.27, 1.30 and 1.40, respectively, the binding constants of the aggregates are 2.8 · 104, 9.10 · 104 and 6.49 · 103 and their molar absorptivities are 1.04 · 104, 1.25 · 104 and · 104 L· mol−1, cm−1 at 630 nm. The aggregation may be applied to the spectrophotometric detection of nucleic acids samples.