C. Basavaraja

Studies on Properties of Polyaniline-Dodecylbenzene Sulfonic Acid Composite Films Synthesized Using Different Oxidants

Two types of nano composite were obtained byin situ chemical method in polyaniline (PANI)/dodecylbenzenesulfonic acid (DBSA) system depending on the use of either ammonium persulfate (APS) or ferric chloride (FeCl3) as the oxidant. In order to study the difference of the two composites in the surface characteristics, thermal stability, and electric properties, the composite films were studied by transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and temperature dependent DC electrical conductivity. The results revealed a large difference in the surface morphology, thermal stability, and the microstructure properties between the two composites, and these differences were considered responsible for the molecular order and conductivity.

Characterization and electrochemical behaviors of honeycomb-patterned poly(N-vinylcarbazole)/polystyrene composite films

Poly(N-vinylcarbazole)/polystyrene composites were prepared through simple radical polymerization of N-vinylcarbazole in the presence of polystyrene. Honeycomb-patterned composite thin films were fabricated by casting the composite solutions under humid conditions. The scanning electron microscopy (SEM) images of the resulting honeycomb pattern on the composites show a higher regular structure compared to those of films prepared from the poly(N-vinylcarbazole) homopolymer. The pressure-area isotherms and photoelectrochemical behaviors of the patterned films were also observed. The photoconductivity of the patterned thin films increased with increasing poly(N-vinylcarbazole) concentration. This enhancement is attributed to the effects of the honeycomb structures and the charge transfer across the donor/acceptor hybrid interface in the composite films.

Morphology and electrical properties of poly(3,4-ethylenedioxythiophene)/titanium dioxide nanocomposites

Poly(3,4-ehtylenedioxythiophene) (PEDOT) nanocomposites including nano-sized titanium dioxide were prepared by in situ polymerization technique and were characterized by Fourier transform infrared (FTIR) and UV-visible spectroscopy. Morphological studies of the nanocomposites were performed using scanning electron microscopy and transmission electron microscopy to support the formation of PEDOT-TiO2 nanocomposites. Results suggested that the TiO2 nanoparticles were well-dispersed in the PEDOT polymer matrix. The electric properties of the nanocomposites were obtained by measuring the temperature-dependent direct current (DC) conductivity between 300 and 500 K and low frequency alternate current conductivity between 0 and 10 kHz. The PEDOT-TiO2 nanocomposites exhibited remarkable improvement in the temperature-dependent DC conductivity with decreased dielectric constants and dielectric losses, compared to pure PEDOT polymer, which indicates their higher ability to store electric potential energy under the influence of an alternating electric field.

Reversible adsorption-desorption oscillations of nanoparticles on a patterned hydrogel surface induced by a pH oscillator in a closed chemical system

Oscillatory adsorption-desorption of Ag nanoparticles on a pH-responsive hydrogel surface was induced by a pH oscillator in a closed reaction system. The hydrogel surface was prepared as a honeycomb-patterned film using a honeycomb-patterned polystyrene film as a template to speed up the response time in the stimuli-responsive hydrogel. The surface morphology and hydrophobic interaction of the patterned hydrogel surface were significantly altered by the pH change of the aqueous solution that came into contact with the gel. The surface of the hydrogel became hydrophobic for adsorption in a lower-pH solution but became hydrophilic with decreased adsorptivity at higher pH conditions. A closed system chemical pH oscillator composed of CaSO3-H2O2-NaHCO3-H2SO4 was applied to force the periodic adsorption-desorption of Ag nanoparticles on the gel surface. The experimental conditions for the chemical oscillator were optimized to obtain long-lasting high-amplitude pH oscillations in a closed reactor. The periodic adsorption-desorption was proved to be induced by the periodic pH change in the solution, although the two phenomena were not completely synchronized. That is, the periodic time was longer and the number of oscillations was less for the adsorption-desorption compared with the pH oscillations that occurred in the solution state. However, the heterogeneous oscillations obtained in this study clearly suggested that the hydrophobic interaction was reversibly changed in the patterned pH-responsive hydrogel surface, similar to various biological systems in nature.

Characterization and electrical behavior of biodegradable poly(N-vinylcarbazole)/poly(3-hydroxybutyric acid) composite films

AbstractPoly(N-vinylcarbazole) (PVK) composites containing poly(3-hydroxybutyric acid) (PHB) were synthesized via in situ deposition. The oxidative polymerization of N-vinylcarbazole was carried out by dissolving different weight percentages (10, 20, 30, 40, and 50 wt%) of PHB using ferric chloride as an oxidant. The as-synthesized composites were characterized by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. The surface morphology of the resulting composites was studied by transmission electron microscopy, and the biodegradability of the composites was tested by the Sturm method. The temperature-dependent DC conductivity of the synthesized composite films was measured, and the activation energy responsible for the conductivity was examined. The incorporation of PHB in the synthesis of PVK composites significantly increased the conductivity and biodegradability of the resulting products. Thus, the newly synthesized composites have potential applications in the biological, medical, and engineering fields.

Preparation and characterization of smart hydrogel nanocomposites sensitive to oxidation–reduction

Honeycomb-patterned hydrogel films sensitive to environmental oxidation–reduction supporting nanoparticle by adsorption were fabricated through the photopolymerization of ruthenium(4-vinyl-4′-methyl-2,2′-bipyridine)bis(2,2′-bipyridine)bis(hexaflurophosphate) and N-isopropylacrylamide. Nanoparticle adsorption by the hydrogel film was controlled by the dynamic changes in the surface morphology of the film in relation to environmental oxidation–reduction, which induces change of the oxidized and reduced states of ruthenium ion included in the hydrogel. For the adsorption of nanoparticles in the patterned hydrogel film, silver nanoparticles were immobilized in the hydrogel surface. Adsorptivity was obtained through measuring the released concentration of the silver nanoparticles using UV–vis spectroscopy in an aqueous solution. Desorption of Ag nanoparticles from the hydrogel surface was found to be larger in the oxidizing solution than in the reducing solution.

Electron transport and photoelectrical behavior of poly( N -vinylcarbazole)/Poly(3,4-ethylenedioxythiophene) composite honeycomb-patterned films

New type of poly(N-vinylcarbazole) (PVK) polymer nanocomposites were prepared by a solid-state polymerization of N-vinylcarbazole in the presence of different concentration (wt%) of poly(3,4-ethylenedioxythiophene) (PEDOT). The prepared PVK/PEDOT nanocomposites were characterized by using Fourier transform infrared (FTIR) and UV-vis spectra. The transmission electron microscopy (TEM) and X-diffraction studies were performed to understand the surface morphology and nature of the polymer composites. The characterization and morphological studies suggest that there is a conjugation between PVK and PEDOT. Furthermore, the honeycomb-patterned films were obtained by dissolving the PVK/PEDOT nanocomposites into the chloroform solvent under humid conditions. The temperature-dependent DC electrical conductivity and room temperature photo-electrical conductivity of the honeycomb-patterned films were measured. Results showed that the incorporation of PEDOT in PVK polymer has greatly improved the electrical conductivity and photo-electrical behavior of the PVK/PEDOT nanocomposites.