Ozlem Erol

Synthesis, characterization and electrorheological properties of biodegradable chitosan/bentonite composites

Abstract Biodegradable chitosan/bentonite composites with three different compositions were synthesized by the intercalation method using cetyltrimethylammonium bromide as the cationic surfactant. The composites were characterized using conductivity, density, particle size measurements, FTIR, TGA, XRD and SEM methods. Colloidal stabilities of the suspensions prepared in silicone oil (SO) were observed to increase with decreasing density. The effects of dispersed particle concentration, shear rate, electric field strength, electric field frequency and temperature on the electrorheological (ER) activities of the suspensions were investigated. The electric field viscosities of the suspensions showed typical shear thinning non-Newtonian viscoelastic behaviour. Yield stresses of the suspensions were observed to change in proportion to the square of applied electric field (E). Further, according to creep and creep-recovery analysis, reversible viscoelastic deformations were observed in the suspensions under E ≠ 0 kV mm-1.

Effect of surfactant on electrokinetic properties of polyindole/TiO2-conducting nanocomposites in aqueous and nonaqueous media

In this study, polyindole (PIN)/TiO2 nanocomposites were synthesized with and without the presence of sodium dodecylsulfate, anionic surfactant, with two different PIN contents. The synthesized materials were subjected to various characterizations namely: particle size, apparent density, conductivity, dielectric constants, magnetic susceptibility, elemental analysis, Fourier transform infrared spectroscopy spectroscopy, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Characterization results revealed the successful preparations of PIN/TiO2 hybrid nanocomposites. Electrokinetic properties of all the materials were determined by zeta (ζ)-potential measurements in aqueous and nonqueous media. Effects of pH, temperature, presence of various electrolytes, and surfactants on electrokinetic properties of the materials were examined.

Electrorheological properties of polyaniline/K-feldspar conducting composite

In this study, synthesis of conducting polyaniline (PAn)/potassium-feldspar (K-feldspar) composites, having various amounts of PAn, was carried out using (NH4)2S2O8 as oxidizing agent. The conducting composites were characterized by a series of techniques namely: Fourier transform–infrared, X-ray diffraction, scanning electron microscopy, thermogravimetry analysis, two-probe conductivity, magnetic susceptibility, and particle size measurements. For electrorheological (ER) measurements, the conductivities of the composites were reduced by a dedoping process. A series of suspensions were prepared in silicone oil, having various volume fractions, and then subjected to colloidal stability, flow rate, ER and creep-recovery tests. Enhancement in the electric field-induced viscosities and shear thinning non-Newtonian viscoelastic behavior was observed for all the composite materials studied. Recoverable viscoelastic deformations were detected from the creep and creep-recovery tests under externally applied electric field thus; they were classified as smart materials.

SYNTHESIS, CHARACTERIZATION, AND ELECTROKINETIC PROPERTIES OF POLYINDENE/COLEMANITE CONDUCTING COMPOSITE

The aim of the aqueous electrokinetic experiments in the present study was to assess the relative contribution of the conducting polyindene (PIn) and inorganic colemanite components to the zeta (ζ) potentials of the composite particles, thus providing further insight into their surface composition in the dispersed state and establishing colloidally stable conditions for potential rheological, industrial applications. For this, PIn and a PIn/colemanite composite (containing 5 wt.% colemanite) were synthesized by chemical oxidative polymerization using FeCl3 as an oxidizing agent. Colemanite, PIn, and PIn/colemanite composite samples were characterized by Fourier-transform infrared spectroscopy, elemental analysis, conductivity, dielectric constant, magnetic susceptibility, density, particle-size measurements, thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction analysis, and scanning electron microscopy methods. The electrokinetic properties of colemanite and PIn/colemanite composite dispersions were determined by ζ-potential measurements in aqueous medium, taking into account the effects of time, pH, various electrolytes, surfactants, and temperature. The pH was observed to have a greater effect on the ζ potentials of colemanite in water but caused only slight changes in the presence of cationic (NaCl, BaCl2, AlCl3) and anionic (NaCl, Na2SO4) electrolytes. Increased pH values shifted the ζ potentials of PIn/colemanite composite dispersions to more negative values. The most effective surfactant acting on the ζ potentials of colemanite and PIn/colemanite composite dispersions was cetyltrimethylammonium bromide (CTAB), which shifted the ζ potentials to more positive regions. Elevated temperatures caused almost no change to the ζ potentials of either the colemanite or the PIn/colemanite composite dispersions.

Electrorheology and creep-recovery behavior of conducting polythiophene/poly(oxymethylene)-blend suspensions

Electrorheological properties and creep-recovery behavior of polythiophene/polyoxymethylene-blend having PT(50%)/POM(50%) composition were investigated. Particle size, conductivity and dielectric values were measured to be 24.77 μm, 3.85 × 10−5 S·m−1 and 26.75, respectively. Sedimentation ratio was measured to be 64% at the end of 16 days. The effects of dispersed particle volume fraction, external electric field strength, shear rate, frequency and temperature on ER properties and storage modulus of PT/POM-blend/silicone oil (SO) suspensions were examined. Enhancement were observed in the electric field viscosities of the suspensions and thus they were classified as a smart material. Shear thinning non-Newtonian viscoelastic behavior was determined for PT/POM-blend/SO system. Further, time-dependent deformation was examined by creep-recovery tests and recoverable viscoelastic deformation established.