Halil Ibrahim Unal

Synthesis and Characterization of Polyindole/Poly(vinyl acetate) Conducting Composites

Composites of a polyindole (PIN) and poly(vinyl acetate) (PVAc) were prepared chemically using FeCl3 as an oxidant agent in anhydrous media. The composite compositions were altered by varying the indole monomer during preparation. The composites were characterized by FTIR and UV‐visible spectroscopies, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), stress‐strain experiments and conductivity measurements. Moreover, the film of PVAc and PIN/PVAc composites were prepared by casting on glass Petri dishes to examine their stress‐strain properties. PIN/PVAc composites are thermally more stable than PIN. It was found that the conductivities of PIN/PVAc composites depend on the indole content in the composites.

The use of sepiolite for decolorization of sugar juice

Abstract Brown, beige and dolomitic (white) sepiolites from the area around Ankara–Polatli–Turktaciri village were tested for the decolorization of sugar solutions at different pH and temperature. The decolorizing effect of various quaternary ammonium salts in combination with the sepiolites was also investigated. The sepiolites were characterized by its zeta potential, filtration capacity, particle size and specific surface area. Before and after the treatment of sepiolite with the sugar juice, the sepiolites were investigated by DTA/TG and SEM. The brown sepiolite had a more developed fiber structure, smaller particle size when dispersed in water, a larger surface area and a greater decolorizing activity than the other samples. Addition of small quantities of quaternary ammonium salts to the brown sepiolite improved the removal of sugar juice color by up to 80%.

Synthesis, Characterization and Electrorheological Properties of Polyindene/Kaolinite Composites

In this study, synthesis, characterization and electrorheological (ER) properties of polyindene (PIN) and polyindene/kaolinite composites were carried out by cationic radical polymerization using FeCl3 as the oxidizing agent. The homopolymer and composites, containing different amounts of PIN were characterized by FTIR spectroscopy, thermo‐gravimetric (TGA) analyses, scanning electron microscopy (SEM) and dynamic light scattering (DLS) methods. The conductivity and dielectric properties of PIN and PIN/kaolinite composites were determined. Suspensions of PIN and PIN/kaolinite composites were prepared in silicone oil (SO), at a series of concentrations (c=5–25 m/m %). The effects of concentration, shear rate, electric field strength, frequency, temperature and promoter on ER activities of suspensions were investigated.

Graft Copolymerization of Acrylamide on Swollen poly (Ethylene Terephthalate) Fibers Using Cerium Ammonium Nitrate Initiator

Abstract In this study the graft copolymerization of acrylamide (AAm) on swollen poly(ethylene terephthalate) (PET) fibers using cerium ammonium nitrate (CeAN) initiator was investigated. Five organic solvents, dimethylsulfoxide (DMSO), morpholine, acetic acid (HAc), n-butanol, and 1,2-dichloroethane (DCE), were used as swelling agents. DMSO was found to be the most suitable swelling agent. Solvent diffusion into the fibers was observed to increase with treatment time and temperature. The optimum graft yield was obtained when fibers were grafted after having been swollen in DMSO for a period of 1 hour at 140°C. Variation of graft yield with polymerization time and temperature, and monomer, initiator, and acid concentrations were investigated. Graft yields were observed to increase initially with polymerization time, then to level off, and were found to increase up to a certain monomer and Ce4+ concentration, then to decrease slightly. The effect of grafting on such fiber properties as diameter, viscosity,...

Graft copolymerization of n-vinyl-2-pyrrolidone on dimethyl sulfoxide pretreated poly(ethylene terephthalate) films using azobisisobutyronitrile initiator

Poly(ethylene terephthalate) (PET) films were grafted with n-vinyl-2-pyrrolidone (n-VP) using an azobisisobutyronitrile (AIBN) initiator. Films were pre-treated in dimethyl sulfoxide (DMSO) for 1 h at 140°C before the polymerization reaction was carried out. Variations of graft yield with time, temperature, initiator, and monomer concentrations were investigated. The optimum temperature and polymerization time was found to be 70°C and 4 h, respectively. Increasing monomer concentration from 0.28 to 1.22M and initiator concentration from 1.77 × 10−3 to 4.20 × 10−3M enhanced the percent grafting. The effects of monomer and initiator diffusion on PET films were also studied. The overall activation energy for grafting was calculated as 11.5 kcal/mol. Further changes in properties of PET films such as water-absorption capacity and intrinsic viscosity were determined. The grafted films were characterized with FTIR and scanning electron microscopy (SEM).

Colloidal, electrorheological, and viscoelastic properties of polypyrrole-graft-chitosan biodegradable copolymer:

In this study, colloidal, electrorheological, and viscoelastic properties of conducting polypyrrole, biodegradable chitosan, and polypyrrole-graft-chitosan copolymer were investigated. Some physical properties such as particle size, apparent density, conductivity, magnetic susceptibility, and elemental analysis of the materials were determined. Electrokinetic properties of the materials were investigated by means of zeta (ζ)-potential measurements in aqueous and non-aqueous (silicone oil) media. The effects of time, pH, various electrolytes, surfactants, and temperature onto ζ-potentials of the dispersions prepared in aqueous media were examined. It was concluded that the positive ζ-potential of polypyrrole shifted to more positive regions, and the isoelectric point of the polypyrrole concomitantly shifted to higher pH values after interaction with polycationic chitosan matrix. Polypyrrole-graft-chitosan/silicone oil suspensions were observed to be electrorheological active when subjected to external electric field strength. Creep and creep–recovery tests were applied to the suspensions and a relationship was established between viscoelastic response and ζ-potential of the materials. Furthermore, polypyrrole-graft-chitosan-based smart electrorheological fluid was observed to behave as a viscoelastic material and exhibited a reversible nonlinear viscoelastic deformation under externally applied electric field strength.

Core/shell-structured, covalently bonded TiO2/poly(3,4-ethylenedioxythiophene) dispersions and their electrorheological response: the effect of anisotropy

As a new electrorheological (ER) material, core/shell nanorods composed of a titania core and conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) shell were prepared via covalent bonding to achieve a thin polymer shell and make the interfacial interactions between the two components more impressive. The successful coating of PEDOT on the nanorod-TiO2 particles was confirmed by TEM analysis. The antisedimentation stability of the core/shell nanorod-TiO2/PEDOT particles was determined to be 100%. The ER properties of the materials were studied under controlled shear, oscillatory shear and creep tests. The dielectric spectra of the dispersions were obtained to further understand their ER responses and fitted with the Cole–Cole equation. The ER behavior of the dispersions was also observed using an optical microscope. The flow curves of these ER fluids were determined under various electric field strengths and their flow characteristics examined via a rheological equation using the Cho–Choi–Jhon (CCJ) model. In addition, the results were also compared with nanoparticle-TiO2/PEDOT. It was concluded that the conducting thin polymer shell and elongated structure of the hybrid material introduced a synergistic effect on the electric field induced polarizability and colloidal stability against sedimentation, which resulted in stronger ER activity, storage modulus and higher recovery after stress loadings when compared to nanoparticle-TiO2/PEDOT.

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.

Swelling-assisted graft copolymerization of 4-vinyl pyridine on poly(ethylene terephthalate) films using a benzoyl peroxide initiator

Graft copolymerization of 4-vinyl pyridine (4-VP) on poly(ethylene terephthalate) (PET) films using a benzoyl peroxide (Bz2O2) initiator was investigated under different conditions including polymerization time, temperature, monomer concentration, and initiator concentration. Dimethyl sulfoxide (DMSO) was used as swelling agent to promote the incorporation and the subsequent polymerization of 4-VP to PET films. Maximum percent grafting was obtained when the polymerization was carried for a period of two hours at 65°C. Increasing the monomer concentration from 0.2M to 0.8M and Bz2O2 concentration from 1.0×10−3M to 2.5×10−3M was accompanied by a significant enhancement in percent grafting. Monomer diffusion on PET films and its effect on the grafting yield were studied and intrinsic viscosities of grafted films were also measured.