Mustafa Yavuz

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.

Investigation of electrorheological properties of biodegradable modified cellulose/corn oil suspensions

Considerable scientific and industrial interest is currently being focused on a class of materials known as electrorheological (ER) fluids, which display remarkable rheological behaviour, being able to convert rapidly and repeatedly from a liquid to solid when an electric field (E) is applied or removed. In this study, biodegradable cellulose was modified and converted to their carboxyl salts. Modified cellulose is characterised by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, energy dispersive spectroscopy (EDS), thermogravimetric analysis (TGA) and conductivity measurements. Suspensions of cellulose (C) and modified cellulose (MC) were prepared in insulated corn oil (CO). The effects of electric field strength, shear rate, shear stress, temperature, etc. of these suspensions onto ER activity were determined. Rheological measurements were carried out via a rotational rheometer with a high-voltage generator to investigate the effects of electric field strength and particle concentration on ER performance. The results show that the ER properties are enhanced by increasing the particle concentration and electric field strength. Also the cellulose-based ER fluids exhibit viscoelastic behaviour under an applied electric field due to the chain formation induced by electric polarization between particles.

Influence of PVA and silica on chemical, thermo-mechanical and electrical properties of Celluclast-treated nanofibrillated cellulose composites

This study reports on the effects of organic polyvinyl alcohol (PVA) and inorganic silica polymer on properties of Celluclast-treated nanofibrillated cellulose composites. Nanofibrillated cellulose was isolated from Eucalyptus camaldulensis and prior to high-pressure homogenizing was pretreated with Celluclast enzyme in order to lower energy consumption. Three nanocomposite films were fabricated via the casting process: nanofibrillated cellulose (CNF), nanocellulose-PVA (CNF-P) and nanocellulose-silica (CNF-Si). Chemical characterization, crystallization and thermal stability were determined using FT-IR and TGA. Morphological alterations were monitored with SEM. The Youngs and storage moduli of the nanocomposites were determined via a universal testing machine and DTMA. The real and imaginary parts of permittivity and electric modulus were evaluated using an impedance analyzer. The crystallinity values of the nanocomposites calculated from the FT-IR were in agreement with the TGA results, showing that the lowest crystallinity value was in the CNF-Si. The CNF-P displayed the highest tensile strength. At a high temperature interval, the storage modulus of the CNF-Si was greater than that of the CNF or CNF-P. The CNF-Si also exhibited a completed singular relaxation process, while the CNF and the CNF-P processes were uncompleted. Consequently, in terms of industrial applications, although the CNF-P composite had mechanical advantages, the CNF-Si composite displayed the best thermo-mechanical properties.

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.

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.

Some Novel Conducting Polythiophene Derivatives: Theoretical Analysis, Synthesis, Characterization and Electroreological Properties

A series of alternating phylene and symmetrically bithiophene containing repeat units and the respective homopolymers have been synthesized and characterized by combining FTIR, UV-Vis spectroscopy, four probe conductivity measurement, TGA and SEM analysis. Quantum mechanical calculations of the structures and infrared spectra of the monomers and respective dimers were compared with experimental results. The polymers are soluble in N-methyl-pyrrolidone (NMP). The samples have conductivities of 10−5 S/cm levels. Thermal degradation analysis results indicated that poly-bithiophene derivatives have higher thermal stabilities than poly-monothiophene derivatives. All samples exhibited different surface morphologies. The electrorheological (ER) properties of polymer suspensions in silicone oil were prepared and ER behavior was investigated as a function of shear rate, electric field strength and frequency.

Electrorheological Properties of Polyaniline/Red Mud Composite

Abstract In this study, electrorheological (ER) properties of polyaniline (PANI) and polyaniline/red mud (RM) composites were investigated. Polyaniline and polyaniline/red mud (PRM) composites were prepared by oxidative polymerization. PANI and PRM particle-based ER suspensions were prepared in silicone oil (SO) and their ER behavior was investigated as a function of concentration, shear rate, electric field strength, frequency, and temperature. Sedimentation stabilities of these suspensions were determined. ER activities of all the suspensions were observed to increase with increasing electric field strength, dispersed particle concentration, and decreasing shear rate. The suspensions show shear thinning non-Newtonian viscoelastic behavior, in which viscosity of suspension decreases with increasing shear rate. Shear stress of composite suspensions increases linearly with increasing applied electric field strength and concentration of the particles. Effect of high temperature on ER activity of ER fluids system was also investigated.