Tez özetleri Astronomi ve Uzay Bilimleri Anabilim Dalı

The Preparation and Characterization of Chitosan-Metal Oxide Composite Films
In this study, mainly two types of chitosan (CS) films were prepared: nanosized iron (II, III) oxide (magnetite : Fe₃O₄) containing chitosan (CS2-M) films and glutaraldehyde (GA)-crosslinked (CS-GA) films. The properties of both chitosan films were compared with those of chitosan (CS/CS2) films which were prepared by the evaporation of 1 (w/v) % or 2 (w/v) % chitosan solution in 2 (v/v) % aqueous acetic acid.
In the synthesis of crosslinked CS-GA films, constant volume of aqueous GA solution at five different GA concentrations were added into the 1 (w/v) % chitosan solution in 2 (v/v) % aqueous acetic acid. GA concentration in the solution was adjusted to crosslink the 25 %, 50%, 75%, 100% and 200% of –NH₂ groups in CS. The reaction mixtures were decanted to the Teflon petri dishes, and then they were held there at room temperature to obtain CS-GA films by the evaporation of solvent.
In the synthesis of Fe₃O₄ containing chitosan (CS2-M) films, various amounts of Fe₃O₄ (1, 2, 3, 4, and 6 wt % of CS) was added in 2 (w/v) % chitosan solution in 2 (v/v) % aqueous acetic acid, and the mixture was ultrasonically stirred in order to homogeneously dispers Fe₃O₄. CS2-M films were obtained by drying the mixture in Teflon petri dishes at room temperature. The characterization of CS/CS2, CS-GA, and CS2-M films were performed by FTIR, XRD, DSC, and SEM analyses.
Dielectric constant (ε’) and dielectric loss (ε’’) of the films were determined by dielectric spectroscopy between 12Hz - 100KHz in room temperature and between 5 Hz – 5 kHz at 293 - 463K temperature range. The increase of the temperature led to the increase in dielectric constant while increasing frequency caused to decrease in dielectric constant. It was observed that dielectric constant of CS-GA films decreased with frequency and crosslinker GA content due to the decrease in polarization in crosslinked films. It was also determined that dielectric constant of CS-GA films increased with temperature. In the CS2-M films, dielectric constant values increased with temperature and Fe₃O₄ content of the film. In CS2-M films, the increase in Fe₃O₄ content of the film shifted the frequency values corresponding to the maximum value of the imaginary part of the electric modulus (M'') to the higher frequencies. This finding is the indication for both the increase in conductivity and the decrease in relaxation time. For the CS-GA films, the increase in the GA amount, frequency values ​​corresponding to the maximum values of M'' shifted to lower frequencies​​ indicating the increase in relaxation time and the decrease in conductivity. Tanδ-temperature measurements of CS2-M films carried out in 3 different frequency and with the increase of frequency, relaxation peaks were shifted to higher temperatures due to the polarization.