N.A. El-Ghamaz

Correlation between ionic radii of metal azodye complexes and electrical conductivity.

5-(2,3-Dimethyl-1-phenylpyrazol-5-one azo)-2-thioxo-4-thiazolidinone (HL) and its metal complexes with copper(II) (1), cobalt(II) (2) and nickel(II) (3) are synthesized and characterized by physico-chemical techniques. The thermal properties of the ligand (HL) and its metal complexes (1-3) are discussed. The thermal activation energies of decomposition (Ea) of HL and its metal complexes with Cu(II), Co(II) and Ni(II) are found to be 48.76, 36.83, 30.59 and 40.45 kJ/mol, respectively. The frequency and temperature dependence of ac conductivity, dielectric constants for HL and its complexes (1-3) are investigated in the temperature range 300-356 K and frequency range 0.1-100 kHz. Both of the ac conductivity and the values of the thermal activation energy for conduction, as well as the dielectric properties of the complexes of HL are found to depend on the nature of the metallic ions. The values of the thermal activation energies of electrical conductivity decrease with increasing the value of test frequency. The small polarons tunneling (SPT) is the dominant conduction mechanism for the ligand (HL), while for complex (2) the overlapping large tunneling model (OLPT) is the dominant conduction mechanism. The correlated barrier hopping (CBH) is the dominant conduction mechanism for both of the complexes (1) and (3).

Conducting Polymers. VII. Effect of Doping with Iodine on the Dielectrical and Electrical Conduction Properties of Polyaniline

The oxidative chemical polymerization of aniline monomer in acidic aqueous media by using potassium dichromate as unconventional initiator was carried out at room temperature based on two different comparative methods. In the first method, in situ polymerization of polyaniline, polymerization was carried out in the presence of iodine solution (PANI/I2-In). In the second method, ex situ polymerization, after complete polymerization polyaniline was doped with iodine (PANI/I2-Ex). FTIR, UV measurements, and TGA analysis for undoped polyaniline (PANI), iodine doped polyaniline (PANI/I2-Ex), and iodine doped polyaniline (PANI/I2-In) show that iodine doping process occurred at the quinoid units in the polyaniline backbone of (PANI/I2-Ex) while iodine doping occurred at benzenoid units in polyaniline, in addition the iodination occurred at the rings of polyaniline backbone of (PANI/I2-In.). The data extracted from the XRD patterns shows the crystalline nature of synthesized samples and particles sizes are in the range 37–42 nm. The activation energies of thermal degradation of polyaniline or iodine doped polyaniline were determined from the TGA thermogram for PANI, (PANI/I2-In), and (PANI/I2-Ex) are 24.1, 43.4, and 44.19 KJ/mol, respectively. Doping of PANI with iodine enhances the ac conductivity of PANI whatever the method of doping, The room temperature values of σac measured under test frequency 100 kHz are found to be 6×10−5, 2.5×10−4, and 1×10−3 Ω−1.m−1 for PANI, (PANI/I2-In), and (PANI/I2-Ex), respectively.

Photodegradation of methylene blue with PVA/PVP blend under UV light irradiation.

Homogenous films of PVA/PVP blend (1:1) doped with different levels of methylene blue dye (MB) were prepared using the casting technique. The absorption spectra of doped PVA/PVP blend showed two absorption peaks due to the chromophor groups of MB while the pure PVA/PVP blend does not. The UV irradiation causes photodegradation of MB dye. The recovery of photodegraded MB is observed after keeping the sample 3h in atmospheric air. The value of the optical energy gap (Eg) decreases with increasing the doping levels with MB. The spectral distribution of absorption index (k) and refractive index (n) are determined from the reflection and transmission spectra in the spectral range 200-2500nm. The dependence of both n and k on wavelength of the incident light and the wt% content of MB in PVA/PVP blend is discussed. A normal dispersion observed at wavelength λ>370nm for pure PVA/PVP blend and λ>800nm for MB doped samples. The obtained results suggest the possible use of the studied system in many applications.