M. Zulfequar

Metal-containing polyurethanes from tetradentate Schiff bases: synthesis, characterization, and biocidal activities

N,N′-bis(salicylidene)thiosemicarbazide Schiff base has been synthesized by the reaction of thiosemicarbazide with salicylaldehyde and then reacted with formaldehyde to generate phenolic groups, resulting in the formation of Schiff-base monomeric ligand. It was further incorporated with transition metals, Mn+2, Co+2, Ni+2, Cu+2, and Zn+2, to form Schiff-base metal complex, which was then polymerized with toluene 2,4-diisocyanate to form metal-chelated polyurethanes. Monomeric ligand, its metal complexes, and its metal polychelates were characterized and compared by elemental analysis, FT-IR, 1H NMR, thermal, and biocidal activities to evaluate the enhancement in physical and chemical properties on coordination with metal and on polymerization. SEM images of ligand and polymer metal complexes showed changes in surface morphology, while electronic spectra of polymer metal complexes were used to predict the geometry. Antimicrobial activities were determined by using agar-diffusion method with Staphylococcus aureus, Escherichia coli, Bacillus subtilis (bacteria), Aspergillus niger, Candida albicans, and Aspergillus flavus (yeast). The polymeric ligand had varied antibacterial and antifungal activities, enhanced after chelation and polymerization. Comparative results show that coordination of metal to the ligand enhances its physical and chemical properties which were meliorated on polymerization.

Synthesis, spectral, and antibacterial screening studies of chelating polymers of bisphenol-A–formaldehyde resin bearing barbituric acid

A new polymeric ligand was synthesized by the reaction of bisphenol-A and formaldehyde in the basic medium, followed by condensation polymerization with barbituric acid in the acidic medium. Polymer metal complexes were prepared by reaction of this resin with Mn(II), Co(II), Ni(II), Cu(II), and Zn(II). The polymeric resin and its metal polychelates were characterized by elemental analysis, FT-IR, 13C-NMR, and 1H-NMR spectra. The geometry of the polymer metal complexes was evaluated by electronic spectra (UV-Vis) and magnetic moment measurement. Thermal stabilities show an increased thermal stability of the metal polychelates compared to the ligand. The antibacterial activities of all the synthesized polymers were investigated against Bacillus subtilis, Staphylococcus aureus, and Escherichia coli, showing good antibacterial activities against these bacteria. Cu(II) polychelate showed highest biocidal activity.

Effect of moisture on the dielectric behaviour of hot-pressed AlN ceramic

Abstract In the present paper the effect of moisture on the dielectric behaviour of hot-pressed AlN ceramic having different volume percentages of porosity is reported. The annealed samples do not show any dielectric dispersion at room temperature in the audiofrequency range. However, a strong dispersion is observed after the samples have been exposed to moisture (relative humidity, 60%–95%); the effect is greater in the sample having the higher porosity. A quite different behaviour of moisture absorption is observed at low porosities (4 vol.% or less) from that at high porosities (9 and 15 vol.%); this is explained in terms of closed and open porosity in AlN samples. The recovery studies show that the low porosity samples return to the original state simply by evacuating the sample holder at room temperature. However, in the case of the higher porosity samples, water may be retained inside the sample even up to 600 K. The highly dense sample (porosity, 0.2 vol.%) did not show any appreciable effect of moisture; this indicates that highly dense samples of AlN can be used for insulation without moisture having any appreciable effect.

Electrical conductivity of hot-pressed AIN ceramic: effect of various oxide additives

The paper describes the effect of the addition of 1 mol% of various oxide additives (MgO, BeO and Y2O3) on the electrical conductivity of hot-pressed AIN ceramic in the temperature range 500 to 950 K. lt is observed that the electrical conductivity increases quite appreciably at all temperatures, in the above temperature range, when these oxides are added to AIN. The effect of moisture has also been studied for all the samples. The moisture affects the conductivity appreciably only when the porosity is more than 6%. However, in the case of Y2O3 additive, no moisture effect is observed even at higher porosity (11.5%). The results have been explained in terms of closed and open porosity in these samples.

Synthesis and characterization of ZnO nanostructures

Nanostructures of zinc oxide are synthesized by physical vapor condensation method. From the SEM image, it is observed that these nano structures look like nanosprings mixed with nanorods. The typical diameter of these nanostructures is in the range of 80-150 nm and the length is of the order of several micrometers. The XRD data shows a sharp peak at 36.87deg which is very close to that of zinc oxide nanorods grown by oxidation in the presence of ambient gases i.e. oxygen mixed with argon. UV visible spectra of these nanostructures shows a peak at 371 nm and 373 nm. The broad peak at 373 nm is responsible for the conversion of zinc into zinc oxide.

Effect of laser irradiation on structural and optical properties of thermally evaporated thin films of amorphous Cd5Se95−xZnx

Thin films of Cd5Se95−xZnx (x = 0, 2, 4) were deposited by a thermal evaporation technique on glass substrates. These films were irradiated by pulsed laser at different durations of time. Laser irradiation of Cd5Se95−xZnx (x = 0, 2, 4) was accompanied structural changes which in turn leads to the change in optical properties of the material. The X-ray diffraction pattern of Cd5Se95−xZnx (x = 0, 2, 4) shows that the grain size increases due to the addition of Zn and decreases after laser irradiation. It was also found that the value of dislocation density increases after laser irradiation. The surface morphology of laser-irradiated thin films of Cd5Se95−xZnx (x = 0, 2, 4) shows that the disorderness or defects are produced due to laser irradiation. Energy dispersive X-ray spectroscopy confirms the elemental composition of the ternary alloy of Cd5Se95−xZnx (x = 0, 2, 4). The optical constants of Cd5Se95−xZnx (x = 0, 2, 4) were calculated from optical transmission spectra. The value of optical band gap increases after laser irradiation and decreases due to the addition of Zn.

Kinetics of crystallization in a.Se80In20-xPbx under isothermal annealing: Activation energy determination

In the past few years research on phase change optical data storage media has concentrated on increasing the erase speed. The chalcogenide glasses have been the subject of extensive investigation due to their interesting properties. The most widely exploited property of chalcogenide glasses is their large infrared transmittance in combination with their chemical and mechanical durability. The most unique property of chalcogenides glasses is that they are semiconducting in the amorphous phase, and they can become highly conductive in the crystallization phase, hence the electrical switching ability. In addition, crystalline chalcogenide can be much more reflective than amorphous chalcogenides. In recent years, efforts have been made to develop chalcogenide based erasable optical storage media. Since the write and erase time is closely related to the melting temperature (Tm) and the speed of crystallization, a detailed investigation of the compositional dependence and of the effect of a small quantity of additive on crystallization is necessary [1]. There are many methods of activation energy determination from the isothermal experiments. All of them can be divided in two groups: local and global methods. Local methods use only certain points from the experimental curve obtained during isothermal annealing. In the global method, which has been presented in many papers [2, 3], a general scaling factor is used to make the experimental curves obtained for different annealing temperature collapse into a single temperature-independent curve. Another method, which is also quite convenient for crystallization measurement, because of its simplicity and accuracy of continuous measurements, is conductivity measurements [4, 5]. This method was used in our experiment. The aim of the present work is to study the isothermal crystallization kinetics by using conductivity measurements and to discuss the effect of Pb on the crystallization of a Se-In alloy. Since the conductivity of the amorphous state is much lower than that of the crystalline state, the electrical measurements are expected to be sensitive to phase changes in these materials [6]. The selection of Se is because of its wide commercial applications. Its device applications like switching, memory and xerography, etc., made it attractive. It also exhibits [7] a unique property of reversible transformation. This property makes very useful in optical memory devices. But in the pure state it has disadvantages because of its short lifetime and low sensi-