Influence of injection molding on the electrical properties of polyamide 12 filled with multi-walled carbon nanotubes

Microinjection-molded and compression-molded polyamide (PA12) matrix composites filled with 0.67, 1.33, 2 and 4 wt% multi-walled carbon nanotubes (MWNTs) were prepared from twin-screw extruded pellets. The compression molded samples have an electrical percolation threshold close to 1.2 wt%. Coupled rheological and electrical measurements show that their electrical properties start decreasing as soon as shear begins and are partially restored during flow, suggesting successively breakage and reconstruction of a percolating network. On the other hand, the electrical properties of the microinjection molded composites are close to the matrix ones, showing that cooling is too fast for the MWNTs to form a network. There is some electrical anisotropy in these composites, as evidenced by a greater conductivity measured in the flow direction. However polarized Raman spectroscopy analysis does not reveal a significant orientation of the MWNTs.     

Photovoltaic properties of nanocrystalline CdS films deposited by SILAR and CBD techniques—a comparative study

CdS films were fabricated using Successive Ionic Layer Adsorption and Reaction (SILAR) technique from starting solutions having S:Cd ratio 1:1, 3:1, 5:1 and 7:1 and their structural, surface morphological and optical properties were investigated and compared with that of their chemical bath deposited counterparts. The X-ray diffraction profiles showed that the films have cubic crystal structure with preferential orientation along the (111) plane and the intensity of the (111) plane increases for both the techniques as the S:Cd ratio increases. The energy dispersive X-ray analysis revealed that for SILAR deposited films, the S/Cd ratio in the sample increases from 0.8308 (for S:Cd 1:1) to 1.04 (for S:Cd 7:1) as the molar concentration of sulphur in the starting solution increases. But for CBD films, the S/Cd is only ~0.80 for all concentrations of sulphur in the starting solution. The optical band gap increases with the increase in S:Cd ratio in the starting solution in both the techniques.     

Studies on monobenzo 18-crown-6-ether substituted phenylenevinylene oligomer: synthesis,photoluminescent, and dielectric properties

Partially conjugated monobenzo 18-crown-6 substituted oligo (p-phenylenevinylene) (MB-OPV) was synthesized via Wittig route. Formation of the oligomer was characterized by spectral (FTIR, ¹H NMR, and ¹³C NMR), elemental and gel permeation chromatography analysis. The morphology of the oligomer film of one-dimensional (1D) and three-dimensional (3D) architectures were observed using atomic force microscopy. The oligomer showed excellent photoluminescence (PL) of bluish green emission at shorter wavelength of 542 nm. Stability of the polymer and glass transition temperature was determined by TGA/DSC. The dielectric properties such as dielectric constant and loss factor for the oligomer have also been studied with respect to change of frequency (50 Hz–5 MHz) and temperature (30–90 °C). The value of dielectric constant decreased with increasing frequency which indicates that the major contribution comes from orientation polarization. The value of dielectric constant increased with increasing temperature which is due to greater freedom of movement of the dipole molecular chains within the oligomer at high temperature.     

Nontoxic pH-sensitive silver nanocomposite hydrogels for potential wound healing applications

ABSTRACT

Silver nanocomposite (SNC) containing pH sensitivity with fascinating attention may be recommended for extensive utilization in eco-friendly nanomaterial applications. In the present investigation, a strategy to fabricate new biodegradable and biocompatible hydrogels based on sodium alginate/ethylene glycol/acrylic acid functionalized with silver nanocomposites, which were synthesized by a facile greener method. The swelling profile is enhanced the stimuli responsive behavior of nanocomposite hydrogels. The synthesized nanocomposite hydrogels has showed a significant pH-sensitive behavior which induced the degradation profile, cell viability, and antimicrobial activity. Hence, this kind of biomaterials has been utilized for nontoxic, degradable wound healing dressing.     

Compressed sensing based foreground detection vector for object detection in Wireless Visual Sensor Networks

Compressed sensing based background subtraction (CS-BS) plays a significant role in video surveillance applications in Wireless Visual Sensor Networks. This paper implements a CS-BS framework with a novel thresholding strategy to detect the anomaly with fewer measurements in a secured indoor environment. In CS-BS, the CS is performed on the difference frame which is sparse, thereby reducing energy, memory and bandwidth. In this framework, a foreground threshold is proposed based on the measurement matrix to extract the moving object from a scene. The performance of the CS-BS framework with FDV is evaluated using metrics such as detection accuracy, energy complexity, percentage of reduction in samples and measurements. The proposed CS-BS framework with hybrid matrix based FDV achieves around 95.8% reduction of measurements and 91% reduction of samples.     

Studies on the nonlinear optical single crystal: Ammonium d,l-tartrate (C4H9NO6)

The organic nonlinear optical material ammonium d,l-tartrate single crystal has been successfully grown by slow evaporation solution technique (SEST). The grown crystals were characterized by single crystal XRD and the lattice parameters have been confirmed. The structural perfection of the grown crystal was analyzed by high-resolution X-ray diffraction measurement. The optical transmittance spectrum shows that the material has a good optical transparency in the entire visible region with the UV cut-off wavelength at 234 nm. Thermogravimetric and differential scanning calorimetric measurements were performed to study the thermal properties of the grown crystal. Chemical etching studies were attempted to determine the dislocation density of the grown crystal. Mechanical behavior was assessed using Vickers hardness testing carried out on (0 0 1) crystallographic plane. The Kurtz–Perry powder SHG technique confirms the NLO property of the grown crystal and the efficiency of AMT crystal was found to be 1.3 times that of standard KDP crystal.     

Optical investigations on Tb3+ doped l-Histidine hydrochloride mono hydrate single crystals grown by low temperature solution techniques

The potential nonlinear optical material of Terbium (Tb³⁺) ion doped l-Histidine hydrochloride monohydrate (LHHC) single crystals were successfully grown. Tb³⁺:LHHC crystals of 7 mm × 5 mm × 3 mm and 59 mm length and 15 mm diameter have been grown by the slow solvent evaporation and Sankaranarayanan-Ramasamy (SR) techniques respectively. The grown crystals were characterized by single crystal X-ray diffraction analysis to confirm the crystalline structure and morphology. High resolution X-ray diffraction (HRXRD) studies revealed that the SR grown sample shows relatively good crystalline nature with 9″ full-width at half-maximum (FWHM) for the diffraction curve. Functional groups were identified by Fourier transform infra-red spectroscopy (FTIR). The optical transparency and band gaps of grown crystals were measured by UV–Vis spectroscopy. Thermogravimetric and differential thermal analysis (TG/DTA) studies reveal that the crystal was thermally stable up to 155 °C in SR grown crystal. Surface morphology of the growth plane was observed using scanning electron microscopy (SEM). The incorporation of Tb ion was estimated by EDAX. The frequency-dependent dielectric properties of the crystals were carried out for different temperatures. Vickers hardness study carried out on (1 0 0) face at room temperature shows increased hardness of the SR method grown crystal. Second harmonic generation efficiency of SEST and SR grown crystals are 3.2 and 3.5 times greater than that of pure KDP. The Photoluminescence (PL) studies of Tb³⁺ ions result from the radiative intra-configurational f-f transitions that occur from the ⁵D₄ excited state to the ⁷F_j (j = 6, 5, 4, 3) ground states. The decay curve of the ⁵D₄ level of emission was observed with a long life time of 319.2041 μs for the SR grown Tb³⁺:LHHC crystal.     

Metalloporphyrins encapsulated mesoporous molecular sieves as efficient heterogeneous catalysts for oxidation of cyclohexene with iodosylbenzene

The cationic Fe, Mn or VO porphyrins were encapsulated in Si, Al, Ti and V-MCM-41. The catalytic activity was investigated for the oxidation of cyclohexene with iodosylbenzene (PhIO) as oxidant. Manganese porphyrin supported catalysts produces epoxide as major products whereas iron and vanadyl porphyrins gave allylic oxidation products as major constituents. The results obtained clearly shows that the selectivity of various products depends not only on the nature of the support materials but also on the combined effects of metalloporphyrins and the supports. The recyclability of the heterogeneous catalysts was also investigated. The decrease in catalytic activity and leaching of active centers were observed when porphyrins were supported on Si-MCM-41.