All-organic PANI–DBSA/PVDF dielectric composites with unique electrical properties

Novel all-organic polymer high-dielectric permittivity composites of polyaniline (PANI)/poly (vinylidene fluoride) (PVDF) were prepared by solution method and their dielectric and electric properties were studied over the wide ranges of temperatures and frequencies. To improve the interface bonding between two polymers, dodecylbenzenesulfonic acid (DBSA), a bulky molecule containing a polar head and a long non-polar chain was used both as a surfactant and as dopant in polyaniline (PANI) synthesis. Synthesized conducting PANI–DBSA particles were dispersed in poly(vinylidene fluoride) (PVDF) matrix to form an all-organic composite with different PANI–DBSA concentrations. Near the percolation threshold, the dielectric permittivity of the composites at 100 Hz frequency and room temperature was as high as 170, while the dielectric loss tangent value was as low as 0.9. Like typical percolation system, composites experienced high dielectric permittivity at low filler concentrations. However, their dielectric loss tangent was low enough to match with non-percolative ceramic filler-based polymer composites. Maximum electrical conductivity at 24 wt% of PANI–DBSA was mere 10^?6 S/cm, a remarkably low value for percolative-type composites. Increase in the dielectric permittivity of the composites with increase in temperature from 25 to 115 °C for different PANI–DBSA concentrations was always in the same range of 50–60 %. However, the degree of increase in the electrical conductivity with the temperature was more prominent at low filler concentrations compared with high filler concentrations. Distinct electrical and their unique thermal dependence were attributed to an improved interface between the filler and the polymer matrix.     

An intermediate range solution to a diffraction problem with impedance conditions

An intermediate range solution for the problem of plane wave diffraction by a finite plate with impedance boundaries is presented. Initially, the problem is expressed in terms of two Wiener–Hopf equations with the help of Fourier transform and the boundary conditions in the transformed domain. The consideration of the intermediate range approximation in terms of source position renders integrals that are generally elusive to tackle because of the presence of branch points. These integrals are evaluated by invoking a modified stationary phase method, thereby a field valid over an intermediate range is calculated. The graphical analysis is preformed for various parameters of physical interest for both intermediate and far-field solutions.     

Drag reduction for flow past a square cylinder through corner chamfering

This study investigates the unsteady incompressible flow around a square cylinder with different chamfer ratios (CRs) using a commercial finite volume code, ANSYS Fluent. CR ranges from 0.0 (sharp square cylinder) to 0.5 (diamond cylinder) with variable increments. Detailed analysis of flow characteristics is conducted at Reynolds number (Re) = 2100. Additionally, simulation is extended to cover Re, i.e., Re = 100, 500, and 10000. The simulation results show that cylinder with CR = 0.1 outperforms all other cases by enabling a drag reduction of about 60 % at Re = 10⁴. Drag has an inverse relationship with the wake closure length. Time-averaged coefficient of pressure, streamlines, and vorticity contours are also discussed to better understand near-wake features and the physics of drag reduction.

     

Isolation and characterization of tetracycline-resistant Citrobacter spp. from catfish

Fifty-two tetracycline-resistant Citrobacter spp. strains were isolated from farm-raised catfish. Morphological and biochemical characteristics indicated that 38 of the 52 citrobacters were Citrobacter freundii, 7 were C. amalonaticus and 7 were C. braakii. All isolates were resistant to multiple antibiotics. Polymerase chain reaction (PCR) protocols were developed to detect the presence of 3 tetracycline-resistance genes (tetA, tetB and tetG) from Citrobacter isolates. Oligonucleotide primers specifically targeting a 967-bp region of tetB successfully amplified the PCR amplicons from 3238 (85.0%) of C. freundii strains, 57 (71.0%) of C. amalonaticus and 47 (57%) from C. braakii. Oligonucleotide primers specific for the detection of tetA gene amplified the 417-bp PCR amplicons from 738 (18.0%) of tetracycline-resistant C. freundii only. The assay failed to amplify tetA genes from C. brakii or C. amalonaticus. Plasmids (2.0-16.0kb) were isolated from 14 of the 38 strains of C. freundii. Strains of C. amalonaticus and C. brakii did not contain any plasmids. Dendrogram analysis of the SpeI pulsed field gel electrophoresis (PFGE) results identified 23 distinct macrorestriction patterns (mrps) among the 36 strains of C. freundii, 3 distinct mrps among the 7 strains of C. braakii and 4 unique mrps among the 7 strains of C. amalonaticus. Our results indicate that citrobacters from catfish could serve as reservoirs of tetracycline-resistance determinants.     

Mechanical,dielectric and EMI shielding response of styrene acrylonitrile,styrene acrylonitrile/polyaniline polymer blends,upon incorporation of few layer graphene at low filler loadings

The malfunction of electronic devices and many health-related issues may be caused due to electromagnetic interference (EMI) pollution. To overcome this problem a new set of material SAN/PANI/FLG hybrid composite with better EMI shielding properties is prepared using solution casting technique. Conductive polyaniline (PANI) is added (5 wt% and 10 wt%) to otherwise, an insulative polymer styrene acrylonitrile (SAN). Furthermore, few layer graphene (FLG) is added (0.1–1 wt%) to SAN/PANI polymer blends for preparation of SAN/PANI/FLG hybrid composites. The incorporation of PANI in SAN produces a phase separated morphology, whereas graphene appears in sheet like structure. For 0.1 wt% FLG/SAN/PANI-10 composite, total shielding effectiveness (SE_T) is enhanced from 1.1 to 24.3 dB (100 Hz), mainly due to enhanced dielectric characteristics. However, the maximum increase in tensile strength (49.6 MPa) and modulus (1.5 GPa) is observed for 0.5 wt% FLG/SAN/PANI-5.0 hybrid composite. The increase in dielectric properties and shielding efficiency of SAN/PANI/FLG may be credited to the accumulation of space charges or electric dipoles at the insulator conductor-interface.     

Thermal-diffusion and diffusion-thermo effects on axisymmetric flow of a second grade fluid

This study investigates the thermal-diffusion and diffusion-thermo effects on the two-dimensional magnetohydrodynamics (MHD) axisymmertric flow of a second grade fluid. Mathematical analysis has been carried out in the presence of Joule heating and first order chemical reaction. Using momentum, energy and concentration laws, the governing partial differential equations have been reduced to the ordinary differential equations by suitable transformations. Series solutions are constructed by homotopy analysis method (HAM). Convergence of the derived series solutions is ensured. Plots are displayed in order to examine the influence of emerging parameters on the dimensionless components of velocity, temperature and concentration fields. Numerical computations for skin friction coefficient, Nusselt number and Sherwood number are tabulated.