In situ preparation of polyaniline within neutral,anionic, and cationic superporous cryogel networks as conductive,semi‐interpenetrating polymer network cryogel composite systems

Polyaniline [p(An)], one of the most known conducting polymers, was prepared within superporus nonionic polyacrylamide [p(AAm)], anionic poly(2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid sodium salt) [p(AMPS)], and cationic poly(3‐acrylamidopropyltrimethyl ammonium chloride) [p(APTMACl)] cryogels. After they were synthesized, washed, and dried, the neutral p(AAm), anionic p(AMPS), and cationic p(APTMACl) cryogels were soaked in an ammonium persulfate/aniline solution (1:1.25 ratio) in 1 M hydrochloric acid for the in situ oxidative polymerization of p(An) with the cryogel matrices as templates or reactors. The prepared p(AAm)/p(An), p(AMPS)/p(An), and p(APTMACl)/p(An) semi‐interpenetrating polymer network (semi‐IPN) conductive cryogel composites were characterized with scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and conductivity analysis. The SEM images revealed that the superporus cryogel networks were almost completely filled with p(An) conductive polymers (CPs). Among the cryogel–CP semi‐IPNs, we found that p(AAm)/p(An) semi‐IPN conductive cryogel composites provided the highest conductivity values of 1.4 × 10^?2 ± 4 × 10^?4 S/cm; this was a 6.4 × 10⁶ fold increase in the conductivity from the values of 2.2 × 10^?9 ± 1 × 10^?10 for p(AAm) cryogels. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44137.     

Accessing Time–Varying Forces on the Vibrating Tip of the Dynamic Atomic Force Microscope to Map Material Composition

In dynamic atomic force microscopes the primary physical quantities being measured are the amplitude/phase or amplitude/frequency of the vibrating force probe. Topographic images with spatial resolutions down to the atomic scale can be obtained by mapping these measurements across the sample surface under feedback control. During the imaging process the vibrating tip is observing tip–sample interaction potentials (force–distance relationships) at every point on the surface. The interaction potential is a superposition of short- and long–distance interactions of various origins determined by the material compositions of the tip, sample, and the medium of imaging. In principle, measurement of tip–sample interaction potential should allow determination and mapping of material composition of the sample. However, a single measurement of amplitude/phase or amplitude/frequency in dynamic atomic force microscopes is not enough to characterize a complicated tip–sample interaction potential. Recent developments in the understanding of dynamics of the vibrating force probe (cantilever), together with specially designed cantilevers that utilize torsional vibrations in addition to conventional vertical vibrations, enable the recovery of tip–sample interaction potentials at a timescale less than a millisecond. Here, with theory and experiments, we discuss how these cantilevers recover the information about the tip–sample interaction forces and give an example of compositional mapping on a polymeric material system.     

The in vitro antimicrobial and antioxidant activities of the essential oils and methanol extracts of endemic Thymus spathulifolius

The present study was conducted to evaluate the in vitro antimicrobial and antioxidant properties of essential oil and methanol extracts from a unique and endemic plant, Thymus spathulifolius (Hausskn. and Velen.). The antimicrobial test results showed that the essential oil of T. spathulifolius strongly inhibited the growth of test microorganisms studied, except for 4 fungi species while polar and non-polar subfractions of the methanol extract had moderate antibacterial, but not antifungal and anticandidal activity. The antioxidative potential of the samples was evaluated using two separate methods, inhibition of free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) and β-carotene–linoleic acid systems. The polar subfraction of the methanol extract was able to reduce the stable free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) with an IC₅₀ of 16.15 ± 0.5 μg/ml, which was lower than that of synthetic antioxidant, BHT, (19.8 ± 0.5 μg/ml). Inhibition values of linoleic acid oxidation were calculated as 92% and 89% for the oil and the polar subfraction, respectively. Gallic acid equivalent total phenolic constituent of the polar subfraction was 141.00 ± 0.90 μg/mg (14.1%, w/w). The chemical composition of a hydrodistilled essential oil of T. spathulifolius was analyzed by a GC and GC/MS system. A total of 28 constituents representing 99.2% of the oil were identified; thymol (36.5%), carvacrol (29.8%), p-cymene (10.0%) and γ-terpinene (6.3%) were the main components comprising 82.6% of the oil. Results presented here may suggest that the essential oil and extracts of T. spathulifolius possess antimicrobial and antioxidant properties, and therefore, they can be used as a natural preservative ingredient in food and/or pharmaceutical industry.     

Dual solution of heat transfer in hydromagnetic micropolar fluid flow over a stretching sheet in a porous media: A numerical approach

In this study, the researcher looks at the heat transmission of an incompressible magnetohydrodynamics micropolar fluid across a moving stretched surface in a Darcian permeable medium. The proper boundary conditions are used to facilitate the numerical solution (bvp4c) of the transformed governing equations. Graphical discussions have been made of the influence of the physical parameters on the velocity, angular velocity (microrotation), and temperature, and the distributions are accentuated on the plots via MATLAB. The study is validated by the previous work and it is found appropriate for investigation, where the absolute difference between the previous work and the present investigation by adopting the finite difference scheme is smaller than which implies that the scheme is stable and convergent. The microrotation has a great impact on the micropolar fluid with the influences of buoyancy forces, source, and suction over the stretching surface in a Darcian regime. With a rise in the heat source parameter, both velocity and microrotational profiles lessen, but the opposite is true for temperature. Eringen number () rises with the flow velocity, whereas temperature and microrotational profiles show the reverse relationship. The current study focused on particular applications in non-Newtonian fluid mechanics, polymer flows in filtration systems and metallurgical procedures that included cooling unbroken strips or filaments via a static fluid.     

Thermal properties and stability of n‐octadecane based composites containing multiwalled carbon nanotubes

In this study, multiwalled carbon nanotubes (MWNT) were added to n‐octadecane at weight percentages of 1.25, 2.5, 5, 10 and changes of thermal properties of n‐octadecane were analyzed. Structural characterization of the materials was carried out by transmission electron microscope (TEM) and optical microscope. Thermal properties of n‐octadecane and its composites were evaluated through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The thermal measurements show that the highest contribution to latent heat absorbing capacity with 18% was provided by the addition of 1.25% MWNT to n‐octadecane. The thermal properties and the thermal stability of pure n‐octadecane and its composites with MWNT were also investigated by subjecting the samples to 1440 melting‐cooling cycles. The sample with 1.25% MWNT content also showed the best thermal stability. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers