Investigations on Structural, Mechanical, and Dielectric Properties of PVDF/Ceramic Composites

Polymer ceramic composites are widely used for embedded capacitor application. In the present work PVDF has been used as a matrix and CCTO and LaCCTO have been used as reinforcement. Extrusion process has been used for the synthesis of composites. X-ray diffraction (XRD) patterns confirm the formation of single phase CCTO, and LaCCTO in its pure as well as composite state. It is found that La doping in CCTO considerably increases the dielectric constant and reduces the dielectric loss. A similar trend is observed in the composites with the increasing content of CCTO and LaCCTO

Influence of chain structure on the miscibility of poly(vinylidene fluoride) with poly(methyl acrylate)

The blending ability of poly(vinylidene fluoride) (PVF<SUB>2</SUB>) depends on the head-to-head (H-H) defect structure present in the chain. With increasing H-H defect content, the lower critical solution temperatures (LCST) of PVF<SUB>2</SUB>/PMA blends decrease. This has been explained from the polymer-polymer interaction parameter (χ<SUB>12</SUB>) values measured from the equilibrium melting point (T<SUP>o</SUP><SUB>m</SUB>) depression of the α phase of PVF<SUB>2</SUB>. A critical analysis on the method of measuring the equilibrium melting point from the Hoffman-Weeks plot has been done. For Hoffman-Weeks plots the T<SUB>m</SUB> (melting point) should be determined for the same and low level of crystallinity at each T<SUB>c</SUB> (crystallization temperature) to obtain correct results. If T<SUB>m</SUB> is counted for the same time of crystallization at each T<SUB>c</SUB>, erroneous results are obtained. Extrapolation of the T<SUB>m</SUB>-T<SUB>a</SUB> (T<SUB>a</SUB> = annealing temperature) plot to the T<SUB>m</SUB> = T<SUB>a</SUB> line also yields the correct T<SUP>0</SUP><SUB>m</SUB>. χ<SUB>12</SUB> values are determined with all these T<SUP>0</SUP><SUB>m</SUB>s, and it has been observed that the annealing method and the same crystallinity method yield almost same value of χ<SUB>12</SUB>, which can explain the LCST phase diagram of PVF<SUB>2</SUB> blends. Annealing results yield that PVF<SUB>2</SUB> up to 24 mol % H-H defect concentration would be miscible with PMA. χ<SUB>12</SUB> measured from T<SUB>m</SUB>s of the same time of crystallization and from the apparent melting points of PVF<SUB>2</SUB> blends yield incorrect results

Morphology of poly(vinylidene fluoride)/poly(methyl acrylate) blends: influence of chain structure

The morphology of blends of poly(vinylidene fluoride) (PVF2) fractions with poly(methyl acrylate) (PMA), studied by means of polarized light microscopy, exhibits a gradual change in morphology from spherulitic → dendritic → spherulitic both for increasing PMA concentration in the blend and for increasing crystallization temperature. Possible reasons for this change in morphology, viz. the ratio of diffusion constant and growth rate, are discussed. The influence of head to head (H-H) defects of PVF2 on the morphology of the blends is discussed on the basis of the polymer-polymer interaction parameter

Influence of chain structure on the crystallization mechanism of poly (vinylidene fluoride)/poly (methyl acrylate) blends: evidence of chain extension due to blending

The head to head (H-H) defect structure of poly(vinylidene fluoride) (PVF<SUB>2</SUB>) has a dramatic effect on the crystallization rate of PVF<SUB>2</SUB> and its blends. At a fixed temperature the crystallization rate decreases with increase in H-H defect and also with increase in the concentration of amorphous polymer, poly(methyl acrylate) (PMA), in the blend. But under the same degree of supercooling the crystallization rate of PVF<SUB>2</SUB> increases with increase in H-H defect concentration. The molecular mechanism of crystallization of PVF<SUB>2</SUB> is very much dependent on the H-H defect structure present in the chains. Analysis by the Lauritzen and Hoffman (L-H) equation of crystallization rate indicates a regime I-regime II break for lower defect content (3.75%) PVF<SUB>2</SUB> fraction and a regime II-regime III break for higher defect content (5% and 5.6%) PVF<SUB>2</SUB> fractions. However, analysis of the kinetic data of PVF<SUB>2</SUB> blends by the modified L-H equation indicates only the regime II → III break irrespective of the H-H defect present in the PVF<SUB>2</SUB> samples. The regime transition temperature is dependent on both the H-H defect concentration and also on the PMA concentration in the blend. The chain extension factor (α), calculated from the ratio of the lateral surface energy (σ) values of pure polymer and that of blends, have values greater than unity for almost all cases

Bio‐based polyurethane‐graphene composites for adhesive application

Abstract Natural oil‐based polyurethanes are prepared through solvent‐less and easily processable approach for adhesive applications. The polyurethane is optimized through varying the volume fractions of the precursors which was then confirmed through the different analyses to achieve the better combination for composite formation with graphene. The graphene‐polyurethane composites are processed in a simple hand mixing process with different graphene loadings and the role of the addition of graphene is studied using different analyses. The addition of graphene and the interaction with the polymer is well established through structural and thermal studies. The increase in the mechanical property with the addition of graphene to adequate amount at room temperature confirms better interfacial interaction with the polymer. The maximum peel strength obtained for the PU is around 1.05 N/mm, which supports the applicability of the prepared material for adhesive‐based applications

Antimitotic, apoptotic and antineoplastic potential of leaf extract of Eupatorium ayapana

Eupatorium ayapana of Asteraceae family was found to possess useful therapeutic properties like hypoglycaemic, antimicrobial, hematoprotective, hepatoprotective, and antioxidant activities. The present study was aimed to evaluate the antimitotic, cytotoxic and apoptotic potential of the ethanolic and water extracts of Eupatorium ayapana leaf on Ehrlich’s ascites carcinoma. Antimitotic study was done by using Allium cepa root tips model. In vitro cytotoxicity was determined by MTT assay, apoptosis was determined by fluorescence microscopy, and cell cycle progression was analysed using flow cytometry; in vivo antitumor activity was performed in Ehrlich’s ascites carcinoma bearing mice. Ethanolic and water extracts of Eupatorium ayapana leaf showed significant decrease in mitotic index. The IC50 value of ethanolic, and water extracts were 100.6 g/mL, 112.7 g/ml respectively in Ehrlich’s ascites carcinoma cells. Fluorescence microscopy analysis showed significant increase in apoptotic cell death which was further confirmed through the flow cytometry analysis, which showed that the ethanolic extract arrests the cells in G0/G1 phase of the cell cycle. The in vivo study illustrated significant increase in the survival time and reduction in the tumor induced angiogenesis in Ehrlich’s ascites carcinoma bearing mice after the treatment of the extracts. Of this work the ethanolic and water extracts of Eupatorium ayapana leaf reveal antimitotic, cytotoxic and apoptotic potential on the Ehrlich’s ascites carcinoma

On the gelation rates of thermoreversible poly(vinylidene fluoride) gels

The gelation rates of poly(vinylidene fluoride) (PVF2) gels have been measured for three commercial samples each in two different solvents at different polymer concentrations and also at different temperatures. The rate has been expressed as a combination of temperature-dependent function f(T) and concentration-dependent function (&#966;)n ; &#966; is the reduced overlapping concentration of the polymer chains. &#966; has a resemblance with the P - Pc term of percolation theory, P being the conversion factor and Pc its critical value. Exponent n has been measured from double logarithmic plots of tgel-1 and &#966;, and it lies between 0.45 and 0.6 which is closer to percolation exponent &#946; (0.45) of a three-dimensional lattice. This indicates that three-dimensional percolation is a suitable model for this thermoreversible gelation process. The temperature-dependent function of the gelation rate has been found to be analogous to the temperature-dependent function of the nucleation rate of crystalline polymers in dilute solutions. There is some dependency of the gelation rate on the amount of H-H defect (-CF2CF2-) structures present in the polymers and also on the molecular weight of the samples. Solvents also have a significant influence on the gelation rate of the polymer : the poorer the solvent, the faster is the gelation rate. The critical gelation concentration (Ct=&#945;&#8727; ) measured from gelation kinetics by an extrapolation procedure increases with temperature in each case. Thermodynamic analysis of the variation of Ct=&#945;&#8727; with temperature reveals that about three to six crystallites (depending on the solvent and sample) are involved to produce a single crosslink in the gel

Performance simulation of polymer-based nanoparticle and void dispersed photonic structures for radiative cooling

Abstract Passive radiative cooling is an emerging field and needs further development of material. Hence, the computational approach needs to establish for effective metamaterial design before fabrication. The finite difference time domain (FDTD) method is a promising numerical strategy to study electromagnetic interaction with the material. Here, we simulate using the FDTD method and report the behavior of various nanoparticles (SiO2, TiO2, Si3N4) and void dispersed polymers for the solar and thermal infrared spectrums. We propose the algorithm to simulate the surface emissive properties of various material nanostructures in both solar and thermal infrared spectrums, followed by cooling performance estimation. It is indeed found out that staggered and randomly distributed nanoparticle reflects efficiently in the solar radiation spectrum, become highly reflective for thin slab and emits efficiently in the atmospheric window (8–13 µm) over the parallel arrangement with slight variation. Higher slab thickness and concentration yield better reflectivity in the solar spectrum. SiO2-nanopores in a polymer, Si3N4 and TiO2 with/without voids in polymer efficiently achieve above 97% reflection in the solar spectrum and exhibits substrate independent radiative cooling properties. SiO2 and polymer combination alone is unable to reflect as desired in the solar spectrum and need a highly reflective substrate like silver