Girish M. Joshi

Electrical characterization of polymer composite gel under biasing as polar medium

Polyvinyl alcohol (PVA) composed with polymethyl methacrylate (PMMA) polymer hydrogel was prepared by using boric acid as a cross-linking agent. The semicrystalline phase of composite gel was detected by X-ray diffraction tool. The occupied polymer PMMA morphology exhibits cross-linked alignment shown by scanning electron microscopy (SEM). The two-polymer system demonstrates an excellent dielectric property (with values, ε = 590 for composite gel versus 400 compare to virgin PVA). The nonfluid media exhibit the impulse DC bias polarization. The basic principle of this work is to understand and control the electrical parameters under external stimuli (field) response by Impedance tool. In the biomedical field, this gel may be an excellent supporting media for sonographic as one of the best polar medium.

Effect of sodium alginate modification of graphene (by ‘anion-π’ type of interaction) on the mechanical and thermal properties of polyvinyl alcohol (PVA) nanocomposites

Layered aligned dispersion of graphene in graphene/polyvinyl alcohol (PVA) nanocomposites is prepared in the form of films through simple solution processing route. The results indicate that there exist an interfacial interaction between PVA and graphene because of hydrogen bonding. This is responsible for the change in structure of PVA (such as decrease in the level of crystallization) and exhibiting ductile PVA nanocomposite film with improved tensile modulus, tensile strength, and thermal stability. Moreover, to improve the mechanical properties of PVA nanocomposites, graphene is successfully modified using a non-covalent modifier, sodium alginate (SA) and there exist an ‘anion-π’ type of interaction in between SA and graphene. The modification results in finer dispersion of the graphene in PVA/SA-m-graphene nanocomposites. In addition, there exist a hydrogen bonding in between PVA and SA. This has resulted in the remarkable improvement in mechanical properties of PVA/SA-m-graphene nanocomposites as compared to pure PVA and PVA/graphene nanocomposites. The increase in mechanical properties of PVA/SA-m-graphene nanocomposites is achieved through better load transfer from graphene to polymer matrix, despite decrease in crystallinity of PVA. Improvement in tensile modulus and tensile strength is highest at 0.5 wt.% of SA-modified graphene in PVA/SA-m-graphene nanocomposites because of finer dispersion of graphene and is 62 and 40% higher than that of pure PVA. Addition of SA-modified graphene also improves the thermal stability of PVA/SA-m-graphene nanocomposites remarkably as compared to unmodified graphene PVA nanocomposites.

Polymer composites for thermal management: a review

Abstract The aim of this review article is to consolidate the important research works dedicated to polymers which are mainly used target material for heat transfer applications. The requirement of present day heat transfer equipment is compactness, lightweight, manufacturability, and lower cost. Materials like copper and aluminum though have better thermal conductivity but they are expensive and also heavy. Polymers are cheaper and easy to manufacture, recycle though they have sufficiently lower thermal conductivity compared to copper and aluminum. Polymer materials are thermally insulating material. It is too difficult to improve the amorphous nature of polymer material in order to achieve high thermal conductivity. One key path to increase the thermal conductivity of a polymer is to reinforce high thermal conductive fillers in the host matrix. In this review paper, an attempt is made to explore and summarize various key paths suggested by the researchers to develop high thermal conductive polymer composites.

Novel nanocomposites of graphene oxide reinforced poly (3,4-ethylenedioxythiophene)-block-poly (ethylene glycol) and polyvinylidene fluoride for embedded capacitor applications

The fabrication and characterization of nanocomposites consisting of graphene oxide (GO) reinforced poly(3,4-ethylenedioxythiophene)-block-poly (ethylene glycol) (PEDOT-block-PEG)/polyvinylidenefluoride (PVDF) were investigated. The characterization of the nanocomposites was carried out using UV-vis spectroscopy, X-ray diffraction (XRD), Differential Scanning Calorimetry (DSC), Thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) and FT-Raman spectroscopy. Dielectric properties were investigated using an impedance analyzer as a function of frequency (50 Hz to 35 MHz) and temperature in the range 40–150 °C. Atomic force microscopy (AFM) was employed to study the surface morphology of the nanocomposites. Atomic force microscopy reveals that the surface roughness increases as a function of GO loading. The presence of high surface area GO within the polymer matrix resulted in substantially improved thermal stability. Better dispersion resulted in an increase in the dielectric constant from 58.684 for 0.5 wt% to 266.091 for 3 wt% GO loading and dielectric loss from 1.758 for 0.5 wt% GO to 17.694 for 3 wt% GO. High values of dielectric constant are obtained with comparatively low dielectric loss. Hence, polymer nanocomposites with high dielectric constant and low dielectric loss have the potential to be used in the electronics and electric industry.

Modified PVA moiety with PbO as humidity sensor

Polyvinyl alcohol (PVA)-composed lead oxide (PbO) films were prepared by solution casting method. Proposed composite moiety reveals the presence of orthorhombic and monoclinic multiphase structural modification due to loading of PbO which was demonstrated by X-ray diffraction. The electronic transition due to oxide impurity decreases the transmission intensity and shift of wavelength confirmed by ultraviolet tool. The magnitude of dielectric polarization is directly proportional to the loaded PbO% and is based on the Debye model. The composite morphology demonstrates the presence of inorganic filler with a cross linked network of polymer PVA confirmed by AFM. The synthetic film loaded with PbO sensing for varying RH% with linearity (decreasing) in resistance may apply as humidity sensor.

Preparation of modified polymer blend and electrical performance

In this study, a modified binary polymer blend made up of polycarbonate and polystyrene blend has been prepared by loading of aluminum oxide (Al2O3) as a dopant. The role of alumina with polymer blend system was addressed in view of interfacing criteria. The filler concentration of modified blend was taken as 5, 10, and 15%. The morphological, thermal, and electrical properties were characterized by various techniques. Optical microscopy confirms the homogenous dispersion of Al2O3 in blend. The presence of alumina was detected by subatomic level using atomic force microscope (both two and three dimensional approach). The differential scanning calorimetric thermographs demonstrate decreasing softing point as function of alumina loading. The dielectric properties such as dielectric constant, loss, and electrical modulus were studied under DC bias. The effect of DC bias exhibits significant changes at low amount of Al2O3. The dielectric polarization supports Maxwell Wagner (MW) theory due to low frequency response. 15% Al2O3 gives the highest dielectric constant (ε′) value (3.5 × 105) at 10 Hz. The polymer modified blend with Al2O3 may be used as a one of the best dielectric medium.

Ultrasonic Force Microscopy on Poly(vinyl alcohol) / SrTiO3 Nano-Perovskites hybrid films

Atomic Force Microscopy (AFM) and Ultrasonic Force Microscopy (UFM) have been applied to the characterization of composite samples formed by SrTiO3 (STO) nanoparticles (NPs) and polyvinyl alcohol (PVA). The morphological features of the STO NPs were much better resolved using UFM than contact-mode AFM topography. For high STO concentrations the individual STO NPs formed nanoclusters, which gathered in microaggregates. The STO aggregates, covered by PVA, exhibited no AFM frictional contrast, but were clearly distinguished from the PVA matrix using UFM. Similar aggregation was observed for NPs in the composite samples and for NPs deposited on top of a flat silicon substrate from milliQ water solution in the absence of polymer. In the hybrid films, most STO nanoparticles typically presented a lower UFM contrast than the PVA matrix, even though stiffer sample regions such as STO should give rise to a higher UFM contrast. STO NPs with intermediate contrast were characterized by an UFM halo of lower contrast at the PVA/STO interface. The results may be explained by considering that ultrasound is effectively damped on the nanometer scale at PVA/STO interfaces. According to our data, the nanoscale ultrasonic response at the PVA/STO interface plays a fundamental role in the UFM image contrast.

Preparation and Performance Characterization of Soft Polymer Composites as a Function of Single and Mixed Nano Entities

Soft polymer composite (SPC) was prepared by mixing a polyvinyl alcohol (PVA) host system with conducting carbon black (CCB) as a single nano entity (SNE) and CCB+Montmorillonite (MMT) clay as mixed nano entities (MNE). The modified crystalline phase to amorphous exhibits the impact of filler. The destroyed crystalline phases are also evident from XRD spectra where interplanar distance decreased. Addition of MNE resulted in inhibition of foreign bond formation and also prevented stretching and bending of substrate molecules, which were detected by Fourier Transform Infrared (FTIR) spectroscopy. The morphology of SPC was studied by optical and scanning electron microscopy (SEM). Improvement of glass transition temperature (Tg), Youngs modulus and AC conductivity was observed as a function of SNE and MNE loading.

Fabrication, performance and applications of integrated nanodielectric properties of materials – a review

Abstract The design and development of modern technological composites for the electrical and electronic applications are highly crucial. The minitualization, performance and durability of nanocomposites are achieved by integrating the nanodielectric properties of materials. In this review article, the entire upcoming trends in the domain of nanodielectric illustrated with important applications co-related to the various fabrication techniques of integrated nanodielectric composites are provided. The factors affecting the nanodielectric due to operating electric field and material interface which exhibit the high dielectric constant, low loss and moderate breakdown voltage. The complete sketch from concept, fabrication, factors co-related and applications of nanodielectric properties with the future scope are taken into consideration for further developments.

Electrical performance of lithium ion based polymer electrolyte with polyethylene glycol and polyvinyl alcohol network

ABSTRACT A solid polymer electrolyte based on lithium hydroxide (LiOH) added with polyethylene glycol and polyvinyl alcohol polymers was synthesized by solution casting. The structural variation with respect to loading wt% of LiOH reveals the semicrystalline property of polymer electrolyte. The differential scanning calorimetry data shows the onset of crystalline to amorphous transition, which occurs nearly to the melting peak, for higher salt content. The structural properties and cross-linking between polymer and salt were demonstrated by polarized optical microscopy. The polymer electrolytes were subjected to AC impedance analysis spectra for obtaining the ionic conductivity at different temperature. The charge carriers relax much faster for higher lithium salt concentration based polymer electrolyte and produces higher conductivity. The highest room temperature conductivity 2.63 × 10−5 S/cm is obtained for 8 wt% loading of lithium salt based polymer electrolyte, confirming their use in preparation of ion conducting devices. GRAPHICAL ABSTRACT