DR.GIRISH JOSHI

... S. Mahboob Á G. Prasad Á GS Kumar (&) Materials Research Laboratory, Department of Physics, Osmania University, Hyderabad 500 007 Andhra Pradesh, India e-mail: gskumar1948@sify ... For all the sam-ples a change in slope was observed at different tempera-ture regions. ...

The present nano science domain focussed on sample preparation and inhibition of chemical reaction achieved by several techniques based on the principle of cavitation process using ultrasonic frequency-sonochemical routes. The effect of sonochemical routes is highly advantageous in reaction methods such as triggering reaction pathways, inducing the speedy reaction of inter-particle collision. In polymers, high intensity ultrasound waves are used for the polymerization of monomers by step growth process. This review is an outlook of sonochemical approach for polymer nanocomposites, which follows the physics of ultrasonic frequency bands, chemical reactions and the properties of acoustic cavitation highly applicable for the development of modern target materials. Introduction. The modern trend of material science follows various techniques to process the materials. Casting routes deals with various chemical and physical preparation processes which are suitable for building components with various applications. Sonochemical method is one of the most convenient and productive methods among various polymerization and polymer composite preparation techniques. It is achieved by applying high frequency ultrasound waves (20 kHz to 2 MHz) at the initial step [1]. The agitation of the solution due to the ultrasound irradiation produces cavitation. In this cavitation process, bubbles are formed and collapse routinely to evoke different types of chemical reactions. During the processing of polymer nanocomposites, in order to enhance the even dispersion of nanoparticles in the polymer matrix ultrasonic wave sonochemical method has been employed as a significant route [2]. This method is highly advantageous in the preparation of various fillers and polymer composites where fine dispersion of particles can be achieved [3, 4]. The interfacial region between the polymers and the fillers are tuned well with the help of ultrasound irradiation by varying the ultrasound frequency range from high to low. In the present investigation we have discussed various synthesized materials and their properties by sonochemical technique, physics and chemistry of sonochemistry, role of sonochemical route, advantages of sonochemical routes over bath sonication and its application in detail.

In view of engineering, the materials for industrial and domestic applications, optimization of barrier properties are considered as highly important. The barrier properties of polymers include low or high surface energy, relative contact angle (θ), surface roughness and work of adhesion. These parameters of a polymer surface can be tailored by applying plasma treatment without the loss in its bulk form. The effect of plasma treatment on the surface of polymers has been characterized by determining the variation in contact angle and the relative surface free energy. In this review, we consolidated the tunable surface properties of polymer composites and filler modified polymer blends with the help of different types of plasma treatment employed with varying magnitudes. Plasma treatment is highly effective to tailor the surface of polymer blends hence providing an open opportunity to the community of material science.

We have demonstrated the successful preparation of polyvinyl alcohol (PVA) composed CuBi2S3 polyionic (PI) composites. Polymer composites were sensitive to the external stimuli, the modified PVA moiety exhibits excellent electrical property as a function of temperature. The volume resistance measured by impedance analyzer (40 to 150 o C) under broadband frequency (50Hz-1MHz). The negative temperature coefficient (NTC) was observed in the temperature range of 40 to 150 o C. It offers the nonlinear resistivity, ρ= 10 5 (Ω-m) across pure PVA moiety. The influence of polycationic-ions crucial to obtain the gradual decrease of resistivity (ρ) up to 10 4 (Ω-m). The thermistor characteristics were disclosed as function of polyionic loading (wt %).

Carbon black (CCB)/Hydroxypropyl methylcellulose (HPMC) composites were useful for the sensor applications. Easily available Carbon black was preferred for the modification of polymer moieties. Due to an excellent coloring agent, printing inks, resin coloring, paint, and toners. Further, CCB is also used in various electrical conducting agent, antistatic film, fibers and floppy disk. In the present investigation we demonstrated the successful preparation of Hydroxypropyl methylcellulose with (CCB) composites. We have observed the linear phase relation as a function of temperature for the sample 1wt% loading of CCB. The linearity of phase measurement based on temperature is useful for various engineering applications.

The preparation of polyvinyl chloride (PVC)/cellulose acetate (CA) blends has been performed by solution casting. The structural, morphology, thermal, dielectric properties and softness have been tested as a function of the weight fraction of the CA. The decrease in inter-planar distance has been confirmed by X-ray diffraction (XRD) spectroscopy. The decrease in direct band gap has been influenced by CA composition demonstrated by ultraviolet-visible (UV) spectroscopy technique. Scanning electron microscopy (SEM) demonstrates the micro porous nature of blends. Thermo gravimetric analysis (TGA) confirms the increase in thermal stability of the miscible blends. The real dielectric polarization (r) has been measured as a function of frequency. The low dielectric loss tangent (tanδ) in PVC/CA blends has been observed based on the principle of restricted polarizibility. The shore 'A' durometer test enables to confirm the softness of miscible blends. Optimized low dielectric constant and softness properties would be suggested for various electrical and electronic engineering applications.

We have demonstrated the successful preparation of polyvinyl alcohol (PVA) composed CuBi2S3 polyionic (PI) composites. Polymer composites were sensitive to the external stimuli, the modified PVA moiety exhibits excellent electrical property as a function of temperature. The volume resistance measured by impedance analyzer (40 to 150 o C) under broadband frequency (50Hz-1MHz). The negative temperature coefficient (NTC) was observed in the temperature range of 40 to 150 o C. It offers the nonlinear resistivity, ρ= 10 5 (Ω-m) across pure PVA moiety. The influence of polycationic-ions crucial to obtain the gradual decrease of resistivity (ρ) up to 10 4 (Ω-m). The thermistor characteristics were disclosed as function of polyionic loading (wt %).

Polyvinyl alcohol (PVA)-composed lead oxide (PbO) films were prepared by solution casting method. Proposed composite moiety reveals the presence of ortho-rhombic 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.

Composites comprising Polycarbonate (PC) and CaCu 3 Ti 4 O 12 (CCTO) were fabricated via melt mixing followed by hot pressing by employing both micron (1-7µm) and Nano (75-100 nm) sized crystallites of CCTO. Both the micro and Nano CCTO powders were self-synthesized using solid state and co-precipitation routes respectively.These were characterized using X-ray Diffraction (XRD), Thermo Gravimetric (TGA), Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM),Impedance analyzer for their structural, morphology and dielectric properties. Nanocomposites inducted with nCCTO-50 wt% exhibited better thermal stability than that of pure PC and composite embedded with micron sized CCTO. However, there was no significant difference in the glass transition (T g) temperature between the polymer and the composites. The Nano composites (PC+nCCTO-50 wt%) exhibited 2.5times higher permittivity values as compared to that of composites having 50 vol% micron sized CCTO crystallites.

Graphene is under intense investigation as a high performance reinforcing nanofiller for the fabrication of polymer nanocomposites. The challenge is to achieve uniform dispersion of graphene nanosheets and tailor the polymer-graphene nanosheets interface. In this regard, the graphene nanosheetshave been modified using two different non-covalent modifiers, which are sodium dodecyl sulfate (SDS) and sodium alginate (SA). The effect ofthese non-covalent modificationsof graphenenanosheets on the mechanical, thermal and crystallization behavior of polyvinyl alcohol (PVA) nanocompositeshave been studied. The results indicate that the graphenenanosheets areexfoliatedin the PVA matrix, when the graphenenanosheets are modified using SDS and SA. SDS assisted dispersion of graphene nanosheetsdepicts the intercalated state of dispersion of graphenenanosheets in the PVA matrix. This has resulted in remarkable improvement in tensile modulus and tensile strength of PVA nanocomposites containing SDS and SA modified graphenenanosheets, as compared with pure PVA and PVA/SDS-m-graphene nanocomposites. The remarkable increase in mechanical properties is due to an efficient load transfer from PVA to graphenenanosheets, as well as hydrogen bonding between PVA and SA. However,a remarkable increase in the mechanical properties of PVA nanocompositesis achieved despite the decrease in the crystallinity of PVA, revealing the reinforcing efficiency of graphenenanosheets. In addition, the thermal stability of PVA nanocomposites also increases with theaddition of a small concentration of SDS and SA modified graphene.

In this work, polymer nanocomposites consisting of a poly(vinyl chloride) (PVC) and polyvinylidene fluoride (PVDF) polymer network with ZnO nanoparticles as a dopant were prepared by solution casting. An XRD study of the PVC/PVDF/ZnO polymer nanocomposites shows predominantly sharp and high intensity peaks. However, the intensity and sharpness of the XRD peaks decreases with further increment in loading of ZnO (wt%), which reveals a proper intercalation of ZnO nanoparticles within the PVC/PVDF polymer system. Fourier transform infrared spectroscopy has been used to verify the chemical compositional change as a function of ZnO nanoparticle loading. TGA analysis clearly describes the thermal degradation of the pure polymer and polymer nanocomposites. The complex dielectric function, AC electrical conductivity and impedance spectra of these nanocomposites were investigated over the frequency range from 10 Hz to 35 MHz. These spectra were studied with respect to the Wagner − Maxwell − Sillars phenomenon in the low frequency region. Nyquist plots of the PVC/PVDF/ZnO nanocomposites were established from impedance measurements. The temperature-dependent DC ionic conductivity obtained from the Nyquist plots follows Arrhenius behaviour.

We have successfully demonstrated the effect of
-irradiation on Polyacrylonitrile (PAN)
gel in terms of admittance (Y), Susceptance (B) and Conductance (G). The trend of Y and B
decreases by 297 μS and 138 μS respectively and conductance (G) increases by 100 μS. Electrical
mechanism associated with microstructure of PAN gel under external DC bias potential is the
novelty of this work. External field stimuli responded due to delocalization of charge carriers. These
properties are important as novel electronic material.

We demonstrated the synthesis and measurement of temperature dependent electrical resistivity of graphene
oxide (GO) reinforced poly (3, 4 - ethylenedioxythiophene) - tetramethacrylate (PEDOTTMA)/Polymethylmethacrylate
(PMMA) based nanocomposites. Negative temperature coefficient (NTC) was observed for 0.5, 1 % GO loading and the
positive temperature coefficient (PTC) was observed for 1.5 and 2 % Go loading in the temperature (40 to 120 0C). The GO
inducted nanocomposite perform as an excellent thermistor and suitable for electronic and sensor domain.

We prepared the Polyvinyl alcohol (PVA)/CdCl2 and PVA/Polyvinylpyrrolidone (PVP)/CdCl2 composites by solution blending known as the soft polymer ionic membrane (SPIM). The loading of CdCl2 divalent ions demonstrates an influence over the electronic structure was confirmed by UV analysis. The bright divalent ionic morphology observed by scanning electron microscopy (SEM). The optimization of specific capacitance (Cp) and the dielectric constant disclosed as a function of an external DC bias potential. The trend of polarization was inversely proportional to the DC bias with the PVA system and directly to the PVP system. We disclosed the dielectric constant as a function of ionic loading. The optimized dielectric constant for various applications.