Shantanu Bhowmik

Surface modification of high density polyethylene and polypropylene by DC glow discharge and adhesive bonding to steel

Abstraet-The surface modification of high density polyethylene (HDPE) and polypropylene (PP) has been carried out by exposure to a DC glow discharge in air at different power levels of 5.28, 11, and 13 W. The surface energies of polymers exposed to glow discharge were estimated by measuring the contact angles of two test liquids: de-ionized water and formamide, whose surface energy components are known. Both the polar and the dispersion components of the surface energy increased rapidly at short exposure times but the increase of the polar component was relatively more than that of the dispersion component. At low power levels of 5.28 and 11 W, the polar component of the surface energy reached a maximum plateau depending on the exposure time, but at a 13 W power level the polar component of the surface energy decreased from a maximum value to a saturation level. For PP, this saturation level could not be attained in this study. The maximum total surface energy measured in this study corresponds to the max...

Thermoelectric power in carbon nanotubes and quantum wires of nonlinear optical, optoelectronic, and related materials under strong magnetic field: Simplified theory and relative comparison

We study thermoelectric power under strong magnetic field (TPM) in carbon nanotubes (CNTs) and quantum wires (QWs) of nonlinear optical, optoelectronic, and related materials. The corresponding results for QWs of III-V, ternary, and quaternary compounds form a special case of our generalized analysis. The TPM has also been investigated in QWs of II-VI, IV-VI, stressed materials, n-GaP, p-PtSb2, n-GaSb, and bismuth on the basis of the appropriate carrier dispersion laws in the respective cases. It has been found, taking QWs of n-CdGeAs2, n-Cd3As2, n-InAs, n-InSb, n-GaAs, n-Hg1?xCdxTe, n-In1?xGaxAsyP1?y lattice-matched to InP, p-CdS, n-PbTe, n-PbSnTe, n-Pb1?xSnxSe, stressed n-InSb, n-GaP, p-PtSb2, n-GaSb, and bismuth as examples, that the respective TPM in the QWs of the aforementioned materials exhibits increasing quantum steps with the decreasing electron statistics with different numerical values, and the nature of the variations are totally band-structure-dependent. In CNTs, the TPM exhibits periodic oscillations with decreasing amplitudes for increasing electron statistics, and its nature is radically different as compared with the corresponding TPM of QWs since they depend exclusively on the respective band structures emphasizing the different signatures of the two entirely different one-dimensional nanostructured systems in various cases. The well-known expression of the TPM for wide gap materials has been obtained as a special case under certain limiting conditions, and this compatibility is an indirect test for our generalized formalism. In addition, we have suggested the experimental methods of determining the Einstein relation for the diffusivity-mobility ratio and the carrier contribution to the elastic constants for materials having arbitrary dispersion laws.

Physicochemical and Adhesion Characteristics of High-Density Polyethylene when Treated in a Low-Pressure Plasma under Different Electrodes

ABSTRACT The present investigation studys the effects of different electrodes such as copper, nickel, and stainless steel under low-pressure plasma on physicochemical and adhesion characteristics of high-density polyethylene (HDPE). To estimate the extent of surface modification, the surface energies of the polymer surfaces exposed to low-pressure plasmas have been determined by measuring contact angles using two standard test liquids of known surface energies. It is observed that the surface energy and its polar component increase with increasing exposure time, attain a maximum, and then decrease. The increase in surface energy and its polar component is relatively more important when the polymer is exposed under a stainless-steel electrode followed by a nickel and then a copper electrode. The dispersion component of surface energy remains almost unaffected. The surfaces have also been studied by optical microscopy and electron spectroscopy for chemical analysis (ESCA). It is observed that when the HDPE is exposed under these electrodes, single crystals of shish kebab structure form, and the extent of formation of crystals is higher under a stainless-steel electrode followed by nickel and then copper electrodes. Exposure of the polymer under low-pressure plasma has essentially incorporated oxygen functionalities on the polymer surface as detected by ESCA. Furthermore the ESCA studies strongly emphasize that higher incorporation of oxygen functionalities are obtained when the polymer is exposed to low-pressure plasma under a stainless-steel electrode followed by nickel and then copper electrodes. These oxygen functionalities have been transformed into various polar functional groups, which have been attributed to increases in the polar component of surface energy as well as the total surface energy of the polymer. Therefore, the maximum increase in surface energy results in stronger adhesion of the polymer when the polymer is exposed under a stainless-steel electrode rather than nickel and copper electrodes.

Influence of chemically and plasma-functionalized carbon nanotubes on high-performance polymeric nanocomposites

This investigation highlights different surface functionalization processes of multi-walled carbon nanotubes (MWCNTs) and their effects on mechanical properties of polyetherimide nanocomposite. Surfaces of MWCNTs were modified by chemical process and by low-pressure plasma process. There is a significant change in physicochemical characteristics of MWCNTs after chemical and low plasma treatment evident from scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy studies. Due to surface modification of CNTs, there is a significant change in surface morphology and increase in oxygen functionalities such as C=O, C–O, and COOH especially evident in low-pressure plasma treatment; however, differential scanning calorimeter and thermogravimetric analysis studies reveal that thermal properties of the composite do not alter as such. There is a significant increase in mechanical properties of high-performance polymeric nanocomposites when surface-functionalized MWCNTs are dispersed in polymeric matrix; however, surface characteristics of the composite remain almost unchanged evident from contact angle and surface energy studies.

Plasma nitriding on titanium surface for adhesion promotion

Abstract This investigation highlights the influence of plasma nitriding on titanium surface in order to improve its interfacial adhesion strength with epoxy and epoxy nanocomposites adhesive. Surface energy of titanium increases considerably due to plasma nitriding implantation. X-ray photoelectron spectroscopy studies indicate the formation of various titanium nitrides, which are responsible for the increase in surface polarity. A reduction in equilibrium contact angle improve wetting on the surface and proper intimacy of the adhesive layer with two joining titanium surfaces. The atomic force microscopic study indicates smoothening of treated titanium surface. Thus, a greater surface area of contact with the adhesive layer helps uniform splitting of adhesive over the two titanium surfaces. A further improvement in bond strength is achieved on incorporation of 5% nanosilicate as reinforcement within the adhesive.

Physico-chemical characteristics of high performance polymer modified by low and atmospheric pressure plasma

In this work, the effect of low pressure plasma and atmospheric-pressure plasma treatment on surface properties and adhesion characteristics of high performance polymer, Polyether Ether Ketone (PEEK) are investigated in terms of Fourier Transform Infrared Spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Atomic Force Microscopy (AFM). The experimental results show that the PEEK surface treated by atmospheric pressure plasma lead to an increase in the polar component of the surface energy, resulting in improving the adhesion characteristics of the PEEK/Epoxy adhesive system. Also, the roughness of the treated surfaces is largely increased as confirmed by AFM observation. These results can be explained by the fact that the atmospheric pressure plasma treatment of PEEK surface yields several oxygen functionalities on hydrophobic surface, which play an important role in increasing the surface polarity, wettability, and the adhesion characteristics of the PEEK/Epoxy adhesive system.

Titanium nitride deposition on aluminium for adhesion promotion

This investigation highlights the adhesion characteristics of unmodified and titanium nitride deposited aluminium. Due to titanium nitride deposition on aluminium, surface energy, especially the polar component of surface energy of aluminium, increases considerably. There is a significant change in physicochemical characteristics due to titanium nitride deposition on aluminium observed under atomic force microscopy and X-ray photoelectron spectroscopy analysis. Lap shear tensile test results reveal that due to titanium nitride deposition on aluminium, the adhesive joint strength of aluminium to aluminium increases considerably and increases further if silicate nanoparticulates are dispersed into the epoxy adhesive. Dispersion of silicate nanoparticles into the silicon adhesive deteriorates the adhesive bond strength. Failure mode of adhesive bonding of unmodified aluminium is primarily interfacial and changes to cohesive due to the titanium nitride deposition on aluminium.

Processing and Characterization of Space-Durable High-Performance Polymeric Nanocomposite

In this investigation, efforts were given to develop carbon-nanofiber-reinforced polybenzimidazol nanocomposite for space application. Processing of polybenzimidazol was carried out by using polybenzimidazol in powder and solution forms. Thermomechanical properties of compression-molded polybenzimidazol, unfilled polybenzimidazol films, and nanofiber-reinforced polybenzimidazol films were investigated using thermogravimetric analysis, dynamic mechanical analysis, and tensile testing. Thermogravimetric analysis revealed that both compression-molded polybenzimidazol and polybenzimidazol films show high thermal stability. Dynamic mechanical analysis studies depicted that both compression-molded polybenzimidazol and polybenzimidazol neat films exhibited a high storage modulus, even at a temperature of 250°C. Polybenzimidazol nanocomposite films were cast with different loadings of carbon nanofibers from 0.5 to 2 wt % in polymer solution. Addition of carbon nanofibers improved the thermal stability and storage modulus of polybenzimidazol film. Mechanical testing showed that both compression-molded polybenzimidazol and polybenzimidazol films resulted in the highest ultimate tensile strength in comparison to any unfilled polymer. Investigation under scanning electron microscopy confirmed uniform dispersion of carbon nanofibers in polymer solution. Analysis of fractured surfaces revealed that neat polybenzimidazol film exhibited ductile failure and dispersion of carbon nanofibers into the polybenzimidazol, resulting in transformation from ductile to brittle failure.

The Einstein relation in quantum wires of III-V, ternary, and quaternary materials in the presence of light waves: Simplified theory, relative comparison, and suggestion for experimental determination

We study the Einstein relation for the diffusivity to mobility ratio (DMR) in quantum wires (QWs) of III-V, ternary, and quaternary materials in the presence of light waves, whose unperturbed energy band structures are defined by the three band model of Kane. It has been found, taking n-InAs, n-InSb, n-Hg1?xCdxTe, n-In1?xGaxAsyP1?y lattice matched to InP as examples, that the respective DMRs exhibit decreasing quantum step dependence with the increasing film thickness, decreasing electron statistics, increasing light intensity and wavelength, with different numerical values. The nature of the variations is totally band structure dependent and is influenced by the presence of the different energy band constants. The strong dependence of the DMR on both the light intensity and the wavelength reflects the direct signature of the light waves which is in contrast as compared to the corresponding QWs of the said materials in the absence of photoexcitation. The classical equation of the DMR in the absence of any field has been obtained as a special case of the present analysis under certain limiting conditions and this is the indirect test of the generalized formalism. We have suggested an experimental method of determining the DMR in QWs of degenerate materials having arbitrary dispersion laws and our results find six applications in the field of quantum effect devices.

Epoxy–novolac interpenetrating network adhesive for bonding of plasma-nitrided titanium

This investigation highlights rationale to synthesize epoxy–novolac adhesive by novel interpenetrating network (IPN) technique. Physicochemical characteristics of the plain adhesive and IPN adhesive were carried out by Fourier transform infrared spectroscopy and thermal gravimetric analysis. Performing lap-shear test carried out plasma-nitrided titanium was fabricated with these adhesives and mechanical property of these adhesives. The blend of epoxy and novolac was optimized at 4:1 ratio, and the formation of IPN was confirmed by the suppression of creep with reference to neat epoxy and its swelling behavior. The adhesive with IPN shows significantly higher thermal stability than epoxy and leaves higher amount of residuals at the elevated temperature. Due to surface modification of titanium by plasma nitriding, wetting characteristics of titanium increases considerably and consequently, there was a significant increase in lap-shear strength adhesively of bonded titanium substrate.