A. K. Tomar

Optical and structural properties of poly(vinyl alcohol) films embedded with citrate-stabilized gold nanoparticles

Hydrosol of Au nanoparticles was prepared by citrate reduction of chloroauric acid. The synthesized nanoparticles were characterized through transmission electron microscopy (TEM) and UV–Visible spectroscopy. The prepared nanoparticles were almost spherical in shape with their mean diameter ~6 nm and possessed face-centred-cubic (fcc) structure. The absorption spectrum of the as-prepared nanoparticles shows the SPR peak at 530 nm in agreement with that predicted from calculations based on Mie theory. These nanoparticles were dispersed in poly(vinyl alcohol) (PVA) using the sol–gel method to prepare PVA–Au nanocomposite films with different concentrations of Au. Optical and structural properties of these nanocomposites were studied using UV–Visible spectroscopy, x-ray diffraction (XRD) and FTIR spectroscopy. The value of optical band gap deduced from the UV–Visible absorption spectroscopy is found to be reduced from 4.98 eV (for pure PVA) to 3.85 eV after embedding 0.074 wt% of Au nanoparticles. Further, the refractive index behaviour for pure PVA and PVA–Au nanocomposite films was studied through transmission and reflection behaviour. The induced structural changes, revealed through XRD and FTIR spectroscopy, are responsible for the observed changes in optical behaviour of PVA after embedding Au nanoparticles in it.

Tuning of refractive index of poly(vinyl alcohol): Effect of embedding Cu and Ag nanoparticles

In this article, we have reported the results of our measurements, related to the tuning of the refractive index of the poly(vinyl alcohol) (PVA) polymer on embedding Cu and Ag nanoparticles at different concentrations. The size distribution and dispersion behaviour of embedded nanoparticles within PVA have been studied through transmission electron microscopy. A systematic increase in refractive index of PVA on increasing the concentration of embedded nanoparticles has been observed. These results have been tried to be explained using Bhar and Pinto model based on the Lorimars theory for polymer composites. The values of refractive index of these nanocomposites have also been calculated using the Lorentz-Lorenz effective medium theory and found to be in close agreement with the experimental data. Nanoparticles embedded induced modifications in the structure of PVA have been revealed through FTIR spectroscopy.

Optical behaviour of swift heavy ions irradiated poly(vinyl alcohol) films

Polyvinyl alcohol films were irradiated to 90 MeV O 6+ and 150 MeV Si 14+ ions at fluence ranging from 1010 to 1012 ions/cm2. The observed changes in optical energy gap of this polymer have been investigated and results are tried to be explained in terms of energy transferred by the incident ions. It has been noticed that the value of optical energy gap decreases with increasing energy loss during the ion–polymer interaction process.

MODIFICATION IN OPTICAL AND ELECTRICAL PROPERTIES OF POLY(METHYL METHACRYLATE) ON BLENDING WITH POLYANILINE

The chemically synthesized Polyaniline (PAni) was characterized through UV-Visible spectroscopy. The appearance of intense peak due to polarons at around 830 nm in electronic absorption spectrum signifies its conducting nature. Characteristics of PMMA–PAni blends with different concentration (by wt) of as-synthesized PAni, prepared via solution casting method, were studied using SEM, UV-Visible spectroscopy and current–voltage (I–V) measurements. Reduction in optical band gap value of PMMA from 3.06 eV to 2.16 eV and about 7 orders of increase in conductivity were observed in PMMA–PAni blend (10% by wt of PAni). Further, investigations of I–V curves suggest the Ohmic conduction in lower voltage region and space-charge limited current (SCLC) as the dominating conduction mechanism at higher voltages (i.e., above 60 V), in both pure PMMA and blended films.

Study of Dielectric Behavior and Charge Conduction Mechanism of Poly(Vinyl Alcohol) (PVA)-Copper (Cu) and Gold (Au) Nanocomposites as a Bio-resorbable Material for Organic Electronics

Poly(vinyl alcohol) (PVA) embedded with varying concentrations of chemically synthesized copper (Cu) and gold (Au) nanoparticles (NPs) were prepared using ex situ sol–gel casting method. The addition of almost the same concentration of CuNPs in PVA improves the conducting properties, while that of AuNPs improves the dielectric nature of composite films. It has been found that addition of AuNPs up to ∼0.4 wt.% concentration enhaneces the capacitive nature due to the formation of small Coulomb tunneling knots as internal capacitors. The dielectric studies suggest the Maxwell–Wagner interfacial polarization as the dominant dielectric relaxation process, whereas the I–V characteristics indicate bulk limited Poole–Frenkel emission at high voltages as the dominant charge transport mechanism operating at room temperature in all specimens. These novel features lead to the conclusion that addition of a small quantity of metal nanoparticles can help tune the properties of PVA for desired applications in bio-compatible polymer-based organic electronic devices.

Synthesis and Characterization of Silver‐Poly(vinyl alcohol) Nanocomposites

Silver nanoparticles were synthesized by chemical reduction of silver salt in water with sodium borohydride as a reducing agent. The optical absorption spectrum shows the presence of characteristic SPR band peaking at ∼400 nm. The size of silver nanoparticles obtained through TEM measurements was found to be 9±2 nm. After embedding silver nanoparticles in PVA matrix, red shift in SPR band has been observed. The positions of SPR band of silver nanoparticles in aqueous medium and PVA matrix were reconstructed using Mie theory and found to be in good agreement with those obtained experimentally.

PVA-Ag nanocomposite: As glucose sensing material

Surface plasmon behavior of the silver nanoparticles embedded in PVA matrix has been analyzed. The progressive shift in SPR caused by the addition of increasing amount of glucose from 30 to 50 mg/dl has been investigated to monitor the sensing operation of this nanocomposite and tried to correlate with the refractive index behavior by calculating refractive index sensitivity (S). To understand the reason of shifting of SPR, interaction of glucose molecules with embedded silver nanoparticles has been studied through FTIR spectroscopy.

Photoluminescence and Refractive Index Behaviour of PMMA-PAni Blends

The optical properties of PMMA-PAni blends have been investigated. Increase in intensity of photoluminescence (PL) peak and decrease in refractive index have been observed with increase in the PAni concentration in PMMA-PAni blends prompting the utilization of such materials in various optical applications.

Thermal properties of PMMA doped with Polyaniline

PMMA‐PAni conducting blends have been prepared through solution blending of PMMA with different wt. % concentration of chemically synthesized PAni‐DBSA, taking chloroform as solvent. These blends were characterized through the UV‐Visible and TGA spectroscopy. UV‐Visible spectroscopic results show the interaction of PAni with PMMA. Further, as the concentration of PAni increases, the value of thermal activation energy of blended films increases, leading to the increased thermal stability of PMMA‐PAni blends with increasing concentration of PAni..