• B V R Tata

      Articles written in Pramana – Journal of Physics

    • Quasi-elastic laser light scattering study of polyacrylamide hydrogel immersed in water and salt solutions

      M Sivanantham B V R Tata

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      Polyacrylamide (PAAm) hydrogels immersed in water and aqueous NaCl solutions were investigated for their structure and dynamics using static and quasi-elastic laser light scattering (QELS) techniques. Ensemble-averaged electric field correlation function $f (q, t)$ obtained from the non-ergodic analysis of intensity-autocorrelation function for PAAm gel immersed in water and in 5 M NaCl showed an exponential decay to a plateau with an initial decay followed by saturation at long times. The value of the plateau was found to depend on NaCl concentration and was higher than that of water. Collective diffusion coefficient, 𝐷, of the polymer network of the hydrogel immersed in water and in different concentrations of NaCl was determined by analysing $f (q, t)$. The measured diffusion coefficient showed linear decrease with increase in concentration of NaCl. The characteristic network parameters were obtained by analyzing $f (q, t)$ with harmonically bound Brownian particle model and from static light scattering studies.

    • A confocal laser scanning microscopic study on thermoresponsive binary microgel dispersions incorporated with CdTe quantum dots

      J Brijitta B V R Tata K Saravanan B K Panigrahi T Kaliyappan

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      Monodisperse poly(N -isopropylacrylamide) (PNIPAM) particles loaded with cadmium telluride (CdTe) quantum dots (QDs) of two different sizes (4.7 nm and 5.6 nm) were synthesized in aqueous medium by bonding the capping agent on the quantum dots to the amide groups of PNIPAM and incubating the samples at 45° C. A huge increase in the photoluminescence (PL) intensity (green and red regions) is observed for the PNIPAM–CdTe QDs composites compared to the parent CdTe QDs. We report here for the first time the imaging of binary dispersion of green and red luminescent PNIPAM–CdTe QDs composites using a fluorescence confocal laser scanning microscope. These composites have potential applications both in material science and biology.

    • Swelling/deswelling of polyacrylamide gels in aqueous NaCl solution: Light scattering and macroscopic swelling study

      M Sivanantham B V R Tata

      More Details Abstract Fulltext PDF

      Swelling kinetics of water-swollen polyacrylamide (PAAm) hydrogels (WSG) was investigated in various concentrations of aqueous NaCl by macroscopic swelling measurements. For lower concentration of NaCl, WSG showed exponential swelling whereas at higher concentration of NaCl it underwent deswelling at short times and exponential swelling at long times. From these studies, collective diffusion coefficient, 𝐷, of the polymer network and polymer–solvent interaction parameter, 𝜒 , were calculated and found to decrease with increase in [NaCl]. Collective diffusion coefficients measured from dynamic light scattering (DLS) and that obtained from macroscopic swelling measurements are found to agree well. Measured ensemble-averaged dynamic structure factor $f (q, t)$ for WSG and salt-swollen gels (SSG) showed an initial decay followed by a plateau at long times and it can be described by harmonically bound Brownian particle (HBBP) model. Enhanced scattering intensity at low scattering angles using static light scattering (SLS) measurements revealed the presence of inhomogeneities in PAAm gels. The reasons for increased scattering intensity of SSG over WSG gel and the linear decrease of 𝐷 with increase in NaCl concentration are explained.

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