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I am a Post doctoral fellow in Surface Physics Division, Saha Institute of Nuclear Physics and currently working at Indian Beamline at Photon Factory, KEK, Japan for the installation and setting up various experimental facilities in the beamline. My research interest is mainly in the area of structure and dynamics of materials in the soft matter regime, like fatty acids, lipids and polymers. I started my research carrier during Ph.D to study the phase transitions in ultra thin organic films. These organic films were prepared using Langmuir Blodgett (LB) film growth technique. The LB deposition technique involves the vertical deposition on solid substrates through a monolayer of amphiphilic molecules at the air-water interface. The elusive role of molecular reorganization and the effect of hydrophilicity or hydrophobicity of the substrate in determining molecular orientation in the growth and structure of LB films have been investigated using x-ray and neutron reflectivity. The controlled method of building of super molecular assemblies with this technique also offers a systematic study of evolution of structure and phase transition as the system evolves from two to three dimensions. We observed the evolution of the sharp melting transition from the continuous two dimensional melting in LB films. This LB film growth technique also can be used to prepare a large stack of magnetically decoupled literally two-dimensional spin-membranes of magnetic ions. The conventional low temperature magnetometry and polarized neutron scattering measurements revealed the two-dimensional short range ferromagnetic order with no spontaneous magnetization as the field is applied along the normal to the growth direction of these multilayer stack. At sub Kelvin temperatures, the nature of growth of magnetic domains verifies the predictions of the spin-wave theory of 2D in-plane spin system with ferromagnetic interaction. During the post doctoral period in UC, San Diego, I started to work in the area of structure and dynamics of polymer melts, bio membranes, and nanoparticles in solution using small angle x-ray scattering (SAXS) and x-ray photon correlation spectroscopy (XPCS). We calculated the structure factor corresponding to the density fluctuations within the interior of the films by studying the diffuse x-ray scattering from polymer films of thickness of the order of polymer radius of gyration (Rg). The change in structure factor shows the fascinating effect of preferential stacking of the polymer chains parallel to the surface when the film thickness is of the order of Rg. XPCS is relatively new technique to study the slow dynamics (in the range of 30 ms – 1000 Sec) of the sample and we investigated the surface dynamics of polymer melts near the glass transition temperature. The change in dynamics of polymer chains in the melt from Rouse dynamics to the Reptation dynamics has been observed. Recently I started working on structure and dynamics of lipid membranes which are the major constituent in the outer boundaries of cells and organelles. This will provide important information on some biological functions such as switchable gateways, controlling the flow of nutrients into and metabolic wastes out of the cells and organelles.
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