Suman Mitra

Exfoliation of Nanolayer Assemblies for Improved Natural Rubber Properties: Methods and Theory

Natural rubber (NR)-based nanocomposites were prepared by conventional processing techniques using various natural and modified nanoclays. For modified montmorillonite (Cloisite® 15A), the 300% modulus, tensile, and tear strength exhibited substantial increments of over the gum due to better dispersion. The unmodified montmorillonite clay (Cloisite® Na+) failed to improve the above properties significantly. The limitations of Cloisite® Na+-based NR nanocomposites prepared by the conventional method were alleviated using latex blending technique. Pre-exfoliated aqueous suspension of Cloisite® Na+ was blended with NR latex under special conditions and cured by pre-vulcanization as well as conventional curing. These showed predominantly exfoliated morphology along with substantially improved physical and mechanical properties. A simple theory based on effective surface area factor was proposed to account for the structure—property correlations.

Influence of Nanogels on Mechanical, Dynamic Mechanical, and Thermal Properties of Elastomers

Use of sulfur crosslinked nanogels to improve various properties of virgin elastomers was investigated for the first time. Natural rubber (NR) and styrene butadiene rubber (SBR) nanogels were prepared by prevulcanization of the respective rubber lattices. These nanogels were characterized by dynamic light scattering, atomic force microscopy (AFM), solvent swelling, mechanical, and dynamic mechanical property measurements. Intermixing of gel and matrix at various ratios was carried out. Addition of NR gels greatly improved the green strength of SBR, whereas presence of SBR nanogels induced greater thermal stability in NR. For example, addition of 16 phr of NR gel increased the maximum tensile stress value of neat SBR by more than 48%. Noticeable increase in glass transition temperature of the gel filled systems was also observed. Morphology of these gel filled elastomers was studied by a combination of energy dispersive X-ray mapping, transmission electron microscopy, and AFM techniques. Particulate filler composite reinforcement models were used to understand the reinforcement mechanism of these nanogels.

Synthesis and Characterization of Chemically Crosslinked Styrene-Butadiene Rubber Nanogels and their Effect on Various Properties of the Rubber

Abstract Nano-sized styrene-butadiene rubber (SBR) latex gels were prepared by pre-vulcanizing SBR latex with different sulfur to accelerator ratios. These gels were characterized by swelling studies, dynamic light scattering, atomic force microscopy, mechanical and dynamic mechanical properties. With the increase in sulfur to accelerator ratio, the gels had higher amount of crosslink density and gel content. Particle size distribution did not alter much in the crosslinked gels. Incorporation of these nanogels into raw SBR led to the considerable drop in viscosity of the gel filled systems under capillary melt flow conditions. However, the reduction in viscosity was found to be dependent on the loading and crosslink density of the nanogels. Energy dispersive X-ray mapping of sulfur was used to check the dispersion of these gels into raw SBR matrix. The die swell values of gel filled SBR were much lower than that of the raw SBR. The reduction in principal normal stress difference values combined with the r...

Cellular automata based architecture of a database query processor

In large databases the objects form certain classes and all objects in a class possesses common attributes. The relational database for a such a set of classified objects requires a class-relation-identifying the class corresponding to each object, and an attribute-relation containing the attributes for each class. For efficient processing of the queries, multi-level indexing scheme is employed requiring large memory to store the index files. The access to the index files adds to the time overhead of query processing. In this paper, a Multiple Attractor Cellular Automata (MACA) based chip has been reported that stores the class-relation in an implicit manner, eliminating multi-level indexing altogether.

Effect of static charge on the tarnishing behaviour of silver in iodine atmosphere at low temperatures

The kinetics of Agl film growth on silver under the action of applied static charge of both the polarities, as well as under normal iodination conditions in the temperature range of 294 to 338 K and in the iodine partial pressure range of 0.03 to 0.22kPa, conform to parabolic rate law. Compared to normal iodination, an enhancement in rate under both positive and negative surface charge conditions at the Ag/Agl interface and a decrease in rate under either surface charge condition at the Agl/l2 interface have been observed. The increased rate with negative charge at the Ag/Agl interface and the decreased rate with same kind of charge at the Agl/l2 interface, compared to normal iodination, can be explained on the basis of positive hole transport, while the observed effects with positive charge at either of the interfaces receive reasonable support from cation migration as the rate limiting factor during the film growth process.