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Thursday, September 20, 2012
2:00 PM - 3:00 PM
CNLS Conference Room (TA-3, Bldg 1690)

Postdoc Seminar

STATISTICAL MECHANICS OF NANOPARTICLE SUSPENSIONS AND GRANULAR MATERIALS

Lena Lopatina
T-1 and CNLS

In this talk we discuss topics united by the idea of using statistical mechanics to study systems in which the main component is an ensemble of particles. We study a distribution of particles either in an interacting ensemble by itself or in a host medium, and analyze connections between the internal properties of individual particles and the resulting macroscopic properties of the material with many particles. Recent experiments have reported that ferroelectric nanoparticles have drastic effects on nematic liquid crystals—increasing the isotropic-nematic transition temperature by about 5 K, and greatly increasing the sensitivity to applied electric fields. We modeled these effects through a Landau theory and Maier-Saupe-type model, based on coupled orientational order parameters for the liquid crystal and the nanoparticles. A Landau-like theory provides a simple approach to the statistical mechanics of the suspension, and a Maier-Saupe-type model gives more detailed predictions for full range of the parameters. Jamming has attracted growing attention as a possible unifying theme for granular materials, glasses and threshold behavior in materials. Recent results for frictionless granular systems suggest that jamming is a second order phase transition with critical properties. A question of paramount importance is whether this behavior is universal to more complex systems. To address this issue we have simulated the compression of granular polymers. The jamming density of the granular polymers decreases with increasing chain length due to formation of loops or voids, in agreement with recent experiments. We show that the nature of the jamming in granular polymer systems has pronounced differences from the jamming behavior observed for polydisperse two-dimensional disk systems. This result indicates that there is more than one type of jamming transition. Under shear, the behaviour of the system depends on its density: at low densities, the system unjams independently of boundary conditions, while at high densities, for a slip wall the system develops plug flow, and for a non-slip wall, after a finite time the system develops a fluctuating shear band.

Host: Kipton Barros, T-4 and CNLS