Electrostatic and Solvation Effects in Soft Matters
Akira Onuki
Department of Physics, Kyoto University

The electrostatic interaction has been extensively studied in electrolytes and many soft matters. However, not enough attention has yet been paid on the molecular interactions in charged fluid systems. Particularly, the ion-dipole interaction gives rise to the solvation shell around each charged particle, whose characteristic energy much exceeds the thermal energy k_BT. The resultant solvation interaction drastically affects phase transitions and structure formations, sometimes leading to mysterious effects. I will discuss such aspects in electrolytes, polyelectrolytes, ionic surfactants, colloids, and so on. In particular, some unique effects appear with addition of salt composed of hydrophilic and hydrophobic ions in mixtures of water+less polar component, where such ion pairs behave antagonistically in the presence of composition heterogeneities.

Bio:
Prof Akira Onuki received his PhD in Physics from University of Tokyo in Japan and later was assistant in Physics at Kyusyu University. Currently, he is a professor at Department of Physics of Kyoto University. He has been studying phase transition dynamics in various systems including fluids, solids, and superfluids. He wrote ”Phase Transition Dynamics” (Cambridge, 2002), which give precise mathematical explanations of various theories treating a broad range of physical systems. He has recently begun to work on the charge effects in soft matters combined with the solvation effects. He is also working on two-phase hydrodynamics on the basis of the dynamic van der Waals theory presented by himself. Some predictions are being made on Marangoni effects in binary fluid mixtures.

Structural and Dynamical Heterogeneities in Two-Dimensional Melting
Hayato Shiba
Institute for Solid State Physics, University of Tokyo

The melting in two-dimensional systems is an old but still unsolved issue. Using molecular dynamics simulations, I will visualize structural and dynamical heterogeneities emerging in the hexatic phase intermediate between crystal and liquid. We find long-wavelength divergence of the structure factor S(k) and the dynamic density-correlation function S(k, t) in the hexatic phase. The latter gives infomation of cooperative dynamics of the free volume near the melting. Some of our results can be seen at arXiv:0808.1453.
If time will be allowed, I will also discuss dynamics of two component fluids by changing the size ratio and the temperature.

Surface Dynamic Switching in LCD Devices: A Study Based on Generalized Nematohydrodynamic Boundary Conditions
Angbo Fang
Department of Physics, The Hong Kong University of Science & Technology

The widely used nematic liquid crystal (NLC) displays consist of a liquid-crystal layer confined between two substrate surfaces. Most nematic displays rely mainly on voltage-induced reorientation of the average molecular direction (director) within the bulk of the NLC layer. The Ericksen-Leslie hydrodynamic theory is well established to describe NLC bulk dynamics. In this work we derive a set of coupled hydrodynamic boundary conditions to treat the NLC dynamics near NLC-solid interfaces. In our boundary conditions, translational flux (flow slippage) and rotational flux (surface director relaxation) are coupled according to the Onsager variational principle of least energy dissipation. The application of our boundary conditions to the truly bistable $\pi$-twist NLC cell reveals the complete picture of its dynamic switching processes. It is found that the thus far overlooked translation-rotation dissipative coupling at solid surfaces can accelerate surface director relaxation and enhance the flow rate. This can be utilized to improve the performance of electro-optical nematic devices by lowering the required switching voltages and reducing the switching times.