(507h) The State of Confined Fluids: Liquid, Solid or Glass

When a fluid is confined to nanoscopic dimensions the structure and dynamics are considerably altered. Using grand ensemble simulations on simple non-polar molecules confined between surfaces that make up a slit-shaped pore, we map out the variety of phases that exist upon confinement. The state of the fluid is both a function of the fluid-wall interactions and the thermodynamic conditions of the bulk fluid that is in equilibrium with the pore. Specifically for the octamethyltetracyclohexane(OMCTS)-mica system we illustrate that the confined fluid can freeze giving rise to triangular, square and buckled and phases reminiscent of the phases observed in confined colloids. We also illustrate that under certain conditions fluids confined in slit pores exhibits relaxation dynamics that are glass-like as characterized by a two step relaxation in the self intermediate scattering function. The relaxation dynamics appear to follow the scalings predicted by mode coupling theory for bulk systems. The findings are important in interpreting data from surface force and atomic force microscopy experiments where forces betweeen molecularly confined fluids