Diffusion in the lamellar phase of a rod-sphere mixture

摘要

Molecular dynamics computer simulations have been used to study translation diffusivity in thelamellar phase of a model rod-sphere mixture. This liquid-crystalline phase is characterized bylayers of rods, with the spheres preferentially located in the interlayer region. Notwithstanding theordered nature of this stratified phase, spheres have been seen to diffuse isotropically across thesample. Their mean square displacement does not manifest any subdiffusive behavior. The sameholds for the mean square displacement of rods in the direction perpendicular to the director. On thecontrary, the mean square displacement of rods parallel to the director exhibits, at intermediatetimes, a subdiffusive regime, albeit tenuous, caused by the layered nature of the lamellar phase.Rods nevertheless prefer to diffuse along rather than transverse to the director. The mechanism ofdiffusion is analogous to that previously observed in systems of pure rods in their smectic phase.The presence of spheres, chiefly positioned as they are in the interlayer region, is of aid to monitorthe central instants of the progression of a rod from one to an adjacent stratum. Time dependent pairpositional correlation functions have been calculated, which are consistent with a local temporarynematization concomitant to a rod passage.