Although in the real world, most of the liquids are made of non-spherical molecules, and most of the probes used are also non-spherical, only a limited number of theoretical studies exist on the dynamic effects of molecular shapes. Both rotational and translational motion of molecules could depend critically on shape. Furthermore, the coupling between the translational and rotational diffusion of these non-spherical molecules possesses considerable interdisciplinary interests due to its importance in physical (liquid crystals), chemical (micelles), and biological (lipids, proteins, DNA) systems. We introduce a new model system of molecular liquid, which consists of a binary mixture of prolates and oblates (80:20 mixture) interacting through modified Gay-Berne potential. The system is found to exhibit a pressure-induced glass transition that is reflected both in thermodynamic and dynamic properties. We address the validity of the hydrodynamic predictions in the translational-rotational coupling of ellipsoidal molecules. The density relaxation function is well described by the Williams-Watts stretched exponential function, f_s(q,t) = exp(- (t/τ)^β), where the exponent beta is found to exhibit a sharp fall as the relaxation time starts to increase as the glass transition conditions are approached. The distribution of instantaneous diffusion coefficient and rotational relaxation times suggest the presence of a mosaic-like structure in the deeply supercooled liquid phase.

(a) Snapshot of the system consisting of prolate and oblate binary mixture, (b) representation of a pair of ellipsoids interacting via the Gay-Berne potential, and (c) distribution of instantaneous diffusion coefficient at four different temperatures suggesting the presence of mosaic-like structure in the deeply supercooled liquid phase.

Sarmistha Sarkar

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