Entropy-Driven Enhanced Self-Diffusion in Confined Reentrant Supernematics

Abstract

We present a molecular dynamics study of reentrant nematic phases using the Gay-Berne-Kihara model of a liquid crystal in nanoconfinement. At densities above those characteristic of smectic A phases, reentrant nematic phases form that are characterized by a large value of the nematic order parameter S≃1. Along the nematic director these "supernematic" phases exhibit a remarkably high self-diffusivity, which exceeds that for ordinary, lower-density nematic phases by an order of magnitude. Enhancement of self-diffusivity is attributed to a decrease of rotational configurational entropy in confinement. Recent developments in the pulsed field gradient NMR technique are shown to provide favorable conditions for an experimental confirmation of our simulations.

High-resolution dielectric study reveals pore-size-dependent orientational order of a discotic liquid crystal confined in tubular nanopores

“…Molecular dynamics simulations on rod-like systems have successfully contributed to a more detailed understanding of the isotropic-to-nematic transition in confinement [38,41,[64][65][66]. In fact, a recent molecular dynamics study documented radial movements of phase fronts analogous to the ones inferred here, however for a rod-like system in nanochannels [44].…”

“…However, similarly as the dynamical and structural behavior of rod-like liquid crystalline systems [34][35][36][37][38][39][40][41][42][43][44][45][46][47], the properties of DLCs has turned out to be particularly susceptible to nano confinement [27][28][29][30][31][32][48][49][50]. Thus, new, simple experimental methods that are able to monitor the type of molecular ordering inside nanoporous media are strongly demanded.…”

Diffusivity Maximum in a Reentrant Nematic Phase

“…Some of the present authors recently studied a model system of rod-like LC with molecular dynamics (MD) simulations [23,24]. We showed that as P is raised the usual sequence of phase transitions isotropic → nematic → smectic A is followed by a RN phase.…”

“…The RN phase exhibits a self-diffusion coefficient significantly larger than in the nematic phase. It was shown that the self-diffusion coefficient in the direction of the nematic director varies inversely proportional to the width of the distribution of molecular orientations or, in other words, the decrease in orientational entropy in the RN phase leads to an enhanced diffusivity [23]. …”

Adhesion of surfaces mediated by adsorbed particles: Monte Carlo simulations and a general relationship between adsorption isotherms and effective adhesion energies

“…In addition to these static effects, diffusion of liquid crystals in nanoconfinement is also quite unique. 29 We have focused here on planar surfaces. An interesting aspect of flexible surfaces such as lipid membranes is that they can wrap around adhesive particles.…”