Isotropic-Nematic Transition of Hard Ellipsoid Fluids

Abstract

We numerically study the thermodynamic properties of a hard ellipsoid fluid by mainly focusing on its phase transition from an isotropic phase into a nematic phase (i.e. isotropic—nematic phase transition). To improve the accuracy, precision, and efficiency of our computations, we attempt to employ the Wang—Landau NPT Monte Carlo algorithm in our simulations to calculate the function p(V) that gives the probability of arriving at the threshold density of the isotropic—nematic transition. Our results directly reveal that the nematic fluid phase, which is characterized by an ordered direction rather than an ordered configuration, appears and coexists with the isotropic phase when the aspect ratio α of the ellipsoid is located in a relatively narrow range of α = 2.0–2.25, and it becomes dominant and is fully established when α ≥ αcut = 2.25. We find that our estimated αcut is significantly lower than previously reported values of around 2.75. This prediction is further confirmed by the calculations of both the fluid reduced density and pressure of coexistence which show that the pressure grows up as the density increases and the probability function p(V) exhibits double peaks when the pressure enters the coexistence region. Based on these consistent results we are able to conclude that when α ≥ 2.25 an ellipsoid fluid can fully display the nematic behavior. This study will place a useful and tight theoretical constraint on investigations of the isotropic—nematic phase transition in the future.