Exploring Liquid Crystal Properties through the Two-Phase Thermodynamic Model: Structural, Dynamic, and Thermodynamic Properties.

Abstract

This work provides a comprehensive analysis of the structural, dynamic, and thermodynamic properties of liquid crystals (LCs) along with their evolution through phase transitions and mesophases. A model of purely repulsive semiflexible spherocylinders is used in a molecular dynamics scheme through simulations involving NPT and NVT combinations. The two-phase thermodynamic model was used to obtain the translational, rotational, and vibrational density of states as well as the absolute values of thermodynamic parameters. We show evidence that during the isotropic-nematic-smectic-solid transitions, the translational diffusion coefficient becomes anisotropic, initially increasing by 15% in the nematic mesophase with a 129% rise along the director vector. Subsequent transitions result in a reduction of the diffusion coefficient by 42% in the smectic phase and 90% in the crystalline phase. Rotational diffusion decreases across all transitions (12, 35, and 26% for nematic, smectic, and solid transitions), although a notable increase in rotation around the principal axis is observed during the last transition. Thermodynamic analysis reveals that the primary contribution to the Gibbs free energy arises from the mechanical term (PV). With regard to the components, rotational motion is the dominant contribution to the Helmholtz free energy in the first transition, while translational motion dominates in the last transition. For the intermediate transition, translational, rotational, and vibrational contributions are comparable. A thorough analysis has been conducted into the Cartesian projections and the principal axes of rotation, in addition to the "solid and gas components" from the two-phase thermodynamic model analysis.