Molecular Dynamics Investigation of the Impact of Methylation on the Nematic Phase of Phenyl Benzoate Mesogens and Dimers

Abstract

Liquid crystals (LCs) possess anisotropic mechanical and optical properties with applications ranging from soft robotics to display technology. Despite advances in the precise synthesis of liquid crystalline materials, the microscopic origins of substituent effects, which impact functional performance, are not always well understood. Here, we use molecular dynamics (MD) simulations to investigate how methyl substitution affects the nematic-phase behavior of liquid crystal monomers and dimers composed of phenyl benzoate cores flanked by aliphatic tails. Methylation induces a decrease in the nematic-isotropic transition temperature. Using data-driven analysis, we find that for monomers this decrease is associated with an increase in flexibility of core-adjacent aliphatic torsions that influence overall mesogen conformation. For dimers, this manifests as a shift from a continuum of accessible conformations in the isotropic phase to occupying more distinct hairpin and extended states in the nematic phase. The latter exhibits a bend angle consistent with experimental signatures of a modulated nematic phase. Together, these results show how minor changes in chemical structure can impact the conformational ensemble of liquid crystals, trading local conformational entropy for global nematic order, in turn influencing their macroscopic transition temperatures.