Towards an equation of state for dense nematics with steric interactions

Wednesday, February 28, 2018 - 11:30am - 12:20pm
Lind 305
Peter Palffy-Muhoray (Kent State University)
There is emerging interest in using soft materials for energy conversion, particularly in the conversion of light and heat energy into mechanical work. Liquid crystals, where the coupling of orientational order and strain/stress may be employed for this purpose, are promising materials for such applications.
The celebrated work of Onsager [1] on hard particle systems, based on the truncated second order virial expansion, is valid at relatively low volume fractions and for large aspect ratio particles. While it predicts the isotropic-nematic phase transition, it fails to provide a realistic equation of state in that the pressure remains finite for arbitrarily high densities. In this talk, I will describe a mean field density functional form of the Helmholtz free energy for nematics with hard core repulsion. In addition to predicting the isotropic-nematic transition, the model provides a more realistic equation of state in that the pressure diverges at a critical density [2]. The energy landscape is much richer than in the low density approximation. The orientational probability distribution function in the nematic phase possesses a unique feature–it vanishes on a nonzero measure set in orientation space.
The equation of state gives information about pressure changes caused by changes in the order parameter, such as those that may be caused by light.

1. Onsager, L., The effects of shape on the interaction of colloidal particles. Annals of the New
York Academy of Sciences, 51(4), 627-659 (1949).
2. E. Nascimento et al.,. Density functional theory for dense nematic liquid crystals with steric interactions, Phys. Rev. E 96, 022704 (2017)