On the Defect Structure of Biaxial Nematic Droplets

C Chiccoli,R Teixeira De Souza,C Zannoni,L R Evangelista,P Pasini,G Skačej

doi:10.1038/s41598-018-20492-0

Abstract

We present a detailed Monte Carlo study of the effects of molecular biaxiality on the defect created at the centre of a nematic droplet with radial anchoring at the surface. We have studied a lattice model based on a dispersive potential for biaxial mesogens [Luckhurst et al., Mol. Phys. 30, 1345 (1975)] to investigate how increasing the biaxiality influences the molecular organisation inside the confined system. The results are compared with those obtained from a continuum theory approach. We find from both approaches that the defect core size increases by increasing the molecular biaxiality, hinting at a non universal behaviour previously not reported.

Highlights

It is well known that a sufficiently large nematic droplet embedded in a host matrix with perpendicular alignment at the interface presents a defect at the centre of the system[1]
This problem has been the object of a renewed interest[17,18], using molecular level, off-lattice, simulations[21], like in the work of de Pablo and his group[22,23], but the majority of the studies concerns uniaxial nematics formed of uniaxial particles, notwithstanding the fact that, even if biaxial nematics[24] are still rare, the majority of mesogens is not uniaxial and would be better represented by biaxial objects
We deal with a discretised version of the orientational biaxial potential of dispersive nature put forward many years ago by Luckhurst et al.[26], and whose phase diagram for bulk systems has already been studied in detail by some of us, with Monte Carlo computer simulations[27,28]

Summary

Introduction

It is well known that a sufficiently large nematic droplet embedded in a host matrix with perpendicular (homeotropic) alignment at the interface presents a defect at the centre of the system[1]. We deal with a discretised version of the orientational biaxial potential of dispersive nature put forward many years ago by Luckhurst et al.[26], and whose phase diagram for bulk systems has already been studied in detail by some of us, with Monte Carlo computer simulations[27,28]. This lattice model reproduces the rich phase diagram of a biaxial nematic system with isotropic, uniaxial, and biaxial phases, and it reduces to the well known Lebwohl-Lasher[29] uniaxial model for nematics when the molecular biaxiality vanishes. The model is a purely orientational one and the spins are assumed to be at the sites of a cubic lattice and to interact by means of the second rank attractive pair potential derived from dispersive interactions as described in detail in:

Objectives

Results

Conclusion