Confinement of two-dimensional rods in slit pores and square cavities

TL;DR

This study uses Monte Carlo simulations to explore how two-dimensional rods behave under various confined geometries, revealing novel states and defect formations at different densities and confinements.

Contribution

It provides new insights into the complex ordering and defect structures of 2D rods in confined geometries, highlighting states with lower symmetry than bulk.

Findings

Unexpected low-symmetry states under extreme confinement

Disclination formation at intermediate densities

Domain walls with director rotation at high densities

Abstract

Using Monte Carlo simulation, we analyse the behaviour of two-dimensional hard rods in four different types of geometric confinement: (i) a slit pore where the particles are confined between two parallel walls with homeotropic anchoring; (ii) a hybrid slit pore formed by a planar and a homeotropic wall; square cavities that frustrate the orientational order by imposing either (iii) homeotropic or (iv) planar wall anchoring. We present results for the state diagram as a function of the packing fraction and the degree of confinement. Under extreme confinement, unexpected states appear with lower symmetries than those of the corresponding stable states in bulk, such as the formation of states that break the anchoring constraints or the symmetry imposed by the surfaces. In both types of square cavities the particles form disclinations at intermediate densities. At high densities, however, the elastic stress is relaxed via the formation of domain walls where the director rotates abruptly by ninety degrees.