Spontaneous ordering of magnetic particles in liquid crystals: From chains to biaxial lamellae

TL;DR

This study uses Monte Carlo simulations to investigate how magnetic nanoparticles self-assemble within liquid crystals, revealing complex ordering behaviors including chain formation and biaxial lamellae, influenced by particle size and nematic order.

Contribution

It demonstrates the spontaneous formation of magnetic chains and biaxial lamellae in a hybrid liquid crystal system, highlighting the interplay between magnetic particles and liquid crystal ordering.

Findings

Magnetic chains form along the nematic director without an external field.

Increasing particle size leads to biaxial lamellar structures.

The magnetic and liquid crystal components mutually enhance each other's order.

Abstract

Using Monte Carlo (MC) computer simulations we explore the self-assembly and ordering behavior of a hybrid, soft magnetic system consisting of small magnetic nano-spheres in a liquid-crystalline (LC) matrix. Inspired by recent experiments with colloidal rod-matrices we focus on conditions where the sphere and rod diameters are comparable. Already in the absence of a magnetic field, the nematic ordering of the LC can stabilize formation of magnetic chains along the nematic or smectic director, yielding a state with local (yet no macroscopic) magnetic order. The chains, in turn, increase the overall nematic order, reflecting the complex interplay of the structure formation of the two components. Increasing the sphere diameter the spontaneous uniaxial ordering is replaced by biaxial lamellar morphologies characterized by alternating layers of rods and magnetic chains oriented perpendicular to the rod's director. These novel ordering scenarios at zero field suggest complex response of the resulting hybrid to external stimuli such as magnetic fields and shear forces.