Events in Physics

Modelling of topological defects entangled around nanoparticles of nematic liquid crystal colloids

We aim to study topological defects around nanoparticles in liquid crystals. Large-scale molecular dynamics simulations are used to obtain a better understanding of their molecular-level behaviour. Spherical nanoparticles of different sizes inserted into a nematic were simulated using the Gay-Berne (GB) potential [1]. Around the nanoparticles the liquid crystal molecules are frustrated. This is due to the competition between aligning along the main direction of the liquid crystal molecules, called the director, and the anchoring conditions at the nanoparticles surface. For homeotropic, normal, anchoring, Saturn ring defects were found [2], while for planar anchoring, Boojum defects were observed, which is in excellent agreement with Laundau-de Gennes theory (LdG) [3]. We are also investigating the Satellite defect, which is often found to be stable for large colloids.[4] This defect has a dipolar structure whereas the Saturn ring has a quadrupolar structure. Molecular simulations of pairs of colloids approaching each other were carried out. At small particle separations the defect loops around each colloid start to bend and at very close distances entangled defect structures were observed [5].

[1] J.G. Gay and B.J. Berne, J. Chem. Phys., 74, (1981) 3316.

[2] D. Andrienko, G. Germano and M.P. Allen, Phys. Rev. E, 63, (2001) 041701.

[3] M. Ravnik and S. Zumer, Liq. Crystals 36, (2009) 1201.

[4] P. Poulin and D.A. Weitz, Phys. Rev. E, 57, (1998) 625.

[5] V. Tomar, T.F. Roberts, N.L. Abbott, J.P. Hernández-Ortiz and J.J. de

Pablo, Langmuir, 28, (2012) 6124.