Anja Humpert: Molecular dynamics simulations of defects around nanoparticles in nematic liquid crystals
Molecular dynamics simulations of defects around nanoparticles in nematic liquid crystals
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. Žumer, 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.
