Entangled liquid crystal colloids: knots and links

When?

Friday 12 November 2010, 14:00 to 15:00

Where?

30 BB 03 Physics Seminar Room

Open to:

Staff, Students

Speaker:

Dr Miha Ravnik, Department of Physics, University of Oxford

Liquid crystal colloids have dual nature, combining orientational ordering of liquid crystalline continuum phase and discrete ordering of the dispersed colloidal inclusions. Overlap of perturbations in liquid crystalline order produced by inclusions generates structural forces between the inclusions which allows for assembly of complex colloidal structures. Such effective elasticity of liquid crystals permits structuring of inclusions based on entanglement, hierarchical ordering, and self-assembly.

Here, assembly of entangled colloidal structures in confined nematic will be presented. The work applies numerical modelling based on minimization of phenomenological Landau-de Gennes free energy, which proves to give good qualitative agreement with experiments. In entangled colloidal structures, delocalized defect lines stabilize new topological objects and effectively behave as elastic belts. We found entangled defect configurations first in uniform nematic cells, yet true entangling of particles becomes possible in a non-homogeneous chiral configuration of the nematic. Beside simple loops, i.e. unknots and unlinks, we find also single and multiple defect loops which form knots and links. Both prime and composite knots/links are observed, such as trefoil knot and Hopf link. Controlled switching between knotted states is shown. Finally, entanglement of particles is generalized to 3D colloidal crystals.

Acknowledgement: This work is done together with U. Tkalec, S. Copar, S. Zumer, and I. Musevic.