Defect curvature energy on nematic shells

Dr Andre Sonnet (University of Strathclyde)

Thursday 9th March, 2017 14:00-15:00 Maths 515

Abstract

(Lunch with the speaker will be at One A The Square, leaving from the school front foyer at 12.45.)

Nematic shells are colloidal particles coated with nematic liquid crystal molecules which may freely glide and rotate on the colloid's surface while keeping their long axis on the local tangent plane. As usual, defects are points where the order parameter is undefined. On such shells, defects may serve as hotspots where chemical bonds with other shells or functional molecules can be formed. We describe the nematic order on a shell by a unit director field on a closed orientable surface. Equilibrium fields can then be found by minimising the elastic energy, which is a function of a gradient of the director field. While it might seem natural to use the covariant director gradient, because the surface is embedded in three-dimensional space, the surface gradient is a better choice. We use our model to predict the equilibrium defect location on ellipsoids of revolution depending on their aspect ratio. We find good qualitative agreement with results obtained from molecular dynamics simulations.

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