Julia Yeomans OBE FRS

Abstract:

We present a lattice Boltzmann solution of the equations of motion describing the spreading of droplets on topologically patterned substrates. We apply it to model superhydrophobic behavior on surfaces covered by an array of micrometer-scale posts. We find that the patterning results in a substantial increase in contact angle, from 110 degrees to 156 degrees. The dynamics of the transition from drops suspended on top of the posts to drops collapsed in the grooves is described.

Abstract:

We present a lattice Boltzmann algorithm which can be used to explore the spreading of droplets on chemically and topologically patterned substrates. As an example we use the method to show that the final configuration of a drop on a substrate comprising hydrophobic and hydrophilic stripes can depend sensitively on the dynamical pathway by which the state is reached. We also consider a substrate covered with micron-scale posts and investigate how this can lead to superhydrophobic behaviour. Finally we model how a Namibian desert beetle collects water from the wind. © Indian Academy of Sciences.

Abstract:

We study the static properties of cubic blue phases by numerically minimizing the three-dimensional, Landau-de Gennes free energy for a cholesteric liquid crystal close to the isotropic-cholesteric phase transition. Thus we are able to refine the powerful but approximate, semianalytic frameworks that have been used previously. We obtain the equilibrium phase diagram and discuss it in relation to previous results. We find that the value of the chirality above which blue phases appear is shifted by 20% (toward experimentally more accessible regions) with respect to previous estimates. We also find that the region of stability of the O5 structure-which has not been observed experimentally-shrinks, while that of blue phase I ( O-8 ) increases thus giving the correct order of appearance of blue phases at small chirality. We also study the approach to equilibrium starting from the infinite chirality solutions and we find that in some cases the disclination network has to assemble during the equilibration. In these situations disclinations are formed via the merging of isolated aligned defects.