"Complex fluids at complex surfaces: simply complicated?" by Prof. Jose Manuel Romero

We study wetting and filling of patterned surfaces by a nematic liquid crystal. We focus on three important classes of periodic surfaces: saw-toothed, sinusoidal and stepwise, which have been considered in the literature as promising candidates to develop less-consuming zenithal bistable switches for practical applications. For saw-toothed substrates, geometry induces the nucleation of disclination lines on the wedges and apexes of the substrate, so  the nematic surface free energy density develops an elastic contribution which scales as qlnq (with q being the wavenumber associated with the substrate periodicity). This leads to a large departure from Wenzel's prediction for the wetting transition. For the sinusoidal substrate, the interplay of geometry, surface and elastic energies can lead to the suppression of either filling or wetting, which are observed for a same substrate only for a narrow range of roughness parameters. Finally, periodic stepwise surface displays re-entrant transitions, with a sequence dry-filled-wet-filled, in the relevant region of parameter space.

References:

[1]  P. Patricio, C.-T. Pham and J. M. Romero-Enrique, Eur. Phys. J. E 26, 97 (2008).
[2] J. M. Romero-Enrique, C.-T. Pham and P. Patricio, Phys. Rev. E 82, 011707 (2010)
[3] P. Patrício, J. M. Romero-Enrique, N. M. Silvestre; N. R. Bernardino and M.M. Telo da Gama, Molec. Phys. 109, 1067-1075 (2011)
[4] P. Patrício, N. M. Silvestre, C.-T. Pham and J. M. Romero-Enrique, accepted for publication in Phys. Rev. E (2011).