Surface Driven-Organization In Nematic Liquid Crystalline Nanodrops

The structure of nematic liquid crystals confined in a spherical nano-droplet is examined using a combination of many-body molecular dynamics simulations and a continuum molecular theory. Surface anchoring conditions, homeotropic or planar, are modified according to the local surfactant-to-water ratio at the droplet's surfaces. Phases and structure are studied as a function of temperature and total surfactant coverage. For the continuum theory an Euler-Lagrange approach is used, where the free energy functional of an order tensor parameter is minimized using a Ginzburg-Landau relaxation. In addition, a diffusion equation is solved at the surface for the surfactant-water ratio. A un-symmetric radial function approach is used for the numerical approximation. The molecular dynamics simulations rely on Gay-Berne type potentials to model liquid crystal and surfactant molecules. The confinement of nematic liquid crystals within nano-droplets creates remarkable bulk-to-surface self-organization, contrary to the regular surface-to-bulk self-organization. The nematic drives the formation of patterns and non-homogeneous regions at the droplet surface. This patterns appear as a response of the minimization of the liquid crystal free energy functional, which drives diffusion in a Nernst-Planck-like fashion. Theoretical predictions and molecular simulations are in quantitative agreement,thereby lending credibility to the predictions presented in this work.