Prof Ramin Golestanian

Abstract:

The dynamics of the deformations of a moving contact line was analyzed using two different dissipation mechanism. The contact lines relax to their equilibrium from a distorted configuration with a characteristic inverse decay time because of their anomalous elasticity. It is found that the velocity of the contact lines depends on the dissipation mechanism of the system.

Abstract:

The dynamics of the deformations of a moving contact line is studied assuming two different dissipation mechanisms. It is shown that the characteristic relaxation time for a deformation of wavelength 2pi/|k| of a contact line moving with velocity v is given as tau(-1)(k)=c(v)|k|. The velocity dependence of c(v) is shown to depend drastically on the dissipation mechanism: we find c(v)=c(v=0)-2v for the case in which the dynamics is governed by microscopic jumps of single molecules at the tip (Blake mechanism), and c(v) approximately c(v=0)-4v when viscous hydrodynamic losses inside the moving liquid wedge dominate (de Gennes mechanism). We thus suggest that the debated dominant dissipation mechanism can be experimentally determined using relaxation measurements similar to the Ondarcuhu-Veyssie experiment [T. Ondarcuhu and M. Veyssie, Nature 352, 418 (1991)].

Abstract:

The torque induced between bounding surfaces in nematic liquid crystals due to thermal fluctuations was reported. The existence of Casimir torque due to anisotropy in the shape of the objects immersed in the complex fluid depended on the relative orientation of these objects. The torques were calculated for a simple geometry in the absence of elastic effects. These calculations suggested a direct measure of the torque exerted between two plates at fixed separation and a measure of force as a function of separation for plates at various angles.

Abstract:

Fluctuation-induced interactions between anisotropic objects immersed in a nematic liquid crystal are shown to depend on the relative orientation of these objects. The resulting long-range "Casimir" torques are explicitly calculated for a simple geometry where elastic effects are absent. Our study generalizes previous discussions restricted to the case of isotropic walls, and leads to new proposals for experimental tests of Casimir forces and torques in nematics.

Abstract:

Equilibrium distribution of interacting ionic particles in a charged disordered background is studied using the nonlinear Poisson-Boltzmann equation. For an arbitrarily given realization of the disorder, an exact solution of the equation is obtained in one dimension using a mapping of the nonlinear Poisson-Boltzmann equation to a self-consistent Schrodinger equation. The resulting density profile shows that the ions are delocalized, despite what the equivalent Schrodinger formulation in one dimension would suggest. It is shown that the ions are not distributed so as to locally neutralize the background, presumably due to their mutual interactions.