Computer simulations of wetting of solid surfaces by liquid crystals

Atomistic computer simulations are presented, consisting of droplets of model liquid crystal molecules wetting a generic crystalline surface. It is shown that the type of wetting that occurs is highly dependent on the value of the surface interaction parameter epsilon{fs} , switching between partial wetting (no spreading) for epsilon{fs}=2.0 to complete wetting for epsilon{fs}=2.5 . epsilon{fs} is the multiplicative factor which scales the well depth of the fluid-surface interaction energy. During complete wetting, the spreading occurs through the growth of a precursor layer, and a set of secondary terraces. The temperature affects the structure of the droplet, as might be expected when different phases are sampled, and also the shape of the spreading droplet, and the rate of spreading. In particular, in the smectic-A phase at 350K, for values of epsilon{fs} just large enough to induce complete wetting, the precursor film assumes a diamond shape, with edges normal to the [110] directions in the crystal surface. It is shown that spreading occurs through diffusion across the surface, with the radius of the precursor layer increasing with the square root of time. Mass flow studies indicate that the spreading occurs by molecules cascading over the top of the droplet to feed the growing precursor layer. Calculations of contact angle relaxation are in qualitative agreement with experimental findings.