As their name indicates, liquid crystals simultaneously exhibit some characteristics common to both ordinary isotropic liquids and solid crystals. This ambivalence is also found in the effects of surfaces on these systems which lead to a great diversity of phenomena. These phenomena are reviewed focusing on nematic liquid crystals which have the simplest structure among the many existing types and which have been the most extensively studied. Three main kinds of effects can be distinguished. The first concerns the perturbation of the liquid crystalline structure close to the surface. Beyond this transition region, the bulk liquid crystalline structure is recovered with an orientation which is fixed by the surface; this phenomenon of orientation of liquid crystals by surfaces is the so-called anchoring. Finally, close to bulk phase transitions, critical adsorption or wetting can occur at surfaces as is also seen in isotropic systems.

We consider the stability with respect to dewetting of thin films deposited on a substrate they thermodynamically wet. We show that if density fluctuations with a sufficiently large amplitude appear in a film, the resulting gradient of disjoining pressure in the film destibilizes the free surface eventually leading to the breaking up of the film in droplets. This dewetting mechanism is expected to play a role in films undergoing significant restructuring after deposition or for materials close to a critical point.

Thin polystyrene films were produced by spin coating from solutions in toluene. The amount of solvent retained in the films after drying for different times was measured using gas chromatography. Whereas for thicker films (thickness > 200 nm), the relative amount of solvent in the films is less than a few percent, the proportion of toluene increases significantly in thinner films. The thickness dependence of the mass of retained solvent shows that the solvent is mainly retained at the polymer-substrate interface. The solvent desorption rate exhibits no variation on the film thickness.