Microscopic theory is used to investigate surface-induced order in a model nematic subjected to an external orienting field. The wall-particle interaction tends to orient particles perpendicular to the surface. It is shown that if the wall is tilted at approximately 45 degrees to the field, the reorientational effects can be an order of magnitude larger than those observed for perpendicular or parallel orientations. The surprising observation is associated with the breaking of a particular bulk symmetry. A possible practical application of the tilted geometry is briefly discussed.

Microscopic theory is used to obtain effective interactions between colloidal particles in nematic fluids subjected to an external orienting field. It is shown that the field can dramatically change the effective intercolloidal interactions without altering the symmetry of the director configuration around a single particle. Our calculations suggest that a rich variety of colloidal structures can be promoted by varying the external field.

A fluid of uniaxial particles in a disorienting field is considered as a simple model of biaxial nematics. The model stability with respect to the spontaneous formation of a biaxial phase is investigated by means of the integral equation method. The orientational instability condition is obtained explicitly and turns into known results for the limiting cases of zero and of infinite fields. It is shown that the biaxiality induced by small fields can expand considerably the region of spontaneously ordered fluid and could be useful to obtain mesomorphic phases in nonmesogens. The effect of small disorienting fields is more pronounced in systems with short-range anisotropic interactions between particles.