Nematic model in the presence of a finite disorienting field: integral equation approach.

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.