We investigate the phase transition from an isotropic to a nematic liquid crystal embedded in a porous network. We model this situation by a simple lattice spin model with a field of finite strength $D$, but random orientation at a fraction $p$ of randomly selected lattice sites. Monte Carlo simulations show the existence of a nematic phase with quasi-long-range order for a large $D$. The isotropic $\to$ quasi-long-range nematic transition line has a tricritical point.

• Received 28 May 1997

DOI:https://doi.org/10.1103/PhysRevLett.81.385