Nematic-smectic-A phase transition in porous media

We study the effects of both orientational and translational disorder on the nematic-smectic-A (NA) phase transition, using the Landau-de Gennes treatment. The only influence of random-field orientational disorder is to slightly increase the NA transition temperature, whereas the translational randomness has four important effects. (i) The NA transition temperature is decreased by the randomness. (ii) The bulk second-order NA phase transition is transformed into a first-order one. (iii) There is a small degree of translational order even in the high-temperature phase. (iv) The strict long-range smectic-A order is converted into a quasi-long-range order by any finite amount of disorder. (C) 2001 Elsevier Science B.V. All rights reserved.