Swelling and tilting in smectic layers

Smectic liquid crystals are quasi-solid materials, in that they possess mic rostructure both of the material and the local type (the nematic microstruc ture and the lamellae). In the standard approach, the rod-like molecules ar e supposed to be strictly normal to the layers; here we abandon this constr aint and admit the possibility for the molecules to change orientation with respect to the layers, paying in energy. As a consequence, we obtain two e quations: one expresses the balance of micromomentum, the other is Cauchy's equation. We derive also their form in the linear approximation and solve two typical problems. (C) 2001 Elsevier Science Ltd. All rights reserved.