Some smectic ordering often shows up, in an isotopic liquid, near a solid wall. When two such walls face each other at a distance D, and D is an exact multiple (nα) of the smectic period (α), the two walls should attract each other with an energy f0 = -Q exp(-D/ε), where is the smectic correlation length. But when D≠ na, an elastic contribution /e appears: the distortion is not uniform and is located preferentially in the weaker region near the midpoint. The contribution fe is oscillatory, but the average fe over the oscillations is strongly positive. Thus the overall coarse-grained interaction f0 = +Q exp(-D/ε) should be repulsive. In the present model, there are no metastable states: the transition from n - 1 to n layers does not require the nucleation of a dislocation loop. These presmectic forces might be of interest for colloid stabilization or for lubrication in extreme conditions. © 1990, American Chemical Society. All rights reserved.
