DIRECT MEASUREMENT OF THE INTERACTION BETWEEN 2 ORDERING SURFACES CONFINING A PRESMECTIC FILM

With a surface forces apparatus, we have investigated the isotropic and the nematic phases of a lyotropic solution near its lamellar phase. A smectic ordering shows up near walls, giving a specific oscillatory force profile which is shown to be the sum of two contributions. The symmetric distribution of the smectic order between the walls leads to an attractive background upon which oscillations arising from the elastic response of the layers are superimposed. In the isotropic phase, the oscillatory force is preceded by an attractive regime. We ascribe the attraction to a deeper penetration of the orientational ordering compared to the positional ordering range. © 1994 The American Physical Society.