J. Phys. II France
Volume 5, Numéro 1, January 1995
Page(s) 103 - 112
DOI: 10.1051/jp2:1995116
J. Phys. II France 5 (1995) 103-112

Measurement of the Interactions between Macroscopic Surfaces Inducing a First-Order Phase Transitions: the Sponge-Lamellar Transformation

D. A. Antelmi1, P. Kékicheff1 and P. Richetti2

1  Department of Applied Mathematics, Research School of Physical Sciences and Engineering, Australian National University, Canberra, A.C.T. 0200, Australia
2  C.R.P.P.-C.N.R.S., Château Brivazac, Avenue Schweitzer, 33600 Pessac, France

(Received 12 September 1994, accepted in final form 2 November 1994)

The interactions between two macroscopic walls immersed in an isotropic symmetric sponge phase (L 3) at different volume fractions, $\Phi$, were studied with a surface force apparatus. At temperatures well below the lamellar (L $_\alpha)/{\rm L}_3$ bulk transition, the force-distance profile is weakly oscillatory with a period that is twice the correlation length ( $\xi$) of the L 3 phase measured from SAXS. The oscillations are superimposed on an exponentially attractive background with an order correlation length of 2-4 cell sizes of the sponge structure. When the temperature is raised, a first-order phase transition to a lamellar structure can be induced for separations below a threshold. Another oscillatory interaction results which has a period that is twice the reticular distance for an L $_\alpha$ phase of similar $\Phi$. In addition, the thickness of the induced lamellar film increases (reversibly) with temperature. The compressibility modulus extracted from the oscillatory interaction is consistent with that expected for lamellae stabilized by undulation forces.

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