M. Tasinkevych et A. Ciach, Structural transformations in confined lamellar phases in oil-water-surfactant mixtures, J CHEM PHYS, 115(18), 2001, pp. 8705-8713
Lamellar phases in oil-water-surfactant mixtures are studied in a slit geom
etry. Within a lattice vector model we obtain the following results in a me
an-field approximation. (i) In the case of swollen phases the lamellae are
parallel to the walls for all distances L between them and for all surface-
field strengths; the system responds elastically to the external stress. (i
i) For shorter periods of the bulk phase (surfactant volume fraction rho (s
)approximate to1/3) the lamellae are parallel to hydrophilic, and perpendic
ular to neutral or very weakly hydrophilic surfaces. For a small range of t
he surface-fields changes of L lead to a switch from the parallel to the pe
rpendicular orientation, as found previously for confined block copolymers.
(iii) For still shorter periods (rho (s)greater than or equal to1/2) the p
erpendicular orientation is stable up to much higher hydrophilicity of the
walls. Changes of L induce the switch between the two orientations for a la
rge range of the surface fields. For rho (s)greater than or equal to1/2 the
structure in the slit can no longer be described by one-dimensional densit
y profiles even for the parallel orientation. Structural deformations simil
ar to dislocations lead to an inelastic response to compression or expansio
n. (C) 2001 American Institute of Physics.