title: Confinement-induced symmetry breaking of interfacial surfactant layers.
abstract: Interaction forces between mesoscopic objects are fundamental to soft-condensed matter and are among the prime targets of investigation in colloidal systems. Surfactant molecules are often used to tailor these interactions. The forces are experimentally accessible and for a first theoretical analysis one can make use of a parallel-plate geometry. We present molecularly realistic self-consistent field calculations for an aqueous nonionic surfactant solution near the critical micellization concentration, in contact with two hydrophobic surfaces. The surfactants adsorb cooperatively, and form a monolayer onto each surface. At weak overlap the force increases with increasing compression of the monolayers until suddenly a symmetry braking takes place. One of the monolayers is removed jump-like and as the remaining monolayer can relax, some attraction is observed, which gives way to repulsion at further confinement. The restoring of symmetry at strong confinement occurs as a second-order transition and the force jumps once again from repulsion to attraction. It is anticipated that the metastable branch of the interaction curve will be probed in a typical force experiment. Under normal conditions pronounced hysteresis in the surface force is predicted, without the need to change the adsorbed amount jump-like.
authors.affiliation: Laboratory of Physical Chemistry and Colloid Science, Wageningen University, Dreijenplein 6, 6703 HB Wageningen, The Netherlands.
authors.forename: F A M
authors.initials: FA
authors.lastname: Leermakers
authors.forename: L K
authors.initials: LK
authors.lastname: Koopal
authors.forename: T P
authors.initials: TP
authors.lastname: Goloub
authors.forename: A W P
authors.initials: AW
authors.lastname: Vermeer
authors.forename: J
authors.initials: J
authors.lastname: Kijlstra