Effects of fluctuations on the wetting transition in amphiphilic systems

Fluctuation-induced constraints on the observation of unbinding in a confined complex fluid

An extensive study of the effect of fluctuations on the unbinding of an interface from a wall in a ternary system is presented. The framework upon which the analysis is based is a linear functional renormalization group scheme of the appropriate effective interface Hamiltonian. The interface model includes position-dependent gradient coefficients, and their presence is shown to be equivalent to modifications of the bare interface potential that are highly relevant in determining the renormalized critical behavior. We analyze the modified interface potential in a mean-field-like way for both bare critical and first-order unbinding transitions in order to highlight the key effects. We further perform a detailed study of the linearized renormalization group equations identifying three fluctuation regimes and recovering earlier predictions for nonuniversal critical exponents. The surface phase diagram changes dramatically under renormalization with, most notably, fluctuation-induced reentrant behavior. We show that in the revised phase diagram the unbound region is limited in extent indicating that the opportunity for observing an unbinding transition in a confined complex fluid is highly restricted.

Adsorption phenomena in amphiphilic systems

The wetting behavior of a ternary mixture of oil, water, and amphiphile in the presence of a surface is studied. An interface model carefully derived from an underlying Ginzburg-Landau theory is introduced, which contains position dependent rigidity and stiffness coefficients. Using this model we predict a rich surface phase diagram containing thin-thick, first-order, and continuous wetting transitions. Application of the model to other interface behavior in these mixtures is also addressed.