Intrinsic contact angle of aqueous phases at membranes and vesicles.

Biomimetic membranes exposed to several aqueous phases are studied theoretically. Specific examples are provided by lipid vesicles and phase separating polymer solutions. The theory reveals the existence of an intrinsic contact angle, theta(in), between the membranes and the aqueous phases. An explicit relation is derived by which this intrinsic angle can be determined from the effective contact angles as measured by optical microscopy. A detailed comparison between theory and experiment provides strong evidence that the intrinsic contact angle theta(in) represents a material parameter, in contrast to the effective contact angles.