Molecular mechanism of the stabilization of vesicles bearing terminally anchored polymers

The stabilization of colloidal dispersions by adsorbed polymers is a well-known phenomena. In this work, we have used surface force measurements to examine the molecular mechanism of vesicle stabilization by incorporated nonionic PEG surfactants. Two polymeric surfactants were used in which the polymer headgroup consisted of 10 (NP10) or 50 (NP50) ethyleneoxide units, and the hydrocarbon tail was the nonylphenol moiety (NP-PEG surfactants). The measurements with NP-PEG surfactants elucidated the molecular mechanisms of and the conditions for the achievement of colloidal stability with these materials in aqueous solutions. Under conditions of low surfactant coverage where the underlying hydrophobic surface remains partially exposed, aggregation will occur due to the residual intersurface attraction. In contrast, when the underlying hydrophobic surface is coated by co-adsorption of DLPC with the NP-PEG surfactants, the long-range attraction is abolished and the interpolymer repulsion dominates the interactions; consequently, colloidal stability will be achieved. Thus, since vesicles with membrane anchored NP-PEG are analogous to the latter configuration, the molecular mechanism for stabilization is attributable to steric repulsion between the anchored polymers at the surface.