Effect of amphiphilic block copolymers on the structure and phase behaviorof oil-water-surfactant mixtures

The effect of amphiphilic diblock copolymers of several molecular weights o n the structure and phase behavior of ternary amphiphilic systems (water, o il, and nonionic surfactant) is investigated. Small amounts of amphiphilic block copolymer polyethyleneoxide-polyethylpropylene lead to a dramatic dec rease of the amount of total surfactant needed to solubilize given equal vo lumes of water and oil in a bicontinuous microemulsion. Neutron scattering experiments employing a high-precision two-dimensional contrast variation t echnique demonstrate that the polymer is distributed uniformly on the surfa ctant membrane. Based on these observations, we propose a mechanism for the enhancement of swelling behavior, which is due to the variation of the mem brane curvature elasticity by polymer mushrooms anchored to the interface. (C) 2001 American Institute of Physics.