Amphiphilic block copolymers as efficiency boosters in microemulsions: a SANS investigation of the role of polymers (original) (raw)
2002, Applied Physics A: Materials Science & Processing
The effect of amphiphilic block copolymers on ternary microemulsions (water, oil and non-ionic surfactant) is investigated. Small amounts of PEP-PEO block copolymer lead to a dramatic expansion of the one-phase region where water and oil can be solubilized by the mediation of surfactant molecules. Small-angle neutron-scattering experiments employing a high-precision two-dimensional contrast-variation technique demonstrate that the polymer is distributed uniformly on the surfactant membrane, where it modifies the membrane curvature elasticity. Furthermore, a new approach to determine the bending rigidity of an amphiphilic membrane is proposed, which is precise enough to measure the logarithmic scale dependence of the bending rigidity and its universal prefactor in bicontinuous microemulsions. PACS: 61.12.Ex; 68.05.Gh; 61.25.Hq Membrane systems represented by surfactant monolayers in microemulsions or by lipid bilayers have received much interest recently. Experimentally the interaction between polymers and membranes, which is very common in all kinds of biological membranes, has been studied intensively. A good example is "stealth liposomes" effective drug carrier systems where polymers anchored to phospholipid bilayers protect artificial vesicles against the body's immune response . Theoretically the concept of the curvature elasticity [2] has been found to be very useful in understanding many phenomena in these systems, which are the shapes, fluctuations, phase behavior and more. For a detailed comparison of theory and experiment, it is necessary to measure the parameters of this model, which are the spontaneous curvature c 0 , the bending rigidity κ, and the saddle-splay modulusκ.
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