Modification of a reverse microemulsion with a fluorinated triblock copolymer.

A w/o microemulsion consisting of n-decane, AOT, and water with a droplet volume fraction Phi=0.2 and a molar ratio of water to AOT omega=40 has been used as a model system to investigate the effect of added amphiphilic triblock copolymers on structure and conductivity of the system. Structure of the system is determined by small-angle X-ray scattering. Conductivity is measured in a wide frequency and temperature range. The pure microemulsion displays the known phenomenon of conductivity increase with temperature at the percolation temperature T(p). Droplets are found to decrease in size in the same temperature range. The triblock copolymer poly(perfluorohexylethyl methacrylate)-b-poly(ethylene oxide)-b-poly(perfluorohexylethyl methacrylate) has been added to the microemulsion such that the number of polymers per droplet z is between 0.5 and 2. The polymer dissolves in the microemulsion and is located in the droplet. Microemulsion droplets deform continuously from spherical to prolate ellipsoidal shape with increasing polymer content. Furthermore, a strong shift of T(p) to higher T with increasing polymer content is observed. For z > or = 1.5 DeltaT(p) is nearly constant. Besides the confinement effect the specific interaction of the polymer blocks with the surfactant layer are of importance.