Effects of a Novel Amphiphilic Graft Copolymer on Ternary Mixtures of Surfactant, Water, and Oil

Sammanfattning: An amphiphilic graft copolymer, with hydrophilic poly(ethylene glycol) monomethyl ether side chains grafted onto a hydrophobic poly(dodecyl methacrylate) backbone, has been synthesized. The side chains are water soluble and the backbone is soluble in oils such as cyclohexane and isooctane. The graft copolymer is not soluble in oil or water, but it is quite soluble in AOT oil-continuous microemulsions (AOT= sodium bis(2-ethylhexyl) sulfosuccinate). The backbone polymer dissolves in the microemulsion over a wide range of compositions, but segregative phase separation occurs at high volume fractions of droplets. Entirely different phase behavior is observed for mixtures of the graft copolymer with the microemulsion. A high concentration of droplets is required to solubilize even small amounts of polymer, and phase separation occurs when the droplet concentration becomes sufficiently low. Mixtures of the graft copolymer with oil-continuous microemulsions have been studied using viscometry, the time-resolved fluorescence quenching technique, the PFG NMR technique, and dynamic and static light scattering. The graft copolymer enhances the microemulsion viscosity, and strong effects are promoted by increased degrees of grafting, increased polymer concentration, and large water droplets. A maximum in the viscosity is obtained when the droplet concentration is increased progressively at a constant polymer concentration. Systems with high viscosities exhibit slow polymer self-diffusion. Polydisperse polymer-droplet aggregates are formed when the graft copolymer is dissolved in oil-continuous microemulsions. The clusters coexist with a large fraction of free droplets, i.e., droplets not connected to polymer-droplet aggregates, and the cluster size varies considerably with the polymer concentration, but only at high polymer concentration is there evidence of a fraction of very large (possibly infinite) clusters. The graft copolymer affects the microemulsion by increasing the size of the water droplets.