Unusually large acrylamide induced effect on the droplet size in AOT/Brij30 water-in-oil microemulsions.
Droplet microemulsions are widely used as templates for controlled synthesis of nanometer sized polymer gel beads for use as, e.g., nanobiosensors. Here we examine water-in-oil microemulsions typically used for preparation of sensors. The cores of the microemulsion droplets are constituted by an aqueous component consisting of water, reagent monomer mixture, buffer salts, and the relevant dyes and/or enzymes. The cores are encapsulated by a mixture of the surfactants Brij30 and AOT and the resulting microemulsion droplets are suspended in a continuous hexane phase. The size of the final polymer particles may be of great importance for the applications of the sensors. Our initial working hypothesis was that the size of the droplet cores and therefore the size of the synthesized polymer gel beads could be controlled by the surfactant-to-water ratio of the template microemulsion. In the present work we have tested this hypothesis and investigated how the monomers and the ratio between the two surfactants affect the size of the microemulsion droplets and the microemulsion domain. We find that the monomers in water have a profound effect on the microemulsion domain as well as on the size of the microemulsion droplets. The relation between microemulsion composition and droplet size is in this case more complicated than assumed in standard descriptions of microemulsions [R. Strey, Colloid Polym. Sci. 272 (1994) 1005-1019; I. Danielsson, B. Lindman, Colloids Surf. 3 (1981) 391-392; Y. Chevalier, T. Zemb, Rep. Progr. Phys. 53 (1990) 279-371].