Polymer-Modified Microemulsions as a New Type of Template for the Nanoparticle Formation

Polymer-modified microemulsions can be obtained by adding polymers to a mixture consisting of water, oil, and a cosurfactant. Depending on the type of polymer used quite different effects can be observed. For example water soluble polymers can be incorporated into the individual water droplets of a water-in-oil microemulsion, can induce a cluster formation, or the formation of a sponge phase, that means a bicontinuous microemulsion. It is shown that the cationic polyelectrolyte, i.e. poly (diallyldimethylammonium chloride) (PDADMAC), of low molar mass can be incorporated up to a polymer concentration of 20% into individual inverse microemulsion droplets consisting of water, heptanol, and a surfactant with a sulfobetaine head group (SB). These PDADMAC-modified microemulsions, well characterized by means of conductometry, rheology, calorimetry, H-1 NMR self-diffusion, ultrasound relaxation measurements, and electron microscopy, can be successfully used as a template for the formation of ultrafine spherical BaSO4 nanoparticles. By adding nonionic polymers like poly (N-vinyl-2-pyrrolidone) or poly (ethyleneglycol) to the quasiternary system water/toluenepentanol/ sodium dodecyl sulfate (SDS), polyampholytes or polycations, one can induce the formation of a single phase channel between the water-in-oil and the oil-in-water microemulsion. The resulting sponge phase can be used as a template for producing BaSO4 nanorods.