Colloid Chemistry - Prof. Koetz

Nanoparticle formation in polyelectrolyte-modified microemulsions

Microemulsions are thermodynamically stable oil/water/surfactant mixtures, with extremely small droplet size (droplet diameter smaller than 20 nm). In the case of a water-in-oil microemulsion, the tiny water droplets are surrounded by a "surfactant skin" with the hydrophilic head groups protruding into the water phase and the hydrophobic "tails" reaching the oil phase. These tiny water droplets can now be used as nanoreactors, by carrying out specific reactions in the droplets. For example, if two microemulsions with different reaction partners are mixed, then nanostructured reaction products are formed. A classical example is the reaction of BaCl2 and Na2SO4 to insoluble BaSO4. The problem with this method, however, is the insufficient stability of the surfactant skin so that the growth of the particles often goes beyond the droplet size and results in different sized particles.

Based on this knowledge, we first attempted to introduce polyelectrolytes into the microemulsion, in order to increase the stability of the surfactant skin and to regulate the particle growth process. The conformation as well as the local position of the polymer in the microemulsion droplet can be specifically influenced by electrostatic interactions between the surfactant and the polyelectrolyte, as demonstrated by MD simulations.

If such microemulsions are used as a template phase, nanoparticles with extremely small particle dimensions can be produced.


Figure 4: HRTEM image of spherical gold nanoparticles.