Surface deposition and phase behaviour of oppositely charged polyelectrolyte-surfactant complexes

There are two main objectives to my PhD, one is a theoretical approach to understanding colloid interactions in nonpolar solvents, and the other is to investigate the structure of polymer-surfactant complexes found in shampoo. Linking these two themes together is the technique of blinking optical tweezers which we use to measure the interaction force between two charged particles in a liquid media. Currently the technique is limited to measuring longer-ranged interactions common to nonpolar systems, however we will adapt this technique to be used in the aqueous, polymer-surfactant systems. By measuring these interactions strengths we can test the current theories of electrostatics in nonpolar solvents, and try to understand the mechanisms involved in particle deposition onto the hair during the rinsing stage of a shampoo. With the shampoo formulations in mind, we are hoping to further understand how the structure of the complexes formed affects deposition onto a surface during rinsing, possibly through neutron or light scattering. Then we wish to observe how these mechanisms may be affected by additional particles such as oil droplets or polymer particles. The more theoretical part involves measuring the interactions between dissimilar charged spheres in a low dielectric solvent, where electrostatic behaviour are not well defined, and comparing this data with current models for colloid systems which are usually developed with high polarity solvents in mind, and locating where these models fail in oils where difference in surface charge densities can cause unexpected behaviour at short range, e.g. like-charge attractions and opposite-charge repulsions.