100 YEARS OF COLLOID SCIENCE FASCINATING PHENOMENA IN SURFACTANT SOLUTIONS

The lecture begins by reviewing some facts that were already known in colloid science of hundred years ago. The importance of colloid science for the development of human civilization and modern technology is then outlined. The main part of the lecture deals with surfactant science, a subdivision of colloid science: Amphiphillic molecules can assemble in aqueous solution into a variety of micellar structures such as globules, rods, disks and vesicles. For a given system the micellar structures are determined by the packing parameter of the surfactant which controls the spontaneous curvature of a micellar interface. The spontaneous curvature of micelles can be varied continuously by the addition of cosurfactant to the micellar solution. With increasing mole fraction X(c) of the cosurfactant, the system develops then from micelles with interfaces that are strongly curved around the micellar core over planar interfaces towards interfaces that are curved away from the micellar core. Results are presented for the ternary systems of alkyldimethylaminoxides, n-alcohols and water. As a consequence of the change of the spontaneous curvatures with X(c) the systems undergo several macroscopic phase transitions in dilute solutions. In total eleven different single and multiphase situations are observed when one passes from the dilute surfactant to the dilute cosurfactant solution. The single phase regions are the micellar L1-phase, two different lamellar liquid crystalline L(alpha)-phases (L(alpha1) L(alphah) and the isotropic L3 or sponge phase. The microstructures of the various phases are identified by electronmicrographs which were obtained with the freeze fracture method. The macroscopic properties of the phases are discussed on the basis of their microstructures. The influence of charges by ionic surfactants on the structures and properties of the mesophase is determined. It is found that the L(alphah) and the L3-phase are transformed into phase with multilamellar vesicles. This phase has a rheological yield stress value and can be used as a particle suspending fluid. The influence of excess salt on the microstructures and the properties of the charged phases is determined. Some of the observed phases show bright colours when illuminated with white light. Some of the phases show colour effects when viewed through crossed polarizers.