|M.Sc Thesis||Department of Biotechnology and Food Engineering|
|Supervisor:||Assoc. Prof. Danino Dganit|
The study focuses on the relationship between rheological properties and nanostructure in binary mixtures of surfactants. Two mixed systems were studied; the cationic/anionic octyltrimethylammonium bromide (OTAB) / sodium oleate (NaOA) system and the nonionic/anionic n-dodecyl b-D glucopyranoside (DDGP) / sodium dodecylsulfate (SDS) system. Both systems display several orders of magnitude rise of the viscosity upon increasing the relative ratio between the two surfactants, a rheological behavior which is also found in cationic/salt systems. The initial rise in the viscosity has been generally attributed to a sphere-to-rod structural transformation. The additional viscosity increase, up to the peak, has been correlated with the growth of long flexible thread-like micelles, and the peak has been considered as a point of transformation from linear micellar growth to the formation of a network of branched micelles.
However, our work shows that the rheological findings can be explained by other mechanisms. Specifically, in both systems we provide clear evidence that the viscosity is mainly controlled by changes in the linear length of the micelles, and not by branching.
Our structural analysis is based primarily on cryo-transmission electron microscopy (cryo-TEM), accompanied by self-diffusion NMR. This is one of the fewest studies that exhibit clear direct proofs of surfactant systems whose rheological behavior is not directly controlled only by the formation of junction points. This study also emphasizes the importance of combining direct and indirect methods, in characterization of the properties and nanostructure morphology of complex fluid systems.