Evolution of the structure of lamellar gel networks based on fatty alcohols and cationic surfactants during cooling and shearing

Long chain fatty alcohols (FAs) are amphiphilic molecules commonly associated to surfactants in aqueous solution to produce cosmetic and pharmaceutical cream products. In appropriate concentration, the addition of surfactants to long chain fatty alcohols leads to the formation of lamellar gel networks (LGNs) at the origin of the creamy texture. The ternary system leads to lamellar structure forming a percolated network giving rise to a gel. The rheological properties of the cream result from a preparation process combining shearing, heating and cooling steps. Therefore, the cooling step and shearing rate are the two crucial parameters governing the resulting rheological properties of the cream. Despite much research into the properties of creams and their many years of use, however, a perfect understanding on the nanoscale that is to say on the morphology, size, and composition of the lamellar structures during the cooling and shearing process is still not known. This can be probed directly through rheo-SANS, because of the high contrast achieved by using protonated fatty alcohols and surfactant formulated with D2O with a precise control in temperature.