Anna Kharlamova – Interfacial and bulk crystallization in mixtures of surfactant SDS with NaCl and KCl

Anna Kharlamova, Université Paris-Saclay, Laboratoire de Physique des Solides

Solutions of surfactants, such as anionic surfactant sodium dodecyl sulfate (SDS), can form crystals depending on surfactant concentration, temperature and presence of salts. The crystals melt above a characteristic temperature called the Krafft temperature/boundary. Surfactant crystallization is generally considered as an undesirable phenomenon, as it leads to heterogeneity in detergent products. However, the crystals have also been shown to be useful in foam stabilization, where they accumulate at the interface of bubbles rendering them ultrastable. The foams stabilized by surfactant crystals are thermostimulable – they can be destroyed by heating, which can be utilised in some applications. In presented work we studied crystallization of SDS induced by addition of NaCl or KCl. The Krafft temperature, the crystallization kinetics and the crystal structure are considered. The study is hoped to be interesting from the fundamental point of view, as well as for applications in design of interfaces with controlled properties.