Structures of Physical Gels in the EHEC−SDS−Water System

Abstract

The system EHEC + SDS + water has a temperature-induced gelation and a temperature-induced phase separation. Phase studies and small angle neutron scattering experiments have been performed in order to establish the link between these two phenomena. At low temperatures, neutron scattering curves show a mesh of polymer + surfactant “necklaces” coexisting with undissociated macromolecules. As the temperature is raised, EHEC macromolecules are expelled from the mesh of necklaces to lumps of a polymer-rich phase. In the early stages of this microphase separation, small lumps of the polymer-rich phase are immersed in a mesh of surfactant + polymer necklaces; the mesh controls the swelling properties of the mixture, and the lumps act as cross-links which cause the mixture to become a gel. In later stages, most of the polymer is expelled to the lumps, and the mesh collapses. These phenomena result from polymer−polymer interactions that are temperature dependent and competing against the polymer−surfactant interactions.