A sponge morphology in an elementary coacervate

A zwitterionic gemini surfactant forms a coacervate which is "elementary" i n the sense that it consists of a single solute as opposed to the multicomp onents (e.g., cetylpyridinium chloride/hexanol/water/NaCl) common in the co acervate literature. The gemini dissolves in water but then quickly separat es as oily droplets which, despite the high water content, of 83 wt %, are immiscible with water. Cryogenic temperature high-resolution scanning elect ron microscopy (cryo-HRSEM) examination of the droplets shows a distinct "s ponge" structure. Although previously proposed for coacervate phases, a spo nge morphology has never before been clearly depicted. The absence of previ ous electron microscopy (EM) pictures of the coacervate network is attribut ed to artifacts associated with transmission electron microscopy (TEM) meth ods, to the fragility of the coacervate toward physical perturbations, and to possible compositional changes with complex mixtures during sample prepa ration. When the gemini coacervate was exposed to mild shear, the honeycomb structure disappeared and was replaced by a lamellar phase.