The structure of gelatin-water/oil microemulsion sols and gels. An EPR spin-probe and spin-labelling study

The microenvironments of sols and gels of gelatin in water-in-oil microemulsions formed by sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in isooctane have been characterized by EPR spin-labelling and spin-probe techniques. Using spin-labelled gelatin, incorporated both in sol and gel, the changes in the microstructure(s) around the gelatin have been monitored, at different water and gelatin compositions. Specific locations of the gelatin have been found: some of the gelatin is located at the water/surfactant interface and part in pools of water. Gelatin is not found in the apolar phase. The spin-probe technique, with amphiphilic probes, provides information on changes in the structure of the aggregates as a result of gelatin incorporation. Increased microviscosity, and a tighter packing of the AOT chains is observed, confirming the location of gelatin at the water/surfactant interface. Our results favour a model for the gel structure in which all the gelatin is covered by water and surfactant, with large cavities of polar and apolar solvent.