INTERACTION BETWEEN PHOTOGRAPHIC GELATIN AND SODIUM DODECYL-SULFATE

The interaction of sodium dodecyl sulfate (SDS) and photographic gelatin has been studied using a variety of physical and photophysical techniques. The interaction involves the formation of micelles attached to the polymer in a necklace-and-bead model much as described for the interaction of SDS with neutral synthetic polymers. The micelles have aggregation numbers similar to micelles formed in the absence of gelatin under the same conditions and bind by a mixture of electrostatic and hydrophobic forces. Electrostatic repulsion among bound micelles determines the course of micellization. Two results of this repulsion are that micelles bind sequentially to the polymer and that the activity of monomeric surfactant increases monotonically as the binding increases. A simple, thermodynamic model based on electrostatic effects rationalizes not only the binding isotherm but also the unexpected fluorescence of anilinonaphthalene-sulfonate (ANS) when used as a probe of the system. The model should have general applicability to the treatment of interactions between neutral or weakly charged polymers and charged surfactants.