INTERACTION BETWEEN PHOTOGRAPHIC GELATIN AND SODIUM DODECYL-SULFATE

The interaction of sodium dodecyl sulfate (SDS) and photographic gelat in has been studied using a variety of physical and photophysical tech niques. The interaction involves the formation of micelles attached to the polymer in a necklace-and-bead model much as described for the in teraction of SDS with neutral synthetic polymers. The micelles have ag gregation 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 deter mines the course of micellization. Two results of this repulsion are t hat 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 rationa lizes not only the binding isotherm but also the unexpected fluorescen ce of anilinonaphthalene-sulfonate (ANS) when used as a probe of the s ystem. The model should have general applicability to the treatment of interactions between neutral or weakly charged polymers and charged s urfactants.