A LB film morphological study with reference to biopolymer-surfactant interaction taking gelatin-CTAB system as a model

The interaction of gelatin with cetyltrimethylammonium bromide (CTAB) studied at pH 9 and an ionic strength of 0.005, produces an interfacial surface active gelatin-CTAB (monomer) complex (GSnI), a surface inactive gelatin-CTAB (micelle) complex in bulk (GSmB), followed by coacervation, and its solubilization in micellar solution of CTAB. We have herein attempted to probe the interfacial morphological changes of gelatin and its CTAB complexes, and not the bulk properties like coacervation and/or micellar solubilization. The morphologies of pure gelatin and CTAB films and that of gelatin-CTAB interacted complex at the interface have been investigated using LB, SEM, AFM and ellipsometric techniques. The stability of the gelatin monolayer at varied concentrations with and without CTAB has been examined. The SEM images of stabilized films of gelatin and gelatin-CTAB complex have witnessed compact smooth as well as rough surfaces with formation of distinct domains. Drastic morphological change in the film before the critical aggregational concentration of CTAB (T2) has been in line with an initial abrupt decrease in surface tension. This has been corroborated by AFM measurements, which along with morphology demonstration has provided information on the diameter of the ensembles formed and roughness of the LB films constituted of pure components and their complexes. Thickness of the film was at its maximum in the domain region, as corroborated by ellipsometric technique. Such an elaborate interfacial monolayer and film morphology study of biopolymer-amphiphile system has been rarely documented in literature.