Interaction of gelatin and sodium dodecyl benzene sulphonate at oil and water interfaces

Interaction between sodium dodecyl benzene sulphonate (SDBS) and gelatin was studied in relation to emulsification behaviour and emulsion stability. We chose two different oils to study influences of oil phase characteristics, namely, tricresyl phosphate (TCP) as an oil with polar and slightly hydrophilic nature, and n-docedane (nC12) as its apolar contrast. Our interfacial tension measurements showed that both TCP and n-C12 give critical values (i.e., cac and cmc) very close to those of surface tension measurement. This result indicates that the complexation behaviour in bulk solution is independent of the presence or the nature of the oil phase. Absolute tension values above the cmc and slope values at the cmc in gelatin free systems, however, imply SDBC's weaker adsorption to TCP than to n-C12. Our emulsification results for the TCP system revealed the existence of an optiomal point for emulsion stability in the SDBS concentration region between the cac and the cmc. Above this point, emulsion stability deteriorates remarkably. The behaviour is in line with our findings from the dynamic sorption expriments (ellipsometry, TIRF, and SPR) reported elsewhere, which showed a rapid desorption of gelatin from the hydrophobic surfaces above the cac. The results suggest that the adsorption of gelatin/ surfactant complexes at the interface is a key factor for stability of the polar oil emulsion system. Contrary to that , the n-c12 system did not show any deterioration, even above the cmc, which is presumably due to a strong double layer effect from the firmly adsorbed layer of SDBS at the interface.