Interaction Between Gelatin and Cationic Gemini Surfactant with Long Unsaturated Tail

Abstract

The interaction of cationic gemini surfactant 1,2-ethane-bis-[N,N,N-dimethyl-(Z-13- docosenyl)quaternary ammonium bromide] (hereafter noted 22-2-22) with gelatin above its isoelectric point were studied by pH measurements, viscosity and fluorescence spectroscopy. It has been found that three critical concentrations of 22-2-22, referred to as C_inter, C_intra and C_a respectively, can be detected by steady state fluorescence measurements. However, only C_intra can be noted effectively by viscosity measurement. The experimental results indicate that the polymer bound micelles act as transient cross-links resulting in the inter-polymer or intra-polymer association, which is depending on both surfactant and gelatin concentrations. When C_22-2-22 > C_inter micelles bound to more than one polymer strand act as transient cross-links between gelatin molecules, that is, inter-molecular association. As C_22-2-22 is greater than C_intra, more surfactant micelles tend progressively to envelop and "neutralize" the binding sites of polymer chains and break the inter-chain junctions. And relatively rich surfactant micelles made each gelatin strand accommodate surfactant micelle which bind with several sites of the same polymer chain, i.e., the intra-polymer association occurs. Finally one gelatin chain may bind several surfactant micelles. However if C_gelatin reaches the overlap concentration C* the intra-polymer association may be screened by the entanglement of polymer chains.