Interaction of mixture of anionic surfactants with collagen

Study focused on interaction of collagen fibres of collagen I with anionic surfactants sodium dodecylbenzene sulphonate (SDBS), sodium dodecyl sulphate (SDS) and their mixtures at pH = 6, at two ionic strengths (I = 0.06 mol L(-1) and I = 0.4 mol L(-1)) and laboratory temperature. Surfactants and their mixtures were characterised by their critical micelle concentration (c.m.c.), composition of mixed micelles and interaction factor beta according to Rubingh. Dependency of c.m.c. on mixture composition has an opposite tendency at both ionic strengths, which proves the greater influence of added electrolyte on behaviour of SDS than of SDBS. Interaction was evaluated by means of binding isotherms and mass swelling degree alpha(m). The bound quantity partly depends on mixture composition, partly on ionic strength. SDS and mixtures containing its greater quantities are bound more than SDBS (approx. 150% related to SDBS). Increased ionic strength of the environment increases bound quantity in approximately same manner, heedless of adsorbate composition. Even composition of the mixture after interaction with fibres does not markedly alter from initial composition. Fibre swelling is affected by composition of swelling mixture similarly to binding - it increases with growing quantity of surfactants. Greater ionic strength acts against collagen swelling, and at given ionic strength (I = 0.4 mol L(-1)) swelling attains half values compare to swelling at low ionic strength (I = 0.06 mol L(-1)). There are characteristic concentrations of both surfactants and their mixtures (c(s) approximately 0.5 - 1.0 mmol L(-1)) that do not produce swelling. It is assumed that this range of concentrations corresponds to amount of surfactants bound to collagen through electrostatic forces and thus to temporary increase in fibre hydrophobity.