Interaction of unmodified and hydrophobically modified alginate with sodium dodecyl sulfate in dilute aqueous solution: Calorimetric, rheological, and turbidity studies

Interactions between hydrophobically modified alginate (HM-alginate) and the anionic surfactant sodium dodecyl sulfate (SDS) have been investigated by microcalorimetry, rheology and turbidimetry. Significant polymer–surfactant interactions were observed between HM-alginate and SDS, whereas for mixtures of unmodified alginate and SDS only a weak synergism was detected. The intrinsic viscosity of HM-alginate solutions with added SDS showed a strong upturn at low SDS concentrations, indicating a polyelectrolyte effect. The zero-shear viscosity of the semidilute HM-alginate solution was found to increase at a low level of SDS addition, and then decrease with increasing SDS concentration. The turbidity curves exhibit the same profile as those of the viscosity. The maximum of the turbidity is located at the same SDS concentration as the viscosity maximum for the semidilute solution. This picture is consistent with the conjecture of the formation and breakup of the associations as the SDS concentration increases.