Calorimetric studies of the interaction between sodium alginate and sodium dodecyl sulfate in dilute solutions at different pH values

Interactions between the polyelectrolyte sodium alginate (NaAlg) and the anionic surfactant sodium dodecyl sulfate (SDS) have been investigated by microcalorimetric techniques. The polymer–surfactant interactions were observed between NaAlg and SDS at different pH values in dilute solution. The thermodynamic parameters for their interaction process are evaluated from the results of the observed dilution enthalpy curves. As the pH value of the solution decreases from 7 to 6, NaAlg polymers have an obvious effect on the cmc of SDS as a simple salt, which indicates no association between SDS and NaAlg owing to electrostatic repulsion. With the progressive decrease of pH value from 5 to 3, the hydrophobic segments in the alginate chains are increasing and the hydrophilic segments decreasing, and the aggregation between SDS and alginate due to hydrophobic interactions is observed.

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