Acoustic and viscosity studies of sodium dodecyl sulfate in aqueous solutions of gelatin

Ultrasonic velocities and densities of anionic surfactant, sodium dodecyl sulfate (SDS), in aqueous solutions of gelatin (0.25, 0.50, 1.00%w/v) have been measured over a wide temperature range (20-40 °C) at an interval of 2 °C by using DSA-5000. The data was used to calculate partial molar volume (Фv), adiabatic compressibility (β) and apparent molar compressibility (Фk) in order to explain protein-surfactant interactions. Viscosity measurements (viscous relaxation time and activation energy parameter) of SDS in aqueous solutions of gelatin were also carried out to support the explanation. A minimum observed in case of activation parameter in the concentration region 6-8 mmol kg− 1 of SDS supported the results obtained by other parameters indicating micellar solubilisation of the SDS in this region. The behaviour of both Фk and Фv data indicates that SDS binding to gelatin is non-cooperative at low surfactant concentration but becomes cooperative at higher concentration.