Ultrasonic relaxation studies of sodium octyl sulphate complexes with synthetic polymers and a protein in aqueous solution

The ultrasonic relaxation spectra of sodium octyl sulphate solutions in the presence of poly(vinylpyrrolidone), poly(vinyl alcohol), poly(4-vinylpyridine) and bovine serum albumin have been investigated. When these results are compared with those found for pure micellar sodium octyl sulphate solution it is found that in all cases the relaxation times τ for the monomer ⇌ aggregate exchange process are such that graphs of 1/τ against surfactant concentration exhibit minima at concentrations close to the critical micelle concentration (c.m.c.) of the pure surfactant. In the sodium octyl sulphate/macromolecule complexes the minima observed in the 1/τ plots are more pronounced than in the pure soap. At concentrations well above the c.m.c. the relaxation behaviour in the presence of polymer is very similar to that of pure surfactant. The minima in 1/τ are discussed in terms of the Aniansson and Wall equation for monomer–micelle exchange.