The size and flexibility of grown sodium dodecyl sulfate micelles in aqueous sodium chloride solutions

We have used light scattering techniques to measure the size and flexibility of grown sodium dodecyl sulfate (SDS) micelles in aqueous NaCl solutions as a function of temperature, surfactant concentration, and salt concentration. The mean hydrodynamic radius (R̄h) was determined using quasielastic light scattering, and the mean radius of gyration (R̄g) was measured using static light scattering. A theory of flexible rod-like objects is compared to the data. This theory predicts that for flexible rod-like micelles R̄g/R̄h will depend not only on R̄h but also on the persistence length, a measure of micellar flexibility. The data are found to be consistent with flexible rod-like micelles whose mean persistence length (〈l〉) depends weakly on SDS concentration and strongly on temperature and NaCl concentration. In the temperature range from 20–37 °C in 0.8 M NaCl and 30–50 °C in 1 M NaCl solution we find 〈l〉∝exp(−w/kBT) with w=4.7±0.5×10−12 erg.