Flexibility of charged and uncharged polymer-like micelles

We have performed a series of small-angle neutron scattering (SANS) and static light scattering (SLS) experiments with dilute and semidilute solutions of polymer-like micelles formed by C16E6 in D2O at two different temperatures (T = 26 degrees C, 35 degrees C). The local structure has been investigated by applying indirect Fourier transformation and square-root deconvolution techniques. We demonstrate that the micelles maintain their locally cylindrical structure in this temperature regime despite the significant change in the spontaneous curvature of the surfactant. Detailed information on the micellar flexibility has been obtained from the SANS data by applying a nonlinear least-squares fitting procedure based upon a numerical expression for the single-chain scattering function of a worm-like chain with excluded volume effects. Particular attention has been given to the determination of quantitative numbers for the "intrinsic" persistence length as well as for the contribution from electrostatic interactions upon the addition of a small fraction of an ionic surfactant. The results have been compared with predictions from theoretical models for polyelectrolytes.