BINDING OF SDS TO ETHYL(HYDROXYETHYL)CELLULOSE - EFFECT OF HYDROPHOBIC MODIFICATION OF THE POLYMER

The binding of SDS to cellulose polymers in the semidilute concentrati on regime has been studied by means of NMR, ion-selective electrode, a nd a time-resolved fluorescence technique. Two polymers have been used , differing only in a low degree of hydrophobic modification of one of them. NMR self-diffusion and activity measurements show that the bind ing of SDS to the nonmodified polymer has a fairly pronounced critical aggregation concentration (cac), while binding to the hydrophobically modified polymer is less cooperative up to a concentration of about t he cac in the nonmodified polymer/SDS system. NMR T-2 relaxation and f luorescence studies indicate that surfactants bound to the hydrophobic ally modified polymers in the noncooperative regime have slow dynamics compared to micellized surfactants, to surfactants bound to the unmod ified polymer, and to surfactants bound to the hydrophobically modifie d polymer in the cooperative regime. Furthermore, in the non-cooperati ve regime the fluorescence studies imply that the SDS aggregation numb er of the mixed micelles is low and that the number of hydrophobic zon es is invariant with respect to the surfactant concentration.