COIL-GLOBULE TRANSITION OF POLY(N-ISOPROPYLACRYLAMIDE) - A STUDY OF POLYMER-SURFACTANT ASSOCIATION

Time-resolved fluorescence depolarization is applied to investigate th e association of sodium n-dodecyl sulfate (SDS) micelles with poly(N-i sopropylacrylamide) in aqueous solutions using an amphiphilic fluoresc ent probe (3-perylenedodecanoic acid) which is incorporated into the S DS micelles. First, the effect of the surfactant concentration was mea sured: in the presence of the polymer, above the critical aggregation concentration (CAC) of SDS, the rotational relaxation of the probe exh ibits a slow and a fast component. The relaxation time of the fast com ponent is the same as in a polymer-free solution above the CMC of SDS where, however, only one component is observed. The slower relaxation time is attributed to polymer-bound micelles which incorporate polymer segments into their core. Second, the effect of the temperature induc ed coil-globule transition is investigated: in the course of the trans ition the rotational motion slows down almost 10-fold, indicating that the probe remains firmly associated with the polymer even in its dens e globular state.