COMPLEXATION BETWEEN POLY(N-ISOPROPYLACRYLAMIDE) AND SODIUM N-DODECYL SULFATE - COMPARISON OF FREE AND COVALENTLY BOUND FLUORESCENT-PROBES

Cloud point, calorimetric, and fluorescence probe methods were combined to examine aqueous mixtures of poly(N-isopropylacrylamide) (PNIPAAM) and sodium n-dodecyl sulfate (SDS). Addition of the surfactant to PNIPAAM (0.40 mg/ml) leads to a continuous elevation of the LCST above an SDS concentration of 0.75 mm. This concentration was essentially identical to the critical aggregation concentration (CAC) of SDS in the presence of the polymer as detected by both free and covalently bound fluorescent probes. Thus the binding of SDS micelles to PNIPAAM is the driving force for the enhanced polymer solubility. The CAC was ten-fold lower than the critical micelle concentration (CMC) and could be successfully predicted by the theory of Nagarajan and Ruckenstein.