SINGLE-CHAIN DIFFUSION-COEFFICIENT OF F-DEXTRAN IN POLY(VINYLPYRROLIDONE) WATER - FLUORESCENCE RECOVERY AFTER PHOTOBLEACHING EXPERIMENTS

Fluorescence recovery after photobleaching (FRAP) experiments have bee n performed on a fluorescent dextran/poly(vinylpyrrolidone) (PVP) mixt ure in water. The experiments were made at several total Polymer conce ntrations C(T), from dilute to semidilute solution (0.1-10C) in the h omogeneous and disordered state. The composition of the ''visible'' po lymer fluorescent dextran in the mixture was around 0.5 % in the semid ilute regime. The dynamics of such a system as revealed by FRAP exhibi t one relaxation mode identified as a self-diffusion coefficient. This mode has been compared to the extracted D(S) value from the two relax ation modes (cooperative and interdiffusive) obtained using dynamic li ght scattering (DLS; Macromolecules 1993, 26, 2592). As expected in bo th techniques, the measured (FRAP) and the extracted (DLS) D(S) decrea se with the concentration. Comparison between the results shows that i n the semidilute range of concentration the agreement is reasonable be tween both D(S). As the concentration decreases, the agreement becomes less and less satisfactory. This result confirms that the extrapolati on to infinite dilution of D(S) (deduced from DLS) is not valid and sh ows the importance of the hydrodynamic interactions in the dilute tern ary systems.