SPATIAL HETEROGENEITY OF SOLVENT DYNAMICS IN MULTICOMPONENT POLYMER-SOLUTIONS

Oscillatory electric birefringence has been used to examine the rotati onal dynamics of the solvent Aroclor 1248 (A1248), in dilute and semid ilute polymer solutions containing both polystyrene (PS) and poly(1,4- butadiene) (PB) segments. Three systems were employed: an 8.0 x 10(4)- 8.0 x 10(4) PS-PB block copolymer, 0 less than or equal to c less than or equal to 0.162 g/mL; a 40-60 wt % PS-PB random copolymer, 0 less t han or equal to c less than or equal to 0.126 g/mL; a 50-50 wt % homop olymer blend of 7.8 x 10(3) PS and 5 x 10(3) PB, 0 less than or equal to c less than or equal to 0.251 g/mL. Measurements were performed for six temperatures ranging from -17.00 to 2.81 degrees C, and data were collected for frequencies from 1 Hz to 100 kHz. Previous extensive me asurements of solvent rotation in homopolymer PS/A1248 and PB/A1248 so lutions have established that PS acts to retard, and PB to accelerate, the solvent relaxation. Thus, in the multicomponent solutions examine d there is competition between the effects of the different segments, and the results of this competition give insight into the length scale associated with the influence of the polymer on the solvent dynamics. In the block copolymer and blend solutions, the distribution of solve nt relaxation times is very broad, demonstrating that the solvent dyna mics are spatially inhomogeneous. The results are qualitatively consis tent with a combination of the separate influences of PS and PB, but i n general the PB component exerts a stronger influence on the solvent. Computer simulations were employed to extract an estimate of the corr elation length associated with the influence that a given polymer segm ent has on the solvent dynamics; the results are consistent with a cor relation length of approximately one solvent diameter.