DYNAMICS OF HAIRY-ROD POLYMERS - SEMIDILUTE REGIME

Photon correlation spectroscopy was employed in both the polarized (VV ) and depolarized (VH) geometries in order to investigate the dynamics of concentration and orientation fluctuations of model hairy-rod poly (p-phenylenes) in semidilute solution. These materials possess a large inherent optical anisotropy, which allowed the unambiguous detection of orientation relaxation. By probing the dynamics in two solvents of different qualities, chloroform, a good solvent, and toluene, it was p ossible to distinguish nearly molecular from aggregate processes. Two modes were detected in the VV correlation function: the fast cooperati ve diffusion, D-c, which increased nearly linearly with concentration (D-c/D-o - 1 similar to c(0.9)), and a slow mode, D-slow, which slowed with concentration (D-slow similar to c(-1)). The latter process was assigned to the self-diffusion of small aggregates, as confirmed by in dependent pulsed field gradient NMR measurements. Broad VH correlation functions were obtained at high concentrations and revealed the prese nce of a dominant mode exhibiting a decay rate, Gamma(VH) which decrea sed with increasing q and concentration (Gamma(VH) similar to c(-0.25) ). This mode was assigned to orientational correlations in space, due to some local ordering of parts of the molecules. These findings canno t be accounted for by the existing theories.