ORIENTATION FLUCTUATIONS IN CONCENTRATED-SOLUTIONS OF HAIRY-ROD POLYMERS

Photon correlation spectroscopy in the depolarized geometry was employed to measure the orientation relaxation correlation function C(q,t) in poly(p-2,5-dodecyl-1,4-phenylene)/toluene solutions at different scattering wavevectors q. The large optical anisotropy of this hairy rod molecule with an average length L = 117 nm allowed a detailed analysis of both amplitude and shape of C(q,t) that revealed two mechanisms for relaxing the orientation fluctuations in the concentrated regime (10 < cL(3) < 230). The comparison of the rotational diffusivity and the anisotropic scattering intensity with theoretical, simulation and experimental results of rigid rods indicated quantitatively different behavior for the present stiff-chain bearing two long side groups per repeating unit.