Pretransitional orientational ordering of rigid-rod polymers in shear flow

We present the results of our experimental and theoretical study of the orientational ordering of rigid-rod-like polymers in the presence of shear flow. Shear-induced birefringence was measured to determine the dependence of the orientational order parameter S=〈3 ${\cos }^2$θ-1〉/2 on the shear rate for rod volume fractions below the critical value at which spontaneous ordering at zero shear appears. Experimental results are discussed in terms of an approximate solution of the rotational diffusion equation in the presence of shear flow based on the construction of the effective interaction energy.