Rotational and Translational Dynamics of Rodlike Polymers: A Combined Transient Electric Birefringence and Dynamic Light Scattering Study

Dynamic light scattering (DLS) and transient electric birefringence decay measurements are performed on poly(γ-benzyl-α- l -glutamate) solutions over a wide concentration range. We interpret the primary dynamic decay rate always observed from dynamic light scattering experiments by extending the expression for the decay rate beyond the original limits of the mean field (DSO theory) theory of Doi, Shimada and Okano, ( J. Chem. Phys. 1988, 88, 4070) to more general time and length scales. Our result, expressed as a power series in the scattering vector magnitude q, shows that, as expected, the primary decay rate from dynamic light scattering experiments at small q directly provides diffusion coefficients for mutual translation, whereas that at larger q contains contributions from both rotation and translation, including terms containing the translational anisotropy. The rotational relaxation times are obtained independently from the transient electric birefringence experiments and are used in our formula to extract concentration dependencies of the self-diffusion coefficients from the DLS time correlation functions at large scattering vector q . Finally, from the data at large q, we report the transverse and longitudinal translational self-diffusion coefficients as functions of concentration.