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 m easurements are performed on poly(gamma-benzyl-alpha-L-glutamate) solutions over a nide concentration range. We interpret the primary dynamic decay ra te always observed from dynamic light scattering experiments by extending t he expression for the decay rate beyond the original limits of the mean fie ld (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 p ower 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 t hat at larger q contains contributions from both rotation and translation, including terms containing the translational anisotropy. The rotational rel axation times are obtained independently fi om the transient electric biref ringence experiments and are used in our formula to extract concentration d ependencies of the self-diffusion coefficients from the DLS time correlatio n functions at large scattering vector q. Finally, from the data at large q , we report the transverse and longitudinal translational self-diffusion co efficients as functions of concentration.