Molecular weight estimation of cellulose in ionic liquid solution by fitting dynamic viscoelastic data to Rouse Model

As a molecular weight (M) estimation method for cellulose in ionic liquid solution, fitting procedure of dynamic viscoelastic data to Rouse-Zimm (RZ) model with a correction term (LT term), introduced by Osaki et al. and examined for standard polystyrene samples, is examined in this study. Since the RZ model calculation with and without LT term for loss modulus G" almost coincide, the data are first fitted to RZ model to get the best fit of G″ by using M as a single fitting parameter, while fixing other parameters from experimental conditions and using experimentally determined relaxation time τ_RZ. Then the LT term, calculated from intrinsic viscosity [η] and two adjusting parameters, is employed to judge the appropriateness of the estimation of molecular weight by further fitting storage modulus G'. The measured G' and G" can be well fitted with RZ model plus LT term in the terminal region though small discrepancy in the transition region was observed. The estimated M showed ±10% error due to ±15% error of τ_RZ. It is concluded that this procedure is useful when τ_RZ can be determined within a small error. The estimated M can be used at least for the comparison of cellulose/IL solutions differently prepared.