Rheology of ethyl cellulose solutions

Steady state flow and dynamic viscoelastic measurements of ethyl cellulose / m-Cresol solutions reveal the existence of an isotropic and anisotropic phase, as well as a biphasic interval. The effect of the applied shear rate is to shift the anisotropic phase to lower concentrations. The anisotropic phase, which is found from 20 wt.-% polymer concentration, is characterized by the following features: A) Three flow regions, pseudoplastic, Newtonian and pseudoplastic, respectively, are observed in $ eta - dot gamma _{21} $ plots but not in η* - ω plots, b) “Grainy” and “thread” textures correspond to regions I and II respectively, c) Activation energies of flow are similar to that of the pure solvent, d) Both dynamic viscoelastic functions G′ and G″ scale with frecuency as ω^0.75, a dependence already observed in complex liquids, like heterogeneous block copolymers. On the other hand, dynamic viscoelastic measurements performed with isotropic systems allow to determine the entanglement modulus and the associated molecular weight between entanglement couplings, M_e⁰=7830.