Viscometric behavior of mesomorphic ethyl cellulose solution in chloroform

A simple modification of the viscometer used to determine the viscosity of concentrated solutions is described which permits the ready measurement of viscosity versus shear rate behavior above room temperature. Basic experimental viscometry was performed on the ethyl cellulose–chloroform system using a B‐type (Brookfield‐like) rotating‐cylinder viscometer. Data are compared with theoretical predictions. The flow curves exhibit yield stress at low shear rate. The yield stress is dependent on concentration and temperature. The viscosity versus concentration curves show typical mesomorphic behavior. The concentration dependences of viscosity and yield stress are similar. The critical concentration increases with temperature. In the single‐phase region (isotropic or anisotropic state) the viscosity decreases with temperature and the apparent activation energy (Ea) for flow is positive, but in the biphasic range the viscosity increases with temperature andEais negative. The experimental results for the critical concentration appear to agree with Flory's theory of rodlike molecules when the ratio of persistence length to diameter of the chain is taken as the aspect ratio.