An evaluation of the Larson-Doi model for liquid crystalline polymers using recoil

The mesoscopic models for the rheological properties of liquid crystalline polymers proposed by Larson and Doi in 1991 and Kawaguchi and Denn in 1999 are based on phenomenological expressions that describe the evolution of th e defect density and the contribution of the "texture" to the stress. In th e present work, we attempt to assess some of these assumptions by monitorin g how the energy stored in the texture of liquid crystalline materials evol ves during shear flows. For that purpose, strain recovery is measured as a function of the applied strain for flow reversal and intermittent flow. Sol utions of poly-benzylglutamate in nz-cresol, hydroxypropylcellulose in wate r and a nematic surfactant solution are used as model systems. Although the behaviour is described qualitatively by the model, discrepancies between t he predictions and the experiments are observed, especially when the shear history includes rest periods.