||Relaxation Dynamics of the Normal Stress of Polymer Gels
Yamamoto, Tetsuya ,
Masubuchi, YuichiDoi, Masao
5213 , 2017-09-26 , ACS Publications
We use the two-fluid model to theoretically predict the relaxation dynamics of the normal stress of a gel, which is twisted by a rotational rheometer in the parallel plate geometry. We derive the equations of motion of solvent and polymer network by using an expansion of the free energy of the statistical thermodynamic model of polymer gels by the leading order nonlinear terms and solve these equations in the spirit of the lubrication approximation. Our theory predicts that the normal stress of the gel decreases exponentially with time due to the redistribution of solvent. The time scale of the normal stress relaxation scales with the square of the distance between the plates because the solvent redistribution results in the parabolic distribution of network displacements between the plates.