A hybrid Brownian Dynamics model for yielding, aging, and rejuvenation in deforming polymeric glasses

We describe the rheology of polymeric glasses by combining a simple constitutive equation for the fast segmental modes, borrowed from Fielding, et al.[1], with Brownian dynamics (BD) simulations of the slow polymer modes. The BD simulations determine the polymeric stress from ensembles of finitely extensible bead-spring chains, where the bead drag coefficient is governed by solutions to the equation for segmental relaxation. Thus the model treats the short glassy segmental mode as ``solvent'' for the polymer modes. With rubbery modulus for the slow-relaxing polymer modes as one of our model parameters, stress-dependent relaxation, physical aging, flow rejuvenation as well as strain-hardening and recovery can be successfully accounted for in uniaxial extension and steady shear, without the use of an artificial ``crinkle factor'' used to account for recoil dynamics in previous work [1]. Our simulation results remarkably agree with the experimental data from Lee et al.[2] A comparison between our model and the barrier-hopping theory [3] is also made.\\[0pt] [1] Fielding, S.M.; Larson, R.G.; Cates, M. E. Simple model for the deformation-induced relaxation of glassy polymers. Physical Review Letters, 2012, 108, 048301. [2] Lee, H-N.; Paeng, K.; Swallen, S.F.; Ediger, M.D. Direct measurement of molecular mobility in actively deformed polymer glasses. Science, 2009, 323, 231-234. [3] Chen, K.; Schweizer, K.S. Theory of relaxation and elasticity in polymer glasses. The Journal of Chemical Physics, 2007, 126, 014904.