A classical problem revisited: rheology of nematic polymer monodomains in small amplitude oscillatory shear |
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Authors: | Eric P Choate M Gregory Forest |
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Institution: | (1) Department of Mathematics, University of North Carolina, Chapel Hill, NC 27599-3250, USA |
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Abstract: | We revisit the classical problem of the viscoelastic response of nematic (liquid crystal) polymers to small amplitude oscillatory
shear. A multiple time scale perturbation analysis is applied to the Doi–Hess mesoscopic orientation tensor model to describe
key features observed of longtime experiments, both physical (Moldenaers and Mewis, J Rheol, 30:567–584, 1986; Larson and Mead, J Rheol, 33:1251–1281, 1989b) and numerical (herein). First, there is a very slow time scale drift in the envelope of oscillations of the major director;
we characterize the mean director angle and the envelope of oscillation. Second, there are bistable asymptotic orientational
states, distinguished in that they are precisely the zero-stress orientational distributions noted in Larson and Mead (J Rheol,
33:185–206, 1989a). Third, the drift dynamics and asymptotic mean director angle are determined by the initial orientation of the director,
not by material properties; we characterize the domain of attraction of each bistable state. Finally, the director drift leads
to a predicted longtime decrease in the storage and loss moduli, consistent with experimental observations.
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