Plastic relaxation via twist disclination motion in polymers

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Abstract
Measurements of the internal friction in polymers exhibit a spectrum of peaks at low temperatures that are related to the plastic behavior at higher temperatures. This manuscript deals with a particular supramolecular defect that behaves mechanically in a manner consistent with the observations. The defect is a twist disclination consisting of two molecules that cross over one another. The energies of formation and motion for the twist disclination are calculated in terms of the width of the twisted region, the displacement that is produced by the twist, the molecular radius, and the elastic stiffnesses of the molecules. For motion to occur dilatations caused by contour modulations of the molecules must be overcome. This effect yields expressions for the motion activation energy and stress for nonactivated motion. It is shown that molecular bending occurs more readily by elastic deformation than by conformation-change deformation unless the radius of curvature is less than a critical value (of the order of atomic dimensions).

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