Analysis of the α, β, and γ relaxations in polychlorotrifluoroethylene and polyethylene: Dielectric and mechanical properties

Theoretical models for the ac and γe relaxation effects found in chain-folded polymer crystals (single crystal mats and bulk) are presented and compared with the available dielectric and mechanical loss data for polyethylene and polychlorotrifluoroethylene. Details of morphology and crystal structure that can be varied by crystallization and annealing procedures, e.g., roughness of chain-folded surfaces, number of intercrystalline links and cilia, number of chain-end defects and dislocations, and the existence of the extended-chain phase, are brought into the discussion. The αc process, which consists of two overlapping mechanisms, is a result of motions of chain folds and reorientation (with translation) of chains in the interior. (Chain twisting also occurs for long chains.) The theory connects the data on the n-paraffins and their polar derivatives (n-ketones, esters, ethers) with the results on polymers: the common feature is the chain reorientation and twisting process. A new theory of chain twisting is introduced. The β relaxation is a result of reorientation of chains in a “loose” chain-end induced defect (a vacancy row) in the polymer crystal. When the effect of chain twisting is included, the theory successfully predicts the unusually broad and asymmetric loss curve found in the polymer, and is consistent with the experimental activation energies. The β relaxation arising in the amorphous component of PCTFTC is analyzed, and its upward shift in temperature with increasing crystallinity discussed in terms of the Adam-Gibbs theory of relaxation in the glassy state. The γa amorphous relaxation, and the δ relaxation which is found at cryogenic temperatures, are also discussed.