Ionic thermal current study of the α′ process in poly(hexamethylene adipamide)

The ionic thermoconductivity (ITC) method has been used to study the α′ transition in the polyamide \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \hbox{--}\rlap{--} NH(CH}_{\rm 2} )_6 {\rm NH}\hbox{---} \rm CO(CH_2 )_4 {\rm CO\hbox{--}\rlap{--} ]}_{{\rm x}} $\end{document} (nylon 66). Depending on the thermal history of the sample, the maximum of the thermocurrent peak attributed to the α′ relaxation is found somewhere between ca. 45°C and ca. 66°C; on one heating, it shifts to higher temperatures. The high sensitivity and resolving power of the ITC method permit resolution of this peak into four elementary “pure” activated processes, with constant activation energies in the relevant temperature range. Each of the four corresponding relaxation times follows an Arrhenius law, with a well-defined characteristic temperature T₀ = 83°C at which all these relaxation times are equal. When this last result is interpreted in the light of Eyring's or Bauer's theory, it gives a linear relation between “apparent” activation entropy and activation enthalpy of the elementary processes. The characteristic temperature T₀ is independent of the thermal history of the sample, and the temperature shift of the thermocurrent maximum can be interpreted by the observed variation of the relative intensities of the elementary processes, without modification of their other characteristic features.