Physicochemical changes in epoxy-amine systems studied by ionic conductivity and ionic carriers mobility measurements

Abstract

Physicochemical changes in epoxy-amine systems studied by ionic conductivity and ionic carriers mobility measurements Summary-The main objective of this work was to find the correlations between the ionic conductivity, viscosity and physicochemical changes occurring during the isothermal cure of the epoxy-amine systems. The studies of the ionic conductivity evolutions have been performed using dielectric and direct-current techniques. The measurement data were compared with the ion mobility values evaluated from the time-of-flight investigations and with the dynamic viscosity determined by dynamic mechanical analysis. Different epoxy-amine reacting systems have been analyzed: the diglycidyl ether of bisphenol A with diamino-4,4'-dimethyl-3,3'-dimethyldicyclohexylmethane (DGEBA-3DCM) which gelates and vitrifies during the cure and the diglycidyl ether of 1,4-butanediol with 4,9-dioxa-1,12-dodecane diamine (DGEBD-4D) which only gelates during its polycondensation. It was found that even with an appearing of gelation or viscoelastic properties the conduction process could be described as thermally activated. The inconsistencies between ionic conductivity and ion mobility evolutions indicate that the concentration of the mobile charge carriers in the medium changes during the reaction. It was also observed that the vitrification could be responsible for the large changes of free volume in the system influencing the ionic conduction mechanism and therefore the ionic conductivity evolutions. It was also found that the Stokes's law is fulfilled at the beginning of the cure only.

Glass transition temperature-temperature-property (TgTP) diagram for EPY epoxy system

“…Epoxy resins are the most important thermosetting polymers, widely used as structural adhesives, composite materials, surface coatings, electronic devices [1][2][3][4][5]. The chemical reactions occurring during the cure of epoxy resins cause physical changes associated with the two distinct macroscopic transitions of gelation and vitrification [6][7][8].…”