Isothermal curing of epoxy resins as seen by direct current and rheological measurements Summary-The investigations of epoxy-amine systems' curing were carried out by direct-current (DC) measurements in order to get better understanding of the evolutions of ionic conductivity and viscosity in the reactive medium. This study extends our earlier DC and ion mobility investigations (Time-of-Flight method) on this subject. The additional rheological examinations (Dynamic Mechanical Analysis) have allowed to determine the correlations between evolution of electric and viscoelastic properties such as dynamic viscosity. The experiments have been carried out for the epoxy-amine reacting system that gelates and vitrifies: diglycidyl ether of bisphenol A with 4,4'-methylenebis(3-chloro-2,6-diethylaniline) (DGEBA-MCDA) and for the reacting system that gelates only: diglycidyl ether of 1,4-butanediol with 4,9-dioxa-1,12-dodecane diamine (DGEBD-4D). An inconsistency between the time dependence of ionic conductivity and viscosity was explained by the fact that the concentration of the mobile ion charge carriers is decreasing with the advancement of reaction. This observation lead to the conclusion of limited application of the electric techniques for the direct in situ monitoring of chemical reactions.
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.
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