Mesoscopic Heterogeneity in the Curing Process of an Epoxy–Amine System

Abstract

Epoxy resins are composed of a three-dimensional network formed by chemical reactions between epoxy and amino compounds, which plays an important role in the mechanical properties. Thus, to use epoxy resins in various applications, it is necessary to gain a better understanding of their network structure. Here, we study the structural heterogeneity evolved in an epoxy−amine mixture during the curing process on the basis of a particle tracking technique, in which the thermal motion of probe particles in the mixture was tracked, small-angle X-ray scattering measurements in conjunction with coarse-grained molecular dynamics simulation. The heterogeneous environment was generated even at the initial stage of the curing process. Notably, the characteristic length scale was on the order of several hundreds of nanometers down to several tens of nanometers, depending on the extent of curing. Once a reaction occurs between a pair of epoxy and amino groups, the temperature at the site is locally elevated due to the heat of formation, accelerating a subsequent reaction nearby. Repeating such a situation, actively and scarcely reacted domains are formed. This is the main origin of the structural heterogeneity in epoxy resins.

Biphasic epoxy-ionic liquid structural electrolytes: minimising feature size through cure cycle and multifunctional block-copolymer addition

“…The SANS data are consistent with models developed for cross-linked polymer gels [35][36][37][38] and later applied to thermosets [39][40][41][42]. Thus, the total scattering is given by the sum of two separate contributions: I(Q) tot = I(Q) L + I(Q) S due to small structures at high Q, I(Q) L , and large structures, I(Q) S , at low Q.…”

Heterogeneous dynamics in the curing process of epoxy resins

“…Future studies are needed to investigate the dynamics of these various epoxy resins to provide a more general insight. Moreover, although we used the nanoparticles having diameters of 120 nm in the present study, it has been reported in particle-tracking measurements of the curing process of an epoxy-amine mixture that the particle size can affect particle movement 53 . Thus, it will be interesting to analyze the size dependence of probe particles.…”

Molecular Size Effect on Curing Process for Epoxy and Amine Mixture

“…Although the ∆E a value depends on the combination of epoxy and amine, the current objective is to gain insight to the effect of molecular size. Hence, the values obtained experimentally in the previous studies were here used [28][29][30] . That is, the values for the 1 st and 2 nd reactions were 56.8 and 55.3 kJ‧mol −1 , respectively.…”

“…The heat generated by the reaction was taken into consideration by raising the kinetic energy of molecules involved in the reaction. The value of heat of formation, 58.6 kJ‧mol −1 , which was obtained in previous experiments was set for the both reactions [28][29][30] .…”

“…The distance at which the reaction possibly occurs has been often set to 0.4 to 0.6 nm 23,[26][27][28] . However, the effect of the reaction distance on the progress of curing process seems to be not discussed.…”