Molecular Size Effect on Curing Process for Epoxy and Amine Mixture

Abstract

The curing process of epoxy and amine mixtures was investigated from the viewpoint of molecular size of reactants via all-atom molecular dynamics simulation. Of four mixtures composed of either smaller or larger epoxy and amine molecules, the system of both smaller epoxy and amine reached the highest conversion at a given time, whereas the conversion for the combination of both larger epoxy and amine was the lowest. These can be explained in terms of their diffusion coeffi cients. In addition, the size effect on the reaction kinetics was more striking for epoxy than amine in the curing process. This was because epoxy reacted only once but amine did twice. When the primary amine reacted with epoxy, the resultant secondary amine was incorporated into the three-dimensional network. Hence, even if the primary amine had a higher mobility, the movement of the part after the reaction slowed down, making the further reaction to be the tertiary amine slow. Finally, it was shown that although the smaller epoxy reacted faster than the larger one in the mixed system of larger/smaller epoxy and amine, there was no difference in the reaction progress depending on the molecular size of amine.

Addressing diffusion behavior and impact in an epoxy–amine cure system using molecular dynamics simulations

“…From this perspective, the diffusion coefficients of TGAP decreased more than those of DGEBF with increasing crosslinking conversion ratio. These results show a similar trend as previously reported diffusion coefficients associated with amine and epoxy resins 42 . In region III, where the crosslinking conversion ratio is greater than 60%, the diffusion coefficients of DGEBF and TGAP converge to zero because not only DGEBF but also TGAP can react to form three-dimensional crosslinks with the amine group of 3,3′-DDS.…”

“…Based on the above explanations, MD simulation can computationally image diffusion properties of components in the epoxy system and thermal properties as changing crosslinking conversion ratio and curing temperatures. Especially, the detailed diffusion properties of epoxy resin and curing agents with different sizes and molecular weights can calculate during the curing reaction 42 . Therefore, we constructed epoxy systems that contained two types of epoxy resin, a curing agent, and a toughening agent; then changed the temperature and conversion ratio on the basis of the MD simulation approach to elucidate their diffusion properties.…”

Network Formation and Physical Properties of Epoxy Resins for Future Practical Applications

“…We studied the effect of the molecular size of epoxies and amines on the reaction kinetics. 146 In the combination of larger and smaller molecules of epoxy and amine, it was seen that the smaller the epoxy the faster the reaction. This is because when a primary amine reacts to become a secondary amine it is incorporated into the network, so that even if the initial diffusion is fast, the movement becomes slow.…”

“…We studied the effect of the molecular size of epoxies and amines on the reaction kinetics . In the combination of larger and smaller molecules of epoxy and amine, it was seen that the smaller the epoxy the faster the reaction.…”

Effects of Chemistry of Silicon Surfaces on the Curing Process and Adhesive Strength for Epoxy Resin

“…The curing reaction in the epoxy-amine system was carried out using the methods reported previously . When an epoxy group and an amino group come close within a reaction distance of 0.6 nm, the Arrhenius-type reaction probability consisting of E a , the local temperature, and the acceleration factor becomes larger than a generated random number [0,1], and the reaction is permitted. − In previous calculations for the bulk system, the reaction distance was set to 0.4 nm . However, because the reaction was suppressed near the interface, the reaction progress was very slow and thereby no gelation took place within the simulation time.…”