Molecular Simulation Of Amine-cure Epoxy Resins That Modified By Side Chains

The excellent thermodynamic properties of epoxy resin are derived from the three-dimensional network structure that formed by epoxy resin and curing agent,but its brittleness is also from the network structure that can restrict the movement of the internal chain segments.Compared with the traditional toughening method of introducing the second phase particles,the method by introducing side chains into the network can effectively avoided the damage to the network structure,which can increase the toughness and modulus synchronously.However,due to the complexity of epoxy resin network and the limitations of current experimental characterization methods,it is still unclear how the side chain realizes the simultaneous improvement of modulus and toughness.In our work,the molecule dynamic simulation is employed to learn the mechanism of simultaneous improvement of modulus and toughness.A series of amine-cured epoxy resin systems with side chains was constructed,the relationship between microstructure and macroscopic performance were established through the analysis of radial distribution function,energy,free volume,mean square displacement,crosslink density,modulus and other parameters,and it's found that the increase in toughness was caused by the decrease of crosslink density,while the increase in modulus was derived from The decrease in free volume and free volume fraction that caused by side chain aggregation.Firstly,a series of amine cured epoxy resins systems with different contents of single-end aliphatic amine chains was established by all atom molecular dynamic simulation.The aggregation of single-end aliphatic amine was confirmed by the radial distribution function,which was caused by the minimization of system energy and the incompatibility of the single-ended aliphatic amine chains with the network;it is found that the aggregation of the single-ended aliphatic amine can effectively reduce the free volume and free volume fraction of systems,the reduction of free volume and the free volume fraction directly leads to an increase in the modulus.Then,the ratio of epoxy resin to side was fixed and the relationship between the modification effect and the length of single-end fatty amine was explored by changing the length of single-end fatty amine.It was found that single-end fatty amines showed different "stiffness" and "flexibility" due to their different lengths in the highly cross-linked system.When the side chains were "soft",strong bond spin makes the side chains spontaneously adjustment themselves in a small range,which was advantageous for the reduction of free volume and free volume fraction.The change of free volume will lead to the difference of system modulus,and the increase in length of side chain was not conducive to the improvement of system modulus.Finally,the effect of curing agent with different rigidity and flexibility was explored by changing the rigidity and flexibility of curing agent.It was found that the stronger the rigidity of the curing agent,the better the modulus was improved when the length is matched with the side chain.This research breaks through the restrictive relationship between the modulus and toughness in the three-dimensional epoxy resin network,and provides a good theoretical support for the design and preparation of high-modulus and high-toughness epoxy resin,which has a good guiding significance.