Reactive Molecular Dynamics Study of Hygrothermal Degradation of Crosslinked Epoxy Polymers

Abstract

Epoxy thermosets are often exposed to high humidity environments in various applications, undergoing reversible and irreversible degradation depending on the environment. This study presents a reactive molecular dynamics (MD) simulation framework to gain deeper insights into the hygrothermal aging process, which is essential to develop a targeted approach to combat water-assisted degradation in epoxy thermosets. By applying ReaxFF potential, an epoxy−amine network is created at low temperatures to avoid unwanted hightemperature side reactions, where the water molecules are added to achieve the desired degree of moisture contamination. The simulations show that in addition to the plasticization effect from the moisture ingress, the epoxy network shows recovery in mechanical properties and density due to the multi-site interaction of the water molecule with the electronegative sites within the network. Moreover, long-term exposure to humidity or direct exposure due to cracking can induce irreversible changes in the epoxy−amine network. The protonation of the water molecule and nucleophilic attack on the C−O bond of the ether linkages in the epoxy−amine networks are successfully simulated by applying reactive MD simulations. Remarkably, the simulations show that the selectivity of water molecules for the hydrolysis reaction in the epoxy network depends on the spatial arrangement and the steric hindrance of the network. This work provides molecular level insights into hygrothermal aging by elucidating the interplay between free volume and polarity of the network in the physical aging of the moist epoxy networks, paving a way for advanced design strategy toward better durability and performance of epoxy thermosets in humid environments.

Atomic surface achieved through a novel cross-scale model from macroscale to nanoscale

“…35,36 As a type of extension, reactive force field-molecular dynamics (ReaxFF-MD) breaks through the classic system and introduces a description of the chemical reactions into the potential function by introducing the relationship between the bond order and potential function. 37,38 The ReaxFF-MD method has been successfully applied for revealing the microscopic material-removal mechanism of different materials (Cu, fused silica, and diamond) under different working conditions. [39][40][41][42] However, the above studies are based on single sides of an aspect with significant scale limitations that do not allow for in-depth mechanism investigations.…”

Thermodynamics of Tri- and Tetraepoxyimidazolium NTf2 Amine Polyaddition: A Theoretical Perspective

“…One method of adding molecular variation that can have effects on physical properties is altering the degree of cross-linking in polymers. , Cross-linking and its effects on epoxy–amine polymers have been heavily studied in many applications due to its ability to influence the polymer’s physical properties. , Covalent cross-linking has been previously seen to occur primarily from additions of two epoxy groups to a single amine group. , In the instance wherein there are more than two epoxy groups present in the epoxy monomer, there is also seen to be cross-linking occurring within the epoxy monomer, introducing an additional aspect of cross-linking to be possible . The level of cross-linking has been found to correlate to the physical behavior of the polymer, with more cross-linking generating a higher yield stress and elastic stiffness constant. , Highly cross-linked polymers have been previously utilized in applications which require a highly durable polymer even above a certain temperature, with high cross-linking shown to improve durability and glass transition temperature ( T g ) of polymers. , There are several methods to determine the degree of cross-linking occurring within a system, with experimental analysis of physical properties such as tensile testing and dynamic mechanical analysis. , Alternatively, there have also previously been many studies utilizing simulations implementing molecular dynamics to predict the degree of cross-linking. − These studies have been used to predict many physical properties of the cross-linked polymer, such as the glass transition temperature and Young’s modulus.…”

Combined Machine Learning, Computational and Experimental Analysis of the Iridium(III) Complexes with Red to Near-IR Emission

“…QSAR modeling has been successfully used to model structure and the ground state electronic property models for polymers, organic and inorganic materials, semiconductors, and organometallic complexes. [37][38][39] QSAR has been successfully applied to generate a toxicity model of organometallic complexes. 40 In another work, the relative binding affinity of diverse organometallic estradiol derivatives is also modeled using the QSAR approach.…”