Structure, microparameters and properties of crosslinked DGEBA/MTHPA: A molecular dynamics simulation

Abstract

Investigating the relationship between microstructure and macroscopic properties of epoxy resin (EP) materials for high-voltage insulation at the molecular level can provide theoretical guidance for the synthetic design of EP. Here, using diglycidyl ether (DGEBA) as the resin matrix and methyl tetrahydrophthalic anhydride (MTHPA) as the curing agent, a set of crosslinked EP molecular models at different curing stages were constructed based on the proposed crosslinking method. We studied the influences of crosslinking density on micro-parameters and macro-properties employing molecular dynamics (MD) simulations. The results indicate that crosslinking of DGEBA/MTHPA is a contraction and exothermic process. The structural parameters and macroscopic properties are closely related to the degree of crosslinking. With the increase of crosslinking density, the mean square displacement (MSD) of the system decreases, and the segment motion in the models is weakened gradually, while, the fractional free volume (FFV) first decreases and then increases. In addition, the thermal and mechanical properties of DGEBA/MTHPA have a significant dependence on the crosslinking density. Increasing crosslinking density can improve the glass transition temperature (Tg), reduce the coefficient of thermal expansion (CTE), and enhances the static mechanical properties of DGEBA/MTHPA system. Furthermore, the relationship between microparameters and properties has been fully investigated. Free volume is an important factor that causes thermal expansion of DGEBA/MTHPA. Moreover, there is a negative correlation between MSD and mechanical moduli. By elevating temperature, the decline in mechanical moduli may be due to the exacerbated thermal motion of the molecules and the increasing MSD values.

Molecular Dynamics Simulation and Experimental Studies on the Thermomechanical Properties of Epoxy Resin with Different Anhydride Curing Agents

“…The research results of [29] indicate the cell size had no large effect on the calculated properties, while [3,30] investigated the thermomechanical properties of epoxy resin using the small system (the amorphous cells containing 4, 8, 12 and 16 DGEBA). Meanwhile, to verify the accuracy of the model, the DGEBA/MTHPA system containing 40 DGEBA, 90 MTHPA and 10 DGEBA-MTHPA was constructed [31]. The T g of this system was 400.46 K at a crosslinking density of 89%.…”

“…(4) The script of the automatic crosslinking reaction program for epoxy resin/anhydride curing agent was written according to the mechanism of the acid anhydride curing reaction in Section 2.1.1, as shown in Figure 1. To simplify the process, the following assumptions were made [19,31]: (i) The step (1) in Section 2.1.1 was omitted, and the carboxyl in primary crosslinking structure reacted with the epoxy group as the initial reaction site. (ii) The reactivity of each reaction group was the same.…”

“…(iv) The reactions were synchronized. The flow chart of cross-linking reaction program [31] is shown in Figure 2c, where TCD , T , R n and R max are target crosslink density, temperature, truncation radius and maximum truncation radius, respectively. T was set at 300 K, and R n and R max were set at 3.5 and 7.5 Å, respectively.…”

Molecular dynamics study on thermal and mechanical properties of AOO modified DGEBA‐anhydride insulating materials for high voltage GIS

“…Within a certain error, the cross‐linked system can be regarded as an isotropic material, and thus the stiffness matrix can be simplified to the following equation 27 : From the simplified stiffness matrix, we can obtain the Lame constant λ and μ , and further obtain the mechanical property parameters of the cross‐linked system such as bulk modulus K , Young's modulus E , and shear modulus G . The equations are as follows 28 : The dynamics of the cross‐linked system at 298 K was simulated at 300 ps at each ratio. The last 10 conformations of the equilibrium structure of each model were selected for the calculation of the mechanical properties of the operation, and the mean elastic modulus was finally obtained.…”

“…From the simplified stiffness matrix, we can obtain the Lame constant λ and μ, and further obtain the mechanical property parameters of the cross-linked system such as bulk modulus K, Young's modulus E, and shear modulus G. The equations are as follows 28 :…”