石蜡强韧化环氧树脂体系的试验结合分子动力学模拟研究

Strengthening-toughening epoxy resin system with paraffin:an experimental and molecular dynamics simulation study

通过硫醇-烯点击化学合成了一种具有柔性烷基侧链的特种环氧树脂(D12),随后利用其作为增容剂,将正二十烷(C20,石蜡模型化合物)均匀混合到环氧树脂基体(DGEBA)中,固化得到一系列D12和C20协同增韧的环氧树脂体系(EPDA-X体系)。通过结合试验和分子动力学模拟方法,系统研究了DGEBA/D12/C20三元体系的强韧化机理。研究结果表明:(1)当D12和C20的物质的量比为1∶2且二者在固化体系中的质量分数为2.5%时,体系具有最优异的综合性能,拉伸强度为99.3 MPa,拉伸模量为2.8 GPa,断裂伸长率为4.5%。三者均高于纯EP体系,实现了环氧树脂强度、模量和韧性的协同提升。(2)EPDA-X体系中存在微相分离结构,且初步证明体系中的微相分离结构是由C20在D12侧链周围自组装引起的。自组装效应所形成的物理缠结结构可以为体系提供额外的物理交联点,从而可以实现环氧树脂强度、模量和韧性的协同提升。(3)使用分子动力学模拟计算了所有体系的杨氏模量,发现EPDA-X体系的模量均高于纯EP体系。EPDA-X体系径向分布函数的计算结果表明,C20与D12的主链相互作用很弱,但与D12的侧链相互作用很强。这进一步证明了C20在D12的侧链周围发生了自组装效应,从而在分子和原子尺度上证明了C20和D12自组装协同强韧化环氧树脂的机理。

A special epoxy resin(D12)with flexible alkyl side chains was synthesized through thiol-ene click chemistry,and then using it as a compatibilizer,n-eicosane(C20,paraffin model compound)was uniformly mixed into the epoxy resin matrix(DCEBA).A series of D12 and C20 synergistic toughening epoxy resin systems S(EPpA-X systems)were obtained by curing.Thestrengthening-toughening mechanism of DGEBA/D12/C20 ternary system was systematically studied by combining experimental and molecular dynamics simulation methods.The research results showed that,(1)When the mass ratio of D12 and C20 was 1:2 and their mass fraction in the curing system was 2.5%,the system had the best comprehensive performance,with the tensile strength of 99.3 MPa,the tensile modulus of 2.8 CPa,and the elongation at break of 4.5%.All three were higher than the pure EP system,achieving a synergistic improvement in the strength,modulus,and toughness of epoxy resin.(2)There was a microphase separation structure in the EPpa-x system,and it had been preliminarily proven that the microphase separation structure in the system was caused by the self-assembly of C20 around the D12 side chain.The physical entanglement structure formed by the self-assembly effect could provide additional physical crosslinking points for the system,thereby achieving a synergistic improvement in the strength,modulus,and toughness of epoxy resin.(3)Molecular dynamics simulation was used to calculate the Young's modulus of all systems,and it was found that the modulus of EPpA-x system was higher than that of the pure EP system.The calculation results of the radial distribution function of EPpa-x system indicated that the main chain interaction between C20 and D12 was weak,but the side chain interaction with D12 was strong.This further confirmed the selfassembly effect of C20 around the side chains of D12,thereby proving the mechanism of synergistically strengthening-toughening of epoxy resin by C20 and D12 self-assembly at the molecular and atomic scales.