Yamamoto Satoru, Tanaka Keiji
Centre for Polymer Interface and Molecular Adhesion Science, Kyushu University, Fukuoka 819-0395, Japan.
Soft Matter. 2021 Feb 15;17(5):1359-1367. doi: 10.1039/d0sm01600d.
The composition of an epoxy resin at the interface with the adherend is usually different from that in the bulk due to the enrichment of a specific constituent, a characteristic called interfacial segregation. For better adhesion, it should be precisely understood how epoxy and amine molecules exist on the adherend surface and react with each other to form a three-dimensional network. In this study, the entropic factor of the segregation in a mixture of epoxy and amine at the copper interface before and after the curing reaction is discussed on the basis of a full-atomistic molecular dynamics (MD) simulation. Smaller molecules were preferentially segregated at the interface regardless of the epoxy and amine, and this segregation remained after the curing process. No segregation occurred at the interface for a combination composed of epoxy and amine molecules with a similar size. These findings make it clear that the size disparity between constituents affects the interfacial segregation via the packing and/or translational entropy. The curing reaction was slower near the interface than in the bulk, and a large amount of unreacted molecules remained there. Finally, the effect of molecular shape was also examined. Linear molecules were more likely to segregate than round-shaped ones even though they were similar in volume. We believe that these findings, which are difficult to obtain experimentally, contribute to the understanding of the interfacial adhesion phenomena on a molecular scale.
由于特定成分的富集，环氧树脂与被粘物界面处的组成通常与本体中的组成不同，这种特性称为界面偏析。为了实现更好的粘附，需要精确了解环氧树脂和胺分子如何存在于被粘物表面并相互反应形成三维网络。在本研究中，基于全原子分子动力学（MD）模拟，讨论了固化反应前后铜界面处环氧树脂和胺混合物中偏析的熵因素。无论环氧树脂和胺如何，较小的分子优先在界面处偏析，并且这种偏析在固化过程后仍然存在。对于由尺寸相似的环氧树脂和胺分子组成的组合，界面处未发生偏析。这些发现表明，组分之间的尺寸差异通过堆积和/或平移熵影响界面偏析。界面处的固化反应比本体中慢，并且大量未反应的分子留在那里。最后，还研究了分子形状的影响。即使线性分子和圆形分子体积相似，线性分子也比圆形分子更容易偏析。我们相信，这些难以通过实验获得的发现有助于从分子尺度上理解界面粘附现象。
