Interfacial Structure of Epoxy Resins on Amorphous Silica Surface under Dry and Wet Conditions

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  • Yamamoto Satoru
    Center for Polymer Interface and Molecular Adhesion Science, Kyushu University
  • Kuwahara Riichi
    Dassault Systèmes K. K.
  • Tanaka Keiji
    Center for Polymer Interface and Molecular Adhesion Science, Kyushu University Department of Automotive Science, Kyushu University Department of Applied Chemistry, Kyushu University International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University

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<p>In silica-filled epoxy resins, amorphous silica particles are generally covered with silanol groups on their surfaces, rendering them susceptible to moisture adsorption. Thus, the importance lies in better understanding the aggregation states of epoxy resins on the surface of amorphous silica and the influence of adsorbed water on the silica surface on the curing reaction. Here, we propose a method to generate amorphous silica by inserting oxygen atoms into the Si-Si bonds of amorphous silicon, serving as a model construction for molecular dynamics (MD) simulations. The surface structure of the silica was then extracted, and a mixture of an epoxy base (diglycidyl ether of bisphenol-A, DGEBA) and an amine hardener (4,4’-diaminodiphenyl sulfone, DDS) was placed on top of it. SO2 groups of DDS strongly adsorbed on the silica surface through hydrogen bonding and remained after curing, although this interaction was weakened due to the reduced degree of freedom caused by cross-linking. On the other hand, DGEBA did not exhibit such a strong interaction with the silica surface. After curing, OH groups generated by the ring-opening of epoxy groups formed slight hydrogen bonds with the silica surface. When a small amount of water was adsorbed onto the silica surface, it diffused slightly into the epoxy resin, enhancing the mobility of the reactants in the system, and consequently accelerating the curing reaction.</p>

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