Paradoxical Role of an Organic Modifier in Enhancing Interfacial Strength of a Polymer Coating on Clay

The interfacial strength between a clay substrate and a polymer coating develops with contributions from factors at different length scales. At molecular length scale, the primary contribution comes in the form of chemical interactions and physical interactions, such as hydrogen bonding, van der Waals, and electrostatic interaction. The major contributing factors at the micron length scale are in the form of surface roughness, voids, and other mechanical interlocking. Although rare, sometimes a contribution from one length scale can potentially inhibit a positive contribution from another length scale in the development of interfacial strength. In this work, we demonstrate how organic modification of clay, which is intended to turn clay more organophilic, hinders or negatively corelates with the contribution from micron scale pores toward building the interfacial strength between clay and epoxy coating. The motivation behind using organic modifiers originates from the fact that clays are treated with organic modifiers to enhance their interaction with polymer in a polymer-clay-nanocomposite (PCN). We investigate the underlying mechanisms behind this negative correlation by applying different experimental techniques, such as Mercury Intrusion Porosimetry (MIP), Fourier Transform Infrared Spectroscopy (FT-IR), contact angle meter, and others. This study brings out the predominant role of impregnated polymers in developing interfacial strength in clay-polymer coating.