Surface Engineering of Halloysite with Graphene Oxide Via Primary and Secondary Forces, Characterizations, and Electrokinetic Properties

The functionalization of halloysite nanotubes (HNT) with graphene oxide (GO) can improve the electroactive smart behavior such as electrorheology, which is the fibrillation of dispersed particles inside an insulating oil under externally applied electric field. Therefore, it is important to reveal electrokinetic properties of HNT/GO composites in aqueous and non-aqueous media. In this study, two types of composites, (HNT/GO)PF and (HNT/GO)SF, were prepared by the modification of HNT surfaces with GO through different molecular interactions namely: primary and secondary. Their differences were illuminated by series of techniques such as DLS, ATR-FTIR, Raman, XPS, XRD, SEM, TEM, and TGA analyses. Further electrokinetic studies in an aqueous media were carried out to expose the changes in surface charges by measuring zeta(ζ)-potentials under different pH, electrolytes, surfactants, and temperature conditions. The results revealed that the surfaces of HNT/GO composites are dominated characteristically with GO and HNT for (HNT/GO)PF and (HNT/GO)SF, respectively. The ζ-potentials, electrophoretic mobilities and conductivities of the composites in aqueous and non-aqueous media were also studied to identify the dispersed particles behaviors. The results exhibited that electric field induced electroactive behaviors might differentiate in dispersions due to the higher electrophoretic mobility of (HNT/GO)PF and the higher conductivity of (HNT/GO)SF.