Aqueous-Based Functionalizations of Titanate Nanotubes: A Straightforward Route to High-Performance Epoxy Composites with Interfacially Bonded Nanofillers

Nanotube surface treatment is crucial in preparation of high-quality nanomaterials for advanced applications. Herein, we provide an environmentally friendly and practical route to the design of high performance composites using the surface chemistry of titanate nanotubes (TiNT) to enhance the interfacial nanotubeepoxy bonding. Insights presented here improve understanding of how different organic layers (a low-molecular-weight bisphosphonate (APMBP), branched polyethylenimine (PEI), or polydopamine (PDA)) coated on TiNT surface and bearing active hydrogen functionalities (NH, OH) affect epoxyamine cross-link reaction and network buildup and consequently morphology and thermomechanical properties of the final epoxyTiNT composites. The kinetics of cross-linking was experimentally studied and successfully fitted by a mechanistic kinetic model, which considered the effects of NH and OH functionalities. We found that APMBP was not involved in the epoxyamine cross-link reaction entering only into physical interactions with epoxy precursors, while the PEI and PDA modifications of TiNT accelerated cross-linking and formed covalent linkages with the epoxy network. All functionalizations improved dispersion of TiNT in the epoxyamine matrix. The prepared epoxy/TiNT composites showed a dramatic increase in the rubbery storage modulus (up to +92%) and an excellent thermal stability with the onset degradation temperature of similar to 400 degrees C. This study demonstrates that TiNT functionalized with fully aqueous-based protocols are promising alternatives to carbon nanotubes in epoxy composites.