Abigail Advincula1,2,Justin Brackenridge3,1,Philip Barnett4,Christopher Muratore3,Madeline Buxton5,Vladimir Tsukruk5,Yury Gogotsi6,Dhriti Nepal1
Air Force Research Laboratory1,ARCTOS2,University of Dayton3,University of Tennessee Knoxville4,Georgia Institute of Technology5,Drexel University6
Abigail Advincula1,2,Justin Brackenridge3,1,Philip Barnett4,Christopher Muratore3,Madeline Buxton5,Vladimir Tsukruk5,Yury Gogotsi6,Dhriti Nepal1
Air Force Research Laboratory1,ARCTOS2,University of Dayton3,University of Tennessee Knoxville4,Georgia Institute of Technology5,Drexel University6
Organic-inorganic hybrid structures found in nature, e.g., nacre (“mother-of-pearl”), are often remarkably tough and exhibit multi-functional properties due to highly ordered arrangements of organic and inorganic components in such structures at the nanometer-to-micron length scale. Inspired by these hierarchical biological structures, this work details our efforts to fabricate a hybrid composite of ordered, alternating layers of organic vitrimer polymer and inorganic MXenes. Vitrimers, as a new class of polymers, ideally exhibit thermoset-like behavior at lower temperatures and thermoplastic-like reformability at higher temperatures due to their permanent yet dynamic polymer networks. MXenes, as a class of inorganic two-dimensional (2D) transition metal carbides and nitrides, exhibit excellent metallic conductivity, good transparency in the visible wavelength range, and high photon-to-phonon conversion efficiency. <br/><br/>In this work, we demonstrate the fabrication of highly ordered, ultra-thin (nearly single to a few layers) MXene films onto thin, free-standing sheets of vitrimer, yielding electrically conductive, highly transmissive vitrimer-MXene sheets for self-healing coatings and multi-functional composites. Large area (20 x 20 cm), thin (<65 µm) free-standing vitrimer sheets are first obtained utilizing industrially-relevant compression molding techniques. Thermomechanical testing (TGA, DSC, DMA, TMA, micro-indentation) indicates excellent spot-to-spot consistency in the fabricated sheets. Subsequently, a thin film of MXene is deposited onto the vitrimer sheet surface using an advanced deposition technique that leverages Rayleigh-Benard convection and the Marangoni effect. Surface morphology and mechanical properties of the vitrimer-MXene sheets are investigated at different length scales using micro-indentation testing and quantitative nanomechanical (QNM) analysis. UV-vis measurements and electrical conductivity measurements additionally indicate reasonably good transparency (>75 %T in the visible spectrum) and electrical conductivity values (~100 S/cm) for the vitrimer-MXene layers. Self-healing mechanisms of the vitrimer-MXene sheets in response to light are demonstrated, leveraging the high photon-to-phonon conversion efficiency of MXene. Finally, compression molding of multiple individual MXene-coated vitrimer layers together yields a hybrid composite with alternating ordered layers of vitrimer and MXene. DMA and tensile testing are subsequently used to evaluate modulus, creep resistance, and toughness. This work presents a novel approach to accessing composites with ordered layers of vitrimer and MXene, techniques useful towards further enhancing vitrimer functionality towards structurally robust electronic applications.