The Controllable Fabrication And Properties Of Three-Dimensional Graphene Based Multifunctional Material

Graphene aerogel（GA） represents a new kind of porous carbon nanomaterial of monolithic graphene in three-dimensional（3D） macroscopic scale, due to its high porosity, lightweight density, large specific surface area, low thermal conductivity, high electrical conductivity, excellent mechanical compressibility and structure stability, such 3D GA suggests its promising applications in electronic engineering, protective engineering, thermal engineering and energy storage. With GA as a template framework, how to realize the controllable fabrication and tailorable structure design for 3D graphene based multifunctional materials is a meaningful subject for promoting development of advanced graphene multifunctional materials by optimized modification strategies of structure and properties. Because of poor controllability of microstructure, weak tailorability of macroscopic configuration, low structure stability and large challenge of scale-up fabrication of current 3D graphene monoliths, the objective of this study is to develop controllable fabrication approaches and property investigation of 3D graphene based multifunctional material, the detailed research contents are highlighted as follows:1. Controllable fabrication and property investigation of 3D graphene aerogelUtilizing the large-area graphene oxide（LGO） aqueous as precursor, 3D GA with well-order honeycomb-like microstructure, lightweight density, high porosity and stable structure was fabricated by optimizing parameters of hydrothermal reaction（temperature, time and agent dosage of ethylenediamine（EDA））, adjusting dialysis and vacuum freeze-drying conditions, by which the 2D micro/nano-scaled LGO sheets were induced to assemble and controllably construct. Meanwhile, the experimental investigation has demonstrated that such 3D GA exhibits 95% nonlinear elastic reversible compression, multi-cycle stable loading processes at 80% strain and high energy density（0.85 J/g）. Furthermore, GA presents superior electrical conductivity（¹.148 S/cm） at ultralow density（¹0 mg/cm3）, sensitive piezo-resistance effect and stable temperature-resistance response.2. The fabrication and property investigation of 3D graphene based/PDMS polymer compositeWith ’bottom-up’ process by self-infiltration under vacuum and ice-bath conditions, 3D graphene based/polydimethylsiloxane（PDMS） flexible conductive composite was fabricated with intact 3D GA scaffolds and stable bonding interfaces of microstructure. Such 3D GA based polymer composite experimentally verifies its outstanding stretchable non-linear elastic deformability（including 80% reversible compression strain and 90% reversible tensile strain）, stable electro-mechanical sensing property, high joule heating performance and remarkable thermal conduction capacity.3. The fabrication and property investigation of 3D graphene based/Al₂O₃ nanoceramic compositeWith 3D GA framework as a substrate, nano-layer thick Al₂O₃ nanoceramic was deposited by ’atomic layer deposition（ALD）’ technique to fabricate 3D graphene based/Al₂O₃ nanoceramic composite, by which graphene substrate was chemically bonded with nanoceramic to form ’sandwiched’ multilayer structures in microscale（nanoceramic-graphene-nanoceramic）. This composite demonstrates low thermal conduction, high electrical conductive（1 S/cm） and superelastic properties（80% reversible compression strain）, which verifies the remarkable strengthening effect of mechanical properties between 3D GA and nanoceramic, and presents outstanding elastic deformation property and size effect of ceramic composite in nano-scale.4. The fabrication of 3D graphene metamaterial and negative Poisson’s ratio investigationBy controlling orientation of ice crystal growth in freezing-casting process, 3D graphene metamaterial with hyperbolically patterned microstructure was prepared, which presents the macroscopic negative Poisson’s ratio response, superelasticity（99% reversible superelastic strain, >1000 cycles stable loading process）, stable structure and excellent damping capacity. The in situ compression observation of microstructure evolution in SEM reveals the deformation mechanism triggering negative Poisson’s ratio, the graphene sheets in micro-scale with ultralarge aspect ratio present oriented buckling, leading to the transverse contraction of macroscopic geometry shape. In addition, due to the longitudinal compression induced transverse contraction, the whole bulk of 3D graphene metamaterial undergoes triaxial compression stress, overcoming the shortage of stacked graphene sheets being poor shear resistance with mechanical properties significantly improved.5. 3D printing graphene material tailorable design and property investigation3D printing platform for two aqueous materials is developed based ’drop-ondemand（DOD） inkjet’ mechanism, realizing the controllable fabrication and tailorable design of 3D graphene material with over-hang elements and complex topological structures. Employing the graphene aqueous ink as precursor and ice as support components for over-hang graphene elements, the ’DOD inkjet’ technique and the low temperature freeze-casting approach were used to resolve the issues that current continues 3D inkjet printing techniques are facing with, including high viscosity limitation of rheological ink, demand of assisted particles filler, microstructure delamination, poor stability of mechanical property, the filler particle interlayer diffusion and weak interface formation. The experimental results verify such 3D printing graphene material has excellent mechanical properties（>50% reversible compression deformation and 10 cycles stable loading processes）, electrical conductivity（ 15.4 S/m）, linear dependent sensitive piezo-resistance（20% strain leading to-26.2% resistance change） and negative temperature coefficient effect.