3D Printing Highly Stretchable Graphene Aerogels And Their Property Modulation

Graphene holds great prospects as a paradigmatic 2D material for constructing macroscopic carbonaceous materials due to its extraordinary mechanical properties and the record electrical and thermal conductivity.Among multiple graphene macroscopic assemblies,graphene aerogels(GAs),with full expression of surface characteristics of graphene as their building blocks,has been widely applied in various fields like composite materials,energy storage,sensors and catalysts.The inner pore structures of graphene aerogels can be well controlled by existing methods,and the sponge-like compressive elasticity has been achieved with in-depth research on structural performance.But achieving rubbery stretchability in graphene aerogels is still a challenging.In response to this important scientific problem,the thesis proposed the idea of“programmatic design and construction of hierarchical structures”.Based on the "trace ion gelation" method,high-precision 3D printing to prepare graphene aerogel microlattice was achieved.Further,we prepared highly stretchable graphene aerogels by “fine control on hierarchical structures” strategy.The applications of GAs with both stretchability and compressibility in logic sensing and shape memory nanocomposite materials were also expanded.we proposed a facile “trace ion gelation” method and achieved direct 3D printing of GAs from graphene oxide(GO)gelation ink at ambient surroundings,which represented a universal strategy in fabricating high-performance,ultra-light GAs without additives.Gelation effect by trace ions was deep studied,based on which the rheology of GO gel ink was effectively controlled.The relationship between rheology and the accuracy and fidelity of the printed structure was also systematically investigated.Based on this method,GAs with various topological structure were fabricated by regulating their inner porous structure.Printed GAs exhibited cyclic compressibility under 80% maximum strain and outstanding structural stability.The strategy of “precise control on hierarchical structures” was proposed,and the multiscale hierarchical structure from nanometer to centimeter scale was constructed by 3D printing.By introducing synergistic effect between 2D and 1D carbon materials,graphene/carbon nanotube composite aerogels(CAs)with high stretchability(～200%),low energy loss coefficient(～0.11),outstanding structural stability and wide service temperature range were achieved,which breaks the intrinsic conflicts between high porosity and high elasticity in porous materials.By tracking the evolution of multiscale hierarchical structures during the elastic deformation,we confirmed the crumpled conformation of planar graphene building blocks was the key structure for stretchability of aerogels.At the same time,the nature of the synergistic enhancement effect of 1D carbon nanotubes and 2D graphene sheets was revealed.The application potential of GAs with both stretchability and compressibility as new generation logic sensor was expanded.By integrating the highly stretchable graphene conductive network with shape memory polymer(SMP)nano networks,we realized bicontinuous nanocomposite aerogels with millisecond response,comparable to that of shape memory alloys.This nanocomposite aerogel overcome the long-standing problem of low response speed in SMP materials.The relationship between the electrical response time of the nanocomposite aerogel,the thickness of the SMP film,and the applied electrical work was systematically studied.The energy conversion and transfer of the graphene conductive network,which promoted the high-speed response of nanocomposite aerogels,were elucidated according to the Fourier’s law of thermal conduction.we also depicted the quantitative relationship between the thickness of the SMP film and the aerogel response time.Through in-situ experiments,the microscopic shape memory response behavior of the basic building block in aerogel was confirmed,and the applications of millisecond response nanocomposite aerogels in micro-relays and electromagnetic actuators were demonstrated.This thesis solves the problem of high stretchability of graphene aerogels.Guided by the idea of "accurate construction and precise control of hierarchical structure",the 3D printing fabrication of graphene aerogels without additives was achieved,which provided a technical basis for the accurate construction of the various topological structures inside the aerogels.Hierarchical structures across multiple scales were constructed and precisely controlled,realizing the high stretchability of graphene aerogels,and solving the intrinsic contradiction between high porosity and high stretchability.The prepared graphene aerogels were adapted to complex strain scenarios as sensors and highly stretchable fast electrical-response nanocomposite materials.