Determinative scrolling and folding of membranes through shrinking channels.

Flat membranes ubiquitously transform into mysterious complex shapes in nature and artificial worlds. Behind the complexity, clear determinative deformation modes have been continuously found to serve as basic application rules but remain unfulfilled. Here, we decipher two elemental deformation modes of thin membranes, spontaneous scrolling and folding as passing through shrinking channels. We validate that these two modes rule the deformation of membranes of a wide thickness range from micrometer to atomic scale. Their occurrence and the determinative fold number quantitatively correlate with the Föppl-von Kármán number and shrinkage ratio. The unveiled determinative deformation modes can guide fabricating foldable designer microrobots and delicate structures of two-dimensional sheets and provide another mechanical principle beyond genetic determinism in biological morphogens.

High Performance Nacre Fibers by Engineering Interfacial Entanglement.

Biological materials exhibit fascinating mechanical properties for intricate interactions at multiple interfaces to combine superb toughness with wondrous strength and stiffness. Recently, strong interlayer entanglement has emerged to replicate the powerful dissipation of natural proteins and alleviate the conflict between strength and toughness. However, designing intricate interactions in a strong entanglement network needs to be further explored. Here, we modulate interlayer entanglement by introducing multiple interactions, including hydrogen and ionic bonding, and achieve ultrahigh mechanical performance of graphene-based nacre fibers. Two essential modulating trends are directed. One is modulating dynamic hydrogen bonding to improve the strength and toughness up to 1.58 GPa and 52 MJ/m3, simultaneously. The other is tailoring ionic coordinating bonding to raise the strength and stiffness, reaching 2.3 and 253 GPa. Modulating various interactions within robust entanglement provides an effective approach to extend performance limits of bioinspired nacre and optimize multiscale interfaces in diverse composites.

Falling-Leaves Stacking Aggregation of Two-Dimensional Macromolecular Graphene Oxide in Solution.

Understanding the dynamical behaviors of two-dimensional (2D) macromolecules is of fundamental importance for the precise modulation of their assembled structures and material performances. However, considerably less is known about how discrete macromolecular sheets aggregate into extended macroscopic assemblies in solutions. The absence of a quantitative description of the assembly process limits the precise structural control of assemblies. Here, we investigated the aggregation thermodynamic transition and kinetic behavior of 2D macromolecules in the model of single layer graphene oxide (GO). Combining Flory-Huggins theory with experimental observations, we unveiled the critical thermodynamic transition of GO to correlate with the solvent property. We proposed a theoretical falling-leaf model to quantitatively describe the kinetic aggregation process of 2D GO sheets. Experimental analysis validated the theoretical prediction that the thickness of GO aggregates has a power law relation with the poor solvent content. Our work provides a fundamental understanding of phase separation of 2D macromolecules and offers an insight into modulating the aggregated structures of their assembled materials.

Superior Strong and Tough Nacre-Inspired Materials by Interlayer Entanglement.

Natural materials teach that mechanical dissipative interactions relieve the conflict between strength and toughness and enable fabrication of strong yet tough artificial materials. Replicating natural nacre structure has yielded rich biomimetic materials; however, stronger interlayer dissipation still waits to be exploited to extend the performance limits of artificial nacre materials. Here, we introduce strong entanglement as a new artificial interlayer dissipative mechanism and fabricate entangled nacre materials with superior strength and toughness, across molecular to nanoscale nacre structures. The entangled graphene nacre fibers achieved high strength of 1.2 GPa and toughness of 47 MJ/m3, and films reached 1.5 GPa and 25 MJ/m3. Experiments and simulations reveal that strong entanglement can effectively dissipate interlayer energy to relieve the conflict between strength and toughness, acting as natural folded proteins. The strong interlayer entanglement opens up a new path for designing stronger and tougher artificial materials to mimic but surpass natural materials.

Vertical Array of Graphite Oxide Liquid Crystal by Microwire Shearing for Highly Thermally Conductive Composites.

Excellent through-plane thermally conductive composites are highly demanded for efficient heat dissipation. Giant sheets have large crystalline domain and significantly reduce interface phonon scattering, making them promising to build highly thermally conductive composites. However, realizing vertical orientation of giant sheets remains challenging due to their enormous mass and huge hydrodynamic drag force. Here, we achieve highly vertically ordered liquid crystals of giant graphite oxide (more than 100 µm in lateral dimension) by microwire shearing, which endows the composite with a recorded through-plane thermal conductivity of 94 W m-1 K-1 . Microscale shearing fields induced by vertical motion of microwires conquer huge hydrodynamic energy barrier and vertically reorient giant sheets. The resulting liquid crystals exhibit extremely retarded relaxation and impart large-scale vertical array with bidirectional ordering degree as high as 0.82. The graphite array-based composites demonstrate an ultrahigh thermal enhancement efficiency of over 35 times per unit volume. Furthermore, the composites improve cooling efficiency by 93% for thermal management tests compared to commercial thermal interface materials. This work offers a novel methodology to precisely manipulate the orientation of giant particles and promote large-scale fabrication of vertical array with advanced functionalities.

Monodomain Liquid Crystals of Two-Dimensional Sheets by Boundary-Free Sheargraphy.

Eliminating topological defects to achieve monodomain liquid crystals is highly significant for the fundamental studies of soft matter and building long-range ordered materials. However, liquid crystals are metastable and sensitive to external stimuli, such as flow, confinement, and electromagnetic fields, which cause their intrinsic polycrystallinity and topological defects. Here, we achieve the monodomain liquid crystals of graphene oxide over 30 cm through boundary-free sheargraphy. The obtained monodomain liquid crystals exhibit large-area uniform alignment of sheets, which has the same optical polarized angle and intensity. The monodomain liquid crystals provide bidirectionally ordered skeletons, which can be applied as lightweight thermal management materials with bidirectionally high thermal and electrical conductivity. Furthermore, we extend the controllable topology of two-dimensional colloids by introducing singularities and disclinations in monodomain liquid crystals. Topological structures with defect strength from - 2 to + 2 were realized. This work provides a facile methodology to study the structural order of soft matter at a macroscopic level, facilitating the fabrication of metamaterials with tunable and highly anisotropic architectures.

2D-Topology-Seeded Graphitization for Highly Thermally Conductive Carbon Fibers.

Highly thermally conductive carbon fibers (CFs) have become an important material to meet the increasing demand for efficient heat dissipation. To date, high thermal conductivity has been only achieved in specific pitch-based CFs with high crystallinity. However, obtaining high graphitic crystallinity and high thermal conductivity beyond pitch-CFs remains a grand challenge. Here, a 2D-topology-seeded graphitization method is presented to mediate the topological incompatibility in graphitization by seeding 2D graphene oxide (GO) sheets into the polyacrylonitrile (PAN) precursor. Strong mechanical strength and high thermal conductivity up to 850 W m- 1 K-1 are simultaneously realized, which are one order of magnitude higher in conductivity than commercial PAN-based CFs. The self-oxidation and seeded graphitization effect generate large crystallite size and high orientation to far exceed those of conventional CFs. Topologically seeded graphitization, verified in experiments and simulations, allows conversion of the non-graphitizable into graphitizable materials by incorporating 2D seeds. This method extends the preparation of highly thermally conductive CFs, which has great potential for lightweight thermal-management materials.

Precise Thermoplastic Processing of Graphene Oxide Layered Solid by Polymer Intercalation.

The processing capability is vital for the wide applications of materials to forge structures as-demand. Graphene-based macroscopic materials have shown excellent mechanical and functional properties. However, different from usual polymers and metals, graphene solids exhibit limited deformability and processibility for precise forming. Here, we present a precise thermoplastic forming of graphene materials by polymer intercalation from graphene oxide (GO) precursor. The intercalated polymer enables the thermoplasticity of GO solids by thermally activated motion of polymer chains. We detect a critical minimum containing of intercalated polymer that can expand the interlayer spacing exceeding 1.4 nm to activate thermoplasticity, which becomes the criteria for thermal plastic forming of GO solids. By thermoplastic forming, the flat GO-composite films are forged to Gaussian curved shapes and imprinted to have surface relief patterns with size precision down to 360 nm. The plastic-formed structures maintain the structural integration with outstanding electrical (3.07 × 105 S m-1) and thermal conductivity (745.65 W m-1 K-1) after removal of polymers. The thermoplastic strategy greatly extends the forming capability of GO materials and other layered materials and promises versatile structural designs for more broad applications.

High-Speed Blow Spinning of Neat Graphene Fibrous Materials.

Achieving high spinning speed is critical to the production efficiency and viable application of fiber species. Graphene fiber (GF) has recently emerged as a carbonaceous fiber with excellent functionality. However, the extremely low wet spinning speed of GF has limited its applications. We realized high-speed blow spinning of neat GF and fabric by modulating the rheological properties of the graphene oxide (GO) dispersion. We achieved a speed of 556 m min-1, 2 orders of magnitude faster than that for wet spinning. We chose ultrahigh molecular weight polymers as transient additives to circumvent the intrinsic barrier effect of GO and achieve high spinning dope stretchability at low polymer percentages-down to 25 wt %. Minimizing the polymer additive content ensures the high electrical/thermal conductivity of the blow-spun fiber and fabric. This work provides insight into the unique flow properties of 2D sheets and will promote the efficient production of graphene-based fibrous materials.

Artificial Bicontinuous Laminate Synergistically Reinforces and Toughens Dilute Graphene Composites.

Strength and toughness are usually exclusive in polymer nanocomposites with dispersed nanofillers. This intrinsic conflict has been relieved in a high filler loading range by mimicking the nacre structure of natural selection. However, at the low loading extreme, it still remains a great challenge. Here, we design a bicontinuous lamellar (BCL) structure to synergistically reinforce and toughen nanocomposites in the dilute range of nanofiller below 1 wt %. At a typical loading of 0.3 wt %, the BCL composite of graphene oxide (GO) and poly(vinyl alcohol) (PVA) has an 8200% toughness and a comparably reinforced hardness of the dispersed counterpart, accompanying a 53-fold higher failure elongation that even exceeds that of pure PVA. Theoretical modeling and experimental analyses reveal that the continuous generation of massive crazes of GO layers endows the BCL composite with high toughness and surprising breakage elongation beyond those of pure PVA. The BCL organization is an alternatively optimal structure model to merge the exclusive strength and toughness together for damage-tolerant nanocomposites with a dilute range of nanofillers, other than nacre-like and well-dispersed structure, providing an alternative methodology to fabricate mechanically robust composites.