As a newly developed three dimensional (3D) graphene material, graphene aerogel (GA) has attracted tremendous interest due to their unique attributes that other forms of two dimensional (2D) graphene sheets lack. The unique 3D structure and multi-functional characteristics of GA offer totally new processing routes to fabricate composites with much improved properties. In this research, GAs with ordered and controllable structures are fabricated using novel processing techniques. Mechanical and functional properties of GA-based polymer composites are explored in an effort to tailor these properties for useful applications.

GAs with a unique anisotropic structure are produced through one-step chemical reduction induced self-assembly of ultra-large graphene oxide (GO) sheets. The as-pro...[ Read more ]

As a newly developed three dimensional (3D) graphene material, graphene aerogel (GA) has attracted tremendous interest due to their unique attributes that other forms of two dimensional (2D) graphene sheets lack. The unique 3D structure and multi-functional characteristics of GA offer totally new processing routes to fabricate composites with much improved properties. In this research, GAs with ordered and controllable structures are fabricated using novel processing techniques. Mechanical and functional properties of GA-based polymer composites are explored in an effort to tailor these properties for useful applications.

GAs with a unique anisotropic structure are produced through one-step chemical reduction induced self-assembly of ultra-large graphene oxide (GO) sheets. The as-produced GAs possess ultralow density, high porosity, high electrical conductivity, and excellent compressibility. The solid composites prepared by infiltrating GA with epoxy resin present excellent electrical conductivities, together with high mechanical properties and fracture toughness. The unusual anisotropic structure of GA gives rise to ∼67% and ∼113% higher electrical conductivity and fracture toughness of the composites, respectively, in the alignment direction than that transverse to it. The unique anisotropic electrical and mechanical properties of GA/epoxy composites make them promising candidates for applications such as anisotropic conductive adhesives and outer structures in multilayered biological systems.

Apart from self-assembly of ultra-large graphene sheets, a novel unidirectional freeze casting method is also developed to fabricate GAs highly aligned porous structure. The unique graphene orientation in a preferred direction is achieved due to the large temperature gradient generated during freeze casting, in which GO sheets are expelled by the rapidly advancing ice front to assemble between the aligned ice crystals. The resulting unidirectional GAs (UGAs) possess ultralow densities, high porosities, and large surface areas, as well as excellent electrical conductivities. The solid UGA/epoxy composites fabricated by vacuum-assisted infiltration of liquid epoxy present an extremely low percolation threshold of 0.007 vol %, which is the lowest value for all graphene/polymer composites reported in the literature. Besides, the anisotropic structure of UGAs gives rise to significant anisotropic electrical conductivities of UGA/epoxy composites, a potentially useful attribute for many important applications. A new analytical model is formulated on the basis of the interparticle distance concept to explain the percolation behaviors of composites with aligned anisotropic nanofillers, and the prediction agrees well with experimental data.

Following a similar unidirectional freeze casting technique developed above, a novel two-step route is utilized to prepare GA/poly(vinyl alcohol) (PVA) composites with exceptional dielectric performance. The composites obtained from the initial unidirectional freeze casting possess a highly-aligned, conducting graphene skeleton with an ultralow density, a high porosity and remarkable thermal stability, showing ultrahigh dielectric constants combined with moderate losses. The losses are significantly reduced by means of PVA barriers introduced between the neighboring conductive main skeletons of the aligned GA/PVA networks in the 2^nd freeze casting process. The insulating barriers effectively block the current leakage by removing the transversely interconnected, conductive ligaments. The compaction of barrier-shielded, porous GA/PVA composites yield fully consolidated, solid composites which deliver both exceptional dielectric constants and very stable, low losses. The approach developed here paves the way for rational design and assembly of GA/PVA composites as a lightweight, tunable and high-performance dielectric material, satisfying various requirements for emerging applications.

In an effort to precisely control the morphology of GAs, graphene honeycomb (GHC) with a long-range ordered porous structure is produced using 3D printing technique, which possess a high electrical conductivity of 72 S/m, while an ultralow density of only 3.25 mg/cm³. This is the lightest honeycomb structure ever achieved in the open literature. A highly conductive and stretchable graphene honeycomb sandwich is fabricated using GHC/polydimethylsiloxane (PDMS) composites as the core material and ultrahigh-density graphene foams (UDGF)/PDMS composites as the face sheets. The resultant honeycomb sandwich delivers excellent durability and minimal resistance change under large external loadings, including stretching, bending, and twisting, due to the long-range ordered porous structure of GHC. A stretchable light-emitting display constructed using the sandwich as the electric circuit and light emitting diodes (LEDs) as the pixels is demonstrated, which is capable of showing input information through scrolling texts, in the meanwhile providing reliable electronic performances even under various deformation modes.