Effects of graphene sheet size on multi-functional properties of unidirectional graphene aerogel/epoxy nanocomposites

Abstract

Graphene aerogel (GA) has attracted vast interest in recent years due to its unique ability to feature the exceptional properties of graphene as a porous structure with large accessible surface area, presenting improved properties in chemical sensors, energy storage materials, thermal interface materials, and multifunctional nanocomposites. As a composite filler material, its 3D structure ensures consistent interconnections between graphene sheets, enabling the fabrication of high performance nanocomposites even at very low graphene content. However, it is important to have a comprehensive understanding in the assembly of graphene oxide (GO) sheets under freeze casting, which may be influenced by several factors including GO sheet size, in order to precisely control the GA microstructure. The purpose of this research is to elucidate the effects of GO sheet size on the morphology and properties of GA and its polymer composites. By varying the size of precursor graphene oxide (GO) sheets between 1.1 to 1595.8 μm², unidirectional graphene aerogels (UGAs) with controllable densities, degree of alignment and electrical conductivities are prepared using the unidirectional freeze casting method. The UGAs prepared using ultralarge GO (UL-UGA) deliver the best properties compared with those made using small GO (S-UGA). UL-UGAs exhibit a low density of 0.27 mg cm^-3, a high degree of alignment, and a high electrical conductivity of 0.178 S cm^-1. The UL-UGA/epoxy composites prepared by infiltrating liquid epoxy resin into the porous UGA exhibit excellent electrical conductivities as high as 0.135 S cm^-1, along with an ultralow percolation threshold of 0.0066 vol% which is one of the lowest values for all graphene-based composites. Owing to their 3D interconnection, high degree of alignment and effective reduction, the UL-UGAs are shown to significantly enhance the fracture toughness of epoxy by up to 69% at 0.11 vol% graphene content, through several toughening mechanisms such as crack pinning, crack deflection, interfacial debonding, and graphene rupture.

Date of Award	2017
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology