TY - JOUR
T1 - Ultralow Electrical Percolation in Graphene Aerogel/Epoxy Composites
AU - Wang, Zhenyu
AU - Shen, Xi
AU - Han, Ne Myo
AU - Liu, Xu
AU - Wu, Ying
AU - Ye, Wenjing
AU - Kim, Jang Kyo
N1 - Funding Information:
The project was supported by the Research Grants Council (GRF Projects: 61203415 and 12168119) of Hong Kong SAR. Z.W. and X.S. were recipients of the Hong Kong Ph.D. Fellowship. Technical assistance from the Materials Characterization and Preparation Facilities (MCPF), Advanced Engineering Materials Facilities (AEMF), and the Department of Chemical and Biomolecular Engineering at HKUST is appreciated.
Publisher Copyright:
© 2016 American Chemical Society.
PY - 2016/9/27
Y1 - 2016/9/27
N2 - Graphene aerogels (GAs) with a highly aligned, porous structure are prepared using a novel unidirectional freeze casting method, followed by thermal reduction. The unique graphene orientation in a preferred direction is achieved due to the large temperature gradient generated during freeze casting, in which graphene oxide (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. The prediction agrees well with experimental data, and the model validates the importance of aspect ratio and orientation state of nanofillers in controlling the percolation threshold of composites.
AB - Graphene aerogels (GAs) with a highly aligned, porous structure are prepared using a novel unidirectional freeze casting method, followed by thermal reduction. The unique graphene orientation in a preferred direction is achieved due to the large temperature gradient generated during freeze casting, in which graphene oxide (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. The prediction agrees well with experimental data, and the model validates the importance of aspect ratio and orientation state of nanofillers in controlling the percolation threshold of composites.
UR - http://www.scopus.com/inward/record.url?scp=84989172094&partnerID=8YFLogxK
U2 - 10.1021/acs.chemmater.6b03206
DO - 10.1021/acs.chemmater.6b03206
M3 - Article
AN - SCOPUS:84989172094
SN - 0897-4756
VL - 28
SP - 6731
EP - 6741
JO - Chemistry of Materials
JF - Chemistry of Materials
IS - 18
ER -