Impact of size control of graphene oxide nanosheets for enhancing electrical and mechanical properties of carbon nanotube-polymer composites

Graphene oxide (GO) has been explored for improving the dispersion stability of carbon nanotubes (CNTs). In particular, the size and shape of GO sheets have a significant impact on determining their dispersion efficiency and optimizing the properties of the CNT-based composites, but, to date, such effects have never been systematically assessed. In this study, we evaluated the size effects of GOs on the dispersion behavior of multi-walled CNTs (MWCNTs), and exploited them to develop conducting film and polymer-CNT composites with excellent electrical and mechanical properties. Synthesis of a series of five different GOs with varied sizes ranging from 170 to 2060 nm, but nearly the same surface properties, allowed systematical investigation of size effects of GO sheets. The CNT-dispersing ability of the GOs was improved significantly as the size of the sheets decreased. For example, the critical GO-to-MWCNT ratio (W-GO/W-MWCNT) required to produce stable MWCNT dispersion was in proportion to the size of the GO. Furthermore, the minimum value of the W-GO/W-MWCNT ratio required to fabricate a conductive GO-MWCNT film underwent a dramatic decrease from 0.1 to 0.025 as the size of the GO sheets changed from 2060 to 170 nm. Small-sized GOs facilitated the formation of an interconnected MWCNT network more effectively than large-sized GOs. Further investigation of the size effects of the GO on the mechanical properties of polymer-MWCNT composites was performed by measuring the Young's modulus of the composites. A two-fold enhancement in the mechanical properties of the polymer-CNT composites was achieved by controlling the size of GO. Our results provide important guidelines for the design of carbonaceous-material-based composites with excellent electrical and mechanical properties.