Researchers from Shanghai Jiao Tong University, under the direction of Xuzhou Yan, developed a supermaterial by arranging carbon atom layers in a honeycomb structure. Due to its high conductivity and advantageous mechanical qualities, this supermaterial could advance the creation of bendable electronics, new batteries, and cutting-edge composite materials for space travel and aviation. The study was published in the journal Angewandte Chemie.
Image Credit: Angewandte Chemie. doi.org/10.1002/anie.202404481.
The creation of resilient and elastic films is still difficult. One approach to overcome this obstacle is to join graphene nanolayers together using “extendable” bridge structures.
Since the minuscule graphene nanolayers are mostly kept together by very weak interactions, primarily hydrogen bonds, their particular characteristics tend to disappear when the layers are combined into foils.
There is still opportunity for development, especially in the areas of stretchability and toughness, as attempts to strengthen the contacts between the particles in graphene foil to increase their mechanical properties have only been partially effective.
They cross-linked graphene nanolayers using mechanically interlocked molecules whose constituent parts are inseparably spatially entangled rather than chemically bonded. Rotaxanes were the linkage method of choice for the researchers.
A rotaxane is a big ring-shaped molecule “threaded” onto a molecular chain, or “axle.” To stop the wheels from unthreading, bulky groups cap the axles. The team constructed an axle that holds the wheel in place by using a charged group (ammonium). A linker connected the OH group, which serves as a molecular “anchor,” to the axle and wheel.
Graphene oxide was created by oxidizing graphene, which formed various oxygen-containing groups on both sides of the graphene layer. Among these are carboxyl groups, which can esterify bonds with OH groups. Graphene oxide is converted back to graphene following the cross-linking of the layers by the wheel and axle.
Tensile strength is increased when these films are bent or stretched because the ammonium group on the axle and the wheel must overcome attraction forces. The axle eventually “strikes” the end cap after being forced through the wheel by increased tension. The rotaxane-bridges lengthen in this action, enabling the layers to glide over one another and greatly enhancing the film's stretchability.
This graphene-rotaxane foil created flexible electrodes that could be bent and stretched up to 20% without breaking. Their excellent electrical conductivity was also maintained. Stretching by more than 23% only caused fracture.
The novel foils outperformed foils without rotaxanes in terms of strength (247.3 vs. 74.8 MPa), toughness (23.9 vs. 4.0 MJ/m3), and elasticity (23.6 vs. 10.2%). The group also constructed a basic “grasping tool” that included mechanical joints powered by the new foils and fitted with them.
Journal Reference:
Wang, C., et al. (2024) A Stretchable and Tough Graphene Film Enabled by Mechanical Bond. Angewandte Chemie. doi.org/10.1002/anie.202404481