Surprisingly, a few seconds–minutes of compression at room temperature can increase the rate of dynamic bond exchange as measured by better self-healing, even for thermoresponsive dynamic bonds which do not exchange under ambient conditions.

Hysteretic friction behavior has been observed on varied 2D nanofilms. However, no unanimous conclusion has yet been drawn on to the exact mechanism or relative contribution of each mechanism to the observed behavior. Here we report on hysteretic friction behavior of supported atomically thin nanofilms studied using atomic force microscopy (AFM) experiments and molecular dynamics (MD) simulations. Load dependent friction measurements were conducted on unheated and heated samples of graphene, h-BN, and MoS₂ supported by silica substrates. Two diverging friction trends are reported: the unheated samples showed higher friction during unloading than during loading, and the heated samples showed a reversed hysteresis. Further, the friction force increased sub-linearly with normal force for heated samples, compared with unheated samples. Tapping mode AFM suggested that the interaction strength of the substrate was increased with heating. Roughened substrates in the MD simulations that mimicked strong/weak interaction forces reproduced the experimental observations and revealed that the evolution of real contact area in different interface interaction situation caused the diverging behaviors. Surface roughness and interaction strength were found to be the key parameters for controlling the out-of-plane deformation of atomically thin nanofilms.

The tribological behavior of graphene as an additive in a water-based nanofluid lubricant was investigated using pin-on-disk tests on titanium alloy (Ti-6Al-4V) and cemented tungsten carbide (WC–Co) contacts. The effect of graphene concentration and surface roughness was investigated. A non-monotonic trend of friction and wear with increasing concentration was observed. An optimal graphene concentration of 0.10 wt.% was found to provide the lowest friction and wear at different surface roughnesses, with the friction, specific wear rate of the sample surface, and tip wear reduced by 29%, 37%, and 95%, respectively. The friction reduction and anti-wear performance of the nanofluids increased as the sample surface roughness increased. The non-monotonic friction and wear trends can be explained by the agglomeration of graphene around the contact zone, where too small a graphene concentration does not provide enough lubrication and too high a concentration prevents sliding owing to a large amount of agglomeration particles at the contact. The superior friction and wear performance of the graphene nanolubricants demonstrate its potential in minimum quantity lubrication (MQL) and other applications.

Herein, we report the role of wrinkles and surface chemistry on the nanoscale friction and wear behavior of a CVD-grown aged WS₂ monolayer.