About this Research Topic
Nowadays, a significant amount of the global energy output is consumed to overcome friction- and wear-induced problems/damage, a situation that urgently calls for more effective tribological solutions and strategies. 2D-layered nanomaterials such as graphene, graphene oxide (GO), MoS2, etc., have gained substantial attention for use as solid lubricants and lubricant additives, thus serving as promising alternatives to conventional lubrication approaches under harsh conditions. Since 2011, the class of 2D nanomaterials has been significantly expanded by the discovery of a new class of 2D transition metal carbides and/or carbonitrides. These newly emerging nanomaterials, with Ti3C2TX as their most prominent member, are called MXenes due to their origin in MAX-phases and their structural similarity to graphene. Mxene nano-sheets have been extensively used in energy storage, catalysis, and water purification. In the last two years, MXene nano-sheets have experienced more and more attention in the tribological community due to their remarkable solid lubrication ability and outstanding anti-wear performance.
Although they present promising alternatives to conventional lubrication approaches, 2D-layered nanomaterials as solid lubricants and lubricant additives has still some shortcomings that need to be overcome in order to further optimize their friction and wear performance. Concerning solid lubricants, the adhesion strength of the deposited nano-materials/nano-films to the substrate is considered to be critical for the resulting tribological performance. Regarding lubricant additives, the general hydrophilic character of these nano-materials lowers their dispersibility in hydrophobic oils, which goes hand in hand with stability and sedimentation problems over time. Irrespective of the nanomaterial and the application (solid lubricant or lubricant additive), the surface chemistry of the nanomaterials is considered the key factor to solve these problems. The existing surface terminations can be used to chemically functionalize the 2D-layered nanomaterials, thus allowing for enhanced adhesion strength and improved dispersibility. Chemical modifications need to be complemented by advanced, high-resolution materials characterization (chemical and structural) to ensure the success of the functionalization process. Moreover, materials characterization is of utmost importance for shedding light on the very complex nature of tribologically involved interfaces prior to and after the tribological experiments, in order to understand their underlying friction and wear mechanisms.
This Research Topic intends to publish original full research articles, perspectives, and review articles that investigate (but are not limited to) the following themes:
• The use of modern 2D-layered nanomaterials as solid lubricants and lubricant additives
• Chemical functionalization strategies for 2D-layered nanomaterials to improve their adhesion strength on substrates, to modify their wetting and spreading behavior, and to improve their dispersibility and long-term stability in non-polar liquids
• Advanced, high-resolution materials characterization (chemical and structural) to prove the success of the chemical functionalization
• Advanced characterization of the tribological interface to elucidate underlying friction and wear mechanisms
• Numerical DFT and MD studies of chemically functionalized nano-materials to predict chemical reaction pathways, interactions between functional groups, and adhesion strengths, among others
Keywords: 2D nano-materials, Mxene nano-sheets, chemical functionalization, friction, advanced materials characterization
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