I am a postgraduate researcher at the University of Leeds. I have completed my master's degree in the Erasmus Tribos program at the University of Leeds, University of Ljubljana, and University of Coimbra and my bachelor's degree in Mechanical Engineering from VTU in NMIT, India. I am an editor and social networking manager at TriboNet. I have a YouTube channel called Tribo Geek where I upload videos on travel, research life, and topics for master's and PhD students.
Challenges of MXenes in Tribology
MXenes have a unique physical and chemical properties which helps in wide range of applications that includes energy storage, electronics, sensors, electromagnetic shielding, catalysis, biology, and particularly tribology. Unlike the strong M–X bonds, MXenes exhibit weak interlayer interactions, allowing them to easily slide between layers under pressure. Their high specific surface area facilitates the formation of lubricating or transfer films, leading to low friction and wear rates. Additionally, the abundant surface groups on MXenes enable easy modification and surface regulation, enhancing their compatibility with polymer materials. These characteristics that is low shear strength, ease of film formation, and strong interaction with polymer matrices makes MXenes highly promising candidates for various tribological applications.
The synthesis of MXenes plays a crucial role in determining their mechanical properties which involves selective etching of the MAX phase. Unlike graphene, which can be mechanically exfoliated from graphite, MXenes cannot be mechanically separated from the MAX phase. Instead, they are produced through selective etching, and the synthesis conditions such as etchant type, concentration, temperature, environment, and duration. This affects the final mechanical strength, further harsh or concentrated etching conditions may also introduce more defects and reduce flake size. Conversely, synthesis in inert or vacuum conditions and careful temperature control can produce higher-quality MXenes. Additionally, delamination processes impact defect density, flake size, and vacancies, further influencing mechanical strength
Tribological properties of MXenes are influenced by factors such as M–X chemistry and composition, flake size and geometry, surface functional groups, loading conditions, and stoichiometry. Research indicates that thinner MXene flakes, such as single-layer ones, exhibit superior anti-friction properties compared to thicker flakes. Early computational analyses using density functional theory (DFT) have shown that MXenes with larger inter-layer spacings experience easier sliding and lower friction. However, the friction coefficients of MXenes (ranging from 0.06 to 0.1) are still higher than those of other nanomaterials, suggesting a need for further research into the tribological chemistry and physics of MXenes.
Atomic force microscopy studies have found that friction and adhesion forces increase with temperature. Contact pressure also plays a crucial role in tribofilm formation however, at excessively high pressures, these tribofilm can partially rupture which results in losing their protective effect. Additionally, at higher humidity levels, the reduction in wear and friction is not observed due to the expansion of basal spacings. While tribofilm formation is considered a key mechanism for reducing friction and wear in solid lubrication systems, direct characterization to fully understand the tribological behavior of MXene-based lubrication systems is still lacking. The impact of heat and temperature on MXene-based lubricants remains underexplored, with significant gaps in understanding their stability and performance under various loading and environmental conditions. Issues such as degradation over time, particle breakage, agglomeration, oxidation, and reactions among MXene sheets, as well as structural defects, have not been thoroughly characterized in tribological applications. To address these gaps, advanced material characterization techniques should be developed and utilized to study dispersion and agglomeration states, which can change over time. Additionally, further research is needed to investigate how factors such as flake size (both lateral and thickness), surface termination groups, and processing parameters affect the surface and tribological properties of MXene-based lubrication systems.
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