Graphene-based nanolubricants have attracted the attention of researchers because they possess excellent thermal conduction properties. Creating a stable suspension is a prerequisite to producing a unique nanolubricant.
Study: Comparison of dispersion techniques of graphene nanoparticles in polyester oil. Image Credit: H_Ko/Shutterstock.com
A paper published in Materials Today: Proceedings attempts to highlight adequate dispersion methods for producing a stable graphene-based nanolubricant suspension.
An Introduction to Nanolubricants
Thermal characteristics of heat exchange fluids are an important field of research. Traditional heat exchange fluids like oils, ethylene glycol, and water have limited cooling potential due to their poor thermal conductivity.
There is increasing emphasis on the design of highly efficient base fluid thermal systems to improve heat transmission. Base fluids, like oils, are often used for lubrication in various industries.
Nanolubricants can be described as engineered fluid modified by incorporating different nanoscale materials, including metals, carbides, oxides, and nitrides. Nanomaterials like nanoparticles (NPs), nanotubes, or nanorods can be incorporated into base fluids.
Advantages of Nanolubricants
Achieving sustainable performance and energy conservation in mechanical systems necessitates using environmentally friendly and high-performance lubricants. Nanoparticles have recently become increasingly integral as lubricant additives due to their ability to reduce emissions and improve fuel efficiency.
The small size of NPs, often 100 nm or smaller, allows them to access the contact areas. In contrast to natural additives, NPs are thermally stable at high temperatures, making them suitable as additives in lubricants.
A unique nanolubricant has recently been produced, consisting of base oil and dispersed NPs. Scientists were drawn to it owing to its superior heat conduction and tribological performance.
Most of the issues linked with conventional lubrication using phosphorus and sulfur could be addressed by nanolubrication. The presence of NPs in lubricant oils lowers the coefficient of friction and boosts the load-bearing capabilities of connected surfaces in mechanical components.
Synthesis of Nanolubricants
Generally, two main techniques are employed for producing nanolubricants. The two-step technique is extensively used as it is a highly cost-efficient approach for the scalable production of nanolubricants for industrial purposes.
Nanoparticle Aggregation – Main Challenge Faced by Nanolubricants
Nanoparticles aggregate because of their large surface areas and high surface energies.
It is extremely challenging to produce stable suspensions without nanoparticle aggregation over elongated periods. While the advantages of using nanolubricants are undeniable, NP aggregation hampers the effectiveness of nanolubricants with respect to heat conduction and tribological performance.
Some studies have argued that facile strategies may be used for preventing NP aggregation and boosting suspension stability. The most common among these strategies are sonication and the introduction of dispersant materials to the fluid.
The manner of dispersal influences the level of aggregation and variations in surface characteristics of nanoparticles in the solution.
Contingent on NP properties and sonication settings, the suspended nanoparticles may, to varying degrees, dissolve/transform, aggregate, or interact and create complexes with elements of the surrounding medium.
Understanding the effect of sonication on nanoparticle properties (like size, zeta potential, and surface oxides) and the dissolving fraction is thus essential, as this process will substantially impact the toxic behavior of the nanoparticles.
What Did the Researchers Do?
The team investigated the stability of graphene-based polyester oil nanolubricant via two particular two-step dispersion techniques: overhead stirrer with sonication and magnetic stirrer with sonication.
The sedimentation image was used to test the stability of nanolubricant dispersion over the course of a 14-day period.
Once the results of the study were confirmed, the team analyzed the specimens via the zeta potential analyzer to verify the stability of the nanolubricant.
The zeta potential is used to predict the stability of nanofluids. Nanofluids are stable at zeta potentials greater than ±30 mV, whereas any values less than ±30 mV are indicative of severe aggregation of nanoparticles.
Findings of the Study
The team found that different distribution strategies produced varying suspension stabilities.
Of the two-step approaches analyzed in this study, the overhead stirrer with sonication approach proved to be the most effective in developing a stable suspension.
This research concluded that the introduction of surfactants to a nanolubricant impacts its dispersion stability. Hexadecyltrimethylammonium bromide (CTAB) was found to improve nanolubricant stability as a surfactant in all dispersion techniques.
Saufi, M., & Mamat, H. (2022). Comparison of dispersion techniques of graphene nanoparticles in polyester oil. Materials Today: Proceedings. Available at: https://doi.org/10.1016/j.matpr.2022.06.508