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Tribology is the study of interacting surfaces in motion and the measurement of properties such as friction, wear and abrasion. When designing nanoscale devices the consideration of tribology is particularly important because the high surface area ratio enhances problems with friction and wear.
Understanding nanoscale surface changes of tribological properties will also allow for either increased or decreased friction at a greater scale than currently provided by macroscopic lubrication and adhesion. Scanning probe microscopy techniques such as the atomic force microscope are being utilized to assess tribological properties at the nanoscale. The tip of the atomic force microscope provides contact with a solid or lubricated surface in order to study properties such as adhesion, friction and wear. The information provided can be used to further the understanding of nanotribology and predict how this affects nanomaterial surface interactions. Current nanotechnology applications of tribology are leading to the development of new drug delivery techniques, biosensors, data recording systems and microprojectors.
Nanotechnology Applications of Tribology for Biosensors and Drug Delivery
Biosensors for determining the presence and concentration of biomolecules have increased in accuracy through the greater surface area provided by nanotechnology for the immobilization of enzymes used to detect biological analytes. Glucose biosensors are a prominent example; they utilize nanoparticles over a carbon nanotube sheet for immobilizing the enzyme glucose oxidase. Biosensors are developed with nanoelectrochemical systems (NEMS) meaning they integrate electrical, mechanical, fluidic and thermal properties at the nanoscale. By implementing NEMS, tribological properties such as friction, adhesion and cohesive forces can be controlled to model and improve the biochemical reactions necessary for biosensing.
Because the high surface area of nanoscale devices increase tribological problems of friction and wear, further understanding of these issues is important for improving biosensing technologies. Moreover, strengthening the ability to control these properties will also increase the likelihood of providing enhanced drug delivery systems through nanotechnology. Drug delivery of molecules at the nanoscale or for drugs that are transported via nanovectors requires adhesion between biological molecular layers and the substrate. Understanding how friction and wear affects this adhesion is important and extensive measurements of tribological properties for nanomaterial is currently being implemented through the use of atomic force microscopes.
Nanotechnology Applications of Tribology for Data Storage
Nanotechnology is supplying new techniques for nonvolatile digital data storage systems. Magnetic hard disks have a high storage capacity and data is extracted from the physical movement of the recording medium or reading head. Scanning probe microscopy provides the technology for probe based data storage which employs an atomic force microscope tip for scanning at speeds of up to 100 millimeters per second. The technology also has the ability to utilize a multiple probe array for a high data rate.
An obvious limitation to this data storage methodology is wear to the atomic force microscope tip, and the damage produced from the high velocities and temperature required for high data rate recording. Therefore, nanotribological experiments are important for improving the technology. Studies have found differences in the friction properties of storage devices with unlubricated and lubricated film surfaces. As expected, significant probe tip wear is produced from the unlubricated film surface sample but future technology may utilize lubricated surface coatings to the probe to reduce abrasion during data recording.
Nanotechnology Application of Tribology for Microprojectors
The development of handheld electronic devices has produced the requirement for microprojectors to avoid the limitations of smaller screen displays. Adaptive optic components are used to align optics and maintain power output which can be misaligned due to the high temperatures produced from small optic lenses and nanoscale light beams. Enhancing the technology for microprojectors requires the tribological analysis of the lubricant used in the adaptive optics component. In the development of one microprojector patent, tribology tests found that there was a trade-off between the thickness of lubricant film and surface roughness required for optimum friction, adhesive force and durability.
This is because as lubricant thickness increases, the distribution on the optics component improves leading to stable and reliable operation; however, adhesive forces increase because of the lubrication within the connecting areas of the material. Therefore, the lubrication film thickness to sample roughness ratio should be assessed dependent on the level of use and functionality of the microprojector device.
Sources and Further Reading
- Bhushan, B. 2008. Nanotribology, nanomechanics and nanomaterials characterization, Philosophical Transactions of The Royal Society A, 366, pp. 1351-1381. http://rsta.royalsocietypublishing.org/content/366/1869/1351
- Malik, P. et al. 2013. Nanobiosensors: concepts and variations, International Scholarly Research Notices Nanotechnology, 1, e327435. http://dx.doi.org/10.1155/2013/327435
- Bhushan, B. et al. 2008. Nanotribology and nanomechanics of AFM probe-based data recording technology, Journal of Physics: Condensed Matter, 20, e36. http://iopscience.iop.org/article/10.1088/0953-8984/20/36/365207
- Chaparala, S.C. & Bhatia, V. 2016. Nano-tribology Applications in Microprojector Technology, Encyclopedia of Nanotechnology, 1, pp. 1-10. https://link.springer.com/referenceworkentry/10.1007/978-94-007-6178-0_281-2