Controlling Friction and Adhesion Using Charged Hydrogel Lubricants During Manufacturing

This grant supports research that contributes new knowledge related to lubrication in manufacturing processes, promoting both the progress of science and advancing national prosperity. Oil-based lubricants generate pollutants and harmful contaminants and, thus, there is a demand for environmentally benign lubricants that are renewable and, at least, as efficient.

While lubrication in an aqueous medium could solve this need, it is rarely applied in manufacturing due to the low pressure-coefficient of the viscosity of water, among other reasons. In biological tribosystems like cartilage, these challenges are met by employing gel-assisted aqueous lubrication. Thus inspired, this project designs synthetic waterborne films with charged hydrogel-like structures that enable the active control of friction and adhesion during manufacturing.

Active control of hydrogel lubrication not only ensures good manufacturing practices in food, biomedical and pharmaceutical industries, low-carbon footprint and tunable lubrication of machine components, but also enables handling of soft biologically inspired materials and delicate electronic components during manufacturing. Furthermore, the knowledge derived from this research allows machine interfaces to dynamically adapt to their current task, which increases machine versatility, efficiency and product quality.

Therefore, results from this research benefit the U.S. economy and society and help to extend U.S. manufacturing to new application areas. The multi-disciplinary approach helps broaden participation of women and underrepresented minority students in research and positively impacts engineering education.

This research produces fundamental knowledge on active control of hydrogel-based lubrication via electrical modulation. In particular, the project determines how modulating the balance between physical interactions in three hydrogel systems, (1) electrostatic attraction vs. repulsion, (2) hydrogen bonding vs. electrostatic repulsion, and (3) hydrophobic attraction vs. electrostatic repulsion), dictates the self-assembly pathway and microstructure, and how this can be applied to modulate lubrication.

These lubricants are synthesized via microphase separation. The experimental studies combine microscopy, oscillatory shear and normal and lateral force measurements with polymer physics-based models to deliver understanding of the role played by physical associations in the interfacial structure and rheology and how they influence friction and adhesion.

This research also advances the knowledge about how chemical and electrical stimulation drives changes in friction and adhesion mechanisms. The new knowledge includes breakthroughs in discovery of hydrogel lubrication mechanisms enabled by the integration of novel and improved experimental and modeling toolsets, novel design rules for responsive hydrogels with control over the structure-property relationships, and a framework to predict the friction coefficient as a function of the operating conditions and hydrogel composition.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.