A. Dhinojwala, S. Merriman, G. Mallinos
The University of Akron,
United States
Keywords: friction, polyelectrolyte brushes, lubrication
Summary:
Polymer brushes are widely used as nanoscale surface coatings with responsive properties, particularly for achieving tunable friction in solvent environments. In this presentation, I will discuss a unique feature of hygroscopic, polyelectrolyte-grafted brushes, which exhibit a dramatic change in friction, spanning more than two orders of magnitude, within a narrow range of relative humidity. Through combined measurements of nanoscale mechanical modulus, water uptake, frictional response, and surface-sensitive spectroscopy, we show that this sharp transition in friction arises from a humidity-induced glass transition that abruptly alters the mode of sliding. Beyond humidity control, I will also describe how these polyelectrolyte brushes influence water freezing within the brush layer and can be tailored to regulate ice adhesion and friction. By tuning the brush chemistry and water absorption characteristics, we demonstrate the ability to reversibly switch between high- and low-friction states (“on/off” slipperiness). This intrinsic tunability enables design strategies for nanoactuators, ratchets, and biomedical devices such as catheters, without the need for externally applied lubricants.