Continuous Visualization of Time-Dependent Deformation of a Hydrogel Surface

Background

Visualizing the deformation of hydrogels at sliding interfaces remains challenging due to their optical transparency, limiting our understanding of time- and history-dependent surface displacement during continuous sliding.

Objective

To visualize and quantify the lateral surface displacement of hydrogel during continuous sliding and correlate this with frictional behavior.

Methods

Fluorescent markers were embedded in hydrogel samples to enable visualization of surface deformation during sliding. Marker positions were recorded via video and tracked across frames, allowing extraction of time-varying displacement of the hydrogel surface in the sliding direction. The surface displacement was measured at various sliding speeds and compared with friction measurements from tribo-rheometry experiments.

Results

The visualization technique successfully revealed significant time- and history-dependent lateral surface displacement in the hydrogel during continuous sliding. The calculated surface displacement over time at different speeds showed patterns that closely resembled the frictional behavior measured in tribo-rheometry experiments, providing direct visual evidence of surface mechanics.

Conclusions

This work establishes a correlation between visually observed surface displacement and measured friction in hydrogels, supporting the previously proposed rate-and-state hydrogel lubrication model.