The Tribological Properties of Polyacrylamide Hydrogel Particles Open Access

Cuccia, Nicholas Louis (2017)

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Polyacrylamide hydrogel particles are a popular material in all realms of science. In particular, they have recently become a useful system for modeling low-friction, granular materials near the jamming transition. Because a gel consists of a polymer network filled with solvent, its surface behavior exhibits non-classical tribological properties. As a result, the frictional coefficient can vary between 0.001 and 0.03 depending on several factors such as contact area, sliding velocity, normal force, and the gel surface chemistry. Previous tribological experiments of gels utilize two flat surfaces to make measurements, in which the contact area is not well defined. We have built a custom, low-force tribometer to measure the single-contact frictional properties of spherical hydrogel particles on flat hydrogel surfaces under a variety of measurement conditions. From our measurements, we have found a positive correlation between the frictional coefficient and sliding velocity and a negative correlation between the normal load and frictional coefficient. In trying to explain these results, we make use of a hydrodynamic lubrication theory for an object in Hertzian contact. Our measurements have shown that this model is accurate within the high-velocity (>1 cm/s), high-load (>0.1 N) range, but loses precision in the low-velocity (<1 cm/s) and in the low-load (<0.1 N) limit.

Table of Contents


1 Between a solid and liquid

1 Gels are everywhere

2 Granular systems

3 Strange surface properties

4 Strange frictional properties


5 Classical Friction

5 Gel Friction

7 Tribological Methods

8 Lubrication Layer

9 Elasto-Hydrodynamic Model

Materials and Methods

13 Ultra-Low Friction Tribometer

14 Polyacrylamide Hydrogel

Results and Discussions

16 Coefficient vs. Sliding Velocity

17 Coefficient vs. Normal Load

18 Normalization of Curves

20 A Solid Ball

Final Remarks

21 Conclusions

21 Future Directions

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