Influence of the surface free energy of liquids and the liquid distribution on the friction of paper wipers

Various soft materials, e.g., paper, cloth, and sponge, can absorb water. In this study, we demonstrated that the influence of the surface free energy of liquid and the liquid distribution on the friction behaviors of a paper wiper on a glass plate. The friction test was performed by varying the liquid content in the paper wiper. Compared with the dry condition, the friction coefficient increased 5.14 times when a certain part of the interface was occupied with water. We found that this high-friction effect decreased with the surface free energy of the liquid, and contact between the liquid droplets in the paper wiper and the glass plate is required to realize the high-friction effect. This high-friction effect is observed for paper wipers, and other soft materials that can absorb liquids, e.g., cloth and sponge, and the findings of this study are expected to help design the friction properties of such soft materials containing small amounts of liquid.