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The sliding friction of various kinds of hydrogels has been investigated, and it has been found that the frictional behaviors of these hydrogels do not conform to Amonton's law F = μW, which well describes the friction of a solid. Instead, the friction force F of the gel shows slight dependence on the load W in the investigated load range, while it strongly depends on the sliding velocity. Additionally, the frictional coefficient μ of the gel reaches a value as low as ∼10-3, which is smaller than those observed in solid materials.
Gong et al. (Tue,) studied this question.