Friction of Gels. 5. Negative Load Dependence of Polysaccharide Gels

Abstract

The sliding friction of three kinds of polysaccharide gels, agarose, gellan, and κ-carrageenan, against a glass plate has been investigated under aerobic and water condition. The frictional force of these gels slightly increases with the increase in the load applied in air, while it strongly increases with the load in water. However, when the load exceeding a critical value is applied, the frictional force of gellan gel and κ-carrageenan gel showed a pronounced negative load dependence. The observed specific phenomenon seems to be originated from the instability of the network of the polysaccharide gel. High loading leads to the loosing and/or dissolution in part of the cross-linkage and brings about an increased hydrodynamic water layer that serves as a good lubricator under the high load. The mechanism of friction was discussed in terms of the repulsion−adsorption model of friction proposed by the authors.