Characteristic sliding frictional behavior on the surface of nanocomposite hydrogels consisting of organic-inorganic network structure

Sliding frictional behavior on the surface of novel nanocomposite hydrogels (NC gels), composed of poly(N-isopropylacrylamide) and exfoliated clay, was investigated and compared with that of conventional chemically-crosslinked hydrogels (OR gels). Since OR gels are so weak, the sliding test, in general, could not be carried out on their surfaces except when wet. On the contrary, NC gels can withstand sliding friction under high loading and it was found 1 that the frictional forces are sensitive to the environmental surroundings (wet or in-air), the gel composition (water, clay contents), and loading. In air, NC gels exhibit a characteristic force profile with a maximum static frictional force (max-SFF) and subsequent constant dynamic frictional force. In contrast, NC gels exhibit very low frictional forces under wet conditions. The change in frictional force with surroundings was very distinctive for NC gels, particularly for those with low clay contents. Max-SFF for NC1 gel decreased more than 100-fold by changing the environment from in-air to wet. The characteristic sliding frictional behaviors are explained on the basis of a unique organic/inorganic network structure of NC gels.