Tribological properties of N-isopropylacrylamide as studied by scanning force microscopy

The tribological properties of N-isopropylacrylamide (NIPA) gel surfaces were studied using scanning force microscopy (SFM) in air or in a temperature-controlled liquid cell. Topography and friction were probed with smooth, micrometer-sized glass spheres mounted on V-shaped cantilevers. The friction coefficients, μ, were evaluated from the slope of plots of the lateral force versus load. The respective value for the water-swollen NIPA gel (μ=0.42±0.05) was found to be only slightly smaller than that for the dry gel, but higher by a factor of more than 10 compared with macrotribological measurements in water. The high friction of NIPA in water is most probably influenced by the long-range adhesive forces (ranging up to 13 nN) as observed in measurements of force–displacement curves.