Figure 4. Variation of shear forces with load.
(a) Variation of shear forces (Fs) with normal load (Fn) between avidin-bHA-DPPC-bearing surfaces across water (black symbols) and 0.15 M KNO3 solution (red symbols). The black data points are the Fs versus Fn variation for the highest and lowest high-pressure μ (coefficient of friction) values, while the shaded area includes all data with intermediate μ values (omitted for clarity). The limiting pressures P at the maximal loads (Fn, max) for selected profiles and the corresponding values of μ=Fs, max/Fn, max are indicated, while the broken line (μ=1.5 × 10−3) is a guide to the mean of the data. (b) Fs versus Fn variation for first (empty symbols) and second (full symbols) approaches at different contact points, showing the reduction in friction following removal of residual liposomes. (c) Fs versus Fn variation between sliding mica surfaces bearing avidin-bHA alone (before complexation with PC lipids), from this study (stars) and from ref. 30 (crosses); the broken line is taken from the main figure, showing the reduction in μ by over two orders of magnitude once PC lipids complex with the HA. Results reported are based on five different experiments and two to four different contact position within each experiment.