FIGURE 4.

Magnification of surface-force isotherms in the low-force regime. The weak double-layer repulsion forces have been subtracted to illustrate the small hysteresis. Black symbols are loading cycles and gray symbols are unloading cycles; squares stand for 1 mM KCl solution and triangles for water; panel a illustrates the attractive forces in the asymmetric case, and panel b shows those observed in the symmetric case. The loading/unloading speed was 1 nm/s. The absolute errors in this graph are dominated by uncertainties of fitting (and subtracting) the weak double-layer force. For the sake of simplicity the estimated error bar is shown exemplarily for one point only.