Figure 2.
(A) Profiles of the normal force (Fn/R) versus D, the separation between the surfaces of the two mica sheets coated with the HSPC-SUV layers (where R is the mean mica radius of curvature). Open symbols indicate the approach of the surfaces (decreasing D) and solid symbols indicate separation of the surfaces (increasing D); different symbols correspond to different contact points. Two limiting hard-wall values of D at the highest compressions were observed (for different contact points, as discussed in the text), shown by arrow (A: D = 20 ± 2 nm; B: D = 30 ± 2 nm). The inset shows the profiles on a linear scale, revealing the existence of a marked attractive-interaction well for some of the approach profiles, and for all of the separation profiles (see text for discussion of this variance). (B and C) Schematic of the (B) HSPC structure and (C) SFB (see Klein and Kumacheva (34) and the Supporting Material for a more detailed description of the SFB). The two surfaces are mounted in a crossed-cylindrical configuration whose normal and lateral motion is controlled via the sectored piezoelectric cylinder (PZT), and normal Fn and lateral Fs forces are evaluated from the bending of the two orthogonal springs of constants Kn and Ks, respectively.