Quantitative Friction Map on Surface Composed of β-Cyclodextrin Monolayer

Our developing method "quantitative friction map" enables us to compare the spatial distribution of friction forces on the surface among separately scanned samples sensitively. We applied this technique to evaluate the friction acting between mono-[6-deoxy-6-[(mercaptoethyl)amino]]-beta-cyclodextrin (beta-CD-EA-SH) and OH-terminated C11 alkanethiol (OH-C11-SH) self-assembled monolayers (SAMs) in terms of symmetric and asymmetric features. The friction acting between symmetric beta-CD-EA-SH SAMs is significantly larger than that acting between asymmetric beta-CD-EA-SH SAM vs OH-C11-SH SAM and symmetric OH-C11-SH SAMs, although all the surfaces are commonly composed of hydroxyl terminated groups. The different frictional forces on these surfaces are closely correlated with the different adhesion forces, in which symmetric beta-CD-EA-SH SAMs exhibited 1.5- and 1.3-fold larger pull-off force than beta-CD-EA-SH SAM vs OH-C11-SH SAM and symmetric OH-CII-SH SAM vs OH-CII-SH SAM, respectively. Both force data can be explained by the "specific interactions" between glucose units on cyclodextrin heads rather than the deformation of the SAM by cantilever scanning.