Fig. 1
From: Molecular probes reveal deviations from Amontons’ law in multi-asperity frictional contacts
Experimental setup. A rheometer is mounted on top of an inverted confocal laser scanning microscope (not to scale). We excentrically glue a rough sphere to the rheometer plate and make contact with a smooth and flat, float glass, coverslip. The rheometer measures normal and frictional forces on the contact. The inverted microscope excites a monolayer of rigidochromic molecules on the glass surface with 488 nm laser light and point scans images (at a large magnification: ×63, numerical aperture 1.4) the resulting fluorescence that is emitted at the real contact area between the sphere and the glass. Two beam splitters and a long pass filter are used to collect the fluorescent light in a photomultiplier tube. To avoid strong light scattering and optimize image quality, we immerse the contacts in formamide and use transparent materials for the sphere: polystyrene (PS), poly(methyl methacrylate) (PMMA), polytetrafluoroethylene (PTFE), and borosilicate glass
