AFM study of repulsive van der Waals forces between Teflon AF™ thin film and silica or alumina

An atomic force microscope (AFM) was used to measure the interactions between a flat Teflon AF™ surface and an α-alumina or amorphous silica sphere in cyclohexane as a function of distance of separation. Repulsive van der Waals (vdW) forces were predicted for the interactions between Teflon AF™ and α-alumina or amorphous silica according to the negative Hamaker constants, which were calculated from the dielectric response functions of materials using the Lifshitz theory. The measured forces agree well with the theoretically calculated forces, which include the retardation contribution. The retardation effects are apparent at large distance of separation (>4–5 nm) where the measured forces are weaker than the non-retarded prediction.