Nanoscopic adhesion test for polymers by a light-lever system

Abstract

Polymer nano-adhesion between a cantilever tip coated with polymer and a flat polymer film was studied by a light-lever system using an atomic force microscope. The polymer interface was adhered at a temperature above the surface glass transition temperature for a given time. Nano-adhesion force ( F nano ), at which the tip was detached from the surface, was estimated from the deflection of the lever with a known spring constant. Nano-adhesion strength ( G N ) was simply obtained dividing F nano by the contact area, which was estimated on the basis of Johnson-Kendall-Roberts theory. The time evolution of the interfacial thickness was independently examined by dynamic secondary ion mass spectrometry. Interestingly, G N increased with increasing interfacial thickness. However, it can be hardly judged whether G N is proportional to the interfacial thickness with the exponent of 1 or 2. Then, temperature dependence of G N was examined. Above the bulk glass transition temperature, the relation between temperature and G N was well expressed by a Williams-Landel-Ferry type equation. This means that the nano-adhesion strength is governed by friction between segments. Once this is accepted, G N should be proportional to the interfacial thickness with the exponent of 2.