Studying Surface Glass-to-Rubber Transition Using Atomic Force Microscopic Adhesion Measurements

Abstract

Force-distance curves were obtained using a home-built atomic force microscope (AFM) at different temperatures (T ) 30-65°C) and probe rates (f ) 31.25-50 000 Hz) on a 150 nm thick film of a model sample, poly(tert-butyl acrylate) (M w ) 148K Da, Mw/Mn ) 17, and Tg bulk ) 50°C according to DSC). The pull-off force, Fad, at which detachment between the AFM tip and the sample occurred was measured as adhesion. By limiting the loading force, F, to ∼2.5 nN, the tip penetrated by no more than 2 nm into the sample in the glassy state. Therefore, evolution of the rheological properties of the polymer at the free surface with increasing T could be studied. In the vicinity of Tg bulk , Fad was seen to increase rapidly with increasing T or decreasing f. Equivalence between T and f was found using time-temperature superposition in which, upon rescale of f by a temperature-dependent shift factor aT AFM (T), a master curve Fad(aT AFM (T) f) resulted. We showed that Fad(aT AFM (T)f) could be fully accounted for by using an approach based on fracture mechanics of viscoelastic solids. No noticeable enhancement in the surface relaxation could be deduced according to our findings.

Force measurements with the atomic force microscope: Technique, interpretation and applications

“…AFM and dynamic mechanical analysis (DMA) data, and have also determined the coefficients of the Williams-Landel-Ferry equation, in agreement with broadband spectroscopy and DMA (see also [294]). …”

“…The determination of the glass transition temperature of polymer sample via the characterization of the stiffness, of the adhesion, and/or of the elastic-plastic behavior as functions of temperature, has been attempted also with polymer films [292][293][294]. Cappella et al [295] have measured the yielding force and the Young's modulus of PBMA as a function of temperature, showing a very good agreement between Fig.…”

Confinement enhances dispersion in nanoparticle–polymer blend films

“…The sample was heated at a rate of 1°C min À 1 and the force-displacement curve is measured at every 3°C interval. Force-distance spectroscopy is a widely used 42,43 technique that senses the local forces on the sample with a spatial resolution of the order of few tens of nm. Force-displacement curve is a plot between the tip-sample interaction force (F) and the displacement of the sample towards tip (Z).…”

“…Force-displacement curve is a plot between the tip-sample interaction force (F) and the displacement of the sample towards tip (Z). The slope gives a measure of the elastic modulus of the sample 42,43 . The re-trace or trace parts of the force-distance curves were fitted with a straight line and the slopes are extracted at each temperature.…”

Nanomechanical Study of Model Pressure Sensitive Adhesives by Scanning Probe Microscopy

“…As frequency is increased the surface behaves as though it were more stiff 3 . The slopes of the linear portions of the loading curves and the slopes of the initial portions of the unloading curves both increase.…”