Deformation and Adhesion of Elastomer Microparticles Evaluated by AFM

Abstract

An atomic force microscope was used to investigate the adhesion behavior of a viscoelastic particle of micron size on a mica plate in water, by attaching a particle of polydiethylhexyacrylate on the end of the cantilever. Load-penetration curves were obtained by pressing the particle to the mica surface and retracting from it afterward. Our attention was especially focused on the individual contribution of the loading and unloading rates, the maximum load, and the contact time of surfaces to the load-penetration curve. A significant hysteresis between the loading and unloading regimes was observed. Two energy dissipation processes were distinguished in this hysteresis; one was correlated with the viscoelastic loss during the detachment, and the other was correlated with the increase of the adhesive force with the contact time. To analyze the features observed, we employed the Johnson-Kendall-Roberts theory, which was modified to allow the increase of the interfacial energy with the contact time. The proposed model was found to give a very good qualitative description for the particle adhesion, which enabled us to estimate the time dependence of the specific work of adhesion as well as the elasticity modulus of particles.

Application of the Johnson–Kendall–Roberts model in AFM-based mechanical measurements on cells and gel.

“…2B and 5B). The kinetics of adherence of viscoelastic bodies is now under theoretical and experimental study, and a good correspondence between theory and experiments was obtained for such elastomer as poly(dimethylsiloxane) [36,48,49]. However, cells with complex internal structure (membrane, cytoskeleton, and cytoplasm) represent a more complicated case.…”

“…After sample-probe contact is established, the work of adhesion increases to its equilibrium value, probably due to the relaxation of stresses stored in asperities at the probe-sample contact or due to the breakage of adsorbed layers of water molecules and ions between surfaces [36]. For cells, the equilibrium, if actually possible, can only be achieved on a very long timescale.…”

“…3A, S7). It is known that the adhesion force may increase with the holding time, probably due to the relaxation of stresses stored in asperities at the probe-sample contact, or due to the breakage of adsorbed layers of water molecules and ions between surfaces [36]. This fact can be interpreted as an increase of over contact time to its equilibrium value.…”

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

“…[276,277]. Also the effect on the sample deformation of maximum load [278], contact time [279], and loading rate [280] have been characterized.…”

The Colloidal Probe Technique and its Application to Adhesion Force Measurements

“…Hence the adhesion depends on contact time in the first situation but does not in the second. In a different study, Vakarelski et al [69] investigated the adhesion of viscoelastic polymer particles (98 wt % poly(diethylhexacrylate) and 2 wt % poly(acrylmethacrylate), coated with a few nm of poly(methylmethaycrylate) in pure water on mica. The shape of the loading curves was independent of the loading rate (10 ± 1000 nm/s) but the adhesion increased with increased unload rates.…”