A4. Deformation and Adhesion of Elastomer Microparticles Evaluated by AFM

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Ko Higashitani, Ivan U. Vakarelski
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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.