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.

Interactions between a deformable polymer particle and a solid surface of a mica plate in solutions were investigated using atomic force microscopy (AFM), where the particles have the same surface property but different bulk elasticity. Measurements were done in a solution of cetyltrimethylammonium bromide (CTAB), above its critical micelle concentration (cmc). Under these conditions positively charged layers were formed on both mica and particle surfaces, which induce a high repulsive potential between the approaching surfaces. However, above a critical pressure, the surfaces come in adhesive contact by destroying the adsorbed layers. It was found that the total repulsive force between the surfaces and the force required to adhere the particle to the surface increased significantly if the glass transition temperature of the particle was below the ambient temperature. This indicates that the elastic deformation of the particle as the surfaces are brought together greatly increases the total repulsion within the system. A quantitative interpretation of the data was carried out, using a simple model, which was derived from the theory for elastic body deformation developed by Hughes and White. 1 Results of this study provide significant information on the stability of suspensions of low elastic modulus particles.

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