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Andrey V. Dobrynin**, University of Connecticut

Adhesion and contact phenomena play an important role in colloidal science, tribology, pharmaceutical science and technology, biophysics and biochemistry. They provide us with understanding of mechanisms for friction between surfaces, adhesion and deformation of cells, liposomes, micro and nanocapsules. Furthermore, they are of paramount importance for nanofabrication and nanomolding.

Using molecular dynamics simulations and theoretical analysis we study static and dynamics of peeling off of nanoparticles from adhesive substrates. The critical detachment force, *f**, is calculated as a function of the nanoparticle radius, *R*_{p}, shear modulus, *G*, surface energy, _{γp}, and work of adhesion, *W*. The magnitude of the detachment force is shown to increase from *πWR _{p} *to 2.2

We applied Kramers theory of the stochastic barrier crossing in the effective one dimensional potential to study dynamics of nanoparticle detachment. The activation energy, Δ*E*, for nanoparticle detachment first decreases linearly with increasing the magnitude of the applied force, *f*, then it follows a power law *ΔE*_{0}~(*f**-*f*)^{3/2} as magnitude of the pulling force *f* approaches a critical detachment force value, *f**. These two different regimes in activation energy dependence on the magnitude of the applied force are confirmed by analyzing nanoparticle detachment in effective one dimensional potential obtained by Weighted Histogram Analysis Method. In the framework of the scaling approach we show that detachment of nanoparticle proceeds through neck formation and magnitude of the activation energy is determined by balancing surface energy of the neck connecting particle to a substrate with elastic energy of nanoparticle deformation. In this regime the activation energy at zero applied force, *ΔE*_{0}~γ_{p}^{5/2}R_{p}^{1/2}G^{-3/2}δ^{-3.75}, is a universal function of the parameter δ .