Noise-activated dissociation of soft elastic contacts

Abstract

Adhesive forces are capable of deforming a soft elastic object when it comes in contact with a flat rigid substrate. The contact is in stable equilibrium if the total energy of the system arising from the elastic and surface forces exhibits a minimum at a zero or at a slightly negative load.However, as the system is continually unloaded, the energy barrier decreases and it eventually disappears, thus leading to a ballistic separation of the contact. While this type of contact splitting has received wide recognition, what has not been much appreciated with these types of soft adhesion problems is that rupture of a contact can also occur at any finite sub critical load in the presence of a noise. The soft contact problems are unique in that the noise can be athermal, whereas the metastable and stable states of the thermodynamic potential can arise from the competition of the elastic and the interfacial energies of the system. Analysis based on Kramers' theory and simulations based on Langevin dynamics show that the contact rupture dynamics is amenable to an Eyring's form of a force and noise induced escape of a particle from a potential well that is generic to various types of colloidal and macromolecular processes. These ideas are useful in understanding the results of a recent experiment involving the noise activated rolling dynamics of a rigid sphere on a surface, where it is pinned by soft micro-fibrillar contacts.*

Noise-Activated Fast Locomotion of DNA through the Frictional Landscape of Nanoporous Gels

“…The use of external Gaussian noise alleviates the effect of the nonlinear solid friction (“noise lubricity”) and enhances the mobility retaining the resolution characteristics of the gel (Figure a). An earlier report suggests a similar subcritical detachment of a soft elastic body from a rigid contactor in the presence of mechanical noise that promotes diffusive exploration of different states in an energy landscape and selects the least action pathway …”

“…An earlier report suggests a similar subcritical detachment of a soft elastic body from a rigid contactor in the presence of mechanical noise that promotes diffusive exploration of different states in an energy landscape and selects the least action pathway. 17 Modified Langevin Model. The noise used here is the time-dependent acceleration = t ( ) qV t md ( ) , experienced by each base pair unit (see the SI).…”

Mechanical Contact Spectroscopy: Characterizing Nanoscale Adhesive Contacts via Thermal Forces

“…For the case of a 1-μm-diameter polystyrene particle adherent to glass ( E * = 2.5 GPa) with a rather low work of adhesion of 1 mJ·m –2 , U a is ∼58 k B T for the JKR model and ∼28 k B T for the DMT model (i.e., much higher than the thermal energy k B T that drives the stochastic position fluctuations of the particle). Thermal forcing adopted in our adhesion experiments differentiates our approach from the studies reported in ref and , where adherent spheres rolled under the influence of a constant external bias force and controlled mechanical noise. In these experiments, the contact area between the sphere and the supporting substrate moved, and the dynamics of the system was strongly affected by nonlinear, hysteretic forces with the character of dry friction .…”