Related Experiment Video
Updated: Aug 9, 2026

Taking Advantage of Reduced Droplet-surface Interaction to Optimize Transport of Bioanalytes in Digital Microfluidics
Published on: November 10, 2014
Modeling of the detachment of a molecule from a surface: illustration of the "Bell-Evans effect"
J Hemmerlé1, C Picart, C Gergely
1Institut National de la Santé et de la Recherche Médicale, Unité 424, UFR d'Odontologie, Université Louis Pasteur, 11, rue Humann, 67085 Strasbourg Cedex, France.
Abstract:
This article deals with the modeling of the detachment of a molecule initially adsorbed on a surface and submitted to an external force whose strength increases with time. By means of an atomic force microscope (AFM), it is possible to measure the force when the molecule separates from the substrate. However, it is known that this force depends to a large extend on the rate at which the pulling force is applied ("Bell-Evans effect"). Two models are described to illustrate this behavior. First, a random walk approach is suggested to reveal the fundamental principle of the escape over a time-dependent energy barrier. Second, a multi bead-and-spring model is proposed to mimic the AFM experiment and numerical simulations, based on Brownian dynamics, are performed.
Related Concept Videos
Molecular Models
Newman Projections
The organic molecules rotate across the single bonds leading to numerous temporary three-dimensional structures of varying energy known as conformers.
Relative Velocity in Two Dimensions
Maxwell-Boltzmann Distribution: Problem Solving
This distribution function f(v) is defined by saying that the expected number N (v1,v2) of particles with speeds between v1 and v2 is given by
Surface Tension

