Interest in how particles adhere to different substrates is of significant importance in many fields. Understanding this adhesion - the theory and physical contributions behind it - is the backbone to understanding efficient and effective ways of particle removal.
Particles adhere due to a number of attractive forces. Among the most significant of these is the van der Waals force. Other forces that can contribute to the adhesion of particles are electrostatic, solvation, and hydration forces. All of these forces are affected by various physical aspects of the system of interest: geometry, surface roughness, and deformation.
When deformation of a particle or substrate occurs, it brings more surface area into contact. This increase in contact area results in greater adhesion between the two surfaces. In order to accurately estimate how strongly a particle will adhere to a substrate, the amount of particle and/or substrate deformation must be predicted. This predicted deformation is a function of the forces in contact and the material properties of the deformable material; including the Young's Modulus and Hardness. In this study, the dynamics of organic particle deformation, rather than the equilibrium deformation, is of interest. The dynamic deformation was evaluated by first obtaining the material properties of the particle and/or substrate in the system of interest. These were extracted from nanoindentation measurements performed using an atomic force microscope (AFM). AFM-based force measurements were then performed to assess the magnitude of the adhesion force between the particle and substrate of interest. These measurements supplied both the van der Waals force of attraction as a function of the particle-substrate separation distance, and the pull-off force, which is the force required to remove the particle from contact with the substrate. Using an existing modeling and simulation framework to describe the van der Waals force of adhesion, and comparing the expected adhesion force to the measured pull-off force, it was possible to assess the dynamics of deformation as a function of the system composition and the rates at which the particles and substrate were brought into and out of contact.
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