(245d) Dynamic Deformation Studies of Visco-Elastic Particles

Visco-elastic particles provide an interesting challenge for adhesion studies.  The tendency of visco-elastic materials to flow over long time scales causes the interfacial contact area between these particles and the surface on which they are attached to change as a function of time, directly affecting the adhesion force between the particles and underlying substrate.  Detection and analysis of these types of particles frequently involves the removal of particles from the substrate, which is a complicated problem to address given the dynamic nature of the adhesion interaction. 

The first challenge in solving the particle-removal problem, then, is to understand and characterize how a visco-elastic particle will deform on a given substrate.  To this end, dynamic studies of particle deformation have been performed whereby visco-elastic particles are first deposited onto well-characterized model substrates and images of the particle taken with a confocal microscope at specified time intervals.  Confocal microscopy allows the precise construction of a 3-dimensional image of the particle that renders both its exact size and shape.  This size and shape information, in turn, allows an accurate determination of the interfacial contact area.  Over several measurements, the change in contact area as a function of time is readily determined.    

Although the confocal microscope studies are essential to understanding the deformation of visco-elastic particles, one of the constraints of these studies is that they are limited to rather ideal geometries and configurations that are easily accessible to a microscope.  Frequently, the unobservable contact patch between the visco-elastic particle and substrate contains multi-scale roughness (~10nm - ~1μm) that heavily influences the deformation and adhesion characteristics of these particles.  Moreover, the underlying geometry may be such that a single particle cannot be readily observed with the confocal microscope.  To extend the deformation studies of these visco-elastic particles to more complicated regimes, we also conduct Smoothed Particle Hydrodynamics¹ simulations of the deformation process on various surfaces.  Smoothed Particle Hydrodynamics is a particle-based continuum material solver that allows us to implement complex free surfaces of arbitrary roughness as well as study the deformation over several time scales with arbitrary initial particle configurations.  With this tool, we are able to access particle deformation regimes that are unavailable or difficult to execute experimentally.  

1: Mohaghan, J.J. Smoothed Particle Hydrodynamics.  Rep. Prog. Phys. 68 (2005) 1703-1759.