Particle adhesion to rough surfaces

Abstract

While particle adhesion to smooth surfaces is well understood, real surfaces are not perfectly smooth, and the effects of surface roughness on adhesion are not easily characterized. We develop a theory for the effects of surface roughness on the strength of particle adhesion due to van der Waals forces, in the Derjaguin-Muller-Toporov (DMT)-type adhesion regime. We first address a well-defined rough surface created by embedding spheres in a smooth substrate, which had been previously examined experimentally. We derive an analytic expression for the adhesive force of particles to this well-defined surface, with the key distinction from the previous work being the inclusion of interactions from surface asperities not in direct contact with the particle. We show that our theory is in good agreement with experimental results in the DMT regime. Within appropriate limits, we extend our theory to general rough surfaces and verify the theory by comparing to the exact numerical results. We show that the interactions from surface asperities not in direct contact with the particle are the dominant contribution to the adhesive force under some conditions, and our theory predicts the experimental and numerical adhesion forces very accurately.

DLVO Interactions between Particles and Rough Surfaces: An Extended Surface Element Integration Method

“…Furthermore, these exact methods calculate only the van der Waals interaction; to characterize colloidal systems, incorporating double-layer interactions is crucial. Instead, studies calculating both van der Waals and double-layer interactions between particles and surfaces with non-uniform morphology have generally used one of two approximate methods: the SEI method (extension A) ,,,− or modified Derjaguin methods. ,,,− …”

“…Given the limitations of SEI extension A, as well as the restricted geometries available using modified Derjaguin methods, prior methodologies have not been able to characterize DLVO interactions for particles within valleys of rough surfaces. As a result, studies typically consider interactions on only particles positioned well above a rough surface ,,− or, in the case of adhesion, assume the particle is positioned directly above an asperity of the rough surface. ,− ,, Such assumptions are justified when the particle is much larger than the wavelengths of surface roughness and cannot fit in the valleys. However, smaller particles can fit within valleys of rough surfaces, where they have been shown to preferentially deposit. ,, …”

Relative importance of electrostatic and van der Waals forces in particle adhesion to rough conducting surfaces

“…For the particle system, we use our previously developed analytic approximation for the vdW force between a particle and a rough surface in the DMT regime of adhesion [24]:…”

“…Additionally, all surfaces have some degree of roughness. Many studies have examined the effect of surface rough ness on vdW forces in particle adhesion, finding that surface roughness can greatly diminish vdW forces [19][20][21][22][23][24][25][26]. In fact, increasing roughness has been used to intentionally minimize vdW adhesion [16,25,[27][28][29].…”

Harvesting Energy from Falling Droplets

“…However, liquid-solid triboelectric charging, as in these nanogenerators, is likely simpler and more controllable than its solid-solid counterpart. Interactions between solid surfaces are complicated; roughness reduces the contact area between surfaces and concentrates force at certain points, breaking bonds [8][9][10]. Liquids, on the other hand, deform to make full contact with a solid surface, and their flow avoids the concentration of force that breaks bonds.…”