Particle adhesion to rough surfaces

Engineering Large-Area Antidust Surfaces by Harnessing Interparticle Forces

Dust accumulation is detrimental to optical elements, electronic devices, and mechanical systems and is a significant problem in space missions and renewable energy deployment. In this paper, we report the demonstration of antidust nanostructured surfaces that can remove close to 98% of lunar particles solely via gravity. The dust mitigation is driven by a novel mechanism, whereby particle removal is facilitated by the formation of particle aggregates due to interparticle forces, allowing the particles to be removed in the presence of other particles. The structures are fabricated using a highly scalable nanocoining and nanoimprint process, where nanostructures with precise geometry and surface properties are patterned on polycarbonate substrates. The dust mitigation properties of the nanostructures have been characterized using optical metrology, electron microscopy, and image processing algorithms to demonstrate that the surfaces can be engineered to remove nearly all of the particles above 2 μm in size in the presence of Earth's gravity. Compared to the 35.0% area coverage on a smooth polycarbonate surface, the particle coverage on nanostructures with 500 nm period is significantly reduced to 2.4%, an improvement of 93%. This work enhances the understanding of the particulate adhesion on textured surfaces and demonstrates a scalable, effective solution to antidust surfaces that can be broadly applied to windows, solar panels, and electronics.

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

The surface element integration (SEI) method is a computationally facile technique for calculating DLVO interactions between particles and surfaces. This method yields the exact total DLVO interaction between a particle and a flat surface; however, all surfaces have some degree roughness that profoundly affects the interaction. Previously, an ad hoc approximate method has been used to extend the SEI method to interactions between particles and surfaces with arbitrary morphology. Here we derive a more rigorous approximate method based on the fundamental scaling of DLVO interactions, which approaches the exact solution as the separation distance decreases regardless of the particle or surface morphology. We verify this method by comparison to the exact van der Waals energy when roughness is present on the particle and surface. The accuracy of this method at small separations makes it well-suited for the contexts of particle adhesion and deposition in which the length scale of interaction is on the order of angstroms and nanometers, respectively.

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

It is commonly assumed that van der Waals forces dominate adhesion in dry systems and electrostatic forces are of second order importance and can be safely neglected. This is unambiguously the case for particles interacting with flat surfaces. However, all surfaces have some degree of roughness. Here we calculate the electrostatic and van der Waals contributions to adhesion for a polarizable particle contacting a rough conducting surface. For van der Waals forces, surface roughness can diminish the force by several orders of magnitude. In contrast, for electrostatic forces, surface roughness affects the force only slightly, and in some regimes it actually increases the force. Since van der Waals forces decrease far more strongly with surface roughness than electrostatic forces, surface roughness acts to increase the relative importance of electrostatic forces to adhesion. We find that for a particle contacting a rough conducting surface, electrostatic forces can be dominant for particle sizes as small as ∼1-10 μm.

Derjaguin-Landau-Verwey-Overbeek energy landscape of a Janus particle with a nonuniform cap

A colloidal particle is often termed "Janus" when some portion of its surface is coated by a second material which has distinct properties from the native particle. The anisotropy of Janus particles enables unique behavior at interfaces. However, rigorous methodologies to predict Janus particle dynamics at interfaces are required to implement these particles in complex fluid applications. Previous work studying Janus particle dynamics does not consider van der Waals interactions and realistic, nonuniform coating morphology. Here we develop semianalytic equations to accurately calculate the potential landscape, including van der Waals interactions, of a Janus particle with nonuniform coating thickness above a solid boundary. The effects of both nonuniform coating thickness and van der Waals interactions significantly influence the potential landscape of the particle, particularly in high ionic strength solutions, where the particle samples positions very close to the solid boundary. The equations developed herein facilitate more simple, accurate, and less computationally expensive characterization of conservative interactions experienced by a confined Janus particle than previous methods.