A computational study of chemically heterogeneous particles: patchy vs. uniform particles in shear flow

TL;DR

This study uses computational modeling to compare how patchy and uniform particles behave in shear flow, revealing differences in adhesion and capture influenced by surface heterogeneity and ionic strength.

Contribution

It introduces a new computational approach to simulate the near-surface motion of heterogeneous particles and quantifies how surface heterogeneity affects particle capture.

Findings

Patchy particles show fewer separation extrema than uniform particles.

Patchy particles are less likely to be captured on uniform surfaces.

Surface heterogeneity effects are most pronounced near a Debye length of 4 nm.

Abstract

The adhesion of flowing particles and biological cells over fixed collecting surfaces is vitally important in diverse situations and potentially controlled by small-scale surface heterogeneity on the particle. Differences in the behavior of patchy particles (flowing over uniform collectors) relative to the reverse case of uniform particles (flowing over patchy collectors) are quantified. Because a particle rotates more slowly than it translates in the shear field near a collecting surface, the effective interaction time of a patch on a particle is larger than that of a patch on the collector, suggesting distinct particle capture tendencies in each case. This paper presents a new computational approach to simulate the near-surface motion (rotation and translation) of particles having nanoscale surface heterogeneities flowing over uniform collectors. Small amounts of ~10 nm cationic patches randomly distributed on a net-negative particle surface produced spatially varying DLVO interactions that were computed via the Grid Surface Integration (GSI) technique and then combined with hydrodynamic forces in a mobility tensor formulation. Statistical analysis of simulated trajectories revealed fewer extrema in the fluctuating particle-collector separation of heterogeneous particles, compared with the reverse system geometry of uniform particles flowing past a heterogeneous fixed surface. Additionally, the patchy particles were captured to a lesser extent on uniform surfaces compared with the case of uniform particles flowing above patchy collectors. Such behavior was dependent on ionic strength, with the greatest differences obtained near a Debye length of $\kappa^{-1} = 4$ nm for the $2a = 500$ nm simulated particles.