Influence of surface chemical heterogeneity on attachment and detachment of microparticles

This study theoretically examined attachment/detachment of negatively charged microparticles onto/from a negative planar surface carrying a positively charged square patch of different sizes. The surface element integration technique was used to calculate Derjaguin–Landau–Verwey–Overbeek (DLVO) interaction energies at different ionic strengths. Results show that a critical patch size is needed to attach a particle at a given ionic strength. The critical size decreases with increasing ionic strength and decreasing particle size. Colloid attachment on the patch via primary-minimum association is irreversible to reduction of ionic strength, in contrast to the experimental observations in the literature. We attributed the discrepancy to the fact that chemical heterogeneity is commonly accompanied with topographical variation. To account for the coupled effects on colloid detachment, the collector surface was modeled as a negative planar surface carrying a square prism. If the size of the prism is ≤5 nm × 5 nm × 5 nm, whether the prism surface is positively or negatively charged does not have significant influence on the interaction energy curves at ≤0.01 M. These tiny asperities mainly play a role in eliminating the primary minima of interaction energy curves at the low ionic strengths, causing detachment of colloids from primary minima. For larger prisms, the primary-minimum depths can be increased significantly if the prism surfaces are positively charged, resulting in more irreversible attachments in primary minima. Findings from this study have implications to understanding particle–surface interactions that involve only one ligand–receptor bond (e.g., cell–biomaterial interactions via a single contact).