Theoretical and experimental investigation of detachment of colloids from rough collector surfaces

This study systematically examined coupled influence of particle size and surface roughness on colloid detachment during transients in solution chemistry. A modified Derjaguin approach was utilized to three-dimensional which determined the variation of Derjaguin–Landau–Verwey–Overbeek (DLVO) interaction energies in detachment processes for elemental models of a rough surface: a hemisphere on a flat surface or two hemispheres against each other on a flat surface. Theoretical results show that the nano-scale protruding asperities on surfaces play a critical role in detachment of colloids from primary minima upon reduction of solution ionic strength. Critical electrolyte concentrations exist for detachment of colloids from primary minima and they are lower for detachment of larger colloids. Critical electrolyte concentrations disappear if cation exchange is present. The reduction of secondary minima by surface roughness assists detachment of micro-sized colloids at high ionic strengths (e.g., ≥0.1 M in this study). Spontaneous detachments from secondary minimum occur for micro-sized colloids attached at low ionic strengths (e.g., ≤0.01 M) and for nanoparticles attached under unfavorable conditions. The theoretical results of this study are supported by the observations in our experiments and provide plausible explanations for the reported detachment behaviors in literature. Whereas the fact that surface roughness reduces energy barrier and accordingly increases attachment in primary minima has been widely recognized in the literature, our study shows that surface roughness also favors attachment in secondary minima and detachment from both primary and secondary minima.