Probing spatial variation in AFM-measured adhesion: Implication of distributed nanoscale charge heterogeneity

Nanoscale charge heterogeneity is often invoked to explain colloid attachment to grain surfaces in the presence of repulsive energy barriers, yet characterizing its direct impact on the detected spatial variation of colloid-surface interactions through spectroscopy remains unexplored. To gain deeper insights into how intrinsic charge heterogeneity impacts colloid-surface adhesion forces, we measured the spatial distribution of adhesion forces between carboxylated polystyrene latex microspheres and hydrophilic silica substrates in an aqueous solution across different NaCl concentrations (SC) using colloid-probe atomic force microscope (AFM). Trends of mean measured adhesion force with SC were compared to predictions from DLVO and extended DLVO (xDLVO) theories. The xDLVO framework successfully captured the observed trend with NaCl concentration via the impact of NaCl concentration on the repulsive hydration force. Incorporating nanoscale charge heterogeneity into colloid-surface interaction simulations reproduced the experimentally-observed variation around the mean, highlighting the prominent contribution of charge heterogeneity to observed spatial variation of adhesion forces.