Detecting ion-specific forces between fatty acid colloids and salt crystals in brines using colloidal probe AFM

Attraction and adhesion between the lead laurate colloidal probe and the NaCl crystal surface were much stronger than those measured on the KCl crystal surface, explaining the selective separation between NaCl and KCl crystals by flotation in the brines. Theoretical analysis of the measured forces shows the potential role of ion-specific interactions in predicting selective aggregation and flotation separation. Our work provides an innovative approach to quantifying the intermolecular interactions between surfactant colloids and NaCl and KCl crystals, offering new theories on colloid and surface chemistry regarding ion-specific forces that underpin aggregation and separation in brines and beyond.