Deprotonation-Driven Interfacial Packing and Steric Hindrance of a Branched Cationizable Surfactant at Silicate Interfaces

Abstract

The separation of silicate minerals with similar crystal structures requires precise interfacial regulation. In this work, a cationizable surfactant, N-Dodecyl-β-Amino-Methyl-2-Methylpropanoate (DAMM), was synthesized to modulate solid–liquid and gas–liquid interfaces. Microflotation results showed a recovery difference of nearly 90% between quartz and K-feldspar at pH 11 with a DAMM dosage of 20 mg/L. Hydrodynamic and DFT analyses indicated that deprotonation of DAMM at pH 11 reduces its hydration energy, leading to phase separation and the formation of colloidal aggregates. These aggregates suppress bubble coalescence through a Pickering-type stabilization mechanism. Furthermore, XPS analyses and DFT computations clarified the exclusion mechanism at the solid–liquid interface. The electron-withdrawing ester group reduces the electrostatic attraction to K-feldspar. Concurrently, the bulky branched ester group hinders penetration of the interfacial hydration layer, increasing the desolvation penalty and spatial steric constraints, which restricts stable anchoring. This study links molecular structure design with macroscopic interfacial behavior, providing a theoretical reference for silicate separation.