Surface microtopography of surfactant modified montmorillonite

Low-pressure gas adsorption experiments and Atomic Force Microscopy (AFM) were used to investigate the microtopography of surfactant modified montmorillonites. These two methods not only permit measurement of the specific surface area, mapping the images of surfactant modified montmorillonites on the nano-scale, but also provide the possibility to determine surface roughness and irregularities. The fractal Frenkel–Halsey–Hill model (DF) and Neimark–Kiselev model (DN) were applied to quantitatively evaluate the heterogeneities of organo-montmorillonite surface by analyzing low-pressure nitrogen gas adsorption isotherms at 77 K. When the dosage of surfactant, expressed as a function of the cation exchange capacity (CEC), increased from 0.2 to 4 CEC, the fractal dimensions changed from DF = 2.88 to 2.59 and DN = 2.58 to 2.12, reflecting that the surface roughness of montmorillonite was influenced by surfactant loading. Higher surfactant loading caused smoother surfaces, which was consistent with the AFM observation.