Surface Analysis of Silica Gel Particles after Mechanical Dry Coating with Magnesium Stearate

Abstract

A dry coating technique has been used to change the surface properties of silica gel particles (d₅₀=55μm) by coating with different mass ratios of magnesium stearate - MgSt₂ (d₅₀=4.6μm): 1%, 5%, 15% and 30%. The dry coating experiments were performed using a “Hybridizer, a high-speed dry impact blending coater”, manufactured by Nara Machinery (Japan). The surface morphology of the uncoated and coated silica gel particles was observed by environmental scanning electron microscopy (ESEM). The images show that a greater MgSt₂ coverage was observed on the surface of silica gel as the MgSt₂ mass ratio is increased. In addition, atomic force microscopy (AFM) analysis revealed how this coating process makes possible a discrete and uniform dispersion of the MgSt₂ particles. AFM studies were carried out with a scanning probe microscope Multimode Nanoscope IIIA (Digital Instruments/Veeco Metrology Group).