Role of surface roughness for colloidal interactions in aqueous media
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The stability of colloidal dispersions is important for many industrial applications, but there are often discrepancies between theoretical descriptions and experimental observations of surface roughness effects, in part because experimental methods used to vary surface topography simultaneously vary surface chemistry. This work sought to experimentally isolate surface roughness effects on colloidal interactions and to specifically examine how surface roughness modulates the electrostatic, van der Waals, and depletion interactions. Roughness effects on these interactions were determined by measuring particle-plate interactions using total internal reflection microscopy with colloidal probe particles of varied surface topography but similar surface chemistry. Results indicate a systematic weakening of the van der Waals attraction as well as an enhancement of the electrostatic repulsion with increasing particle surface roughness. Increasing surface roughness was also shown to suppress the depletion interaction, a phenomenon that has been predicted theoretically but has never been shown for particles that differed only in surface topography. This experimental work demonstrates the influence of surface topography on the DLVO and depletion interactions and can hopefully be used as a benchmark for future, improved models for surface roughness effects on colloidal interactions.