Abstract
We recently proposed a new method for generating monodispersed nanobubbles from porous glass membranes with uniform pores, in a system consisting of a gaseous phase and a continuous water phase containing a surfactant. In this study, the effect of the surface wettability of the membrane on monodispersed nanobubble formation, using various surface-modified membranes, was examined. The bubbles were generated by forcing air through a surface-modified membrane with mean pore diameters of 72, 210 and 530 nm into distilled water containing 0.3 wt.% of sodium dodecyl sulfate. The membranes were chemically modified with different silane coupler reagents and their surface wettability was evaluated from the contact angle between the membrane surface and the water phase. The contact angle, θ, could be controlled by the number of carbon atoms of the alkyl group in the reagent and/or the concentration of the reagent. Nanobubbles with a narrow diameter distribution were generated from a membrane with θ < 45°. Bubble diameter was determined by the pore diameter and was independent of the contact angle. In contrast, relatively large bubbles with a broad diameter distribution were generated from a membrane with θ > 45°. In this case, an increased contact angle brought about an increase in the mean bubble diameter and a decrease in the monodispersity of the bubbles.
