title: Probing the Effect of Salinity and pH on Surface Interactions between Air Bubbles and Hydrophobic Solids: Implications for Colloidal Assembly at Air/Water Interfaces.
abstract: In this work, a bubble probe atomic force microscope (AFM) was employed to quantify the interactions between two air bubbles and between an air bubble and an octadecyltrichlorosilane (OTS)-hydrophobized mica under various aqueous conditions. The key parameters (e.g., surface potentials, decay length of hydrophobic attraction) were obtained by analyzing the measured forces through a theoretical model based on Reynolds lubrication theory and an augmented Young-Laplace equation by including effect of disjoining pressure. The bubble-OTS hydrophobic attraction with a decay length of 1.0 nm was found to be independent of solution pH and salinity. These parameters were further used to predict the attachment of OTS-hydrophobized particles onto the air/water interface, demonstrating that particle attachment driven by hydrophobic attraction could be facilitated by suppressing electrical double-layer repulsion at low pH or high salinity condition. This facile methodology can be readily extended to quantify interactions of many other colloidal particles with gas/water and oil/water interfaces, with implications for colloidal assembly at different interfaces in many engineering applications.
authors.affiliation: Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, T6G 1H9, Canada.
authors.forename: Xin
authors.initials: X
authors.lastname: Cui
authors.affiliation: Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, T6G 1H9, Canada.
authors.forename: Chen
authors.initials: C
authors.lastname: Shi
authors.affiliation: Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, T6G 1H9, Canada.
authors.forename: Shuo
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, T6G 1H9, Canada.
authors.forename: Lei
authors.initials: L
authors.lastname: Xie
authors.affiliation: Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, T6G 1H9, Canada.
authors.forename: Jing
authors.initials: J
authors.lastname: Liu
authors.affiliation: Department of Materials and Engineering, National University of Defence Technology, Changsha, 410073, P.R. China.
authors.forename: Dazhi
authors.initials: D
authors.lastname: Jiang
authors.affiliation: Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, T6G 1H9, Canada.
authors.forename: Hongbo
authors.identifier: http://orcid.org/0000-0002-1432-5979
authors.initials: H
authors.lastname: Zeng
keywords: air/water interfaces; atomic force microscopy; bubbles; hydrophobic colloidal particles; surface interactions