title: Effect of surface charge density on the affinity of oxide nanoparticles for the vapor-water interface.
abstract: Using in-situ X-ray photoelectron spectroscopy at the vapor-water interface, the affinity of nanometer-sized silica colloids to adsorb at the interface is shown to depend on colloid surface charge density. In aqueous suspensions at pH 10 corrected Debye-Hückel theory for surface complexation calculations predict that smaller silica colloids have increased negative surface charge density that originates from enhanced screening of deprotonated silanol groups (≡Si-O(-)) by counterions in the condensed ion layer. The increased negative surface charge density results in an electrostatic repulsion from the vapor-water interface that is seen to a lesser extent for larger particles that have a reduced charge density in the XPS measurements. We compare the results and interpretation of the in-situ XPS and corrected Debye-Hückel theory for surface complexation calculations with traditional surface tension measurements. Our results show that controlling the surface charge density of colloid particles can regulate their adsorption to the interface between two dielectrics.
authors.affiliation: Institute for Chemical and Bioengineering, ETH Zürich, Zürich, Switzerland. matthew.brown@chem.ethz.ch
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Brown
authors.forename: Nicolas
authors.initials: N
authors.lastname: Duyckaerts
authors.forename: Amaia Beloqui
authors.initials: AB
authors.lastname: Redondo
authors.forename: Inga
authors.initials: I
authors.lastname: Jordan
authors.forename: Frithjof
authors.initials: F
authors.lastname: Nolting
authors.forename: Armin
authors.initials: A
authors.lastname: Kleibert
authors.forename: Markus
authors.initials: M
authors.lastname: Ammann
authors.forename: Hans Jakob
authors.initials: HJ
authors.lastname: Wörner
authors.forename: Jeroen A
authors.initials: JA
authors.lastname: van Bokhoven
authors.forename: Zareen
authors.initials: Z
authors.lastname: Abbas