title: Evidence for negative charge near large area supported graphene in water: A study of silica microsphere interactions.
abstract: This study addresses the electrostatic and van der Waals interactions at the aqueous interface of large area CVD graphene, 1-3 layers thick on a silica support and assessed by Raman spectroscopy to have exclusive sp2 character. Ionic strength was found to substantially alter the interactions of silica microspheres with silica-supported graphene. Particles were nonadhesive at large Debye lengths but became irreversibly adherent at reduced Debye lengths about 2nm or less. This was demonstrated to be qualitatively parallel to the influence of ionic strength on silica-silica interactions. The observed ionic strength effects are best explained by negative charges in the vicinity, within a few nanometers, of the supported graphene. DLVO-based modeling of the silica-water-supported graphene interaction suggests that van der Waals interactions drive particle capture and that the surface potential at the supported graphene surface is at least -10 to -15mV (corresponding to a charge density of 0.02-0.06/nm2). This charge could result from ion adsorption or from charges on silica beneath the graphene. The conclusions are not substantially affected by inclusion of nanometer-scale interfacial roughness in the modeling.
authors.affiliation: Department of Polymer Science and Engineering, UMass Amherst, 120 Governors Drive, Amherst, MA 01003, United States.
authors.forename: Aaron W
authors.initials: AW
authors.lastname: Chen
authors.affiliation: Department of Polymer Science and Engineering, UMass Amherst, 120 Governors Drive, Amherst, MA 01003, United States.
authors.forename: Bing
authors.initials: B
authors.lastname: Fang
authors.affiliation: Department of Polymer Science and Engineering, UMass Amherst, 120 Governors Drive, Amherst, MA 01003, United States.
authors.forename: Hyunbok
authors.initials: H
authors.lastname: Lee
authors.affiliation: Department of Polymer Science and Engineering, UMass Amherst, 120 Governors Drive, Amherst, MA 01003, United States.
authors.forename: Alejandro L
authors.initials: AL
authors.lastname: Briseno
authors.affiliation: Department of Polymer Science and Engineering, UMass Amherst, 120 Governors Drive, Amherst, MA 01003, United States. Electronic address: Santore@mail.pse.umass.edu.
authors.forename: Maria M
authors.initials: MM
authors.lastname: Santore
keywords: Aqueous; Chemically-deposited graphene; Dispersion forces; Double layer; Pristine graphene; Secondary minima; Surface charge; Wetting transparency