title: Heterogeneous Nucleation and Growth of Barium Sulfate at Organic-Water Interfaces: Interplay between Surface Hydrophobicity and Ba(2+) Adsorption.
abstract: Barium sulfate (BaSO4) is a common scale-forming mineral in natural and engineered systems, yet the rates and mechanisms of heterogeneous BaSO4 nucleation are not understood. To address these, we created idealized interfaces on which to study heterogeneous nucleation rates and mechanisms, which also are good models for organic-water interfaces: self-assembled thin films terminated with different functional groups (i.e., -COOH, -SH, or mixed -SH & COOH) coated on glass slides. BaSO4 precipitation on coatings from Barite-supersaturated solutions (saturation index, SI, = 1.1) was investigated using grazing-incidence small-angle X-ray scattering. After reaction for 1 h, a little amount of BaSO4 formed on hydrophilic bare and -COOH coated glasses. Meanwhile, BaSO4 nucleation was significantly promoted on hydrophobic -SH and mixed -SH & COOH coatings. This is because substrate hydrophobicity likely affected the interfacial energy and hence thermodynamic favorability of heterogeneous nucleation. The heterogeneous BaSO4 nucleation and growth kinetics were found to be affected by the amount of Ba(2+) adsorption onto the substrate and incipient BaSO4 nuclei. The importance of Ba(2+) adsorption was further corroborated by the finding that precipitation rate increased under [Ba(2+)]/[SO4(2-)] concentration ratios >1. These observations suggest that thermodynamic favorability for nucleation is governed by substrate-water interfacial energy, while given favorable thermodynamics, the rate is governed by ion attachment to substrates and incipient nuclei.
authors.affiliation: Department of Civil & Environmental Engineering, University of Houston , Houston, Texas 77004, United States.
authors.forename: Chong
authors.initials: C
authors.lastname: Dai
authors.affiliation: Chemical Science Division, Oak Ridge National Laboratory , P.O. Box 2008, MS-6110, Oak Ridge, Tennessee 37831, United States.
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Stack
authors.affiliation: Univ. Grenoble Alpes, ISTerre, 38041 Grenoble, France.
authors.forename: Ayumi
authors.initials: A
authors.lastname: Koishi
authors.affiliation: Univ. Grenoble Alpes, ISTerre, 38041 Grenoble, France.|CNRS, ISTerre, 38041 Grenoble, France.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Fernandez-Martinez
authors.affiliation: Chemical Sciences and Engineering Division, Argonne National Laboratory , 9700 South Cass Avenue, Argonne, Illinois 60439, United States.
authors.forename: Sang Soo
authors.initials: SS
authors.lastname: Lee
authors.affiliation: Department of Civil & Environmental Engineering, University of Houston , Houston, Texas 77004, United States.
authors.forename: Yandi
authors.initials: Y
authors.lastname: Hu