Heterogeneous Nucleation and Growth of Barium Sulfate at Organic–Water Interfaces: Interplay between Surface Hydrophobicity and Ba2+ Adsorption

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• 作者：Chong Dai ; Andrew G. Stack ; Ayumi Koishi ; Alejandro Fernandez-Martinez ; Sang Soo Lee ; Yandi Hu
• 刊名：Langmuir
• 出版年：2016
• 出版时间：May 31, 2016
• 年：2016
• 卷：32
• 期：21
• 页码：5277-5284
• 全文大小：455K
• 年卷期：0
• ISSN：1520-5827

文摘

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 Ba²⁺ adsorption onto the substrate and incipient BaSO₄ nuclei. The importance of Ba²⁺ adsorption was further corroborated by the finding that precipitation rate increased under [Ba²⁺]/[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.