Interface between Water–Solvent Mixtures and a Hydrophobic Surface

• Published in: Langmuir Vol. 36; no. 40; pp. 12077 - 12086
• Main Authors: Prihoda, Annemarie, Will, Johannes, Duchstein, Patrick, Becit, Bahanur, Lossin, Felix, Schindler, Torben, Berlinghof, Marvin, Steinrück, Hans-Georg, Bertram, Florian, Zahn, Dirk, Unruh, Tobias
• Format: Journal Article
• Language: English
• Published: American Chemical Society 13.10.2020
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/acs.langmuir.0c02745

The mechanism behind the stability of organic nanoparticles prepared by liquid antisolvent (LAS) precipitation without a specific stabilizing agent is poorly understood. In this work, we propose that the organic solvent used in the LAS process rapidly forms a molecular stabilizing layer at the interface of the nanoparticles with the aqueous dispersion medium. To confirm this hypothesis, n-octadecyltrichlorosilane (OTS)-functionalized silicon wafers in contact with water–solvent mixtures were used as a flat model system mimicking the solid–liquid interface of the organic nanoparticles. We studied the equilibrium structure of the interface by X-ray reflectometry (XRR) for water–solvent mixtures (methanol, ethanol, 1-propanol, 2-propanol, acetone, and tetrahydrofuran). The formation of an organic solvent-rich layer at the solid–liquid interface was observed. The layer thickness increases with the organic solvent concentration and correlates with the polar and hydrogen bond fraction of Hansen solubility parameters. We developed a self-consistent adsorption model via complementing adsorption isotherms obtained from XRR data with molecular dynamics simulations.