Journal
JOURNAL OF COLLOID AND INTERFACE SCIENCE
Volume 405, Issue -, Pages 189-194Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jcis.2013.05.003
Keywords
Perfluorinated surfactant; Interfacial aggregation; Self-assembly; Surface micelle; Counterion bridging; Molecular dynamics simulation
Categories
Funding
- NNSF of China [21207151, 21277161, 21007083, 41103076]
- State Key Joint Laboratory of Environment Simulation and Pollution Control [12L02ESPC]
- State Key Laboratory of Environmental Aquatic Chemistry [11Y06ESPCR]
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The surface-associated structures and growth modes of perfluorooctane sulfonate (PFOS) at water-rutile TiO2 interfaces were defined by molecular dynamics (MD) simulations. The results showed that a compact PFOS layer was generated at the rutile surfaces, and the assembling structures and dynamic profiles were crystal-face-dependent. PFOS molecules were attached to the (1 1 0) and (0 0 1) surfaces mainly by the sulfonate headgroups. A well-defined monolayer was formed on the (1 1 0) surface with the perfluorinated alkyl chains nearly perpendicular to the substrate, whereas the C-F chains were inclined at an angle (30-75) and formed a hemicylinder-like configuration on the (0 0 1) surface. On the other hand, the perfluorinated amphiphiles interacted with the (1 0 0) plane through both the sulfonate headgroups (relatively strong electrostatic attraction) and the C-F tailgroups (weak van der Waals forces) and yielded an irregular assembling pattern. Water molecules were mostly concentrated more than 17.0 angstrom away from the solid surfaces and formed a continuous solvent layer, suggesting the super hydrophobicity of perfluorinated alkyl chains. A counterion-bridging mechanism suggested in surfactant adsorption was observed at the molecular scale, where the sulfonate headgroups were linked together by the potassium ions at the surfaces and caused the formation of surface aggregates. (C) 2013 Elsevier Inc. All rights reserved.
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