Ion‐Specific Oil Repellency of Polyelectrolyte Multilayers in Water: Molecular Insights into the Hydrophilicity of Charged Surfaces

Abstract

Surface wetting on polyelectrolyte multilayers (PEMs), prepared by alternating deposition of polydiallyldimethylammonium chloride (PDDA) and poly(styrene sulfonate) (PSS), was investigated mainly in water‐solid‐oil systems. The surface‐wetting behavior of as‐prepared PEMs was well correlated to the molecular structures of the uncompensated ionic groups on the PEMs as revealed by sum frequency generation vibrational and X‐ray photoelectron spectroscopies. The orientation change of the benzenesulfonate groups on the PSS‐capped surfaces causes poor water wetting in oil or air and negligible oil wetting in water, while the orientation change of the quaternized pyrrolidine rings on the PDDA‐capped surfaces hardly affects their wetting behavior. The underwater oil repellency of PSS‐capped PEMs was successfully harnessed to manufacture highly efficient filters for oil‐water separation at high flux.Ölabweisend: Die Benetzbarkeit geladener Oberflächen korreliert mit der molekularen Natur der ionischen Gruppen. Bei isotroper Konfiguration haben Änderungen in der Orientierung der Gruppen kaum einen Einfluss auf die Wasserbenetzung. Bei anisotroper Konfiguration erfolgt ein Übergang von einer niedrigen Wasserbenetzung in Öl zu einer niedrigen Wasserentnetzung in Wasser, was zu exzellenten ölabweisenden Eigenschaften unter Wasser führt.