Wetting of planar solid surfaces by bicontinuous sugar surfactant-based microemulsions
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Optimal wetting of solid substrates is an essential prerequisite for extractive mass transport out of the surface into a microemulsion. In contrast to its importance for practical applications, the wetting properties of microemulsions still are partly unknown. Here, we use contact angle goniometry and Wilhelmy-type force measurements to characterize the wetting of bicontinuous microemulsions at hydrophilic and hydrophobic solid substrates. Microemulsions of different oil-to-water ratios from the bicontinuous region of two quaternary systems, built up by oil (a nonpolar (tetradecane) and a polar oil (methyl oleate)) in combination with water, sugar surfactant, and alcohol (pentanol) have been used. For all microemulsions, a partial wetting regime was found at planar model surfaces. The wetting of hydrophobic surfaces shows differences related to the wetting behavior of the oil component and its adhesion to the substrate. The contact angle hysteresis indicates the formation of adsorption layers between surface and microemulsion bulk.
KeywordsMicroemulsions Structural properties Adsorption Ordering
Methyl oleate and surfactant solution Simusol SL55 were kindly provided by BASF and Seppic GmbH. We gratefully acknowledge funding by the Deutsche Forschungsgemeinschaft (DFG) (Grants HE2995/3-1 and WE5066/1-1). We thank Dataphysics for kindly providing the DCATS software for performing dynamic contact angle measurements.
This study was funded by Deutsche Forschungsgemeinschaft DFG (grant number WE5066/1-1 (S. Wellert) and HE2995/3-1 (T. Hellweg)).
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Conflict of interests
The authors declare that they have no conflict of interest.
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