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Solvent segregation and capillary evaporation at a superhydrophobic surface investigated by confocal Raman microscopy and force measurements
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
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2011 (English)In: SOFT MATTER, ISSN 1744-683X, Vol. 7, no 3, 1045-1052 p.Article in journal (Refereed) Published
Abstract [en]

Wetting of water, a 1 : 1 water/ethanol mixture and an aqueous dodecylbenzene sulfonic acid surfactant solution on hydrophobic and superhydrophobic surfaces were studied using confocal Raman microscopy. The superhydrophobic surfaces were prepared by immersion of a glass substrate in a silica particle/fluoropolymer formulation followed by silanization. Preparation of hydrophobic surfaces was done in the same way with the exception that the silica particles were excluded from the formulation. The hydrophobic and superhydrophobic surfaces were characterized with respect to surface roughness using AFM, and by contact angle measurements using different liquids. Confocal Raman microscopy measurements in a 1 : 1 water/ethanol mixture showed an enrichment of ethanol close to the superhydrophobic surface, which could not be observed for the hydrophobic surface. Unexpectedly, the Raman spectrum of a pure water film in close proximity to the superhydrophobic surface displayed some differences compared to that of bulk water and indicated a stronger hydrogen-bonding close to the superhydrophobic surface. Evidence for capillary evaporation next to the superhydrophobic surface was also found, and this results in very long-range capillary attraction between one superhydrophobic surface and a hydrophobic colloidal probe as shown by AFM colloidal probe force measurements. Addition of a surfactant or ethanol suppresses capillary evaporation.

Place, publisher, year, edition, pages
2011. Vol. 7, no 3, 1045-1052 p.
National Category
Physical Chemistry
URN: urn:nbn:se:kth:diva-30500DOI: 10.1039/c0sm00704hISI: 000286615500034ScopusID: 2-s2.0-79251504899OAI: diva2:404558

QC 20110317

Available from: 2011-03-17 Created: 2011-02-28 Last updated: 2012-10-11Bibliographically approved
In thesis
1. Hydrophobic surfaces: Effect of surface structure on wetting and interaction forces
Open this publication in new window or tab >>Hydrophobic surfaces: Effect of surface structure on wetting and interaction forces
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The use of hydrophobic surfaces is important for many processes both in nature and industry. Interactions between hydrophobic species play a key role in industrial applications such as water-cleaning procedures and pitch control during papermaking but they also give information on how to design surfaces like hydrophobic mineral pigments.

In this thesis, the influence of surface properties on wetting and interaction forces has been studied. Surfaces with close-packed particles, pore arrays, randomly deposited nanoparticles as well as reference surfaces were prepared. The atomic force microscope (AFM) was utilized for force and friction measurements while contact angles and confocal Raman microscopy experiments were mainly used for wetting studies.

The deposition of silica particles in the size range of nano- to micrometers using the Langmuir-Blodgett (LB) technique resulted in particle coated surfaces exhibiting hexagonal close-packing and close to Wenzel state wetting after hydrophobization. Force measurements displayed long-range interaction forces assigned to be a consequence of air cavitation. Smaller roughness features provided larger forces and interaction distances interpreted as being due to fewer restrictions of capillary growth. Friction measurements proved both the surface structure and chemistry to be important for the observed forces.

On hydrophobic pore array surfaces, the three-phase contact line of water droplets avoided the pores which created a jagged interface. The influence of the pores was evident in the force curves, both in terms of the shape, in which the three-phase contact line movements around the pores could be detected, as well as the depth of the pores providing different access and amount of air. When water/ethanol mixtures were used, the interactions were concluded to be due to ethanol condensation.

Confocal Raman microscopy experiments with water and water/ethanol mixtures on superhydrophobic surfaces gave evidence for water depletion and ethanol/air accumulation close to the surface. Force measurements using superhydrophobic surfaces showed extremely long-range interaction distances.

This work has provided evidence for air cavitation between hydrophobic surfaces in aqueous solution. It was also shown that the range and magnitude of interaction forces could, to some extent, be predicted by looking at certain surface features like structure,roughness and the overall length scales.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xii, 73 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2012:52
hydrophobic surface, superhydrophobic surface, atomic force microscopy, surface forces, capillary forces, cavitaion, surface roughness, friction, wetting, confocal Raman, contact angles, surface preparation, Langmuir-Blodgett
National Category
Chemical Sciences
urn:nbn:se:kth:diva-103409 (URN)978-91-7501-506-4 (ISBN)
Public defence
2012-11-02, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)

QC 20121011

Available from: 2012-10-11 Created: 2012-10-11 Last updated: 2012-10-11Bibliographically approved

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Hansson, Petra M.Claesson, Per Martin
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