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Influence of Surface Topography on the Interactions between Nanostructured Hydrophobic Surfaces
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
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2012 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, no 21, 8026-8034 p.Article in journal (Refereed) Published
Abstract [en]

Nanostructured particle coated surfaces, with hydrophobized particles arranged in close to hexagonal order and of specific diameters ranging from 30 nm up to 800 nm, were prepared by Langmuir-Blodgett deposition followed by silanization. These surfaces have been used to study interactions between hydrophobic surfaces and a hydrophobic probe using the AFM colloidal probe technique. The different particle coated surfaces exhibit similar water contact angles, independent of particle size, which facilitates studies of how the roughness length scale affects capillary forces (previously often referred to as "hydrophobic interactions") in aqueous solutions. For surfaces with smaller particles (diameter < 200 nm), an increase in roughness length scale is accompanied by a decrease in adhesion force and bubble rupture distance. It is suggested that this is caused by energy barriers that prevent the motion of the three-phase (vapor/liquid/solid) line over the surface features, which counteracts capillary growth. Some of the measured force curves display extremely long-range interaction behavior with rupture distances of several micrometers and capillary growth with an increase in volume during retraction. This is thought to be a consequence of nanobubbles resting on top of the surface features and an influx of air from the crevices between the particles on the surface.

Place, publisher, year, edition, pages
2012. Vol. 28, no 21, 8026-8034 p.
Keyword [en]
Adhesion, Contact angle, Hydrophobicity, Surface chemistry, Thin film transistors
National Category
Chemical Sciences
URN: urn:nbn:se:kth:diva-98328DOI: 10.1021/la300628mISI: 000304492700011ScopusID: 2-s2.0-84861619050OAI: diva2:536949

QC 20120625

Available from: 2012-06-25 Created: 2012-06-25 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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