Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Trapping of Water Drops by Defects on Superhydrophobic Surfaces
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
Solid Mechanics , Department of Management and Engineering, the Institute of Technology, Linköping University.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.ORCID iD: 0000-0001-8622-0386
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In this work the effect of line‑shaped defects on the motion of water drops on superhydrophobic surfaces have been investigated using high‑speed video. The defects were introduced on superhydrophobic wax surfaces by a simple scratching method. It is shown that the motion of the drop in the vicinity of the defect can be approximated by a damped harmonic oscillator. Whether a drop gets trapped or not while traversing the defect is determined by the incident speed and the characteristics of the oscillator, more specifically by the damping ratio z and the nondimensional forcing constant â. We also show that it is possible to predict the trapping speed as well as the exit speed using a simple work‑energy consideration in systems with negligible viscous dissipation.

National Category
Materials Chemistry
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-156400OAI: oai:DiVA.org:kth-156400DiVA: diva2:766502
Note

QS 2014

Available from: 2014-11-27 Created: 2014-11-27 Last updated: 2015-05-01Bibliographically approved
In thesis
1. Fundamentals of Wetting and Mechanical Durability of Superhydrophobic Coatings
Open this publication in new window or tab >>Fundamentals of Wetting and Mechanical Durability of Superhydrophobic Coatings
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In paper I the friction between three different superhydrophobic surfaces and water drops were investigated using high‑speed video. The surfaces were two based on a hydrophobic wax and the third was the leaf of a Lotus (Nelumbo Nucifera). The acceleration of water drops was measured as a function of drop size and surface inclination. For small capillary numbers it was shown that the dissipation was dominated by pinning‑depinning transitions along the trailing contact line. A parameter called the superhydrophobic sliding resistance bsh has been introduced. The motion of drops on superhydrophobic surfaces of a general macroscopic topography can be predicted provided that bsh and the drop size are known. This theory also infers the existence of an equilibrium sliding angle, beq, at which the drop acceleration is zero.

The effect of line‑shaped defects on the motion of water drops on superhydrophobic surfaces were also investigated using high‑speed video in paper II. It was shown that the motion of the drop in the vicinity of the defect can be approximated by a damped harmonic oscillator. Whether a drop got trapped or not while traversing the defect was determined by the incident speed and the characteristics of the oscillator. In systems with low viscous dissipation it is possible to predict the trapping speed as well as the exit speed using a simple work‑energy consideration.

The resistance of wax based superhydrophobic coatings subjected to different types of mechanical damage were investigated in paper III. Scratch tests were performed using atomic force microscopy (AFM) and rubbing with an index finger. Coatings were also subjected to compression with a silicone rubber stamp. The effect of impacting water drops was also investigated. A load of 12 nN was enough to remove the coating from the substrate. The coatings remained superhydrophobic at compression pressures up to 59 kPa but the superhydrophobic properties were lost after only one stroke with a finger. The coatings resisted at least 200 000 impacts of falling water drops without losing their superhydrophobic properties.

In paper IV superhydrophobic coatings were fabricated in a semi‑continuous process, where an alkyl ketene dimer (AKD) was dissolved in supercritical carbon dioxide (scCO2) and sprayed onto the substrate. Several different substrates such as: glass, aluminium, paper, poly (ethylene terephthalate) (PET) and poly (tetrafluoroethylene) (PTFE) were successfully coated. The most efficient spray process, considering surface properties and mass of extracted AKD, was obtained at the lowest temperature investigated, 67 °C, and the highest pressure evaluated in this study, 25 MPa. The influence of the pre‑expansion conditions (p, T) on the surface temperature (at a spray distance of 3 cm) was also shown to be negligible.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. xvii, 60 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2014:58
National Category
Polymer Chemistry Materials Chemistry
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-156402 (URN)978-91-7595-375-5 (ISBN)
Public defence
2014-12-18, D3, Lindstedtsvägen 5, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Foundation for Strategic Research
Note

QC 20141202

Available from: 2014-12-02 Created: 2014-11-27 Last updated: 2016-06-02Bibliographically approved

Open Access in DiVA

fulltext(754 kB)51 downloads
File information
File name FULLTEXT01.pdfFile size 754 kBChecksum SHA-512
397475eab046cf084f843647e93521297d0e21019f07c18acb34ac267cd51e33f1a8aa72527134e60e870f48624ca2cc49f92198f873cb06959765af67287524
Type fulltextMimetype application/pdf

Authority records BETA

Wågberg, Lars

Search in DiVA

By author/editor
Olin, PontusWågberg, Lars
By organisation
Fibre TechnologyWallenberg Wood Science Center
Materials Chemistry

Search outside of DiVA

GoogleGoogle Scholar
Total: 51 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

urn-nbn

Altmetric score

urn-nbn
Total: 119 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf