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Superhydrophobic polymeric coatings produced by rapid expansion of supercritical solutions combined with electrostatic depostion (RESS-ED)
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
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2014 (English)In: Journal of Supercritical Fluids, ISSN 0896-8446, Vol. 95, 610-617 p.Article in journal (Refereed) Published
Abstract [en]

In this paper we present a method to produce superhydrophobic polymeric coatings by combining the rapid expansion of supercritical solutions (RESS) with electrostatic deposition (ED). A copolymer, poly(vinyl acetate)-poly(vinyl pivalate) was dissolved in a mixture of supercritical carbon dioxide and acetone and sprayed through a nozzle with an applied voltage of 8 kV onto a surface placed on a earthed collector. Spray distance and polymer concentration were altered to find the most suitable spraying conditions. Superhydrophobic surfaces were produced when spraying both with and without a voltage, although the water repellent surfaces could be produced at a larger variety of processing parameters using the RESS-ED technique. The greatest improvement of using the RESS-ED process was that larger and thinner coatings were produced with a more even surface coverage of the created polymer particles compared to spraying without the applied voltage.

Place, publisher, year, edition, pages
2014. Vol. 95, 610-617 p.
Keyword [en]
Acetone, Carbon dioxide, Deposition, Electric grounding, Electromagnetic wave emission, Electrostatic coatings, Electrostatics, Hydrophobicity, Plastic coatings, Polymers, Supercritical fluid extraction, Volatile fatty acids, Electrostatic deposition, Poly(vinyl pivalate), RESS, Supercritical solution, Superhydrophobic coatings
National Category
Polymer Chemistry
URN: urn:nbn:se:kth:diva-151442DOI: 10.1016/j.supflu.2014.09.014ISI: 000347360800072ScopusID: 2-s2.0-84916638240OAI: diva2:748755
Swedish Foundation for Strategic Research , RMA08-0044Swedish Research Council, 2010-33

QC 20150205

Available from: 2014-09-22 Created: 2014-09-22 Last updated: 2015-02-05Bibliographically approved
In thesis
1. Superhydrophobic coatings of wax and polymers sprayed from supercritical solutions
Open this publication in new window or tab >>Superhydrophobic coatings of wax and polymers sprayed from supercritical solutions
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The possibility of using supercritical carbon dioxide (scCO2) as the primary solvent in a spray process for producing superhydrophobic surfaces have been examined in this work. Using scCO2 as solvent will have considerably lower environmental impact compared to an organic solvent since scCO2 is considered a green solvent as it is non-toxic, non-flammable and recyclable. To be able to work at the pressures needed to reach the supercritical state of carbon dioxide, a high-pressure technique called rapid expansion of supercritical solutions (RESS) has been used to produce the coatings. Fluorinated compounds are often used when producing superhydrophobic coatings due to their intrinsic water repellent properties, but generally these compound do not degrade in nature. Due to this, a wax and a biodegradable polymer have been used as the coating materials in this work.

Two RESS set-ups were used to spray a polymer from solutions of scCO2 and acetone. The first system was based on a continuous flow of the solvent mixture and the polymer particles were collected on silica surfaces. Some of the coatings had superhydrophobic properties and the limitation with this technique was the loss of particles between the nozzle and the surface. In the second set-up, RESS was combined with electrostatic deposition (ED) to improve the particle collection. Different processing parameters were examined and most of the RESS-ED sprayed surfaces were superhydrophobic. This was demonstrated by high contact angles against water, low contact angle hysteresis and low tilt angles at which a water droplet rolls off the surface. It was also shown that the surface structures created when spraying using RESS-ED induced the important two-level roughness that was needed to achieve superhydrophobicity. A semi-continuous process for scaling-up the RESS system when spraying the wax has been developed. Temperature and pressure was investigated to find the highest solubility of the wax in scCO2, and 250 bar and 67 °C resulted in the largest amount of sprayed wax. It was also shown that the system is suitable for spray-coating the wax on different substrates such as glass, paper, aluminium etc. since all of these surfaces showed superhydrophobic properties. The wear resistance of the coatings were examined by different methods. Scratch resistance, vertical compression and the friction between the surface and a finger were analysed. The polymer coated surfaces showed a larger robustness compared with the wax surfaces in the scratch tests. The superhydrophobicity was lost for the wax coatings exposed to compression loads above 59 kPa and in the frictions test, one finger stroke over the coating destroyed the surface roughness. Finally, the wax surfaces were investigated as coating barriers to protect steel from corrosion. The superhydrophobic coating was stable up to 10 days before corrosion of the steel started.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. ix, 54 p.
TRITA-CHE-Report, ISSN 1654-1081 ; 2014:38
superhydrophobic coatings, polymer, wax, supercritical carbon dioxde, RESS
National Category
Polymer Technologies
Research subject
Chemical Engineering
urn:nbn:se:kth:diva-151305 (URN)978-91-7595-268-0 (ISBN)
Public defence
2014-10-10, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Swedish Foundation for Strategic Research , RMA08-0044

QC 20140922

Available from: 2014-09-22 Created: 2014-09-17 Last updated: 2015-03-24Bibliographically approved

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