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Superhydrophobic coatings of wax and polymers sprayed from supercritical solutions
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
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.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2014:38
Keyword [en]
superhydrophobic coatings, polymer, wax, supercritical carbon dioxde, RESS
National Category
Polymer Technologies
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-151305ISBN: 978-91-7595-268-0 (print)OAI: oai:DiVA.org:kth-151305DiVA: diva2:747686
Public defence
2014-10-10, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Foundation for Strategic Research , RMA08-0044
Note

QC 20140922

Available from: 2014-09-22 Created: 2014-09-17 Last updated: 2015-03-24Bibliographically approved
List of papers
1. Towards superhydrophobic coatings made by non-fluorinated polymers sprayed from a supercritical solution
Open this publication in new window or tab >>Towards superhydrophobic coatings made by non-fluorinated polymers sprayed from a supercritical solution
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2013 (English)In: Journal of Supercritical Fluids, ISSN 0896-8446, E-ISSN 1872-8162, Vol. 77, 134-141 p.Article in journal (Refereed) Published
Abstract [en]

The objective of this study was to create a superhydrophobic surface using polymers that are non-fluorinated and applying them to a surface via rapid expansion of a supercritical solution (RESS). Solubility studies of poly(epsilon-caprolactone) (PCL) and a statistical copolymer of vinyl acetate and vinyl pivalate (P(VAc-VPi))in supercritical carbon dioxide (scCO(2)) were carried out using an extraction procedure. It was found that the most suitable process parameters for spraying these polymers using the RESS technique were 30 MPa, 40 degrees C and 10% (v/v) acetone as a co-solvent. The surfaces produced were characterized in terms of their morphology and hydrophobic properties by scanning electron microscopy and contact angle measurements, respectively. The most hydrophobic surfaces were obtained by spraying the P(VAc-VPi) copolymers, giving advancing water contact angles in the range of 120-155 degrees due to the hydrophobic character of the polymer and the microstructure formed with the RESS technique. These results show great promise for the creation of superhydrophobic surfaces using non-fluorinated polymers applied to surfaces via RESS technique.

Keyword
Supercritical carbon dioxide, Polymer, RESS, Surface coating
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-124052 (URN)10.1016/j.supflu.2013.02.019 (DOI)000318830100017 ()2-s2.0-84876102727 (Scopus ID)
Funder
Swedish Foundation for Strategic Research , 2005:0073/13 RMA08-0044Swedish Research Council, 2010-33
Note

QC 20130626

Available from: 2013-06-26 Created: 2013-06-25 Last updated: 2017-12-06Bibliographically approved
2. Superhydrophobic polymeric coatings produced by rapid expansion of supercritical solutions combined with electrostatic depostion (RESS-ED)
Open this publication in new window or tab >>Superhydrophobic polymeric coatings produced by rapid expansion of supercritical solutions combined with electrostatic depostion (RESS-ED)
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2014 (English)In: Journal of Supercritical Fluids, ISSN 0896-8446, E-ISSN 1872-8162, 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.

Keyword
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
Identifiers
urn:nbn:se:kth:diva-151442 (URN)10.1016/j.supflu.2014.09.014 (DOI)000347360800072 ()2-s2.0-84916638240 (Scopus ID)
Funder
Swedish Foundation for Strategic Research , RMA08-0044Swedish Research Council, 2010-33
Note

QC 20150205

Available from: 2014-09-22 Created: 2014-09-22 Last updated: 2017-12-05Bibliographically approved
3. Development of a semi-continuous spray process for production of superhydrophobic coatings from supercritical carbon dioxide solutions
Open this publication in new window or tab >>Development of a semi-continuous spray process for production of superhydrophobic coatings from supercritical carbon dioxide solutions
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(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:se:kth:diva-151443 (URN)
Note

QS 2014

Available from: 2014-09-22 Created: 2014-09-22 Last updated: 2016-06-02Bibliographically approved
4. Wear studies of superhydrophobic coatings of wax and polymers sprayed from rapid expansion of supercritical solutions (RESS)
Open this publication in new window or tab >>Wear studies of superhydrophobic coatings of wax and polymers sprayed from rapid expansion of supercritical solutions (RESS)
(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:se:kth:diva-151445 (URN)
Note

QS 2014

Available from: 2014-09-22 Created: 2014-09-22 Last updated: 2014-09-22Bibliographically approved
5. The effect of superhydrophobic wetting state on corrosion protection - The AKD example
Open this publication in new window or tab >>The effect of superhydrophobic wetting state on corrosion protection - The AKD example
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2013 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 412, 56-64 p.Article in journal (Refereed) Published
Abstract [en]

Corrosion is of considerable concern whenever metal is used as construction material. In this study we address whether superhydrophobic coatings could be used as part of an environmentally friendly corrosion-protective system, and specific focus is put on how the wetting regime of a superhydrophobic coating affects corrosion inhibition. Superhydrophobic alkyl ketene dimer (AKD) wax coatings were produced, using different methods resulting in hierarchical structures, where the coatings exhibit the same surface chemistry but different wetting regimes. Contact angle measurements, ESEM, confocal Raman microscopy, open circuit potential and electrochemical impedance spectroscopy were used to evaluate the surfaces. Remarkably high impedance values of 1010Ωcm2 (at 10-2Hz) were reached for the sample showing superhydrophobic lotus-like wetting. Simultaneous open circuit potential measurements suggest that the circuit is broken, most likely due to the formation of a thin air layer at the coating-water interface that inhibits ion transport from the electrolyte to the metal substrate. The remaining samples, showing superhydrophobic wetting in the rose state and hydrophobic Wenzel-like wetting, showed less promising corrosion-protective properties. Due to the absence of air films on these surfaces the coatings were penetrated by the electrolyte, which allowed the corrosion reaction to proceed.

Keyword
Alkyl ketene dimer (AKD), Corrosion protection, Superhydrophobic coating, Wetting state
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-136081 (URN)10.1016/j.jcis.2013.09.006 (DOI)000326665700009 ()2-s2.0-84885028398 (Scopus ID)
Funder
Swedish Foundation for Strategic Research , 2005:0073/13 RMA08-0044
Note

QC 20131204

Available from: 2013-12-04 Created: 2013-12-03 Last updated: 2017-12-06Bibliographically approved

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