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Towards superhydrophobic polydimethylsiloxane-silica particle coatings
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden.
2016 (English)In: Journal of Dispersion Science and Technology, ISSN 0193-2691, E-ISSN 1532-2351, Vol. 37, no 9, 1375-1383 p.Article in journal (Refereed) Published
Abstract [en]

Hydrophobized silica nanoparticles of different sizes, from 16 to 500 nm, were used to impart roughness to a hydrophobic polydimethylsiloxane (PDMS) coating with the aim of obtaining superhydrophobic properties. The particle silanization process and the curing process of the PDMS coating were optimized to increase the contact angle of the particle containing coating. The evaluation of the coatings, by means of water contact angle measurements and scanning electron microscopy imaging, show that superhydrophobicity in the adhesive rose state was achieved using combinations of two differently sized particles, with an excess of the small 16 nm ones. Superhydrophobicity in the Lotus state was obtained when the filler concentration of 16 nm particles was 40 wt%, but under such conditions the coating was found to partially crack, which is detrimental in barrier applications. The preference for the rose wetting state can be explained by the round shape of the particles, which promotes the superhydrophobic rose wetting state over that of the superhydrophobic Lotus state.

Place, publisher, year, edition, pages
Taylor & Francis, 2016. Vol. 37, no 9, 1375-1383 p.
Keyword [en]
Silica particles, silanization, particle functionalization, superhydrophobic coating, wetting, rose state, Lotus state
National Category
Other Chemistry Topics
Research subject
Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-175401DOI: 10.1080/01932691.2015.1101610ISI: 000374897300017Scopus ID: 2-s2.0-84963606497OAI: oai:DiVA.org:kth-175401DiVA: diva2:860815
Funder
Swedish Foundation for Strategic Research , 2005:0073/13
Note

QC 20160530

Available from: 2015-10-14 Created: 2015-10-14 Last updated: 2017-12-01Bibliographically approved
In thesis
1. Hydrophobic and superhydrophobic coatings for corrosion protection of steel
Open this publication in new window or tab >>Hydrophobic and superhydrophobic coatings for corrosion protection of steel
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Since metals in general, and steels in particular, are vital construction materials in our modern society, the corrosion protection of said materials is of great importance, both to ensure safety and to reduce costs associated to corrosion. Previously, chromium (VI) and other harmful substances were effectively used to provide corrosion protection to steel, but since their use was heavily regulated around year 2000, no coating has yet been developed that, in a fully satisfactory manner, replaces their corrosion protective properties.In this thesis, the use of hydrophobic and superhydrophobic surface coatings as part of corrosion protective coating systems has been studied. Since the corrosion mechanism relies on the presence of water to take place, the use of a superhydrophobic coating to retard the penetration of water to an underlying metal surface is intuitive. The evaluation of corrosion protective properties of the hydrophobic and superhydrophobic surfaces was performed using mainly contact angle measurements and electrochemical measurements in severely corrosive 3 wt% NaCl water solution.First, the differences in corrosion protection achieved when employing different hydrophobic wetting states were investigated using a model alkyl ketene dimer wax system. It was found that superhydrophobicity in the Lotus state is superior to the other states, when considering fairly short immersion times of less than ten days. This is due to the continuous air film that can form between such a superhydrophobic surface and the electrolyte, which can retard the transport of electrolyte containing corrosive ions to the metal surface to the point where the electrical circuit is broken. Since corrosion cannot occur unless an electrical current is flowing, this is a very efficient way of suppressing corrosion.An air layer on an immersed superhydrophobic surface is, however, not stable over long time, and to investigate long-term corrosion protection using hydrophobic coatings a polydimethylsiloxane formulation containing hydrophobic silica nanoparticles was developed. This system showed enhancement in corrosion protective properties with increasing particles loads, up until the point where the particle load instead causes the coating to crack (at 40 wt%). The conclusion is that the hydrophobicity of the matrix and filler, in combination with the elongatedivdiffusion path supplied by the addition of particles, enhanced the corrosion protection of the underlying substrate.To further understand how hydrophobicity and particle addition affect the corrosion protective properties of a coating a three layer composite coating system was developed. Using this coating system, consisting of a polyester acrylate base coating, covered by TiO2 particles (with diameter < 100 nm) and finally coated with a thin hexamethyl disiloxane coating, it was found that both hydrophobicity and particles are needed to reach a great enhancement in corrosion protective properties also for this system.

Abstract [sv]

Eftersom metaller, och då särskilt stål, är viktigta konstruktionsmaterial i vårt moderna samhälle är korrosionsskydd av stor betydelse, både för att garantera säkerhet och för att minska kostnader som uppkommer i samband med korrosion. Tidigare har sexvärt krom och andra skadliga ämnen använts för att på ett effektivt sätt skydda stål från korrosion, men efter att deras användning kraftigt reglerades runt år 2000 har ännu ingen beläggning utvecklats som helt kan ersätta krombeläggningarna med avseende på funktion.I denna avhandling har hydrofoba och superhydrofoba ytbeläggningar och deras möjliga applikation som en del av ett korrosionsskyddande beläggningssystem studerats. Eftersom korrosionsmekanismen är beroende av närvaron av vatten, är användandet av en superhydrofob beläggning för att fördröja transporten av vatten till den underliggande metallytan intuitiv. De korrosionsskyddande egenskaperna hos superhydrofoba ytbeläggningar utvärderades här främst med hjälp av kontaktvinkelmätningar och elektrokemisk utvärdering i korrosiv lösning bestående av 3 vikts% NaCl i vatten.Först undersöktes skillnaden i korrosionsskydd som uppnås vid användandet av ytbeläggningar med olika hydrofoba vätningsregimer med hjälp av ett modellsystem bestående av ett alkylketendimer vax. Det konstaterades att superhydrofobicitet i Lotusregimen är överlägset bättre än de andra hydrofoba vätningsregimerna, i alla fall när man ser till relativt korta exponeringstider, typiskt mindre än tio dagar. Detta beror på att den kontinuerliga luftfilm som kan bildas på en sådan typ av superhydrofob yta kan minska transporten av elektrolyt (som innehåller korrosiva joner) till metallytan till den grad att den elektriska kretsen bryts. Eftersom korrosion inte kan ske utan en sluten elektrisk krets är detta ett mycket effektivt sätt att förhindra korrosion från att ske.Ett luftskikt på en superhydrofob yta nedsänkt i vatten är dock inte stabilt under lång tid. För att undersöka möjligheten till korrosionsskydd under längre tid med hjälp av hydrofoba beläggningar utvecklades en hydrofob ytbeläggning bestående av polydimetylsiloxan och hydrofoba nanopartiklar av kiseldioxid. Detta system visade en förbättring av korrosionsskyddet vid ökat partikelinnehåll upp till den koncentration (40 wt%) där i stället sprickbildning i ytbeläggningen observerades. Från detta system kunde slutsatsen dras att matrisens och partiklarnasvihydrofobicitet i kombination med den längre diffusionsvägen som partiklarna orsakade förbättrade korrosionsskyddet av den underliggande metallen.För att ytterligare förstå hur hydrofobicitet och partikeltillsatser påverkar en ytbeläggnings korrosionsskyddande egenskaper har dessutom ett treskikts kompositbeläggningssystem utvecklats. Genom att använda detta beläggningssystem, som består av en basbeläggning av polyesterakrylat, ett lager TiO2-partiklar (med en diameter på <100 nm) slutligen belagt med ett tunt ytskikt bestående av hexametyldisiloxan så kunde slutsatsen dras att både en hydrofob matris och partiklar behövs för att nå en markant förbättring av ytbeläggningens korrosionsskyddande egenskaper.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xvi, 57 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:54
Keyword
Superhydrophobic coating, hydrophobic coating, corrosion protection, contact angles, electrochemical measurements, surface characterization
National Category
Engineering and Technology
Research subject
Chemistry
Identifiers
urn:nbn:se:kth:diva-175405 (URN)978-91-7595-703-6 (ISBN)
Public defence
2015-11-06, F3, Lindstedsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Foundation for Strategic Research , 2005:0073/13
Note

QC 20151015

Available from: 2015-10-15 Created: 2015-10-14 Last updated: 2015-10-15Bibliographically approved

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