Suppression of Hydrophobic Recovery in Photo-Initiated Chemical Vapor Deposition

Photo-initiated chemical vapor deposition (PICVD) functionalizes carbon nanotube (CNT)-enhanced porous substrates with a highly polar polymeric nanometric film, rendering them super-hydrophilic. Despite its ability to generate fully wettable surfaces at low temperatures and atmospheric pressure, PIC...

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Bibliographic Details
Published inCatalysts Vol. 10; no. 5; p. 534
Main Authors Aufoujal, Alessio, Legrand, Ulrich, Meunier, Jean-Luc, Tavares, Jason Robert
Format Journal Article
LanguageEnglish
Published Basel MDPI AG 01.05.2020
Subjects
Bilayers
Carbon
Carbon nanotubes
Catalysts
Chemical reactions
Chemical vapor deposition
Contact angle
Crosslinking
Functional groups
homogenous catalysis
Hydrophilicity
hydrophobic recovery
Hydrophobic surfaces
Hydrophobicity
Low temperature
photochemistry
Plasma
Polymer films
Polymerization
Polymers
Recovery
Substrates
superhydrophilicity
Thin films
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Summary:Photo-initiated chemical vapor deposition (PICVD) functionalizes carbon nanotube (CNT)-enhanced porous substrates with a highly polar polymeric nanometric film, rendering them super-hydrophilic. Despite its ability to generate fully wettable surfaces at low temperatures and atmospheric pressure, PICVD coatings normally undergo hydrophobic recovery. This is a process by which a percentage of oxygenated functional group diffuse/re-arrange from the top layer of the deposited film towards the bulk of the substrate, taking the induced hydrophilic property of the material with them. Thus, hydrophilicity decreases over time. To address this, a vertical chemical gradient (VCG) can be deposited onto the CNT-substrate. The VCG consists of a first, thicker highly cross-linked layer followed by a second, thinner highly functionalized layer. In this article, we show, through water contact angle and XPS measurements, that the increased cross-linking density of the first layer can reduce the mobility of polar functional groups, forcing them to remain at the topmost layer of the PICVD coating and to suppress hydrophobic recovery. We show that employing a bi-layer VCG suppresses hydrophobic recovery for five days and reduces its effect afterwards (contact angle stabilizes to 42 ± 1° instead of 125 ± 3°).
ISSN:2073-4344
2073-4344
DOI:10.3390/catal10050534