Abstract
A solution-based, large-area coating procedure is developed to produce conductive polymer composite films consisting of hollow-core carbon nanofibers (CNFs) and a fluoroacrylic co-polymer available as a water-based dispersion. CNFs (100 nm dia., length ∼130 μm) were dispersed by sonication in a formic acid/acetone co-solvent system, which enabled colloidal stability and direct blending of the CNFs and aqueous fluoroacrylic dispersions in the absence of surfactants. The dispersions were sprayed on smooth and microtextured surfaces, thus forming conformal coatings after drying. Nanostructured composite films of different degrees of oil and water repellency were fabricated by varying the concentration of CNFs. The effect of substrate texture and CNF content on oil/water repellency was studied. Water and oil static contact angles (CAs) ranged from 98° to 164° and from 61° to 164°, respectively. Some coatings with the highest water/oil CAs displayed self-cleaning behavior (droplet roll-off angles <10°). Inherent conductivity of the composite films ranged from 63 to 940 S/m at CNF concentrations from 10 to 60 wt.%, respectively. Replacement of the long CNFs with shorter solid-core carbon nanowhiskers (150 nm dia., length 6–8 μm) produced stable fluoropolymer–nanowhisker dispersions, which were ink-jetted to generate hydrophobic, conductive, printed line patterns with a feature size ∼100 μm.
Highlights
Stable polymer-particle dispersions suitable for spray casting of nanostructured carbon composite coatings are important for a variety of industries seeking simple methods to apply large-area, functional surface treatments [1,2,3,4,5,6,7,8,9]
Nanofillers, such as carbon nanotubes (CNTs) or carbon nanofibers (CNFs), in order to be combined with polymer dispersions or solutions must be dispersible and stable in liquids, which generally requires the use of either sonication, chemical functionalization, co-solvents or a combination of these techniques [11]
Dispersion Considerations Superoleophobic composite design and fabrication is considerably more difficult to achieve than superhydrophobicity, mainly because the former requires the creation of special hierarchical surface texture using very low surface energy materials [28]
Summary
Stable polymer-particle dispersions suitable for spray casting of nanostructured carbon composite coatings are important for a variety of industries seeking simple methods to apply large-area, functional surface treatments [1,2,3,4,5,6,7,8,9]. Instead of treating CNFs with strong acids, such as sulfuric or trifluoroacetic acid [11], we use formic acid, a relatively weak carboxylic acid, which is completely compatible with the water-PMC dispersion, and facilitates efficient mixing of CNFs in polymer dispersions Using this approach we obtain a number of such dispersions capable of producing superhydrophobic (water sessile contact angle, CA > 150°), self-cleaning (sliding angle < 10°), and superoleophobic (oil sessile CA > 150°) composite coatings when spray cast and dried on either smooth or low-cost textured surfaces (i.e., sand paper). We demonstrate, as an example, the application of the present technique with an alternative carbon nanofiller; by replacing the long hollow-core CNFs with similar diameter but shorter solid-core carbon fibers ( termed nanowhiskers), PMC-carbon nanowhisker inks were prepared and ink-jetted producing linear patterns with feature size ~100μm These inks can be formulated to display good substrate adhesion and electrical conductivity, in addition to their water and oil repellent properties, which are envisioned for the microelectronics industry. Only CNT-based suspensions (no polymer matrix) have been demonstrated for ink-jet applications (e.g. thin film transistors, etc.) with no studies reported on the wettability or adhesion of the deposited ink patterns [15,16,17,18,19,20,21,22,23,24,25]
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