Abstract
Highly hydrophobic surfaces have been intensively investigated in the last years because their properties may lead to very promising technological spillovers encompassing both everyday use and high-tech fields. Focusing on textiles, hydrophobic fabrics are of major interest for applications ranging from clothes to architecture to environment protection and energy conversion. Gas diffusion media – made by a gas diffusion layer (GDL) and a microporous layer (MPL) – for fuel cells are a good benchmark to develop techniques aimed at characterizing the wetting performances of engineered textiles. An experimental investigation was carried out about carbon-based, PTFE-treated GDLs with and without MPLs. Two samples (woven and woven-non-woven) were analysed before and after coating with a MPL. Their three-dimensional structure was reconstructed and analysed by computer-aided X-ray microtomography (µCT). Static and dynamic wettability analyses were then carried out using a modified axisymmetric drop shape analysis technique. All the surfaces exhibited very high hydrophobicity, three of them near to a super-hydrophobic behavior. Water drop impacts were performed, evidencing different bouncing, sticking and fragmentation outcomes for which critical values of the Weber number were identified. Finally, a µCT scan of a drop on a GDL was performed, confirming the Cassie-Baxter wetting state on such surface.
Highlights
Engineered surfaces have been gaining more and more importance since the last years, as the ability to finely tune the surface properties, at least in part independently from the bulk material properties, may lead to very promising technological applications
Polytetrafluoroethylene (PTFE) and other fluoropolymers may grant contact angles with water higher than 110° [7], but the known materials cannot at present reach the so-called super-hydrophobicity for smooth surfaces [8]
E.g. for clothes, umbrellas and architectural surfaces, the response to impacting drops is the most representative. Studies about the latter are available in the literature, but almost only concerning smooth surfaces or surfaces where the superhydrophobic behavior is obtained by regular patterns of micro- and nano- pillars [17] or square posts [18]
Summary
Engineered surfaces have been gaining more and more importance since the last years, as the ability to finely tune the surface properties, at least in part independently from the bulk material properties, may lead to very promising technological applications. An important sub-topic is the study of highly hydrophobic textiles (cloths, felts, papers), that is of major interest for applications ranging from manufacturing of consumer goods to Architecture and Civil Engineering, to Design, environment.
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