Plasma Deposition of Superhydrophobic Ag@TiO₂ Core@shell Nanorods on Processable Substrates

Abstract

---------This work reports the low temperature plasma formation of Ag@TiO 2 nanorods consisting of a silver core and an external shell of TiO 2 deposited on silver coated processable substrates.Layers of supported nanorods have been analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and time of flight secondary ion mass spectroscopy (TOF-SIMS). The analysis of the nanorods morphologies as a function of the preparation conditions has revealed that the effect of the plasma sheath, the high mobility of the silver and the incoming direction of the precursor moieties are key factors determining the morphology, dimensions and tilting orientation of the core@shell nanostructures. Post-annealing of the asprepared samples at 673 K induced the crystallization of the amorphous TiO 2 shell into the anatase phase. The as-grown amorphous and anatase Ag@TiO 2 NRs surfaces present a superhydrophobic behavior with water contact angles higher than 150º, that turn into superhydrophilic through a two-step kinetic by irradiation with UV light. This wetting behavior is discussed within the framework of the Wenzel and Cassie-Baxter models, a Supporting Information is available at Wiley Online Library or from the author. ((Other reference to the authors can also appear here, such as Author-One and Author-Two contributed equally to this work.)) -2 -including the effect of the water penetration in the inter-NR space during the light-mediated superhydrophobic-superhydrophilic transformation.

In Situ Determination of the Water Condensation Mechanisms on Superhydrophobic and Superhydrophilic Titanium Dioxide Nanotubes

“…1 a), b)) reveal a superhydrophobic behavior, characterized by water contact angles (WCA) higher than 150º, low contact angle hysteresis (<10º) and a small sliding angle (<2º). In good agreement with previous reports on one-dimensional photoactive surfaces, [13,23,24,[35][36][37][38][39][40] a reversible change from this initial superhydrophobic situation to a superhydrophilic (WCA<10º) state occurs after UV light irradiation of the surface for a time span of several minutes. Figure 1 f) shows the time dependence of WCA for the same TiO2 NTs surface when subjected to pre-irradiation for increasing periods of time.…”

Perspectives on oblique angle deposition of thin films: From fundamentals to devices

“…Furthermore, by tailoring the density, morphology and chemical characteristics of these 1D nanostructures, we have been able to fabricate ultrahydrophobic surfaces; i.e., surfaces with an apparent WCA of 180° [242,569]. In addition, by working with Ag@metal-oxide nanorods and nanowires prepared by PECVD in an oblique configuration, we have taken advantage of the well-known photoactivity of TiO 2 and ZnO to reversibly modify the WCA of their surfaces from superhydrophobic to superhydrophilic [188,242,563] by irradiating them with UV light, and in some cases, with visible light [186,187,563]. This illumination does not alter the nanostructure of the films, but rather only their surface properties, thus enabling fine control over the final WCA of the system.…”

“…In the so-called remote PECVD processes, where the plasma source is outside the deposition zone, the preferential direction of arrival of precursor species moving from the dispenser toward the vacuum outlet has been used to fabricate metal-oxide composite layers consisting of well-separated vertical and tilted nanocolumns, as well as other types of branched nanostructures [186][187][188]. An example of such a nanostructure is depicted in Fig.…”

“…The high versatility of this technique in obtaining different nanostructures (metals, organic compounds, oxides, hybrids and other complex heterostructures) is an additional feature that supports its use for wetting applications. Important achievements have been made in the last few years through the OAD fabrication of surfaces possessing singular adhesive properties [555], hydrophobicity [556][557][558][559], superhydrophobicity [186][187][188]557,[560][561][562][563], superhydrophilicity [366] or superolephobicity [564,565]. Initial approaches to the development of highly hydrophobic surfaces by OAD combined the surface nanostructuration capability of this technique with the chemical modification of the surface composition by different methods.…”

“…To this end, our group has developed different plasma approaches for the deposition of nanofibers, nanorods and nanowires made of inorganic semiconductors (TiO 2 and ZnO) [568], small-molecules [569] and hybrid and heterostructured nanostructures (metal@metal-oxide [186][187][188]563] and organic@inorganic core@shell nanowires [570]) that can be activated by light illumination. Furthermore, by tailoring the density, morphology and chemical characteristics of these 1D nanostructures, we have been able to fabricate ultrahydrophobic surfaces; i.e., surfaces with an apparent WCA of 180° [242,569].…”