Factors Affecting the Spontaneous Motion of Condensate Drops on Superhydrophobic Copper Surfaces

Abstract

The coalescence-induced condensate drop motion on some superhydrophobic surfaces (SHSs) has attracted increasing attention because of its potential applications in sustained dropwise condensation, water collection, anti-icing, and anticorrosion. However, an investigation of the mechanism of such self-propelled motion including the factors for designing such SHSs is still limited. In this article, we fabricated a series of superhydrophobic copper surfaces with nanoribbon structures using wet chemical oxidation followed by fluorization treatment. We then systematically studied the influence of surface roughness and the chemical properties of as-prepared surfaces on the spontaneous motion of condensate drops. We quantified the "frequency" of the condensate drop motion based on microscopic sequential images and showed that the trend of this frequency varied with the nanoribbon structure and extent of fluorination. More obvious spontaneous condensate drop motion was observed on surfaces with a higher extent of fluorization and nanostructures possessing sufficiently narrow spacing and higher perpendicularity. We attribute this enhanced drop mobility to the stable Cassie state of condensate drops in the dynamic dropwise condensation process that is determined by the nanoscale morphology and local surface energy.

Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

“…First, the interspaces of the building blocks should be as small as possible, e.g., sub-micrometer scale, to avoid moisture penetration. [66][67][68][69] Second, their tip size should be as small as possible to minimize the interface adhesion. [31,50,51,[66][67][68][69] Third, the building blocks must have a certain height or depth to avoid the collapse of the suspended water bridges.…”

“…[66][67][68][69] Second, their tip size should be as small as possible to minimize the interface adhesion. [31,50,51,[66][67][68][69] Third, the building blocks must have a certain height or depth to avoid the collapse of the suspended water bridges. [68] Following these design principles and inspired by nature, our group proposed and demonstrated that efficient self-propelling of small-scale condensed microdrops can be [5] Copyright 2007, Wiley-VCH.…”

“…In principle, any sub-microscale structures with a small feature size (tip size and interspace) and a certain height (or depth) can become effective candidates for creating CMDSP surfaces. In fact, except for arrays of closely packed nanotips, including nanocones, [22,27,50,69,70] nanoneedles, [21,28,31,66,71] nanopencils, [23] and tip-like nanotubes, [72,73] other architectures such as nano wires, [24,74] nanosheet arrays, [20,29,62,75] nanorod-capped nano pores, [68,76] the porous structure of nanoparticles, [67] nanoparticle aggregates, [73,[77][78][79][80] and two-tier structures [25,57,63,[81][82][83][84][85][86][87][88][89] have all been verified to be effective in endowing material surfaces with the desired CMDSP functionality as long as they follow these basic construction rules.…”

“…Similarly, various wetchemistry methods have been developed for the in situ growth of bionic CMDSP nanostructures on the surfaces of metal materials. [20][21][22][23][24][27][28][29]31,[66][67][68]70,[72][73][74][75][76]87] It is known that copper and aluminum are the most widely used metal materials, and the latest advances in their surface functionalization have shown remarkable potential in energy-related applications. Accordingly, we will briefly review recent progress in metal-based CMDSP surfaces.…”

“…Until now, much effort has been devoted to fabricating copper-based CMDSP surfaces consisting of various inorganic oxide nanostructures. [20][21][22][23][27][28][29]66,67,72,94] Inspired by nature, Qu et al [23] synthesized a type of Cu-based zinc oxide nanopencil array structure with CMDSP functionality, which was realized by diffusionlimited wet-chemistry crystal growth and silane modification (Figure 3a). Based on this, Luo et al [72] utilized zinc oxide nanopencils as a template and proposed a skillful preferential etching strategy to realize the controllable fabrication of [23] Copyright 2016, The Royal Society of Chemistry.…”