Spatial Control of Condensation on Chemically Homogeneous Pillar-Built Surfaces

Abstract

The random nature of dropwise condensation impedes spatial control hereof and its use for creating microdroplet arrays, yet here we demonstrate the spatial control of dropwise condensation on a chemically homogeneous pillar array surface, yielding ∼8000 droplets/mm under normal atmospheric pressure conditions. The studied pillar array surface is defined by photolithography and etched in silicon by deep reactive ion etching. Subsequently, the surface is covered with a self-assembled monolayer of perfluorodecyltrichlorosilane (FDTS) to render the surface hydrophobic. To obtain a perfect droplet array, with one droplet per pillar, we exploit a phenomenon where the water vapor flux is focused on the apexes of surface asperities by diffusion while matching the nucleation point density to the array dimensions. Matching is here achieved through the variation of interpillar distance and vapor flow conditions.

Mapping the transition to superwetting state for nanotextured surfaces templated from block-copolymer self-assembly

“…for at least four months. As an additional benefit, the nanotexture, further delays the aging effect of the attached CH bonds caused by environmental contamination, as the incoming diffusive flux of hydrocarbon groups is focused onto the apexes of pillars, 7,11 thereby shielding the more critical interpillar area from the contamination.…”

“…1 Fortunately, Nature has developed a vast range of intriguing wetting properties readily solving major challenges. Examples include hierarchically structured self-cleaning surfaces inspired by the Lotus leaf, 1-4 as well as surfaces to control dropwise condensation, [5][6][7][8] ice formation, [8][9][10] and fogging 11,12 . Such surfaces can alleviate issues with fogging of lenses, mirrors, goggles, and wind shields; 13 reduction of sunlight harvesting in photovoltaic devices; 13,14 and poor field visibility in endoscopy 15 .…”

Nanotextured Si surfaces derived from block-copolymer self-assembly with superhydrophobic, superhydrophilic, or superamphiphobic properties

“…25 With the exception of super-wetting surfaces made by means of photocatalytic activation of metal-oxides, 26 fabrication methods for surfaces with enhanced wetting properties, typically involve steps of providing both the required surface chemistry and a surface texture. Such fabrication methods can be roughly divided into top-down methodologies requiring a pattern-design step for nano-and micro-lithography 23,[27][28][29][30] or bottom-up methodologies such as self-assembly of macro-molecular domains and colloids followed by selective reactive ion etching, [31][32][33][34][35][36][37] random etching processes, 22,[38][39][40] tensile elongation of surface textures 14,41 or coating with nanoparticles. 42 High-performance surfaces such as the self-healing, slippery, liquid-infused porous surface reported by Wong et al 43 may even employ combinations of various fabrication strategies.…”

Capillary-Assisted Enhanced Condensation Heat Transfer for Low Surface Tension Liquids

“…Shaping the nanopillars, as cones, resulting in a nanocone array, similar to the nanostructures on cicada wings, seemed to have higher superhydrophobic performance and antifogging abilities even for microdroplets as investigated by Mouterde et al [82]. Mandsberg et al [83] fabricated a chemically homogeneous micro pillar array by photolithography and treated to obtain a self-assembled monolayer of perfluorodecyltrichlorosilane to make it hydrophobic [83]. They showed that by having control over the micropillar dimensions and spacing, and also the way by which the vapor is introduced onto the surface, spatial control of condensing microdroplets is possible (cf.…”

“…Chemically homogeneous micropillar array (left) and microdroplets controlled on the tips of these pillars (right) Copyright of Mandsberg et al[83]). A novel cost effective method to spatially control a condensing microdroplet array was experimented by Xie et al[84].…”