Characterization of ultrahydrophobic hierarchical surfaces fabricated using a single-step fabrication methodology

Abstract

Hydrophobic surfaces with microscale roughness can be rendered ultrahydrophobic by the addition of sub-micron scale roughness. A simple yet highly effective concept of fabricating hierarchical structured surfaces using a single-step deep reactive ion etch process is proposed. Using this method the complexities generally associated with fabrication of two-tier roughness structures are eliminated. Three two-tier roughness surfaces with different roughness parameters are fabricated and tested. The surfaces are characterized in terms of static contact angle and roll-off angle and are compared with surfaces consisting of only single-tier microscale roughness. The evaporation characteristics of a sessile droplet on the hierarchical surfaces is also assessed relative to comparable single-roughness surfaces. The robustness of the new hierarchical roughness surfaces is verified through droplet impingement tests. The hierarchical surfaces exhibit very high contact angle and lower contact angle hysteresis compared to the single roughness surfaces and are more resistant to wetting. The energy loss during impact on the surfaces is quantified in terms of the coefficient of restitution for droplets bouncing off the surface.

Nanotextured superhydrophobic electrodes enable detection of attomolar-scale DNA concentration within a droplet by non-faradaic impedance spectroscopy

“…In contrast to the previously reported passive (super)hydrophobic surfaces (in the sense that the surface cannot be electrically or thermally activated 2,3,22,23 ), the proposed nanotextured surface acts simultaneously as (i) a sensing electrode array, eliminating the need for integrating a separate sensing unit, and (ii) a superhydrophobic fluid delivery scheme that beats the diffusion limit and eliminates the need for packaging techniques. The nanotextured superhydrophobic electrodes are optimized so that the surface-energy distribution results in localization (pinning) of the target droplet immediately after deposition on the electrode surface, thereby creating a platform to continuously monitor the impedance ( Z ( t )) of a single droplet as a function of time, t .…”

Effect of superhydrophobic surface morphology on evaporative deposition patterns

“…Droplet evaporation on superhydrophobic (SH) surfaces [20][21][22] has received growing attention; however, there are no standard measures to characterize and predict the size and location of deposits on rough surfaces with non-wetting properties. In recent studies, [23][24][25] the droplet evaporation rate was reported to be reduced on superhydrophobic surfaces due to increased influence of evaporative cooling at the droplet interface.…”

“…21 In the present work, five different superhydrophobic surfaces are designed with Teflon-coated, microscale pillars that offer a range of wetting characteristics as predicted by the global minimum energy. 31 The design procedure and fabrication of the surfaces are further discussed in the supplementary material.…”

Bioinspired Interfacial Materials with Enhanced Drop Mobility: From Fundamentals to Multifunctional Applications

“…The water hammer pressure is produced at the contact area with a diameter estimated as d WH = D 0 v / c and can be expressed as P WH = kρvc , where D 0 is the initial drop diameter, c the speed of sound in the drop, and k the pre‐factor determined by the surface morphology, shape and velocity of the drop . Based on the interplay between P C , P WH and P D , drops hitting textured surfaces can display total wetting, partial wetting, or the non‐wetting state . However, it was also reported by Maitra et al that on textured SHS, the compressibility of draining air caused dimple formation and that a subsequent pressure rise between the drop and the substrate, rather than the water hammer pressure effect, should be responsible for the observed liquid meniscus penetration in We range 10 2 –10 3 .…”