Fog Collection Based on Secondary Electrohydrodynamic-Induced Hybrid Structures with Anisotropic Hydrophilicity

Abstract

The outcomes of the study of plant surfaces, such as rice leaves or bamboo leaves, have led to extensive efforts being devoted to fabricating anisotropic arrays of micro/nanoscale features for exploring anisotropic droplet spreading. Nonetheless, precise engineering of the density and continuity of three-phase contact lines for anisotropic wetting remains a significant challenge without resorting to chemical modifications and costly procedures. In this work, we investigated secondary electrohydrodynamic instability in polymer films for producing secondary nanosized patterns between the micrometer-sized grooves by controlling the timescale parameter, 1/τm (>10–4 s–1). We experimentally demonstrated facile morphological control of anisotropic wettability without the use of any chemical modifications. Thus, anisotropic hydrophilic surfaces fabricated by the secondary phase instability of polymer films are advantageous for both droplet condensation and removal, thereby outperforming the water collection efficiency of conventional (isotropic) hydrophilic surfaces in water harvesting applications (∼200 mg·cm–2·h–1) with excellent durability.

Electrohydrodynamic Nanopatterning: A Novel Solvent-Assisted Technique for Unconventional Substrates

“…In this study, the time-scale parameter, 1/τ m , was adjusted as a parametric guide to control the growth velocity. As previously reported, − 1/τ m not only indicates the growth velocity of the EHD-induced structure but also strongly affects the feature uniformity over the entire surface of the film in a facile and controllable manner (Experimental Section). To describe the degree of growth velocity, τ 0 /τ m was introduced, where the value of 1/τ 0 was defined as 0.346 s –1 .…”

“…Figure a shows the structured area with columnar-shaped features having a typical diameter of 1–3 μm. The structured film area was extended to the area of the top electrode (2 × 2 cm 2 ) by increasing τ 0 /τ m from 0.419 – 6.709 because the fast structure growth permits a broader range of valid parameters for a large-scale structure formation. − After EHD-induced structure formation, the sample was dipped into cyclohexane for 11 s to selectively and partially remove the PS thin film. One edge of the sample was dipped into a water bath to initiate water permeation through the PS–substrate interface.…”

Bio‐Inspired Instability‐Induced Hierarchical Patterns Having Tunable Anisotropic Wetting Properties

“…These preliminary results suggest that future work could be focused on precise control of the chemical compositions of the hierarchical patterns to attain desired anisotropic wetting properties for designated volumes of water droplets. Regarding technological applications, the hierarchical patterns could be exploited to fabricate functional surfaces for fog harvesting and water collection when they are combined with appropriate chemical compositions; [ 27 ] the small wrinkles may play a role in the nucleation and growth of water droplets, while the large ridges may facilitate directional transport of the grown droplets (Figure S8e,f, Supporting Information). Detailed investigations of such functions would be exciting research directions.…”

Pattern formation in thin polymeric films via electrohydrodynamic patterning

“…26 Park et al also investigated secondary electrohydrodynamic instability in polymer lms by controlling the timescale parameter to produce secondary nanosized patterns between the micrometer-sized grooves. 127 Goldberg-Oppenheimer et al proposed a tunable carbon nanotubes-based electrohydrodynamic patterning (CNT-EHDP) to fabricate unique multiscale structured cones and nanohairlike architectures with various periodicities and dimensions, successfully enabling surface energy minimization, as shown in Fig. 11.…”

“… 26 Park et al also investigated secondary electrohydrodynamic instability in polymer films by controlling the timescale parameter to produce secondary nanosized patterns between the micrometer-sized grooves. 127 …”