Motion of a Droplet on an Anisotropic Microgrooved Surface

Kumar, Manish; Bhardwaj, Rajneesh; Sahu, Kirti Chandra

doi:10.1021/acs.langmuir.8b03604

Cited by 38 publications

(18 citation statements)

References 22 publications

(36 reference statements)

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“…We used the fabrication process described in Refs. 13,29 and is briefly described as follows in the following steps:…”

Section: Methods Experimental Detailsmentioning

confidence: 99%

Wetting characteristics of Colocasia esculenta (Taro) leaf and a bioinspired surface thereof

Kumar

Bhardwaj

2020

Sci Rep

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We investigate wetting and water repellency characteristics of Colocasia esculenta (taro) leaf and an engineered surface, bioinspired by the morphology of the surface of the leaf. Scanning electron microscopic images of the leaf surface reveal a two-tier honeycomb-like microstructures, as compared to previously-reported two-tier micropillars on a Nelumbo nucifera (lotus) leaf. We measured static, advancing, and receding angle on the taro leaf and these values are around 10% lesser than those for the lotus leaf. Using standard photolithography techniques, we manufactured bioinspired surfaces with hexagonal cavities of different sizes. The ratio of inner to the outer radius of the circumscribed circle to the hexagon (b/a) was varied. We found that the measured static contact angle on the bioinspired surface varies with b/a and this variation is consistent with a free-energy based model for a droplet in cassie-Baxter state. the static contact angle on the bioinspired surface is closer to that for the leaf for b/a ≈ 1. However, the contact angle hysteresis is much larger on these surfaces as compared to that on the leaf and the droplet sticks to the surfaces. We explain this behavior using a first-order model based on force balance on the contact line. finally, the droplet impact dynamics was recorded on the leaf and different bioinspired surfaces. The droplets bounce on the leaf beyond a critical Weber number (We ~ 1.1), exhibiting remarkable water-repellency characteristics. However, the droplet sticks to the bioinspired surfaces in all cases of We. At larger We, we recorded droplet breakup on the surface with larger b/a and droplet assumes full or partial Wenzel state. The breakup is found to be a function of We and b/a and the measured angles in full Wenzel state are closer to the predictions of the free-energy based model. the sticky bioinspired surfaces are potentially useful in applications such as waterharvesting. Superhydrophobic and hydrophobic surfaces have generated significant interest in the last two decades due to their potential technical applications in designing functional surfaces that exhibit properties such as self-cleaning, low drag, antifouling, water harvesting, anti-icing etc. 1-5. In order to design such functional non-wetting surfaces, several researchers have been inspired by non-wetting characteristics of leaves of different species of plants. A remarkable example is a lotus leaf, that exhibits non-wetting characteristics due to the presence of micro-and nanoscale features on its surface. A notable review by Neinhuis and Barthlott 6 compiled published data of wetting characteristics and morphology of leaves of around 200 plants. In particular, they attributed non-wetting characteristics to microstructures and wax present on the surface. Similarly, Koch et al. 7 and Koch and Barthlott 8 discussed diversity in the morphology of the surface of the leaves of the different plants and their role in determining the wetting characteristics. These reviews also discuss how to engineer or biomimic a...

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“…We used the fabrication process described in Refs. 13,29 and is briefly described as follows in the following steps:…”

Section: Methods Experimental Detailsmentioning

confidence: 99%

Wetting characteristics of Colocasia esculenta (Taro) leaf and a bioinspired surface thereof

Kumar

Bhardwaj

2020

Sci Rep

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“…The contact angle is θ = 92° and θ = 139° in the longitudinal and transverse direction, respectively; the contact angles θ in the longitudinal direction to the nanochannels without plasma is close to the θ s of plain PUA surface, whereas θ in the transverse direction is higher than θ s due to the confinement effect of the nanochannels. [ 44 ] On the other hand, the contact angle θ after the plasma treatment rapidly decreases with the time due to the capillary‐driven spreading; the contact angle spontaneously decreases from θ = 88° to θ = 14° in 23 ms and from θ = 130° to θ = 14° in 250 ms in the longitudinal direction and the transverse direction, respectively (Figure 4c).…”

Section: Resultsmentioning

confidence: 99%

The Design of Hydrophilic Nanochannel‐Macrostripe Fog Collector: Enabling Wicking‐Assisted Vertical Liquid Delivery for the Enhancement in Fog Collection Efficiency

Lee

Bae

et al. 2020

Adv Materials Inter

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The design of water collectors that capture atmospheric fogs has been challenging due to the reliability issue. In particular, the small openings of collecting surfaces are often clogged by large‐size droplets. The additional hydraulic resistances added to the collecting surfaces prevent the fog pathways and further lower the overall performance coefficients by decreasing the shade coefficient of the collectors. The clogging issues can be addressed by modulating the fog harvesters' surface chemistry and surface structures to deliver water droplets efficiently and to prevent re‐entrainment of droplets to the openings. Herein, the novel design of fog collectors that consist of both nanochannels and macrostripes is demonstrated. The combination of those two structures provides the anisotropic wettability and thereby directional spreading in the longitudinal direction to the nanochannels. The directional liquid spreading facilitates continuous liquid transport through the formation of a thin liquid film. As a result, the fog collector successfully enhances the fog harvesting performance by 50% compared to conventional mesh‐like fog collectors.

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“…The micropillars and the reference smooth surface of SU8 photoresist polymer (MicroChem Inc.) were fabricated on a silicon wafer using the same procedure as described in Kumar et al 43 Here, we briefly describe the fabrication procedure with process parameters unique to the present work for the sake of completeness. First, a computer-aided design (CAD) file with the desired geometry to be used as an input for the laser writer (LW405, Microtech Inc.) is created (as shown in Figure S2 of the Supporting Information).…”

Section: ■ Experimental Methodsmentioning

confidence: 99%

“…The present geometrical structures of the surfaces are such that the backlight does not cross the spacing between the pillars, which typically occurs with aligned pillars microtextured surfaces as considered in the literature. 43,47 The pillars are not visualized from the side view, for this reason. Here, we demonstrated different regimes of the wetting dynamics on the RD and RI configurations by showing the extreme cases in terms of the wetting diameter for a fixed value of k and the parameters considered in the present study.…”

Section: ■ Experimental Methodsmentioning

confidence: 99%

Wetting Dynamics of a Water Droplet on Micropillar Surfaces with Radially Varying Pitches

2020

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The wetting dynamics of a sessile droplet on square micropillar substrates with radially varying pitches, prepared on silicon wafers using a photolithography technique, is investigated experimentally. Two configurations are considered, namely, substrates with radially increasing pitch and radially decreasing pitch. The droplet initially placed at the center experiences a wettability gradient because of the variation in pitch of the micropillar substrate leading to complex wetting dynamics. We observed that the droplet remains in the Cassie–Baxter state in the case of a radially increasing pitch and exhibits a higher contact angle than that on a smooth surface during its spreading stage. In contrast, the droplet experiences the Wenzel condition in the case of a radially decreasing pitch and assumes a lower contact angle relative to that observed on a smooth surface. The wetted diameter of the droplet in the radially decreasing pitch configuration is found to be smaller than that observed in the radially increasing pitch configuration. Our study also reveals that increasing the size of the pillars increases the wetted diameter of the droplet in both configurations. Theoretical models developed using the Cassie–Baxter and Wenzel states for the radially increasing and radially decreasing pitches satisfactorily predict the experimental behaviors.

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Motion of a Droplet on an Anisotropic Microgrooved Surface

Cited by 38 publications

References 22 publications

Wetting characteristics of Colocasia esculenta (Taro) leaf and a bioinspired surface thereof

Wetting characteristics of Colocasia esculenta (Taro) leaf and a bioinspired surface thereof

The Design of Hydrophilic Nanochannel‐Macrostripe Fog Collector: Enabling Wicking‐Assisted Vertical Liquid Delivery for the Enhancement in Fog Collection Efficiency

Wetting Dynamics of a Water Droplet on Micropillar Surfaces with Radially Varying Pitches

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