Controlling Liquid Drops with Texture Ratchets

Duncombe, Todd A.; Erdem, E. Yegan; Shastry, Ashutosh; Baskaran, Rajashree; Böhringer, K. F.

doi:10.1002/adma.201104446

Cited by 75 publications

(91 citation statements)

References 28 publications

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“…The experiments of Duncombe et al (2012a) have demonstrated that vertical vibrations of a horizontal ratcheted substrate can induce a unidirectional motion, thus suggesting heterogeneities can also be used as another mechanism for breaking the symmetry in the system. Even though a detailed investigation of ratcheted substrates is beyond the scope of the present work, we have performed a few sample calculations to demonstrate that our model can also capture this behaviour.…”

Section: Horizontal Substratesmentioning

confidence: 99%

Low-frequency vibrations of two-dimensional droplets on heterogeneous substrates

Savva

Kalliadasis

2014

J. Fluid Mech.

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We present a theoretical investigation of the effects of low-frequency vibrations on the motion of two-dimensional droplets on heterogeneous substrates in the presence of gravity and substrate heterogeneities, both chemical and topographical. A combined analytical and numerical approach is undertaken, extending the work of Savva & Kalliadasis on inclined heterogeneous substrates (J. Fluid Mech., vol. 725, 2013, p. 462) to include the effects of substrate vibrations and obtain, via a matching procedure and under the quasistatic assumption, evolution equations for the moving fronts. These equations are then invoked in a wide variety of case studies. It is demonstrated that vertically vibrated horizontal ratcheted substrates can induce unidirectional motion; for inclined substrates, we focus on a number of qualitative aspects of the peculiar vibration-induced climbing of droplets reported in experiments by Brunet, Eggers & Deegan (Phys. Rev. Lett., vol. 99, 2007, 144501). We examine the effects of weak inertia on the dynamics, deduce analytical criteria for the uphill motion in the limit of weak gravitational and vibrational effects, and demonstrate that substrate heterogeneities may be utilised to enhance droplet transport.

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Section: Horizontal Substratesmentioning

confidence: 99%

Low-frequency vibrations of two-dimensional droplets on heterogeneous substrates

Savva

Kalliadasis

2014

J. Fluid Mech.

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“…Horizontal droplet motion continued to proceed against the pillar tilt due to asymmetric depinning of the contact line forming the droplet footprint as the droplet moved alternately through advancing and receding motions with each oscillation of the structured surface. [ 13,24,31,32 ] To understand this length scale dependent switch in directionality, the wetting properties of the tilted pillar arrays were investigated further. First, we analyzed the CAH values and corresponding roll-off angles for droplets placed onto the TPAs, as summarized in Table 1 .…”

Section: Introductionmentioning

confidence: 99%

Length Scale Selects Directionality of Droplets on Vibrating Pillar Ratchet

Agapov

Boreyko

Briggs

et al. 2014

Adv Materials Inter

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Directional control of droplet motion at room temperature is of interest for applications such as microfluidic devices, self‐cleaning coatings, and directional adhesives. Here, arrays of tilted pillars ranging in height from the nanoscale to the microscale are used as structural ratchets to directionally transport water at room temperature. Water droplets deposited onto vibrating chips with a nanostructured ratchet move preferentially in the direction of the feature tilt while the opposite directionality is observed in the case of microstructured ratchets. This remarkable switch in directionality is consistent with changes in the contact angle hysteresis. To glean further insights into the length scale dependent asymmetric contact angle hysteresis, the contact lines formed by a nonvolatile room temperature ionic liquid placed onto the tilted pillar arrays were visualized and analyzed in situ in a scanning electron microscope. The ability to tune droplet directionality by merely changing the length scale of surface features all etched at the same tilt angle would be a versatile tool for manipulating multiphase flows and for selecting droplet directionality in other lap‐on‐chip applications.

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“…The concept of directional fluid transport, which is also called "one-way liquid transport" or "fluid diode" is a phenomenon widely found in daily life. Examples can be found in one-dimensional (1D) materials, such as spider silk and its inspired designs for water-harvesting [9][10][11][12][13][14][15][16][17], two-dimensional (2D) solid surfaces which are fabricated typically by forming a chemical gradient [18][19][20][21][22][23], or chemically homogeneous but surface roughness variation [24][25][26][27][28] using various approaches, and three-dimensional (3D) porous materials such as textile fabrics [1,[5][6][7][29][30][31][32][33], cellulosic paper substrate [34], and electrospun nanofibrous membranes [3,7]. The 3D porous materials with directional water transport property are prepared either by forming a hydrophobicity-to-hydrophilicity gradient or two zones with opposite wettability across thickness.…”

Section: Introductionmentioning

confidence: 99%

Heat Transfer in Directional Water Transport Fabrics

Zeng

Wang

Zhou

et al. 2016

Fibers

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Directional water transport fabrics can proactively transfer moisture from the body. They show great potential in making sportswear and summer clothing. While moisture transfer has been previously reported, heat transfer in directional water transport fabrics has been little reported in research literature. In this study, a directional water transport fabric was prepared using an electrospraying technique and its heat transfer properties under dry and wet states were evaluated, and compared with untreated control fabric and the one pre-treated with NaOH. All the fabric samples showed similar heat transfer features in the dry state, and the equilibrium temperature in the dry state was higher than for the wet state. Wetting considerably enhanced the thermal conductivity of the fabrics. Our studies indicate that directional water transport treatment assists in moving water toward one side of the fabric, but has little effect on thermal transfer performance. This study may be useful for development of "smart" textiles for various applications.

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Controlling Liquid Drops with Texture Ratchets

Abstract: Controlled vibration selectively propels multiple microliter-sized drops along microstructured tracks, leading to simple microfluidic systems that rectify oscillations of the three-phase contact line into asymmetric pinning forces that propel each drop in the direction of higher pinning.

Cited by 75 publications

References 28 publications

Low-frequency vibrations of two-dimensional droplets on heterogeneous substrates

Low-frequency vibrations of two-dimensional droplets on heterogeneous substrates

Length Scale Selects Directionality of Droplets on Vibrating Pillar Ratchet

Heat Transfer in Directional Water Transport Fabrics

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