Droplet motion and oscillation on contrasting micro-striated surfaces

Zhao, Hongyu; Orejon, Daniel; Sefiane, Khellil; Shanahan, M. E. R.

doi:10.1017/jfm.2021.211

Cited by 9 publications

(7 citation statements)

References 41 publications

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“…The DSA100 consists of a computer-controlled dosing system for the deposition of controlled volumes, a moveable sample stage can move in x-, y-, z-axis directions, backlight to illuminate the droplet opposite to a CMOS USB 3.0 IDS camera with a frame rate set at f 50 fps, 640 x 480 pixels resolution and a field of view (FOV) of 2.85 mm connected to a video digitiser board as represented We note here the same equilibrium contact angle for water from this work and the work of Zhao et al 46 where θ = 111° ± 2°, and the monotonic decreasing trend as ethanol concentration increases similar to the work of Liu et al 14 and Boreyko et al 27 . Note that if the droplets were to be place at the boundary of two different microstructured configurations, the migration of the droplet towards the more wetting surface, i.e., towards the higher solid fraction surface [46][47][48] , would ensue with the consequent further deviation from equilibrium owed to the dynamics of the droplet migration. Hence we limit this investigation to address wetting at the centre of the surfaces, i.e., homogeneous topography.…”

Section: Contact Angle Measurements and Wettability Characterisationmentioning

confidence: 99%

Binary mixture droplet wetting on micro-structure decorated surfaces

Balushi

Sefiane

Orejon

2022

Journal of Colloid and Interface Science

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Section: Contact Angle Measurements and Wettability Characterisationmentioning

confidence: 99%

Binary mixture droplet wetting on micro-structure decorated surfaces

Balushi

Sefiane

Orejon

2022

Journal of Colloid and Interface Science

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“…4 Capillary forces are also utilized in microfluidics, 5 enabling the transport of fluids by using, e.g., surface acoustic waves, [6][7][8][9][10] molecular motors, 11 or static wetting gradients. [12][13][14][15][16][17][18][19] Wetting gradients can also be actively controlled by applying an electric potential between the droplet and the (conducting or dielectric) substrate, as in electrowetting, [20][21][22][23] and by using materials that exhibit a chemically induced modification of the contact angle when exposed to light. 24 Additionally, electrostatic charging in combination with a superhydrophobic surface can be used to switch the mobility of droplets by controlling the different wetting states.…”

Section: Introductionmentioning

confidence: 99%

Mechanowetting drives droplet and fluid transport on traveling surface waves generated by light-responsive liquid crystal polymers

et al. 2021

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In nature, capillary forces are often driving microfluidic propulsion and droplet manipulation, and technologies have been developed to utilize these forces in applications such as lab-on-a-chip biosensors and microfluidic systems. At the same time, responsive materials have been developed that can be activated by a variety of external triggers, including light, electric fields, and temperature, to locally deform and create dynamic surface structures, such as traveling waves. Here, we combine these developments into a system that enables capillary-driven droplet transport and fluid propulsion generated by light-induced surface waves in azobenzene-embedded liquid crystal polymers. We demonstrate that the traveling waves are able to efficiently propel fluids by means of mechanowetting. We couple the wave profiles to the fluid simulations using a multiphase computational fluid dynamics approach. We study three different fluid propulsion systems, i.e., peristaltic flow, liquid slug transport, and free-standing droplet transport. The first system operates on a fluid-filled single channel and achieves relative flow speeds of u=u wave < 0:01. In contrast, the slugs and droplets are transported at two orders of magnitude higher speed equal to the wave speed (u=u wave ¼ 1) by exploiting the mechanowetting effect. We quantify the capillary forces generated by the traveling surface waves. Our method opens new avenues in light-driven (digital) microfluidic systems with enhanced control of fluid flow.

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“…Since the two droplets have different surface tensions and different contact angles, the imbalanced Laplace pressure further generates an obvious horizontal movement. Therefore, we trace the horizontal movement of the droplet centroid, X, in the side-view images by image processing, which could represent the bulk movement of the droplet (Somwanshi, Muralidhar & Khandekar 2017;Zhao et al 2021), to investigate the droplet oscillation dynamics. In the present sessile droplet configuration, the values of Bond number Bo = ρgR 2 /σ are rather low, being around 0.034 and 0.078 for 1 mm water droplet and oil droplet in air, respectively.…”

Section: Oscillation Of the Coalescing Dropletmentioning

confidence: 99%

Coalescence of immiscible sessile droplets on a partial wetting surface

Xu,

Ge,

Wang

et al. 2023

J. Fluid Mech.

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Droplet coalescence is a common phenomenon and plays an important role in multidisciplinary applications. Previous studies mainly consider the coalescence of miscible liquids, even though the coalescence of immiscible droplets on a solid surface is a common process. In this study, we explore the coalescence of two immiscible droplets on a partial wetting surface experimentally and theoretically. We find that the coalescence process can be divided into three stages based on the time scales and force interactions involved, namely (I) the growth of a liquid bridge, (II) the oscillation of the coalescing sessile droplet and (III) the formation of a partially engulfed compound sessile droplet and the subsequent retraction. In stage I, the immiscible interface is found not to affect the scaling of the temporal evolution of the liquid bridge, which follows the same 2/3 power law as that of miscible droplets. In stage II, by developing a new capillary time scale considering both surface and interfacial tensions, we show that the interfacial tension between the two immiscible liquids functions as a non-negligible resistance to the oscillation which decreases the oscillation periods. In stage III, a modified Ohnesorge number is developed to characterize the visco-capillary and inertia-capillary time scales involved during the displacement of water by oil; a new model based on energy balance is proposed to analyse the maximum retraction velocity, highlighting that the viscous resistance is concentrated in a region close to the contact line.

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Droplet motion and oscillation on contrasting micro-striated surfaces

Abstract: Abstract

Cited by 9 publications

References 41 publications

Binary mixture droplet wetting on micro-structure decorated surfaces

Binary mixture droplet wetting on micro-structure decorated surfaces

Mechanowetting drives droplet and fluid transport on traveling surface waves generated by light-responsive liquid crystal polymers

Coalescence of immiscible sessile droplets on a partial wetting surface

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