From Rolling Ball to Complete Wetting:  The Dynamic Tuning of Liquids on Nanostructured Surfaces

Krupenkin, Tom N.; Taylor, J. Ashley; Schneider, Tobias; Yang, Shu

doi:10.1021/la036093q

Cited by 481 publications

(447 citation statements)

References 31 publications

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“…From the above description of super-hydrophobicity and electrowetting, it appears that these two mechanisms are complementary with one providing an increase in hydrophobicity and the other a reduction simultaneously applicable to a single surface. In a recent report of electrowetting on nanostructured surfaces [6] it was demonstrated that dynamic electrical control of the wetting behavior of liquids could be achieved from superhydrophobicity to almost complete wetting. In this work we report studies of electrowetting on superhydrophobic surfaces of micro-patterned SU-8 photoresist structures.…”

Section: Introductionmentioning

confidence: 99%

Electrowetting on superhydrophobic SU-8 patterned surfaces

Herbertson

Evans

Shirtcliffe

et al. 2006

Sensors and Actuators A: Physical

101

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Electrowetting on micro-patterned layers of SU8 photoresist with an amorphous Teflon ® coating has been observed. The cosine of the contact angle is shown to be proportional to the square of the applied voltage for increasing bias.However, this does not apply below 40V and we suggest that this may be explained in terms of penetration of fluid into the pattern of the surface.Assuming that the initial application of a bias voltage converts the drop from Cassie-Baxter to Wenzel regime, we have used this as a technique to estimate the roughness factor of the surface.

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Section: Introductionmentioning

confidence: 99%

Electrowetting on superhydrophobic SU-8 patterned surfaces

Herbertson

Evans

Shirtcliffe

et al. 2006

Sensors and Actuators A: Physical

101

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“…Apart from technological applications, EW has also proven to be a very useful tool for studying fundamental problems in wetting and thin film hydrodynamics, where the contact angle is often a crucial parameter that is difficult if not impossible to vary experimentally without changing other important aspects of the system. Examples include wetting of complex surfaces [3,4], capillary pinch-off and microdroplet generation [5][6][7], and deposition [8]. Frequently, electrowetting experiments are performed in an ambient oil bath in order to minimize both the evaporation of liquid and contact angle hysteresis.…”

mentioning

confidence: 99%

Electrowetting-Induced Oil Film Entrapment and Instability

Staicu

Mugele

2006

Phys. Rev. Lett.

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We investigate the spreading at variable rate of a water drop on a smooth hydrophobic substrate in an ambient oil bath driven by electrowetting. We find that a thin film of oil is entrapped under the drop. Its thickness is described by an extension of the Landau-Levich law of dip coating that includes the electrostatic pressure contribution. Once trapped, the thin film becomes unstable under the competing effects of the electrostatic pressure and surface tension and dewets into microscopic droplets, in agreement with a linear stability analysis. Our results recommend electrowetting as an efficient experimental approach to the fundamental problem of dynamic wetting in the presence of a tunable substrate-liquid interaction. Apart from technological applications, EW has also proven to be a very useful tool for studying fundamental problems in wetting and thin film hydrodynamics, where the contact angle is often a crucial parameter that is difficult if not impossible to vary experimentally without changing other important aspects of the system. Examples include wetting of complex surfaces [3,4], capillary pinch-off and microdroplet generation [5][6][7], and deposition [8]. Frequently, electrowetting experiments are performed in an ambient oil bath in order to minimize both the evaporation of liquid and contact angle hysteresis. It has been indicated by several authors [9][10][11][12][13] that thin layers of the ambient oil might form between the drop and substrate in such a twophase configuration. Quilliet and Berge [9] found theoretically that the balance between electrical forces and the disjoining pressure should give rise to an equilibrium thickness of the films of approximately 10 -20 nm for typical values of the applied voltage. However, despite the importance of these layers-for instance for the reduction of contact angle hysteresis, but also for the protection of the surfaces from adsorption of biomolecules [10,14]their properties and formation mechanism remained elusive in previous experimental studies [11].In the present Letter we study the dynamics of moving contact lines in EW systems with a two-phase configuration, as just described. We show that a layer of oil is indeed entrapped under the drop with an initial thickness that is determined by the hydrodynamics of the moving contact line rather than by equilibrium properties. To describe the entrapment process we extend the Landau-Levich [15] treatment of dynamic wetting by an additional electrostatic pressure contribution, a topic that attracted considerable attention in the recent wetting literature [16 -18]. Following the entrapment, the oil film turns out to be unstable and breaks up into a number of smaller oil droplets. The size distribution of these droplets is described by a linear stability analysis of the thin film in the lubrication approximation, taking into account the balance between surface tension and electrostatic pressure. The problem thus combines two aspects: the entrapment process itself and the subsequent time evolution of the entra...

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“…Another important phenomenon is also reported, i.e., the apparent contact angle will reduce suddenly at a critical voltage, because the liquid penetrates into the grooves [25,28]. The rate of change of the cosine of the contact angle is different before or after this critical voltage.…”

Section: Extended Electrowetting Equationmentioning

confidence: 89%

“…In an electrowetting experiment, one can achieve from superhydrophobicity to almost complete wetting for liquids on microstructured surfaces [28]. Another important phenomenon is also reported, i.e., the apparent contact angle will reduce suddenly at a critical voltage, because the liquid penetrates into the grooves [25,28].…”

Section: Extended Electrowetting Equationmentioning

confidence: 90%

An Electrowetting Model for Rough Surfaces Under Low Voltage

Dai¹,

Zhao²

2008

Journal of Adhesion Science and Technology

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Electrowetting is one of the most effective methods to enhance wettability. A significant change of contact angle for the liquid droplet can result from the surface microstructures and the external electric field, without altering the chemical composition of the system. During the electrowetting process on a rough surface, the droplet exhibits a sharp transition from the Cassie-Baxter to the Wenzel regime at a low critical voltage. In this paper, a theoretical model for electrowetting is put forth to describe the dynamic electrical control of the wetting behavior at the low voltage, considering the surface topography. The theoretical results are found to be in good agreement with the existing experimental results.  Koninklijke Brill NV, Leiden, 2008

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From Rolling Ball to Complete Wetting: The Dynamic Tuning of Liquids on Nanostructured Surfaces

Cited by 481 publications

References 31 publications

Electrowetting on superhydrophobic SU-8 patterned surfaces

Electrowetting on superhydrophobic SU-8 patterned surfaces

Electrowetting-Induced Oil Film Entrapment and Instability

An Electrowetting Model for Rough Surfaces Under Low Voltage

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