Electrowetting without external voltage using paint-on electrodes

Eaker, Collin B.; Joshipura, Ishan D.; Maxwell, Logan R.; Heikenfeld, Jason; Dickey, Michael D.

doi:10.1039/c6lc01500j

Cited by 16 publications

(10 citation statements)

References 31 publications

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“…In contrast to the high contact angles on structured diamond, a rather low contact angle of around 131°(small droplets) or −138°(droplet volume bigger than 250 μL) is detected on (hydrophilic and smooth) glass, which is ascribed to the smoothness of the glass slide and hydrophilic interactions between the glass slide and the hydrophilic oxide skin. 41,42 Furthermore, contact angles on PTFE were measured after treatment with vibration Vib II, yielding a rather broad scatter of contact angles with contact angles ranging between 135 and 160°, one reason for excluding horizontal vibrations. Examples of contact angles of galinstan on glass and structured diamond after exposure to vibrations are given in Figure 2b.…”

Section: Resultsmentioning

confidence: 99%

Surface Tension of the Oxide Skin of Gallium-Based Liquid Metals

et al. 2021

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Gallium-based alloys have garnered considerable attention in the scientific community, particularly as they are in an atypical liquid state at and near room temperature. Though physical parameters, such as thermal conductivity, electrical conductivity, viscosity, yield stress, and surface tension, of these alloys are broadly known, the surface tension (surface free energy) of the oxide skin remains intangible due to the high yield stress of the oxide skin. In this article, we propose to employ gradually attenuated vibrations to obtain equilibrium shapes, which are analyzed along the lines of the puddle height method. The surface tension of the oxide skin was determined on quartz glass and liquid metal-phobic diamond coating to be around 350−365 mN/m, thus independent of the substrate surface or employed liquid metal (i.e., eutectic Ga−In (EGaIn) and galinstan). The similarity of the surface tension for different alloys was ascribed to the composition of the oxide skin, which predominantly comprises gallium oxides due to thermodynamic constraints. We envision that this method can also be applied to other liquid metal alloys and liquid metal marble systems facilitating modeling, simulation, and optimization processes.

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Section: Resultsmentioning

confidence: 99%

Surface Tension of the Oxide Skin of Gallium-Based Liquid Metals

et al. 2021

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“…We sought to modulate the surface chemistry to see if it would induce adhesion of the oxide to the protrusions. Because the native oxide is hydrophilic, 46 we reasoned that it may adhere to rough, hydrophilic surfaces.…”

Section: ■ Introductionmentioning

confidence: 99%

Patterning and Reversible Actuation of Liquid Gallium Alloys by Preventing Adhesion on Rough Surfaces

Joshipura¹,

Ayers²,

Castillo³

et al. 2018

ACS Appl. Mater. Interfaces

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105

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This work reports a simple approach to form, study, and utilize rough coatings that prevent the adhesion of gallium-based liquid metal alloys. Typically, liquids with large interfacial tension do not wet nonreactive surfaces, regardless of surface topography. However, these alloys form a surface oxide “skin” that adheres to many substrates, even those with low surface energy. This work reports a simple approach to render closed channels and surfaces, including soft materials, to be “oxide-phobic” via spray-coating (NeverWet, which is commercially available and inexpensive). Surface spectroscopic techniques and metrology tools elucidate the coatings to comprise silica nanoparticles grafted with silicones that exhibit dual length scales of roughness. Although prior work shows the importance of surface roughness in preventing adhesion, the present work confirms that both hydrophobic and hydrophilic rough surfaces prevent oxide adhesion. Furthermore, the coating enables reversible actuation through submillimeter closed channels to form a reconfigurable antenna in the gigahertz range without the need for corrosive acids or bases that remove the oxide. In addition, the coating enables open surface patterning of conductive traces of liquid metal. This shows it is possible to actuate liquid metals in air without leaving neither metal nor oxide residue on surfaces to enable reconfigurable electronics, microfluidics, and soft electrodes.

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“…Electrowetting on dielectric (EWOD or EW) is one of the most versatile tools in controlling the wettability of conductive liquid drop on a dielectric surface; therefore, it is implemented in many microfluidic devices [ 1 , 2 ]. Generally, amorphous fluoropolymers are used as a dielectric coating on a planar electrode in many of these applications like optical lens component [ 3 , 4 ], video displays [ 5 , 6 ], beam steering devices [ 7 ], lab-on-a-chip devices [ 8 ], digital microfluidics [ 9 , 10 ], biomedical applications [ 11 ] etc.…”

Section: Introductionmentioning

confidence: 99%

Large tuning in the electrowetting behaviour on ferroelectric PVDF-HFP/Teflon AF bilayer

et al. 2021

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Electrowetting (EW) response on a dielectric depends on its permittivity value, Young contact angle and voltage amplitude. We present a large change in EW contact angle, from 163° to 80°, on the bilayer dielectric made up of ferroelectric PVDF-HFP with a thin layer of fluoropolymer. The thickness values of both layers were separately optimized for high effective capacitance essential for the large EW response. It reveals that the bilayer with ~ 500 nm thick PVDF-HFP layer and ~ 50 nm thin layer of Teflon results in the maximum value of effective dielectric constant, ε ≈ 8. Besides this gain, dc-voltage EW response exhibits hysteresis mainly due to polarization in the ferroelectric layer such that, hysteretic offset voltage was found to depend on the applied voltage amplitude and thickness of the dielectrics. Finally, bilayer was subjected to ac-voltage EW in silicone oil for ambient temperature ranging from − 25 to 70 °C. The consistent EW response in this ambient without any degradation/delamination of polymer surface confirmed the durability of the bilayer on the transparent ITO electrodes. Supplementary Information The online version contains supplementary material available at 10.1007/s10853-021-06308-z.

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Electrowetting without external voltage using paint-on electrodes

Cited by 16 publications

References 31 publications

Surface Tension of the Oxide Skin of Gallium-Based Liquid Metals

Surface Tension of the Oxide Skin of Gallium-Based Liquid Metals

Patterning and Reversible Actuation of Liquid Gallium Alloys by Preventing Adhesion on Rough Surfaces

Large tuning in the electrowetting behaviour on ferroelectric PVDF-HFP/Teflon AF bilayer

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