Intelligent Control of Surface Hydrophobicity

Gras, Sally L.; Mahmud, Tanveer; Rosengarten, Gary; Mitchell, Arnan; Kalantar‐zadeh, Kourosh

doi:10.1002/cphc.200700222

Cited by 122 publications

(105 citation statements)

References 142 publications

(157 reference statements)

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“…An ITO glass (1 Â 1 cm) and stainless steel (5 Â 5 cm) were employed as the working and counter electrode, respectively. An electric field of 3 V/cm was imposed for 15 min at 26 C to render a PS template with 6.56 m thickness. Afterward, the PS template was carefully removed and dried in air at 50 C for 10 min.…”

Section: Methodsmentioning

confidence: 99%

“…To date, research activities on the EWOD have produced impressive progresses and relevant information can be found in several review papers. [24][25][26][27] Zinc oxide (ZnO) is a low-cost semiconductor with direct wide band gap (3.36 eV at room temperature) and large exciton binding energy (60 mV). 28 Because the ZnO exhibits notable chemical stability and biological compatibility, it has attracted significant attention for applications in photocatalysis, electronics, optoelectronics, and sensors.…”

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confidence: 99%

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Electrowetting of Superhydrophobic ZnO Inverse Opals

Chen

Lai

et al. 2011

J. Electrochem. Soc.

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ZnO inverse opals are fabricated by electrophoresis of polystyrene (PS) microspheres (720 nm in diameter) on a ITO glass to form a close-packed colloidal crystal, followed by potentiostatic deposition of ZnO in the interstitial voids among the PS microspheres and chemical removal of the PS colloidal template. By adjusting the electrodeposition time, we obtain semi-layered and multilayered ZnO inverse structures with significantly reduced defects and considerable surface uniformity. The semi-layered ZnO inverse opals display a bowl-like morphology with individual cavities isolated from each other. In contrast, the multi-layered ZnO inverse opals exhibit a three-dimensional skeleton with hexagonally-arranged cavities interconnected to each other. After surface coating of perfluorodecyltriethoxysilane, both samples reveal a superhydrophobic nature with contact angle larger than 150. In electrowetting measurements, the contact angles are decreasing with increasing applied voltages. The droplet on the semi-layered ZnO inverse opals demonstrates a notable transition from the Cassie-Baxter state to the Wenzel one. However, the droplet on the multi-layered ZnO inverse opals indicates three distinct regimes; Cassie-Baxter state, mixed Cassie-Baxter/Wenzel state, and Wenzel state. Repelling pressure of the entrapped air in the cavities is estimated to explain the observed contact angle variation upon the applied voltage for both samples. The surface property for a solid material can be deliberately controlled from hydrophilic to hydrophobic in order to affect the wetting behavior of a water droplet that is in contact with the solid surface. So far, external stimuli such as electric field, mechanical force, magnetic field, electrochemical reaction, and photon excitation have been employed to manipulate physical and chemical attributes of the surface.1-5 Among them, the electrical route, known as electrowetting (EW), is recognized for its fast response, reversibility, and compatibility with microdevices.6-8 To date, the implementation of EW for applications such as microfluidics and optoelectronic components have been explored. [9][10][11] In EW, the water droplet on the solid surface reveals a significant morphological alteration from a large contact angle (hydrophobic) to a reduced one (hydrophilic) upon the imposition of voltage across the solid surface and water droplet. This is because the electrical field engenders a capacitive charging on the interface that increases its surface energy considerably. As a result, the water droplet is able to wet the solid surface lowering the overall interfacial energy.For a desirable EW material, a large contact angle at zero voltage and a stronger capacitive effect are always preferred. To achieve these objectives, recent research attention has focused on the design and fabrication of one-dimensional materials such as nanowires and nanorods. [12][13][14][15] In general, the wetting behavior for the water droplet on a nanostructured surface can be categorized in Cassie-Baxter model o...

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Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

Electrowetting of Superhydrophobic ZnO Inverse Opals

Chen

Lai

et al. 2011

J. Electrochem. Soc.

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“…The superomniphobic membranes were fabricated by dip-coating interwoven nylon membranes with polymer-fluoroPOSS blends. As a consequence of electrowetting, [95][96][97] a polar liquid droplet in the Cassie-Baxter state on a porous membrane can transition to the Wenzel state when an electric field is applied across the porous membrane. 98,99 Typically, a non-polar liquid does not undergo such a transition.…”

Section: Applications Of Superomniphobic Surfacesmentioning

confidence: 99%

The design and applications of superomniphobic surfaces

2014

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Surfaces that display contact angles 41501 along with low contact angle hysteresis with essentially all high and low surface tension liquids, including water, oils and alcohols, are known as superomniphobic surfaces. Such surfaces have a range of commercial applications, including self-cleaning, non-fouling, stain-free clothing, drag reduction, corrosion prevention and separation of liquids. Such surfaces have thus generated immense academic and industrial interest in recent years. In this review, we discuss the systematic design of superomniphobic surfaces. In particular, we discuss the significance of surface energy, roughness and the critical role of re-entrant texture in obtaining the so-called Cassie-Baxter state with low surface tension liquids. We also discuss how hierarchical scales of texture can yield high contact angles and decrease the contact angle hysteresis of superomniphobic surfaces by reducing the solid-liquid contact area. On the basis of this understanding, we discuss dimensionless design parameters that allow for the systematic design of superomniphobic surfaces. We also review the current literature on superomniphobic surfaces, paying particular attention to surfaces that demonstrate good mechanical, chemical and radiation durability-traits that are essential for any commercial application of superomniphobic surfaces. Finally, we conclude by identifying the unresolved challenges in the fabrication of durable superomniphobic surfaces and highlight the future needs in the field.

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“…20,31 Below the LCST, pNIPAM chains exist in an extended coil conformation and solvation is driven by the enthalpic gain from intermolecular hydrogen bonding between the pNIPAM chains and water molecules. 19,25 As the temperature is increased towards the LCST, pNIPAM chains undergo a coil-to-globule transition. 19 Intramolecular hydrogen bonding between carboxyl and amide groups on the pNIPAM chains result in the interruption of hydrogen bonding of these groups with water molecules, ultimately resulting in chains adopting a collapsed conformation, driving out the water, and causing the polymer to precipitate out of solution.…”

Section: Introductionmentioning

confidence: 99%

Study of Water Adsorption in Poly(N-isopropylacrylamide) Thin Films Using Fluorescence Emission of 3-Hydroxyflavone Probes

et al. 2010

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. (2010) 'Study of water adsorption in PolyN-isopropylacrylamide) thin films using fluorescence emission of 3-hydroxyflavone probes'. Macromolecules, 43 (22):9488-9494. Publisher ACS PublicationsLink to publisher ' Abstract:The non-contact, measurement of water uptake in micro-scale (1-100 µm), thermoresponsive Poly(N-isopropylacrylamide) thin films is challenging. We assessed the efficacy of three different 3-Hydroxyflavone (3-HF) based fluorophores; to monitor water uptake in pNIPAM thin films close to the Lower Critical Solution Temperature (LCST) at 25 and 37 ºC. These 3-HF fluorophores undergo excited state intramolecular proton transfer, yielding emission from normal (N*) and tautomeric (T*) excited-state forms. The emission intensity ratio, log(I N* /I T* ) and N* band position are environmentally sensitive. Water adsorption in pNIPAM thin films follows a non-linear, two phase process: at low relative humidity, the adsorbed water disrupts polymerfluorophore hydrogen bonding, yielding small changes in log(I N* /I T* ) ratios, and overall intensity, at higher relative humidity, these intensity parameters (but not fluorescence lifetime) change dramatically, indicating a larger change in local polarity. These probes are thus sensitive indicators of water uptake in pNIPAM.

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Intelligent Control of Surface Hydrophobicity

Cited by 122 publications

References 142 publications

Electrowetting of Superhydrophobic ZnO Inverse Opals

Electrowetting of Superhydrophobic ZnO Inverse Opals

The design and applications of superomniphobic surfaces

Study of Water Adsorption in Poly(N-isopropylacrylamide) Thin Films Using Fluorescence Emission of 3-Hydroxyflavone Probes

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