Super-Water-Repellent Fractal Surfaces

Onda, Tomohiro; Shibuichi, Satoshi; Satoh, Naoki; Tsujii, Kaoru

doi:10.1021/la950418o

Cited by 1,597 publications

(1,146 citation statements)

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“…100 μm. The fractal dimension of the surfaces, D, was thus evaluated to be 2.1 which was smaller than that of AKD D 2.3 1 . We speculate that the decrease of D from that of AKD surface was caused by the low fluidity of raw materials of urethane and silicone elastomers.…”

Section: Resultsmentioning

confidence: 99%

Preparation and Characterization of Fractal Elastomer Surfaces

et al. 2013

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INTRODUCTIONFractal structures on solid substrates affect certain physical phenomena. Onda et al. proposed that fractal surfaces are super-water-repellent when the surfaces were composed of hydrophobic materials, and they subsequently prepared a super-water-repellent fractal surface made of alkylketene dimer AKD 1 . We prepared agar gels with hierarchically rough surfaces, called fractal agar gel, by transferring fractal surface structures of AKD as a model of hydrophilic biological surfaces such as tongue and smallintestine wall surfaces and showed that the rough structure accelerated the spreading of water droplets. Numerous other fractal surfaces, such as human skin, exist in our body. Actually, human skin can be expected to be hieralchical because some crista cutis enclosed by deeper sulcus cutis form area cutanea 5 . These hierarchical rough structures change the physical properties of human skin, i.e., its wettability and friction properties 6 8 . However, fractal surfaces consistng of AKD and agar gel are not suitable as a skin model because they are too hydrophobic or hydrophilic and fragile: the contact angle of water droplet on human skin and elastic modulus of epidermics are about 90 and 0.72 MPa, respectively 9, 10 . In the present study, we prepared urethane resin and silicone resin elastomers with fractal surfaces as a new human skin model. The fractal

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Section: Resultsmentioning

confidence: 99%

Preparation and Characterization of Fractal Elastomer Surfaces

et al. 2013

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“…Recently many methods have been developed to fabricate such superhydrophobic surfaces [5], [6], [7], [8], [9] and [10]. Erbil et al [5] described a simple and inexpensive method for forming a superhydrophobic coating using polypropylene and a suitable selection of solvents and temperatures to control the surface roughness.…”

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“…Recently, lithography has been used to create ordered structures on surfaces to demonstrate superhydrophobicity [6]. Onda et al [7] achieved a contact angle of 174° on the surface of the fractal structure of alkylketene. Other methods include the sol-gel process to generate a porous rough surface [8], the anodic oxidation of aluminum surfaces [9] and plasma polymerization [10].…”

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Superhydrophobic properties of ultrathin rf-sputtered Teflon films coated etched aluminum surfaces

2008

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Superhydrophobicity has been demonstrated on ultrathin rf-sputtered Teflon coated etched aluminum surfaces. The etching of aluminum surfaces has been performed using dilute hydrochloric acid. An optimized etching time of 2.5 min is found to be essential, before Teflon coating, to obtain a highest water contact angle of 164 ± 3° with a lowest contact angle hysteresis of 2.5 ± 1.5°, with the water drops simply rolling off these surfaces with even the slightest inclination of the sample. The presence of − CF3 radicals along with − CF2 radicals in the ultrathin rf-sputtered Teflon films, as investigated by X-ray photoelectron spectroscopy (XPS), contributes to the lowering of the surface energy on the aluminum surfaces. The presence of patterned microstructure as revealed by field emission scanning electron microscope (FESEM) together with the low surface energy ultrathin rf-sputtered Teflon films renders the aluminum surfaces highly superhydrophobic.

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“…[3,4] These studies address the critical issue of inducing surface roughness, which is required for true ultrahydrophobic behavior. [5][6][7][8][9][10][11][12][13][14][15] Soeno et al [3] described a multilayered polyelectrolyte/silica nanoparticle system which was heated to sinter the particles and burn off the polymer, then treated with a fluorosilane to induce the required hydrophobicity. Zhai et al [4] reported the formation of a pH-sensitive multilayer which undergoes a porosity-inducing phase transition in acidic solutions.…”

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Hydrophobic and Ultrahydrophobic Multilayer Thin Films from Perfluorinated Polyelectrolytes

2005

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Interest in surfaces exhibiting large water contact angles is stimulated both by important technological implications and by novel aspects of surface physics. Since wetting can be controlled by a single monolayer of material, novel materials or surface treatments can yield a fascinating range of properties. Such treatments, which are capable of generating particularly hydrophobic surfaces, include conventional coating processes such as spraying or dipping, [1a] vacuum deposition techniques, [1b] and such surface-modification technologies as diffusion, [1c] laser and plasma processes, [1d] chemical plating, [1e] grafting [1f] or bonding hydrogel encapsulation, [1g] and bombardment with high-energy particles. [1h] The use of the layer-by-layer sequential adsorption [2] method for the assembly of an ultrathin film has very recently been reported for making ultrahydrophobic surfaces. [3,4] These studies address the critical issue of inducing surface roughness, which is required for true ultrahydrophobic behavior. [5][6][7][8][9][10][11][12][13][14][15] Soeno et al. [3] described a multilayered polyelectrolyte/silica nanoparticle system which was heated to sinter the particles and burn off the polymer, then treated with a fluorosilane to induce the required hydrophobicity. Zhai et al. [4] reported the formation of a pH-sensitive multilayer which undergoes a porosity-inducing phase transition in acidic solutions. Additional treatment steps, including crosslinking, deposition of silica nanoparticles, fluorosilane treatment, and thermal annealing, yielded stable ultrahydrophobic materials. Although the targeted surface properties were obtained, multiple processing steps are not desirable. Herein, we describe a multilayering process that uses both fluorinated polyanions and polycations, with a roughening step, by utilizing a naturally occurring nanorod that can be inserted conveniently into the layering sequence.The polyelectrolytes used were nafion (Scheme 1), which is a commercially available sulfonated fluorinated material, and a polycation synthesized from poly(vinylpyridine) and a fluorinated alkyl iodide. Polyelectrolyte components were deposited on silicon wafers under ambient conditions using dilute solutions/dispersions. Although fluorinated solvents, such as trifluoroethanol, were useful for dispersing the polyelectrolytes, we were interested in employing more common solvents as vehicles for manipulating all the components. Methanol was effective in this respect. Figure 1 shows the layer-by-layer build-up of the fluorinated polyelectrolytes. The regular growth of the multilayer alleviated our concerns that the polyelectrolytes, probably existing as micellar, nanoparticulate dispersions rather than true solutions, might not produce acceptable multilayering behavior. Some curvature of the build-up curve hints at exponential growth (a topic of recent interest [16,17] ), but the fact that such curvature is so slight suggests it might result from increasing surface roughness, which was found to be 2.9, 3.2...

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Super-Water-Repellent Fractal Surfaces

Cited by 1,597 publications

References 2 publications

Preparation and Characterization of Fractal Elastomer Surfaces

Preparation and Characterization of Fractal Elastomer Surfaces

Superhydrophobic properties of ultrathin rf-sputtered Teflon films coated etched aluminum surfaces

Hydrophobic and Ultrahydrophobic Multilayer Thin Films from Perfluorinated Polyelectrolytes

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