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1

Thermal stability of superhydrophobic, nanostructured surfaces.  

PubMed

The thermal stability of superhydrophobic, nanostructured surfaces after thermal annealing was explored. Flat surfaces coated with hydrophobic diamond-like carbon (DLC) via plasma polymerization of hexamethyldisiloxane (HMDSO) showed a gradual decrease in the water contact angle from 90(o) to 60(o) while nanostructured surfaces maintained superhydrophobicity with more than 150° for annealing temperatures between 25 and 300°C. It was also found that surfaces with nanostructures having an aspect ratio of more than 5.2 may maintain superhydrophobicity for annealing temperatures as high as 350°C; above this temperature, however, the hydrophobicity on surfaces with lower aspect ratio nanostructures gradually degraded. It was observed that regardless of the aspect ratios of the nanostructure, all superhydrophobic surfaces became superhydrophilic after annealing at temperatures higher than 500°C. PMID:23116849

Cha, Sung-Chul; Her, Eun Kyu; Ko, Tae-Jun; Kim, Seong Jin; Roh, Hyunchul; Lee, Kwang-Ryeol; Oh, Kyu Hwan; Moon, Myoung-Woon

2013-02-01

2

Superhydrophobic elastomer surfaces with nanostructured micronails  

NASA Astrophysics Data System (ADS)

New approaches to the fabrication of microstructures of special shape were developed for polymers. Unusual superhydrophobic surface structures were achieved with the use of flexible polymers and hierarchical molds. Flexible polyurethane-acrylate coatings were patterned with microstructures with use of microstructured aluminum mold in a controlled UV-curing process. Electron microscope images of the UV-cured coatings on polymethylmethacrylate (PMMA) substrates revealed micropillars that were significantly higher than the corresponding depressions of the mold (even 47 vs. 35 ?m). The elongation was achieved by detaching the mold from the flexible, partially cured acrylate surface and then further curing the separated microstructure. The modified acrylate surface is superhydrophobic with a water contact angle of 156° and sliding angle of < 10°. Acrylic thermoplastic elastomers (TPE) were patterned with micro-nanostructured aluminum oxide molds through injection molding. The hierarchical surface of the elastomer showed elongated micropillars (57 ?m) with nail-head tops covered with nanograss. Comparison with a reference microstructure of the same material (35 ?m) indicated that the nanopores of the micro-nanomold assisted the formation of the nail-shaped micropillars. The elasticity of the TPE materials evidently plays a role in the elongation because similar elongation has not been found in hierarchically structured thermoplastic surfaces. The hierarchical micronail structure supports a high water contact angle (164°), representing an increase of 88° relative to the smooth TPE surface. The sliding angle was close to zero degrees, indicating the Cassie-Baxter state.

Saarikoski, Inka; Joki-Korpela, Fatima; Suvanto, Mika; Pakkanen, Tuula T.; Pakkanen, Tapani A.

2012-01-01

3

Jumping-Droplet-Enhanced Condensation on Scalable Superhydrophobic Nanostructured Surfaces  

NASA Astrophysics Data System (ADS)

When droplets coalesce on a superhydrophobic nanostructured surface, the resulting droplet can jump from the surface due to the release of excess surface energy. If designed properly, these superhydrophobic nanostructured surfaces can not only allow for easy droplet removal at micrometric length scales during condensation but promise to enhance heat transfer performance. However, the rationale for the design of an ideal nanostructured surface, as well as heat transfer experiments demonstrating the advantage of this jumping behavior are lacking. Here, we show that silanized copper oxide surfaces created via a simple fabrication method can achieve highly efficient jumping-droplet condensation heat transfer. We experimentally demonstrated a 25% higher overall heat flux and 30% higher condensation heat transfer coefficient compared to state-of-the-art hydrophobic condensing surfaces at low supersaturations. This work not only shows significant condensation heat transfer enhancement, but promises a low cost and scalable approach to increase efficiency for applications such as atmospheric water harvesting and dehumidification. Furthermore, the results offer insights and an avenue to achieve high flux superhydrophobic condensation.

Miljkovic, Nenad; Enright, Ryan; Nam, Youngsuk; Lopez, Ken; Dou, Nicholas; Sack, Jean; Wang, Evelyn

2013-03-01

4

Jumping-droplet-enhanced condensation on scalable superhydrophobic nanostructured surfaces.  

PubMed

When droplets coalesce on a superhydrophobic nanostructured surface, the resulting droplet can jump from the surface due to the release of excess surface energy. If designed properly, these superhydrophobic nanostructured surfaces can not only allow for easy droplet removal at micrometric length scales during condensation but also promise to enhance heat transfer performance. However, the rationale for the design of an ideal nanostructured surface as well as heat transfer experiments demonstrating the advantage of this jumping behavior are lacking. Here, we show that silanized copper oxide surfaces created via a simple fabrication method can achieve highly efficient jumping-droplet condensation heat transfer. We experimentally demonstrated a 25% higher overall heat flux and 30% higher condensation heat transfer coefficient compared to state-of-the-art hydrophobic condensing surfaces at low supersaturations (<1.12). This work not only shows significant condensation heat transfer enhancement but also promises a low cost and scalable approach to increase efficiency for applications such as atmospheric water harvesting and dehumidification. Furthermore, the results offer insights and an avenue to achieve high flux superhydrophobic condensation. PMID:23190055

Miljkovic, Nenad; Enright, Ryan; Nam, Youngsuk; Lopez, Ken; Dou, Nicholas; Sack, Jean; Wang, Evelyn N

2013-01-01

5

Monolithically integrated micro- and nanostructured glass surface with antiglare, antireflection, and superhydrophobic properties.  

PubMed

Hierarchical micro- and nanostructured surfaces have previously been made using a variety of materials and methods, including particle deposition, polymer molding, and the like. These surfaces have attracted a wide variety of interest for applications including reduced specular reflection and superhydrophobic surfaces. To the best of our knowledge, this paper reports the first monolithic, hierarchically structured glass surface that combines micro- and nanoscale surface features to simultaneously generate antiglare (AG), antireflection (AR), and superhydrophobic properties. The AG microstructure mechanically protects the AR nanostructure during wiping and smudging, while the uniform composition of the substrate and the micro- and nanostructured surface enables ion exchange through the surface, so that both the substrate and structured surface can be simultaneously chemically strengthened. PMID:24960031

Tulli, Domenico; Hart, Shandon D; Mazumder, Prantik; Carrilero, Albert; Tian, Lili; Koch, Karl W; Yongsunthon, Ruchirej; Piech, Garrett A; Pruneri, Valerio

2014-07-23

6

Dropwise condensation on superhydrophobic nanostructured surfaces: literature review and experimental analysis  

NASA Astrophysics Data System (ADS)

It is well established that the dropwise condensation (DWC) mode can lead up to significant enhancement in heat transfer coefficients as compared to the filmwise mode (FWC). Typically, hydrophobic surfaces are expected to promote DWC, while hydrophilic ones induce FWC. To this end, superhydrophobic surfaces, where a combination of low surface energy and surface texturing is used to enhance the hydrophobicity, have recently been proposed as a promising approach to promote dropwise condensation. An attractive feature of using superhydrophobic surfaces is to facilitate easy roll-off of the droplets as they form during condensation, thus leading to a significant improvement in the heat transfer associated with the condensation process. High droplet mobility can be obtained acting on the surface chemistry, decreasing the surface energy, and on the surface structure, obtaining a micro- or nano- superficial roughness. The first part of this paper will present a literature review of the most relevant works about DWC on superhydrophobic nanotextured substrates, with particular attention on the fabrication processes. In the second part, experimental data about DWC on superhydrophobic nanotextured samples will be analyzed. Particular attention will be paid to the effect of vapour velocity on the heat transfer. Results clearly highlight the excellent potential of nanostructured surfaces for application in flow condensation applications. However, they highlight the need to perform flow condensation experiments at realistic high temperature and saturation conditions in order to evaluate the efficacy of superhydrophobic surfaces for practically relevant pure vapor condensation applications.

Bisetto, A.; Torresin, D.; Tiwari, M. K.; Del, D., Col; Poulikakos, D.

2014-04-01

7

Drop impact upon micro- and nanostructured superhydrophobic surfaces.  

PubMed

We experimentally investigate drop impact dynamics onto different superhydrophobic surfaces, consisting of regular polymeric micropatterns and rough carbon nanofibers, with similar static contact angles. The main control parameters are the Weber number We and the roughness of the surface. At small We, i.e., small impact velocity, the impact evolutions are similar for both types of substrates, exhibiting Fakir state, complete bouncing, partial rebouncing, trapping of an air bubble, jetting, and sticky vibrating water balls. At large We, splashing impacts emerge forming several satellite droplets, which are more pronounced for the multiscale rough carbon nanofiber jungles. The results imply that the multiscale surface roughness at nanoscale plays a minor role in the impact events for small We less than or approximately equal 120 but an important one for large We greater than or approximately equal 120. Finally, we find the effect of ambient air pressure to be negligible in the explored parameter regime We less than or approximately equal 150. PMID:19821629

Tsai, Peichun; Pacheco, Sergio; Pirat, Christophe; Lefferts, Leon; Lohse, Detlef

2009-10-20

8

Optically transparent, mechanically durable, nanostructured superhydrophobic surfaces enabled by spinodally phase-separated glass thin films.  

PubMed

We describe the formation and properties of atomically bonded, optical quality, nanostructured thin glass film coatings on glass plates, utilizing phase separation by spinodal decomposition in a sodium borosilicate glass system. Following deposition via magnetron sputtering, thermal processing and differential etching, these coatings are structurally superhydrophilic (i.e., display anti-fogging functionality) and demonstrate robust mechanical properties and superior abrasion resistance. After appropriate chemical surface modification, the surfaces display a stable, non-wetting Cassie-Baxter state and exhibit exceptional superhydrophobic performance, with water droplet contact angles as large as 172°. As an added benefit, in both superhydrophobic and superhydrophilic states these nanostructured surfaces can block ultraviolet radiation and can be engineered to be anti-reflective with broadband and omnidirectional transparency. Thus, the present approach could be tailored toward distinct coatings for numerous markets, such as residential windows, windshields, specialty optics, goggles, electronic and photovoltaic cover glasses, and optical components used throughout the US military. PMID:23857991

Aytug, Tolga; Simpson, John T; Lupini, Andrew R; Trejo, Rosa M; Jellison, Gerald E; Ivanov, Ilia N; Pennycook, Stephen J; Hillesheim, Daniel A; Winter, Kyle O; Christen, David K; Hunter, Scott R; Haynes, J Allen

2013-08-01

9

Full-field dynamic characterization of superhydrophobic condensation on biotemplated nanostructured surfaces.  

PubMed

While superhydrophobic nanostructured surfaces have been shown to promote condensation heat transfer, the successful implementation of these coatings relies on the development of scalable manufacturing strategies as well as continued research into the fundamental physical mechanisms of enhancement. This work demonstrates the fabrication and characterization of superhydrophobic coatings using a simple scalable nanofabrication technique based on self-assembly of the Tobacco mosaic virus (TMV) combined with initiated chemical vapor deposition. TMV biotemplating is compatible with a wide range of surface materials and applicable over large areas and complex geometries without the use of any power or heat. The virus-structured coatings fabricated here are macroscopically superhydrophobic (contact angle >170°) and have been characterized using environmental electron scanning microscopy showing sustained and robust coalescence-induced ejection of condensate droplets. Additionally, full-field dynamic characterization of these surfaces during condensation in the presence of noncondensable gases is reported. This technique uses optical microscopy combined with image processing algorithms to track the wetting and growth dynamics of 100s to 1000s of microscale condensate droplets simultaneously. Using this approach, over 3 million independent measurements of droplet size have been used to characterize global heat transfer performance as a function of nucleation site density, coalescence length, and the apparent wetted surface area during dynamic loading. Additionally, the history and behavior of individual nucleation sites, including coalescence events, has been characterized. This work elucidates the nature of superhydrophobic condensation and its enhancement, including the role of nucleation site density during transient operation. PMID:24882117

Olçero?lu, Emre; Hsieh, Chia-Yun; Rahman, Md Mahamudur; Lau, Kenneth K S; McCarthy, Matthew

2014-07-01

10

Effect of droplet morphology on growth dynamics and heat transfer during condensation on superhydrophobic nanostructured surfaces.  

PubMed

Condensation on superhydrophobic nanostructured surfaces offers new opportunities for enhanced energy conversion, efficient water harvesting, and high performance thermal management. These surfaces are designed to be Cassie stable and favor the formation of suspended droplets on top of the nanostructures as compared to partially wetting droplets which locally wet the base of the nanostructures. These suspended droplets promise minimal contact line pinning and promote passive droplet shedding at sizes smaller than the characteristic capillary length. However, the gas films underneath such droplets may significantly hinder the overall heat and mass transfer performance. We investigated droplet growth dynamics on superhydrophobic nanostructured surfaces to elucidate the importance of droplet morphology on heat and mass transfer. By taking advantage of well-controlled functionalized silicon nanopillars, we observed the growth and shedding behavior of suspended and partially wetting droplets on the same surface during condensation. Environmental scanning electron microscopy was used to demonstrate that initial droplet growth rates of partially wetting droplets were 6× larger than that of suspended droplets. We subsequently developed a droplet growth model to explain the experimental results and showed that partially wetting droplets had 4-6× higher heat transfer rates than that of suspended droplets. On the basis of these findings, the overall performance enhancement created by surface nanostructuring was examined in comparison to a flat hydrophobic surface. We showed these nanostructured surfaces had 56% heat flux enhancement for partially wetting droplet morphologies and 71% heat flux degradation for suspended morphologies in comparison to flat hydrophobic surfaces. This study provides insights into the previously unidentified role of droplet wetting morphology on growth rate, as well as the need to design Cassie stable nanostructured surfaces with tailored droplet morphologies to achieve enhanced heat and mass transfer during dropwise condensation. PMID:22293016

Miljkovic, Nenad; Enright, Ryan; Wang, Evelyn N

2012-02-28

11

UVO Tunable Superhydrophobic to Superhydrophilic Wetting Transition on Biomimetic Nanostructured Surfaces  

NASA Astrophysics Data System (ADS)

A novel strategy for a tunable sigmoidal wetting transition from superhydrophobicity to superhydrophilicity on a continuous nanostructured hybrid film via gradient UV-ozone (UVO) exposure is presented. Along a single wetting gradient surface (40 mm), we could visualize the superhydrophobic (?H2O> 165^o and low contact angle hysteresis), transition (165^ o > ?H2O> 10^ o) and superhydrophilic (?H2O< 10^o within 0.5 s or less) regions simply through the optical image of water droplets on the surface. The film is prepared through layer-by-layer assembly of negatively charged silica nanoparticles (11 nm) and positively charged poly(allylamine hydrochloride) with a initial deposition of fractal manner. The extraordinary wetting transition on chemically modified nanoparticle layered surfaces with submicron to microns scale pores represents a competition between chemical wettability and hierarchical roughness of surfaces as often occurs in nature (e.g., lotus leaves, insect's wings, etc).

Karim, Alamgir; Tark Han, Joong; Kim, Sangcheol

2007-03-01

12

Oxygen adsorption induced superhydrophilic-to-superhydrophobic transition on hierarchical nanostructured CuO surface.  

PubMed

Hierarchical nanostructured CuO surface was embellished to amplify the wettability. The pristine superhydrophilic CuO surface spontaneously transited to be superhydrophobic after exposed in air at room temperature for about 3 weeks. The wettability change is attributed to the adsorption of oxygen molecules on the topmost layer according to the surface chemical analysis. The adsorbed oxygen molecules could be removed by dipping the sample into l-Ascorbic acid solution for 10 s, leading to the recovery of the pristine superhydrophilicity. PMID:22484170

Wang, Guoyong; Zhang, Tong-Yi

2012-07-01

13

A "non-sticky" superhydrophobic surface prepared by self-assembly of fluoroalkyl phosphonic acid on a hierarchically micro/nanostructured alumina gel film.  

PubMed

A hierarchically micro/nanostructured alumina gel film was prepared by using a simple sol-gel process; upon self-assembly of fluoroalkyl phosphonic acid, a "non-sticky" superhydrophobic surface was obtained. PMID:22655297

Ma, Wei; Wu, Hui; Higaki, Yuji; Otsuka, Hideyuki; Takahara, Atsushi

2012-07-11

14

Optically Transparent, Mechanically Durable, Nanostructured Superhydrophobic Surfaces Enabled by Spinodally Phase-Separated Glass Thin Films  

SciTech Connect

Inspired by highly non-wetting natural biological surfaces (e.g., lotus leaves and water strider legs), artificial superhydrophobic surfaces that exhibit water droplet contact angles exceeding 150o have previously been constructed by utilizing various synthesis strategies.[ , , ] Such bio-inspired, water-repellent surfaces offer significant potential for numerous uses ranging from marine applications (e.g., anti-biofouling, anti-corrosion), anti-condensation (e.g., anti-icing, anti-fogging), membranes for selective separation (e.g., oil-water, gas-liquid), microfluidic systems, surfaces requiring reduced maintenance and cleaning, to applications involving glasses and optical materials.[ ] In addition to superhydrophobic attributes, for integration into device systems that have extended operational limits and overall improved performance, surfaces that also possess multifunctional characteristics are desired, where the functionality should match to the application-specific requirements.

Aytug, Tolga [ORNL; Christen, David K [ORNL; Hillesheim, Daniel A [ORNL; Hunter, Scott Robert [ORNL; Ivanov, Ilia N [ORNL; Jellison Jr, Gerald Earle [ORNL; Lupini, Andrew R [ORNL; Pennycook, Stephen J [ORNL; Trejo, Rosa M [ORNL; Winters, Kyle O. [University of Tennessee, Knoxville (UTK); Haynes, James A [ORNL; Simpson, John T [ORNL

2013-01-01

15

Electrokinetics on superhydrophobic surfaces.  

PubMed

On a superhydrophobic surface a liquid is exposed to a large air-water interface. The reduced wall friction is expected to cause a higher electro-osmotic mobility. On the other hand, the low charge density of a superhydrophobic surface reduces the electro-osmotic mobility. Due to a lack of experimental data it has not been clear so far whether the reduced wall friction or the reduced charge density dominate the electrokinetic mobilities. To separate the relative contributions of electrophoresis and electro-osmosis, the mobilities of colloids on a negatively charged hydrophilic, a superhydrophobic (Cassie) and a partially hydrophilized superhydrophobic (Cassie composite) coating were measured. To vary the charge density as well as its sign with respect to those of the colloids the partially hydrophilized surfaces were coated with polyelectrolytes. We analyzed the electrokinetic mobilities of negatively charged polystyrene colloids dispersed in aqueous medium on porous hydrophilic and superhydrophobic surfaces by confocal laser scanning electron microscopy. In all cases, the external electric field was parallel to the surface. The total electrokinetic mobilities on the superhydrophobic (Cassie) and negatively charged partially hydrophilized (Cassie composite) surfaces were similar, showing that electro-osmosis is small compared to electrophoresis. The positively charged Cassie composite surfaces tend to 'trap' the colloids due to attracting electrostatic interactions and rough morphology, reducing the mobility. Thus, either the charge density of the coatings in the Cassie composite state or its slip length is too low to enhance electro-osmosis. PMID:23113983

Papadopoulos, Periklis; Deng, Xu; Vollmer, Doris; Butt, Hans-Jürgen

2012-11-21

16

Electrokinetics on superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

On a superhydrophobic surface a liquid is exposed to a large air-water interface. The reduced wall friction is expected to cause a higher electro-osmotic mobility. On the other hand, the low charge density of a superhydrophobic surface reduces the electro-osmotic mobility. Due to a lack of experimental data it has not been clear so far whether the reduced wall friction or the reduced charge density dominate the electrokinetic mobilities. To separate the relative contributions of electrophoresis and electro-osmosis, the mobilities of colloids on a negatively charged hydrophilic, a superhydrophobic (Cassie) and a partially hydrophilized superhydrophobic (Cassie composite) coating were measured. To vary the charge density as well as its sign with respect to those of the colloids the partially hydrophilized surfaces were coated with polyelectrolytes. We analyzed the electrokinetic mobilities of negatively charged polystyrene colloids dispersed in aqueous medium on porous hydrophilic and superhydrophobic surfaces by confocal laser scanning electron microscopy. In all cases, the external electric field was parallel to the surface. The total electrokinetic mobilities on the superhydrophobic (Cassie) and negatively charged partially hydrophilized (Cassie composite) surfaces were similar, showing that electro-osmosis is small compared to electrophoresis. The positively charged Cassie composite surfaces tend to ‘trap’ the colloids due to attracting electrostatic interactions and rough morphology, reducing the mobility. Thus, either the charge density of the coatings in the Cassie composite state or its slip length is too low to enhance electro-osmosis.

Papadopoulos, Periklis; Deng, Xu; Vollmer, Doris; Butt, Hans-Jürgen

2012-11-01

17

Facile Synthesis of Three-Dimensional ZnO Nanostructure: Realization of a Multifunctional Stable Superhydrophobic Surface  

PubMed Central

Background After comprehensive study of various superhydrophobic phenomena in nature, it is no longer a puzzle for researchers to realize such fetching surfaces. However, the different types of artificial surfaces may get wetted and lose its water repellence if there exist defects or the liquid is under pressure. With respect to the industry applications, in which the resistance of wetting transition is critical important, new nanostructure satisfied a certain geometric criterion should be designed to hold a stable gas film at the base area to avoid the wet transition. Methodology A thermal deposition method was utilized to produce a thin ZnO seeds membrane on the aluminum foil. And then a chemical self-assemble technology was developed in present work to fabricate three-dimensional (3D) hierarchical dune-like ZnO architecture based on the prepared seeds membrane. Results Hierarchical ZnO with micro scale dune-like structure and core-sharing nanosheets was generated. The characterization results showed that there exist plenty of gaps and interfaces among the micro-dune and nanosheets, and thus the surface area was enlarged by such a unique morphology. Benefited from this unique 3D ZnO hierarchical nanostructure, the obtained surface exhibited stable water repellency after modification with Teflon, and furthermore, based on solid theory analysis, such 3D ZnO nanostructure would exhibit excellent sensing performance.

Wu, Jun; Xia, Jun; Lei, Wei; Wang, Baoping

2011-01-01

18

Superhydrophobic thin films with nanostructured surface prepared with Au nanoparticle masks.  

PubMed

The hydrophobicity of a perfluoropolyether bisurethane methacrylate polymer film was investigated along with the formation of nano-hairs on its surface through reactive ion etching using gold nanoparticles (Au NPs) as masks. It was found that the hydrophobicity of the polymer film was strongly dependent on the number density of the nano-hairs which was determined by that of the Au NPs. The superhydrophobic surface was obtained when the number density was higher than 250 microm(-2). The effects of surface functionalization, Au NP immobilization, and etching time on the hydrophobicity of the polymer film were also examined extensively and discussed based on the results of the contact angle measurements and the scanning electron microscopy. PMID:22121761

Lee, Cho Yeon; Yoon, Suk Bon; Jang, Gun-Eik; Yun, Wan Soo

2011-07-01

19

Superhydrophobic Copper Surfaces  

NSDL National Science Digital Library

This lesson from The Lawrence Hall of Science was taught in fall 2012 and focuses on superhydrophobic and superhydrophilic surfaces. Students will experiment with these materials by chemically modifying copper. This page includes links to the Source Article for the Hands-on Module as well as four documents for instructor use in teaching the lab.

2014-06-03

20

Slip on Superhydrophobic Surfaces  

Microsoft Academic Search

This review discusses the use of the combination of surface roughness and hydrophobicity for engineering large slip at the fluid-solid interface. These superhydrophobic surfaces were initially inspired by the unique water-repellent properties of the lotus leaf and can be employed to produce drag reduction in both laminar and turbulent flows, enhance mixing in laminar flows, and amplify diffusion-osmotic flows. We

Jonathan P. Rothstein

2010-01-01

21

Antibacterial Fluorinated Silica Colloid Superhydrophobic Surfaces  

PubMed Central

A superhydrophobic xerogel coating synthesized from a mixture of nanostructured fluorinated silica colloids, fluoroalkoxysilane, and a backbone silane is reported. The resulting fluorinated surface was characterized using contact angle goniometry, SEM, and AFM. Quantitative bacterial adhesion studies performed using a parallel plate flow cell demonstrated that the adhesion of Staphylococcus aureus and Pseudomonas aeruginosa were reduced by 2.08 ± 0.25 and 1.76 ± 0.12 log over controls, respectively. This simple superhydrophobic coating synthesis may be applied to any surface regardless of geometry and does not require harsh synthesis or processing conditions, making it an ideal candidate as a biopassivation strategy.

Privett, Benjamin J.; Youn, Jonghae; Hong, Sung A; Lee, Jiyeon; Han, Junhee

2011-01-01

22

Superhydrophobic surfaces fabricated by surface modification of alumina particles  

NASA Astrophysics Data System (ADS)

The fabrication of superhydrophobic surfaces has attracted intense interest because of their widespread potential applications in various industrial fields. Recently, some attempts have been carried out to prepare superhydrophobic surfaces using metal oxide nanoparticles. In the present work, superhydrophobic surfaces were fabricated with low surface energy material on alumina particles with different sizes. It was found that particle size of alumina is an important factor in achieving stable superhydrophobic surface. It was possible to obtain alumina surface with water contact angle (WCA) of 156° and a sliding angle of <2°. Superhydrophobicity of the modified alumina is attributed to the combined effect of the micro-nanostructure and low surface energy of fatty acid on the surface. The surface morphology of the alumina powder and coatings was determined by FESEM. The stability of the coatings was assessed by conducting water immersion test. Effect of heat treatment on WCA of the coating was also studied. The transition of alumina from hydrophilic to superhydrophobic state was explained using Wenzel and Cassie models. The method is shown to have potential application for creating superhydrophobic surface on cotton fabrics.

Richard, Edna; Aruna, S. T.; Basu, Bharathibai J.

2012-10-01

23

Superhydrophobic nanostructured Kapton® surfaces fabricated through Ar + O2 plasma treatment: Effects of different environments on wetting behaviour  

NASA Astrophysics Data System (ADS)

Kapton® [poly (4,4'-oxy diphenylene pyromellitimide)] polyimides have widespread usage in semiconductor devices, solar arrays, protective coatings and space applications, due to their excellent chemical and physical properties. In addition to their inherent properties, imparting superhydrophobicity on these surfaces will be an added advantage. Present work describes the usage of Ar + O2 plasma treatment for the preparation of superhydrophobic Kapton® surfaces. Immediately after the plasma treatment, the surfaces showed superhydrophilicity as a result of high energy dangling bonds and polar group concentration. But the samples kept in low vacuum for 48 h exhibited superhydrophobicity with high water contact angles (>150°). It is found that the post plasma treatment process, called ageing, especially in low vacuum plays an important role in delivering superhydrophobic property to Kapton®. Field emission scanning electron microscopy and atomic force microscopy were used to probe the physical changes in the surface of the Kapton®. The surfaces showed formation of nano-feathers and nano-tussock microstructures with variation in surface roughness against plasma treatment time. A thorough chemical investigation was performed using Fourier transform infrared spectroscopy and micro-Raman spectroscopy, which revealed changes in the surface of the Ar + O2 plasma treated Kapton®. Surface chemical species of Kapton® were confirmed again by X-ray photoelectron spectroscopy spectra for untreated surfaces whereas Ar + O2 plasma treated samples showed the de-bonding and re-organization of structural elements. Creation of surface roughness plays a dominant role in the contribution of superhydrophobicity to Kapton® apart from the surface modifications due to Ar + O2 plasma treatment and ageing in low vacuum.

Barshilia, Harish C.; Ananth, A.; Gupta, Nitant; Anandan, C.

2013-03-01

24

Transparent nanostructured coatings with UV-shielding and superhydrophobicity properties  

Microsoft Academic Search

Visible light transparent, UV-shielding and superhydrophobic nanostructured coatings have been successfully fabricated through a facile layer-by-layer deposition of TiO2 and SiO2 nanoparticles. The coatings are composed of an underlying UV-shielding TiO2 layer and a top fully covered protective SiO2 layer. The resulting coatings can block 100% of UVB and UVC and almost 85% of UVA. The fabricated surfaces have contact

Taoye Wang; Tayirjan T. Isimjan; Jianfeng Chen; Sohrab Rohani

2011-01-01

25

Dropwise condensation on superhydrophobic surfaces with two-tier roughness  

NASA Astrophysics Data System (ADS)

Dropwise condensation can enhance heat transfer by an order of magnitude compared to film condensation. Superhydrophobicity appears ideal to promote continued dropwise condensation which requires rapid removal of condensate drops; however, such promotion has not been reported on engineered surfaces. This letter reports continuous dropwise condensation on a superhydrophobic surface with short carbon nanotubes deposited on micromachined posts, a two-tier texture mimicking lotus leaves. On such micro-/nanostructured surfaces, the condensate drops prefer the Cassie state which is thermodynamically more stable than the Wenzel state. With a hexadecanethiol coating, superhydrophobicity is retained during and after condensation and rapid drop removal is enabled.

Chen, Chuan-Hua; Cai, Qingjun; Tsai, Chialun; Chen, Chung-Lung; Xiong, Guangyong; Yu, Ying; Ren, Zhifeng

2007-04-01

26

Flow condensation on copper-based nanotextured superhydrophobic surfaces.  

PubMed

Superhydrophobic surfaces have shown excellent ability to promote dropwise condensation with high droplet mobility, leading to enhanced surface thermal transport. To date, however, it is unclear how superhydrophobic surfaces would perform under the stringent flow condensation conditions of saturated vapor at high temperature, which can affect superhydrophobicity. Here, we investigate this issue employing "all-copper" superhydrophobic surfaces with controlled nanostructuring for minimal thermal resistance. Flow condensation tests performed with saturated vapor at a high temperature (110 °C) showed the condensing drops penetrate the surface texture (i.e., attain the Wenzel state with lower droplet mobility). At the same time, the vapor shear helped ameliorate the mobility and enhanced the thermal transport. At the high end of the examined vapor velocity range, a heat flux of ~600 kW m(-2) was measured at 10 K subcooling and 18 m s(-1) vapor velocity. This clearly highlights the excellent potential of a nanostructured superhydrophobic surface in flow condensation applications. The surfaces sustained dropwise condensation and vapor shear for five days, following which mechanical degradation caused a transition to filmwise condensation. Overall, our results underscore the need to investigate superhydrophobic surfaces under stringent and realistic flow condensation conditions before drawing conclusions regarding their performance in practically relevant condensation applications. PMID:23249322

Torresin, Daniele; Tiwari, Manish K; Del Col, Davide; Poulikakos, Dimos

2013-01-15

27

Pattern-dependent tunable adhesion of superhydrophobic MnO2 nanostructured film.  

PubMed

Tuning the adhesive force on a superhydrophobic MnO(2) nanostructured film was achieved by fabricating different patterns including meshlike, ball cactus-like, and tilted nanorod structures. The marvelous modulation range of the adhesive forces from 130 to nearly 0 ?N endows these superhydrophobic surfaces with extraordinarily different dynamic properties of water droplets. This pattern-dependent adhesive property is attributed to the kinetic barrier difference resulting from the different continuity of the three-interface contact line. This finding will provide the general strategies for the adhesion adjustment on superhydrophobic surfaces. PMID:21370908

Zhao, Xiao Dan; Fan, Hai Ming; Liu, Xiang Yang; Pan, Haihua; Xu, Hong Yao

2011-04-01

28

Anti-icing performance of superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

This article studies the anti-ice performance of several micro/nano-rough hydrophobic coatings with different surface chemistry and topography. The coatings were prepared by spin-coating or dip coating and used organosilane, fluoropolymer or silicone rubber as a top layer. Artificially created glaze ice, similar to the naturally accreted one, was deposited on the nanostructured surfaces by spraying supercooled water microdroplets (average size ˜80 ?m) in a wind tunnel at subzero temperature (-10 °C). The ice adhesion strength was evaluated by spinning the samples in a centrifuge at constantly increasing speed until ice delamination occurred. The results show that the anti-icing properties of the tested materials deteriorate, as their surface asperities seem to be gradually broken during icing/de-icing cycles. Therefore, the durability of anti-icing properties appears to be an important point for further research. It is also shown that the anti-icing efficiency of the tested superhydrophobic surfaces is significantly lower in a humid atmosphere, as water condensation both on top and between surface asperities takes place, leading to high values of ice adhesion strength. This implies that superhydrophobic surfaces may not always be ice-phobic in the presence of humidity, which can limit their wide use as anti-icing materials.

Farhadi, S.; Farzaneh, M.; Kulinich, S. A.

2011-05-01

29

Effective slip on textured superhydrophobic surfaces  

Microsoft Academic Search

We study fluid flow in the vicinity of textured and superhydrophobically coated surfaces with characteristic texture sizes on the order of 10 mum. Both for droplets moving down an inclined surface and for an external flow near the surface (hydrofoil), there is evidence of appreciable drag reduction in the presence of surface texture combined with superhydrophobic coating. On textured inclined

Salil Gogte; Peter Vorobieff; Richard Truesdell; Andrea Mammoli; Frank van Swol; Pratik Shah; C. Jeffrey Brinker

2005-01-01

30

Micro Droplet Transfer between Superhydrophobic Surfaces via a High Adhesive Superhydrophobic Surface  

NASA Astrophysics Data System (ADS)

Micro droplet handling is very important for micro and nano fluidic devices and an intelligent bio interface. Micro droplet transfer via a high adhesive superhydrophobic surface has been reported in recent years. We demonstrated water droplet adhesion controllable superhydrophobic metal-polymer surfaces. Moreover we achieved micro droplet transfer between superhydrophobic surfaces by using different droplet adhesion properties. Water micro droplets were transferred from a low-adhesive superhydrophobic surface to a midium-adhesive superhydrophobic surface via a high-adhesive superhydrophobic surface without any mass loss. After droplet transfer, water contact angle was about 150°. Droplet handlings on the adhesive superhydrophobic surfaces will be expected for fluidic bio devices with energy saving.

Ishii, Daisuke; Yabu, Hiroshi; Shimomura, Masatusgu

31

Wettability Switching Techniques on Superhydrophobic Surfaces  

NASA Astrophysics Data System (ADS)

The wetting properties of superhydrophobic surfaces have generated worldwide research interest. A water drop on these surfaces forms a nearly perfect spherical pearl. Superhydrophobic materials hold considerable promise for potential applications ranging from self cleaning surfaces, completely water impermeable textiles to low cost energy displacement of liquids in lab-on-chip devices. However, the dynamic modification of the liquid droplets behavior and in particular of their wetting properties on these surfaces is still a challenging issue. In this review, after a brief overview on superhydrophobic states definition, the techniques leading to the modification of wettability behavior on superhydrophobic surfaces under specific conditions: optical, magnetic, mechanical, chemical, thermal are discussed. Finally, a focus on electrowetting is made from historical phenomenon pointed out some decades ago on classical planar hydrophobic surfaces to recent breakthrough obtained on superhydrophobic surfaces.

Verplanck, Nicolas; Coffinier, Yannick; Thomy, Vincent; Boukherroub, Rabah

2007-12-01

32

Superhydrophobic behaviors of polymeric surfaces with aligned nanofibers.  

PubMed

In this article, nanostructured superhydrophobic polymeric surfaces were fabricated by a simple (one-step) reproductive method of anodic aluminum oxide (AAO) template extrusion. By tuning the diameter of the AAO template and the pressure to extrude, high-density polyethylene (HDPE) nanofiber surfaces with different nanometer roughness were prepared, and various sliding angles (SAs) of drops on these surfaces were measured. The results of the impact of drops on the nanostructured HDPE surfaces indicated that SAs were very important for the dynamic wettability of superhydrophobic surfaces. The one-step AAO template extrusion method has the advantage of tailoring the SA values on polymeric surfaces. Therefore, we believe it to be a promising industrial basis for manufacturing functional materials in the fields of agriculture, electronics, and optics. PMID:19326870

Sheng, Xianliang; Zhang, Jihua

2009-06-16

33

Air layer on superhydrophobic surface underwater  

Microsoft Academic Search

Sustaining an air layer on superhydrophobic surface is known necessary for the applications of the “air layer effect” underwater on basis of previous literatures. However, the air layer becomes unstable when put underwater and even disappears when the hydraulic pressure increases. Thus much attention has been focused on the sustainability of an air layer on a superhydrophobic surface. This article

Xianliang Sheng; Jihua Zhang

2011-01-01

34

Turbulent Drag Reduction Using Superhydrophobic Surfaces  

Microsoft Academic Search

Superhydrophobic surfaces have received considerable attention for their ability to reduce drag in laminar flows. In this talk we demonstrate that engineered, micropatterned, superhydrophobic surfaces produce the same effect, with similar geometric scaling, in turbulent flows. Direct velocity measurements were used to measure slip velocities up to 40% of the mean flow. Shear stress reductions up to 60% were noted

Robert J. Daniello; Jonathan P. Rothstein

2008-01-01

35

The numerical simulation of superhydrophobic surface's flow field characteristic  

Microsoft Academic Search

Based on the flow field mathematical model of superhydrophobic surfaces, the numerical simulation of superhydrophobic surfaces with microcosmic topography in turbulence was carried out. The flow field characteristics of superhydrophobic surfaces were analyzed from the flow field structure, the shear stress distribution, the velocity distribution of gas-liquid interface and the turbulent kinetic energy distribution. The results show that the superhydrophobic

Qiaogao Huang; Haibao Hu; Guang Pan; Baowei Song

2012-01-01

36

Surfaces with combined microscale and nanoscale structures: a route to mechanically stable superhydrophobic surfaces?  

PubMed

Materials with superhydrophobic properties are usually generated by covering the surfaces with hydrophobic nanoscale rough features. A major problem, however, for any practical application of such strongly water-repellent surfaces is the mechanical fragility of the nanostructures. Even moderate forces caused by touching or rubbing the surfaces are frequently strong enough to destroy the nanostructures and lead to the loss of the superhydrophobic properties. In this article, we study the mechanical stability of superhydrophobic surfaces with three different topographies: nano- and microscale features and surfaces carrying a combination of both. The surfaces are generated by silicon etching and subsequent coating with a monolayer of a fluoropolymer (PFA). We perform controlled wear tests on the different surfaces and discuss the impact of wear on the wetting properties of the different surfaces. PMID:23363078

Groten, Jonas; Rühe, Jürgen

2013-03-19

37

Shear flow on super-hydrophobic surfaces.  

SciTech Connect

Super-hydrophobic surfaces, which exhibit large contact angles, can give rise to slip flow of aqueous fluids. We present our work on shear flow of atomistic fluids over simple super-hydrophobic surfaces. Molecular dynamic simulations are employed to investigate the flow field of fluid between two parallel surfaces, one of which is moving. Exploring a range of fluid thermodynamic state points, we demonstrate the influence of fluid phase and structure near the surfaces on prevalence, and degree, of slip at the super-hydrophobic surface.

van Swol, Frank B.; Truesdell, Richard; Vorobieff, Peter V.; Challa, Sivakumar R.; Mammoli, Andrea A.

2007-10-01

38

Hierarchically sculptured plant surfaces and superhydrophobicity.  

PubMed

More than 400 million years of evolution of land plants led to a high diversity of adapted surface structures. Superhydrophobic biological surfaces are of special interest for the development of biomimetic materials for self-cleaning, drag reduction, and energy conservation. The key innovation in superhydrophobic biological surfaces is hierarchical sculpturing. In plants, a hydrophobic wax coating creates water-repelling surfaces that in combination with two or more levels of sculpturing leads to superhydrophobicity. Hierarchical structuring is of special interest for technical "biomimetic" materials with low adhesion and self-cleaning properties. Here we introduce hierarchical surface sculptures of plants with up to six levels. The article gives an overview of the composition of hierarchical surfaces for superhydrophobicity and their use as models for the development of artificial self-cleaning or drag-reducing surfaces. PMID:19634871

Koch, Kerstin; Bohn, Holger Florian; Barthlott, Wilhelm

2009-12-15

39

Slip on Superhydrophobic Surfaces  

Microsoft Academic Search

This review discusses the use of the combination of surface roughness and hy- drophobicity for engineering large slip at the fluid-solid interface. These su- perhydrophobic surfaces were initially inspired by the unique water-repellent properties of the lotus leaf and can be employed to produce drag reduction in both laminar and turbulent flows, enhance mixing in laminar flows, and amplify diffusion-osmotic

Jonathan P. Rothstein

2010-01-01

40

Unidirectional superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

It has long been known that the hairy, waxy cuticle of water-walking insects renders them water-repellent; they thus exhibit high static contact angles. We have recently demonstrated that by the virtue of the geometry and flexibility of the hair, the integument is also directionally anisotropic and so plays a key propulsive role. We here report our attempts to design and implement an analogous synthetic surface that exhibits unidirectional adhesion. The surface effectively acts like a fluidic-diode; allowing contact lines to advance in only one direction. When vibrated randomly, drops suspended on the surface advance in only one direction. Applications in valve-less pumps and drop transport in microfluidic devices are discussed.

Prakash, Manu; Bush, John

2007-11-01

41

Turbulent Drag Reduction Using Superhydrophobic Surfaces  

NASA Astrophysics Data System (ADS)

Superhydrophobic surfaces have received considerable attention for their ability to reduce drag in laminar flows. In this talk we demonstrate that engineered, micropatterned, superhydrophobic surfaces produce the same effect, with similar geometric scaling, in turbulent flows. Direct velocity measurements were used to measure slip velocities up to 40% of the mean flow. Shear stress reductions up to 60% were noted in comparison between smooth and superhydrophobic walls, with slip lengths up to 230?m for several microridge geometries. Drag reduction was noted to increase with microfeature spacing and with reduced laminar sublayer thickness for a fixed shear free area ratio.

Daniello, Robert J.; Rothstein, Jonathan P.

2008-11-01

42

Hierarchically nanotextured surfaces maintaining superhydrophobicity under severely adverse conditions.  

PubMed

Superhydrophobic surfaces are highly desirable for a broad range of technologies and products affecting everyday life. Despite significant progress in recent years in understanding the principles of hydrophobicity, mostly inspired by surface designs found in nature, many man-made surfaces employ readily processable materials, ideal to demonstrate principles, but with little chance of survivability outside a very limited range of well-controlled environments. Here we focus on the rational development of robust, hierarchically nanostructured, environmentally friendly, metal-based (aluminum) superhydrophobic surfaces, which maintain their performance under severely adverse conditions. Based on their functionality, we superpose selected hydrophobic layers (i.e. self-assembled monolayers, thin films, or nanofibrous coatings) on hierarchically textured aluminum surfaces, collectively imparting high level robustness of superhydrophobicity under adverse conditions. These surfaces simultaneously exhibit chemical stability, mechanical durability and droplet impalement resistance. They impressively maintained their superhydrophobicity after exposure to severely adverse chemical environments like strong alkaline (pH ? 9-10), acidic (pH ? 2-3), and ionic solutions (3.5 weight% of sodium chloride), and could simultaneously resist water droplet impalement up to an impact velocity of 3.2 m s(-1) as well as withstand standard mechanical durability tests. PMID:24947006

Maitra, Tanmoy; Antonini, Carlo; Auf der Mauer, Matthias; Stamatopoulos, Christos; Tiwari, Manish K; Poulikakos, Dimos

2014-07-10

43

Superhydrophobic ceramic coatings enabled by phase-separated nanostructured composite TiO2–Cu2O thin films  

NASA Astrophysics Data System (ADS)

By exploiting phase-separation in oxide materials, we present a simple and potentially low-cost approach to create exceptional superhydrophobicity in thin-film based coatings. By selecting the TiO2–Cu2O system and depositing through magnetron sputtering onto single crystal and metal templates, we demonstrate growth of nanostructured, chemically phase-segregated composite films. These coatings, after appropriate chemical surface modification, demonstrate a robust, non-wetting Cassie–Baxter state and yield an exceptional superhydrophobic performance, with water droplet contact angles reaching to ?172° and sliding angles <1°. As an added benefit, despite the photo-active nature of TiO2, the chemically coated composite film surfaces display UV stability and retain superhydrophobic attributes even after exposure to UV (275 nm) radiation for an extended period of time. The present approach could benefit a variety of outdoor applications of superhydrophobic coatings, especially for those where exposure to extreme atmospheric conditions is required.

Aytug, Tolga; Bogorin, Daniela F.; Paranthaman, Parans M.; Mathis, John E.; Simpson, John T.; Christen, David K.

2014-06-01

44

Superhydrophobic surfaces developed by mimicking hierarchical surface morphology of lotus leaf.  

PubMed

The lotus plant is recognized as a 'King plant' among all the natural water repellent plants due to its excellent non-wettability. The superhydrophobic surfaces exhibiting the famous 'Lotus Effect', along with extremely high water contact angle (>150°) and low sliding angle (<10°), have been broadly investigated and extensively applied on variety of substrates for potential self-cleaning and anti-corrosive applications. Since 1997, especially after the exploration of the surface micro/nanostructure and chemical composition of the lotus leaves by the two German botanists Barthlott and Neinhuis, many kinds of superhydrophobic surfaces mimicking the lotus leaf-like structure have been widely reported in the literature. This review article briefly describes the different wetting properties of the natural superhydrophobic lotus leaves and also provides a comprehensive state-of-the-art discussion on the extensive research carried out in the field of artificial superhydrophobic surfaces which are developed by mimicking the lotus leaf-like dual scale micro/nanostructure. This review article could be beneficial for both novice researchers in this area as well as the scientists who are currently working on non-wettable, superhydrophobic surfaces. PMID:24714190

Latthe, Sanjay S; Terashima, Chiaki; Nakata, Kazuya; Fujishima, Akira

2014-01-01

45

Fabrication of Superhydrophobic Surface on Aluminum Substrate  

NASA Astrophysics Data System (ADS)

The authors develop a simple and economic method to fabricate the superhydrophobic surface by means of electrochemical machining. The fabrication mechanism is based on the fact that the grain boundaries/dislocations are micro/nano-scale and more likely to be anodic dissolved than that of grain self, so the multi-scale micro/nano-structures surface can be generated by an applied electric field and the chemical solution. The relationship of processing quality, efficiency and conditions is studied in experiments in this paper. The results show that electrochemical processing can be used to fabricate dual-scale micro/nano-structures on aluminum surfaces, and further applying to generate the large size of superhydrophobic surface. The method is easier to control the reaction process than chemical etching meanwhile more economical than other techniques. After modified with low surface energy materials, the surface exhibits superhydrophobic property with water contact angle of 160° and tilt angle less than 5°.

Xu, W. J.; Dou, Q. L.; Wang, X. Y.; Sun, J.; Wang, L. J.

2011-01-01

46

Drag Reduction on a Patterned Superhydrophobic Surface  

Microsoft Academic Search

We present an experimental study of a low-Reynolds number shear flow between two surfaces, one of which has a regular grooved texture augmented with a superhydrophobic coating. The combination reduces the effective fluid-surface contact area, thereby appreciably decreasing the drag on the surface and effectively changing the macroscopic boundary condition on the surface from no slip to limited slip. We

Richard Truesdell; Andrea Mammoli; Peter Vorobieff; Frank van Swol; C. Jeffrey Brinker

2006-01-01

47

Superhydrophobic surfaces from hierarchically structured wrinkled polymers.  

PubMed

This work reports the creation of superhydrophobic wrinkled surfaces with hierarchical structures at both the nanoscale and microscale. A nanoscale structure with 500 nm line gratings was first fabricated on poly(hydroxyethyl methacrylate) films by nanoimprint lithography while a secondary micro-scale structure was created by spontaneous wrinkling. Compared with random wrinkles whose patterns show no specific orientation, the hierarchical wrinkles exhibit interesting orientation due to confinement effects of pre-imprinted line patterns. The hierarchically wrinkled surfaces have significantly higher water contact angles than random wrinkled surfaces, exhibiting superhydrophobicity with water contact angles higher than 160° and water sliding angle lower than 5°. The hierarchically structured wrinkled surfaces exhibit tunable wettability from hydrophobic to superhydrophobic and there is an observed transition from anisotropic to isotropic wetting behavior achievable by adjusting the initial film thickness. PMID:24131534

Li, Yinyong; Dai, Shuxi; John, Jacob; Carter, Kenneth R

2013-11-13

48

Microdroplet growth mechanism during water condensation on superhydrophobic surfaces.  

PubMed

By promoting dropwise condensation of water, nanostructured superhydrophobic coatings have the potential to dramatically increase the heat transfer rate during this phase change process. As a consequence, these coatings may be a facile method of enhancing the efficiency of power generation and water desalination systems. However, the microdroplet growth mechanism on surfaces which evince superhydrophobic characteristics during condensation is not well understood. In this work, the sub-10 ?m dynamics of droplet formation on nanostructured superhydrophobic surfaces are studied experimentally and theoretically. A quantitative model for droplet growth in the constant base (CB) area mode is developed. The model is validated using optimized environmental scanning electron microscopy (ESEM) imaging of microdroplet growth on a superhydrophobic surface consisting of immobilized alumina nanoparticles modified with a hydrophobic promoter. The optimized ESEM imaging procedure increases the image acquisition rate by a factor of 10-50 as compared to previous research. With the improved imaging temporal resolution, it is demonstrated that nucleating nanodroplets coalesce to create a wetted flat spot with a diameter of a few micrometers from which the microdroplet emerges in purely CB mode. After the droplet reaches a contact angle of 130-150°, its base diameter increases in a discrete steplike fashion. The droplet height does not change appreciably during this steplike base diameter increase, leading to a small decrease of the contact angle. Subsequently, the drop grows in CB mode until it again reaches the maximum contact angle and increases its base diameter in a steplike fashion. This microscopic stick-and-slip motion can occur up to four times prior to the droplet coalescence with neighboring drops. Lastly, the constant contact angle (CCA) and the CB growth models are used to show that modeling formation of a droplet with a 150° contact angle in the CCA mode rather than in the CB mode severely underpredicts both the drop formation time and the average heat transfer rate through the drop. PMID:22548441

Rykaczewski, Konrad

2012-05-22

49

Vapor stabilizing surfaces for superhydrophobicity  

Microsoft Academic Search

The success of rough substrates designed for superhydrophobicity relies crucially on the presence of air pockets in the roughness grooves. This air is supplied by the surrounding environment. However, if the rough substrates are used in enclosed configurations, such as in fluidic networks, the air pockets may not be sustained in the roughness grooves. In this work a design approach

Neelesh Patankar

2010-01-01

50

Effective slip on textured superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

We study fluid flow in the vicinity of textured and superhydrophobically coated surfaces with characteristic texture sizes on the order of 10 ?m. Both for droplets moving down an inclined surface and for an external flow near the surface (hydrofoil), there is evidence of appreciable drag reduction in the presence of surface texture combined with superhydrophobic coating. On textured inclined surfaces, the drops roll faster than on a coated untextured surface at the same angle. The highest drop velocities are achieved on surfaces with irregular textures with characteristic feature size ~8 ?m. Application of the same texture and coating to the surface of a hydrofoil in a water tunnel results in drag reduction on the order of 10% or higher. This behavior is explained by the reduction of the contact area between the surface and the fluid, which can be interpreted in terms of changing the macroscopic boundary condition to allow nonzero slip velocity.

Gogte, Salil; Vorobieff, Peter; Truesdell, Richard; Mammoli, Andrea; van Swol, Frank; Shah, Pratik; Brinker, C. Jeffrey

2005-05-01

51

Self-cleaning efficiency of artificial superhydrophobic surfaces.  

PubMed

The hierarchical structured surface of the lotus (Nelumbo nucifera, Gaertn.) leaf provides a model for the development of biomimetic self-cleaning surfaces. On these water-repellent surfaces, water droplets move easily at a low inclination of the leaf and collect dirt particles adhering to the leaf surface. Flat hydrophilic and hydrophobic, nanostructured, microstructured, and hierarchical structured superhydrophobic surfaces were fabricated, and a systematic study of wettability and adhesion properties was carried out. The influence of contact angle hysteresis on self-cleaning by water droplets was studied at different tilt angles (TA) of the specimen surfaces (3 degrees for Lotus wax, 10 degrees for n-hexatriacontane, as well as 45 degrees for both types of surfaces). At 3 degrees and 10 degrees TA, no surfaces were cleaned by moving water applied onto the surfaces with nearly zero kinetic energy, but most particles were removed from hierarchical structured surfaces, and a certain amount of particles were captured between the asperities of the micro- and hierarchical structured surfaces. After an increase of the TA to 45 degrees (larger than the tilt angles of all structured surfaces), as usually used for industrial self-cleaning tests, all nanostructured surfaces were cleaned by water droplets moving over the surfaces followed by hierarchical and microstructures. Droplets applied onto the surfaces with some pressure removed particles residues and led to self-cleaning by a combination of sliding and rolling droplets. Geometrical scale effects were responsible for superior performance of nanostructured surfaces. PMID:19239196

Bhushan, Bharat; Jung, Yong Chae; Koch, Kerstin

2009-03-01

52

Microtextured superhydrophobic surfaces: a thermodynamic analysis.  

PubMed

Superhydrophobic surfaces with a contact angle (CA) larger than 150 degrees have recently attracted great interest in both academic research and practical applications due to their water-repellent or self-cleaning properties. However, thermodynamic mechanisms responsible for the effects of various factors such as surface geometry and chemistry, liquids, and environmental sources have not been well understood. In this study, a pillar microtexture, which has been intensively investigated in experiments, is chosen as a typical example and thermodynamically analyzed in detail. To gain a comprehensive insight into superhydrophobic behavior, the roles of pillar height, width and spacing (or roughness and solid fraction), intrinsic CA, drop size, and vibrational energy are systematically investigated. Free energy (FE) and free energy barrier (FEB) are calculated using a simple and robust model. Based on the calculations of FE and FEB, various CAs, including apparent, equilibrium (stable), advancing and receding CAs, and contact angle hysteresis (CAH) can be determined. Especially, the design of practical superhydrophobic surfaces is emphasized in connection with the transition between noncomposite and composite states; a criterion for judging such transition is proposed. The theoretical results are consistent with the Wenzel's and the Cassie's equations for equilibrium CA values and experimental observations. Furthermore, based on these results and the proposed criterion, some general principles to achieve superhydrophobic performance are suggested. PMID:17331459

Li, W; Amirfazli, A

2007-04-28

53

Polymeric Fluid Flow Over Superhydrophobic Surfaces  

NASA Astrophysics Data System (ADS)

Superhydrophobic (SHP) surfaces are characterized by their exceptionally low surface energies and distinct surface roughnesses that create a vapor layer between the fluid and the surface. The reduced contact area at the interface can create a dewetted state resulting in slip, drag reduction, and improved flow of fluids. Most previous superhydrophobic studies have utilized simple liquids (e.g. water) in focusing on characterization of the quiescent interface and on drag reduction or slip modifications of fluid flow. As polymeric fluid flows have exhibited similar slip and drag reduction phenomena, this study attempts to utilize SHP surfaces to improve the flow behavior of more complex multi-component fluids, such as polymer solutions. By merging the research fields of SHP surfaces and polymer fluids, we investigate the potential to enhance slip and drag reduction effects as a result of surface interactions. Microfluidic channels, interfacial rheometry and goniometry are used to evaluate slip length and fluid flow.

Landherr, Lucas; Hudson, Steven; Migler, Kalman

2012-02-01

54

Manipulating Liquids on the Tunable Nanostructured Surfaces  

Microsoft Academic Search

Recently demonstrated electrically tunable nanostructured superhydrophobic surfaces provide a promising new way of manipulating liquids at both micro and macro scale. Dynamic control over the interaction of liquids with the solid substrate is of great interest to many research areas ranging from biology and chemistry to physics and nanotechnology. In this work the influence of the nano-scale topography on the

Tom Krupenkin

2005-01-01

55

Hydrodynamic friction of fakir-like superhydrophobic surfaces  

Microsoft Academic Search

A fluid droplet located on a super-hydrophobic surface makes contact with the surface only at small isolated regions, and is mostly in contact with the surrounding air. As a result, a fluid in motion near such a surface experiences very low friction, and super-hydrophobic surfaces display strong drag-reduction in the laminar regime. Here we consider theoretically a super-hydrophobic surface composed

Anthony M. J. Davis; Eric Lauga

2010-01-01

56

Creation of a Superhydrophobic Surface from an Amphiphilic Polymer  

Microsoft Academic Search

Superhydrophobic surfaces, with a water contact angle (CA) greater than 1508, have attracted great interest for both fundamental research and practical applications.(1) Conven- tionally, superhydrophobic surfaces are fabricated by com- bining appropriate surface roughness with low-surface-energy materials (hydrophobic materials, CA greater than 908).(2-18) It has been commonly acknowledged that it is impossible to obtain superhydrophobic surfaces from amphiphilic materi- als.

Lin Feng; Yanlin Song; Jin Zhai; Biqian Liu; Jian Xu; Lei Jiang; Daoben Zhu

2003-01-01

57

Facile fabrication of superhydrophobic surface with excellent mechanical abrasion and corrosion resistance on copper substrate by a novel method.  

PubMed

A novel method for controllable fabrication of a superhydrophobic surface with a water contact angle of 162 ± 1° and a sliding angle of 3 ± 0.5° on copper substrate is reported in this Research Article. The facile and low-cost fabrication process is composed from the electrodeposition in traditional Watts bath and the heat-treatment in the presence of (heptadecafluoro-1,1,2,2-tetradecyl) triethoxysilane (AC-FAS). The superhydrophobicity of the fabricated surface results from its pine-cone-like hierarchical micro-nanostructure and the assembly of low-surface-energy fluorinated components on it. The superhydrophobic surface exhibits high microhardness and excellent mechanical abrasion resistance because it maintains superhydrophobicity after mechanical abrasion against 800 grit SiC sandpaper for 1.0 m at the applied pressure of 4.80 kPa. Moreover, the superhydrophobic surface has good chemical stability in both acidic and alkaline environments. The potentiodynamic polarization and electrochemical impedance spectroscopy test shows that the as-prepared superhydrophobic surface has excellent corrosion resistance that can provide effective protection for the bare Cu substrate. In addition, the as-prepared superhydrophobic surface has self-cleaning ability. It is believed that the facile and low-cost method offer an effective strategy and promising industrial applications for fabricating superhydrophobic surfaces on various metallic materials. PMID:24796223

Su, Fenghua; Yao, Kai

2014-06-11

58

Single-step direct fabrication of pillar-on-pore hybrid nanostructures in anodizing aluminum for superior superhydrophobic efficiency.  

PubMed

Conventional electrochemical anodizing processes of metals such as aluminum typically produce planar and homogeneous nanopore structures. If hydrophobically treated, such 2D planar and interconnected pore structures typically result in lower contact angle and larger contact angle hysteresis than 3D disconnected pillar structures and, hence, exhibit inferior superhydrophobic efficiency. In this study, we demonstrate for the first time that the anodizing parameters can be engineered to design novel pillar-on-pore (POP) hybrid nanostructures directly in a simple one-step fabrication process so that superior surface superhydrophobicity can also be realized effectively from the electrochemical anodization process. On the basis of the characteristic of forming a self-ordered porous morphology in a hexagonal array, the modulation of anodizing voltage and duration enabled the formulation of the hybrid-type nanostructures having controlled pillar morphology on top of a porous layer in both mild and hard anodization modes. The hybrid nanostructures of the anodized metal oxide layer initially enhanced the surface hydrophilicity significantly (i.e., superhydrophilic). However, after a hydrophobic monolayer coating, such hybrid nanostructures then showed superior superhydrophobic nonwetting properties not attainable by the plain nanoporous surfaces produced by conventional anodization conditions. The well-regulated anodization process suggests that electrochemical anodizing can expand its usefulness and efficacy to render various metallic substrates with great superhydrophilicity or -hydrophobicity by directly realizing pillar-like structures on top of a self-ordered nanoporous array through a simple one-step fabrication procedure. PMID:22201335

Jeong, Chanyoung; Choi, Chang-Hwan

2012-02-01

59

From superhydrophobic to superhydrophilic surfaces tuned by surfactant solutions  

NASA Astrophysics Data System (ADS)

The wettability of hydrophobic surfaces is generally improved by surfactant solutions. The wetting behavior of superhydrophobic surfaces can be classified into two types, in terms of the variation of contact angle with surfactant concentration cs. Contact angle is controlled by surface tension for common linear surfactants and becomes independent of cs as cs>critical micelle concentration. Consequently, superhydrophobic surfaces remain in hydrophobic range, as reported. However, for branch-tailed surfactants such as sodium-bisethylhexylsulfosuccinate and didodecyldimethylammonium bromide, superhydrophobic surfaces can turn superhydrophilic by increasing cs owing to continuous reduction of solid-liquid interfacial tension. The superhydrophobicity is recoverable simply by water rinsing.

Chang, Feng-Ming; Sheng, Yu-Jane; Chen, Hui; Tsao, Heng-Kwong

2007-08-01

60

Dynamic air layer on textured superhydrophobic surfaces.  

PubMed

We provide an experimental demonstration that a novel macroscopic, dynamic continuous air layer or plastron can be sustained indefinitely on textured superhydrophobic surfaces in air-supersaturated water by a natural gas influx mechanism. This type of plastron is an intermediate state between Leidenfrost vapor layers on superheated surfaces and the equilibrium Cassie-Baxter wetting state on textured superhydrophobic surfaces. We show that such a plastron can be sustained on the surface of a centimeter-sized superhydrophobic sphere immersed in heated water and variations of its dynamic behavior with air saturation of the water can be regulated by rapid changes of the water temperature. The simple experimental setup allows for quantification of the air flux into the plastron and identification of the air transport model of the plastron growth. Both the observed growth dynamics of such plastrons and millimeter-sized air bubbles seeded on the hydrophilic surface under identical air-supersaturated solution conditions are consistent with the predictions of a well-mixed gas transport model. PMID:23919719

Vakarelski, Ivan U; Chan, Derek Y C; Marston, Jeremy O; Thoroddsen, Sigurdur T

2013-09-01

61

Drag Reduction on a Patterned Superhydrophobic Surface  

NASA Astrophysics Data System (ADS)

We present an experimental study of a low-Reynolds number shear flow between two surfaces, one of which has a regular grooved texture augmented with a superhydrophobic coating. The combination reduces the effective fluid-surface contact area, thereby appreciably decreasing the drag on the surface and effectively changing the macroscopic boundary condition on the surface from no slip to limited slip. We measure the force on the surface and the velocity field in the immediate vicinity on the surface (and thus the wall shear) simultaneously. The latter facilitates a direct assessment of the effective slip length associated with the drag reduction.

Truesdell, Richard; Mammoli, Andrea; Vorobieff, Peter; van Swol, Frank; Brinker, C. Jeffrey

2006-07-01

62

Drag reduction on a patterned superhydrophobic surface.  

PubMed

We present an experimental study of a low-Reynolds number shear flow between two surfaces, one of which has a regular grooved texture augmented with a superhydrophobic coating. The combination reduces the effective fluid-surface contact area, thereby appreciably decreasing the drag on the surface and effectively changing the macroscopic boundary condition on the surface from no slip to limited slip. We measure the force on the surface and the velocity field in the immediate vicinity on the surface (and thus the wall shear) simultaneously. The latter facilitates a direct assessment of the effective slip length associated with the drag reduction. PMID:16907578

Truesdell, Richard; Mammoli, Andrea; Vorobieff, Peter; van Swol, Frank; Brinker, C Jeffrey

2006-07-28

63

Superhydrophobics  

SciTech Connect

A water repellent developed by researchers at the Department of Energy's Oak Ridge National Laboratory outperforms nature at its best and could open a floodgate of commercial possibilities. The super-water repellent (superhydrophobic) material, developed by John Simpson, is easy to fabricate and uses inexpensive base materials. The process could lead to the creation of a new class of water repellant products, including windshields, eyewear, clothing, building materials, road surfaces, ship hulls and self-cleaning coatings. The list of likely applications is virtually endless.

Schaeffer, Daniel; Winter, Kyle

2013-05-02

64

Superhydrophobics  

ScienceCinema

A water repellent developed by researchers at the Department of Energy's Oak Ridge National Laboratory outperforms nature at its best and could open a floodgate of commercial possibilities. The super-water repellent (superhydrophobic) material, developed by John Simpson, is easy to fabricate and uses inexpensive base materials. The process could lead to the creation of a new class of water repellant products, including windshields, eyewear, clothing, building materials, road surfaces, ship hulls and self-cleaning coatings. The list of likely applications is virtually endless.

Schaeffer, Daniel; Winter, Kyle

2014-05-23

65

Superhydrophobics  

ScienceCinema

A water repellent developed by researchers at the Department of Energy's Oak Ridge National Laboratory outperforms nature at its best and could open a floodgate of commercial possibilities. The super-water repellent (superhydrophobic) material, developed by John Simpson, is easy to fabricate and uses inexpensive base materials. The process could lead to the creation of a new class of water repellant products, including windshields, eyewear, clothing, building materials, road surfaces, ship hulls and self-cleaning coatings. The list of likely applications is virtually endless.

66

Effect of electro-osmotic flow on energy conversion on superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

It has been suggested that superhydrophobic surfaces, due to the presence of a no-shear zone, can greatly enhance transport of surface charges, leading to a considerable increase in the streaming potential. This could find potential use in micro-energy harvesting devices. In this paper, we show using analytical and numerical methods, that when a streaming potential is generated in such superhydrophobic geometries, the reverse electro-osmotic flow and hence current generated by this, is significant. A decrease in streaming potential compared to what was earlier predicted is expected. We also show that, due to the electro-osmotic streaming-current, a saturation in both the power extracted and efficiency of energy conversion is achieved in such systems for large values of the free surface charge densities. Nevertheless, under realistic conditions, such microstructured devices with superhydrophobic surfaces have the potential to even reach energy conversion efficiencies only achieved in nanostructured devices so far.

Seshadri, Gowrishankar; Baier, Tobias

2013-04-01

67

Superhydrophobic nature of nanostructures on an indigenous Australian eucalyptus plant and its potential application  

PubMed Central

In this preliminary study, the morphology and nanostructured features formed by the epicuticular waxes of the mottlecah (Eucalyptus macrocarpa) leaf were investigated and quantified. The surface features formed by the waxes give the leaf remarkable wetting and self-cleaning properties that enhance the plant’s survival in an arid climate. This paper also provides experimental evidence of the self-assembly properties of the epicuticular waxes. Analysis of the water contact angle measurements gave a mean static contact angle of 162.00 ± 6.10 degrees, which clearly indicated that the mottlecah’s leaf surface was superhydrophobic. Detailed field emission scanning electron microscopy examination revealed that the surface was covered by bumps approximately 20 ?m in diameter and regularly spaced at a distance of around 26 ?m. The bumps are capped by nanotubules/pillars with an average diameter of 280 nm at the tips. Self-cleaning experiments indicated that the mottlecah’s leaf could be effectively cleaned by a fine spray of water droplets that rolled over the surface picking up contaminants. Field emission scanning electron microscopy investigation of extracted epicuticular waxes revealed that the waxes were capable of self-reassembly and formed features similar to those of the original leaf surface. Furthermore, also reported is a simple technique for surface treating one side of a planar surface to produce a superhydrophobic surface that can be used as a planar floatation platform for microdevices.

Poinern, Gerrard Eddy Jai; Le, Xuan Thi; Fawcett, Derek

2011-01-01

68

Drag reduction in turbulent flows over superhydrophobic surfaces  

Microsoft Academic Search

In this paper, we demonstrate that periodic, micropatterned superhydrophobic surfaces, previously noted for their ability to provide laminar flow drag reduction, are capable of reducing drag in the turbulent flow regime. Superhydrophobic surfaces contain micro- or nanoscale hydrophobic features which can support a shear-free air-water interface between peaks in the surface topology. Particle image velocimetry and pressure drop measurements were

Robert J. Daniello; Nicholas E. Waterhouse; Jonathan P. Rothstein

2009-01-01

69

DRAG REDUCTION IN TURBULENT FLOWS OVER MICROPATTERNED SUPERHYDROPHOBIC SURFACES  

Microsoft Academic Search

Periodic, micropatterned superhydrophobic surfaces, previously noted for their ability to provide drag reduction in the laminar flow regime, have been demonstrated capable of reducing drag in the turbulent flow regime as well. Superhydrophobic surfaces contain micro or nanoscale hydrophobic features which can support a shear-free air-water interface between peaks in the surface topology. Particle image velocimetry and pressure drop measurements

Robert J. Daniello

2009-01-01

70

Capillary origami and superhydrophobic membrane surfaces  

NASA Astrophysics Data System (ADS)

Capillary origami uses surface tension to fold and shape solid films and membranes into three-dimensional structures. It uses the fact that solid surfaces, no matter how hydrophobic, will tend to adhere to and wrap around the surface of a liquid. In this work, we report that a superhydrophobic coating can be created, which can completely suppress wrapping as a contacting water droplet evaporates. We also show that using a wetting azeotropic solution of allyl alcohol, which penetrates the surface features, can enhance liquid adhesion and create more powerful Capillary Origami. These findings create the possibility of selectively shaping membrane substrates.

Geraldi, N. R.; Ouali, F. F.; Morris, R. H.; McHale, G.; Newton, M. I.

2013-05-01

71

Thermodynamic analysis on wetting behavior of hierarchical structured superhydrophobic surfaces.  

PubMed

Superhydrophobicity of biological surfaces has recently been studied intensively with the aim to design artificial surfaces. It has been revealed that nearly all of the superhydrophobic surfaces consist of the intrinsic hierarchical structures. However, the role of such structures has not been completely understood. In this study, different scales of hierarchical structures have been thermodynamically analyzed using a 2-D model. In particular, the free energy (FE) and free energy barrier (FEB) for the composite wetting states are calculated, and the effects of relative pillar height (h(r)) and relative pillar width (a(r)) on contact angle (CA) and contact angle hysteresis (CAH) have been investigated in detail. The results show that if the geometrical parameter ratio is the same (e.g., a:b:h = 2:2:1), the equilibrium CA for the composite of the three-, dual-, and single- scale roughness structures is 159.8°, 151.1°, and 138.6°, respectively. Furthermore, the nano- to microstructures of such surfaces can split a large FEB into many small ones and hence can decrease FEB; in particular, a hierarchical geometrical structure can lead to a hierarchical "FEB structure" (e.g., for a dual-scale roughness geometrical structure, there is also a dual-scale FEB structure). This is especially important for a droplet to overcome the large FEBs to reach a stable superhydrophobic state, which can lead to an improved self-cleaning property. Moreover, for extremely small droplets, the secondary or third structure (i.e., submicrostructure or nanostructure) can play a dominant role in resisting the droplets into troughs, so that a composite state can be always thermodynamically favorable for such a hierarchical structured system. PMID:21495711

Liu, H H; Zhang, H Y; Li, W

2011-05-17

72

Microcones and nanograss: toward mechanically robust superhydrophobic surfaces.  

PubMed

We describe the generation of mechanically robust superhydrophobic surfaces, which carry a hierarchical roughness that is composed of silicon microcones and silicon nanograss. Both micro and nanostructures were fabricated using mask-free dry etching processes. The microcones were obtained utilizing a cryogenic deep reactive ion etching (DRIE) process run in the overpassivation regime. By varying process parameters, surfaces with different microcones geometries and densities were achieved. The nanograss was fabricated using a modified DRIE process with alternating etching and passivation cycles ('BOSCH process'). All surfaces were covered with a layer of a fluorinated film so that superhydrophobic structures resulted. Depending on microcone geometry and density, the advancing contact angle ranged between 170° and 180°, and roll-off angles of 10 ?L drops between 30' (0.5°) and 6° were observed. The samples were exposed to varying shear loads, and the changes in the morphology were recorded by using electron microscopy. The wetting angles of the mechanically challenged surfaces were recorded and correlated with the mechanical properties of the samples. PMID:24628022

Kondrashov, Vitaliy; Rühe, Jürgen

2014-04-22

73

A simple approach to fabricate stable superhydrophobic glass surfaces  

NASA Astrophysics Data System (ADS)

We present a facile method to fabricate superhydrophobic glass surface via one-step hydrothermal method and chemical modification. The etched glass surface shows the hierarchical textured morphology as well as the multiple scales of roughness and large numbers of nanorods and pores. The formation mechanism of the hierarchically structured surface is discussed in detail. After surface modification with vinyltriethoxysilane, the glass surface exhibits stable superhydrophobicity with a high contact angle of 155° and a low sliding angle of 5°. A water droplet of 10 ?L can bounce away from the surface when it vertically hit the superhydrophobic glass surface. Moreover, the contact angle of the superhydrophobic glass surface under different pH values and storage time are measured to study the stability of the superhydrophobic property.

Ji, Haiyan; Chen, Gang; Yang, Jin; Hu, Jie; Song, Haojie; Zhao, Yutao

2013-02-01

74

Plastron properties of a superhydrophobic surface  

NASA Astrophysics Data System (ADS)

Most insects and spiders drown when submerged during flooding or tidal inundation, but some are able to survive and others can remain submerged indefinitely without harm. Many achieve this by natural adaptations to their surface morphology to trap films of air, creating plastrons which fix the water-vapor interface and provide an incompressible oxygen-carbon dioxide exchange surface. Here the authors demonstrate how the surface of an extremely water-repellent foam mimics this mechanism of underwater respiration and allows direct extraction of oxygen from aerated water. The biomimetic principle demonstrated can be applied to a wide variety of man-made superhydrophobic materials.

Shirtcliffe, Neil J.; McHale, Glen; Newton, Michael I.; Perry, Carole C.; Pyatt, F. Brian

2006-09-01

75

Direct Numerical Simulations of Turbulent Flows over Superhydrophobic Surfaces  

Microsoft Academic Search

Direct numerical simulations are used to investigate the drag reducing performance of superhydrophobic surfaces in turbulent channel flow. Slip velocities, wall shear stresses, and Reynolds stresses are considered for a variety of superhydrophobic surface micro-feature geometry configurations at a friction Reynolds number of Retau = 180. For the largest micro-feature spacing of 90mum an average slip velocity over 75% of

Michael B. Martell; J. Blair Perot; Jonathan P. Rothstein

2008-01-01

76

Superhydrophobic Surface Based on a Coral-Like Hierarchical Structure of ZnO  

PubMed Central

Background Fabrication of superhydrophobic surfaces has attracted much interest in the past decade. The fabrication methods that have been studied are chemical vapour deposition, the sol-gel method, etching technique, electrochemical deposition, the layer-by-layer deposition, and so on. Simple and inexpensive methods for manufacturing environmentally stable superhydrophobic surfaces have also been proposed lately. However, work referring to the influence of special structures on the wettability, such as hierarchical ZnO nanostructures, is rare. Methodology This study presents a simple and reproducible method to fabricate a superhydrophobic surface with micro-scale roughness based on zinc oxide (ZnO) hierarchical structure, which is grown by the hydrothermal method with an alkaline aqueous solution. Coral-like structures of ZnO were fabricated on a glass substrate with a micro-scale roughness, while the antennas of the coral formed the nano-scale roughness. The fresh ZnO films exhibited excellent superhydrophilicity (the apparent contact angle for water droplet was about 0°), while the ability to be wet could be changed to superhydrophobicity after spin-coating Teflon (the apparent contact angle greater than 168°). The procedure reported here can be applied to substrates consisting of other materials and having various shapes. Results The new process is convenient and environmentally friendly compared to conventional methods. Furthermore, the hierarchical structure generates the extraordinary solid/gas/liquid three-phase contact interface, which is the essential characteristic for a superhydrophobic surface.

Wu, Jun; Xia, Jun; Lei, Wei; Wang, Baoping

2010-01-01

77

Manipulating Liquids on the Tunable Nanostructured Surfaces  

NASA Astrophysics Data System (ADS)

Recently demonstrated electrically tunable nanostructured superhydrophobic surfaces provide a promising new way of manipulating liquids at both micro and macro scale. Dynamic control over the interaction of liquids with the solid substrate is of great interest to many research areas ranging from biology and chemistry to physics and nanotechnology. In this work the influence of the nano-scale topography on the liquid-solid interaction is further investigated. The dependence of the superhydrophobic -- wetting transition on the topography of the nanostructured layer, its electrical properties, and its surface coating is discussed. The reversibility of this transition and its dependence on the geometry of the nano-size features are addressed. Several emerging applications of these surfaces, including lab-on-a-chip, chemical microreactor, and skin drag reduction are discussed.

Krupenkin, Tom

2005-03-01

78

Modeling superhydrophobic surfaces comprised of random roughness  

NASA Astrophysics Data System (ADS)

We model the performance of superhydrophobic surfaces comprised of randomly distributed roughness that resembles natural surfaces, or those produced via random deposition of hydrophobic particles. Such a fabrication method is far less expensive than ordered-microstructured fabrication. The present numerical simulations are aimed at improving our understanding of the drag reduction effect and the stability of the air--water interface in terms of the microstructure parameters. For comparison and validation, we have also simulated the flow over superhydrophobic surfaces made up of aligned or staggered microposts for channel flows as well as streamwise or spanwise ridge configurations for pipe flows. The present results are compared with other theoretical and experimental studies. The numerical simulations indicate that the random distribution of surface roughness has a favorable effect on drag reduction, as long as the gas fraction is kept the same. The stability of the meniscus, however, is strongly influenced by the average spacing between the roughness peaks, which needs to be carefully examined before a surface can be recommended for fabrication.

Samaha, M. A.; Vahedi Tafreshi, H.; Gad-El-Hak, M.

2011-11-01

79

Superhydrophobic surfaces fabricated from nano- and microstructured cellulose stearoyl esters.  

PubMed

Robust, superhydrophobic and self-cleaning films were fabricated using nano- or microstructured cellulose fatty acid esters, which were prepared via nanoprecipitation. The superhydrophobic films could be coated on diverse surfaces with non-uniform shapes by distinct coating techniques. PMID:23609473

Geissler, Andreas; Chen, Longquan; Zhang, Kai; Bonaccurso, Elmar; Biesalski, Markus

2013-05-28

80

Superhydrophobic surfaces: From natural to biomimetic to functional  

Microsoft Academic Search

Nature is the creation of aesthetic functional systems, in which many natural materials have vagarious structures. Inspired from nature, such as lotus leaf, butterfly’ wings, showing excellent superhydrophobicity, scientists have recently fabricated a lot of biomimetic superhydrophobic surfaces by virtue of various smart and easy routes. Whilst, many examples, such as lotus effect, clearly tell us that biomimicry is dissimilar

Zhiguang Guo; Weimin Liu; Bao-Lian Su

2011-01-01

81

Enhanced super-hydrophobic and switching behavior of ZnO nanostructured surfaces prepared by simple solution--immersion successive ionic layer adsorption and reaction process.  

PubMed

A simple and cost-effective successive ionic layer adsorption and reaction (SILAR) method was adopted to fabricate hydrophobic ZnO nanostructured surfaces on transparent indium-tin oxide (ITO), glass and polyethylene terephthalate (PET) substrates. ZnO films deposited on different substrates show hierarchical structures like spindle, flower and spherical shape with diameters ranging from 30 to 300 nm. The photo-induced switching behaviors of ZnO film surfaces between hydrophobic and hydrophilic states were examined by water contact angle and X-ray photoelectron spectroscopy (XPS) analysis. ZnO nanostructured films had contact angles of ~140° and 160°±2 on glass and PET substrates, respectively, exhibiting hydrophobic behavior without any surface modification or treatment. Upon exposure to ultraviolet (UV) illumination, the films showed hydrophilic behavior (contact angle: 15°±2), which upon low thermal stimuli revert back to its original hydrophobic nature. Such reversible and repeatable switching behaviors were observed upon cyclical exposure to ultraviolet radiation. These biomimetic ZnO surfaces exhibit good anti-reflective properties with lower reflectance of 9% for PET substrates. Thus, the present work is significant in terms of its potential application in switching devices, solar coatings and self-cleaning smart windows. PMID:21831394

Suresh Kumar, P; Sundaramurthy, J; Mangalaraj, D; Nataraj, D; Rajarathnam, D; Srinivasan, M P

2011-11-01

82

Drying of colloidal droplets on superhydrophobic surfaces.  

PubMed

Recent research on the flow patterns during the drying of droplets of solutions or suspensions has revealed a characteristic flow of dissolved or suspended material to the droplet periphery to produce the 'coffee ring' phenomenon. This effect was used to make ceramic well-plates by spontaneous manufacturing. Here we demonstrate that when a colloidal droplet dries on a superhydrophobic surface, the effect is rather different. Evaporation from the region adjacent to the three phase line becomes so restricted that the interior flows, and hence the final destination of particles, changes and the characteristic bowl-shape becomes inverted. PMID:20692671

Chen, Lifeng; Evans, Julian R G

2010-11-01

83

Superhydrophobic ceramic coatings enabled by phase-separated nanostructured composite TiO2-Cu2O thin films.  

PubMed

By exploiting phase-separation in oxide materials, we present a simple and potentially low-cost approach to create exceptional superhydrophobicity in thin-film based coatings. By selecting the TiO2-Cu2O system and depositing through magnetron sputtering onto single crystal and metal templates, we demonstrate growth of nanostructured, chemically phase-segregated composite films. These coatings, after appropriate chemical surface modification, demonstrate a robust, non-wetting Cassie-Baxter state and yield an exceptional superhydrophobic performance, with water droplet contact angles reaching to ?172° and sliding angles <1°. As an added benefit, despite the photo-active nature of TiO2, the chemically coated composite film surfaces display UV stability and retain superhydrophobic attributes even after exposure to UV (275 nm) radiation for an extended period of time. The present approach could benefit a variety of outdoor applications of superhydrophobic coatings, especially for those where exposure to extreme atmospheric conditions is required. PMID:24857856

Aytug, Tolga; Bogorin, Daniela F; Paranthaman, Parans M; Mathis, John E; Simpson, John T; Christen, David K

2014-06-20

84

Fabrication of superhydrophobic surfaces on engineering material surfaces with stearic acid  

Microsoft Academic Search

Via a simple wet chemical etching followed by stearic acid modification, the presence of synergistic binary structures at micro- and nanometer scales and stearic acid bestows superhydrophobic property on steel and aluminum alloy surfaces. The as-prepared surfaces show superhydrophobic not only for pure water but also for corrosive liquids such as acid, basic and salt solutions. The stable superhydrophobicity of

Qi Wang; Bingwu Zhang; Mengnan Qu; Junyan Zhang; Deyan He

2008-01-01

85

Superhydrophobic and superhydrophilic plant surfaces: an inspiration for biomimetic materials.  

PubMed

The diversity of plant surface structures, evolved over 460 million years, has led to a large variety of highly adapted functional structures. The plant cuticle provides structural and chemical modifications for surface wetting, ranging from superhydrophilic to superhydrophobic. In this paper, the structural basics of superhydrophobic and superhydrophilic plant surfaces and their biological functions are introduced. Wetting in plants is influenced by the sculptures of the cells and by the fine structure of the surfaces, such as folding of the cuticle, or by epicuticular waxes. Hierarchical structures in plant surfaces are shown and further types of plant surface structuring leading to superhydrophobicity and superhydrophilicity are presented. The existing and potential uses of superhydrophobic and superhydrophilic surfaces for self-cleaning, drag reduction during moving in water, capillary liquid transport and other biomimetic materials are shown. PMID:19324720

Koch, Kerstin; Barthlott, Wilhelm

2009-04-28

86

Superhydrophobic graphene-based materials: surface construction and functional applications.  

PubMed

Many naturally occurring surfaces have superhydrophobicity that fulfils their functional demands, which has inspired considerable interest to develop similar artificial superhydrophobic surfaces with a variety of functionalities. Graphene is an ideal candidate for functional superhydrophobic surfaces due to its exceptional physicochemical properties. The recent advances in this emerging field are summarized, including the wetting behavior of water on graphene and the formation of crumpling/nanoparticle/foam-induced hierarchical structures, with emphasis on fundamental understanding for related processes. The potential applications in energy, environmental remediation, and thermal management are also discussed. PMID:24089354

Chen, Zhongxin; Dong, Lei; Yang, Dong; Lu, Hongbin

2013-10-01

87

Fabrication of a superhydrophobic surface on a wood substrate  

NASA Astrophysics Data System (ADS)

A layer of lamellar superhydrophobic coating was fabricated on a wood surface through a wet chemical process. The superhydrophobic property of the wood surface was measured by contact angle (CA) measurements. The microstructure and chemical composition of the superhydrophobic coating were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). An analytical characterization revealed that the microscale roughness of the lamellar particles was uniformly distributed on the wood surface and that a zinc stearate monolayer (with the hydrophobic groups oriented outward) formed on the ZnO surface as the result of the reaction between stearic acid and ZnO. This process transformed the wood surface from hydrophilic to superhydrophobic: the water contact angle of the surface was 151°, and the sliding angle was less than 5°.

Wang, Shuliang; Shi, Junyou; Liu, Changyu; Xie, Cheng; Wang, Chengyu

2011-09-01

88

Fabrication of the micro/nano-structure superhydrophobic surface on aluminum alloy by sulfuric acid anodizing and polypropylene coating.  

PubMed

The preparation of the superhydrophobic surface on aluminum alloy by anodizing and polypropylene (PP) coating was reported. Both the different anodizing process and different PP coatings of aluminum alloy were investigated. The effects of different anodizing conditions, such as electrolyte concentration, anodization time and current on the superhydrophobic surface were discussed. By PP coating after anodizing, a good superhydrophobic surface was facilely fabricated. The optimum conditions for anodizing were determined by orthogonal experiments. After the aluminium-alloy was grinded with 600# sandpaper, pretreated by 73 g/L hydrochloric acid solution at 1 min, when the concentration of sulfuric acid was 180 g/L, the concentration of oxalic acid was 5 g/L, the concentration of potassium dichromate was 10 g/L, the concentration of chloride sodium was 50 g/L and 63 g/L of glycerol, anodization time was 20 min, and anodization current was 1.2 A/dm2, anodization temperature was 30-35 degrees C, the best micro-nanostructure aluminum alloy films was obtained. On the other hand, the PP with different concentrations was used to the PP with different concentrations was used to coat the aluminum alloy surface after anodizing. The results showed that the best superhydrophobicity was achieved by coating PP, and the duration of the superhydrophobic surface was improved by modifying the coat the aluminum alloy surface after anodizing. The results showed that the best superhydrophobicity was surface with high concentration PP. The morphologies of micro/nano-structure superhydrophobic surface were further confirmed by scanning electron microscope (SEM). The material of PP with the low surface free energy combined with the micro/nano-structures of the surface resulted in the superhydrophobicity of the aluminum alloy surface. PMID:23755692

Wu, Ruomei; Liang, Shuquan; Liu, Jun; Pan, Anqiang; Yu, Y; Tang, Yan

2013-03-01

89

Electro-osmosis on anisotropic superhydrophobic surfaces.  

PubMed

We give a general theoretical description of electro-osmotic flow at striped superhydrophobic surfaces in a thin double layer limit, and derive a relation between the electro-osmotic mobility and hydrodynamic slip-length tensors. Our analysis demonstrates that electro-osmotic flow shows a very rich behavior controlled by slip length and charge at the gas sectors. In the case of an uncharged liquid-gas interface, the flow is the same or inhibited relative to the flow in a homogeneous channel with a zero interfacial slip. By contrast, it can be amplified by several orders of magnitude provided slip regions are uniformly charged. When gas and solid regions are oppositely charged, we predict a flow reversal, which suggests the possibility of a huge electro-osmotic slip even for electroneutral surfaces. On the basis of these observations we suggest strategies for practical microfluidic devices. PMID:21929273

Belyaev, Aleksey V; Vinogradova, Olga I

2011-08-26

90

Electro-osmosis on Anisotropic Superhydrophobic Surfaces  

NASA Astrophysics Data System (ADS)

We give a general theoretical description of electro-osmotic flow at striped superhydrophobic surfaces in a thin double layer limit, and derive a relation between the electro-osmotic mobility and hydrodynamic slip-length tensors. Our analysis demonstrates that electro-osmotic flow shows a very rich behavior controlled by slip length and charge at the gas sectors. In the case of an uncharged liquid-gas interface, the flow is the same or inhibited relative to the flow in a homogeneous channel with a zero interfacial slip. By contrast, it can be amplified by several orders of magnitude provided slip regions are uniformly charged. When gas and solid regions are oppositely charged, we predict a flow reversal, which suggests the possibility of a huge electro-osmotic slip even for electroneutral surfaces. On the basis of these observations we suggest strategies for practical microfluidic devices.

Belyaev, Aleksey V.; Vinogradova, Olga I.

2011-08-01

91

A novel fabrication of superhydrophobic surfaces for universal applicability  

NASA Astrophysics Data System (ADS)

The present work reports a novel and facile approach to fabricate stable superhydrophobic surfaces for universal applicability in practice. Poly(furfuryl alcohol)/copper composite coatings were prepared on substrates via a brush-painting method; after being immersed in a stearic acid solution, the superhydrophobic surfaces were obtained due to the formation of copper stearate on the substrates. These products were characterized by field-emission scanning electron microscopy, Fourier transform infrared spectrometry, X-ray powder diffraction and the X-ray photoelectron spectrum. Results demonstrate that the superhydrophobic surfaces formed originally on copper substrates can also be generated on other substrates without the copper element. Furthermore, this work will provide a simple and universal method to create large-scale superhydrophobic surfaces on various substrates.

Chen, Su-Wen; Guo, Bo-Long; Wu, Wang-Suo

2011-12-01

92

Design and fabrication of a superhydrophobic glass surface with micro-network of nanopillars.  

PubMed

The wetting property of a superhydrophobic glass surface with a micro-network of nanopillars fabricated from colloidal lithography and plasma etching is investigated in this paper. The micro-network distribution of nanospheres can be modulated by diluting the nanosphere concentration and controlling the spin rate. The micro-network of nanospheres spun on the glass surface serves as a mask for nanopillars during the plasma etching process. After the fabrication, the nano-structured surface is treated with fluoroalkylsilane self-assembled monolayers to obtain superhydrophobicity. Among several spin rates, the minimum colloidal network area density from a 100 nm polystyrene nanosphere solution diluted to 0.026% was found at a spin rate of 4000 rpm. The sample with the lowest network area density shows a good quality of superhydrophobicity, having the highest water contact angle and the lowest sliding angle among samples with other network area densities. In particular, samples with a micro-network of pillars also showed mechanical robustness against finger rubbing. To assess the superhydrophobic behavior in-depth, a size-dependent contact angle equation is proposed for use with a high contact angle (>135°) and with a Bo (Bond number) ? 1. Furmidge's sliding angle equation is also modified; it is derived considering a static contact angle to simplify the prediction of the sliding angle. The contact and sliding angle measurements from samples with a micro-network of nanopillars show good agreement with the proposed equations. PMID:21565358

Park, Joonsik; Lim, Hyuneui; Kim, Wandoo; Ko, Jong Soo

2011-08-01

93

Superhydrophobic nanostructured coating for anti-icing applications  

NASA Astrophysics Data System (ADS)

In this work, anti-icing superhydrophobic (SHP) tungsten nanorod (WNR) surfaces were fabricated. The fabrication of WNR surfaces as rough surfaces was carried out using the Glancing Angle Deposition (GLAD) technique. Using the magnetron-sputtering deposition method, the deposition Ar pressure, Ar flow rate, and substrate tilting angle were varied to fabricate WNRs with different surface morphologies and porosities. The surface energy of the WNR films was lowered by coating them with a nano-layer (10-15nm) of Teflon AF2400 using an effusion cell. Static contact angle (SCA) measurements of the sessile water droplet gently dispensed on surfaces were used to characterize the static wetting properties of those surfaces. After surface treatment of the fabricated WNRs with different spacing, heights, and nanorod natural pyramidal tips, surfaces with tunable hydrophobic properties with SCAs ranging from 120° to 160° were obtained. The well-known classical Wenzel and Cassie models were used to predict the observed CAs. The proposed geometrically modified Cassie model showed consistent agreement with the observed high SCAs. The dynamic study of the wetting properties of the fabricated surfaces was carried out using water droplet evaporation on the surfaces. The kinetics of water droplet evaporation showed a significant influence of surface wetting properties, morphology, and porosity on the three modes of evaporation. Moreover, the contact angle hysteresis (CAH) of the surfaces was measured by the dynamic approach of adding/withdrawing water to/from the surfaces, respectively. The SHP-WNR films maintained a relatively low CAH of 30 degrees. The CAHs obtained by both kinetics of evaporation and the dynamic approach were consistent. Finally, the ability of the supercooled SHP-WNRs, kept at a temperature of -10 °C, to repel supercooled water droplets with a subzero temperature as low as -10 °C was tested. The SHP-WNRs' surfaces were able to repel supercooled water droplets released from a height of 15 mm with an impact velocity of 0.54 m/s. Calculations of energy dissipation in the course of bouncing due to the water droplets' physical properties and the surface wetting properties were performed. In addition to surface CAH and water droplet vibration, a significant energy loss due to an increase in supercooled water droplet viscosity as a function of its temperature was observed.

Khedir, Khedir R.

94

Nano-engineering of superhydrophobic aluminum surfaces for anti-corrosion  

NASA Astrophysics Data System (ADS)

Metal corrosion is a serious problem, both economically and operationally, for engineering systems such as aircraft, automobiles, pipelines, and naval vessels. In such engineering systems, aluminum is one of the primary materials of construction due to its light weight compared to steel and good general corrosion resistance. However, because of aluminum's relatively lower resistance to corrosion in salt water environments, protective measures such as thick coatings, paints, or cathodic protection must be used for satisfactory service life. Unfortunately, such anti-corrosion methods can create other concerns, such as environmental contamination, protection durability, and negative impact on hydrodynamic efficiency. Recently, a novel approach to preventing metal corrosion has emerged, using superhydrophobic surfaces. Superhydrophobic surfaces create a composite interface to liquid by retaining air within the surface structures, thus minimizing the direct contact of the liquid environment to the metal surface. The result is a highly non-wetting and anti-adherent surface that can offer other benefits such as biofouling resistance and hydrodynamic low friction. Prior research with superhydrophobic surfaces for corrosion applications was based on irregular surface roughening and/or chemical coatings, which resulted in random surface features, mostly on the micrometer scale. Such microscale surface roughness with poor controllability of structural dimensions and shapes has been a critical limitation to deeper understanding of the anti-corrosive effectiveness and optimized application of this approach. The research reported here provides a novel approach to producing controlled superhydrophobic nanostructures on aluminum that allows a systematic investigation of the superhydrophobic surface parameters on the corrosion resistance and hence can provide a route to optimization of the surface. Electrochemical anodization is used to controllably modulate the oxide layer thickness and pore dimensions at the aluminum surface. The results show that thicker oxide layers with larger pore sizes allow the nanostructured surface to retain more gas (air) and hence provide a more effective barrier to corrosion. The anodizing techniques are further advanced to design and produce hierarchical three-dimensional nanostructures for better retention of the gaseous barrier layer at the surface.

Jeong, Chanyoung

95

Femtosecond laser irradiation of metallic surfaces: effects of laser parameters on superhydrophobicity  

NASA Astrophysics Data System (ADS)

This work studies in detail the effect of femtosecond laser irradiation process parameters (fluence and scanning speed) on the hydrophobicity of the resulting micro/nano-patterned morphologies on stainless steel. Depending on the laser parameters, four distinctly different nano-patterns were produced, namely nano-rippled, parabolic-pillared, elongated sinusoidal-pillared and triple roughness nano-structures. All of the produced structures were classified according to a newly defined parameter, the laser intensity factor (LIF); by increasing the LIF, the ablation rate and periodicity of the asperities increase. In order to decrease the surface energy, all of the surfaces were coated with a fluoroalkylsilane agent. Analysis of the wettability revealed enhanced superhydrophobicity for most of these structures, particularly those possessing the triple roughness pattern that also exhibited low contact angle hysteresis. The high permanent superhydrophobicity of this pattern is due to the special micro/nano-structure of the surface that facilitates the Cassie-Baxter state.

Moradi, Sona; Kamal, Saeid; Englezos, Peter; Hatzikiriakos, Savvas G.

2013-10-01

96

Wetting of soap bubbles on hydrophilic, hydrophobic, and superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

Wetting of sessile bubbles on various wetting surfaces (solid and liquid) has been studied. A model is presented for the apparent contact angle of a sessile bubble based on a modified Young's equation--the experimental results agree with the model. Wetting a hydrophilic surface results in a bubble contact angle of 90° whereas using a superhydrophobic surface one observes 134°. For hydrophilic surfaces, the bubble angle diminishes with bubble radius whereas on a superhydrophobic surface, the bubble angle increases. The size of the plateau borders governs the bubble contact angle, depending on the wetting of the surface.

Arscott, Steve

2013-06-01

97

Transformation of a simple plastic into a superhydrophobic surface.  

PubMed

Superhydrophobic surfaces are generally made by controlling the surface chemistry and surface roughness of various expensive materials, which are then applied by means of complex time-consuming processes. We describe a simple and inexpensive method for forming a superhydrophobic coating using polypropylene (a simple polymer) and a suitable selection of solvents and temperature to control the surface roughness. The resulting gel-like porous coating has a water contact angle of 160 degrees. The method can be applied to a variety of surfaces as long as the solvent mixture does not dissolve the underlying material. PMID:12610300

Erbil, H Yildirim; Demirel, A Levent; Avci, Yonca; Mert, Olcay

2003-02-28

98

Fabrication of superhydrophobic polyurethane/organoclay nano-structured composites from cyclomethicone-in-water emulsions  

NASA Astrophysics Data System (ADS)

Nano-structured polyurethane/organoclay composite films were fabricated by dispersing moisture-curable polyurethanes and fatty amine/amino-silane surface modified montmorillonite clay (organoclay) in cyclomethicone-in-water emulsions. Cyclomethicone Pickering emulsions were made by emulsifying decamethylcyclopentasiloxane (D 5), dodecamethylcyclohexasiloxane (D 6) and aminofunctional siloxane polymers with water using montmorillonite particles as emulsion stabilizers. Polyurethane and organoclay dispersed emulsions were spray coated on aluminum surfaces. Upon thermosetting, water repellent self-cleaning coatings were obtained with measured static water contact angles exceeding 155° and low contact angle hysteresis (<8°). Electron microscopy images of the coating surfaces revealed formation of self-similar hierarchical micro- and nano-scale surface structures. The surface morphology and the coating adhesion strength to aluminum substrates were found to be sensitive to the relative amounts of dispersed polyurethane and organoclay in the emulsions. The degree of superhydrophobicity was analyzed using static water contact angles as well as contact angle hysteresis measurements. Due to biocompatibility of cyclomethicones and polyurethane, developed coatings can be considered for specific bio-medical applications.

Bayer, I. S.; Steele, A.; Martorana, P. J.; Loth, E.

2010-11-01

99

Drag Reduction on Micro-Structured Super-hydrophobic Surface  

Microsoft Academic Search

This paper presents numerical and experimental investigation of drag reduction on the micro-engineered surface, which is inspired by nature. Computational simulation has been performed to examine the flow characteristics on both smooth and rough surfaces, and an experimental investigation is conducted by using artificial super-hydrophobic surface fabricated by MEMS fabrication technique. The artificial surface is made of silicon wafer, where

Doyoung Byun; Saputra; Hoon Cheol Park

2006-01-01

100

Modeling of the process of superhydrophobic surface formation  

NASA Astrophysics Data System (ADS)

Thin composite films of nanoparticles formed by Layer-by-Layer method on a glass substrate from colloid solutions of titanium oxide, zinc oxide or silicon oxide are studied. Atomic Force microscopy, Scanning Electronic Microscopy and contact angle measurements were used for investigation of the surface properties of coatings. Bicomponent TiO2/SiO2 and ZnO/SiO2 films modified by octadecyltrichlorosilane are found to acquire superhydrophobic properties depending on the surface coatings roughness. To simulate superhydrophobic surface formation process, roughness coefficient was calculated by equation of Ventelia-Deragina. Correlation of the effect of film roughness on surface wettability depending on the number of the layers and the size of nanoparticles were demonstrated. The method developed for producing of superhydrophobic materials and can be used for production of self-cleaning surfaces.

Lisovskaya, Galina B.; Chizhik, Sergei A.; Salamianski, Alexander E.; Agabekov, Vladimir E.; Zhavnerko, Gennady K.

2008-07-01

101

Drag reduction in Stokes flows over spheres with nanostructured superhydrophilic surfaces  

Microsoft Academic Search

Nanostructured surfaces offer opportunities to modify flow induced drag on solid objects. Measurements of the terminal velocity reveal that the drag associated with laminar Stokes flows can be reduced for spheres with nanostructured superhydrophilic as well as superhydrophobic surfaces. Numerical simulations suggest that the formation of recirculating or nearly stagnant flow zones leads to significant reduction in the friction drag.

Chan Byon; Youngsuk Nam; Sung Jin Kim; Y. Sungtaek Ju

2010-01-01

102

A simple immersion approach for fabricating superhydrophobic Mg alloy surfaces  

NASA Astrophysics Data System (ADS)

A simple immersion approach for fabricating superhydrophobic Mg alloy surfaces is present here. Micro/nanometer-scale rough structures composed of micrometer-scale island-like rough structures and nanometer-scale sheets are generated on the Mg alloy surfaces after immersion in the aqueous CuSO4 solution. After ultrasonic cleaning, the micro/nanometer-scale rough structures are disappeared, whereas the lump-like rough structures appear on the Mg alloy surfaces. After modification with stearic acid, the as-prepared micro/nanometer-scale rough structures and the micrometer-scale lump-like rough structures all show superhydrophobicity. The contact angles of the water droplet on the aforementioned two structures are respectively 151.3° and 161.8°. The rolling angles are respectively 3° and 13°. The results indicate that the cooperation of suitable rough structures and stearic acid modification is responsible for the obtained superhydrophobicity on the Mg alloy surfaces.

Song, Jinlong; Lu, Yao; Huang, Shuai; Liu, Xin; Wu, Libo; Xu, Wenji

2013-02-01

103

Superhydrophobic bio-fibre surfaces via tailored grafting architecture.  

PubMed

Superhydrophobic bio-fibre surfaces with a micro-nano-binary surface structure have been achieved via the surface-confined grafting of glycidyl methacrylate, using a branched "graft-on-graft" architecture, followed by post-functionalisation to obtain fluorinated brushes. PMID:17047775

Nyström, Daniel; Lindqvist, Josefina; Ostmark, Emma; Hult, Anders; Malmström, Eva

2006-09-14

104

A novel preparation of polystyrene film with a superhydrophobic surface using a template method  

NASA Astrophysics Data System (ADS)

Inspired by the self-cleaning superhydrophobic taro leaf, a polystyrene (PS) film with superhydrophobic surface was obtained using a natural taro leaf as template. The water contact angle and the sliding angle of the superhydrophobic PS surface were 158° ± 1.6° and 3°, respectively. The PS surface was still superhydrophobic when contacting with black ink, fresh blood and even viscous glue water. SEM shows that the surface structure comprises many uniform papillae with the diameters ranging from 10 to 15 µm, which is similar to the surface structure of natural taro leaf. Such a special surface morphology may result in the superhydrophobic property.

Yuan, Zhiqing; Chen, Hong; Tang, Jianxin; Gong, Huifang; Liu, Yuejun; Wang, Zhengxiang; Shi, Pu; Zhang, Jide; Chen, Xin

2007-06-01

105

Patterned superhydrophobic surface based on Pd-based metallic glass  

NASA Astrophysics Data System (ADS)

Without any modification or post-treatment, superhydrophobic surfaces with good stability were fabricated by hot-embossing honeycomb patterns on Pd40Cu30Ni10P20 bulk metallic glass (BMG). The water contact angle reaches above 150° when the pitch between adjacent cells is larger than the critical size of 115.5 ?m. The wetting behavior on the patterned BMG can be well rationalized in terms of the modified Cassie-Baxter theory [A. B. D. Cassie and S. Baxter, Trans. Faraday Soc. 40, 546 (1944)] by considering surface energy gradient. The achievement of the superhydrophobicity on BMG surface opens a window for the functional applications of metallic glasses.

Xia, Ting; Li, Ning; Wu, Yue; Liu, Lin

2012-08-01

106

Fabrication of superhydrophobic surfaces of n-hexatriacontane.  

PubMed

Superhydrophobic surfaces of n-hexatriacontane were fabricated in a single-step process. The low surface energy of n-hexatriacontane together with the randomly distributed micro- and nanoscale roughness features guarantees very large contact angles and a small roll-off angle for water drops. The advantage of n-hexatriacontane superhydrophobic surfaces is their stability in the sense that they are impervious to chemical reactions and retain their wetting characteristics over a long period of time, as confirmed by XPS analysis and contact angle measurements. PMID:16768473

Tavana, H; Amirfazli, A; Neumann, A W

2006-06-20

107

Direct Numerical Simulations of Turbulent Flows over Superhydrophobic Surfaces  

NASA Astrophysics Data System (ADS)

Direct numerical simulations are used to investigate the drag reducing performance of superhydrophobic surfaces in turbulent channel flow. Slip velocities, wall shear stresses, and Reynolds stresses are considered for a variety of superhydrophobic surface micro-feature geometry configurations at a friction Reynolds number of Re? = 180. For the largest micro-feature spacing of 90?m an average slip velocity over 75% of the bulk velocity is obtained, and the wall shear stress reduction is nearly found to be nearly 40%. The simulation results suggest that the mean velocity profile near the superhydrophobic wall continues to scale with the wall shear stress, but is offset by a slip velocity that increases with increasing micro-feature spacing.

Martell, Michael B.; Blair Perot, J.; Rothstein, Jonathan P.

2008-11-01

108

Collapse and Reversibility of the Superhydrophobic State on Nanotextured Surfaces  

NASA Astrophysics Data System (ADS)

Superhydrophobic coatings repel liquids by trapping air inside microscopic surface textures. However, the resulting composite interface is prone to collapse under external pressure. Nanometer-size textures should facilitate more resilient coatings owing to geometry and confinement effects at the nanoscale. Here, we use in situ x-ray diffraction to study the collapse of the superhydrophobic state in arrays of ?20 nm-wide silicon textures with cylindrical, conical, and linear features defined by block-copolymer self-assembly and plasma etching. We reveal that the superhydrophobic state vanishes above critical pressures which depend on texture shape and size. This phenomenon is irreversible for all but the conical surface textures which exhibit a spontaneous, partial reappearance of the trapped gas phase upon liquid depressurization. This process is influenced by the kinetics of gas-liquid exchange.

Checco, Antonio; Ocko, Benjamin M.; Rahman, Atikur; Black, Charles T.; Tasinkevych, Mykola; Giacomello, Alberto; Dietrich, Siegfried

2014-05-01

109

Bacterial growth on a superhydrophobic surface containing silver nanoparticles  

NASA Astrophysics Data System (ADS)

The antibacterial effect of silver can be exploited in the food and beverage industry and medicinal applications to reduce biofouling of surfaces. Very small amount of silver ions are enough to destructively affect the metabolism of bacteria. Moreover, superhydrophobic properties could reduce bacterial adhesion to the surface. In this study we fabricated superhydrophobic surfaces that contained nanosized silver particles. The superhydrophobic surfaces were manufactured onto stainless steel as combination of ceramic nanotopography and hydrophobication by fluorosilane. Silver nanoparticles were precipitated onto the surface by a chemical method. The dissolution of silver from the surface was tested in an aqueous environment under pH values of 1, 3, 5, 7, 9, 11 and 13. The pH value was adjusted with nitric acid and ammonia. It was found that dissolution rate of silver increased as the pH of the solution altered from the pH of de-ionized water to lower and higher pH values but dissolution occurred also in de-ionized water. The antimicrobial potential of this coating was investigated using bacterial strains isolated from the brewery equipment surfaces. The results showed that the number of bacteria adhering onto steel surface was significantly reduced (88%) on the superhydrophobic silver containing coating.

Heinonen, S.; Nikkanen, J.-P.; Laakso, J.; Raulio, M.; Priha, O.; Levänen, E.

2013-12-01

110

On Drag Reduction in Turbulent Channel Flow over Superhydrophobic Surfaces  

Microsoft Academic Search

Recent simulations and experiments suggest that flow over superhydrophobic surfaces may exhibit significantly reduced drag in both laminar [8, 9] and turbulent [7, 10] regimes due to the existence of a thin layer of gas on the surface which allows a slip velocity. The current paper explores this using estimates of drag based on high-resolution PIV in a low-Reynolds number

C. Peguero; K. Breuer

2009-01-01

111

Superhydrophobic Surface Coatings for Microfluidics and MEMs.  

SciTech Connect

Low solid interfacial energy and fractally rough surface topography confer to Lotus plants superhydrophobic (SH) properties like high contact angles, rolling and bouncing of liquid droplets, and self-cleaning of particle contaminants. This project exploits the porous fractal structure of a novel, synthetic SH surface for aerosol collection, its self-cleaning properties for particle concentration, and its slippery nature 3 to enhance the performance of fluidic and MEMS devices. We propose to understand fundamentally the conditions needed to cause liquid droplets to roll rather than flow/slide on a surface and how this %22rolling transition%22 influences the boundary condition describing fluid flow in a pipe or micro-channel. Rolling of droplets is important for aerosol collection strategies because it allows trapped particles to be concentrated and transported in liquid droplets with no need for a pre-defined/micromachined fluidic architecture. The fluid/solid boundary condition is important because it governs flow resistance and rheology and establishes the fluid velocity profile. Although many research groups are exploring SH surfaces, our team is the first to unambiguously determine their effects on fluid flow and rheology. SH surfaces could impact all future SNL designs of collectors, fluidic devices, MEMS, and NEMS. Interfaced with inertial focusing aerosol collectors, SH surfaces would allow size-specific particle populations to be collected, concentrated, and transported to a fluidic interface without loss. In microfluidic systems, we expect to reduce the energy/power required to pump fluids and actuate MEMS. Plug-like (rather than parabolic) velocity profiles can greatly improve resolution of chip-based separations and enable unprecedented control of concentration profiles and residence times in fluidic-based micro-reactors. Patterned SH/hydrophilic channels could induce mixing in microchannels and enable development of microflow control elements. Acknowledgements This work was funded by Sandia National Laboratory's Laboratory Directed Research & Development program (LDRD). Some coating processes were conducted in the cleanroom facility located at the University of New Mexico's Center for High Technology Materials (CHTM). SEM images were performed at UNM's Center for Micro-Engineering on equipment funded by a NSF New Mexico EPSCoR grant. 4

Branson, Eric D.; Singh, Seema [Sandia National Laboratories, Livermore, CA] [Sandia National Laboratories, Livermore, CA; Houston, Jack E.; van Swol, Frank B.; Brinker, C. Jeffrey

2006-11-01

112

Designing robust alumina nanowires-on-nanopores structures: superhydrophobic surfaces with slippery or sticky water adhesion.  

PubMed

Hierarchical alumina surfaces with different morphologies were fabricated by a simple one-step anodization method. These alumina films were fabricated by a new raw material: silica gel plate (aluminum foil with a low purity of 97.17%). The modulation of anodizing time enabled the formation of nanowires-on-nanopores hybrid nanostructures having controllable nanowires topographies through a self-assembly process. The resultant structures were demonstrated to be able to achieve superhydrophobicity without any hydrophobic coating layer. More interestingly, it is found that the as-prepared superhydrophobic alumina surfaces exhibited high contrast water adhesion. Hierarchical alumina film with nanowire bunches-on-nanopores (WBOP) morphology presents extremely slippery property which can obtain a sliding angle (SA) as low as 1°, nanowire pyramids-on-nanopores (WPOP) structure shows strongly sticky water adhesion with the adhesive ability to support 15 ?L inverted water droplet at most. The obtained superhydrophobic alumina surfaces show remarkable mechanical durability even treated by crimping or pressing without impact on the water-repellent performance. Moreover, the created surfaces also show excellent resistivity to ice water, boiling water, high temperature, organic solvent and oil contamination, which could expand their usefulness and efficacy in harsh conditions. PMID:23981676

Peng, Shan; Tian, Dong; Miao, Xinrui; Yang, Xiaojun; Deng, Wenli

2013-11-01

113

Characterization of underwater stability of superhydrophobic surfaces using quartz crystal microresonators.  

PubMed

We synthesized porous aluminum oxide nanostructures directly on a quartz crystal microresonator and investigated the properties of superhydrophobic surfaces, including the surface wettability, water permeation, and underwater superhydrophobic stability. After increasing the pore diameter to 80 nm (AAO80), a gold film was deposited onto the AAO80 membrane, and the pore entrance size was reduced to 30 nm (AAO30). The surfaces of the AAO80 and AAO30 were made to be hydrophobic through chemical modification by incubation with octadecanethiol (ODT) or octadecyltrichlorosilane (OTS), which produced three different types of superhydrophobic surfaces on quartz microresonators: OTS-modified AAO80 (OTS-AAO80), ODT-modified AAO30 (ODT-AAO30), and ODT-OTS-modified AAO30 (TS-AAO30). The loading of a water droplet onto a microresonator or the immersion of a resonator into water induced changes in the resonance frequency that corresponded to the water permeation into the nanopores. TS-AAO30 exhibited the best performance, with a low degree of water permeation, and a high stability. These features were attributed to the presence of sealed air pockets and the narrow pore entrance diameter. PMID:24978595

Lee, Moonchan; Yim, Changyong; Jeon, Sangmin

2014-07-15

114

Superhydrophobic metallic glass surface with superior mechanical stability and corrosion resistance  

NASA Astrophysics Data System (ADS)

Superhydrophobic surface with mechanical stability and corrosion resistance is long expected due to its practical applications. We show that a micro-nano scale hierarchical structured Pd-based metallic glass surface with superhydrophobic effect can be prepared by the thermoplastic forming, which is a unique and facile synthesis strategy for metallic glasses. The superhydrophobic metallic glass surface without modification of low surface energy chemical layer also exhibits superior mechanical stability and corrosion resistance compared with conventional superhydrophobic materials. Our results indicate that the metallic glass is a promising candidate superhydrophobic material for applications.

Ma, J.; Zhang, X. Y.; Wang, D. P.; Zhao, D. Q.; Ding, D. W.; Liu, K.; Wang, W. H.

2014-04-01

115

Spatially controlled surface energy traps on superhydrophobic surfaces.  

PubMed

Water wetting and adhesion control on polymeric patterns are achieved by tuning the configuration of their surface's structural characteristics from single to dual and triple length-scale. In particular, surfaces with combined micro-, submicrometer-,and nanoroughness are developed, using photolithographically structured SU-8 micro-pillars as substrates for the consecutive spray deposition of polytetrafluoroethylene (PTFE) submicrometer particles and hydrophobically capped iron oxide colloidal nanoparticles. The PTFE particles alone or in combination with the nanoparticles render the SU-8 micropillars superhydrophobic. The water adhesion behaviour of the sprayed pillars is more complex since they can be tuned gradually from totally adhesive to completely non adhesive. The influence of the hierarchical geometrical features of the functionalized surfaces on this behaviour is discussed within the frame of the theory. Specially designed surfaces using the described technique are presented for selective drop deposition and evaporation. This simple method for liquid adhesion control on superhydrophobic surfaces can find various applications in the field of microfluidics, sensors, biotechnology, antifouling materials, etc. PMID:24386959

Milionis, Athanasios; Fragouli, Despina; Martiradonna, Luigi; Anyfantis, George C; Cozzoli, P Davide; Bayer, Ilker S; Athanassiou, Athanassia

2014-01-22

116

Drag reduction in laminar and turbulent flows past superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

A series of experiments and direct numerical simulations (DNS) will be presented which demonstrate significant drag reduction for both laminar and turbulent flows of water through channels using superhydrophobic surfaces with well-defined micron-sized surface roughness. The surfaces are fabricated from PDMS to incorporate precise patterns of ridges or posts that can support a shear-free air-water interface. A flow cell is used to measure the pressure drop and velocity profile as a function of the flow rate for a series of channel geometries and superhydrophobic surface designs. DNS are performed for flow past superhydrophobic surfaces which both complement and extend the range of geometries and Reynolds number obtained in the experiments. We will show that drag reductions up to 75% and slip lengths up to 150?m can be obtained in turbulent flows past superhydrophobic surfaces. Additionally, we will show that slip along the air water interface forestalls the transition from laminar to turbulent flow. The drag reduction is found to increases with increasing post/ridge spacing and the fraction of air-water interface. In turbulent flows, the drag reduction increases with Reynolds number before eventually reaching a plateau. These results suggest that in turbulent flows, the drag reduction scales with the thickness of the viscous sublayer and not the overall channel height as in laminar flows.

Rothstein, Jonathan P.

2009-11-01

117

Facile and fast fabrication of superhydrophobic surface on magnesium alloy  

NASA Astrophysics Data System (ADS)

Superhydrophobic surface has many special functions and is widely investigated by researchers. Magnesium alloy is one of the lightest metal materials among the practice metals. It plays an important role in automobile, airplane and digital product for reducing devices weight. But due to the low standard potential, magnesium alloy has a high chemical activity and easily be corroded. That seriously impedes the application of magnesium alloy. In the process of fabrication a superhydrophobic surface on magnesium alloy, there are two ineluctable problems that must be solved: (1) high chemical activity and (2) the chemical activity is inhomogeneous on surface. In this study, we solved those problems by using the two characters to gain a rough surface on magnesium alloy and obtained a superhydrophobic surface after following modification process. The results show that the as-prepared superhydrophobic surface has obvious anti-corrosion effect in typically corrosive solution and naturally humid air. The delay-icing and self-cleaning effects are also investigated. The presented method is low-cost, fast and has great potential value in large-scale industry production.

Wang, Zhongwei; Li, Qing; She, Zuxin; Chen, Funan; Li, Longqin; Zhang, Xiaoxu; Zhang, Peng

2013-04-01

118

Droplet evaporation on heated hydrophobic and superhydrophobic surfaces.  

PubMed

The evaporation characteristics of sessile water droplets on smooth hydrophobic and structured superhydrophobic heated surfaces are experimentally investigated. Droplets placed on the hierarchical superhydrophobic surface subtend a very high contact angle (?160°) and demonstrate low roll-off angle (?1°), while the hydrophobic substrate supports corresponding values of 120° and ?10°. The substrates are heated to different constant temperatures in the range of 40-60?°C, which causes the droplet to evaporate much faster than in the case of natural evaporation without heating. The geometric parameters of the droplet, such as contact angle, contact radius, and volume evolution over time, are experimentally tracked. The droplets are observed to evaporate primarily in a constant-contact-angle mode where the contact line slides along the surface. The measurements are compared with predictions from a model based on diffusion of vapor into the ambient that assumes isothermal conditions. This vapor-diffusion-only model captures the qualitative evaporation characteristics on both test substrates, but reasonable quantitative agreement is achieved only for the hydrophobic surface. The superhydrophobic surface demonstrates significant deviation between the measured evaporation rate and that obtained using the vapor-diffusion-only model, with the difference being amplified as the substrate temperature is increased. A simple model considering thermal diffusion through the droplet is used to highlight the important role of evaporative cooling at the droplet interface in determining the droplet evaporation characteristics on superhydrophobic surfaces. PMID:24827255

Dash, Susmita; Garimella, Suresh V

2014-04-01

119

Drag reduction in turbulent flows over superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

In this paper, we demonstrate that periodic, micropatterned superhydrophobic surfaces, previously noted for their ability to provide laminar flow drag reduction, are capable of reducing drag in the turbulent flow regime. Superhydrophobic surfaces contain micro- or nanoscale hydrophobic features which can support a shear-free air-water interface between peaks in the surface topology. Particle image velocimetry and pressure drop measurements were used to observe significant slip velocities, shear stress, and pressure drop reductions corresponding to drag reductions approaching 50%. At a given Reynolds number, drag reduction is found to increase with increasing feature size and spacing, as in laminar flows. No observable drag reduction was noted in the laminar regime, consistent with previous experimental results for the channel geometry considered. The onset of drag reduction occurs at a critical Reynolds number where the viscous sublayer thickness approaches the scale of the superhydrophobic microfeatures and performance is seen to increase with further reduction in viscous sublayer height. These results indicate superhydrophobic surfaces may provide a significant drag reducing mechanism for marine vessels.

Daniello, Robert J.; Waterhouse, Nicholas E.; Rothstein, Jonathan P.

2009-08-01

120

Drag reduction in external flows using superhydrophobic patterned surfaces  

Microsoft Academic Search

We present an experimental investigation of a laminar boundary layer in water flow over a superhydrophobic patterned surface. The experimental set-up uses a water tunnel to measure the drag over a Joukowski airfoil using a Linear Variable Differential Transducer (LVDT). The experimental results are presented for laminar boundary layers over the airfoil, the flow fields being quantified with Particle Image

Salil Gogte; Richard Truesdell; Andrea Mammoli

2004-01-01

121

Drag reduction in external flows using superhydrophobic patterned surfaces  

NASA Astrophysics Data System (ADS)

We present an experimental investigation of a laminar boundary layer in water flow over a superhydrophobic patterned surface. The experimental set-up uses a water tunnel to measure the drag over a Joukowski airfoil using a Linear Variable Differential Transducer (LVDT). The experimental results are presented for laminar boundary layers over the airfoil, the flow fields being quantified with Particle Image Velocitimetry (PIV) techniques for a range of Reynolds numbers. The Joukowski airfoil is developed and patterned with micron scale grooves using Rapid Prototyping techniques. The surface is then coated with a superhydrophobic aerogel substance, at thickness of less than 500 nm, which results in contact angles greater than 150 degrees. The drag force on the airfoil is also calculated numerically using semi-analytical models and is compared with experiments. Although slip on a superhydrophobic surface with nanoscale roughness is undetectable, the presence of patterns of sizes comparable to the boundary layer thickness (on the order of tens or hundreds of micrometers) in combination with the superhydrophobic coatings may result in substantial drag reduction.

Gogte, Salil; Truesdell, Richard; Mammoli, Andrea

2004-11-01

122

Electro-osmotic flow along superhydrophobic surfaces with embedded electrodes  

NASA Astrophysics Data System (ADS)

The effect of the secondary fluid enclosed in the indentations of a superhydrophobic surface on electro-osmotic flow is investigated. We derive analytical expressions for the net electro-osmotic flow over periodically structured surfaces, accounting for the influence of dissipation within the secondary fluid as well as for the role of charges at the fluid-fluid interfaces that are generated by auxiliary electrodes. Specifically, for a surface with rectangular grooves, the electro-osmotic flow velocity is related to the geometric parameters of the surface and the viscosity of an arbitrary secondary fluid filling the grooves. The results suggest that on specific superhydrophobic surfaces a flow enhancement by more than two orders of magnitude compared to unstructured surfaces can be expected.

Schönecker, Clarissa; Hardt, Steffen

2014-06-01

123

Drag reduction in laminar and turbulent flows past superhydrophobic surfaces  

Microsoft Academic Search

A series of experiments and direct numerical simulations (DNS) will be presented which demonstrate significant drag reduction for both laminar and turbulent flows of water through channels using superhydrophobic surfaces with well-defined micron-sized surface roughness. The surfaces are fabricated from PDMS to incorporate precise patterns of ridges or posts that can support a shear-free air-water interface. A flow cell is

Jonathan P. Rothstein

2009-01-01

124

Micro to nano: Surface size scale and superhydrophobicity.  

PubMed

This work looks at the fundamental question of how the surface mobility of drops in the composite state is related to the size scale of the roughness features of the surface. To this end, relevant literature is first reviewed and the important terms are clarified. We then describe and discuss contact and roll-off angle measurements on a set of hydrophobicized silicon post surfaces for which all parameters except for the surface size scale were held constant. It was found that a critical transition from "sticky superhydrophobic" (composite state with large contact angle hysteresis) to "truly superhydrophobic" (composite state with low hysteresis) takes place as the size of the surface features reaches 1 ?m. PMID:21977446

Dorrer, Christian; Rühe, Jürgen

2011-01-01

125

Structure irregularity impedes drop roll-off at superhydrophobic surfaces.  

PubMed

We study water drop roll-off at superhydrophobic surfaces with different surface patterns. Superhydrophobic microcavity surfaces were fabricated in silicon and coated with 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS). For the more irregular surface patterns, the observed increase in roll-off angles is found to be caused by a decrease of the receding contact angle, which in turn is caused by an increase of the triple phase contact line of the drops for those more irregular surfaces. To understand the observation, we propose to treat the microdrops as rigid bodies and apply a torque balance between the torque exerted by the projected gravity force and the torque exerted by the adhesion force acting along the triple line on the receding side of the drop. This simple model provides a proper order of magnitude estimate of the measured effects. PMID:24735125

Larsen, Simon Tylsgaard; Andersen, Nis Korsgaard; Søgaard, Emil; Taboryski, Rafael

2014-05-01

126

Modeling drag reduction and meniscus stability of superhydrophobic surfaces comprised of random roughness  

Microsoft Academic Search

Previous studies dedicated to modeling drag reduction and stability of the air-water interface on superhydrophobic surfaces were conducted for microfabricated coatings produced by placing hydrophobic microposts\\/microridges arranged on a flat surface in aligned or staggered configurations. In this paper, we model the performance of superhydrophobic surfaces comprised of randomly distributed roughness (e.g., particles or microposts) that resembles natural superhydrophobic surfaces,

Mohamed A. Samaha; Hooman Vahedi Tafreshi; Mohamed Gad-El-Hak

2011-01-01

127

One-step process for the fabrication of superhydrophobic surfaces with easy repairability  

NASA Astrophysics Data System (ADS)

A simple technique for fabrication of superhydrophobic surfaces was developed by spraying copper stearate suspension on various substrates. The copper stearate suspension is prepared by the reaction of copper acetate and stearic acid in ethanol solution. The as-prepared surfaces exhibit both superhydrophobicity and self-cleaning properties. When the superhydrophobic surfaces were destroyed, the damaged surfaces could be easily repaired by spraying the copper stearate suspension on the wrecked surfaces again, and the superhydrophobicity of the surfaces was regenerated at the same time.

Li, Jian; Wan, Hongqi; Ye, Yinping; Zhou, Huidi; Chen, Jianmin

2012-01-01

128

Facile preparation of superhydrophobic surfaces based on metal oxide nanoparticles  

NASA Astrophysics Data System (ADS)

A novel method for fabrication of superhydrophobic surfaces was developed by facile coating various metal oxide nanoparticles, including ZnO, Al2O3 and Fe3O4, on various substrates followed by treatment with polydimethylsiloxane (PDMS) via chemical vapor deposition (CVD) method. Using ZnO nanoparticles as a model, the changes in the surface chemical composition and crystalline structures of the metal oxide nanoparticles by PDMS treatment were investigated by X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD) and Fourier transform infrared (FTIR) analysis. The results show that the combination of the improved surface roughness generated from of the nanoparticles aggregation with the low surface-energy of silicon-coating originated from the thermal pyrolysis of PDMS would be responsible for the surface superhydrophobicity. By a simple dip-coating method, we show that the metal oxide nanoparticles can be easily coated onto the surfaces of various textural and dimensional substrates, including glass slide, paper, fabric or sponge, for preparation of superhydrophobic surfaces for different purpose. The present strategy may provide an inexpensive and new route to surperhydrophobic surfaces, which would be of technological significance for various practical applications especially for separation of oils or organic contaminates from water.

Bao, Xue-Mei; Cui, Jin-Feng; Sun, Han-Xue; Liang, Wei-Dong; Zhu, Zhao-Qi; An, Jin; Yang, Bao-Ping; La, Pei-Qing; Li, An

2014-06-01

129

Reducing contact time of drops on superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

When water drops impact on to a superhydrophobic surface, the drops can recoil to such an extent that they completely bounce off the solid material. The time it takes for the drop to spread and recoil -- the contact time -- scales with the hydrodynamic inertial-capillary timescale. However, there is evidence that the coefficient of this scaling depends on surface-structure interactions, such as pinning. Here we investigate how surface interactions can influence droplet contact time, and we compare our results to existing models. We highlight an assumption in the current theory that imposes a lower-bound on the contact time. By designing around this constraint, we demonstrate novel superhydrophobic surfaces on which water droplets impact with shorter contact times than previously thought possible.

Bird, James; Dhiman, Rajeev; Kwon, Hyuk-Min; Varanasi, Kripa

2011-11-01

130

Fabricating Superhydrophobic Surfaces via a Two-Step Electrodeposition Technique.  

PubMed

This work presents a template-free electrochemical route to producing superhydrophobic copper coatings with the water contact angle of 160 ± 6° and contact angle hysteresis of 5 ± 2°. In this technique, copper deposit with multiscale surface features is formed through a two-step electrodeposition process in a concentrated copper sulfate bath. In the first step, applying a high overpotential results in the formation of structures with dense-branching morphology, which are loosely attached to the surface. In the second step, an additional thin layer of the deposit is formed by applying a low overpotential for a short time, which is used to reinforce the loosely attached branches on the surface. The work also presents a theoretical analysis of the effects of the fabrication parameters on the surface textures that cause the superhydrophobic characteristic of the deposit. PMID:24083366

Haghdoost, A; Pitchumani, R

2014-04-15

131

On Drag Reduction in Turbulent Channel Flow over Superhydrophobic Surfaces  

NASA Astrophysics Data System (ADS)

Recent simulations and experiments suggest that flow over superhydrophobic surfaces may exhibit significantly reduced drag in both laminar [8, 9] and turbulent [7, 10] regimes due to the existence of a thin layer of gas on the surface which allows a slip velocity. The current paper explores this using estimates of drag based on high-resolution PIV in a low-Reynolds number turbulent channel flow.

Peguero, C.; Breuer, K.

132

Direct numerical simulations of turbulent flows over superhydrophobic surfaces  

Microsoft Academic Search

Direct numerical simulations (DNSs) are used to investigate the drag-reducing per- formance of superhydrophobic surfaces (SHSs) in turbulent channel flow. SHSs combine surface roughness with hydrophobicity and can, in some cases, support a shear-free air-water interface. Slip velocities, wall shear stresses and Reynolds stresses are considered for a variety of SHS microfeature geometry configurations at a friction Reynolds number of

MICHAEL B. M ARTELL; LAIR P EROT; JONATHAN P. R OTHSTEIN

2009-01-01

133

Micro-micro hierarchy replacing micro-nano hierarchy: a precisely controlled way to produce wear-resistant superhydrophobic polymer surfaces.  

PubMed

Superhydrophobic polymer surfaces are typically fabricated by combining hierarchical micro-nanostructures. The surfaces have a great technological potential because of their special water-repellent and self-cleaning properties. However, the poor mechanical robustness of such surfaces has severely limited their use in practical applications. This study presents a simple and swift mass production method for manufacturing hierarchically structured polymer surfaces at micrometer scale. Polypropylene surface structuring was done using injection molding, where the microstructured molds were made with a microworking robot. The effect of the micro-microstructuring on the polymer surface wettability and mechanical robustness was studied and compared to the corresponding properties of micro-nanostructured surfaces. The static contact angles of the micro-microstructured surfaces were greater than 150° and the contact angle hysteresis was low, showing that the effect of hierarchy on the surface wetting properties works equally well at micrometer scale. Hierarchically micro-microstructured polymer surfaces exhibited the same superhydrophobic wetting properties as did the hierarchically micro-nanostructured surfaces. Micro-microstructures had superior mechanical robustness in wear tests as compared to the micro-nanostructured surfaces. The new microstructuring technique offers a precisely controlled way to produce superhydrophobic wetting properties to injection moldable polymers with sufficiently high intrinsic hydrophobicity. PMID:23009694

Huovinen, Eero; Hirvi, Janne; Suvanto, Mika; Pakkanen, Tapani A

2012-10-16

134

Bioinspired superhydrophobic, self-cleaning and low drag surfaces  

NASA Astrophysics Data System (ADS)

Nature has evolved objects with desired functionality using commonly found materials. Nature capitalizes on hierarchical structures to achieve functionality. The understanding of the functions provided by objects and processes found in nature can guide us to produce nanomaterials, nanodevices, and processes with desirable functionality. This article provides an overview of four topics: (1) Lotus Effect used to develop superhydrophobic and self-cleaning/antifouling surfaces with low adhesion, (2) Shark Skin Effect to develop surfaces with low fluid drag and anti-fouling characteristics, and (3-4) Rice Leaf and Butterfly Wing Effect to develop superhydrophobic and self-cleaning surfaces with low drag. Rice Leaf and Butterfly Wings combine the Shark Skin and Lotus Effects.

Bhushan, Bharat

2013-09-01

135

Ag 2 Se complex nanostructures with photocatalytic activity and superhydrophobicity  

Microsoft Academic Search

Single-crystalline Ag2Se complex nanostructures have been synthesized via a solvothermal route in which selenophene (C4H4Se) as a selenylation source reacts with AgNO3 at a temperature of 240 °C. An orthorhombic phase ?-Ag2Se nanostructure was identified by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy\\u000a (FE-SEM), high resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) spectroscopy. The wettability\\u000a of

Huaqiang Cao; Yujiang Xiao; Yuexiang Lu; Jiefu Yin; Baojun Li; Shuisheng Wu; Xiaoming Wu

2010-01-01

136

Effective slip over superhydrophobic surfaces in thin channels.  

PubMed

Superhydrophobic surfaces reduce drag by combining hydrophobicity and roughness to trap gas bubbles in a microscopic texture. Recent work has focused on specific cases, such as arrays of pillars or grooves, with limited theoretical guidance. Here, we consider the experimentally relevant limit of thin channels and obtain rigorous bounds on the effective slip length for any two-component (e.g., low-slip and high-slip) texture with given area fractions. Among all anisotropic textures, parallel stripes attain the largest (or smallest) possible slip in a straight, thin channel for parallel (or perpendicular) orientation with respect to the mean flow. Tighter bounds for isotropic textures further constrain the effective slip. These results provide a framework for the rational design of superhydrophobic surfaces. PMID:19257293

Feuillebois, François; Bazant, Martin Z; Vinogradova, Olga I

2009-01-16

137

Effective Slip over Superhydrophobic Surfaces in Thin Channels  

NASA Astrophysics Data System (ADS)

Superhydrophobic surfaces reduce drag by combining hydrophobicity and roughness to trap gas bubbles in a microscopic texture. Recent work has focused on specific cases, such as arrays of pillars or grooves, with limited theoretical guidance. Here, we consider the experimentally relevant limit of thin channels and obtain rigorous bounds on the effective slip length for any two-component (e.g., low-slip and high-slip) texture with given area fractions. Among all anisotropic textures, parallel stripes attain the largest (or smallest) possible slip in a straight, thin channel for parallel (or perpendicular) orientation with respect to the mean flow. Tighter bounds for isotropic textures further constrain the effective slip. These results provide a framework for the rational design of superhydrophobic surfaces.

Feuillebois, François; Bazant, Martin Z.; Vinogradova, Olga I.

2009-01-01

138

In Situ Observation of Liquid Capillary Bridges on Superhydrophobic Surfaces  

NASA Astrophysics Data System (ADS)

We describe a new technique for observing the dynamic behavior of the contact line of a liquid droplet on a superhydrophobic surface using environmental scanning electron microscopy. We find that on a surface patterned with an array of superhydrophobic micropillars, the receding contact line exhibits discrete hierarchical de-pinning events. As the macroscopic contact line recedes across the pillars, capillary bridges are formed along with microscale contact lines, thus perpetuating a self-similar wetting condition. We are able to measure the local receding angle and find that it follows the Gibbs criterion of depinning. By considering the line density of the microscale features and the pinning strength of each of those features, we relate the macroscopic adhesion force to that derived from a model based on pinning of the capillary bridges.

Paxson, Adam; Anand, Sushant; Varanasi, Kripa

2012-02-01

139

Effect of ionizing radiation on the properties of superhydrophobic silicone surfaces  

Microsoft Academic Search

Superhydrophobic surfaces may be useful for a variety of optical applications as these surfaces exhibit high contact angles with water (>150°) and low-drag. These properties prevent the accumulation of water droplets on the optical surface that would otherwise occur due to condensation or the adhesion of droplets from precipitation. Challenges to producing robust superhydrophobic surfaces for optical applications include the

Alan M. Lyons; Mark Barahman; Bikash Mondal; Edward W. Taylor

2010-01-01

140

Superhydrophobic films on glass surface derived from trimethylsilanized silica gel nanoparticles.  

PubMed

The paper deals with the fabrication of sol-gel-derived superhydrophobic films on glass based on the macroscopic silica network with surface modification. The fabricated transparent films were composed of a hybrid -Si(CH(3))(3)-functionalized SiO(2) nanospheres exhibiting the desired micro/nanostructure, water repellency, and antireflection (AR) property. The wavelength selective AR property can be tuned by controlling the physical thickness of the films. Small-angle X-ray scattering (SAXS) studies revealed the existence of SiO(2) nanoparticles of average size ?9.4 nm in the sols. TEM studies showed presence of interconnected SiO(2) NPs of ?10 nm in size. The films were formed with uniformly packed SiO(2) aggregates as observed by FESEM of film surface. FTIR of the films confirmed presence of glasslike Si-O-Si bonding and methyl functionalization. The hydrophobicity of the surface was depended on the thickness of the deposited films. A critical film thickness (>115 nm) was necessary to obtain the air push effect for superhydrophobicity. Trimethylsilyl functionalization of SiO(2) and the surface roughness (rms ?30 nm as observed by AFM) of the films were also contributed toward the high water contact angle (WCA). The coated glass surface showed WCA value of the droplet as high as 168 ± 3° with 6 ?L of water. These superhydrophobic films were found to be stable up to about 230-240 °C as confirmed by TG/DTA studies, and WCA measurements of the films with respect to the heat-treatment temperatures. These high water repellant films can be deposited on relatively large glass surfaces to remove water droplets immediately without any mechanical assistance. PMID:21823656

Goswami, Debmita; Medda, Samar Kumar; De, Goutam

2011-09-01

141

Effective Slip over Superhydrophobic Surfaces in Thin Channels  

Microsoft Academic Search

Superhydrophobic surfaces reduce drag by combining hydrophobicity and roughness to trap gas bubbles in a microscopic texture. Recent work has focused on specific cases, such as arrays of pillars or grooves, with limited theoretical guidance. Here, we consider the experimentally relevant limit of thin channels and obtain rigorous bounds on the effective slip length for any two-component (e.g., low-slip and

François Feuillebois; Martin Z. Bazant; Olga I. Vinogradova

2009-01-01

142

Modeling of the process of superhydrophobic surface formation  

Microsoft Academic Search

Thin composite films of nanoparticles formed by Layer-by-Layer method on a glass substrate from colloid solutions of titanium oxide, zinc oxide or silicon oxide are studied. Atomic Force microscopy, Scanning Electronic Microscopy and contact angle measurements were used for investigation of the surface properties of coatings. Bicomponent TiO2\\/SiO2 and ZnO\\/SiO2 films modified by octadecyltrichlorosilane are found to acquire superhydrophobic properties

Galina B. Lisovskaya; Sergei A. Chizhik; Alexander E. Salamianski; Vladimir E. Agabekov; Gennady K. Zhavnerko

2008-01-01

143

Super-hydrophobic bandages and method of making the same  

DOEpatents

A bandage that includes a material, which can be breathable, having a first surface, and a plurality of superhydrophobic particles attached to the first surface. The plurality of superhydrophobic particles ranging in size from about 100 nanometers to about 10 micrometers. The superhydrophobic particles including a protrusive material defining a plurality of nanopores and a plurality of spaced apart nanostructures that define an external boundary of the hydrophobic particles. The nanopores providing a flow through porosity. The first surface can be rendered superhydrophobic by the attached superhydrophobic particles. The material can have a second surface opposite the first surface that is hydrophilic. The superhydrophobic particles can be adhered to the first surface by a binder. Also included is a method of making the bandages described herein.

Simpson, John T. (Clinton, TN); D'Urso, Brian R. (Pittsburgh, PA)

2012-06-05

144

Comparison of Three Methods for Generating Superhydrophobic, Superoleophobic Nylon Nonwoven Surfaces (Postprint).  

National Technical Information Service (NTIS)

This research deals with creating a superhydrophobic/superoleophobic surface by preparing a metastable Cassie -Baxter (CB) surface. To create a CB surface it is essential to have low surface energy and properly constructed surface morphology. We have expl...

C. Willis H. J. Lee J. R. Owens R. Saraf S. Michielsen

2011-01-01

145

Stabilization of Leidenfrost vapour layer by textured superhydrophobic surfaces.  

PubMed

In 1756, Leidenfrost observed that water drops skittered on a sufficiently hot skillet, owing to levitation by an evaporative vapour film. Such films are stable only when the hot surface is above a critical temperature, and are a central phenomenon in boiling. In this so-called Leidenfrost regime, the low thermal conductivity of the vapour layer inhibits heat transfer between the hot surface and the liquid. When the temperature of the cooling surface drops below the critical temperature, the vapour film collapses and the system enters a nucleate-boiling regime, which can result in vapour explosions that are particularly detrimental in certain contexts, such as in nuclear power plants. The presence of these vapour films can also reduce liquid-solid drag. Here we show how vapour film collapse can be completely suppressed at textured superhydrophobic surfaces. At a smooth hydrophobic surface, the vapour film still collapses on cooling, albeit at a reduced critical temperature, and the system switches explosively to nucleate boiling. In contrast, at textured, superhydrophobic surfaces, the vapour layer gradually relaxes until the surface is completely cooled, without exhibiting a nucleate-boiling phase. This result demonstrates that topological texture on superhydrophobic materials is critical in stabilizing the vapour layer and thus in controlling--by heat transfer--the liquid-gas phase transition at hot surfaces. This concept can potentially be applied to control other phase transitions, such as ice or frost formation, and to the design of low-drag surfaces at which the vapour phase is stabilized in the grooves of textures without heating. PMID:22972299

Vakarelski, Ivan U; Patankar, Neelesh A; Marston, Jeremy O; Chan, Derek Y C; Thoroddsen, Sigurdur T

2012-09-13

146

Programming nanostructured soft biological surfaces by atomic layer deposition.  

PubMed

Here, we present the first successful attempt to programme the surface properties of nanostructured soft biological tissues by atomic layer deposition (ALD). The nanopatterned surface of lotus leaf was tuned by 3-125 nm TiO2 thin films. The lotus/TiO2 composites were studied by SEM-EDX, XPS, Raman, TG-DTA, XRR, water contact angle and photocatalysis measurements. While we could preserve the superhydrophobic feature of lotus, we managed to add a new property, i.e. photocatalytic activity. We also explored how surface passivation treatments and various ALD precursors affect the stability of the sensitive soft biological tissues. As we were able to gradually change the number of nanopatterns of lotus, we gained new insight into how the hollow organic nanotubes on the surface of lotus influence its superhydrophobic feature. PMID:23680967

Szilágyi, Imre Miklós; Teucher, Georg; Härkönen, Emma; Färm, Elina; Hatanpää, Timo; Nikitin, Timur; Khriachtchev, Leonid; Räsänen, Markku; Ritala, Mikko; Leskelä, Markku

2013-06-21

147

Scaling laws for slippage on superhydrophobic fractal surfaces  

NASA Astrophysics Data System (ADS)

We study the slippage on hierarchical fractal superhydrophobic surfaces and find an unexpected rich behavior for hydrodynamic friction on these surfaces. We develop a scaling law approach for the effective slip length, which is validated by numerical resolution of the hydrodynamic equations. Our results demonstrate that slippage does strongly depend on the fractal dimension and is found to be always smaller on fractal surfaces as compared with surfaces with regular patterns. This shows that in contrast to naive expectations, the value of effective contact angle is not sufficient to infer the amount of slippage on a fractal surface: depending on the underlying geometry of the roughness, strongly superhydrophobic surfaces may, in some cases, be fully inefficient in terms of drag reduction. Finally, our scaling analysis can be directly extended to the study of heat transfer at fractal surfaces, in order to estimate the Kapitsa surface resistance on patterned surfaces, as well as to the question of trapping of diffusing particles by patchy hierarchical surfaces, in the context of chemoreception.

Cottin-Bizonne, C.; Barentin, C.; Bocquet, L.

2012-01-01

148

Simulation of meniscus stability in superhydrophobic granular surfaces under hydrostatic pressures  

Microsoft Academic Search

In this work, a series of numerical simulations has been devised to study the performance of granular superhydrophobic surfaces under elevated hydrostatic pressures. Using balance of forces, an analytical expression has also been developed to predict the critical pressure at which a submersed idealized granular superhydrophobic surface comprised of spherical particles, orderly packed next to one another, departs from the

B. Emami; T. M. Bucher; H. Vahedi Tafreshi; D. Pestov; M. Gad-el-Hak; G. C. Tepper

2011-01-01

149

Mechanically robust superhydrophobic polymer surfaces based on protective micropillars.  

PubMed

Considerable attention is currently being devoted less to the question of whether it is possible to produce superhydrophobic polymer surfaces than to just how robust they can be made. The present study demonstrates a new route for improving the mechanical durability of water-repellent structured surfaces. The key idea is the protection of fragile fine-scale surface topographies against wear by larger scale sacrificial micropillars. A variety of surface patterns was manufactured on polypropylene using a microstructuring technique and injection molding. The surfaces subjected to mechanical pressure and abrasive wear were characterized by water contact and sliding angle measurements as well as by scanning electron microscopy and roughness analysis based on optical profilometry. The superhydrophobic polypropylene surfaces with protective structures were found to maintain their wetting properties in mechanical compression up to 20 MPa and in abrasive wear tests up to 120 kPa. For durable properties, the optimal surface density of the protective pillars was found to be about 15%. The present approach to the production of water-repellent polymer surfaces provides the advantages of mass production and mechanical robustness with practical applications of structurally functionalized surfaces. PMID:24483340

Huovinen, Eero; Takkunen, Laura; Korpela, Tarmo; Suvanto, Mika; Pakkanen, Tuula T; Pakkanen, Tapani A

2014-02-11

150

An atomistic-continuum hybrid simulation of fluid flows over superhydrophobic surfaces.  

PubMed

Recent experiments have found that slip length could be as large as on the order of 1 mum for fluid flows over superhydrophobic surfaces. Superhydrophobic surfaces can be achieved by patterning roughness on hydrophobic surfaces. In the present paper, an atomistic-continuum hybrid approach is developed to simulate the Couette flows over superhydrophobic surfaces, in which a molecular dynamics simulation is used in a small region near the superhydrophobic surface where the continuum assumption is not valid and the Navier-Stokes equations are used in a large region for bulk flows where the continuum assumption does hold. These two descriptions are coupled using the dynamic coupling model in the overlap region to ensure momentum continuity. The hybrid simulation predicts a superhydrophobic state with large slip lengths, which cannot be obtained by molecular dynamics simulation alone. PMID:19693344

Li, Qiang; He, Guo-Wei

2009-01-01

151

An atomistic-continuum hybrid simulation of fluid flows over superhydrophobic surfaces  

PubMed Central

Recent experiments have found that slip length could be as large as on the order of 1 ?m for fluid flows over superhydrophobic surfaces. Superhydrophobic surfaces can be achieved by patterning roughness on hydrophobic surfaces. In the present paper, an atomistic-continuum hybrid approach is developed to simulate the Couette flows over superhydrophobic surfaces, in which a molecular dynamics simulation is used in a small region near the superhydrophobic surface where the continuum assumption is not valid and the Navier-Stokes equations are used in a large region for bulk flows where the continuum assumption does hold. These two descriptions are coupled using the dynamic coupling model in the overlap region to ensure momentum continuity. The hybrid simulation predicts a superhydrophobic state with large slip lengths, which cannot be obtained by molecular dynamics simulation alone.

Li, Qiang; He, Guo-Wei

2009-01-01

152

Synthesis of superhydrophobic PTFE-like thin films by self-nanostructuration in a hybrid plasma process  

NASA Astrophysics Data System (ADS)

Superhydrophobic poly(tetrafluoro-ethylene) (PTFE) like thin films were grown on silicon wafers using a plasma-based hybrid process consisting on sputtering a carbon target in an Ar/CF4 atmosphere. The influence of the bias voltage applied to the substrate (VBias) as well as of the gas mixture composition (%CF4) on the chemical composition, the wettability and the morphology of the deposited thin films were evaluated. The chemical composition measured by X-ray Photoelectron Spectroscopy (XPS) has revealed that the F/C atomic ratio is always lower than for conventional PTFE (F/C = 2) and that it decreases when VBias increases (from F/C = 1 for VBias = - 100 V to F/C = 0.75 for VBias = - 200 V). This behavior is associated with the preferential sputtering of the fluorine atoms during the plasma-assisted growth of the films. Consecutively, a self-nanostructuration enhanced when increasing VBias is observed. As a consequence, the water contact angle (WCA) measurements range from 70° up to 150° depending on (i) the fluorine concentration and (ii) on the magnitude of the nanostructuration. In addition, for the films presenting the highest WCAs, a small hysteresis between the advancing and receding WCAs is observed (< 10°) allowing these films to fulfill completely the requirements of superhydrophobicity. The nanostructuration is probably due to the chemical etching by fluorine atoms of the fluorinated group. In order to get more understanding on the wettability mechanisms of these surfaces, the topography of the films has been evaluated by atomic force microscopy (AFM). The data have revealed, for all films, a dense and regular structure composed by conic objects (AvH is their average height and AvD is the average distance between them) for which the dimensions increase with VBias. A correlation between AvH/AvD, defined as the "morphological ratio", with the WCA was established. Theoretical evaluations of the WCA using the Wenzel and Cassie equations with, as inputs, the features of the deposited thin film surfaces measured by AFM suggest that the wetting regime is intermediate between these two ideal situations.

Henry, Frédéric; Renaux, Fabian; Coppée, Séverine; Lazzaroni, Roberto; Vandencasteele, Nicolas; Reniers, François; Snyders, Rony

2012-12-01

153

Static and dynamic characterization of robust superhydrophobic surfaces built from nano-flowers on silicon micro-post arrays  

NASA Astrophysics Data System (ADS)

Superhydrophobic nano-flower surfaces were fabricated using MEMS technology and microwave plasma-enhanced chemical vapor deposition (MPCVD) of carbon nanotubes on silicon micro-post array surfaces. The nano-flower structures can be readily formed within 1-2 min on the micro-post arrays with the spacing ranging from 25 to 30 µm. The petals of the nano-flowers consisted of clusters of multi-wall carbon nanotubes. Patterned nano-flower structures were characterized using various microscopy techniques. After MPCVD, the apparent contact angle (160 ± 0.2°), abbreviated as ACA (defined as the measured angle between the apparent solid surface and the tangent to the liquid-fluid interface), of the nano-flower surfaces increased by 139% compared with that of the silicon micro-post arrays. The measured ACA of the nano-flower surface is consistent with the predicted ACA from a modified Cassie-Baxter equation. A high-speed CCD camera was used to study droplet impact dynamics on various micro/nanostructured surfaces. Both static testing (ACA and sliding angle) and droplet impact dynamics demonstrated that, among seven different micro/nanostructured surfaces, the nano-flower surfaces are the most robust superhydrophobic surfaces.

Chen, Longquan; Xiao, Zhiyong; Chan, Philip C. H.; Lee, Yi-Kuen

2010-10-01

154

Droplet motion on designed microtextured superhydrophobic surfaces with tunable wettability.  

PubMed

Superhydrophobic surfaces have shown promising applications in microfluidic systems as a result of their water-repellent and low-friction properties over the past decade. Recently, designed microstructures have been experimentally applied to construct wettability gradients and direct the droplet motion. However, thermodynamic mechanisms responsible for the droplet motion on such regular rough surfaces have not been well understood such that at present specific guidelines for the design of tunable superhydrophobic surfaces are not available. In this study, we propose a simple but robust thermodynamic methodology to gain thorough insight into the physical nature for the controllable motion of droplets. On the basis of the thermodynamic calculations of free energy (FE) and the free-energy barrier (FEB), the effects of surface geometry of a pillar microtexture are systematically investigated. It is found that decreasing the pillar width and spacing simultaneously is required to lower the advancing and receding FEBs to effectively direct droplets on the roughness gradient surface. Furthermore, the external energy plays a role in the actuation of spontaneous droplet motion with the cooperation of the roughness gradient. In addition, it is suggested that the so-called "virtual wall" used to confine the liquid flow along the undesired directions could be achieved by constructing highly advancing FEB areas around the microchannels, which is promising for the design of microfluidic systems. PMID:18788770

Fang, Guoping; Li, Wen; Wang, Xiufeng; Qiao, Guanjun

2008-10-21

155

Droplet evaporation dynamics on a superhydrophobic surface with negligible hysteresis.  

PubMed

We report on experiments of droplet evaporation on a structured superhydrophobic surface that displays very high contact angle (CA ? 160 deg), and negligible contact angle hysteresis (<1 deg). The droplet evaporation is observed to occur in a constant-contact-angle mode, with contact radius shrinking for almost the entire duration of evaporation. Experiments conducted on Teflon-coated smooth surface (CA ? 120 deg) as a baseline also support an evaporation process that is dominated by a constant-contact-angle mode. The experimental results are compared with an isothermal diffusion model for droplet evaporation from the literature. Good agreement is observed for the Teflon-coated smooth surface between the analytical expression and experimental results in terms of the total time for evaporation, transient volume, contact angle, and contact radius. However, for the structured superhydrophobic surface, the experiments indicate that the time taken for complete evaporation of the droplet is greater than the predicted time, across all droplet volumes. This disparity is attributed primarily to the evaporative cooling at the droplet interface due to the high aspect ratio of the droplet and also the lower effective thermal conductivity of the substrate due to the presence of air gaps. This hypothesis is verified by numerically evaluating the temperature distribution along the droplet interface. We propose a generalized relation for predicting the instantaneous volume of droplets with initial CA > 90 deg, irrespective of the mode of evaporation. PMID:23952149

Dash, Susmita; Garimella, Suresh V

2013-08-27

156

Stable superhydrophobic surface of hierarchical carbon nanotubes on Si micropillar arrays  

PubMed Central

It is of great importance to construct a stable superhydrophobic surface with low sliding angle (SA) for various applications. We used hydrophobic carbon nanotubes (CNTs) to construct the superhydrophobic hierarchical architecture of CNTs on silicon micropillar array (CNTs/Si-?p), which have a large contact angle of 153° to 155° and an ultralow SA of 3° to 5°. Small water droplets with a volume larger than 0.3 ?L can slide on the CNTs/Si-?p with a tilted angle of approximately 5°. The CNTs growing on planar Si wafer lose their superhydrophobic properties after exposing to tiny water droplets. However, the CNTs/Si-?p still show superhydrophobic properties even after wetting using tiny water droplets. The CNTs/Si-?p still have a hierarchical structure after wetting, resulting in a stable superhydrophobic surface.

2013-01-01

157

Switching Fluid Slippage on pH-Responsive Superhydrophobic Surfaces.  

PubMed

Two stimuli-responsive polymer brushes, poly(dimethylaminoethyl methacrylate) and poly(methacrylic acid), were grafted from initiator-modified anodized alumina substrates to prepare two pH-responsive surfaces. By regulating the swelling states of the two polymers, water droplets can roll off or adhere onto the textured surface because of different adhesion forces. These forces also strongly affect boundary slippage. To determine the different slippage effects of fluid on our pH-responsive surfaces, a series of rheological experiments are carried out on two kinds of surfaces. A large slip length is obtained and reversibly regulated by changing the fluid pH. These responsive superhydrophobic surfaces with considerable slip length and pH-responsive properties have extensive potential applications in intelligent micro- and nanofluidic devices or biodevices, which can solve fluid flow problems. PMID:24845303

Wu, Yang; Liu, Zhilu; Liang, Yongmin; Pei, Xiaowei; Zhou, Feng; Xue, Qunji

2014-06-10

158

Formation of superhydrophobic soda-lime glass surface using femtosecond laser pulses  

NASA Astrophysics Data System (ADS)

This paper demonstrates the fabrication of superhydrophobic soda-lime glass surface by engineering periodic microgratings with self-formed periodic micro-ripples inside the microgratings using a single beam femtosecond laser. The wetting property of the microstructured surface is improved from hydrophobic to superhydrophobic, presenting a water droplet contact angle ranges from 152° to 155°. The microstructured glass surface shows excellent transparency, which is higher than 77% in the visible spectrum. We strongly believe that our proposed technology can achieve superhydrophobic glass surfaces over a large area for applications in diverse fields.

Ahsan, Md. Shamim; Dewanda, Fadia; Lee, Man Seop; Sekita, Hitoshi; Sumiyoshi, Tetsumi

2013-01-01

159

Corrosion resistance properties of superhydrophobic copper surfaces fabricated by one-step electrochemical modification process  

NASA Astrophysics Data System (ADS)

Superhydrophobic copper surfaces have been prepared by a one-step electrochemical modification process in an ethanolic stearic acid solution. In this work, the corrosion properties of hydrophobic copper surface and superhydrophobic copper surfaces were analyzed by means of electrochemical analyses and compared with that of as-received bare copper substrate. The decrease of corrosion current density (icorr) as well as the increase of polarization resistance (Rp) obtained from potentiodynamic polarization curves revealed that the superhydrophobic film on the copper surfaces improved the corrosion resistance performance of the copper substrate.

Huang, Ying; Sarkar, D. K.; Gallant, Danick; Chen, X.-Grant

2013-10-01

160

Water droplet impact on superhydrophobic surfaces with microstructures and hierarchical roughness  

NASA Astrophysics Data System (ADS)

Quantitative correlation between the critical impact velocity of droplet and geometry of superhydrophobic surfaces with microstructures is systematically studied. Experimental data shows that the critical impact velocity induced wetting transition of droplet on the superhydrophobic surfaces is strongly determined by the perimeter of single micropillar, the space between the repeat pillars and the advancing contact angle of the sidewall of the micropillars. The proposed model agrees well with the experimental results, and clarifies that the underlying mechanism which is responsible for the superhydrophobic surface with hierarchical roughness could sustain a higher liquid pressure than the surfaces with microstructures.

Hao, PengFei; Lv, CunJing; Niu, FengLei; Yu, Yu

2014-07-01

161

Rapid fabrication of large-area, corrosion-resistant superhydrophobic Mg alloy surfaces.  

PubMed

A superhydrophobic magnesium (Mg) alloy surface was successfully fabricated via a facile electrochemical machining process, and subsequently covered with a fluoroalkylsilane (FAS) film. The surface morphologies and chemical compositions were investigated using a scanning electron microscope (SEM) equipped with an energy-dispersive spectroscopy (EDS) and a Fourier-transform infrared spectrophotometer (FTIR). The results show hierarchal rough structures and an FAS film with a low surface energy on the Mg alloy surfaces, which confers good superhydrophobicity with a water contact angle of 165.2° and a water tilting angle of approximately 2°. The processing conditions, such as the processing time and removal rate per unit area at a constant removal mass per unit area, were investigated to determine their effects on the superhydrophobicity. Interestingly, when the removal mass per unit area is constant at approximately 11.10 mg/cm(2), the superhydrophobicity does not change with the removal rate per unit area. Therefore, a superhydrophobic Mg alloy surface can be rapidly fabricated based on this property. A large-area superhydrophobic Mg alloy surface was also fabricated for the first time using a small-area moving cathode. The corrosion resistance and durability of the superhydrophobic surfaces were also examined. PMID:22008385

Xu, Wenji; Song, Jinlong; Sun, Jing; Lu, Yao; Yu, Ziyuan

2011-11-01

162

Simulations of Turbulence over Superhydrophobic Surfaces  

Microsoft Academic Search

Significant effort has been placed on the development of surfaces which reduce the amount of drag experienced by a fluid as it passes over the surface. Alterations to the fluid itself, as well as the chemical and physical composition of the surface have been investigated with varying success. Investigations into turbulent drag reduction have been mostly limited to those involving

Michael B Martell

2009-01-01

163

Fabrication of superhydrophobic surface from binary micro-/nano-structure of mullite-whisk-based films  

NASA Astrophysics Data System (ADS)

The wettability of solid surface is a very important property of materials, which depends on both surface chemical composition and the geometry of the solid surface. We herein report a simple and inexpensive method to fabricate superhydrophobic surfaces with the use of mullite whisks (MWs) for the first time. Binary micro-/nano-structural surfaces were created by the incorporation of hydrophilic needlelike MWs with poly( ?-methacryloxypropyltrimethoxysilane) to exhibit hydrophobic behavior, which further showed superhydrophobicity with water contact angle of 152.4±2? after modified with stearic acid. The wettability variation from hydrophilicity to hydrophobicity and superhydrophobicity during the assembly process are discussed based on the scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, and contact-angle system. The superhydrophobicity of the surface could be attributed to the hierarchical microstructure of the rough surface induced by MWs and low surface energy of stearic acid.

Deng, Zhengyan; Yin, Yongjin; Yang, Shengyang; Wang, Cai-Feng; Chen, Su

2013-11-01

164

Probing droplets on superhydrophobic surfaces by synchrotron radiation scattering techniques  

PubMed Central

Droplets on artificially structured superhydrophobic surfaces represent quasi contact-free sample environments which can be probed by X-ray microbeams and nanobeams in the absence of obstructing walls. This review will discuss basic surface wettability concepts and introduce the technology of structuring surfaces. Quasi contact-free droplets are compared with contact-free droplets; processes related to deposition and evaporation on solid surfaces are discussed. Droplet coalescence based on the electrowetting effect allows the probing of short-time mixing and reaction processes. The review will show for several materials of biological interest that structural processes related to conformational changes, nucleation and assembly during droplet evaporation can be spatially and temporally resolved by raster-scan diffraction techniques. Orientational ordering of anisotropic materials deposited during solidification at pinning sites facilitates the interpretation of structural data.

Accardo, Angelo; Di Fabrizio, Enzo; Limongi, Tania; Marinaro, Giovanni; Riekel, Christian

2014-01-01

165

Surface microfluidics fabricated by photopatternable superhydrophobic nanocomposite  

Microsoft Academic Search

Surface microfluidics can be of potential use in a variety of emerging applications, including biological and chemical analysis,\\u000a cellular detection and manipulation, high-throughput pharmaceutical screening, and etc. In comparison with the conventional\\u000a closed-channel microfluidic system, surface microfluidics shows the distinct advantages of simple construction, direct surface\\u000a access, no cavitation or interphase obstruction, clear optical path, easy fluidic packaging, and device

Lingfei Hong; Tingrui Pan

2011-01-01

166

Turbulent Boundary Layer Flow over Superhydrophobic Surfaces.  

National Technical Information Service (NTIS)

The objective of this project was to determine whether drag caused by turbulence in boundary layer flow can be reduced through the use of modified surfaces. This study encompassed the testing of four different surfaces: 1) Teflon SLIP, 2) Aluminum SLIP, 3...

A. J. Rydalch

2013-01-01

167

Drag reduction in Stokes flows over spheres with nanostructured superhydrophilic surfaces  

NASA Astrophysics Data System (ADS)

Nanostructured surfaces offer opportunities to modify flow induced drag on solid objects. Measurements of the terminal velocity reveal that the drag associated with laminar Stokes flows can be reduced for spheres with nanostructured superhydrophilic as well as superhydrophobic surfaces. Numerical simulations suggest that the formation of recirculating or nearly stagnant flow zones leads to significant reduction in the friction drag. Such reduction, however, is offset by an increase in the form drag that arises from nonuniform pressure distributions. Our work motivates further studies to optimally balance the friction and form drag and control resistance to laminar flows over objects with nanostructured surfaces.

Byon, Chan; Nam, Youngsuk; Kim, Sung Jin; Ju, Y. Sungtaek

2010-03-01

168

Facile fabrication of superhydrophobic ZnO nanoparticle surfaces with erasable and rewritable wettability  

NASA Astrophysics Data System (ADS)

In this article, ZnO nanoparticle surfaces have been fabricated successfully by a simple spray-coating method without limitations the shape and size of substrates. After being chemically modified with stearic acid, the wettability of ZnO surfaces changed from superhydrophilicity to superhydrophobicity. Furthermore, the superhydrophobicity could be erased and rewrote by the alternation of plasma or heat treatment and stearic acid coating. The process has been repeated with full reproducibility more than eight times, demonstrating that the ZnO surfaces exhibit good erasable and rewritable superhydrophobicity.

Li, Jian; Wan, Hongqi; Liu, Xiaohong; Ye, Yinping; Zhou, Huidi; Chen, Jianmin

2012-09-01

169

Fabrication of superhydrophobic surfaces on interconnected Cu(OH)2 nanowires via solution-immersion  

NASA Astrophysics Data System (ADS)

Superhydrophobic surfaces with a contact angle of about 160° and a tilt angle lower than 4° were fabricated on copper plates via a simple solution-immersion step. Interconnected Cu(OH)2 nanowires were constructed on the copper surface by immersing copper plates in an aqueous solution of sodium hydroxide and potassium persulfate, and the resulting copper plates exhibited excellent superhydrophilic properties. The copper plates changed their wettability from superhydrophilicity to superhydrophobicity after further chemical modification with dodecanoic acid. The results of this study may pave a new pathway to the fabrication of superhydrophobic surfaces on engineering metals.

Pan, Qinmin; Jin, Haizu; Wang, Hongbo

2007-09-01

170

Multimode Multidrop Serial Coalescence Effects during Condensation on Two-Tier Superhydrophobic Surfaces  

NASA Astrophysics Data System (ADS)

Mobile coalescence leading to spontaneous drop motion was initially reported to occur only during water condensation on two-tier superhydrophobic surfaces (SHS), consisting of both nanoscale and microscale topological features. However, subsequent studies have shown that mobile coalescence also occurs on solely nanostructured SHS. Thus, recent focus has been on understanding the condensation process on just nanostructured surfaces rather than on two-tier SHS. Here, we investigate the impact of microscale topography of two-tier SHS on the droplet coalescence dynamics and wetting states during the condensation process. We identify new droplet shedding modes, which consist of serial coalescence events that lead to merging of multiple droplets. The formed drops either depart or remain anchored to the surface. We explain the observed post-merging drop adhesion trends through direct correlation to formation of drops in nanoscale as well as microscale Wenzel and Cassie-Baxter wetting states. We find that optimally designed two-tier SHS, which promote the highest number of departing microdrops, consists of microscale features spaced close enough to enable transition of larger droplets into micro-Cassie state, yet at the same time provide sufficient area in-between the features for occurrence of mobile coalescence.

Rykaczewski, Konrad; Paxton, Adam T.; Anand, Sushant; Chen, Xuemei; Wang, Zuankai; Varanasi, Kripa K.

2013-03-01

171

Superhydrophobic surfaces of the water bug Notonecta glauca: a model for friction reduction and air retention  

PubMed Central

Summary Superhydrophobic surfaces of plants and animals are of great interest for biomimetic applications. Whereas the self-cleaning properties of superhydrophobic surfaces have been extensively investigated, their ability to retain an air film while submerged under water has not, in the past, received much attention. Nevertheless, air retaining surfaces are of great economic and ecological interest because an air film can reduce friction of solid bodies sliding through the water. This opens perspectives for biomimetic applications such as low friction fluid transport or friction reduction on ship hulls. For such applications the durability of the air film is most important. While the air film on most superhydrophobic surfaces usually lasts no longer than a few days, a few semi-aquatic plants and insects are able to hold an air film over a longer time period. Currently, we found high air film persistence under hydrostatic conditions for the elytra of the backswimmer Notonecta glauca which we therefore have chosen for further investigations. In this study, we compare the micro- and nanostructure of selected body parts (sternites, upper side of elytra, underside of elytra) in reference to their air retaining properties. Our investigations demonstrate outstanding air film persistence of the upper side of the elytra of Notonecta glauca under hydrostatic and hydrodynamic conditions. This hierarchically structured surface was able to hold a complete air film under hydrostatic conditions for longer than 130 days while on other body parts with simple structures the air film showed gaps (underside of elytra) or even vanished completely after a few days (sternites). Moreover, the upper side of the elytra was able to keep an air film up to flow velocities of 5 m/s. Obviously the complex surface structure with tiny dense microtrichia and two types of larger specially shaped setae is relevant for this outstanding ability. Besides high air film persistence, the observation of a considerable fluid velocity directly at the air–water interface indicates the ability to reduce friction significantly. The combination of these two abilities makes these hierarchically structured surfaces extremely interesting as a biomimetic model for low friction fluid transport or drag reduction on ship hulls.

Schneider, Erik S; Melskotte, Jan-Erik; Brede, Martin; Leder, Alfred

2011-01-01

172

EWOD driven cleaning of bioparticles on hydrophobic and superhydrophobic surfaces.  

PubMed

Environmental air monitoring is of great interest due to the large number of people concerned and exposed to different possible risks. From the most common particles in our environment (e.g. by-products of combustion or pollens) to more specific and dangerous agents (e.g. pathogenic micro-organisms), there are a large range of particles that need to be controlled. In this article we propose an original study on the collection of electrostatically deposited particles using electrowetting droplet displacement. A variety of particles were studied, from synthetic particles (e.g. Polystyrene Latex (PSL) microsphere) to different classes of biological particle (proteins, bacterial spores and a viral simulant). Furthermore, we have compared ElectroWetting-On-Dielectric (EWOD) collecting efficiency using either a hydrophobic or a superhydrophobic counter electrode. We observe different cleaning efficiencies, depending on the hydrophobicity of the substrate (varying from 45% to 99%). Superhydrophobic surfaces show the best cleaning efficiency with water droplets for all investigated particles (MS2 bacteriophage, BG (Bacillus atrophaeus) spores, OA (ovalbumin) proteins, and PSL). PMID:21103534

Jönsson-Niedzió?ka, M; Lapierre, F; Coffinier, Y; Parry, S J; Zoueshtiagh, F; Foat, T; Thomy, V; Boukherroub, R

2011-02-01

173

Facile fabrication of superhydrophobic surface with nanowire structures on nickel foil  

NASA Astrophysics Data System (ADS)

A simple solution immersion method was developed for the preparation of superhydrophobic surface with nanowire structures on magnetic nickel substrate. The morphology feature, chemical composition and superhydrophobicity of the resultant surface were analyzed by means of scanning electron microscopy, X-ray powder diffraction, X-ray photoelectron spectrum and water contact angle measurements, respectively. The surface wettability could be easily changed from superhydrophilic to superhydrophobic by a simple chemical modification with stearic acid. It is confirmed that the synergic effect of the surface microstructure and surface free energy contribute to the unique water repellence. Interestingly, the superhydrophobic nickel foil can be used to fabricate a miniature magnetic boat with a controlled movement on water surface.

Zhang, Xia; Guo, Yonggang; Liu, Yue; Yang, Xue; Pan, Jieqiong; Zhang, Pingyu

2013-12-01

174

Superhydrophobic Surfaces for Turbulent Drag Reduction: Effect of Geometry and Reynolds Number  

Microsoft Academic Search

Recently, it has been demonstrated that superhydrophobic surfaces are capable of reducing drag in turbulent flows. Superhydrophobic surfaces are chemically hydrophobic with micron or nanometer scale surface features which can support a shear-free air-water interface. In this talk, we will consider the effect of microfeature geometry and flow velocity on the observed drag reduction. Microridge geometries from 15mum to 60mum

Robert Daniello; Jonathan P. Rothstein

2009-01-01

175

Fluorinated Polyhedral Oligosilsesquioxane Surfaces and Superhydrophobicity  

NASA Astrophysics Data System (ADS)

Fluorinated compounds are a logical choice for hydrophobic applications owing to their generally low surface energy. Polyhedral molecules may also improve hydrophobicity by increasing material surface roughness. There have been many recent attempts to synthesize and characterize various types of fluorinated polyhedra. These reports include the fluorination or fluoroalkylation of C60 [1,2]. Unfortunately, C60F48 (fluorinated buckminsterfullerene) cannot be used as a hydrophobic material, since it is metastable and is hydrolyzed by water [3]. However, the perfluorocarborane species, perfluoro-deca-?-methyl-para-carborane, shows remarkable hydrolytic and oxidative stability [4]. Fluorinated carbon nanotubes and nanofibers have also been produced [5]. Many of these fluorinated polyhedral compounds may be useful in hydrophobic applications, but they are generally hazardous to prepare, require air and moisture sensitive manipulations, and have limited economies of scale. For these reasons, alternative fluorinated polyhedra, such as Polyhedral Oligomeric SilSesquioxanes (POS) are highly desired (Figure 6.1).

Iacono, Scott T.; Peloquin, Andrew J.; Smith, Dennis W.; Mabry, Joseph M.

176

Fabrication of superhydrophobic surfaces by a Pt nanowire array on Ti/Si substrates.  

PubMed

Superhydrophobic surfaces were prepared on Ti/Si substrates via the fabrication of a platinum (Pt) nanowire array. The Pt nanowire array was obtained by dc electrodeposition of Pt into the pores of an anodic aluminium oxide (AAO) template on the substrate followed by the removal of the template. Transmission electron microscopy (TEM) examination demonstrated that all the nanowires have uniform diameter of about 30 nm. Field emission scanning electron microscopy (FE-SEM) showed that the structures at both the micrometre scale and nanometre scale bestowed the prerequisite roughness on the surfaces. The chemical surface modification made the Pt nanowire array superhydrophobic. The surface modified Pt nanowire array exhibited superhydrophobicity even in corrosive solutions over a wide pH range, such as acidic or basic solutions. The results demonstrated that the Pt nanowire array will have good potential applications in the preparation of superhydrophobic surfaces. PMID:21817621

Qu, Mengnan; Zhao, Guangyu; Wang, Qi; Cao, Xiaoping; Zhang, Junyan

2008-02-01

177

Self-cleaning of superhydrophobic surfaces by self-propelled jumping condensate  

PubMed Central

The self-cleaning function of superhydrophobic surfaces is conventionally attributed to the removal of contaminating particles by impacting or rolling water droplets, which implies the action of external forces such as gravity. Here, we demonstrate a unique self-cleaning mechanism whereby the contaminated superhydrophobic surface is exposed to condensing water vapor, and the contaminants are autonomously removed by the self-propelled jumping motion of the resulting liquid condensate, which partially covers or fully encloses the contaminating particles. The jumping motion off the superhydrophobic surface is powered by the surface energy released upon coalescence of the condensed water phase around the contaminants. The jumping-condensate mechanism is shown to spontaneously clean superhydrophobic cicada wings, where the contaminating particles cannot be removed by gravity, wing vibration, or wind flow. Our findings offer insights for the development of self-cleaning materials.

Wisdom, Katrina M.; Qu, Xiaopeng; Liu, Fangjie; Watson, Gregory S.; Chen, Chuan-Hua

2013-01-01

178

Superhydrophobic PDMS surfaces with three-dimensional (3D) pattern-dependent controllable adhesion  

NASA Astrophysics Data System (ADS)

In this paper, we demonstrate an effective approach for the three-dimensional (3D) pattern-structured superhydrophobic PDMS surfaces with controllable adhesion by using femtosecond laser etching method. By combining different laser power with a multi-layered etching way, various 3D patterns can be fabricated (for example, convex triangle array, round pit array, cylindrical array, convex rhombus array and concave triangle-cone array). The as-prepared surfaces with 3D patterns show superhydrophobic character and water controllable adhesion that range from ultralow to ultrahigh by designing different 3D patterns, on which the sliding angle can be controlled from 1° to 90° (the water droplet is firmly pinned on the superhydrophobic surface without any movement at any tilted angles). The 3D pattern-dependent adhesive property is attributed to the different contact modes. This work will provide a facile and promising strategy for the adhesion adjustment on superhydrophobic surfaces.

Yong, Jiale; Yang, Qing; Chen, Feng; Zhang, Dongshi; Du, Guangqing; Bian, Hao; Si, Jinhai; Yun, Feng; Hou, Xun

2014-01-01

179

A facile dip-coating process for preparing highly durable superhydrophobic surface with multi-scale structures on paint films.  

PubMed

Superhydrophobic surfaces with multi-scale nano/microstructures have been prepared on epoxy paint surfaces using a feasible dip-coating process. The microstructures with 5-10 microm protuberances were first prepared on epoxy paint surface by sandblast. Then the nanostructures were introduced on the microstructure surface by anchoring 50-100 nm SiO(2) particles (nano-SiO(2)) onto the sandblasted paint surface, which was completed by dip-coating with a nano-SiO(2)/epoxy adhesive solution (M1). At last the surface was further modified for enhancing hydrophobicity by another dip-coating with a solution of a low surface energy polymer, aminopropyl terminated polydimethylsiloxane (ATPS) modified epoxy adhesive (M2). The water contact angle of the as-prepared samples reached as high as 167.8 degrees and the sliding angle was 7 degrees. The prepared superhydrophobic surface exhibited excellent durability to the high speed scouring test and high stability in neutral and basic aqueous solutions and some common organic solvents. In addition, this method can be adopted to fabricate large scale samples with a good homogeneity of the whole surface at very low cost. PMID:19552913

Cui, Zhe; Yin, Long; Wang, Qingjun; Ding, Jianfu; Chen, Qingmin

2009-09-15

180

Super-hydrophobic surfaces from a simple coating method: a bionic nanoengineering approach  

Microsoft Academic Search

Inspired by the self-cleaning behaviour of lotus leaves in nature, we developed a simple coating method that can facilitate the bionic creation of super-hydrophobic surfaces on various substrates, thus providing a feasible way of fabricating super-hydrophobic surfaces for civil and industrial applications. Micro-nanoscale binary structured composite particles of silica\\/fluoropolymer were prepared using an emulsion-mediated sol-gel process, and then these composite

Yuyang Liu; Xianqiong Chen; J. H. Xin

2006-01-01

181

Characterization of Superhydrophobic Surfaces for Anti-icing in a Low-Temperature Wind Tunnel  

Microsoft Academic Search

In this study, a closed loop low-temperature wind tunnel was custom-built and uniquely used to investigate the anti-icing mechanism of superhydrophobic surfaces in regulated flow velocities, temperatures, humidity, and water moisture particle sizes. Silica nanoparticle-based hydrophobic coatings were tested as superhydrophobic surface models. During tests, images of ice formation were captured by a camera and used for analysis of ice

Christopher Swarctz; Elias Alijallis; Scott Robert Hunter; John T Simpson; Chang-Hwan Choi

2010-01-01

182

Flame soot stably deposited on silicone coatings possess superhydrophobic surface  

NASA Astrophysics Data System (ADS)

A flame soot deposited silicone coating was successfully prepared by butane flame along with a deposition process of flame soot. Field emission scanning electron microscopy equipped with an energy-dispersive X-ray analyzer and X-ray photoelectron spectroscopy were used to analyze the chemical compositions and structure of flame soot, showing that the surface is mainly composed of carbon nanoparticles being closely packed and forming tree branch-like network with micro- and nanoscale roughness. Meanwhile, the flame soot can stably deposit on the silicone coatings during the water-flow impact test. When the deposition time is 20 s, the silicone coating possesses a water contact angle of 168 ± 2° combining with a sliding angle less than 1°, and a transmittance reduced less than 28% for wavelengths above 500 nm compared to glass substrate. The superhydrophobicity has a little increase with the extension of deposition time, but at the expense of transmittance.

Shen, Lie; Wang, Wen; Ding, Hongliang; Guo, Qipeng

2013-11-01

183

Targets on superhydrophobic surfaces for laser ablation ion sources  

NASA Astrophysics Data System (ADS)

Target preparation techniques for a laser ablation ion source at the Penning-trap mass spectrometer TRIGA-TRAP have been investigated with regard to future experiments with actinides. To be able to perform mass measurements on these nuclides considering their limited availability, an efficient target preparation technique is mandatory. Here, we report on a new approach for target production using backings, which are pretreated in a way that a superhydrophobic surface is formed. This resulted in improved targets with a more homogeneous distribution of the target material compared to standard techniques with unmodified backings. It was demonstrated that the use of these new targets in a laser ablation ion source improved the ion production significantly.

Renisch, D.; Beyer, T.; Blaum, K.; Block, M.; Düllmann, Ch. E.; Eberhardt, K.; Eibach, M.; Nagy, Sz.; Neidherr, D.; Nörtershäuser, W.; Smorra, C.

2012-06-01

184

Flow past superhydrophobic surfaces with cosine variation in local slip length  

NASA Astrophysics Data System (ADS)

Anisotropic superhydrophobic surfaces have the potential to greatly reduce drag and enhance mixing phenomena in microfluidic devices. Recent work has focused mostly on cases of superhydrophobic stripes. Here, we analyze a relevant situation of cosine variation of the local slip length. We derive approximate formulas for maximal (longitudinal) and minimal (transverse) directional effective slip lengths that are in good agreement with the exact numerical solution and lattice-Boltzmann simulations. Compared to the case of superhydrophobic stripes, the cosine texture can provide a very large effective slip. However, the difference between eigenvalues of the slip-length tensor is smaller, indicating that the flow is less anisotropic.

Asmolov, Evgeny S.; Schmieschek, Sebastian; Harting, Jens; Vinogradova, Olga I.

2013-02-01

185

Flow past superhydrophobic surfaces with cosine variation in local slip length.  

PubMed

Anisotropic superhydrophobic surfaces have the potential to greatly reduce drag and enhance mixing phenomena in microfluidic devices. Recent work has focused mostly on cases of superhydrophobic stripes. Here, we analyze a relevant situation of cosine variation of the local slip length. We derive approximate formulas for maximal (longitudinal) and minimal (transverse) directional effective slip lengths that are in good agreement with the exact numerical solution and lattice-Boltzmann simulations. Compared to the case of superhydrophobic stripes, the cosine texture can provide a very large effective slip. However, the difference between eigenvalues of the slip-length tensor is smaller, indicating that the flow is less anisotropic. PMID:23496608

Asmolov, Evgeny S; Schmieschek, Sebastian; Harting, Jens; Vinogradova, Olga I

2013-02-01

186

Self-cleaning superhydrophobic surface based on titanium dioxide nanowires combined with polydimethylsiloxane  

NASA Astrophysics Data System (ADS)

The present work describes a simple dipping process for the preparation of superhydrophobic coatings based on titanium dioxide nanowires combined with polydimethylsiloxane. The coating surface morphology, composition and wettability were investigated by scanning electron microscope, X-ray photoelectron spectroscope and contact angle measurements, respectively. Interestingly, the superhydrophobic coatings turn into a hydrophilic one after UV irradiation. It is found that the superhydrophobic surface shows almost complete wet self-cleaning of dirt particles with water droplets. Furthermore, the coating surface shows the anti-fouling performance for organic solvents, which can self-remove the organic solvents layer and recovers its superhydrophobic behavior. The advantage of the present approach is that the damaged coating can be easily repaired.

Zhang, Xia; Guo, Yonggang; Zhang, Zhijun; Zhang, Pingyu

2013-11-01

187

Flow over Superhydrophobic Hydrofoils  

Microsoft Academic Search

For several years, superhydrophobic surfaces which are chemically hydrophobic with micron or nanometer scale surface features have been considered for their ability to reduce drag in microfluidic devices. More recently it has been demonstrated that superhydrophobic surfaces reduce friction coefficient in turbulent flows as well. In this talk, we will consider the effect of superhydrophobic surfaces on drag, lift and

Robert Daniello; Jonathan Sullivan; Jonathan Rothstein

2010-01-01

188

Inspired superhydrophobic surfaces by a double-metal-assisted chemical etching route  

SciTech Connect

Graphical abstract: A double-metal-assisted chemical etching method is employed to fabricate superhydrophobic surfaces, showing a good superhydrophobicity with the contact angle of about 170°, and the sliding angle of about 0°. Meanwhile, the potential formation mechanism about it is also presented. Highlights: ? A double-metal-assisted chemical etching method is employed to fabricate superhydrophobic surfaces. ? The obtained surfaces show good superhydrophobicity with a high contact angle and low sliding angle. ? The color of the etched substrate dark brown or black and it is so-called black silicon. -- Abstract: Silicon substrates treated by metal-assisted chemical etching have been studied for many years since they could be employed in a variety of electronic and optical devices such as integrated circuits, photovoltaics, sensors and detectors. However, to the best of our knowledge, the chemical etching treatment on the same silicon substrate with the assistance of two or more kinds of metals has not been reported. In this paper, we mainly focus on the etching time and finally obtain a series of superhydrophobic silicon surfaces with novel etching structures through two successive etching processes of Cu-assisted and Ag-assisted chemical etching. It is shown that large-scale homogeneous but locally irregular wire-like structures are obtained, and the superhydrophobic surfaces with low hysteresis are prepared after the modifications with low surface energy materials. It is worth noting that the final silicon substrates not only possess high static contact angle and low hysteresis angle, but also show a black color, indicating that the superhydrophobic silicon substrate has an extremely low reflectance in a certain range of wavelengths. In our future work, we will go a step further to discuss the effect of temperature, the size of Cu nanoparticles and solution concentration on the final topography and superhydrophobicity.

Chen, Yu [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Lanzhou 730000 (China) [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Lanzhou 730000 (China); School of Mechanical and Electrical Engineering, Wuhan Institute of Technology, Wuhan 430073 (China); Guo, Zhiguang, E-mail: zguo@licp.cas.cn [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Lanzhou 730000 (China) [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Lanzhou 730000 (China); Ministry-of-Education Key Laboratory for the Green Preparation and Application of Functional Materials, Hubei University, Wuhan 430062 (China); Xu, Jiansheng [School of Mechanical and Electrical Engineering, Wuhan Institute of Technology, Wuhan 430073 (China)] [School of Mechanical and Electrical Engineering, Wuhan Institute of Technology, Wuhan 430073 (China); Shi, Lei; Li, Jing; Zhang, Yabin [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Lanzhou 730000 (China)] [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Lanzhou 730000 (China)

2012-07-15

189

Toward understanding whether superhydrophobic surfaces can really decrease fluidic friction drag.  

PubMed

Superhydrophobic surfaces in nature such as legs of water striders can get an extra supporting force from the deformed water surface they contact, leading to an anticipation of using water-repellent surfaces on ship and even submarine hulls to reduce friction drag. Here, we first fabricate superhydrophobic coatings with microstructures on glass balls by introducing hydrophobic silica nanoparticles into a polyethylene terephthalate (PET) film. Then, the movement of a superhydrophobic ball on and below water surface is investigated and compared with that of a highly hydrophilic normal glass ball. The results reveal that a superhydrophobic ball can fall more slowly under water compared with a normal glass ball, because the dense microbubbles trapped at the solid/water interface around the superhydrophobic ball act not as a reducer, but as an enhancer for the friction drag. In contrast, the faster movement of a superhydrophobic ball on the water surface can be mainly attributed to the great reduction of skin friction owing to the increased area of the solid/atmosphere interface. PMID:20000363

Su, Bin; Li, Mei; Lu, Qinghua

2010-04-20

190

A novel fabrication of a superhydrophobic surface with highly similar hierarchical structure of the lotus leaf on a copper sheet  

NASA Astrophysics Data System (ADS)

A novel and facile avenue was developed to successfully fabricate a regular hierarchical surface structure on a copper sheet via the combination of polydimethylsiloxane (PDMS) template and chemical etching method in this paper. The as-prepared hierarchical surface structure was comprised of uniform-sized microprotrusions and nanostructures which was similar to the natural lotus leaf. After modified by stearic acid, the surface was covered with a layer of hydrophobic chemical groups and became superhydrophobic. The values of its water contact angle and sliding angle were about 153° and 7°, respectively. Its wettability kept rather stable when it was exposed to humid conditions for 3 months. This study provides a new way to fabricate uniform surface microstructures that are highly similar to natural biological surfaces on metal materials.

Yuan, Zhiqing; Wang, Xian; Bin, Jiping; Peng, Chaoyi; Xing, Suli; Wang, Menglei; Xiao, Jiayu; Zeng, Jingcheng; Xie, Yong; Xiao, Ximei; Fu, Xin; Gong, Huifang; Zhao, Dejian

2013-11-01

191

In situ surface-modification-induced superhydrophobic patterns with reversible wettability and adhesion.  

PubMed

Herein is described a facile, in situ, ink-regulating approach to rapidly achieve reversible water wettability and adhesion transition, with a large degree of contrast, on superhydrophobic TiO2 nanotube array film. The ink printing and removal process allows the wettability and reversible adhesion transitions to be realized. Experimental results demonstrate the potential application of such site-selective, sticky superhydrophobic patterns for droplet manipulation by in situ surface modification. PMID:23208816

Lai, Yuekun; Pan, Fei; Xu, Cong; Fuchs, Harald; Chi, Lifeng

2013-03-25

192

Frictional slip lengths for unidirectional superhydrophobic grooved surfaces  

NASA Astrophysics Data System (ADS)

The exact solutions due to Philip [ZAMP 23, 353 (1972)] for Stokes shear flow over a periodic array of no-shear slots embedded in a no-slip surface are generalized to account for an arbitrary pattern of no-shear slots in each period window. The slots, or grooves, in each period window run parallel to each other, and are of infinite length, but their widths and separations can be specified arbitrarily. Explicit solutions are found both for longitudinal and transverse flows over the composite grooved surface. Analytical expressions for the transverse and longitudinal slip lengths associated with the microstructured surfaces are then found as functions of the geometrical parameters characterizing the surface. The formulae are relevant to a wide class of flow geometries and are expected to provide a useful tool in the design, analysis, and optimization of the friction properties of grooved microstructured superhydrophobic surfaces. The results are used to show that introducing even a very small wetted region in a no-shear slot can have a significant influence on the effective slip length.

Crowdy, Darren

2011-07-01

193

Facile creation of bio-inspired superhydrophobic Ce-based metallic glass surfaces  

NASA Astrophysics Data System (ADS)

A bio-inspired synthesis strategy was conducted to fabricate superhydrophobic Ce-based bulk metallic glass (BMG) surfaces with self-cleaning properties. Micro-nanoscale hierarchical structures were first constructed on BMG surfaces and then modified with the low surface energy coating. Surface structures, surface chemical compositions, and wettability were characterized by combining scanning electron microscopy, atomic force microscopy, x-ray photoelectron spectroscopy, and contact angle measurements. Research indicated that both surface multiscale structures and the low surface free energy coating result in the final formation of superhydrophobicity.

Liu, Kesong; Li, Zhou; Wang, Weihua; Jiang, Lei

2011-12-01

194

Nanocrystalline nickel films with lotus leaf texture for superhydrophobic and low friction surfaces  

NASA Astrophysics Data System (ADS)

Nanostructured Ni films with high hardness, high hydrophobicity and low coefficient of friction (COF) were fabricated. The surface texture of lotus leaf was replicated using a cellulose acetate film, on which a nanocrystalline (NC) Ni coating with a grain size of 30 ± 4 nm was electrodeposited to obtain a self-sustaining film with a hardness of 4.42 GPa. The surface texture of the NC Ni obtained in this way featured a high density (4 × 10 3 mm -2) of conical protuberances with an average height of 10.0 ± 2.0 ?m and a tip radius of 2.5 ± 0.5 ?m. This structure increased the water repellency and reduced the COF, compared to smooth NC Ni surfaces. The application of a short-duration (120 s) electrodeposition process that deposited "Ni crowns" with a larger radius of 6.0 ± 0.5 ?m on the protuberances, followed by a perfluoropolyether (PFPE) solution treatment succeeded in producing a surface texture consisting of nanotextured protuberances that resulted in a very high water contact angle of 156°, comparable to that of the superhydrophobic lotus leaf. Additionally, the microscale protuberances eliminated the initial high COF peaks observed when smooth NC Ni films were tested, and the PFPE treatment resulted in a 60% reduction in the steady-state COFs.

Shafiei, Mehdi; Alpas, Ahmet T.

2009-11-01

195

Washable and wear-resistant superhydrophobic surfaces with self-cleaning property by chemical etching of fibers and hydrophobization.  

PubMed

Superhydrophobic poly(ethylene terephthalate) (PET) textile surfaces with a self-cleaning property were fabricated by treating the microscale fibers with alkali followed by coating with polydimethylsiloxane (PDMS). Scanning electron microscopy analysis showed that alkali treatment etched the PET and resulted in nanoscale pits on the fiber surfaces, making the textiles have hierarchical structures. Coating of PDMS on the etched fibers affected little the roughening structures while lowered the surface energy of the fibers, thus making the textiles show slippery superhydrophobicity with a self-cleaning effect. Wettability tests showed that the superhydrophobic textiles were robust to acid/alkaline etching, UV irradiation, and long-time laundering. Importantly, the textiles maintained superhydrophobicity even when the textiles are ruptured by severe abrasion. Also colorful images could be imparted to the superhydrophobic textiles by a conventional transfer printing without affecting the superhydrophobicity. PMID:24942304

Xue, Chao-Hua; Li, Ya-Ru; Zhang, Ping; Ma, Jian-Zhong; Jia, Shun-Tian

2014-07-01

196

Spreading Dynamics of a Droplet over a Superhydrophobic Surface  

NASA Astrophysics Data System (ADS)

Aqueous droplet on a microtextured, superhydrophobic surface shows two distinct wetting behaviors, the Wenzel wetting and the Cassie-Baxter wetting. Most research efforts have focused on static energy arguments in which the overall surface energies of the Wenzel and Cassie-Baxter wetting states are compared to discern which is favored as a function of the surface topography and intrinsic surface energy. In this presentation we will construct a more relevant picture by examining the hydrodynamics of the wetting process on the scale of the topography. Our aim is to understand how the flow interacts with the topography to determine the wetting regime. We study the two dimensional spreading due to gravity of an aqueous drop over a well defined topographical pattern consisting of a periodic array of micron-sized posts. The flow in the droplet is assumed to be in the Stokes flow regime, and a boundary integral method is used for numerical solution with slip at the contact line and a velocity dependent relation for the dynamic wetting contact angle. The contact line shows a distinct slip-stick-jump (or slip-stick-penetration) motion over the topography determining the state of wetting.

Bhole, Nikhil; Maldarelli, Charles

2010-11-01

197

Reversible low adhesive to high adhesive superhydrophobicity transition on ZnO nanoparticle surfaces  

NASA Astrophysics Data System (ADS)

Superhydrophobic ZnO surfaces with water contact angle of 162° and sliding angle of 2° were fabricated successfully by spraying hydrophobic ZnO nanoparticle suspensions without limitations the shape and size of substrates. The as-prepared superhydrophobic ZnO surfaces are low adhesive and a water droplet easily rolls off with the surface slightly tilted. However, after being irradiated by UV light through a photomask, it becomes highly adhesive, on which a water droplet is firmly pinned without any movement. Further annealing the irradiated film, water droplets can roll off the surface again. Reversible transition between the low adhesive rolling state and high adhesive pinning state can be realized simply by UV illumination and heat treatment alternately. At the same time, the maximum adhesive force between the superhydrophobic ZnO surfaces and the water droplet changes from extreme low (˜5.1 ?N) to very high (˜136.1 ?N). When irradiated without a photomask, the surface became hydrophilic. Additionally, a water droplet can be transfered from the low adhesive superhydrophobic ZnO surfaces to the hydrophilic ZnO surfaces using the high adhesive superhydrophobic ZnO surfaces as a mechanical hand.

Li, Jian; Jing, Zhijiao; Yang, Yaoxia; Zha, Fei; Yan, Long; Lei, Ziqiang

2014-01-01

198

Underwater Restoration and Retention of Gases on Superhydrophobic Surfaces for Drag Reduction  

Microsoft Academic Search

Superhydrophobic (SHPo) surfaces have shown promise for passive drag reduction because their surface structures can hold a lubricating gas film between the solid surface and the liquid in contact with it. However, the types of SHPo surfaces that would produce any meaningful amount of reduction get wet under liquid pressure or at surface defects, both of which are unavoidable in

Choongyeop Lee; Chang-Jin Kim

2011-01-01

199

Electrochemical machining of super-hydrophobic Al surfaces and effect of processing parameters on wettability  

NASA Astrophysics Data System (ADS)

Super-hydrophobic aluminum (Al) surfaces were successfully fabricated via electrochemical machining in neutral NaClO3 electrolyte and subsequent fluoroalkylsilane (FAS) modification. The effects of the processing time, processing current density, and electrolyte concentration on the wettability, morphology, and roughness were studied. The surface morphology, chemical composition, and wettability of the Al surfaces were investigated using scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS), white-light interferometry, roughness measurements, X-ray diffraction (XRD), Fourier-transform infrared spectrometry (FTIR), and optical contact angle measurements. The results show that hierarchical rough structures and low surface energy films were present on the Al surfaces after electrochemical machining and FAS modification. The combination of the rough structures and the low surface energy materials plays a crucial role in achieving super-hydrophobicity. Compared with the anodic oxidation and chemical etching method, the method proposed in our work does not require strong acid or alkali, and causes less harm to the environment and operators but with high processing efficiency. The rough structures required by the super-hydrophobic surfaces were obtained at 30-s processing time and the best super-hydrophobicity with 164.6? water contact angle and 2? tilting angle was obtained at 360 s. The resulting super-hydrophobic Al surfaces have a long-time stability in air and an excellent resistance to corrosive liquids.

Song, Jin-long; Xu, Wen-ji; Liu, Xin; Lu, Yao; Sun, Jing

2012-09-01

200

Multimode multidrop serial coalescence effects during condensation on hierarchical superhydrophobic surfaces.  

PubMed

The prospect of enhancing the condensation rate by decreasing the maximum drop departure diameter significantly below the capillary length through spontaneous drop motion has generated significant interest in condensation on superhydrophobic surfaces (SHS). The mobile coalescence leading to spontaneous drop motion was initially reported to occur only on hierarchical SHS, consisting of both nanoscale and microscale topological features. However, subsequent studies have shown that mobile coalescence also occurs on solely nanostructured SHS. Thus, recent focus has been on understanding the condensation process on nanostructured surfaces rather than on hierarchical SHS. In this work, we investigate the impact of microscale topography of hierarchical SHS on the droplet coalescence dynamics and wetting states during the condensation process. We show that isolated mobile and immobile coalescence between two drops, almost exclusively focused on in previous studies, are rare. We identify several new droplet shedding modes, which are aided by tangential propulsion of mobile drops. These droplet shedding modes comprise of multiple droplets merging during serial coalescence events, which culminate in formation of a drop that either departs or remains anchored to the surface. We directly relate postmerging drop adhesion to formation of drops in nanoscale as well as microscale Wenzel and Cassie-Baxter wetting states. We identify the optimal microscale feature spacing of the hierarchical SHS, which promotes departure of the highest number of microdroplets. This optimal surface architecture consists of microscale features spaced close enough to enable transition of larger droplets into micro-Cassie state yet, at the same time, provides sufficient spacing in-between the features for occurrence of mobile coalescence. PMID:23259731

Rykaczewski, Konrad; Paxson, Adam T; Anand, Sushant; Chen, Xuemei; Wang, Zuankai; Varanasi, Kripa K

2013-01-22

201

A superhydrophobic surface with high performance derived from STA-APTES organic-inorganic molecular hybrid.  

PubMed

The chemical originals of natural superhydrophobic surfaces are based on botanic or animal wax or fat, which have poor chemical and thermal resistance. Herein, we report a simple chemical modification of stearic acid (STA) with ?-aminopropyl triethoxysilane (APTES), to obtain an organic-inorganic molecular hybrid STA-APTES compound. A flower-like hierarchically structured surface with superhydrophobicity can be obtained simply by casting the STA-APTES solution under ambient circumstance. The crystallization of the hydrocarbon chain from STA leads to the formation of the binary microstructure and reduces the surface tension, contributing to the superhydrophobicity of the as-formed surface. In addition, the condensation of Si(OCH2CH3)3 from APTES can lead to the cross-linking of the resultant surface, which endows the as-formed superhydrophobic surface with high performances, such as excellent thermal and solvent resistance, etc. This superhydrophobic surface prepared is superior to its many analogs in nature, promising a wide application especially in harsh circumstance. PMID:23895948

Si, Fangfang; Zhao, Ning; Chen, Li; Xu, Jian; Tao, Qingsheng; Li, Jinyong; Ran, Chunbo

2013-10-01

202

Linear abrasion of a titanium superhydrophobic surface prepared by ultrafast laser microtexturing  

NASA Astrophysics Data System (ADS)

A novel method of fabricating titanium superhydrophobic surfaces by ultrafast laser irradiation is reported. The ultrafast laser irradiation creates self-organized microstructure superimposed with nano-scale roughness, after which a fluoropolymer coating is applied to lower the surface energy of the textured surface and achieve superhydrophobicity. The focus of this study is to investigate abrasion effects on this mechanically durable superhydrophobic surface. The mechanical durability is analyzed with linear abrasion testing and microscopy imaging. Linear abrasion tests indicate that these surfaces can resist complete microstructure failure up to 200 abrasion cycles and avoid droplet pinning up to ten abrasion cycles at 108.4 kPa applied pressure, which roughly corresponds to moderate to heavy sanding or rubbing in the presence of abrasive particles. The wear mechanisms are also investigated and the primary mechanism for this system is shown to be abrasive wear with fatigue by repeated plowing. Although these results demonstrate an advancement in mechanical durability over the majority of existing superhydrophobic surfaces, it exemplifies the challenge in creating superhydrophobic surfaces with suitable mechanical durability for harsh applications, even when using titanium.

Steele, Adam; Nayak, Barada K.; Davis, Alexander; Gupta, Mool C.; Loth, Eric

2013-11-01

203

Superhydrophobic silver surface with dendrites structure on steel substrate by a facile electroless galvanic deposition process  

NASA Astrophysics Data System (ADS)

A simple electroless galvanic deposition process to prepare superhydrophobic surface on steel substrate is presented here. Micro- and nano roughness structure is generated on steel surface by the deposition of silver dendrites with nanoscale leaves. After modified with stearic acid, the as-prepared surface shows a remarkable superhydrophobicity with a high water contact angle (WCA) of 158° and a low sliding angle of about 2°. The surface also shows non-sticking properties to a 4 ?L water droplet. The cooperation of dendrites structure and stearic acid modification is responsible for the superhydrophobicty of the as-prepared surface. This simple and reliable method is of great significance to the large scale fabrication of superhydrophobic surfaces on steel substrate.

Guo, Feng; Su, Xunjia; Hou, Genliang; Li, Ping

2012-03-01

204

Superhydrophobic Stability of Nanotube Array Surfaces under Impact and Static Forces.  

PubMed

The surfaces of nanotube arrays were coated with poly(methyl methacrylate) (PMMA) using an imprinting method with an anodized alumina membrane as the template. The prepared nanotube array surfaces then either remained untreated or were coated with NH2(CH2)3Si(OCH3)3(PDNS) or CF3(CF2)7CH2CH2Si(OC2H5)3 (PFO). Thus, nanotube arrays with three different surfaces, PDNS, PMMA (without coating), and PFO, were obtained. All three surfaces (PDNS, PMMA, and PFO) exhibited superhydrophobic properties with contact angles (CA) of 155, 166, and 168°, respectively, and their intrinsic water contact angles were 30, 79, and 118°, respectively. The superhydrophobic stabilities of these three surfaces were examined under dynamic impact and static pressures in terms of the transition from the Cassie-Baxter mode to the Wenzel mode. This transition was determined by the maximum pressure (p(max)), which is dependent on the intrinsic contact angle and the nanotube density of the surface. A p(max) greater than 10 kPa, which is sufficiently large to maintain stable superhydrophobicity under extreme weather conditions, such as in heavy rain, was expected from the PFO surface. Interestingly, the PDNS surface, with an intrinsic CA of only 30°, also displayed superhydrophobicity, with a CA of 155°. This property was partially maintained under the dynamic impact and static pressure tests. However, under an extremely high pressure (0.5 MPa), all three surfaces transitioned from the Cassie-Baxter mode to the Wenzel mode. Furthermore, the lost superhydrophobicity could not be recovered by simply relieving the pressure. This result indicates that the best way to maintain superhydrophobicity is to increase the p(max) of the surface to a value higher than the applied external pressure by using low surface energy materials and having high-density binary nano-/microstructures on the surface. PMID:24873475

Zhu, Lin; Shi, Pan; Xue, Jian; Wang, Yuanyi; Chen, Qingmin; Ding, Jianfu; Wang, Qingjun

2014-06-11

205

Preparation of hybrid film with superhydrophobic surfaces based on irregularly structure by emulsion polymerization  

Microsoft Academic Search

A superhydrophobic surface originated from quincunx-shape composite particles was obtained by utilizing the encapsulation and graft of silica particles to control the surface chemistry and morphology of the hybrid film. The composite particles make the surface of film form a composite interface with irregular binary structure to trap air between the substrate surface and the liquid droplets which plays an

Ailan Qu; Xiufang Wen; Pihui Pi; Jiang Cheng; Zhuoru Yang

2007-01-01

206

Designing superhydrophobic surfaces using fluorosilsesquioxane-urethane hybrid and porous silicon gradients  

NASA Astrophysics Data System (ADS)

Here we describe a new class of near superhydrophobic surfaces formed using fluorinated polyhedral oligosilsesquioxane (FluoroPOSS) urethane hybrids and porous silicon gradients (pSi). We demonstrate that the surface segregation behavior of the hydrophobic fluoro component can be controlled by the type and nature of chain extender of the urethane and resultant hydrophobic association via intra or intermolecular aggregation. The surface film formed exhibits near superhydrophobicity. This work has significant potential for applications in antifouling and self-cleaning coatings, biomedical devices, microfluidic systems and tribological surfaces.

Kannan, Aravindaraj G.; McInnes, Steven J. P.; Choudhury, Namita R.; Dutta, Naba K.; Voelcker, Nicolas H.

2008-12-01

207

A thermodynamic approach for determining the contact angle hysteresis for superhydrophobic surfaces.  

PubMed

Contact angle hysteresis (CAH) is critical to superhydrophobicity of a surface. This study proposes a free energy thermodynamic analysis (of a 2-D model surface) that significantly simplifies calculations of free energy barrier associated with CAH phenomena. A microtextured surface with pillar structure, typical of one used in experimental studies, is used as an example. We demonstrate that the predicted CAH and equilibrium contact angles are consistent with experimental observations and predictions of Wenzel's and Cassie's equations, respectively. We also establish a criterion for transition between noncomposite and composite wetting states. The results and methodology presented can potentially be used for designing superhydrophobic surfaces. PMID:15979631

Li, W; Amirfazli, A

2005-12-01

208

The Effects of Superhydrophobic Surfaces on Turbulent Skin Friction and Flow Structure  

NASA Astrophysics Data System (ADS)

The application of superhydrophobic surfaces to the reduction of skin friction in turbulent flows is examined through experiments conducted in two facilities: the low-speed turbulent water channel at Brown University and the moderate speed (U = 8m/s) boundary layer facility at the Naval Undersea Warfare Center in Newport, RI (NUWC). High resolution PIV measurements are taken in the water channel at Brown University for both baseline (hydrophilic) and superhydrophobic surfaces. The mean and fluctuation velocity statistics are compared between the two surfaces. The friction velocity, u*, is estimated from the velocity fields using several independent methods. Direct drag and LDV measurements are taken for both the hydrophilic and superhydrophobic surfaces in the water tunnel at NUWC and will be discussed.

Peguero, Charles; Henoch, Charles; Breuer, Kenneth

2007-11-01

209

Superhydrophobic Surfaces for Turbulent Drag Reduction: Effect of Geometry and Reynolds Number  

NASA Astrophysics Data System (ADS)

Recently, it has been demonstrated that superhydrophobic surfaces are capable of reducing drag in turbulent flows. Superhydrophobic surfaces are chemically hydrophobic with micron or nanometer scale surface features which can support a shear-free air-water interface. In this talk, we will consider the effect of microfeature geometry and flow velocity on the observed drag reduction. Microridge geometries from 15?m to 60?m will be considered with shear free area ratios from 20% to 80%. Drag reductions are found to increase with increasing shear free area ratio up to 75%. For any given shear free area ratio, drag reduction was seen to initiate at lower Reynolds numbers for larger microfeature spacings. Experiments were conducted over the range of Reynolds numbers 1000superhydrophobic surfaces in the laminar regime and persists well past transition to turbulence.

Daniello, Robert; Rothstein, Jonathan P.

2009-11-01

210

Facile fabrication of superhydrophobic surfaces on zinc substrates by displacement deposition of Sn  

NASA Astrophysics Data System (ADS)

Facile preparation of superhydrophobic surfaces of stable and cheap metals is practically important. We report here our findings on fabrication of a superhydrophobic metal Sn surface, which can be obtained at room temperature in 5 min through a displacement reaction between a zinc plate and an acidic SnCl2 solution without needing post-treatment and surface modification. This procedure is facile, time-saving and inexpensive, which is superior to other known displacement depositions of Pt, Ag, Au, or Cu. The effects of preparation conditions on the surface morphology and wettability have been investigated in detail, including reactant concentration and reaction time. It has been observed that superhydrophobicity was closely related with the morphological transition from tin nanoparticles/nanopores to tin dendrites, and the maximal water contact angle (CA) was about 156° with the Cassie state. We expect that this fabrication technique will find practical applications.

Cao, Ling; Liu, Jun; Huang, Wei; Li, Zelin

2013-01-01

211

Fabrication of superhydrophobic polyurethane\\/organoclay nano-structured composites from cyclomethicone-in-water emulsions  

Microsoft Academic Search

Nano-structured polyurethane\\/organoclay composite films were fabricated by dispersing moisture-curable polyurethanes and fatty amine\\/amino-silane surface modified montmorillonite clay (organoclay) in cyclomethicone-in-water emulsions. Cyclomethicone Pickering emulsions were made by emulsifying decamethylcyclopentasiloxane (D5), dodecamethylcyclohexasiloxane (D6) and aminofunctional siloxane polymers with water using montmorillonite particles as emulsion stabilizers. Polyurethane and organoclay dispersed emulsions were spray coated on aluminum surfaces. Upon thermosetting, water repellent self-cleaning

I. S. Bayer; A. Steele; P. J. Martorana; E. Loth

2010-01-01

212

Water droplets' internal fluidity during horizontal motion on a superhydrophobic surface with an external electric field.  

PubMed

On a superhydrophobic surface, the internal fluidity of water droplets with different volumes (15, 30 microL) and their horizontal motion in an external electric field were evaluated using particle image velocimetry (PIV). For driving of water droplets on a superhydrophobic coating between parallel electrodes, it was important to place them at appropriate positions. Droplets moved with slipping. Small droplets showed deformation that is more remarkable. Results show that the dielectrophoretic force induced the initial droplet motion and that the surface potential gradient drove the droplets after reaching the middle point between electrodes. PMID:19924893

Sakai, Munetoshi; Kono, Hiroki; Nakajima, Akira; Sakai, Hideki; Abe, Masahiko; Fujishima, Akira

2010-02-01

213

Mimicking the stenocara beetle--dewetting of drops from a patterned superhydrophobic surface.  

PubMed

This paper describes the preparation of superhydrophobic surfaces that have been selectively patterned with circular hydrophilic domains. These materials mimicked the back of the stenocara beetle and collected drops of water if exposed to mist or fog. Under the effect of gravity, the drops dewetted from the hydrophilic regions once a critical volume had been reached. The surface energy in the hydrophilic regions was carefully controlled and assumed various values, allowing us to study the behavior of drops as a function of the superhydrophobic/hydrophilic contrast. We have investigated the development of drops and quantitatively analyzed the critical volumes as a function of several parameters. PMID:18489186

Dorrer, Christian; Rühe, Jürgen

2008-06-17

214

Electrostatic powder spraying process for the fabrication of stable superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

Nano-sized Al 2O 3 particles were modified by heptadecafluorodecyl trimethoxysilane and 2,3-epoxy propoxy propyl trimethoxysilicane to make it both hydrophobic and reactive. The reactive nano-particles were mixed with polyester resin containing curing agents and electrostatic sprayed on stainless steel substrates to obtain stable superhydrophobic coatings after curing. The water contact angle (WCA) on the hybrid coating is influenced by the content of Al 2O 3 particles in the coating. As the Al 2O 3 concentration in the coating was increased from 0% to 8%, WCA increased from 68° to 165°. Surface topography of the coatings was examined using scanning electron microscopy (SEM). Nano-particles covered on the coating surface formed continuous film with greatly enhanced roughness, which was found to be responsible for the superhydrophobicity. The method is simple and cost effective and can be used for preparing self-cleaning superhydrophobic coating on large areas.

Gu, Guotuan; Tian, Yuping; Li, Zhantie; Lu, Dongfang

2011-03-01

215

Air-directed attachment of coccoid bacteria to the surface of superhydrophobic lotus-like titanium  

Microsoft Academic Search

Superhydrophobic titanium surfaces fabricated by femtosecond laser ablation to mimic the structure of lotus leaves were assessed for their ability to retain coccoid bacteria. Staphylococcus aureus CIP 65.8, S. aureus ATCC 25923, S. epidermidis ATCC 14990 and Planococcus maritimus KMM 3738 were retained by the surface, to varying degrees. However, each strain was found to preferentially attach to the crevices

V. K. Truong; H. K. Webb; E. Fadeeva; B. N. Chichkov; A. H. F. Wu; R. Lamb; J. Y. Wang; R. J. Crawford; E. P. Ivanova

2012-01-01

216

Superhydrophobic surface fabricated by bulk photografting of acrylic acid onto high-density polyethylene  

Microsoft Academic Search

A superhydrophobic polymeric surface was prepared through a very simple bulk photografting method. A thin layer of acrylic acid (AA), a highly hydrophilic monomer, was sandwiched between two high-density polyethylene (HDPE) sheets, followed by UV irradiation for a short time, and then the two sheets were pulled apart and dried. The contact angles on the two grafted surfaces decreased very

Jianmei Han; Xiaoxiao Wang; Huiliang Wang

2008-01-01

217

Fabrication of superhydrophobic aluminium alloy surface with excellent corrosion resistance by a facile and environment-friendly method  

NASA Astrophysics Data System (ADS)

This work develops a facile and environment-friendly method for preparing the superhydrophobic aluminium alloy surface with excellent corrosion resistance. The superhydrophobic aluminium alloy surface is fabricated by the boiling water treatment and stearic acid (STA) modification. Results show that the boiling water treatment endows the aluminium alloy surface with a porous and rough structure, while STA modification chemically grafts the long hydrophobic alkyl chains onto the aluminium alloy surface. Just grounded on the micro- and nano-scale hierarchical structure along with the hydrophobic chemical composition, the superhydrophobic aluminium alloy surface is endued the excellent corrosion resistance.

Feng, Libang; Che, Yanhui; Liu, Yanhua; Qiang, Xiaohu; Wang, Yanping

2013-10-01

218

Fabrication and surface characterization of biomimic superhydrophobic copper surface by solution-immersion and self-assembly  

NASA Astrophysics Data System (ADS)

Biomimic superhydrophobic surfaces with contact angle greater than 150° and low sliding angle on copper substrate were fabricated by means of a facile solution immersion and surface self-assembly method. The scanning electron microscopy showed a nanoneedle structure copper surface with sporadic flower-like aggregates after treatment with sodium hydroxide and potassium persulfate solution. X-ray photoelectron spectroscopy and X-ray diffraction results confirmed that the formed nanoneedles were crystallized Cu(OH) 2. And the hydrophilic Cu(OH) 2 surface can be further modified into superhydrophobic through surface self-assembly with dodecanoic acid.

Yin, Shiheng; Wu, Dongxiao; Yang, Ji; Lei, Shumei; Kuang, Tongchun; Zhu, Bin

2011-08-01

219

A novel and expeditious method to fabricate superhydrophobic metal carboxylate surface  

NASA Astrophysics Data System (ADS)

This article has presented a novel method to fabricate superhydrophobic metal carboxylate surface on substrates like copper, ferrum, etc. This method markedly shortened the fabrication time to less than one second. The superhydrophobic effect is even better that the contact angle (CA) is 170±1° and the sliding angle (SA) <2°. Scanning electron microscopy (SEM) images showed micro-nano flower-like structures. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed that the flower-like structures are composed of Cu[CH3(CH2)12COO]2. The ethanol solution containing fatty acid and metal salt plays a key role in this method. This method has tremendous potentials in industrial production of superhydrophobic materials.

Li, Feng; Geng, Xingguo; Chen, Zhi; Zhao, Lei

2012-01-01

220

Capillary origami: superhydrophobic ribbon surfaces and liquid marbles  

PubMed Central

Summary In the wetting of a solid by a liquid it is often assumed that the substrate is rigid. However, for an elastic substrate the rigidity depends on the cube of its thickness and so reduces rapidly as the substrate becomes thinner as it approaches becoming a thin sheet. In such circumstances, it has been shown that the capillary forces caused by a contacting droplet of a liquid can shape the solid rather than the solid shaping the liquid. A substrate can be bent and folded as a (pinned) droplet evaporates or even instantaneously and spontaneously wrapped on contact with a droplet. When this effect is used to create three dimensional shapes from initially flat sheets, the effect is called capillary origami or droplet wrapping. In this work, we consider how the conditions for the spontaneous, capillary induced, folding of a thin ribbon substrate might be altered by a rigid surface structure that, for a rigid substrate, would be expected to create Cassie–Baxter and Wenzel effects. For smooth thin substrates, droplet wrapping can occur for all liquids, including those for which the Young’s law contact angle (defined by the interfacial tensions) is greater than 90° and which would therefore normally be considered relatively hydrophobic. However, consideration of the balance between bending and interfacial energies suggests that the tendency for droplet wrapping can be suppressed for some liquids by providing the flexible solid surface with a rigid topographic structure. In general, it is known that when a liquid interacts with such a structure it can either fully penetrate the structure (the Wenzel case) or it can bridge between the asperities of the structure (the Cassie–Baxter case). In this report, we show theoretically that droplet wrapping should occur with both types of solid–liquid contact. We also derive a condition for the transition between the Cassie–Baxter and Wenzel type droplet wrapping and relate it to the same transition condition known to apply to superhydrophobic surfaces. The results are given for both droplets being wrapped by thin ribbons and for solid grains encapsulating droplets to form liquid marbles.

Newton, Michael I; Shirtcliffe, Neil J; Geraldi, Nicasio R

2011-01-01

221

A simple solution-immersion process for the fabrication of superhydrophobic cupric stearate surface with easy repairable property  

NASA Astrophysics Data System (ADS)

The present work reports a simple and time-saving method to fabricate cupric stearate film on zinc substrate by a solution-immersion process. Superhydrophobic surfaces are conventionally prepared employing two steps: roughening a surface and lowering its surface energy. The fabrication of superhydrophobic cupric stearate surface is reported using a one-step process by immersing a zinc plate coated with copper into the stearic acid solution, simplifying the complexity of two different steps involved in the conventional methods. The surface of the zinc plate coated with copper is found to be covered with low surface energy cupric stearate film providing the water contact angle of 160 ± 1° with the rolling off properties. In addition, the damaged superhydrophobic surface can restore superhydrophobicity property by immersing the surface into the stearic acid solution again.

Li, Jian; Liu, Xiaohong; Ye, Yinping; Zhou, Huidi; Chen, Jianmin

2011-12-01

222

Dynamics of Nanostructures at Surfaces  

ScienceCinema

Currently, much effort is being devoted to the goal of achieving useful nanotechnologies, which depend on the ability to control and manipulate things on a very small scale. One promising approach to the construction of nanostructures is 'self-assembly', which means that under suitable conditions desired nanostructures might form automatically due to physical and chemical forces. Remarkably, the forces controlling such self-assembly mechanisms are only poorly understood, even though highly successful examples of self-assembly are known in nature (e.g., complex biochemical machinery regularly self-assembles in the conditions inside living cells). This talk will highlight basic measurements of fundamental forces governing the dynamics of nanostructures at prototypical metal surfaces. We use advanced surface microscopy techniques to track the motions of very small structures in real time and up to atomic resolution. One classic example of self-organized nanostructures are networks of surface dislocations (linear crystal defects). The direct observation of thermally activated atomic motions of dislocations in a reconstructed gold surface allows us to measure the forces stabilizing the remarkable long-range order of this nanostructure. In another example, the rapid migration of nano-scale tin crystals deposited on a pure copper surface was traced to an atomic repulsion between tin atoms absorbed on the crystal surface and bronze alloy formed in the footprint of the tin crystals. It is intriguing to consider the clusters as simple chemo-mechanical energy transducers, essentially tiny linear motors built of 100,000 Sn atoms. We can support this view by providing estimates of the power and energy-efficiency of these nano-motors.

223

Numerical investigation on drag reduction with superhydrophobic surfaces by lattice-Boltzmann method  

Microsoft Academic Search

The mechanism of drag reduction by using superhydrophobic surfaces whose contact angle is greater than 150° is still an open problem that needs to be investigated. The main purpose of this paper is to reveal how the pressure drop can be decreased. The lattice-Boltzmann method (LBM) is employed to investigate fluid flows through channels with different wettability conditions and topographical

Jing Cui; Weizhong Li; Wei-Haur Lam

2011-01-01

224

The Effects of Superhydrophobic Surfaces on Turbulent Skin Friction and Flow Structure  

Microsoft Academic Search

The application of superhydrophobic surfaces to the reduction of skin friction in turbulent flows is examined through experiments conducted in two facilities: the low-speed turbulent water channel at Brown University and the moderate speed (U = 8m\\/s) boundary layer facility at the Naval Undersea Warfare Center in Newport, RI (NUWC). High resolution PIV measurements are taken in the water channel

Charles Peguero; Charles Henoch; Kenneth Breuer

2007-01-01

225

A theoretical prediction of friction drag reduction in turbulent flow by superhydrophobic surfaces  

Microsoft Academic Search

We present a theoretical prediction for the drag reduction rate achieved by superhydrophobic surfaces in a turbulent channel flow. The predicted drag reduction rate is in good agreement with results obtained from direct numerical simulations at Retau~=180 and 400. The present theory suggests that large drag reduction is possible also at Reynolds numbers of practical interest (Retau~105-106) by employing a

Koji Fukagata; Nobuhide Kasagi; Petros Koumoutsakos

2006-01-01

226

Oblique impacts of water drops onto hydrophobic and superhydrophobic surfaces: outcomes, timing, and rebound maps  

NASA Astrophysics Data System (ADS)

This paper presents an experimental study on water drop oblique impacts onto hydrophobic and superhydrophobic tilted surfaces, with the objective of understanding drop impact dynamics and the conditions for drop rebound on low wetting surfaces. Drop impact experiments were performed with millimetric water drops with Weber numbers in the range 25 < We < 585, using different surfaces with advancing contact angles 111° < ? A < 160° and receding contact angles 104° < ? R < 155°. The analysis of oblique impacts onto tilted surfaces led to the definition of six different impact regimes: deposition, rivulet, sliding, rolling, partial rebound, and rebound. For superhydrophobic surfaces, surface tilting generally enhanced drop rebound and shedding from the surface, either by reducing drop rebound time up to 40 % or by allowing drop rebound even when impalement occurred in the vicinity of the impact region. On hydrophobic surfaces, rebound was never observed for tilt angles higher than 45°.

Antonini, C.; Villa, F.; Marengo, M.

2014-04-01

227

Fabrication of non-flaking, superhydrophobic surfaces using a one-step solution-immersion process on copper foams  

NASA Astrophysics Data System (ADS)

Non-flaking superhydrophobic surfaces were prepared using a simple one-step solution-immersion process on commercially obtained copper foam substrates. Copper foams were immersed in a 0.05 M ethanolic stearic acid solution at room temperature for several days. This formed coverage of copper stearate with micro- and nano-scale hierarchical surface morphology. The surface of the copper foam after 4 days of immersion demonstrates superhydrophobicity with a water contact angle of 156°. A sliding angel of 4° for a 5 ?L droplet indicates excellent non-sticking behavior. Compared with a flat copper plate, the superhydrophobic surfaces based on copper foams are much more robust and mechanically stable. This work provides a promising strategy for scalable fabrication of superhydrophobic surfaces on 3D porous structures.

Xu, Jia; Xu, Jinliang; Cao, Yang; Ji, Xianbing; Yan, Yuying

2013-12-01

228

Analysis of Stokes flow in microchannels with superhydrophobic surfaces containing a periodic array of micro-grooves  

Microsoft Academic Search

Superhydrophobic surfaces have been demonstrated to be capable of reducing fluid resistance in micro- and nanofluidic applications.\\u000a The objective of this paper is to present analytical solutions for the Stokes flow through microchannels employing superhydrophobic\\u000a surfaces with alternating micro-grooves and ribs. Results are presented for both cases where the micro-grooves are aligned\\u000a parallel and perpendicular to the flow direction. The

C. J. Teo; B. C. Khoo

2009-01-01

229

Superhydrophobic diatomaceous earth  

DOEpatents

A superhydrophobic powder is prepared by coating diatomaceous earth (DE) with a hydrophobic coating on the particle surface such that the coating conforms to the topography of the DE particles. The hydrophobic coating can be a self assembly monolayer of a perfluorinated silane coupling agent. The DE is preferably natural-grade DE where organic impurities have been removed. The superhydrophobic powder can be applied as a suspension in a binder solution to a substrate to produce a superhydrophobic surface on the substrate.

Simpson, John T. (Clinton, TN); D'Urso, Brian R. (Clinton, TN)

2012-07-10

230

Importance of hierarchical structures in wetting stability on submersed superhydrophobic surfaces.  

PubMed

Submersed superhydrophobic surfaces exhibit great potential for reducing flow resistance in microchannels and drag of submersed bodies. However, the low stability of liquid-air interfaces on those surfaces limits the scope of their application, especially under high liquid pressure. In this paper, we first investigate the wetting states on submersed hydrophobic surfaces with one-level structure under hydrostatic pressure. Different equilibrium states based on free-energy minimization are formulated, and their stabilities are analyzed as well. Then, by comparison with the existing numerical and experimental studies, we confirm that a new metastable state, which happens after depinning of the three-phase contact line (TCL), exists. Finally, we show that a strategy of using hierarchical structures can strengthen the TCL pinning of the liquid-air interface in the metastable state. Therefore, the hierarchical structure on submersed surfaces is important to further improve the stability of superhydrophobicity under high liquid pressure. PMID:22642584

Xue, Yahui; Chu, Shigan; Lv, Pengyu; Duan, Huiling

2012-06-26

231

Chemical control of superhydrophobicity of carbon nanotube surfaces: droplet pinning and electrowetting behavior.  

PubMed

We report the remarkable transformation of a superhydrophobic surface of multiwalled carbon nanotubes after chemical manipulation (functionalization, especially by ozonolysis), which leads to a pinning action and eventually hydrophilic behavior, upon the application of an electric field. The effect of droplet pinning on a hydrophobic surface is an indication of the Wenzel formalism, where it is assumed that the liquid fills up the space between the protrusions on the surface. Also, the ozonized bucky surfaces show fascinating electrowetting behavior in the presence of an electrolyte, which follows a transition from a superhydrophobic, Cassie-Baxter state to a hydrophilic, Wenzel state as a function of the electric field, this has been modelled using a simple approach and the corresponding interfacial capacitance has been determined. PMID:23800839

Kakade, Bhalchandra A

2013-08-01

232

Rapid fabrication of superhydrophobic surfaces on copper substrates by electrochemical machining  

NASA Astrophysics Data System (ADS)

Hierarchical micrometer-nanometer-scale binary rough structures were fabricated on copper substrates by electrochemical machining in a neutral NaCl electrolyte. The rough structures are composed of the micrometer scale potato-like structures and the nanometer scale cube-like structures. After modified by the fluoroalkylsilane, the copper surfaces reached superhydrophobicity with a water contact angle of 164.3° and a water tilting angle less than 9°. This method has a high processing efficiency which can take just 3 s to fabricate the roughness required by the superhydrophobic surface. The effect of the processing time on wettability of the copper surfaces was investigated in this paper. The possible mechanism of the formation of the hierarchical roughness was also proposed, and the wettability of the copper surfaces was discussed on the basis of the Cassie-Baxter theory.

Song, Jinlong; Xu, Wenji; Lu, Yao; Fan, Xujuan

2011-10-01

233

Simultaneous fabrication of superhydrophobic and superhydrophilic polyimide surfaces with low hysteresis.  

PubMed

Polyimide is of great interest in the field of MEMS and microtechnology. It is often used for its chemical, thermal, mechanical, and optical properties. In this paper, an original study is performed on controlled variation of polyimide film wettability. A two-step microtexturing method is developed to transform hydrophilic polyimide surfaces into a superhydrophobic surface with low magnitude of hysteresis (?? ? 0° and contact angle ? ? 158°). This method is based on the conception of a new kind of fakir surface with triangular cross-section micropillars, the use of a two-scale roughening, and a C(4)F(8) coating. We demonstrate that the absence of hysteresis is related to a combination of two scales of structuring and the pillar shape. The technology that has been developed results in the simultaneous fabrication of adjacent superhydrophobic and superhydrophilic small areas, which allows an effect of self-positioning of water droplets when deposited on such a checkerboard-like surface. PMID:21520916

Scheen, Gilles; Ziouche, Katir; Bougrioua, Zahia; Godts, Pascale; Leclercq, Didier; Lasri, Tuami

2011-05-17

234

Experimental drag reduction study of super-hydrophobic surface with dual-scale structures  

NASA Astrophysics Data System (ADS)

Hydrophobic surfaces with micro- or nanoscale pillars have been attracting considerable interest from scientists. In nature, such surfaces can be found on lotus leaves or under the feet of pond skaters. One significant property of these surfaces is friction drag reduction (FDR). Many studies have been conducted to demonstrate this reduction in terms of laminar and turbulent flows. The slip-length hypothesis is often used to explain this phenomenon. In this study, processes with the advantages of simplicity and cost effectiveness were used to fabricate dual-scale structures. Durable super-hydrophilic and super-hydrophobic surfaces were easily obtained from these structures. FDR was measured on a super-hydrophobic surface and was compared to that on smooth and super-hydrophilic surfaces. The experimental results in a circulating water channel revealed the Reynolds number range within which substantial FDR can occur on a super-hydrophobic surface. The mechanism of FDR and the role of slip are discussed by comparing experimental results.

Lyu, Sungnam; Nguyen, Dang C.; Kim, Dongseob; Hwang, Woonbong; Yoon, Bumsang

2013-12-01

235

A simple way to achieve pattern-dependent tunable adhesion in superhydrophobic surfaces by a femtosecond laser.  

PubMed

In this paper, we present a new approach to the tunable adhesive superhydrophobic surfaces consisting of periodic hydrophobic patterns and superhydrophobic structures by femtosecond (fs) laser irradiation on silicon. The surfaces are composed of periodic hydrophobic patterns (triangle, circle, and rhombus) and superhydrophobic structures (dual-scale spikes induced by a fs laser). Our results reveal that the adhesive forces of as-prepared surfaces can be tuned by varying the area ratio (AR(s-h)) of superhydrophobic domain to hydrophobic domain, thus resulting in tunable static and dynamic wettabilities. By increasing AR(s-h), (i) the static wetting property, which is characterized by the minimum water droplet volume that enables a droplet to land on the surface, can be tailored from 1 ?L to 9 ?L; (ii) the sliding angle can be flexibly adjusted, ranging from >90° (a droplet cannot slide off when the sample is positioned upside down) to 5°; and (iii) the droplet rebound behaviors can be modulated from partial rebound to triple rebound. In addition, the Cassie-Baxter model and the sliding angle model are used to speculate the contact angles and sliding angles to provide potentially theoretical models to design slippery-to-sticky superhydrophobic surfaces. The tunable adhesive superhydrophobic surfaces achieved by fs laser microfabrication may be potentially used in microfluidic systems to modulate the mobility of liquid droplets. PMID:22909564

Zhang, Dongshi; Chen, Feng; Yang, Qing; Yong, Jiale; Bian, Hao; Ou, Yan; Si, Jinhai; Meng, Xiangwei; Hou, Xun

2012-09-26

236

A theoretical prediction of friction drag reduction in turbulent flow by superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

We present a theoretical prediction for the drag reduction rate achieved by superhydrophobic surfaces in a turbulent channel flow. The predicted drag reduction rate is in good agreement with results obtained from direct numerical simulations at Re?~=180 and 400. The present theory suggests that large drag reduction is possible also at Reynolds numbers of practical interest (Re?~105-106) by employing a hydrophobic surface, which induces a slip length on the order of ten wall units or more.

Fukagata, Koji; Kasagi, Nobuhide; Koumoutsakos, Petros

2006-05-01

237

Chemical control of superhydrophobicity of carbon nanotube surfaces: droplet pinning and electrowetting behavior  

NASA Astrophysics Data System (ADS)

We report the remarkable transformation of a superhydrophobic surface of multiwalled carbon nanotubes after chemical manipulation (functionalization, especially by ozonolysis), which leads to a pinning action and eventually hydrophilic behavior, upon the application of an electric field. The effect of droplet pinning on a hydrophobic surface is an indication of the Wenzel formalism, where it is assumed that the liquid fills up the space between the protrusions on the surface. Also, the ozonized bucky surfaces show fascinating electrowetting behavior in the presence of an electrolyte, which follows a transition from a superhydrophobic, Cassie-Baxter state to a hydrophilic, Wenzel state as a function of the electric field, this has been modelled using a simple approach and the corresponding interfacial capacitance has been determined.We report the remarkable transformation of a superhydrophobic surface of multiwalled carbon nanotubes after chemical manipulation (functionalization, especially by ozonolysis), which leads to a pinning action and eventually hydrophilic behavior, upon the application of an electric field. The effect of droplet pinning on a hydrophobic surface is an indication of the Wenzel formalism, where it is assumed that the liquid fills up the space between the protrusions on the surface. Also, the ozonized bucky surfaces show fascinating electrowetting behavior in the presence of an electrolyte, which follows a transition from a superhydrophobic, Cassie-Baxter state to a hydrophilic, Wenzel state as a function of the electric field, this has been modelled using a simple approach and the corresponding interfacial capacitance has been determined. Electronic supplementary information (ESI) available: Elemental analysis, TGA studies. See DOI: 10.1039/c3nr01359f

Kakade, Bhalchandra A.

2013-07-01

238

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

Microsoft Academic Search

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

D. K. Sarkar; M. Farzaneh; R. W. Paynter

2008-01-01

239

Laser induced surface modification of polydimethylsiloxane as a super-hydrophobic material  

Microsoft Academic Search

In order to render the surface of polydimethylsiloxane (PDMS) super-hydrophobic without changing its bulk properties, a PDMS film without photosensitizer was exposed to CO2 pulsed laser, at room temperature, as the excitation source. The modified surfaces have been studied by performing scanning electron microscopy (SEM) combined with energy dispersive X-ray analysis (EDXA) and attenuated total reflectance infrared (ATR-IR) spectroscopy. To

M. T. Khorasani; H. Mirzadeh; P. G. Sammes

1996-01-01

240

Modeling drag reduction and meniscus stability of superhydrophobic surfaces comprised of random roughness  

NASA Astrophysics Data System (ADS)

Previous studies dedicated to modeling drag reduction and stability of the air-water interface on superhydrophobic surfaces were conducted for microfabricated coatings produced by placing hydrophobic microposts/microridges arranged on a flat surface in aligned or staggered configurations. In this paper, we model the performance of superhydrophobic surfaces comprised of randomly distributed roughness (e.g., particles or microposts) that resembles natural superhydrophobic surfaces, or those produced via random deposition of hydrophobic particles. Such fabrication method is far less expensive than microfabrication, making the technology more practical for large submerged bodies such as submarines and ships. The present numerical simulations are aimed at improving our understanding of the drag reduction effect and the stability of the air-water interface in terms of the microstructure parameters. For comparison and validation, we have also simulated the flow over superhydrophobic surfaces made up of aligned or staggered microposts for channel flows as well as streamwise or spanwise ridges configurations for pipe flows. The present results are compared with theoretical and experimental studies reported in the literature. In particular, our simulation results are compared with work of Sbragaglia and Prosperetti, and good agreement has been observed for gas fractions up to about 0.9. The numerical simulations indicate that the random distribution of surface roughness has a favorable effect on drag reduction, as long as the gas fraction is kept the same. This effect peaks at about 30% as the gas fraction increases to 0.98. The stability of the meniscus, however, is strongly influenced by the average spacing between the roughness peaks, which needs to be carefully examined before a surface can be recommended for fabrication. It was found that at a given maximum allowable pressure, surfaces with random post distribution produce less drag reduction than those made up of staggered posts.

Samaha, Mohamed A.; Vahedi Tafreshi, Hooman; Gad-El-Hak, Mohamed

2011-01-01

241

Vicinal surfaces for functional nanostructures.  

PubMed

Vicinal surfaces are currently the focus of research. The regular arrangements of atomic steps on a mesoscopic scale reveal the possibility to functionalize these surfaces for technical applications, e.g. nanowires, catalysts, etc. The steps of the vicinal surface are well-defined defect structures of atomic size for nucleation of low-dimensional nanostructures. The concentration and therefore the coupling between the nanostructures can be tuned over a wide range by simply changing the inclination angle of the substrate. However, the coupling of these nano-objects to the substrate is just as important in controlling their electronic or chemical properties and making a functionality useable. On the basis of stepped insulating films, these aspects are fulfilled and will be considered in the first part of this review. Recent results for the epitaxial growth of wide bandgap insulating films (CaF(2), MgO, NaCl, BaSrO) on metallic and semiconducting vicinal substrates (Si(100), Ge(100), Ag(100)) will be presented. The change of the electronic structure, the adsorption behavior as well as the kinetics and energetics of color centers in the presence of steps is discussed. The successful bridging of the gap between the atomic and mesoscopic world, i.e. the functionalization of vicinal surfaces by nanostructures, is demonstrated in the second part by metal adsorption on semiconducting surfaces. For (sub)monolayer coverage these systems have in common that the surface states do not hybridize with the support, i.e. the semiconducting surfaces are insulating. Here I will focus on the latest results of macroscopic transport measurements on Pb quantum wires grown on vicinal Si(111) showing indeed a one-dimensional transport behavior. PMID:21817211

Tegenkamp, Christoph

2009-01-01

242

Probing microscopic wetting properties of superhydrophobic surfaces by vibrated micrometer-sized droplets.  

PubMed

We determine contact angles of micrometer-sized NaCl-water droplets on superhydrophobic surfaces by analyzing their lowest-order axisymmetric vibrational resonances driven by vertical oscillations of the surface. Fluorescence spectra of the dye-doped droplets excited by laser light feature whispering-gallery modes (WGMs) whose spectral widths depend on the droplet vibration amplitude, thus enabling precise measurements of the droplet mechanical resonant frequency. Following droplet size determination by WGM mode-matching, we calculate the contact angles from the dependence of the measured mechanical resonant frequency on the droplet size for two surfaces with different superhydrophobicity levels, and find a good correlation with the values measured by direct imaging of millimeter-sized droplets. PMID:21280575

Jonáš, Alexandr; Karadag, Yasin; Tasaltin, Nevin; Kucukkara, Ibrahim; Kiraz, Alper

2011-03-15

243

Facile fabrication of superhydrophobic polytetrafluoroethylene surface by cold pressing and sintering  

NASA Astrophysics Data System (ADS)

A series of superhydrophobic polytetrafluoroethylene (PTFE) surfaces were prepared by a facile cold pressing and sintering method, and their microstructures and wetting behaviors could be artificially tailored by altering sintering temperature and using different masks. Specifically, the microstructures mainly depended on the sintering temperature, whereas the wetting behaviors, water contact angle (WCA) and sliding angle (SA), greatly hinged on both the sintering temperature and mask. Then a preferable superhydrophobic surface with WCA of 162 ± 2° and SA of 7° could be obtained when the sintering temperature was 360 °C and the 1000 grit abrasive paper was used as a mask. In addition, it was worth noting that the as-prepared surfaces exhibited excellent stability under UV illumination, which was the most key factor for them toward practical applications.

Jiang, Cheng; Hou, Weixin; Wang, Qihua; Wang, Tingmei

2011-03-01

244

Role of nanoparticles in phase separation and final morphology of superhydrophobic polypropylene/zinc oxide nanocomposite surfaces  

NASA Astrophysics Data System (ADS)

In this work, phase separation process was revisited to study the effect of nanoparticles in acceleration of phase separation and formation of hierarchical structures. Superhydrophobic surfaces were prepared using polypropylene (PP) and the corresponding nanocomposites containing zinc oxide (ZnO) nanoparticles through a typical solution casting method. The wettability and morphological behavior of the surfaces were investigated via water contact angle (WCA) measurements and scanning electron microscopy (SEM), respectively. It was found that upon introduction of ZnO nanoparticles into the pure PP, the obtained surfaces have become superhydrophobic with WCAs above 150° and sliding angles below 10°. Calcination of ZnO nanoparticles was exploited to explicate the unexpected significant loss in superhydrophobicity of the sample loaded with high ZnO content. Crystallization behavior of the samples were also investigated via differential scanning calorimetry and correlated to superhydrophobicity of the surfaces. X-ray photoelectron and Fourier transform infrared spectroscopies were also utilized to further characterize the samples. An attempt was also made to present a more clear mechanism for formation of hierarchical structures which are responsible for superhydrophobicity. Likewise, the so far proposed mechanisms for formation of micro/nano roughness on the superhydrophobic surfaces were reviewed as well.

Hejazi, Iman; Hajalizadeh, Bardia; Seyfi, Javad; Sadeghi, Gity Mir Mohamad; Jafari, Seyed-Hassan; Khonakdar, Hossein Ali

2014-02-01

245

One-step process for superhydrophobic metallic surfaces by wire electrical discharge machining.  

PubMed

We present a direct one-step method to fabricate dual-scale superhydrophobic metallic surfaces using wire electrical discharge machining (WEDM). A dual-scale structure was spontaneously formed by the nature of exfoliation characteristic of Al 7075 alloy surface during WEDM process. A primary microscale sinusoidal pattern was formed via a programmed WEDM process, with the wavelength in the range of 200 to 500 ?m. Notably, a secondary roughness in the form of microcraters (average roughness, Ra: 4.16 to 0.41 ?m) was generated during the exfoliation process without additional chemical treatment. The low surface energy of Al 7075 alloy (? = 30.65 mJ/m(2)) together with the presence of dual-scale structures appears to contribute to the observed superhydrophobicity with a static contact angle of 156° and a hysteresis less than 3°. To explain the wetting characteristics on dual-scale structures, we used a simple theoretical model. It was found that Cassie state is likely to present on the secondary roughness in all fabricated surfaces. On the other hand, either Wenzel or Cassie state can present on the primary roughness depending on the characteristic length of sinusoidal pattern. In an optimal condition of the serial cutting steps with applied powers of ?30 and ?8 kW, respectively, a stable, superhydrophobic metallic surface was created with a sinusoidal pattern of 500 ?m wavelength. PMID:22732181

Bae, Won Gyu; Song, Ki Young; Rahmawan, Yudi; Chu, Chong Nam; Kim, Dookon; Chung, Do Kwan; Suh, Kahp Y

2012-07-25

246

A fast method to fabricate superhydrophobic surfaces on zinc substrate with ion assisted chemical etching  

NASA Astrophysics Data System (ADS)

A metal assisted chemical etching process was proposed to rapidly fabricate super-hydrophobic surfaces on Zn substrates. The influence of three assisting metal ions (Ag+, Cu2+, Cr3+) on the morphology of the fabricated surfaces, and their hydrophobicity after modification by fluorosilane, were studied. This work indicates that the metal ions play an important role on the structure and the hydrophobicity of the prepared surfaces. The rough structure required for super-hydrophobic surfaces, with contact angles of 158 ± 2° and 161 ± 2°, respectively, can be easily obtained within 5 s with Cu2+ or Ag+ assisted chemical etching process. The treatment conditions of Cu2+ assisted chemical etching method were optimized. The sample with the highest contact angle can be achieved when the concentration of Cu(NO3)2 is 0.08 mol L-1, the concentration of HNO3 is 0.6 mol L-1, and the etching time is 5 s at 30 °C. And the prepared superhydrophobic surfaces exhibited enough stability in the air.

Qi, Yi; Cui, Zhe; Liang, Bin; Parnas, Richard S.; Lu, Houfang

2014-06-01

247

Superhydrophobic surfaces produced by applying a self-assembled monolayer to silicon micro\\/nano-textured surfaces  

Microsoft Academic Search

A novel way of producing superhydrophobic surfaces by applying a self-assembled monolayer (SAM) to silicon micro\\/nano-textured\\u000a surfaces is presented in this paper. The micro\\/nano-textured surfaces on silicon substrates were generated by the aluminum-induced\\u000a crystallization (AIC) of amorphous silicon (a-Si) technique. Octadecyltrichlorosilane (OTS) SAMs were then applied to the\\u000a textured surfaces by dip coating. The topography and wetting properties of the

Yong Song; Rahul Premachandran Nair; Min Zou; Yongqiang Wang

2009-01-01

248

Surface hydrophobic co-modification of hollow silica nanoparticles toward large-area transparent superhydrophobic coatings.  

PubMed

The present paper reports a novel, simple, and efficient approach to fabricate transparent superhydrophobic coatings on glass substrates by spray-coating stearic acid (STA) and 1H,1H,2H,2H-perflurooctyltriethoxysilane (POTS) co-modified hollow silica nanoparticles (SPHSNs), the surfaces of which were hydrophobic. The surface wettability of coatings was dependent on the conditions of post-treatment: the water contact angle of coating increased and then leveled off with increase in either the drying temperature or the drying time. When the coating was treated at 150°C for 5h, the water contact angle was as high as 160° and the sliding angle was lower than 1°, reaching excellent superhydrophobicity. They remained 159° and ?1°, respectively, even after 3months storage under indoor conditions (20°C, 20%RH), demonstrating the long time stability of coating superhydrophobicity. The coating was robust both to the impact of water droplets (297 cm/s) and to acidic (pH=1) and basic (pH=14) droplets. It showed good transparency in the visible-near infrared spectral range, and the maximum transmittance reached as high as 89%. Fourier transform infrared spectroscopy, transmission electron microscopy, differential scanning calorimetry, and thermogravimetric analysis were used to investigate the interactions among STA, POTS, and hollow silica nanoparticles (HSNs). Scanning electron microscopy and atomic force microscopy were used to observe and estimate the morphology and surface roughness of coatings. Optical properties were characterized by a UV-visible-near infrared spectrophotometer. Surface wettability was studied by a contact angle/interface system. The enhancement of hydrophobicity to superhydrophobicity by post-treatment was discussed based on the transition from the Wenzel state to the Cassie state. PMID:23433522

Gao, Liangjuan; He, Junhui

2013-04-15

249

Characterization of Si Nanostructured Surfaces  

SciTech Connect

Surface texturing of Si to enhance absorption particularly in the IR spectral region has been extensively investigated. Previous research chiefly examined approaches based on geometrical optics. These surface textures typically consist of pyramids with dimensions much larger than optical wavelengths. We have investigated a physical optics approach that relies on surface texture features comparable to, or smaller than, the optical wavelengths inside the semiconductor material. Light interaction at this are strongly dependent on incident polarization and surface profile. Nanoscale textures can be tuned for either narrow band, or broad band absorptive behavior. Lowest broadband reflection has been observed for triangular profiles with linewidths significantly less than 100 nm. Si nanostructures have been integrated into large ({approximately}42 cm{sup 2}) area solar cells, Internal quantum efficiency measurements in comparison with polished and conventionally textured cells show lower efficiency in the UV-visible (350-680 mu), but significantly higher IR (700-1200 nm) efficiency.

Brueck, S.R.J.; Gee, James M.; Ruby, Douglas S.; Zaidi, Saleem H.

1999-07-20

250

Fabrication of superhydrophobic surfaces from microstructured ZnO-based surfaces via a wet-chemical route.  

PubMed

The fabrication of a superhydrophobic surface is demonstrated via a wet chemical route, and this method offers advantages of being cleanroom free, cost efficiency, and wide applicability. The preferable growth of ZnO crystalline forms a microstructured surface, and a variety of alkanoic acids were adopted to tune the surface wettability. Although all surfaces show an advancing contact angle greater than 150 degrees , they substantially differ in the wetting mechanisms. It is found that only when the length of alkanoic acid is greater than 16, the microstructured surface shows a stable superhydrophobicity, in which the Cassie state dominates. While for those moderate-length alkanoic acids (C8-C14), their corresponding surfaces have a tendency to fall into the Wenzel state and display a great contact angle hysteresis. PMID:15779932

Wu, Xuedong; Zheng, Lijun; Wu, Dan

2005-03-29

251

Fabrication of superhydrophobic surface of hierarchical ZnO thin films by using stearic acid  

NASA Astrophysics Data System (ADS)

Flower-like hierarchical ZnO microspheres were successfully synthesized by a simple, template-free, and low-temperature aqueous solution route. The morphology and microstructure of the ZnO microspheres were examined by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The bionic films with hydrophobicity were fabricated by the hierarchical ZnO microspheres modified by stearic acid. It was found that the hydrophobicity of the thin films was very sensitive to the added amount of stearic acid. The thin films modified with 8% stearic acid took on strong superhydrophobicity with a water contact angle (CA) almost to be 178° and weak adhersion. The remarkable superhydrophobicity could be attributed to the synergistic effect of micro/nano hierarchical structure of ZnO and low surface energy of stearic acid.

Wang, Yanfen; Li, Benxia; Xu, Chuyang

2012-01-01

252

Superhydrophobic surfaces based on dandelion-like ZnO microspheres  

NASA Astrophysics Data System (ADS)

This study presents a simple method to fabricate superhydrophobic surface based on ZnO nanoneedles. ZnO nanoneedles had been constructed on zinc layers by immersing in an aqueous NH 4OH solution at 80 °C. The ZnO films were characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. The ZnO films exhibited excellent superhydrophilicity (contact angle for water was 0°), while they changed wettability to superhydrophobicity with a water contact angle greater than 150° after further chemical modification with n-dodecanoic acid. The procedure reported here only needs readily available reagents and laboratory equipments, which can be applied to various substrates of any size and shape.

Pan, Qinmin; Cheng, Yuexiang

2009-01-01

253

Sticking of droplets on slippery superhydrophobic surfaces by laser induced forward transfer  

NASA Astrophysics Data System (ADS)

Liquid jets created by the Laser Induced Forward Transfer (LIFT) technique can reach extremely high speeds exceeding 270 m/s. The impact of such a jet on a solid surface can create a dynamic pressure of 35 MPa, enabling the LIFT process to stick liquid droplets on highly slippery superhydrophobic surfaces. In this letter, we demonstrate how LIFT printing can be utilized in order to achieve selective sticky behavior on slippery surfaces, valuable for many biosensor applications, and we suggest it as a tool of evaluating the thermodynamic robustness of the so called Fakir states on various rough hydrophobic surfaces.

Boutopoulos, Christos; Papageorgiou, Dimitrios P.; Zergioti, Ioanna; Papathanasiou, Athanasios G.

2013-07-01

254

Fabrication of microcavity-array superhydrophobic surfaces using an improved template method.  

PubMed

We fabricated the first superhydrophobic (SH) surface with microcavities, using a simple process. The process included an improved template method (ITM) for constructing the SH surface with cavities, using taro leaves as a pattern mask, and a dip-coating method for modifying the SH surface. The results obtained using the ITM are significantly better than those achieved using traditional template methods. In addition, the water-repellence of the microcavities surface was significantly enhanced by decorating with a layer of polymerized n-octadecylsiloxane nanosheets. PMID:23332936

Peng, PanPan; Ke, Qingping; Zhou, Gen; Tang, Tiandi

2013-04-01

255

Experimental investigation of inclined liquid water jet flow onto vertically located superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

In this study, the behaviour of an inclined water jet, which is impinged onto hydrophobic and superhydrophobic surfaces, has been investigated experimentally. Water jet was impinged with different inclination angles (15°-45°) onto five different hydrophobic surfaces made of rough polymer, which were held vertically. The water contact angles on these surfaces were measured as 102°, 112°, 123°, 145° and 167° showing that the last surface was superhydrophobic. Two different nozzles with 1.75 and 4 mm in diameters were used to create the water jet. Water jet velocity was within the range of 0.5-5 m/s, thus the Weber number varied from 5 to 650 and Reynolds number from 500 to 8,000 during the experiments. Hydrophobic surfaces reflected the liquid jet depending on the surface contact angle, jet inclination angle and the Weber number. The variation of the reflection angle with the Weber number showed a maximum value for a constant jet angle. The maximum value of the reflection angle was nearly equal to half of the jet angle. It was determined that the viscous drag decreases as the contact angle of the hydrophobic surface increases. The drag force on the wall is reduced dramatically with superhydrophobic surfaces. The amount of reduction of the average shear stress on the wall was about 40%, when the contact angle of the surface was increased from 145° to 167°. The area of the spreading water layer decreased as the contact angle of the surface increased and as the jet inclination angle, Weber number and Reynolds number decreased.

Kibar, Ali; Karabay, Hasan; Yi?it, K. Süleyman; Ucar, Ikrime O.; Erbil, H. Y?ld?r?m

2010-11-01

256

Super-hydrophobic yolk-shell nanostructure with enhanced catalytic performance in the reduction of hydrophobic nitroaromatic compounds.  

PubMed

A self-templating method to fabricate a super-hydrophobic yolk-shell nano-reactor was reported. Metal nanoparticles were encapsulated in the porous super-hydrophobic shell. This super-hydrophobic catalyst showed excellent performance in the reduction of nitroaromatic compounds in aqueous phase and a positive correlation was found between the reaction rate and the hydrophobicity of the substrate. PMID:24018894

Shi, Song; Wang, Min; Chen, Chen; Gao, Jin; Ma, Hong; Ma, Jiping; Xu, Jie

2013-10-25

257

Toward Superhydrophobic and Durable Coatings: Effect of Needle vs Crater Surface Architecture.  

PubMed

Practical application of sol-gel derived superhydrophobic films is limited by the fragility of "needlelike" surface roughness. An efficient one step procedure is developed to prepare robust thin films with "craterlike" surface roughness from a methyltrimethoxysilane matrix and polymer sphere templates. The films could be readily spray coated to produce roughened surface textures, which are governed by template concentration and geometry. The effect of this on the wettability and robustness of thin films was examined in detail, revealing a rapid trade-off between the two characteristics due to variations in coating porosity. PMID:24830848

Dyett, Brendan P; Wu, Alex H; Lamb, Robert N

2014-06-25

258

Super-hydrophobic surfaces of layer-by-layer structured film-coated electrospun nanofibrous membranes  

NASA Astrophysics Data System (ADS)

We have recently fabricated super-hydrophobic membrane surfaces based on the inspiration of self-cleaning silver ragwort leaves. This biomimetic super-hydrophobic surface was composed of fluoroalkylsilane (FAS)-modified layer-by-layer (LBL) structured film-coated electrospun nanofibrous membranes. The rough fibre surface caused by the electrostatic LBL coating of TiO2 nanoparticles and poly(acrylic acid) (PAA) was used to imitate the rough surface of nanosized grooves along the silver ragwort leaf fibre axis. The results showed that the FAS modification was the key process for increasing the surface hydrophobicity of the fibrous membranes. Additionally, the dependence of the hydrophobicity of the membrane surfaces upon the number of LBL coating bilayers was affected by the membrane surface roughness. Moreover, x-ray photoelectron spectroscopy (XPS) results further indicated that the surface of LBL film-coated fibres absorbed more fluoro groups than the fibre surface without the LBL coating. A (TiO2/PAA)10 film-coated cellulose acetate nanofibrous membrane with FAS surface modification showed the highest water contact angle of 162° and lowest water-roll angle of 2°.

Ogawa, Tasuku; Ding, Bin; Sone, Yuji; Shiratori, Seimei

2007-04-01

259

Fabrication of lotus-leaf-like superhydrophobic surfaces via Ni-based nano-composite electro-brush plating  

NASA Astrophysics Data System (ADS)

Superhydrophobic surface has become a research hot topic in recent years due to its excellent performance and wide application prospect. This paper investigates the method to fabricate superhydrophobic surface on carbon steel substrate via two-layer nano-composite electro-brush plating and subsequent surface modification with low free energy materials. The hydrophobic properties of as-prepared coatings were characterized by a water sliding angle (SA) and a water contact angle (CA) measured by the Surface tension instrument. A Scanning electron microscope was used to analyze the surface structure of plating coatings. Anti-corrosion performance of the superhydrophobic coating was characterized by a potentiodynamic polarization curve measured by the Electrochemical workstation. The research result shows that: the superhydrophobic structure can be successfully prepared by plating nano-C/Ni and nano-Cu/Ni two-layer coating on carbon steel substrate under appropriate technology and has similarity with lotus-leaf-like micro/nano composite structure; the contact angle of the as-prepared superhydrophobic coating can be up to 155.5°, the sliding angle is 5°; the coating has better anti-corrosion performance compared with substrate.

Liu, Hongtao; Wang, Xuemei; Ji, Hongmin

2014-01-01

260

Superhydrophobicity â The Lotus Effect  

NSDL National Science Digital Library

Students are introduced to superhydrophobic surfaces and the "lotus effect." Water spilled on a superhydrophobic surface does not wet the surface, but simply rolls off. Additionally, as water moves across the superhydrophobic surface, it picks up and carries away any foreign material, such as dust or dirt. Students learn how plants create and use superhydrophobic surfaces in nature and how engineers have created human-made products that mimic the properties of these natural surfaces. They also learn about the tendency of all superhydrophobic surfaces to develop water droplets that do not roll off the surface but become "pinned" under certain conditions, such as water droplets formed from condensation. They see how the introduction of mechanical energy can "unpin" these water droplets and restore the desirable properties of the superhydrophobic surface.

NSF CAREER Award and RET Program, Mechanical Engineering and Material Science,

261

Selective transportation of microdroplets assisted by a superhydrophobic surface with pH-responsive adhesion.  

PubMed

We report a new strategy to realize the selective transportation of microdroplets assisted by a superhydrophobic surface with pH-responsive adhesion. On the surface, only basic microdroplets can be pinned and acidic or neutral microdroplets can easily roll off. Therefore, by using the surface as a "mechanical hand", microdroplets can be transported selectively according to one's requirements by simply controlling the pH of the solution. The special ability of the surface to achieve selective transportation is ascribed to the following two reasons: 1) superhydrophobicity, which can avoid the wetting problem, and 2) pH-responsive adhesion, which results from the combined effect of chemical variation of the carboxylic acid group and microstructures on the surface. Furthermore, we also demonstrated a process of selective transportation of microdroplets for applications in droplet-based microreactors through our surface. The results reported herein advance a new method to realize the selective transportation of microdroplets and we believe that this method could potentially be used in a wide range of applications, such as biomolecular detection and transportation in biochips. PMID:24273121

Cheng, Zhongjun; Du, Ming; Lai, Hua; Du, Ying; Zhang, Naiqing; Sun, Kening

2013-12-01

262

Stability of the hydrophilic and superhydrophobic properties of oxygen plasma-treated poly(tetrafluoroethylene) surfaces.  

PubMed

Poly(tetrafluoroethylene) (PTFE) materials were exposed to low and high-energy oxygen plasma, and the stability of the materials' surface was evaluated using contact angle, surface roughness, and surface chemistry characterizations. Lower-energy oxygen plasma treatments exhibited hydrophilic behavior with contact angles as low as 87°, and the higher-energy oxygen plasma treatments exhibited superhydrophobic behavior with contact angles as high as 151°. The wettability of all the treated samples as stored in air and in water was found to be stable in time as evidenced by the statistically insignificant differences in the advancing, receding, and hysteresis contact angles. Low contact angle hysteresis (?H<5°) and low sliding angle (??4°) were exhibited by the superhydrophobic surface. The surface morphology was found to be responsible for the changes in the wettability of the PTFE samples since (1) there was an increase in the surface rms roughness as the plasma discharge energy was increased, and (2) there were no significant changes in the observed group frequencies of the FT-IR spectra of the treated PTFE from the untreated PTFE. PMID:23403114

Salapare, Hernando S; Guittard, Frédéric; Noblin, Xavier; Taffin de Givenchy, Elisabeth; Celestini, Franck; Ramos, Henry J

2013-04-15

263

Fabrication and characterization of stable superhydrophobic surface with good friction-reducing performance on Al foil  

NASA Astrophysics Data System (ADS)

A lotus-leaf-like hierarchical structure with superhydrophobicity was created on Al foil by a facile three-step solution-immersion method involving etching in hydrochloric acid solution and immersing in hot water as well as surface-modification by stearic acid (denoted as STA). As-prepared etched-immersed Al/STA rough surface was characterized by means of scanning electron microscopy and X-ray photoelectron spectroscopy. Moreover, the water contact angles and water sliding angles of as-prepared etched-immersed Al/STA rough surface were measured, and the friction-reducing performance and self-cleaning ability of the as-prepared surface were also evaluated. Results indicate that the etched-immersed Al/STA rough surface consists of interconnected convex-concave micro-structure and uniformly distributed nano-sheets. Besides, it exhibits stable superhydrophobicity and good friction-reducing ability. Namely, it has a contact angle of water as high as 164.2° and a water sliding angle lower than 5°, while it retains good friction-reducing ability during extended sliding and possesses good self-cleaning ability as well. This demonstrates that the etched-immersed Al/STA rough surface may favor the applications of Al and its alloys in various industrial fields.

Li, Peipei; Chen, Xinhua; Yang, Guangbin; Yu, Laigui; Zhang, Pingyu

2014-05-01

264

Anisotropically microstructured and micro/nanostructured polypropylene surfaces  

NASA Astrophysics Data System (ADS)

Anisotropically microstructured and hierarchically micro/nanostructured surfaces were fabricated on polypropylene by injection moulding. Microstructured mould inserts were obtained by structuring electropolished aluminium foils with a micro-working robot, and hierarchically structured mould inserts by anodizing the microstructured aluminium foils. On both types of inserts, the microstructures were anisotropic, consisting of alternating smooth and microstructured zones. Anisotropy, and other properties of microstructures, can be controlled by adjusting the parameters of the micro-working robot. The mould inserts were used to prepare micro- and hierarchically structured polypropylene discs by injection moulding. Replication accuracy at both structure levels can be controlled through the moulding conditions. The behaviour of water on the structures was characterized by measuring the contact and sliding angles parallel and perpendicular to the microstructured zones. Surfaces with microstructures alone were highly hydrophobic, where water droplets adopted the Wenzel state and had clearly different parallel and perpendicular contact angles. Surfaces with dual structures had contact angles near 170° and sliding angles near 0°, and again the angles in parallel and perpendicular directions differed. Superhydrophobic, anisotropic Cassie-Baxter state was achieved.

Rasilainen, Tiina; Suvanto, Mika; Pakkanen, Tapani A.

2009-07-01

265

Underwater restoration and retention of gases on superhydrophobic surfaces for drag reduction.  

PubMed

Superhydrophobic (SHPo) surfaces have shown promise for passive drag reduction because their surface structures can hold a lubricating gas film between the solid surface and the liquid in contact with it. However, the types of SHPo surfaces that would produce any meaningful amount of reduction get wet under liquid pressure or at surface defects, both of which are unavoidable in the real world. In this Letter, we solve the above problem by (1) discovering surface structures that allow the restoration of a gas blanket from a wetted state while fully immersed underwater and (2) devising a self-controlled gas-generation mechanism that maintains the SHPo condition under high liquid pressures (tested up to 7 atm) as well as in the presence of surface defects, thus removing a fundamental barrier against the implementation of SHPo surfaces for drag reduction. PMID:21231747

Lee, Choongyeop; Kim, Chang-Jin

2011-01-01

266

Underwater Restoration and Retention of Gases on Superhydrophobic Surfaces for Drag Reduction  

NASA Astrophysics Data System (ADS)

Superhydrophobic (SHPo) surfaces have shown promise for passive drag reduction because their surface structures can hold a lubricating gas film between the solid surface and the liquid in contact with it. However, the types of SHPo surfaces that would produce any meaningful amount of reduction get wet under liquid pressure or at surface defects, both of which are unavoidable in the real world. In this Letter, we solve the above problem by (1) discovering surface structures that allow the restoration of a gas blanket from a wetted state while fully immersed underwater and (2) devising a self-controlled gas-generation mechanism that maintains the SHPo condition under high liquid pressures (tested up to 7 atm) as well as in the presence of surface defects, thus removing a fundamental barrier against the implementation of SHPo surfaces for drag reduction.

Lee, Choongyeop; Kim, Chang-Jin

2011-01-01

267

Acids and alkali resistant sticky superhydrophobic surfaces by one-pot electropolymerization of perfluoroalkyl alkyl pyrrole.  

PubMed

Over the past few years, electropolymerization of semifluorinated monomers like thiophene or pyrrole has been used as a gentle and effective method to generate, in one step, stable superhydrophobic surfaces. The synthetic route mostly involves the coupling reaction between a carboxylic acid and an alcohol, using a carboxy group-activated reagent and a catalyst. As a consequence, the electroformed surfaces present high liquid repellency due to the concomitant effect of roughness and low surface energy. Nevertheless, the ester connector can be cleaved under acidic and basic conditions, preventing its use under a range of environmental conditions. To overcome this drawback, a new perfluoroalkyl alkyl pyrrole has been synthesized, the fluorinated segment being connected to the electropolymerizable part via an alkyl chain, and electropolymerized, leading to surfaces that exhibit a static contact angle with water superior to 150 degrees and no sliding angle, over a wide pH range and with a long lifetime. This represents the first example of a pure conducting polymer surface with sticky superhydrophobicity not only in pure water but also in corrosive solutions such as acids and bases, giving rise to new prospects in practical applications. PMID:20060984

Nicolas, Mael

2010-03-15

268

Preparation of porous super-hydrophobic and super-oleophilic polyvinyl chloride surface with corrosion resistance property  

NASA Astrophysics Data System (ADS)

Porous super-hydrophobic polyvinyl chloride (PVC) surfaces were obtained via a facile solvent/non-solvent coating process without introducing compounds with low surface energy. The microstructure, wetting behavior, and corrosion resistance of resultant super-hydrophobic PVC coatings were investigated in relation to the effects of dosage of glacial acetic acid and the temperature of drying the mixed PVC solution spread over glass slide substrate. As-prepared PVC coatings had porous microstructure, and the one obtained at a glacial acetic acid to tetrahydrofuran volume ratio of 2.5:10.0 and under a drying temperature of 17 °C had a water contact angle of 150 ± 1.5°, showing super-hydrophobicity. In the meantime, it possessed very small contact angles for liquid paraffin and diiodomethane and good corrosion resistance against acid and alkali corrosive mediums, showing promising applications in self-cleaning, waterproof for outer wall of building, seawater resistant coating, and efficient separation of oil and water.

Kang, Yingke; Wang, Jinyan; Yang, Guangbin; Xiong, Xiujuan; Chen, Xinhua; Yu, Laigui; Zhang, Pingyu

2011-11-01

269

Prolonged Raman lasing in size-stabilized salt-water microdroplets on a superhydrophobic surface.  

PubMed

We demonstrate prolonged Raman lasing from individual salt-water microdroplets with 10-20 microm diameters located on a superhydrophobic surface. The mechanism is based on the absorption heating of a 1064 nm cw IR laser and the resonant heating of a 532 nm pulsed, pump laser. A clear hysteresis is observed in the lasing intensity as the droplet size is photothermally tuned by the IR laser, indicating a self-stabilization mechanism due to the resonant absorption of the pump laser. Using this mechanism, Raman lasing near 650 nm is sustained for up to 25 min, approximately 1000 times longer than lasing durations reported in previous studies. PMID:20548364

Karadag, Y; Gündo?an, M; Yüce, M Y; Cankaya, H; Sennaroglu, A; Kiraz, A

2010-06-15

270

One-step solution immersion process to fabricate superhydrophobic surfaces on light alloys.  

PubMed

A simple and universal one-step process bas been developed to render light alloys (including AZ91D Mg alloy, 5083 Al alloy, and TC4 Ti alloy) superhydrophobic by immersing the substrates in a solution containing low-surface-energy molecules of 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFOTS, 20 ?L), ethanol (10 mL), and H2O (10 mL for Al and Mg alloy)/H2O2 (15%, 10 mL for Ti alloy). Field-emission scanning electron microscopy, X-ray photoelectron spectroscopy, and water contact angle measurements have been performed to characterize the morphological features, chemical composition, and wettability of the surfaces, respectively. The results indicate that the treated light alloys are rough-structured and covered by PFOTS molecules; consequently, the surfaces show static contact angles higher than 150° and sliding angles lower than 10°. This research reveals that it is feasible to fabricate superhydrophobic surfaces (SHS) easily and effectively without involving the traditional two-step processes. Moreover, this one-step process may find potential application in the field of industrial preparation of SHS because of its simplicity and universality. PMID:23895507

Ou, Junfei; Hu, Weihua; Xue, Mingshan; Wang, Fajun; Li, Wen

2013-10-23

271

Preparation of hybrid film with superhydrophobic surfaces based on irregularly structure by emulsion polymerization  

NASA Astrophysics Data System (ADS)

A superhydrophobic surface originated from quincunx-shape composite particles was obtained by utilizing the encapsulation and graft of silica particles to control the surface chemistry and morphology of the hybrid film. The composite particles make the surface of film form a composite interface with irregular binary structure to trap air between the substrate surface and the liquid droplets which plays an essential role in obtaining high water contact angle and low water contact angle hysteresis. The water contact angle on the hybrid film is determined to be 154 ± 2° and the contact angle hysteresis is less than 5°. This is expected to be a simple and practical method for preparing self-cleaning hydrophobic surfaces on large area.

Qu, Ailan; Wen, Xiufang; Pi, Pihui; Cheng, Jiang; Yang, Zhuoru

2007-10-01

272

Improvement of mechanical robustness of the superhydrophobic wood surface by coating PVA/SiO2 composite polymer  

NASA Astrophysics Data System (ADS)

Improvement of the robustness of superhydrophobic surfaces is crucial for the purpose of achieving commercial applications of these surfaces in such various areas as self-cleaning, water repellency and corrosion resistance. We have investigated a fabrication of polyvinyl alcohol (PVA)/silica (SiO2) composite polymer coating on wooden substrates with super repellency toward water, low sliding angles, low contact angle hysteresis, and relatively better mechanical robustness. The composite polymer slurry, consisting of well-mixing SiO2 particles and PVA, is prepared simply and subsequently coated over wooden substrates with good adhesion. In this study, the mechanical robustness of superhydrophobic wood surfaces was evaluated. The effect of petaloid structures of the composite polymer on robustness was investigated using an abrasion test and the results were compared with those of superhydrophobic wood surfaces fabricated by other processes. The produced wood surfaces exhibited promising superhydrophobic properties with a contact angle of 159? and a sliding angle of 4?, and the relatively better mechanical robustness.

Liu, Feng; Wang, Shuliang; Zhang, Ming; Ma, Miaolian; Wang, Chengyu; Li, Jian

2013-09-01

273

Conversion of an electrospun nanofibrous cellulose acetate mat from a super-hydrophilic to super-hydrophobic surface  

NASA Astrophysics Data System (ADS)

We report a new approach to convert an electrospun nanofibrous cellulose acetate mat surface from super-hydrophilic to super-hydrophobic. Super-hydrophilic cellulose acetate nanofibrous mats can be obtained by electrospinning hydrophilic cellulose acetate. The surface properties of the fibrous mats were modified from super-hydrophilic to super-hydrophobic with a simple sol-gel coating of decyltrimethoxysilane (DTMS) and tetraethyl orthosilicate (TEOS). The resultant samples were characterized by field emission scanning electron microscopy (FE-SEM), x-ray photoelectron spectroscopy (XPS), water contact angle, Brunauer-Emmett-Teller (BET) surface area, atomic force microscopy (AFM), and UV-visible measurements. The results of FE-SEM and XPS showed that the sol-gel (I) films were formed on the rough fibrous mats only after immersion in sol-gel. After the sol-gel (I) coating, the cellulose acetate fibrous mats formed in both 8 and 10 wt% cellulose acetate solutions showed the super-hydrophobic surface property. Additionally, the average sol-gel film thickness coated on 10 wt% cellulose acetate fibrous mats was calculated to be 80 nm. The super-hydrophobicity of fibrous mats was attributed to the combined effects of the high surface roughness of the electrospun nanofibrous mats and the hydrophobic DTMS sol-gel coating. Additionally, hydrophobic sol-gel nanofilms were found to be transparent according to UV-visible measurements.

Ding, Bin; Li, Chunrong; Hotta, Yoshio; Kim, Jinho; Kuwaki, Oriha; Shiratori, Seimei

2006-09-01

274

Superhydrophobic hybrid inorganic-organic thiol-ene surfaces fabricated via spray-deposition and photopolymerization.  

PubMed

We report a simple and versatile method for the fabrication of superhydrophobic inorganic-organic thiol-ene coatings via sequential spray-deposition and photopolymerization under ambient conditions. The coatings are obtained by spray-deposition of UV-curable hybrid inorganic-organic thiol-ene resins consisting of pentaerythritol tetra(3-mercaptopropionate) (PETMP), triallyl isocyanurate (TTT), 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (TMTVSi), and hydrophobic fumed silica nanoparticles. The spray-deposition process and nanoparticle agglomeration/dispersion provide surfaces with hierarchical morphologies exhibiting both micro- and nanoscale roughness. The wetting behavior, dependent on the concentration of TMTVSi and hydrophobic silica nanoparticles, can be varied over a broad range to ultimately provide coatings with high static water contact angles (>150°), low contact angle hysteresis, and low roll off angles (<5°). The cross-linked thiol-ene coatings are solvent resistant, stable at low and high pH, and maintain superhydrophobic wetting behavior after extended exposure to elevated temperatures. We demonstrate the versatility of the spray-deposition and UV-cure process on a variety of substrate surfaces including glass, paper, stone, and cotton fabric. PMID:23410965

Sparks, Bradley J; Hoff, Ethan F T; Xiong, Li; Goetz, James T; Patton, Derek L

2013-03-13

275

Friction Reduction in Superhydrophobic Microchannels  

Microsoft Academic Search

Superhydrophobic surfaces are surfaces with fluid contact angles larger than 150^o. Superhydrophobicity can be achieved by means of surface texturing through either a Wenzel or Cassie state. It is widely known, however, that drag reduction is closely related to Cassie state surfaces with low degrees of adhesion and several studies have been widely conducted on the topic. In this research

Tae Jin Kim; Carlos H. Hidrovo

2009-01-01

276

Probing droplets on superhydrophobic surfaces by synchrotron radiation scattering techniques.  

PubMed

Droplets on artificially structured superhydrophobic surfaces represent quasi contact-free sample environments which can be probed by X-ray microbeams and nanobeams in the absence of obstructing walls. This review will discuss basic surface wettability concepts and introduce the technology of structuring surfaces. Quasi contact-free droplets are compared with contact-free droplets; processes related to deposition and evaporation on solid surfaces are discussed. Droplet coalescence based on the electrowetting effect allows the probing of short-time mixing and reaction processes. The review will show for several materials of biological interest that structural processes related to conformational changes, nucleation and assembly during droplet evaporation can be spatially and temporally resolved by raster-scan diffraction techniques. Orientational ordering of anisotropic materials deposited during solidification at pinning sites facilitates the interpretation of structural data. PMID:24971957

Accardo, Angelo; Di Fabrizio, Enzo; Limongi, Tania; Marinaro, Giovanni; Riekel, Christian

2014-07-01

277

Preparation and characterization of superhydrophobic FEP-Teflon surfaces  

Microsoft Academic Search

Abstraet-Supcrhydrophohic FEP-Teflon was prepared by argon ion etching followed by oxygen glow discharge treatment of commercially available FEP-Teflon sheet material. This combined treatment yielded an increase in water contact angle from 109° to > 140°. Ion etching alone caused a small increase in surface roughness and a loss of fluorine from the surface, but the water contact angles increased only

H. J. Busscher; I. Stokroos; H. C. Van Der Mei; P. G. Rouxhet; J. M. Schakenra Ad

1992-01-01

278

The effectiveness of silane and siloxane treatments on the superhydrophobicity and icephobicity of concrete surfaces  

NASA Astrophysics Data System (ADS)

Icy roads lead to treacherous driving conditions in regions of the U.S., leading to over 450 fatalities per year. De-icing chemicals, such as road salt, leave much to be desired. In this report, commercially available silane, siloxane, and related materials were evaluated as solutions, simple emulsions, and complex emulsions with incorporated particulates, for their effectiveness as superhydrophobic treatments. Through the development and use of a basic impact test, the ease of ice removal (icephobicity) was examined as an application of the targeted superhydrophobicity. A general correlation was found between icephobicity and hydrophobicity, with the amount of ice removed on impact increasing with increasing contact angle. However, the correlation was poor in the high performance region (high contact angle and high ice removal.) Polymethylhydrogensiloxane was a top performer and was more effective when used as a "shell" type emulsion with silica fume particulates. An aqueous sodium methyl siliconate solution showed good performance for ice loss and contact angle, as did a commercial proprietary emulsion using a diethoxyoctylsilyl trimethylsilyl ester of silicic acid. These materials have sterically available functional groups that can react or associate with the concrete surface and are potentially film-forming. Materials with less reactive functional groups and a lower propensity to film-form did not perform as well.

Rao, Sunil M.

279

Multifunctional porous silicon nanopillar arrays: antireflection, superhydrophobicity, photoluminescence, and surface-enhanced Raman scattering (SERS)  

PubMed Central

We have fabricated porous silicon nanopillar arrays over large areas with a rapid, simple, and low-cost technique. The porous silicon nanopillars show unique longitudinal features along their entire length and have porosity with dimensions on the single-nanometer scale. Both Raman spectroscopy and photoluminescence data were used to determine the nanocrystallite size to be < 3 nm. The porous silicon nanopillar arrays also maintained excellent ensemble properties, reducing reflection nearly fivefold from planar silicon in the visible range without any optimization and approaching superhydrophobic behavior with increasing aspect ratio, demonstrating contact angles up to 138°. Finally, the porous silicon nanopillar arrays were made into sensitive surface enhanced Raman scattering (SERS) substrates by depositing metal onto the pillars. The SERS performance of the substrates was demonstrated using a chemical dye Rhodamine 6G. With their multitude of properties (i.e., antireflection, superhydrophobicity, photoluminescence, and sensitive SERS), the porous silicon nanopillar arrays described here can be valuable in applications such as solar harvesting, electrochemical cells, self-cleaning devices, and dynamic biological monitoring.

Kiraly, Brian; Yang, Shikuan

2014-01-01

280

Article coated with flash bonded superhydrophobic particles  

DOEpatents

A method of making article having a superhydrophobic surface includes: providing a solid body defining at least one surface; applying to the surface a plurality of diatomaceous earth particles and/or particles characterized by particle sizes ranging from at least 100 nm to about 10 .mu.m, the particles being further characterized by a plurality of nanopores, wherein at least some of the nanopores provide flow through porosity, the particles being further characterized by a plurality of spaced apart nanostructured features that include a contiguous, protrusive material; flash bonding the particles to the surface so that the particles are adherently bonded to the surface; and applying a hydrophobic coating layer to the surface and the particles so that the hydrophobic coating layer conforms to the nanostructured features.

Simpson, John T (Clinton, TN) [Clinton, TN; Blue, Craig A (Knoxville, TN) [Knoxville, TN; Kiggans, Jr., James O [Oak Ridge, TN

2010-07-13

281

Curvature affects superhydrophobicity on flexible silicone microstructured surfaces  

Microsoft Academic Search

The flexure of microstructured polymers affects hydrophobicity. As curvature becomes more positive, droplets suspended on the tops of asperities are suspended on fewer asperities, resulting in an increase in contact angle and a decrease in slide angle. Critical curvature constraints presented here can be used to design microstructure geometries that maintain the suspension of a droplet when curved surfaces are

A. H. Cannon; W. P. King

2009-01-01

282

Constructing a superhydrophobic surface on polydimethylsiloxane via spin coating and vapor-liquid sol-gel process.  

PubMed

In this study, a superhydrophobic surface on polydimethylsiloxane (PDMS) substrate was constructed via the proposed vapor-liquid sol-gel process in conjunction with spin coating of dodecyltrichlorosilane (DTS). Unlike the conventional sol-gel process where the reaction takes place in the liquid phase, layers of silica (SiO(2)) particles were formed through the reaction between the reactant spin-coated on the PDMS surface and vapor of the acid solution. This led to the SiO(2) particles inlaid on the PDMS surface. Followed by subsequent spin coating of DTS solution, the wrinkle-like structure was formed, and the static contact angle of the water droplet on the surface could reach 162 degrees with 2 degrees sliding angle and less than 5 degrees contact angle hysteresis. The effect of layers of SiO(2) particles, concentrations of DTS solution and surface topography on superhydrophobicity of the surface is discussed. PMID:20020726

Peng, Yu-Ting; Lo, Kuo-Feng; Juang, Yi-Je

2010-04-01

283

Elasticity of the contact line for droplets on anisotropic superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

We present an experimental and numerical investigation on the receding of contact line for water droplets on glass superhydrophobic surfaces. In particular, we focus our attention on surfaces textured with anisotropic lattice posts. We measure that the receding contact angle is not affected by the anisotropy of the lattice. This surprising behavior is closely related to the elastic deformations of the contact line which can be by studied by direct observation. We interpret this phenomenon in term of propagation of kink defects along the lattice. We detail the influence of the morphology of the lattice on the propagation of kinks, as well as the importance of the shape of the posts. Three dimensional numerical simulations confirm that kinks are the key ingredient for the comprehension of the receding contact angle.

Rivetti, Marco; Gauthier, Anais; Teisseire, Jeremie; Barthel, Etienne

2013-03-01

284

Ultra lightweight PMMA-based composite plates with robust super-hydrophobic surfaces.  

PubMed

Extremely lightweight plates made of an engineered PMMA-based composite material loaded with hollow glass micro-sized spheres, nano-sized silica particles and aluminum hydroxide prismatic micro-flakes were realized by cast molding. Their interesting bulk mechanical properties were combined to properly tailored surface topography compatible with the achievement of a superhydrophobic behavior after the deposition of a specifically designed hydrophobic coating. With this aim, we synthesized two different species of fluoromethacrylic polymers functionalized with methoxysilane anchoring groups to be covalently grafted onto the surface protruding inorganic fillers. By modulating the feed composition of the reacting monomers, it was possible to combine the hydrophobic character of the polymer with an high adhesion strength to the substrate and hence to maximize both the water contact angle (up to 157°) and the durability of the easy-to-clean effect (up to 2000 h long outdoor exposure). PMID:21855889

Pareo, Paola; De Gregorio, Gian Luca; Manca, Michele; Pianesi, Maria Savina; De Marco, Luisa; Cavallaro, Francesco; Mari, Margherita; Pappadà, Silvio; Ciccarella, Giuseppe; Gigli, Giuseppe

2011-11-15

285

Flow over Superhydrophobic Hydrofoils  

NASA Astrophysics Data System (ADS)

For several years, superhydrophobic surfaces which are chemically hydrophobic with micron or nanometer scale surface features have been considered for their ability to reduce drag in microfluidic devices. More recently it has been demonstrated that superhydrophobic surfaces reduce friction coefficient in turbulent flows as well. In this talk, we will consider the effect of superhydrophobic surfaces on drag, lift and fluid-structure interactions of hydrofoils and the effect of superhydrophobicity on separation point and vortex structure at high angles of attack. Drag reductions and significant changes to the fluid structure interactions are observed with the presence of superhydrophobic coatings. Hydrofoils are coated with patterned microridge geometries from 5?m to 30?m. Selectively coated symmetrical hydrofoils are also examined to characterize the effect of superhydrophobicity on lift behavior. Particle image velocimetry, streak images and direct force measurements will be presented. Experiments were conducted over the range of Reynolds numbers 100

Daniello, Robert; Sullivan, Jonathan; Rothstein, Jonathan

2010-11-01

286

Tailoring the morphology of raspberry-like carbon black/polystyrene composite microspheres for fabricating superhydrophobic surface  

SciTech Connect

In our previous report, raspberry-like carbon black/polystyrene (CB/PS) composite microsphere was prepared through heterocoagulation process. Based on the previous study, in the present work, the morphology of raspberry-like CB/PS particle is tailored through adjusting the polarity and the concentration ratio of CB/PS colloidal suspension with the purpose to prepare particulate film for the fabrication of superhydrophobic surface. Scanning electron microscope (SEM) confirms the morphology of raspberry-like particle and the coverage of CB. Rough surfaces fabricated by raspberry-like particles with proper morphology are observed by SEM and clear evidence of superhydrophobic surface is shown. The structure of raspberry-like particle is analyzed by atom force microscope. The proposed relationship between the hydrophobicity and the structure of CB aggregates on the surface of PS microsphere is discussed in details.

Bao, Yubin [Polymer Alloy Lab., School of Material Science and Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237 (China)] [Polymer Alloy Lab., School of Material Science and Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237 (China); Li, Qiuying, E-mail: liqy@ecust.edu.cn [Polymer Alloy Lab., School of Material Science and Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237 (China) [Polymer Alloy Lab., School of Material Science and Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237 (China); Shanghai Key Laboratory Polymeric Materials (China); Key Laboratory of Ultrafine Materials of Ministry of Education (China); Xue, Pengfei; Huang, Jianfeng; Wang, Jibin; Guo, Weihong; Wu, Chifei [Polymer Alloy Lab., School of Material Science and Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237 (China)] [Polymer Alloy Lab., School of Material Science and Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237 (China)

2011-05-15

287

Temperature-induced coalescence of colliding binary droplets on superhydrophobic surface.  

PubMed

This report investigates the impact of droplet temperature on the head-on collision of binary droplets on a superhydrophobic surface. Understanding droplet collision is critical to many fundamental processes and industrial applications. There are many factors, including collision speed, collision angle, and droplet composition, that influence the outcome of the collision between binary droplets. This work provides the first experimental study of the influence of droplet temperature on the collision of binary droplets. As the droplet temperature increases, the possibility increases for the two droplets to coalesce after collision. The findings in this study can be extended to collision of droplets under other conditions where control of the droplet temperature is feasible. Such findings will also be beneficial to applications that involve droplet collision, such as in ink-jet printing, steam turbines, engine ignition, and spraying cooling. PMID:24603362

Yi, Nan; Huang, Bin; Dong, Lining; Quan, Xiaojun; Hong, Fangjun; Tao, Peng; Song, Chengyi; Shang, Wen; Deng, Tao

2014-01-01

288

Raman lasing near 630 nm from stationary glycerol-water microdroplets on a superhydrophobic surface.  

PubMed

We demonstrate, for the first time to our knowledge, Raman lasing from stationary microdroplets on a superhydrophobic surface. In the experiments, glycerol-water microdroplets with radii in the 11-15 microm range were pumped at 532 nm with a pulsed, frequency-doubled Nd:YAG laser. Two distinct operation regimes of the microdroplets were observed: cavity-enhanced Raman scattering and Raman lasing. In the latter case, the Raman lasing signal was higher than the background by more than 30 dB. Investigation of the Raman spectra of various glycerol-water mixtures indicates that lasing occurs within the glycerol Raman band. Raman lasing was not sustained; rather, oscillation would occur in temporally separated bursts. Increasing the rate of convective cooling by nitrogen purging improved the lasing performance and reduced the average interburst separation from 2.3 to 0.4 s. PMID:17671582

Sennaroglu, A; Kiraz, A; Dündar, M A; Kurt, A; Demirel, A L

2007-08-01

289

Self-assembling of large ordered DNA arrays using superhydrophobic patterned surfaces  

NASA Astrophysics Data System (ADS)

In this paper we present a simple and robust method to realize highly ordered arrays of stretched and suspended DNA molecules over the millimeter length scale. To this end we used an ad hoc designed superhydrophobic surface made of high aspect-ratio silicon pillars, where we deposited a droplet containing genomic DNA. A precise positioning of DNA strands was achieved by shaping the silicon pillars so that sharpened features resembling tips were included. Such features allowed us to accurately control the droplet de-wetting dynamics, pinning DNA strands in a well-defined position above pillars. The proposed technique has the potential to positively impact on the development of novel DNA chips for genetic analysis.

Ciasca, G.; Businaro, L.; Papi, M.; Notargiacomo, A.; Chiarpotto, M.; De Ninno, A.; Palmieri, V.; Carta, S.; Giovine, E.; Gerardino, A.; De Spirito, M.

2013-12-01

290

Switchable static and dynamic self-assembly of magnetic droplets on superhydrophobic surfaces.  

PubMed

Self-assembly is a process in which interacting bodies are autonomously driven into ordered structures. Static structures such as crystals often form through simple energy minimization, whereas dynamic ones require continuous energy input to grow and sustain. Dynamic systems are ubiquitous in nature and biology but have proven challenging to understand and engineer. Here, we bridge the gap from static to dynamic self-assembly by introducing a model system based on ferrofluid droplets on superhydrophobic surfaces. The droplets self-assemble under a static external magnetic field into simple patterns that can be switched to complicated dynamic dissipative structures by applying a time-varying magnetic field. The transition between the static and dynamic patterns involves kinetic trapping and shows complexity that can be directly visualized. PMID:23869012

Timonen, Jaakko V I; Latikka, Mika; Leibler, Ludwik; Ras, Robin H A; Ikkala, Olli

2013-07-19

291

Micro/nanofabrication for a realistic beetle wing with a superhydrophobic surface.  

PubMed

In keeping with the high interest in micro air vehicles, microfabrication technologies have been developed in an attempt to mimic insect wings via a membrane-vein structure. In this work, we present microfabrication techniques that mimic a beetle wing to construct a realistic vein-membrane structure. Full microfabrication processes as well as sophisticated manipulations are introduced for constructing a realistic artificial wing whose key morphological and mechanical parameters can be achieved close to those of the real wing. Secondly, for wing loading reduction whenever moist air is present, we successfully fabricated superhydrophobic nanopillar forests by conventional nanofabrication techniques, such as ion beam and heat treatments. The creation of the nanopillar forests, which exist on the surface of leaves and insect wings, allowed lowering the dispersive component in a hydrophobic material, and the clustered nanopillars enhanced water repellency. PMID:22345393

Ko, Jin Hwan; Kim, Jihoon; Hong, Jongin; Yoo, Yonghoon; Lee, Youngjong; Jin, Tai Lie; Park, Hoon Cheol; Goo, Nam Seo; Byun, Doyoung

2012-03-01

292

Various curing conditions for controlling PTFE micro\\/nano-fiber texture of a bionic superhydrophobic coating surface  

Microsoft Academic Search

A simple and conventional coating-curing process to fabricate superhydrophobic coating surface with both the micro-nano-scale binary structure (MNBS) roughness, and the lowest surface energy hydrophobic groups (?CF3) on engineering materials of stainless steel or other metals was developed by control of curing conditions. Results show that higher temperature and longer cooling time resulted in longer crystallizing process, and the forming

Zhuangzhu Luo; Zhaozhu Zhang; Wenjing Wang; Weimin Liu; Qunji Xue

2010-01-01

293

Measuring air layer volumes retained by submerged floating-ferns Salvinia and biomimetic superhydrophobic surfaces  

PubMed Central

Summary Some plants and animals feature superhydrophobic surfaces capable of retaining a layer of air when submerged under water. Long-term air retaining surfaces (Salvinia-effect) are of high interest for biomimetic applications like drag reduction in ship coatings of up to 30%. Here we present a novel method for measuring air volumes and air loss under water. We recorded the buoyancy force of the air layer on leaf surfaces of four different Salvinia species and on one biomimetic surface using a highly sensitive custom made strain gauge force transducer setup. The volume of air held by a surface was quantified by comparing the buoyancy force of the specimen with and then without an air layer. Air volumes retained by the Salvinia-surfaces ranged between 0.15 and 1 L/m2 depending on differences in surface architecture. We verified the precision of the method by comparing the measured air volumes with theoretical volume calculations and could find a good agreement between both values. In this context we present techniques to calculate air volumes on surfaces with complex microstructures. The introduced method also allows to measure decrease or increase of air layers with high accuracy in real-time to understand dynamic processes.

Reker, Meike; Barthlott, Wilhelm

2014-01-01

294

Preparation and characterization of superhydrophobic surfaces based on hexamethyldisilazane-modified nanoporous alumina.  

PubMed

Superhydrophobic nanoporous anodic aluminum oxide (alumina) surfaces were prepared using treatment with vapor-phase hexamethyldisilazane (HMDS). Nanoporous alumina substrates were first made using a two-step anodization process. Subsequently, a repeated modification procedure was employed for efficient incorporation of the terminal methyl groups of HMDS to the alumina surface. Morphology of the surfaces was characterized by scanning electron microscopy, showing hexagonally ordered circular nanopores with approximately 250 nm in diameter and 300 nm of interpore distances. Fourier transform infrared spectroscopy-attenuated total reflectance analysis showed the presence of chemically bound methyl groups on the HMDS-modified nanoporous alumina surfaces. Wetting properties of these surfaces were characterized by measurements of the water contact angle which was found to reach 153.2 ± 2°. The contact angle values on HMDS-modified nanoporous alumina surfaces were found to be significantly larger than the average water contact angle of 82.9 ± 3° on smooth thin film alumina surfaces that underwent the same HMDS modification steps. The difference between the two cases was explained by the Cassie-Baxter theory of rough surface wetting. PMID:21827683

Tasaltin, Nevin; Sanli, Deniz; Jonáš, Alexandr; Kiraz, Alper; Erkey, Can

2011-01-01

295

A numerical study of the effects of superhydrophobic surface on skin-friction drag in turbulent channel flow  

NASA Astrophysics Data System (ADS)

Superhydrophobic surfaces have attracted much attention lately as they present the possibility of achieving a substantial skin-friction drag reduction in turbulent flows. In this paper, the effects of a superhydrophobic surface, consisting of microgrates aligned in the flow direction, on skin-friction drag in turbulent flows were investigated through direct numerical simulation of turbulent channel flows. The superhydrophobic surface was modeled through a shear-free boundary condition on the air-water interface. Dependence of the effective slip length and resulting skin-friction drag on Reynolds number and surface geometry was examined. In laminar flows, the effective slip length depended on surface geometry only, independent of Reynolds number, consistent with an existing analysis. In turbulent flows, the effective slip length was a function of Reynolds number, indicating its dependence on flow conditions near the surface. The resulting drag reduction was much larger in turbulent flows than in laminar flows, and near-wall turbulence structures were significantly modified, suggesting that indirect effects resulting from modified turbulence structures played a more significant role in reducing drag in turbulent flows than the direct effect of the slip, which led to a modest drag reduction in laminar flows. It was found that the drag reduction in turbulent flows was well correlated with the effective slip length normalized by viscous wall units.

Park, Hyunwook; Park, Hyungmin; Kim, John

2013-11-01

296

Highly efficient and large-scale fabrication of superhydrophobic alumina surface with strong stability based on self-congregated alumina nanowires.  

PubMed

In this study, a large-area superhydrophobic alumina surface with a series of superior properties was fabricated via an economical, simple, and highly effective one-step anodization process, and subsequently modified with low-surface-energy film. The effects of the anodization parameters including electrochemical anodization time, current density, and electrolyte temperature on surface morphology and surface wettability were investigated in detail. The hierarchical alumina pyramids-on-pores (HAPOP) rough structure which was produced quickly through the one-step anodization process together with a low-surface-energy film deposition [1H,1H,2H,2H-perfluorodecyltriethoxysilane (PDES) and stearic acid (STA)] confer excellent superhydrophobicity and an extremely low sliding angle. Both the PDES-modified superhydrophobic (PDES-MS) and the STA-modified superhydrophobic (STA-MS) surfaces present fascinating nonwetting and extremely slippery behaviors. The chemical stability and mechanical durability of the PDES-MS and STA-MS surfaces were evaluated and discussed. Compared with the STA-MS surface, the as-prepared PDES-MS surface possesses an amazing chemical stability which not only can repel cool liquids (water, HCl/NaOH solutions, around 25 °C), but also can show excellent resistance to a series of hot liquids (water, HCl/NaOH solutions, 30-100 °C) and hot beverages (coffee, milk, tea, 80 °C). Moreover, the PDES-MS surface also presents excellent stability toward immersion in various organic solvents, high temperature, and long time period. In particular, the PDES-MS surface achieves good mechanical durability which can withstand ultrasonication treatment, finger-touch, multiple fold, peeling by adhesive tape, and even abrasion test treatments without losing superhydrophobicity. The corrosion resistance and durability of the diverse-modified superhydrophobic surfaces were also examined. These fascinating performances makes the present method suitable for large-scale industrial fabrication of chemically stable and mechanically robust superhydrophobic surfaces. PMID:24593862

Peng, Shan; Tian, Dong; Yang, Xiaojun; Deng, Wenli

2014-04-01

297

Condensation on superhydrophobic surfaces: the role of local energy barriers and structure length scale.  

PubMed

Water condensation on surfaces is a ubiquitous phase-change process that plays a crucial role in nature and across a range of industrial applications, including energy production, desalination, and environmental control. Nanotechnology has created opportunities to manipulate this process through the precise control of surface structure and chemistry, thus enabling the biomimicry of natural surfaces, such as the leaves of certain plant species, to realize superhydrophobic condensation. However, this "bottom-up" wetting process is inadequately described using typical global thermodynamic analyses and remains poorly understood. In this work, we elucidate, through imaging experiments on surfaces with structure length scales ranging from 100 nm to 10 ?m and wetting physics, how local energy barriers are essential to understand non-equilibrium condensed droplet morphologies and demonstrate that overcoming these barriers via nucleation-mediated droplet-droplet interactions leads to the emergence of wetting states not predicted by scale-invariant global thermodynamic analysis. This mechanistic understanding offers insight into the role of surface-structure length scale, provides a quantitative basis for designing surfaces optimized for condensation in engineered systems, and promises insight into ice formation on surfaces that initiates with the condensation of subcooled water. PMID:22931378

Enright, Ryan; Miljkovic, Nenad; Al-Obeidi, Ahmed; Thompson, Carl V; Wang, Evelyn N

2012-10-01

298

The effect of contact angle hysteresis on droplet motion and collisions on superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

The effect of varying the contact angle hysteresis of a superhydrophobic surface on the characteristics and dynamics of water droplet motion and their subsequent collision are investigated using a high-speed camera. The surfaces are created by imparting random roughness to Teflon through sanding. With this technique, it is possible to create surfaces with similar advancing contact angles near 150 degrees, but with varying contact angle hysteresis. This talk will focus on a number of interesting experimental observations pertaining to drop dynamics along a surface with uniform hysteresis, drop motion along surfaces with transition zones from one hysteresis to another, and the collision of droplets on surfaces of uniform hysteresis. For single drop studies, gravity is used as the driving force, while the collision studies use pressurized air to propel one drop into the other. For the case of droplet collision, the effect of hysteresis, Weber number, and impact number on the maximum deformation of the drops, and the post-collision dynamics will be discussed. For the single droplet measurements, the resistance to motion will be characterized as well as the transition from rolling to sliding as a function of drop size, inclination angle, and hysteresis. Additionally, we will quantify the effect of surface transitions on the resulting motion, mixing, and deflection of the drops.

Nilsson, Michael; Rothstein, Jonathan

2010-11-01

299

Creation of superhydrophobic stainless steel surfaces by acid treatments and hydrophobic film deposition.  

PubMed

In this work, we present a method to render stainless steel surfaces superhydrophobic while maintaining their corrosion resistance. Creation of surface roughness on 304 and 316 grade stainless steels was performed using a hydrofluoric acid bath. New insight into the etch process is developed through a detailed analysis of the chemical and physical changes that occur on the stainless steel surfaces. As a result of intergranular corrosion, along with metallic oxide and fluoride redeposition, surface roughness was generated on the nano- and microscales. Differences in alloy composition between 304 and 316 grades of stainless steel led to variations in etch rate and different levels of surface roughness for similar etch times. After fluorocarbon film deposition to lower the surface energy, etched samples of 304 and 316 stainless steel displayed maximum static water contact angles of 159.9 and 146.6°, respectively. However, etching in HF also caused both grades of stainless steel to be susceptible to corrosion. By passivating the HF-etched samples in a nitric acid bath, the corrosion resistant properties of stainless steels were recovered. When a three step process was used, consisting of etching, passivation and fluorocarbon deposition, 304 and 316 stainless steel samples exhibited maximum contact angles of 157.3 and 134.9°, respectively, while maintaining corrosion resistance. PMID:22913317

Li, Lester; Breedveld, Victor; Hess, Dennis W

2012-09-26

300

Insight into drop runback on hydrophilic to superhydrophobic surfaces by shearing airflow  

NASA Astrophysics Data System (ADS)

Drop runback has many diverse applications including airfoil icing and fuel cell flooding. In this talk, we use surface science and fluid dynamics principles to explain incipient runback for a drop exposed to shearing airflow. Through experiments with single drops of water and hexadecane (0.5-100 ?l) on PMMA, Teflon, and a superhydrophobic aluminum surface (SHS), wetting parameters such as surface tension, drop shape and contact angle are found to be major controllers of the minimum required air velocity for drop shedding. Exponential functions are proposed that relate air velocity to drop base length and projected area. By normalizing the results, the three water systems can be collapsed to a single curve that also explains results from other researchers, vastly increasing predictive power. SHS are seen to shed drops more easily compared to the other surfaces, with evidence that the drops roll along the surface instead of sliding. Using high speed video, oscillating drop shape and variation of contact angles are also analyzed as they change with air and drop speed.

Milne, Andrew J. B.; Amirfazli, Alidad

2009-11-01

301

Air-directed attachment of coccoid bacteria to the surface of superhydrophobic lotus-like titanium.  

PubMed

Superhydrophobic titanium surfaces fabricated by femtosecond laser ablation to mimic the structure of lotus leaves were assessed for their ability to retain coccoid bacteria. Staphylococcus aureus CIP 65.8T, S. aureus ATCC 25923, S. epidermidis ATCC 14990T and Planococcus maritimus KMM 3738 were retained by the surface, to varying degrees. However, each strain was found to preferentially attach to the crevices located between the microscale surface features. The upper regions of the microscale features remained essentially cell-free. It was hypothesised that air entrapped by the topographical features inhibited contact between the cells and the titanium substratum. Synchrotron SAXS revealed that even after immersion for 50 min, nano-sized air bubbles covered 45% of the titanium surface. After 1 h the number of cells of S. aureus CIP 65.8T attached to the lotus-like titanium increased to 1.27×10(5) mm(-2), coinciding with the replacement of trapped air by the incubation medium. PMID:22686938

Truong, V K; Webb, H K; Fadeeva, E; Chichkov, B N; Wu, A H F; Lamb, R; Wang, J Y; Crawford, R J; Ivanova, E P

2012-01-01

302

Surface modified nano-patterned SU-8 pillar array optically transparent super-hydrophobic thin film  

NASA Astrophysics Data System (ADS)

We report the fabrication and characterization of a porous nano-patterned SU-8 high aspect ratio pillar array as a transparent super-hydrophobic thin film. A 250 µm thick SU-8 layer was backside exposed through a glass substrate to form an array of high aspect ratio tapered pillars with angles in the range of 3°-5°. The SU-8 pillar array was plasma treated to form nano-porous surfaces, and then subsequently coated with fluorocarbon (FC) or Parylene-C film. Static contact angles and optical transmittance of various surface conditions such as with and without plasma treatment, Parylene-C versus FC, were tested and results were compared. Among various surface treated SU-8 pillar arrays, the plasma-treated nano-porous FC-coated SU-8 pillar array showed the highest static contact angle of 161°. It was found that the optical transmittance at around 530 nm for the nano-porous FC-coated SU-8 pillar array was approximately 65%, while the bare SU-8 film was approximately 95%. These nano-patterned transparent polymer films could be used in various water-repellent applications.

Yoon, Youngsam; Lee, Dong-Weon; Lee, Jeong-Bong

2012-03-01

303

Superhydrophobic surfaces on light alloy substrates fabricated by a versatile process and their corrosion protection.  

PubMed

After hydrothermally treated in H2O (for Mg alloy and Al alloy) or H2O2 (for Ti alloy), microstructured oxide or hydroxide layers were formed on light alloy substrates, which further served as the active layers to boost the self-assembling of 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES) and finally endowed the substrates with unique wettability, that is, superhydrophobicity. For convenience, the so-fabricated superhyrdophobic surfaces (SHS) were abridged as HT-SHS. For comparison, SHS coded as CE-SHS were also prepared based on chemical etching in acid and succedent surface passivation with PFOTES. To reveal the corrosion protection of these SHS, potentiodynamic polarization measurements in NaCl solution (3.5 wt %) were performed. Moreover, to reflect the long-term stability of these SHS, SHS samples were immersed into NaCl solution and the surface wettability was monitored. Experimental results indicated that HT-SHS was much more stable and effective in corrosion protection as compared with CE-SHS. The enhancement was most likely due to the hydrothermally generated oxide layer by the following tow aspects: on one hand, oxide layer itself can lower the corrosion due to its barrier effect; on the other hand, stronger interfacial bonding is expected between oxide layer and PFOTES molecules. PMID:23496751

Ou, Junfei; Hu, Weihua; Xue, Mingshan; Wang, Fajun; Li, Wen

2013-04-24

304

Suppressing surface reconstruction of superhydrophobic PDMS using a superhydrophilic zwitterionic polymer.  

PubMed

Poly(dimethyl siloxane) (PDMS) is extensively used for biomedical applications due to its low cost, ease of fabrication, high durability and flexibility, oxygen permeability, and self-healing properties. PDMS, however, has some significant drawbacks. PDMS endures unacceptably high levels of nonspecific protein fouling when used with biological samples due to its superhydrophobic characteristics. Unfortunately, conventional surface modification methods do not work for PDMS due to its low glass transition temperature. This phenomenon has been well-known for years as "hydrophobic regeneration". For the same reason, it is also very difficult to bring functionalities onto PDMS surfaces. Herein, we demonstrate how a superhydrophilic zwitterionic material, poly(carboxybetaine methacrylate) (pCBMA), can provide a highly stable coating with long-term stabilty due to the sharp contrast in hydrophobicity between pCBMA and PDMS. This material is able to suppress nonspecific protein adsorption in complex media and functionalize desired biomolecules needed in applications, such as diagnostics, without sacrificing its nonfouling characteristics. PMID:22512660

Keefe, Andrew J; Brault, Norman D; Jiang, Shaoyi

2012-05-14

305

Engineering atomic and molecular nanostructures at surfaces  

NASA Astrophysics Data System (ADS)

The fabrication methods of the microelectronics industry have been refined to produce ever smaller devices, but will soon reach their fundamental limits. A promising alternative route to even smaller functional systems with nanometre dimensions is the autonomous ordering and assembly of atoms and molecules on atomically well-defined surfaces. This approach combines ease of fabrication with exquisite control over the shape, composition and mesoscale organization of the surface structures formed. Once the mechanisms controlling the self-ordering phenomena are fully understood, the self-assembly and growth processes can be steered to create a wide range of surface nanostructures from metallic, semiconducting and molecular materials.

Barth, Johannes V.; Costantini, Giovanni; Kern, Klaus

2005-09-01

306

Electrospinning of a functional perfluorinated block copolymer as a powerful route for imparting superhydrophobicity and corrosion resistance to aluminum substrates.  

PubMed

Superhydrophobic aluminum surfaces with excellent corrosion resistance were successfully prepared by electrospinning of a novel fluorinated diblock copolymer solution. Micro- and nanostructuration of the diblock copolymer coating was obtained by electrospinning which proved to be an easy and cheap electrospinning technology to fabricate superhydrophobic coating. The diblock copolymer is made of poly(heptadecafluorodecylacrylate-co-acrylic acid) (PFDA-co-AA) random copolymer as the first block and polyacrylonitrile (PAN) as the second one. The fluorinated block promotes hydrophobicity to the surface by reducing the surface tension, while its carboxylic acid functions anchor the polymer film onto the aluminum surface after annealing at 130 °C. The PAN block of this copolymer insures the stability of the structuration of the surface during annealing, thanks to the infusible character of PAN. It is also demonstrated that the so-formed superhydrophobic coating shows good adhesion to aluminum surfaces, resulting in excellent corrosion resistance. PMID:21141949

Grignard, Bruno; Vaillant, Alexandre; de Coninck, Joel; Piens, Marcel; Jonas, Alain M; Detrembleur, Christophe; Jerome, Christine

2011-01-01

307

Facile spray-coating process for the fabrication of tunable adhesive superhydrophobic surfaces with heterogeneous chemical compositions used for selective transportation of microdroplets with different volumes.  

PubMed

In this paper, tunable adhesive superhydrophobic ZnO surfaces have been fabricated successfully by spraying ZnO nanoparticle (NP) suspensions onto desired substrates. We regulate the spray-coating process by changing the mass percentage of hydrophobic ZnO NPs (which were achieved by modifying hydrophilic ZnO NPs with stearic acid) in the hydrophobic/hydrophilic ZnO NP mixtures to control heterogeneous chemical composition of the ZnO surfaces. Thus, the water adhesion on the same superhydrophobic ZnO surface could be effectively tuned by controlling the surface chemical composition without altering the surface morphology. Compared with the conventional tunable adhesive superhydrophobic surfaces, on which there were only three different water sliding angle values: lower than 10°, 90° (the water droplet is firmly pinned on the surface at any tilted angles), and the value between the two ones, the water adhesion on the superhydrophobic ZnO surfaces has been tuned effectively, on which the sliding angle is controlled from 2 ± 1° to 9 ± 1°, 21 ± 2°, 39 ± 3°, and 90°. Accordingly, the adhesive force can be adjusted from extremely low (?2.5 ?N) to very high (?111.6 ?N). On the basis of the different adhesive forces of the tunable adhesive superhydrophobic surfaces, the selective transportation of microdroplets with different volumes was achieved, which has never been reported before. In addition, we demonstrated a proof of selective transportation of microdroplets with different volumes for application in the droplet-based microreactors via our tunable adhesive superhydrophobic surfaces for the quantitative detection of AgNO3 and NaOH. The results reported herein realize the selective transportation of microdroplets with different volumes and we believe that this method would potentially be used in many important applications, such as selective water droplet transportation, biomolecular quantitative detection and droplet-based biodetection. PMID:24807195

Li, Jian; Jing, Zhijiao; Zha, Fei; Yang, Yaoxia; Wang, Qingtao; Lei, Ziqiang

2014-06-11

308

Turbulent plane Poiseuille-Couette flow as a model for fluid slip over superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

In this study, plane Poiseuille-Couette flow is simulated as a model for specified streamwise slip on one of the channel walls. The relative velocity between the two walls is set to be 1, 2, and 4 in viscous wall units. This is equivalent to the presence of a superhydrophobic surface at one of the channel walls that causes fluid to slip on the boundary. The results show that the streamwise slip forces turbulence in the near-wall region to tend towards a limiting one-component state. This leads to the suppression of small scale turbulence and laminarization close to the wall and then to drag reduction. The selective weakening of the streamwise vorticity close the wall and the observed decrease of turbulence kinetic energy production can then be considered as a consequence of this effect. Changes in the coherent structures, including a decrease of sweep events and increase of ejection events close to the wall where slip occurs, are also observed.

Nguyen, Quoc T.; Papavassiliou, Dimitrios V.

2013-12-01

309

Turbulent plane Poiseuille-Couette flow as a model for fluid slip over superhydrophobic surfaces.  

PubMed

In this study, plane Poiseuille-Couette flow is simulated as a model for specified streamwise slip on one of the channel walls. The relative velocity between the two walls is set to be 1, 2, and 4 in viscous wall units. This is equivalent to the presence of a superhydrophobic surface at one of the channel walls that causes fluid to slip on the boundary. The results show that the streamwise slip forces turbulence in the near-wall region to tend towards a limiting one-component state. This leads to the suppression of small scale turbulence and laminarization close to the wall and then to drag reduction. The selective weakening of the streamwise vorticity close the wall and the observed decrease of turbulence kinetic energy production can then be considered as a consequence of this effect. Changes in the coherent structures, including a decrease of sweep events and increase of ejection events close to the wall where slip occurs, are also observed. PMID:24483565

Nguyen, Quoc T; Papavassiliou, Dimitrios V

2013-12-01

310

Collection efficiencies of an electrostatic sampler with superhydrophobic surface for fungal bioaerosols  

PubMed Central

We recently developed an electrostatic precipitator with superhydrophobic surface (EPSS), which collects particles into a 10- to 40-?l water droplet allowing achievement of very high concentration rates (defined as the ratio of particle concentration in the collection liquid vs. the airborne particle concentration per time unit) when sampling airborne bacteria. Here, we analyzed the performance of this sampler when collecting three commonly found fungal spores – Cladosporium cladosporioides, Penicillium melinii, and Aspergillus versicolor – under different operating conditions. We also adapted adenosine triphosphate (ATP)-based bioluminescence for the analysis of collection efficiency and the concentration rates. The collection efficiency ranged from 10 to 36% at a sampling flow rate of 10 l/min when the airborne fungal spore concentration was approximately 105–106 spores/m3 resulting in concentration rates in the range of 1 × 105–3 × 105/min for a 10-?l droplet. The collection efficiency was inversely proportional to the airborne spore concentration and it increased to above 60% for common ambient spore concentrations, e.g., 104–105 spores/m3. The spore concentrations determined by the ATP-based method were not statistically different from those determined by microscopy and allowed us to analyze spore concentrations that were too low to be reliably detected by microscopy.

Han, T.; Nazarenko, Y.; Lioy, P. J.; Mainelis, G.

2014-01-01

311

Pectin-coated chitosan microgels crosslinked on superhydrophobic surfaces for 5-fluorouracil encapsulation.  

PubMed

5-Fluorouracil (5-FU)-loaded chitosan microgels for oral and topical chemotherapy were prepared applying a superhydrophobic surface-based encapsulation technology. Drug-loaded chitosan dispersions were cross-linked and then coated with drug-free chitosan or pectin layers at the solid-air interface in a highly efficient and environment-friendly way. The size of the microgels (with diameters of ca. 280 and 557 ?m for the chitosan seeds and pectin-coated microgels respectively) was the lowest obtained until now using similar biomimetic methodologies. The microgels were characterized regarding 5-FU release profiles in vitro in aqueous media covering the pH range of the gastrointestinal tract, and cytotoxicity against two cancer cell lines sensitive to 5-FU. Owing to their control of 5-FU release in acidic medium, calcium pectinate-coated microgels can be considered as suitable for oral administration. Growth inhibition of cancer cells by 5-FU was greater when incorporated to chitosan microgels; these being potentially useful for treatment of skin and colorectal tumors. PMID:23987352

Puga, Ana M; Lima, Ana Catarina; Mano, Joao F; Concheiro, Angel; Alvarez-Lorenzo, Carmen

2013-10-15

312

Surface nanostructures in manganite films.  

PubMed

Ultrathin manganite films are widely used as active electrodes in organic spintronic devices. In this study, a scanning tunnelling microscopy (STM) investigation with atomic resolution revealed previously unknown surface features consisting of small non-stoichiometric islands. Based upon this evidence, a new mechanism for the growth of these complex materials is proposed. It is suggested that the non-stoichiometric islands result from nucleation centres that are below the critical threshold size required for stoichiometric crystalline growth. These islands represent a kinetic intermediate of single-layer growth regardless of the film thickness, and should be considered and possibly controlled in manganite thin-film applications. PMID:24941969

Gambardella, A; Graziosi, P; Bergenti, I; Prezioso, M; Pullini, D; Milita, S; Biscarini, F; Dediu, V A

2014-01-01

313

Surface Nanostructures in Manganite Films  

PubMed Central

Ultrathin manganite films are widely used as active electrodes in organic spintronic devices. In this study, a scanning tunnelling microscopy (STM) investigation with atomic resolution revealed previously unknown surface features consisting of small non-stoichiometric islands. Based upon this evidence, a new mechanism for the growth of these complex materials is proposed. It is suggested that the non-stoichiometric islands result from nucleation centres that are below the critical threshold size required for stoichiometric crystalline growth. These islands represent a kinetic intermediate of single-layer growth regardless of the film thickness, and should be considered and possibly controlled in manganite thin-film applications.

Gambardella, A.; Graziosi, P.; Bergenti, I.; Prezioso, M.; Pullini, D.; Milita, S.; Biscarini, F.; Dediu, V. A.

2014-01-01

314

Macroscopically flat and smooth superhydrophobic surfaces: heating induced wetting transitions up to the Leidenfrost temperature.  

PubMed

We present an investigation of the change in wettability of water droplets on 3 different flat, smooth substrates with an elevation in temperature. Two methods were employed. In the first method the droplet was placed on the substrate before it was heated and in the second method the droplets were induced to fall onto a preheated substrate. We find that the intrinsic wettability of the surface is important and that fundamentally different behavior is observed on a hydrophobic surface relative to hydrophilic surfaces. For the hydrophobic surface and employing the first method, we have observed three different regimes over the temperature range of 65 degrees C to 270 degrees C. In regime I (65 degrees C to 110 degrees C), the contact angle of water droplets exhibit a slight decrease from 108 degrees to 105 degrees and an accompanying significant decrease in droplet lifetime (tau) from approximately 111 s to approximately 30 s is observed. In regime II (120 degrees C to 190 degrees C), tau remains constant at approximately 20 s however the contact angle significantly increases from 127 degrees to 158 degrees--that is we enter a superhydrophobic regime on a flat surface. In this regime the droplet remains stationary on the surface. Regime III (210 degrees C to 270 degrees C), is the Leidenfrost regime in which the water droplet exhibits a rapid motion on the solid surface with a contact angle higher than 160 degrees. In comparison, the wetting behavior of a water droplet on two relatively hydrophilic surfaces (Au and GaAs) have also been investigated as a function of temperature. Here no wetting transition is observed from 65 degrees C up to 365 degrees C. In the second method, the wetting behavior on the hydrophobic surface is similar to that observed in the first method for temperatures below the Leidenfrost temperature and the water droplet rebounds from the solid surface at higher temperatures. Additionally, the Leidenfrost phenomenon can be observed above 280 degrees C for the hydrophilic surfaces. PMID:21043419

Liu, Guangming; Craig, Vincent S J

2010-01-01

315

Superhydrophobic surfaces formed using layer-by-layer self-assembly with aminated multiwall carbon nanotubes.  

PubMed

A convenient and simple route to functionalized multiwall carbon nanotubes (MWNTs) using the reaction of the amine (NH) groups of polyethyleneimine (PEI) with MWNTs in N,N-dimethylformamide (DMF) at 50 degrees C is described. The product functionalized MWNTs (MWNT-NH-PEI) contain 6-8% by weight PEI based on elemental analysis, thermal gravimetric analysis, and titration. The products form stable emulsions in water below pH 9 and can be derivatized to form alkylated MWNTs that are dispersible in organic media. Such MWNT-NH-PEI nanoparticles can also be used in covalent or ionic layer-by-layer assembly to form nanocomposite thin films on functionalized polyethylene (PE) films and powders. Such nanocomposite films were analyzed by contact angle analysis, atomic force microscopy (AFM), and confocal Raman microscopy. These analyses show that these superhydrophilic surfaces have micro/nanoroughness with a roughly uniform distribution of MWNT nanoparticles. Superhydrophobic PE films can be formed either from ionic layer-by-layer self-assembly of MWNT-NH-PEIs and poly(acrylic acid) or from covalent layer-by-layer self-assembly of MWNT-NH-PEIs and Gantrez if the final graft is acrylated with a mixed anhydride prepared from ethyl chloroformate and octadecanoic acid. The resulting octadecylated surface produced by five covalent layer-by-layer deposition steps has a water contact angle of 165 degrees and a sliding angle of less than 5 degrees. The corresponding surface produced by five ionic layer-by-layer deposition steps has a water contact angle of 155 degrees but exhibits water pinning. The ionically assembled nanocomposite graft is labile under acidic conditions. The covalently assembled graft is more chemically robust. PMID:18324860

Liao, Kang-Shyang; Wan, Albert; Batteas, James D; Bergbreiter, David E

2008-04-15

316

A low-cost filler-dissolved process for fabricating super-hydrophobic poly(dimethylsiloxane) surfaces with either lotus or petal effect  

NASA Astrophysics Data System (ADS)

A low-cost filler (salt) water-dissolved method is developed to produce large-area and flexible super-hydrophobic surfaces by using poly(dimethylsiloxane) (PDMS) material. Five levels of salt grain sizes are used to examine the filler size effect on fabricating the super-hydrophobic surfaces and on the hydrophobic mechanism involved. The results show that the surfaces fabricated using grain sizes of 53–74 and 74–104 µm exhibit the lotus effect (cell adhesion (CA) > 150° and self-adhesion (SA) < 10°) whereas those using grain sizes of 0–25 µm and above 104 µm reveal the petal effect (CA > 150° and high adhesion even upside-down). The super-hydrophobic characteristic is achieved mainly by the large micro rib-like structures, small micro rock-like bumps, and textures on the bump due to the fillers.

Lin, Yung-Tsan; Chou, Jung-Hua

2014-05-01

317

Droplet compression and relaxation by a superhydrophobic surface: contact angle hysteresis.  

PubMed

In this article, the contact angle hysteresis (CAH) of acrylic glass is experimentally and theoretically studied through the compression-relaxation process of droplets by using a superhydrophobic surface with negligible CAH effect. In contrast to the existing technique in which the volume of the droplet changes during the measurement of CAH, this procedure is carried out at a constant volume of the droplet. By observing the base diameter (BD) and the contact angle (CA) of the droplet during the compression-relaxation process, the wetting behavior of the droplet can be divided into two regimes, the contact line withdrawal and the contact line pinning regimes, depending on the gap thickness (H) at the end of the compression process. During the compression process, both regimes possess similar droplet behavior; the contact line will move outward and the BD will expand while the CA remains at the advancing angle. During the relaxation process, the two regimes are significantly different. In the contact line withdrawal regime, the contact line will withdraw with the CA remaining at the receding angle. In the contact line pinning regime, however, the contact line will be pinned at the final position and the CA will decline to a certain value higher than the receding angle. Furthermore, the advancing pinning behavior can also be realized through a successive compression-relaxation process. On the basis of the liquid-induced defects model, Surface Evolver simulations are performed to reproduce the behavior of the droplet during the compression-relaxation process; both contact line withdrawal and pinning regimes can also be identified. The results of the experiment and simulation agree with each other very well. PMID:22390774

Hong, Siang-Jie; Chou, Tung-He; Chan, Seong Heng; Sheng, Yu-Jane; Tsao, Heng-Kwong

2012-04-01

318

Effects of hydraulic pressure on the stability and transition of wetting modes of superhydrophobic surfaces.  

PubMed

The underlying mechanisms of stability, metastability, or instability of the Cassie-Baxter and Wenzel wetting modes and their transitions on superhydrophobic surfaces decorated with periodic micropillars are quantitatively studied in this article. Hydraulic pressure, which may be generated by the water-air interfacial tension of water droplets or external factors such as raining impact, is shown to be a key to understanding these mechanisms. A detailed transition process driven by increasing hydraulic pressure is numerically simulated. The maximum sustainable or critical pressure of the Cassie-Baxter wetting state on a pillarlike microstructural surface is formulated for the first time in a simple, unified, and precise form. This analytic result reveals the fact that reducing the microstructural scales (e.g., the pillars' diameters and spacing) is probably the most efficient measure needed to enlarge the critical pressure significantly. We also introduce a dimensionless parameter, the pillar slenderness ratio, to characterize the stability of either the Cassie-Baxter or the Wenzel wetting state and show that the energy barrier for transitioning from the Cassie-Baxter to the Wenzel wetting mode is proportional to both the slenderness ratio and the area fraction. Thus, the Cassie-Baxter wetting mode may collapse under a hydraulic pressure lower than the critical one if the slenderness ratio is improperly small. This quantitative study explains fairly well some experimental observations of contact angles that can be modeled by neither Wenzel nor Cassie-Baxter contact angles and eventually leads to our proposals for a mixed (or coexisting) wetting mode. PMID:16342993

Zheng, Q-S; Yu, Y; Zhao, Z-H

2005-12-20

319

Fabrication of superhydrophobic silica-based surfaces with high transmittance by using tetraethoxysilane precursor and different polymeric species  

NASA Astrophysics Data System (ADS)

The preparation of superhydrophobic silica-based surfaces via the sol-gel process through the addition of different polymeric species into the precursor solution was done in this study. The surface roughness of the films was obtained by removing the organic polymer at a high temperature, and then the hydrophobic groups were bonded onto the films with a monolayer by chemical reaction with hexamethyldisilazane (HMDS). The characteristic properties of the as-prepared films were analyzed by contact angle measurements, scanning electron microscopy (SEM), atomic force microscopy (AFM), nitrogen adsorption/desorption, and UV-vis scanning spectrophotometer. The experimental results revealed that the superhydrophobic thin films with high transmittance could easily be prepared using polypropylene (PPG), polyethylene (PEG), and poly(vinylpyrrolidone) (PVP). Surface roughness and pore size were enhanced using PPG polymeric species. The distribution of pore size was from the microporous to the mesoporous and marcoporous regions. In addition, the contact angles of the rough surfaces prepared at 500 °C without modification of HMDS were smaller than 5° but larger than 156° after modified by HMDS.

Chen, Yu-Kai; Chang, Kuei-Chien; Wu, Kuan-Yu; Tsai, Yen-Ling; Lu, Juhng-shu; Chen, Hui

2009-07-01

320

Influence of Slip on the Flow Past Superhydrophobic Circular Cylinders  

Microsoft Academic Search

Superhydrophobic surfaces have been shown to produce significant drag reduction for both laminar and turbulent flows of water through large and small-scale channels. In this presentation a series of experiments will be presented which investigate the effect of superhydrophobic-induced slip on the flow past a circular cylinder. In these experiments, circular cylinders are coated with a series of superhydrophobic surfaces

Jonathan Rothstein; Robert Daniello; Nangelie Ferrer; Pranesh Muralidhar

2010-01-01

321

Interaction of lipid membrane with nanostructured surfaces.  

PubMed

Tiny details of the phospholipid (DMPC) membrane morphology in close vicinity to nanostructured silica surfaces have been discovered in the atomic force microscopy experiments. The structural features of the silica surface were varied in the experiments by the deposition of silica nanoparticles of different diameter on plane and smooth silica substrates. It was found that, due to the barrier function of the lipid membrane, only particles larger than 22 nm in diameter with a smooth surface were completely enveloped by the lipid membrane. However, nanoparticles with bumpy surfaces (curvature diameter of bumps as that of particles <22 nm) were only partially enveloped by the lipid bilayer. For the range of nanostructure dimensions between 1.2 and 22 nm, the lipid membrane underwent structural rearrangements by forming pores (holes). The nanoparticles were accommodated into the pores but not enveloped by the lipid bilayer. The study also found that the lipid membrane conformed to the substrate with surface structures of dimensions less than 1.2 nm without losing the membrane integrity. The experimental results are in accord with the analytical free energy model, which describes the membrane coverage, and numerical simulations which evaluate adhesion of the membrane and dynamics as a function of surface topology. The results obtained in this study are useful for the selection of dimensions and shapes for drug-delivery cargo and for the substrate for supported lipid bilayers. They also help in qualitative understanding the role of length scales involved in the mechanisms of endocytosis and cytotoxicity of nanoparticles. These findings provide a new approach for patterning supported lipid membranes with well-defined features in the 1.2-22 nm range. PMID:19466783

Roiter, Yuri; Ornatska, Maryna; Rammohan, Aravind R; Balakrishnan, Jitendra; Heine, David R; Minko, Sergiy

2009-06-01

322

Fabrication and icing property of superhydrophilic and superhydrophobic aluminum surfaces derived from anodizing aluminum foil in a sodium chloride aqueous solution  

NASA Astrophysics Data System (ADS)

An aluminum foil with a rough surface was first prepared by anodic treatment in a neutral aqueous solution with the help of pitting corrosion of chlorides. First, the hydrophobic Al surface (contact angle around 79°) became superhydrophilic (contact angle smaller than 5°) after the anodizing process. Secondly, the superhydrophilic Al surface became superhydrophobic (contact angle larger than 150°) after being modified by oleic acid. Finally, the icing property of superhydrophilic, untreated, and superhydrophobic Al foils were investigated in a refrigerated cabinet at -12 °C. The mean total times to freeze a water droplet (6 ?L) on the three foils were 17 s, 158 s and 1604 s, respectively. Thus, the superhydrophilic surface accelerates the icing process, while the superhydrophobic surface delays the process. The main reason for this transition might mainly result from the difference of the contact area of the water droplet with Al substrate: the increase in contact area with Al substrate will accelerate the heat conduct process, as well as the icing process; the decrease in contact area with Al substrate will delay the heat conduct process, as well as the icing process. Compared to the untreated Al foil, the contact area of the water droplet with the Al substrate was higher on superhydrophilic surface and smaller on the superhydrophobic surface, which led to the difference of the heat transfer time as well as the icing time.

Song, Meirong; Liu, Yuru; Cui, Shumin; Liu, Long; Yang, Min

2013-10-01

323

Using amphiphilic nanostructures to enable long-range ensemble coalescence and surface rejuvenation in dropwise condensation.  

PubMed

Controlling coalescence events in a heterogeneous ensemble of condensing droplets on a surface is an outstanding fundamental challenge in surface and interfacial sciences, with a broad practical importance in applications ranging from thermal management of high-performance electronic devices to moisture management in high-humidity environments. Nature-inspired superhydrophobic surfaces have been actively explored to enhance heat and mass transfer rates by achieving favorable dynamics during dropwise condensation; however, the effectiveness of such chemically homogeneous surfaces has been limited because condensing droplets tend to form as pinned Wenzel drops rather than mobile Cassie ones. Here, we introduce an amphiphilic nanostructured surface, consisting of a hydrophilic base with hydrophobic tips, which promotes the periodic regeneration of nucleation sites for small droplets, thus rendering the surface self-rejuvenating. This unique amphiphilic nanointerface generates an arrangement of condensed Wenzel droplets that are fluidically linked by a wetted sublayer, promoting previously unobserved coalescence events where numerous droplets simultaneously merge, without direct contact. Such ensemble coalescences rapidly create fresh nucleation sites, thereby shifting the overall population toward smaller droplets and enhancing the rates of mass and heat transfer during condensation. PMID:22456273

Anderson, David M; Gupta, Maneesh K; Voevodin, Andrey A; Hunter, Chad N; Putnam, Shawn A; Tsukruk, Vladimir V; Fedorov, Andrei G

2012-04-24

324

Nanostructure formation on muscovite mica surface induced by ions  

NASA Astrophysics Data System (ADS)

We studied the nanostructure formation induced by ions on muscovite mica surface. A series of AFM measurements of the surface nanostructures are performed for the different projectiles with the energy ranging from several hundred keV to several MeV.

Zhou, P.; Zhang, H. Q.; Zhang, Q.; Liu, Z.; Guan, S.; Chen, X.

2014-04-01

325

Nanofibers-based nanoweb promise superhydrophobic polyaniline: from star-shaped to leaf-shaped structures.  

PubMed

Star-shaped and leaf-shaped polyaniline (PANI) hierarchical structures with interlaced nanofibers on the surface were successfully prepared by chemical polymerization of aniline in the presence of lithium triflate (LT). Chemical structure and composition of the star-like PANI obtained were characterized by FTIR and UV-vis spectra. PANI 2D architectures can be tailored from star-shaped to leaf-shaped structures by change the concentration of LT. The synthesized star-like and leaf-like polyaniline show good superhydrophobicity with water contact angles of both above 150° due to the combination of the rough nanoweb structure and the low surface tension of fluorinated chain of dopant. This method is a facile and applicable strategy for a large-scale fabrication of 2D PANI micro/nanostructures. Many potential applications such as self-cleaning and antifouling coating can be expected based on the superhydrophobic PANI micro/nanostructures. PMID:23978289

Fan, Haosen; Wang, Hao; Guo, Jing; Zhao, Ning; Xu, Jian

2013-11-01

326

Surface Localization of Buried III-V Semiconductor Nanostructures.  

PubMed

In this work, we study the top surface localization of InAs quantum dots once capped by a GaAs layer grown by molecular beam epitaxy. At the used growth conditions, the underneath nanostructures are revealed at the top surface as mounding features that match their density with independence of the cap layer thickness explored (from 25 to 100 nm). The correspondence between these mounds and the buried nanostructures is confirmed by posterior selective strain-driven formation of new nanostructures on top of them, when the distance between the buried and the superficial nanostructures is short enough (d = 25 nm). PMID:20596455

Alonso-González, P; González, L; Fuster, D; Martín-Sánchez, J; González, Yolanda

2009-01-01

327

Facile synthesis of superhydrophobic surface of ZnO nanoflakes: chemical coating and UV-induced wettability conversion  

NASA Astrophysics Data System (ADS)

This work reports an oriented growth process of two-dimensional (2D) ZnO nanoflakes on aluminum substrate through a low temperature hydrothermal technique and proposes the preliminary growth mechanism. A bionic superhydrophobic surface with excellent corrosion protection over a wide pH range in both acidic and alkaline solutions was constructed by a chemical coating treatment with stearic acid (SA) molecules on ZnO nanoflakes. It is found that the superhydrophobic surface of ZnO nanoflake arrays shows a maximum water contact angle (CA) of 157° and a low sliding angle of 8°, and it can be reversibly switched to its initial superhydrophilic state under ultraviolet (UV) irradiation, which is due to the UV-induced decomposition of the coated SA molecules. This study is significant for simple and inexpensive building of large-scale 2D ZnO nanoflake arrays with special wettability which can extend the applications of ZnO films to many other important fields.

Yao, Lujun; Zheng, Maojun; Li, Changli; Ma, Li; Shen, Wenzhong

2012-04-01

328

An experimental investigation into the icing and melting process of a water droplet impinging onto a superhydrophobic surface  

NASA Astrophysics Data System (ADS)

The freezing and melting process of a small water droplet on a superhydrophobic cold surface was investigated using the Laser Induced Fluorescence (LIF) technique. The superhydrophobic surface was prepared using a sol-gel method on a red copper test plate. From the obtained fluorescence images, the phase transition characteristics during the freezing and melting process of a water droplet were clearly observed. It was found that, at the beginning of the droplet freezing process, liquid water turned into ice at a very fast rate. Such phase transition process decreased gradually with time and the volume of frozen ice approached a constant value at the end of the icing process. In addition, the freezing time was found to reduce with the decrease of the test plate temperature. Besides, when the test plate temperature is relatively high, the effect of droplet volume on the freezing time is very significant. Over all, we provide some tentative insights into the microphysical process related to the icing and melting process of water droplets.

Jin, ZheYan; Jin, SongYue; Yang, ZhiGang

2013-11-01

329

Facile synthesis of superhydrophobic surface of ZnO nanoflakes: chemical coating and UV-induced wettability conversion.  

PubMed

This work reports an oriented growth process of two-dimensional (2D) ZnO nanoflakes on aluminum substrate through a low temperature hydrothermal technique and proposes the preliminary growth mechanism. A bionic superhydrophobic surface with excellent corrosion protection over a wide pH range in both acidic and alkaline solutions was constructed by a chemical coating treatment with stearic acid (SA) molecules on ZnO nanoflakes. It is found that the superhydrophobic surface of ZnO nanoflake arrays shows a maximum water contact angle (CA) of 157° and a low sliding angle of 8°, and it can be reversibly switched to its initial superhydrophilic state under ultraviolet (UV) irradiation, which is due to the UV-induced decomposition of the coated SA molecules. This study is significant for simple and inexpensive building of large-scale 2D ZnO nanoflake arrays with special wettability which can extend the applications of ZnO films to many other important fields. PMID:22500967

Yao, Lujun; Zheng, Maojun; Li, Changli; Ma, Li; Shen, Wenzhong

2012-01-01

330

Facile synthesis of superhydrophobic surface of ZnO nanoflakes: chemical coating and UV-induced wettability conversion  

PubMed Central

This work reports an oriented growth process of two-dimensional (2D) ZnO nanoflakes on aluminum substrate through a low temperature hydrothermal technique and proposes the preliminary growth mechanism. A bionic superhydrophobic surface with excellent corrosion protection over a wide pH range in both acidic and alkaline solutions was constructed by a chemical coating treatment with stearic acid (SA) molecules on ZnO nanoflakes. It is found that the superhydrophobic surface of ZnO nanoflake arrays shows a maximum water contact angle (CA) of 157° and a low sliding angle of 8°, and it can be reversibly switched to its initial superhydrophilic state under ultraviolet (UV) irradiation, which is due to the UV-induced decomposition of the coated SA molecules. This study is significant for simple and inexpensive building of large-scale 2D ZnO nanoflake arrays with special wettability which can extend the applications of ZnO films to many other important fields.

2012-01-01

331

A non-aqueous electrodeposition process for fabrication of superhydrophobic surface with hierarchical micro/nano structure  

NASA Astrophysics Data System (ADS)

In this work, we present a novel facile electrodeposition approach to create micro/nano structure on an anodic copper plate with an alkali ethanol electrolyte solution. The electrolyte solution is composed of potassium hydroxide, potassium persulfate and ethanol. Hierarchical structures were formed on an anodic copper surface by an alkali assistant oxidation process, water immersion and fluorination, the as-prepared surface exhibits superhydrophobic property. The creation of morphological structures and chemical compositions on the treated surface was revealed by scanning electron microscopy (SEM) and X-ray diffraction techniques. The resulting surfaces composing of Cu(OH)2 arrays demonstrates that water contact angle is as high as 165° and the rolling angle is less than 3°. The study is expected to create a new avenue for the basic research as well as real application.

Hao, Limei; Chen, Zhi; Wang, Ruiping; Guo, Changli; Zhang, Pengli; Pang, Shaofang

2012-09-01

332

Facile fabrication of superhydrophobic flower-like polyaniline architectures by using valine as a dopant in polymerization  

NASA Astrophysics Data System (ADS)

A facile method was developed to fabricate superhydrophobic, flower-like polyanline (PANI) architectures with hierarchical nanostructures by adding valine in polymerization as a dopant. The water contact angle of the prepared PANI film was measured to be 155.3°, and the hydrophobic surface of the PANI architectures can be tuned easily by varying the polymerization time as well as valine doping quantity. It is believed that valine plays an important role in not only growth of the hierarchical PANI structures but also formation of the superhydrophobic surface, for it provides functional groups such as sbnd COOH, sbnd NH2 and a hydrophobic terminal group which may further increase intra-/inter-molecular interactions including hydrogen bonding, ?-? stacking and hydrophobic properties. Similar flower-like PANI architectures have been prepared successfully by employing other amino acids such as threonine, proline and arginine. This method makes it possible for widespread applications of superhydrophobic PANI film due to its simplicity and practicability.

Sun, Jun; Bi, Hong

2012-03-01

333

A lattice Boltzmann code for direct numerical simulation of skin-friction drag reduction by superhydrophobic surfaces in turbulent channel flow  

Microsoft Academic Search

A lattice Boltzmann code for direct numerical simulation of flow over superhydrophobic surfaces has been developed. The code solves the Boltzmann equation for two different sets of particle distribution functions based on the Shan and Chen model [1], to account for the gas-liquid interactions. The immiscibility and inter-phase interactions are controlled through an interaction body force between the distribution functions.

Amirreza Rastegari; Rayhaneh Akhavan

2010-01-01

334

Rational nanostructuring of surfaces for extraordinary icephobicity  

NASA Astrophysics Data System (ADS)

Icing of surfaces is commonplace in nature, technology and everyday life, bringing with it sometimes catastrophic consequences. A rational methodology for designing materials with extraordinary resistance to ice formation and adhesion remains however elusive. We show that ultrafine roughnesses can be fabricated, so that the ice nucleation-promoting effect of nanopits on surfaces is effectively counteracted in the presence of an interfacial quasiliquid layer. The ensuing interface confinement strongly suppresses the stable formation of ice nuclei. We explain why such nanostructuring leads to the same extremely low, robust nucleation temperature of ~-24 °C for over three orders of magnitude change in RMS size (~0.1 to ~100 nm). Overlaying such roughnesses on pillar-microtextures harvests the additional benefits of liquid repellency and low ice adhesion. When tested at a temperature of -21 °C, such surfaces delayed the freezing of a sessile supercooled water droplet at the same temperature by a remarkable 25 hours.Icing of surfaces is commonplace in nature, technology and everyday life, bringing with it sometimes catastrophic consequences. A rational methodology for designing materials with extraordinary resistance to ice formation and adhesion remains however elusive. We show that ultrafine roughnesses can be fabricated, so that the ice nucleation-promoting effect of nanopits on surfaces is effectively counteracted in the presence of an interfacial quasiliquid layer. The ensuing interface confinement strongly suppresses the stable formation of ice nuclei. We explain why such nanostructuring leads to the same extremely low, robust nucleation temperature of ~-24 °C for over three orders of magnitude change in RMS size (~0.1 to ~100 nm). Overlaying such roughnesses on pillar-microtextures harvests the additional benefits of liquid repellency and low ice adhesion. When tested at a temperature of -21 °C, such surfaces delayed the freezing of a sessile supercooled water droplet at the same temperature by a remarkable 25 hours. Electronic supplementary information (ESI) available: Thermodynamic framework and statistical methods for data analyses; details of ice nucleation delay measurements and prediction of the delays around the median nucleation temperature; additional SEM and AFM images not shown in the main paper and complete contact angle characterization; derivation of the nanoscale interface confinement effect; an error assessment, detailed results of droplet impact experiments on hydrophilic and hydrophobic substrates; methods for surface preparation and characterization; description of the experimental set-up and protocols; five videos supporting the text. See DOI: 10.1039/c3nr06644d

Eberle, Patric; Tiwari, Manish K.; Maitra, Tanmoy; Poulikakos, Dimos

2014-04-01

335

Drag reduction of a miniature boat with superhydrophobic grille bottom  

Microsoft Academic Search

Water strider can slide on water surface with a very small drag force using its long superhydrophobic legs. Inspired by the water strider legs, we report here a novel design of superhydrophobic grille structure for drag reduction. A miniature boat covered with a superhydrophobic grille at the bottom is fabricated and compared with a normal boat with flat bottom in

C. G. Jiang; S. C. Xin; C. W. Wu

2011-01-01

336

Integrating anti-reflection and superhydrophobicity of moth-eye-like surface morphology on a large-area flexible substrate  

NASA Astrophysics Data System (ADS)

This paper proposes an ultraviolet nanoimprint lithography (UV-NIL) roll-to-roll (R2R) process with argon and oxygen (Ar-O2) plasma ashing and coating of a dilute perfluorodecyltrichlorosilane (FDTS) layer to fabricate the large-area moth-eye-like surface morphology on a polyethylene terephthalate substrate. By using Maxwell-Garnett's effective medium theory, the optimal dimensions of the moth-eye-like surface morphology was designed and fabricated with UV-NIL R2R process to obtain maximum transmittance ratio. In addition, the base angle (? = 30.1°) of the moth-eye-like surface morphology was modified with Ar-O2 plasma ashing and coated with a dilute FDTS layer to possess both superhydrophobic and air-retention properties. This increases both the transmittance ratio of 4% and contact angle to 153°.

Liu, Chia-Hsing; Niu, Pei-Lun; Sung, Cheng-Kuo

2014-01-01

337

Making micro soccer balls: Spherical macro-clusters of colloidal particles by droplet evaporation on superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

Imagine a clean capillary droplet evaporating in a fakir state on a superhydrophobic micro-structured surface. When the superhydrophobicity is robust enough, the droplet will always remain on top of the micro-structure and the droplet will retain its spherical shape until its ``death.'' Very often one can observe the remains of the impurities within the droplet left on top of the structure at the end of the process. In this work, instead of using clean liquid droplets, we use dilute colloidal dispersion droplets of monodisperse polymer micro-spheres (sizes from 0.2 to 2?m). The colloidal dispersion droplet retains its spherical shape during its whole life, even when the whole solution has been evaporated. The remaining object consist on a spherical-shaped massive cluster of particles with diameters ranging from a few tens of microns up to several hundreds of microns, depending on the amount of micro-particles present in the solution and on the final packing fraction. We will discuss on the different observed packing fractions, particle arrangements and their governing parameters. Additionally some predictions will also be introduced.

Marin, Alvaro; Susarrey-Arce, Arturo; Gardeniers, Han; Lohse, Detlef

2011-11-01

338

Nanostructured surface made from polymer\\/carbon nanotube has higher conductivity than noble metal surface  

Microsoft Academic Search

We made a nanostructured surface by directly coating carbon nanotubes to a surface that was previously solvent-coated with a polymer\\/CNT composite. Compared to the surface coated with the same polymer composite where the surface carbon nanotubes were buried in the matrix polymer, the surface directly coated with carbon nanotubes had a significant amount of exposed nanostructures. The surface was immersed

Suping Lyu; James Coles; Ken Gardenski; Scott Brabec; Chris Hobot

2010-01-01

339

Surface nanostructuring of Ni\\/Cu foilsby femtosecond laser pulses  

Microsoft Academic Search

This work examines the effect of high-power femtosecond laser pulses on Ni\\/Cu bilayer foils produced by electrodeposition. We consider nanostructures formed at different laser beam parameters and under different ambient conditions. The surface nanostructures obtained in air and water have mostly the form of quasi-periodic ripples with a characteristic period of 400 --- 450 and 370 --- 390 nm, respectively,

V. P. Korol'kov; Andrei A. Ionin; Sergei I. Kudryashov; L. V. Seleznev; D. V. Sinitsyn; R. V. Samsonov; A. I. Maslii; A. Zh Medvedev; B. G. Gol'denberg

2011-01-01

340

Scalable superhydrophobic coatings based on fluorinated diatomaceous earth: Abrasion resistance versus particle geometry  

NASA Astrophysics Data System (ADS)

Bio-inspired superhydrophobic surfaces were fabricated based on fossilized silica fresh water diatomaceous earth (DE) particles. These nanostructured silicified diatom frustules of cylindrical and circular structures were fluorinated to impart them with superhydrophobic properties. Substrates coated with superhydrophobic DE structures of varying size and shape were found to have water contact angles of approximately 170° and sliding angles of approximately 3°. The substrates were subjected to significant abrasion forces using a standard surface abrader. The ability to retain their superhydrophobic properties was observed to depend on the geometry and average size of the DE particles. The wettability of the abraded coatings was determined by their surface topology, and a transition from a non-wetted state to a partially wetted state was observed to occur and was dependent on the surface roughness. The proposed coatings are scalable, cost-effective, and can be applied on a variety of surfaces on critical infrastructures requiring protection from water saturation, ice formation and water based corrosion.

Polizos, Georgios; Winter, Kyle; Lance, Michael J.; Meyer, Harry M.; Armstrong, Beth L.; Schaeffer, Daniel A.; Simpson, John T.; Hunter, Scott R.; Datskos, Panos G.

2014-02-01

341

VIV of cylinders with superhydrophobic coating  

NASA Astrophysics Data System (ADS)

For several years, superhydrophobic surfaces which are chemically hydrophobic with micron or nanometer scale surface features have been considered for their ability to reduce drag in microfluidic devices. More recently it has been demonstrated that superhydrophobic surfaces reduce friction coefficient in turbulent flows as well. In this talk, we will consider the effect of superhydrophobic surfaces on vortex induced vibrations of an elastically mounted circular cylinder. Effects on frequency and amplitude will be considered and particle image velocimetry will be used to examine vortices shed from the superhydrophobically coated moving cylinders. Several unique superhydrophobic microstructures will be used in the Cassie and Wenzel states to demonstrate the effect of microstructure and preferential slip direction on the oscillations of the cylinder.

Daniello, Robert; Rothstein, Jonathan

2011-11-01

342

Morphological evolution of nanostructured surface using anodic aluminum template  

NASA Astrophysics Data System (ADS)

Nanoporous anodic aluminum oxide (AAO) templates are fabricated using an anodization method. The mean diameter of the nanoporous anodic aluminum oxide templates is 100 nm. A molded plastic thin film with nano-structure is fabricated using AAO template as a mold insert by nanoimprint. The surface properties of the molded plastic thin film obtained using various processing parameters in nanoimprint are discussed. The contact angle of the molded polycarbonate (PC) thin film with the nano-structure exceeds that without the nano-structure. The molded PC thin film (with nano-structure) with a hydrophobic surface is formed, and has a water contact angle of 128.5°. The use of anodic aluminum oxide to prepare a mold insert for nanoimprint supports the formation of a nano-structure in the molded PC thin film, and effectively increases its reflectance.

Chiu, Chui-Yu; Huang, Chiung-Fang; Lee, Jeou-Long; Lin, Yi; Shen, Yung-Kang

2011-11-01

343

How superhydrophobicity breaks down  

PubMed Central

A droplet deposited or impacting on a superhydrophobic surface rolls off easily, leaving the surface dry and clean. This remarkable property is due to a surface structure that favors the entrainment of air cushions beneath the drop, leading to the so-called Cassie state. The Cassie state competes with the Wenzel (impaled) state, in which the liquid fully wets the substrate. To use superhydrophobicity, impalement of the drop into the surface structure needs to be prevented. To understand the underlying processes, we image the impalement dynamics in three dimensions by confocal microscopy. While the drop evaporates from a pillar array, its rim recedes via stepwise depinning from the edge of the pillars. Before depinning, finger-like necks form due to adhesion of the drop at the pillar’s circumference. Once the pressure becomes too high, or the drop too small, the drop slowly impales the texture. The thickness of the air cushion decreases gradually. As soon as the water–air interface touches the substrate, complete wetting proceeds within milliseconds. This visualization of the impalement dynamics will facilitate the development and characterization of superhydrophobic surfaces.

Papadopoulos, Periklis; Mammen, Lena; Deng, Xu; Vollmer, Doris; Butt, Hans-Jurgen

2013-01-01

344

From petal effect to lotus effect: a facile solution immersion process for the fabrication of super-hydrophobic surfaces with controlled adhesion.  

PubMed

In this paper, a convenient approach based on the reaction between an alkyl thiol and hierarchical structured Cu(OH)2 substrates is reported for the fabrication of super-hydrophobic surfaces with controlled adhesion. This reaction can etch the Cu(OH)2 microstructures and simultaneously introduce a coating with low surface energy. By simply controlling the reaction time or the chain length of the thiol, super-hydrophobic surfaces with controlled adhesion can be achieved, and the adhesive force between the surface and the water droplet can be adjusted from extreme low (?14 ?N) to very high (?65 ?N). The tunable effect of the adhesion is ascribed to the different wetting states for the droplet on the surface that results from the change of the morphology and microstructure scale after the thiolate reaction. Noticeably, the as-prepared surfaces are acid/alkali-resisting; the acidic and basic water droplets have similar contact angles and adhesive forces to that of the neutral water droplet. Moreover, we demonstrate a proof of water droplet transportation for application in droplet-based microreactors via our surfaces. We believe that the results reported here would be helpful for the further understanding of the effect of wetting states on the surface adhesion and the fabrication principle for a super-hydrophobic surface with controlled adhesion. PMID:23429404

Cheng, Zhongjun; Du, Ming; Lai, Hua; Zhang, Naiqing; Sun, Kening

2013-04-01

345

Rapid fabrication of nanostructured surfaces using nanocoining.  

PubMed

A new process for creating high quality ordered arrays of nanofeatures called nanocoining is presented. A diamond die with a structured area of nanofeatures (1600 features in a 20 ?m × 20 ?m area) is used to physically transfer features to a mold surface. The die is attached to an actuator capable of producing an elliptical tool-path, the dimensions of which are process dependent and enable the die to match velocity with the moving mold during contact to avoid dragging the nanostructured area along the mold surface (smear). Nanocoining process parameters are discussed which enable indents to be indexed precisely to completely cover target areas. Techniques for die alignment and depth control are also required to create large areas (339 mm(2)) of nanofeatures in short times (?20 min). Nanocoining experiments were performed at 1 kHz (1000 indents or 1.6 million features per second) on a flat electroless nickel sample. UV curable replicates were then created from the nickel mold and both the mold and replicate were examined in an SEM and AFM. PMID:23018619

Zdanowicz, Erik; Dow, Thomas A; Scattergood, Ronald O

2012-10-19

346

An introduction to superhydrophobicity.  

PubMed

This paper is derived from a training session prepared for COST P21. It is intended as an introduction to superhydrophobicity to scientists who may not work in this area of physics or to students. Superhydrophobicity is an effect where roughness and hydrophobicity combine to generate unusually hydrophobic surfaces, causing water to bounce and roll off as if it were mercury and is used by plants and animals to repel water, stay clean and sometimes even to breathe underwater. The effect is also known as The Lotus Effect(®) and Ultrahydrophobicity. In this paper we introduce many of the theories used, some of the methods used to generate surfaces and then describe some of the implications of the effect. PMID:19944399

Shirtcliffe, Neil J; McHale, Glen; Atherton, Shaun; Newton, Michael I

2010-12-15

347

Liquid-infused nanostructured surfaces with extreme anti-ice and anti-frost performance.  

PubMed

Ice-repellent coatings can have significant impact on global energy savings and improving safety in many infrastructures, transportation, and cooling systems. Recent efforts for developing ice-phobic surfaces have been mostly devoted to utilizing lotus-leaf-inspired superhydrophobic surfaces, yet these surfaces fail in high-humidity conditions due to water condensation and frost formation and even lead to increased ice adhesion due to a large surface area. We report a radically different type of ice-repellent material based on slippery, liquid-infused porous surfaces (SLIPS), where a stable, ultrasmooth, low-hysteresis lubricant overlayer is maintained by infusing a water-immiscible liquid into a nanostructured surface chemically functionalized to have a high affinity to the infiltrated liquid and lock it in place. We develop a direct fabrication method of SLIPS on industrially relevant metals, particularly aluminum, one of the most widely used lightweight structural materials. We demonstrate that SLIPS-coated Al surfaces not only suppress ice/frost accretion by effectively removing condensed moisture but also exhibit at least an order of magnitude lower ice adhesion than state-of-the-art materials. On the basis of a theoretical analysis followed by extensive icing/deicing experiments, we discuss special advantages of SLIPS as ice-repellent surfaces: highly reduced sliding droplet sizes resulting from the extremely low contact angle hysteresis. We show that our surfaces remain essentially frost-free in which any conventional materials accumulate ice. These results indicate that SLIPS is a promising candidate for developing robust anti-icing materials for broad applications, such as refrigeration, aviation, roofs, wires, outdoor signs, railings, and wind turbines. PMID:22680067

Kim, Philseok; Wong, Tak-Sing; Alvarenga, Jack; Kreder, Michael J; Adorno-Martinez, Wilmer E; Aizenberg, Joanna

2012-08-28

348

Hydrophobization of epoxy nanocomposite surface with 1H,1H,2H,2H-perfluorooctyltrichlorosilane for superhydrophobic properties  

NASA Astrophysics Data System (ADS)

Nature inspires the design of synthetic materials with superhydrophobic properties, which can be used for applications ranging from self-cleaning surfaces to microfluidic devices. Their water repellent properties are due to hierarchical (micrometer- and nanometre-scale) surface morphological structures, either made of hydrophobic substances or hydrophobized by appropriate surface treatment. In this work, the efficiency of two surface treatment procedures, with a hydrophobic fluoropolymer, synthesized and deposited from 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFOTS) is investigated. The procedures involved reactions from the gas and liquid phases of the PFOTS/hexane solutions. The hierarchical structure is created in an epoxy nanocomposite surface, by filling the resin with alumina nanoparticles and micron-sized glass beads and subsequent sandblasting with corundum microparticles. The chemical structure of the deposited fluoropolymer was examined using XPS spectroscopy. The topography of the modified surfaces was characterized using scanning electron microscopy (SEM), and atomic force microscopy (AFM). The hydrophobic properties of the modified surfaces were investigated by water contact and sliding angles measurements. The surfaces exhibited water contact angles of above 150° for both modification procedures, however only the gas phase modification provided the non-sticking behaviour of water droplets (sliding angle of 3°). The discrepancy is attributed to extra surface roughness provided by the latter procedure.

Psarski, Maciej; Marczak, Jacek; Celichowski, Grzegorz; Sobieraj, Grzegorz B.; Gumowski, Konrad; Zhou, Feng; Liu, Weimin

2012-10-01

349

Biomimetic hierarchical ZnO structures with superhydrophobic property  

NASA Astrophysics Data System (ADS)

A simple electrochemical deposition method was developed for the fabrication of ZnO-based hierarchical dual structures on micro and nano scales. A layer of c-axis wellaligned and translucent ZnO micro/nanostructures was deposited on ITO glass substrate from different aqueous electrolytes with systematically varied conditions. Surface morphologies and orientations of the ZnO coatings were characterized using Scanning Electron Microscopy (SEM). The resulting ZnO-modified surface was found to exhibit water contact angle as high as 170°, a superhydrophobic property found on lotus leaf. Results show that the electrochemical deposition potential, electrolyte concentration, deposition temperature and time are the critical factors controlling the growth and formation of ZnO micro/nanostructures. Such biomimetic ZnO structures have potential for self-cleaning applications.

Saidin, N. U.; Kok, K. Y.; Ng, I. K.; Bustamam, F. K. Ahmad

2012-11-01

350

Electrowetting control of Cassie-to-Wenzel transitions in superhydrophobic carbon nanotube-based nanocomposites.  

PubMed

The possibility of effective control of the wetting properties of a nanostructured surface consisting of arrays of amorphous carbon nanoparticles capped on carbon nanotubes using the electrowetting technique is demonstrated. By analyzing the electrowetting curves with an equivalent circuit model of the solid/liquid interface, the long-standing problem of control and monitoring of the transition between the "slippy" Cassie state and the "sticky" Wenzel states is resolved. The unique structural properties of the custom-designed nanocomposites with precisely tailored surface energy without using any commonly utilized low-surface-energy (e.g., polymer) conformal coatings enable easy identification of the occurrence of such transition from the optical contrast on the nanostructured surfaces. This approach to precise control of the wetting mode transitions is generic and has an outstanding potential to enable the stable superhydrophobic capability of nanostructured surfaces for numerous applications, such as low-friction microfluidics and self-cleaning. PMID:19754132

Han, Zhaojun; Tay, Bengkang; Tan, Cherming; Shakerzadeh, Maziar; Ostrikov, Kostya Ken

2009-10-27

351

Modelling of contact angle hysteresis on rough, non-uniform and superhydrophobic surfaces with lattice Boltzmann method  

NASA Astrophysics Data System (ADS)

Contact Angle Hysteresis (CAH) is usually attributed to surface heterogeneity, contact line pinning, adsorption or interdiffusion. A model of CAH developed recently by Kubiak & Wilson is demonstrated using the lattice Boltzmann method. The model is based on the dynamic surface heterogeneity, reorientation of surface molecules under wetting liquid, physical roughness, chemical heterogeneity and liquid adhesion and evaporation. Once the surface is wetted, the local static contact angle (CA) changes from its advancing value to match the receding static CA over time Ta. When the contact line retracts, the surface recovers its initial properties corresponding to the advancing static CA over time period Te, which corresponds to the physical evaporation. Further development of the model to include surface roughness and chemical heterogeneity is presented. The model shows good agreement with experimental results for several practical configurations i.e. droplet impact and coalescence, drops on tilted surface, and drops on superhydrophobic and non-uniform surfaces etc. The extended model exhibits great potential for predictive modelling using the lattice Boltzmann method, but can be also implemented in other schemes.

Kubiak, K. J.; Wilson, M. C. T.; Castrejón-Pita, J. R.; Hutchings, I. M.

2011-11-01

352

Nanostructuring Solid Surfaces with Femtosecond Laser Irradiations for Applications  

NASA Astrophysics Data System (ADS)

Pulsed laser-assisted etching is a simple but effective method for fabricating small regular structures directly onto a surface. We have successfully fabricated submicro- or nano-meter sized spikes on a solid surface immersed in liquids with femtosecond laser pulse irradiations. This method is applicable to different metals such as stainless steel, copper, titanium, cobalt, as well as different semiconductors, such as Si and GaAs. The femtosecond laser method is much faster than other methods. We can control the experimental conditions to design and fabricate nanostructures in different materials and on the surfaces with different morphologies. Here, we discuss the nanostructures formation with femtosecond pulse laser irradiations, and introduce our results of the nanostructure for applications in sensing, biology and artificial photosynthesis. The femtosecond laser irradiation technique can efficiently integrate metal, semiconductor and polymer nanostructures in various small devices to leverage the expertise in other research fields and applications.

Shen, Mengyan

353

An analysis of superhydrophobic turbulent drag reduction mechanisms using direct numerical simulation  

Microsoft Academic Search

Superhydrophobic surfaces combine hydrophobic surface chemistry with topological microfeatures. These surfaces have been shown to provide drag reduction in laminar and turbulent flows. In this work, direct numerical simulation is used to investigate the drag reducing performance of superhydrophobic surfaces in turbulent channel flow. Slip velocities, wall shear stresses, and Reynolds stresses are determined for a variety of superhydrophobic surface

Michael B. Martell; Jonathan P. Rothstein; J. Blair Perot

2010-01-01

354

Stable biomimetic super-hydrophobic engineering materials.  

PubMed

We describe a simple and inexpensive method to produce super-hydrophobic surfaces on aluminum and its alloy by oxidation and chemical modification. Water or aqueous solutions (pH = 1-14) have contact angles of 168 +/- 2 and 161 +/- 2 degrees on the treated surfaces of Al and Al alloy, respectively. The super-hydrophobic surfaces are produced by the cooperation of binary structures at micro- and nanometer scales, thus reducing the energies of the surfaces. Such super-hydrophobic properties will greatly extend the applications of aluminum and its alloy as lubricating materials. PMID:16277486

Guo, Zhiguang; Zhou, Feng; Hao, Jingcheng; Liu, Weimin

2005-11-16

355

Superhydrophobic graphene foams.  

PubMed

The static and dynamic wetting properties of a 3D graphene foam network are reported. The foam is synthesized using template-directed chemical vapor deposition and contains pores several hundred micrometers in dimension while the walls of the foam comprise few-layer graphene sheets that are coated with Teflon. Water contact angle measurements reveal that the foam is superhydrophobic with an advancing contact angle of ?163 degrees while the receding contact angle is ?143 degrees. The extremely water repellent nature of the foam is also confirmed when impacting water droplets are able to completely rebound from the surface. Such superhydrophobic graphene foams show potential in a variety of applications ranging from anti-sticking and self-cleaning to anti-corrosion and low-friction coatings. PMID:22911509

Singh, Eklavya; Chen, Zongping; Houshmand, Farzad; Ren, Wencai; Peles, Yoav; Cheng, Hui-Ming; Koratkar, Nikhil

2013-01-14

356

In situ separation and collection of oil from water surface via a novel superoleophilic and superhydrophobic oil containment boom.  

PubMed

We have prepared a porous, superoleophilic and superhydrophobic miniature oil containment boom (MOCB) for the in situ separation and collection of oils from the surface of water. The MOCB was fabricated by a one-step electrodepositing of Cu2O film on Cu mesh surface without using low surface energy materials. Oils on water surface could be fast contained in the MOCB while water was completely repelled out of the MOCB, thus achieving the separation of oil from water surface. In addition, the contained oil in the MOCB could be in situ collected easily by a dropper, thus achieving the collection of oil. Moreover, the MOCB could be reused for many times in the oil-water separating process with large separation abilities more than 90%. The MOCB also possessed excellent water pressure resistance for about 164 mm water column and good corrosion resistance in simulating seawater. Therefore, the findings in the present study might offer a simple, fast, and low-cost method for the in situ separation and collection of oil spills on seawater surface. PMID:24460039

Wang, Fajun; Lei, Sheng; Xue, Mingshan; Ou, Junfei; Li, Wen

2014-02-11

357

Plasma micro-nanotextured, scratch, water and hexadecane resistant, superhydrophobic, and superamphiphobic polymeric surfaces with perfluorinated monolayers.  

PubMed

Superhydrophobic and superamphiphobic toward superoleophobic polymeric surfaces of polymethyl methacrylate (PMMA), polyether ether ketone (PEEK), and polydimethyl siloxane (PDMS) are fabricated in a two-step process: (1) plasma texturing (i.e., ion-enhanced plasma etching with simultaneous roughening), with varying plasma chemistry depending on the polymer, and subsequently (2) grafting of self-assembled perfluorododecyltrichlorosilane monolayers (SAMs). Depending on the absence or not of an etch mask (i.e., colloidal microparticle self-assembly on it), random or ordered hierarchical micro-nanotexturing can be obtained. We demonstrate that stable organic monolayers can be grafted onto all these textured polymeric surfaces. After the monolayer deposition, the initially hydrophilic polymeric surfaces become superamphiphobic with static contact angles for water and oils >153°, for hexadecane >142°, and hysteresis <10° for all surfaces. This approach thus provides a simple and generic method to obtain superamphiphobicity on polymers toward superoleophobicity. Hydrolytic and hexadecane immersion tests prove that superamphiphobicity is stable for more than 14 days. We also perform nanoscratch and post nanoscratch tests to prove the scratch resistance of both the texture and the SAM and demonstrate lower coefficient of friction of the SAM compared to the uncoated surface. Scanning electron microscope observation after the nanoscratch tests confirms the scratch resistance of the surfaces. PMID:24749933

Ellinas, Kosmas; Pujari, Sidharam P; Dragatogiannis, Dimitrios A; Charitidis, Constantinos A; Tserepi, Angeliki; Zuilhof, Han; Gogolides, Evangelos

2014-05-14

358

In situ X-ray scattering studies of protein solution droplets drying on micro- and nanopatterned superhydrophobic PMMA surfaces.  

PubMed

Superhydrophobic poly(methyl methacrylate) surfaces with contact angles of ?170° and high optical and X-ray transparencies have been fabricated through the use of optical lithography and plasma etching. The surfaces contain either a microscale pattern of micropillars or a random nanofibrillar pattern. Nanoscale asperities on top of the micropillars closely resemble Nelumbo nucifera lotus leaves. The evolution of the contact angle of water and lysozyme solution droplets during evaporation was studied on the micro- and nanopatterned surfaces, showing in particular contact-line pinning for the protein solution droplet on the nanopatterned surface. The microstructural evolution of lysozyme solution droplets was studied on both types of surfaces in situ under nearly contact-free conditions by synchrotron radiation microbeam wide-angle and small-angle X-ray scattering revealing the increasing protein concentration and the onset of precipitation. The solid residuals show hollow sphere morphologies. Rastermicrodiffraction of the detached residuals suggests about a 1/3 volume fraction of ?17 nm lysozyme nanocrystalline domains and about a 2/3 short-range-order volume fraction. About 5-fold larger nanocrystalline domains were observed at the attachment points of the sphere to the substrates, which is attributed to particle growth in a shear flow. Such surfaces represent nearly contact-free sample supports for studies of inorganic and organic solution droplets, which find applications in biochips. PMID:20804171

Accardo, Angelo; Gentile, Francesco; Mecarini, Federico; De Angelis, Francesco; Burghammer, Manfred; Di Fabrizio, Enzo; Riekel, Christian

2010-09-21

359

Nano-structured surface plasmon resonance sensor for sensitivity enhancement  

NASA Astrophysics Data System (ADS)

A new nano-structured SPR sensor was devised to improve its sensitivity. Nano-scaled silica particles were used as the template to fabricate nano-structure. The surface of the silica particles was modified with thiol group and a single layer of the modified silica particles was attached on the gold or silver thin film using Langmuir-Blodgett (LB) method. Thereafter, gold or silver was coated on the template by an e-beam evaporator. Finally, the nano-structured surface with basin-like shape was obtained after removing the silica particles by sonication. Applying the new developed SPR sensor to a model food of alcoholic beverage, the sensitivities for the gold and silver nano-structured sensors, respectively, had 95% and 126% higher than the conventional one.

Kim, Jae-Ho; Kim, Hyo-Sop; Kim, Jin-Ho; Choi, Sung-Wook; Cho, Yong-Jin

2008-08-01

360

Nanostructured surface made from polymer/carbon nanotube has higher conductivity than noble metal surface  

NASA Astrophysics Data System (ADS)

We made a nanostructured surface by directly coating carbon nanotubes to a surface that was previously solvent-coated with a polymer/CNT composite. Compared to the surface coated with the same polymer composite where the surface carbon nanotubes were buried in the matrix polymer, the surface directly coated with carbon nanotubes had a significant amount of exposed nanostructures. The surface was immersed in an electrolyte solution. Its AC conductivity was higher than that of a Pt/Ir surface.

Lyu, Suping; Coles, James; Gardenski, Ken; Brabec, Scott; Hobot, Chris

2010-03-01

361

Preparation of superhydrophobic surface with a novel sol-gel system  

NASA Astrophysics Data System (ADS)

Sol-gel method is a simple and cheap way to prepare superhydrophobic coatings or films, however, most of the researches on sol-gel focus on silica or ZnO sol-gel. The present paper proposes a novel sol-gel which is made from hydrolysis and condensation of the by-product of polymethylhydrosiloxane (PMHS) reacting with ?-aminopropyltriethoxysilane (KH550). The mechanism of formation of the by-product and the sol-gel is discussed and the by-product is characterized by FT-IR. The mass ratio of KH550/PMHS of the sol-gel influences the water contact angle (WCA) and water sliding angle (WSA) of the film made of spraying the sol-gel to microscope glass. When the mass ratio of KH550/PMHS of the sol-gel reaches 0.25, WCA of the corresponding film is 157° and WSA of it is less than 1°. The mechanism of formation of the sol-gel is discussed, and the size of the sol-gel is characterized by polarization microscope as well. The morphology of the film made of the sol-gel is analyzed by means of scanning electron microscope (SEM). It was found that the diameter of the particle of the superhydrophobic film is about 40 ?m, nevertheless, from the larger magnification picture, the particle is found to be composed of micro-balls whose diameter is about 2 ?m, and the micro-ball is composed of nano-sphere whose diameter is less than 200 nm.

Su, Dong; Huang, Chengya; Hu, You; Jiang, Qiangwei; Zhang, Long; Zhu, Yunfeng

2011-11-01

362

Superhydrophobic amorphous carbon/carbon nanotube nanocomposites  

NASA Astrophysics Data System (ADS)

Superhydrophobic amorphous carbon/carbon nanotube nanocomposites are fabricated by plasma immersion ion implantation with carbon nanotube forests as a template. The microstructure of the fabricated nanocomposites shows arrays of carbon nanotubes capped with amorphous carbon nanoparticles. Contact angle measurements show that both advancing and receding angles close to 180° can be achieved on the nanocomposites. The fabrication here does not require patterning of carbon nanotubes or deposition of conformal coatings with low surface energy, which are usually involved in conventional approaches for superhydrophobic surfaces. The relationship between the observed superhydrophobicity and the unique microstructure of the nanocomposites is discussed.

Han, Z. J.; Tay, B. K.; Shakerzadeh, M.; Ostrikov, K.

2009-06-01

363

Bioinspired, cysteamine-catalyzed co-silicification of (1H, 1H, 2H, 2HPerfluorooctyl) triethoxysilane and tetraethyl orthosilicate: formation of superhydrophobic surfaces.  

PubMed

Bioinspired silicification attracts a great deal of interest because of its physiologically relevant, mild conditions for hydrolysis and condensation of silica precursors, which makes the bioinspired approach superior to the conventional sol–gel process, particularly when dealing with biological entities. However, the morphological control of silica structures with incorporation of functional groups in the bioinspired silicilication has been unexplored. In this work, we co-silicificated (1H, 1H, 2H, 2H-perfluorooctyl)triethoxysilane and tetraethyl orthosilicate to investigate the morphological evolution of fluorinated silica structures in the cetyltrimethylammonium bromide-mediated, cysteamine-catalyzed silicification. The generated micrometer-long wormlike and spherical silica structures display superhydrophobicity after film formation. Interestingly, the measurement of dynamic water contact angles shows that the morphological difference leads to a different wetting state, either the self-cleaning or the pinning state of the superhydrophobic surface. PMID:24730056

Park, Ji Hun; Kim, Ji Yup; Cho, Woo Kyung; Choi, Insung S

2014-03-01

364

Curvature-dependent surface energy and implications for nanostructures  

NASA Astrophysics Data System (ADS)

At small length scales, several size-effects in both physical phenomena and properties can be rationalized by invoking the concept of surface energy. Conventional theoretical frameworks of surface energy, in both the mechanics and physics communities, assume curvature independence. In this work we adopt a simplified and linearized version of a theory proposed by Steigmann-Ogden to capture curvature-dependence of surface energy. Connecting the theory to atomistic calculations and the solution to an illustrative paradigmatical problem of a bent cantilever beam, we catalog the influence of curvature-dependence of surface energy on the effective elastic modulus of nanostructures. The observation in atomistic calculations that the elastic modulus of bent nanostructures is dramatically different than under tension - sometimes softer, sometimes stiffer - has been a source of puzzlement to the scientific community. We show that the corrected surface mechanics framework provides a resolution to this issue. Finally, we propose an unambiguous definition of the thickness of a crystalline surface.

Chhapadia, P.; Mohammadi, P.; Sharma, P.

2011-10-01

365

Induction of osteogenic differentiation by nanostructured alumina surfaces.  

PubMed

Permanent orthopedic implants are becoming increasingly important due to the demographic development. Their optimal osseointegration is key in obtaining good secondary stability. For anchorage dependent cells, topographic features of a surface play an essential role for cell adhesion, proliferation, differentiation and biomineralization. We studied the topographical effect of nanostructured alumina surfaces prepared by chemical vapor deposition on osteogenic differentiation and growth of human osteoblasts. Chemical vapor deposition of the single source precursor (tBuOAIH2)2 led to synthesis of one dimensional alumina nanostructures of high purity with a controlled stoichiometry. We fabricated different topographic features by altering the distribution density of deposited one dimensional nanostructures. Although the topography differed, all surfaces exhibited identical surface chemistry, which is the key requirement for systematically studying the effect of the topography on cells. Forty-eight hours after seeding, cell density and cell area were not affected by the nanotopography, whereas metabolic activity was reduced and formation of actin-fibres and focal adhesions was impaired compared to the uncoated control. Induction of osteogenic differentiation was demonstrated via up-regulation of alkaline phosphatase, bone sialoprotein, osteopontin and Runx2 at the mRNA level, demonstrating the potential of nanostructured surfaces to improve the osseointegration of permanent implants. PMID:24734536

Metzger, Wolfgang; Schwab, Benedikt; Miro, Marina M; Grad, Sibylle; Simpson, Angharad; Veith, Michael; Wennemuth, Gunther; Zaporojtchenko, Vladimir; Verrier, Sophie; Hayes, Jessica S; Bubel, Monika; Pohlemann, Tim; Oberringer, Martin; Aktas, Cenk

2014-05-01

366

Spontaneous breakdown of superhydrophobicity.  

PubMed

In some cases water droplets can completely wet microstructured superhydrophobic surfaces. The dynamics of this rapid process is analyzed by ultrahigh-speed imaging. Depending on the scales of the microstructure, the wetting fronts propagate smoothly and circularly or-more interestingly-in a stepwise manner, leading to a growing square-shaped wetted area: entering a new row perpendicular to the direction of front propagation takes milliseconds, whereas once this has happened, the row itself fills in microseconds ("zipping"). Numerical simulations confirm this view and are in quantitative agreement with the experiments. PMID:17995188

Sbragaglia, Mauro; Peters, Alisia M; Pirat, Christophe; Borkent, Bram M; Lammertink, Rob G H; Wessling, Matthias; Lohse, Detlef

2007-10-12

367

Photothermal self-stability and optical bistability of single NaCl-water microdroplets on a superhydrophobic surface.  

PubMed

A self-stabilization mechanism locking the size of single inorganic salt (NaCl)-water microdroplets that are standing on a superhydrophobic surface and kept in a humidity-controlled chamber is demonstrated. The effect is based on the hysteretic behavior of a photothermal tuning cycle caused by the whispering gallery mode (WGM) absorption resonances that are observed when scanning the power of an infrared laser focused at the rim of a microdroplet. When locked, the microdroplet size and WGM spectrum are resilient to environmental perturbations and can be maintained for hours as the mechanism does not rely on a photobleachable dye. The bistable nature of the system is also demonstrated, enabling reversible switching between two sizes. A rate equation-based thermodynamical model of the hysteretic behavior is provided, giving good agreement with the experimental results. Our results may be used to establish stable experimental conditions for ultrahigh resolution spectroscopy of microdroplets. Other optical and biological applications that require exactly size-matched microdroplets can also benefit from the demonstrated self-stabilization mechanism. PMID:19672523

Karadag, Y; Mestre, M; Kiraz, A

2009-09-01

368

Imprinted and injection-molded nano-structured optical surfaces  

NASA Astrophysics Data System (ADS)

Inspired by nature, nano-textured surfaces have attracted much attention as a method to realize optical surface functionality. The moth-eye antireflective structure and the structural colors of Morpho butterflies are well- known examples used for inspiration for such biomimetic research. In this paper, nanostructured polymer surfaces suitable for up-scalable polymer replication methods, such as imprinting/embossing and injection-molding, are discussed. The limiting case of injection-moulding compatible designs is investigated. Anti-reflective polymer surfaces are realized by replication of Black Silicon (BSi) random nanostructure surfaces. The optical transmission at normal incidence is measured for wavelengths from 400 nm to 900 nm. For samples with optimized nanostructures, the reflectance is reduced by 50 % compared to samples with planar surfaces. The specular and diffusive reflection of light from polymer surfaces and their implication for creating structural colors is discussed. In the case of injection-moulding compatible designs, the maximum reflection of nano-scale textured surfaces cannot exceed the Fresnel reflection of a corresponding flat polymer surface, which is approx. 4 % for normal incidence. Diffraction gratings provide strong color reflection defined by the diffraction orders. However, the apperance varies strongly with viewing angles. Three different methods to address the strong angular-dependence of diffraction grating based structural color are discussed.

Christiansen, Alexander B.; Højlund-Nielsen, Emil; Clausen, Jeppe; Caringal, Gideon P.; Mortensen, N. Asger; Kristensen, Anders

2013-09-01

369

Surface and interface magnetism in nanostructures and thin films  

Microsoft Academic Search

Nanostructured systems composed of two or more technologically important materials are useful for device applications and intriguing for the new fundamental physics they may display. Magnetism at the nanoscale is dominated by size and surface effects which combined with other media lead to new spin dynamics and interfacial coupling phenomena. These new properties may prove to be useful for optimizing

Natalie A. Frey

2008-01-01

370

Surface Chemistry of Nano-Structured Mixed Metal Oxide Films.  

National Technical Information Service (NTIS)

We have synthesizes and studied nano-structured porous mixed metal oxide thin films with high surface area and catalytic activity. By temporally controlling the deposition of two different metals in low-pressure oxygen we synthesized mixed metal oxide cat...

C. B. Mullins

2012-01-01

371

Reactive oxygen plasma-enabled synthesis of nanostructured CdO: tailoring nanostructures through plasma surface interactions  

Microsoft Academic Search

Plasma-assisted synthesis of nanostructures is one of the most precise and effective approaches used in nanodevice fabrication. Here we report on the innovative approach of synthesizing nanostructured cadmium oxide films on Cd substrates using a reactive oxygen plasma-based process. Under certain conditions, the surface morphology features arrays of crystalline CdO nano\\/micropyramids. These nanostructures grow via unconventional plasma-assisted oxidation of a

Uros Cvelbar; Miran Mozetic

2008-01-01

372

Characterization of nanostructured plasmonic surfaces with second harmonic generation.  

PubMed

Because of its high surface and interface sensitivity, the nonlinear optical technique of second harmonic generation (SHG) is a designated method for investigating nanostructured metal surfaces. Indeed, the latter present a high surface-to-volume ratio, but even more importantly, they can exhibit strong near-field enhancements or "hot spots". Hot spots often appear as a result of geometric features on the nanoscale or surface plasmon resonances, which are collective electron oscillations on the surface that, on the nanoscale, can readily be excited by light. In the last 10 years, near-field hot spots have been responsible for dramatic developments in the field of nano-optics. In this Feature Article, the influence of hot spots on the SHG response of nanostructured metal surfaces is discussed on both the microscopic and macroscopic levels. On the microscopic level, the nanostructured metal surfaces were characterized by scanning SHG microscopy, complemented by rigorous numerical simulations of the near-field and of the local electric currents at the fundamental frequency. On the macroscopic level, SHG-circular dichroism and magnetization-induced SHG characterization techniques were employed. PMID:22889193

Valev, V K

2012-11-01

373

Nanostructure-Based Localized Surface Plasmon Resonance Biosensors  

NASA Astrophysics Data System (ADS)

This chapter reviews the characteristics of localized surface plasmon resonance (LSPR), the excitation of which is mediated by nanostructures, and its applications to biosensing. The LSPR is explored in three regimes in terms of creation and coupling of localized surface plasmons (LSPs): LSPs created in surface-relief patterns coupled to propagating surface plasmons (SPs), LSPs in surface-relief patterns coupled to particle plasmons, and LSPs created in particles. The results, in general, suggest that localized field enhancement in the near-field be correlated with enhanced detection sensitivity for LSPR over conventional thin film-based SP resonance while LSPR-based biosensors can potentially maintain flexibility by using nanoparticles.

Kim, Donghyun

374

Curvature effects on surface electron states in ballistic nanostructures  

NASA Astrophysics Data System (ADS)

The curvature effect on the electronic states of a deformed cylindrical conducting surface of variable diameter is theoretically investigated. The quantum confinement of electrons normal to the curved surface results in an effective potential energy that affects the electronic structures of the system at low-energies. This suggests the possibility that ballistic transport of electrons in low-dimensional nanostructures can be controlled by inducing a local geometric deformation.

Taira, Hisao; Shima, Hiroyuki

2007-11-01

375

Organic-inorganic composite nanocoatings with superhydrophobicity, good transparency, and thermal stability.  

PubMed

Superhydrophobic, highly transparent, and stable organic-inorganic composite nanocoating is successfully prepared by a simple sol-gel dip-coating method. This method involves control of the aggregation of inorganic colloid particles by polymerization and ultrasonic vibration to create the desired micro/nanostructure in the coating. Superhydrophobicity and transparency of the coating can be controlled by adjusting the initial concentration of monomer and the size of aggregates in the sol-gel. Thus, superhydrophobicity and high transparency can be concurrently achieved in a single coating. The prepared coating also possesses good thermal stability. Its superhydrophobicity can be maintained from 20 to 90 degrees C. PMID:20302323

Xu, Qian Feng; Wang, Jian Nong; Sanderson, Kevin D

2010-04-27

376

Electrodeposition fabrication of Co-based superhydrophobic powder coatings in non-aqueous electrolyte  

NASA Astrophysics Data System (ADS)

A rapid, facile, one-step process was developed to fabricate Co-based superhydrophobic powder coatings on the stainless steel surfaces with a nonaqueous electrolyte by the electrodeposition method. The structure and composition of the superhydrophobic surfaces were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and contact angle measurement. The results show that the special hierarchical structures along with the low surface energy lead to the high superhydrophobicity of the substrate surface. The shortest process of constructing the superhydrophobic surface is only 30 seconds, the high contact angle is greater than 160°, and the rolling angle is less than 2°. The method can be used to fabricate the superhydrophobic powder coatings at any conductive cathodic surface, and the as-prepared superhydrophobic powder coatings have advantages of transferability, repairability, and durability. It is expected that this facile method will accelerate the large-scale production of superhydrophobic material.

Chen, Zhi; Hao, Limei; Duan, Mengmeng; Chen, Changle

2013-05-01

377

Universal dispersion of surface plasmons in flat nanostructures  

NASA Astrophysics Data System (ADS)

Dimensionality has a significant impact on the optical properties of solid-state nanostructures. For example, dimensionality-dependent carrier confinement in semiconductors leads to the formation of quantum wells, quantum wires and quantum dots. While semiconductor properties are governed by excitonic effects, the optical response of metal nanostructures is dominated by surface plasmons. Here we find that, in contrast to excitonic systems, the mode dispersions in plasmonic structures of different dimensionality are related by simple scaling rules. Employing electron energy loss spectroscopy, we show that the modes of silver nanodisks can be scaled to the surface and edge modes of extended silver thin films. We thereby introduce a general and intuitive ordering scheme for plasmonic excitations with edge and surface modes as the elementary building blocks.

Schmidt, Franz-Philipp; Ditlbacher, Harald; Hohenester, Ulrich; Hohenau, Andreas; Hofer, Ferdinand; Krenn, Joachim R.

2014-04-01

378

Universal dispersion of surface plasmons in flat nanostructures  

PubMed Central

Dimensionality has a significant impact on the optical properties of solid-state nanostructures. For example, dimensionality-dependent carrier confinement in semiconductors leads to the formation of quantum wells, quantum wires and quantum dots. While semiconductor properties are governed by excitonic effects, the optical response of metal nanostructures is dominated by surface plasmons. Here we find that, in contrast to excitonic systems, the mode dispersions in plasmonic structures of different dimensionality are related by simple scaling rules. Employing electron energy loss spectroscopy, we show that the modes of silver nanodisks can be scaled to the surface and edge modes of extended silver thin films. We thereby introduce a general and intuitive ordering scheme for plasmonic excitations with edge and surface modes as the elementary building blocks.

Schmidt, Franz-Philipp; Ditlbacher, Harald; Hohenester, Ulrich; Hohenau, Andreas; Hofer, Ferdinand; Krenn, Joachim R.

2014-01-01

379

Fabrics coated with lubricated nanostructures display robust omniphobicity  

NASA Astrophysics Data System (ADS)

The development of a stain-resistant and pressure-stable textile is desirable for consumer and industrial applications alike, yet it remains a challenge that current technologies have been unable to fully address. Traditional superhydrophobic surfaces, inspired by the lotus plant, are characterized by two main components: hydrophobic chemical functionalization and surface roughness. While this approach produces water-resistant surfaces, these materials have critical weaknesses that hinder their practical utility, in particular as robust stain-free fabrics. For example, traditional superhydrophobic surfaces fail (i.e., become stained) when exposed to low-surface-tension liquids, under pressure when impacted by a high-velocity stream of water (e.g., rain), and when exposed to physical forces such as abrasion and twisting. We have recently introduced slippery lubricant-infused porous surfaces (SLIPS), a self-healing, pressure-tolerant and omniphobic surface, to address these issues. Herein we present the rational design and optimization of nanostructured lubricant-infused fabrics and demonstrate markedly improved performance over traditional superhydrophobic textile treatments: SLIPS-functionalized cotton and polyester fabrics exhibit decreased contact angle hysteresis and sliding angles, omni-repellent properties against various fluids including polar and nonpolar liquids, pressure tolerance and mechanical robustness, all of which are not readily achievable with the state-of-the-art superhydrophobic coatings.

Shillingford, Cicely; MacCallum, Noah; Wong, Tak-Sing; Kim, Philseok; Aizenberg, Joanna

2014-01-01

380

Self-assembled biomimetic superhydrophobic hierarchical arrays.  

PubMed

Here, we report a simple and inexpensive bottom-up technology for fabricating superhydrophobic coatings with hierarchical micro-/nano-structures, which are inspired by the binary periodic structure found on the superhydrophobic compound eyes of some insects (e.g., mosquitoes and moths). Binary colloidal arrays consisting of exemplary large (4 and 30 ?m) and small (300 nm) silica spheres are first assembled by a scalable Langmuir-Blodgett (LB) technology in a layer-by-layer manner. After surface modification with fluorosilanes, the self-assembled hierarchical particle arrays become superhydrophobic with an apparent water contact angle (CA) larger than 150°. The throughput of the resulting superhydrophobic coatings with hierarchical structures can be significantly improved by templating the binary periodic structures of the LB-assembled colloidal arrays into UV-curable fluoropolymers by a soft lithography approach. Superhydrophobic perfluoroether acrylate hierarchical arrays with large CAs and small CA hysteresis can be faithfully replicated onto various substrates. Both experiments and theoretical calculations based on the Cassie's dewetting model demonstrate the importance of the hierarchical structure in achieving the final superhydrophobic surface states. PMID:23786830

Yang, Hongta; Dou, Xuan; Fang, Yin; Jiang, Peng

2013-09-01

381

Femtosecond laser induced nanostructuring for surface enhanced Raman spectroscopy  

NASA Astrophysics Data System (ADS)

The formation of periodical nanostructures with femtosecond laser pulses was used to create highly efficient substrates for surface-enhanced Raman spectroscopy (SERS). We report about the structuring of silver and copper substrates and their application to the SERS of DNA (herring sperm) and protein molecules (egg albumen). The maximum enhancement factors were found on Ag substrates processed with the second harmonic generation (SHG) of a 1-kHz Ti:sapphire laser and structure periods near the SHG wavelength. In the case of copper, however, the highest enhancement was obtained with long-period ripples induced with at fundamental wavelength. This is explained by an additional significant influence of nanoparticles on the surface. Nanostructured areas in the range of 1.25 mm2 were obtained in 10 s. The surfaces were characterized by scanning electron microscopy, Fast Fourier Transform and Raman spectroscopy. Moreover, the role of the chemical modification of the metal structures is addressed. Thin oxide layers resulting from working in atmosphere which improve the biocompatibility were indicated by vibration spectra. It is expected that the detailed study of the mechanisms of laser-induced nanostructure formation will stimulate further applications of functionalized surfaces like photocatalysis, selective chemistry and nano-biology.

Messaoudi, H.; Das, S. K.; Lange, J.; Heinrich, F.; Schrader, S.; Frohme, M.; Grunwald, R.

2014-03-01

382

Friction Reduction in Superhydrophobic Microchannels  

NASA Astrophysics Data System (ADS)

Superhydrophobic surfaces are surfaces with fluid contact angles larger than 150^o. Superhydrophobicity can be achieved by means of surface texturing through either a Wenzel or Cassie state. It is widely known, however, that drag reduction is closely related to Cassie state surfaces with low degrees of adhesion and several studies have been widely conducted on the topic. In this research we investigate the effects of surface texturing on superhydrophobic microchannels. Both PDMS and silicon based samples were fabricated and used to experimentally characterize the effects that microtexturing geometry has on the friction reduction behavior. We developed a layered-two-fluid system model to simulate the slip velocity condition and approximate the drag reducing behavior of the microtexturing. A surface energy formulation was also introduced to account for the effects that pressure has on the transition from a Cassie (non-wetting) to Wenzel (wetting) state of the microtexturing. Pressure effects in the wetting of the microtexturing are essential since the flow is driven by a pressure gradient. Experimental results on both friction reduction and pressure induced microtexturing wetting were compared against the models.

Kim, Tae Jin; Hidrovo, Carlos H.

2009-11-01

383

Surface nanostructures by single highly charged ions.  

PubMed

It has recently been demonstrated that the impact of individual, slow but highly charged ions on various surfaces can induce surface modifications with nanometer dimensions. Generally, the size of these surface modifications (blisters, hillocks, craters or pits) increases dramatically with the potential energy of the highly charged ion, while the kinetic energy of the projectile ions seems to be of little importance. This paper presents the currently available experimental evidence and theoretical models and discusses the circumstances and conditions under which nanosized features on different surfaces due to the impact of slow highly charged ions can be produced. PMID:21715750

Facsko, S; Heller, R; El-Said, A S; Meissl, W; Aumayr, F

2009-06-01

384

Nanostructured Surfaces for Drug Delivery and Anti-Fibrosis  

NASA Astrophysics Data System (ADS)

Effective and cost-efficient healthcare is at the forefront of public discussion; on both personal and policy levels, technologies that improve therapeutic efficacy without the use of painful hypodermic needle injections or the use of harsh chemicals would prove beneficial to patients. Nanostructured surfaces as structure-mediated permeability enhancers introduce a potentially revolutionary approach to the field of drug delivery. Parental administration routes have been the mainstay technologies for delivering biologics because these therapeutics are too large to permeate epithelial barriers. However, there is a significant patient dislike for hypodermic needles resulting in reduced patient compliance and poor therapeutic results. We present an alternative strategy to harness the body's naturally occurring biological processes and transport mechanisms to enhance the drug transport of biologics across the epithelium. Our strategy offers a paradigm shift from traditional biochemical drug delivery vehicles by using nanotopography to loosen the epithelial barrier. Herein, we demonstrate that nanotopographical cues can be used to enable biologics > 66 kDa to be transported across epithelial monolayers by increasing paracellular transport. When placed in contact with epithelial cells, nanostructured films significantly increase the transport of albumin, IgG, and a model therapeutic, etanercept. Our work highlights the potential to use drug delivery systems which incorporate nanotopographical cues to increase the transport of biologics across epithelial tissue. Furthermore, we describe current advancements in nano- and microfabrication for applications in anti-fibrosis and wound healing. Influencing cellular responses to biomaterials is crucial in the field of tissue engineering and regenerative medicine. Since cells are surrounded by extracellular matrix features that are on the nanoscale, identifying nanostructures for imparting desirable cellular function could greatly impact the field. Due to the rise in micro and nanofabrication techniques borrowed from the advances in the microelectronics industry, previously unattainable nanostructured surfaces on a variety of biomaterials can be generated. We investigated how nanostructured surfaces with varying nanofeature aspect ratios can influence fibrosis. Thus, nanostructured surfaces show substantial progress for therapeutic applications in drug delivery and wound healing.

Kam, Kimberly Renee

385

Silver nanostructured catalyst for modification of dielectrics surface  

Microsoft Academic Search

The preparation of nano-size Ag particles and their application for forming nanostructured catalysts on various surfaces are described. Silver colloid solutions were prepared by reduction of Ag(I) salt by tin(II) and characterized by electron microscopy, X-ray diffraction and light absorption spectra. Depending on the colloid preparation conditions metal particles of 5–100nm size were obtained. According to XRD data, the colloid

Algirdas Vaškelis; Aldona Jagminien?; Remigijus Jušk?nas

2005-01-01

386

Sustainability of superhydrophobicity under pressure  

NASA Astrophysics Data System (ADS)

Prior studies have demonstrated that superhydrophobicity of submerged surfaces is influenced by hydrostatic pressure and other environmental effects. Sustainability of a superhydrophobic surface could be characterized by both how long it maintains the trapped air in its surface pores, so-called ``longevity,'' and the pressure beyond which it undergoes a global wetting transition, so-called ``terminal pressure.'' In this work, we investigate the effects of pressure on the performance of electrospun polystyrene fibrous coatings. The time-dependent hydrophobicity of the submerged coating in a pressure vessel is optically measured under elevated pressures. Rheological studies are also performed to determine the effects of pressure on drag reduction and slip length. The measurements indicate that surface longevity exponentially decays with increasing pressure in perfect agreement with the studies reported in the literature at lower pressures. It is found, however, that fibrous coatings could resist hydrostatic pressures significantly higher than those of previously reported surfaces. Our observations indicate that superhydrophobic fibrous coatings could potentially be used for underwater applications.

Samaha, Mohamed A.; Vahedi Tafreshi, Hooman; Gad-el-Hak, Mohamed

2012-11-01

387

An optimization of superhydrophobic polyvinylidene fluoride/zinc oxide materials using Taguchi method  

NASA Astrophysics Data System (ADS)

This article is focused on the preparation and characterization of PVDF/ZnO composite materials. The superhydrophobic surface was prepared through spray coating of a mixture of PVDF polymer and ZnO nanoparticles on aluminum substrate. Stearic acid was added to improve the dispersion of ZnO. Taguchi's design of experiment method using MINITAB15 was used to rank several factors that may affect the superhydrophobic properties in order to formulate the optimum conditions. The Taguchi orthogonal array L9 was applied with three level of consideration for each factor. ANOVA were carried out to identify the significant factors that affect the water contact angle. Confirmation tests were performed on the predicted optimum process parameters. The crystallinity and morphology of PVDF-ZnO membranes were determined by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The results of Taguchi method indicate that the ZnO and stearic acid contents were the parameters making significant contribution toward improvement in hydrophobicity of PVDF materials. As the content of ZnO nanoparticles increased, the values of water contact angle increased, ranging from 122° to 159°, while the contact angle hysteresis and sliding angle decreased to 3.5° and 2.5°, respectively. The SEM results show that hierarchical micro-nanostructure of ZnO plays an important role in the formation of the superhydrophobic surface. FTIR results showed that, in the absence or present ZnO nanoparticles, the crystallization of the PVDF occurred predominantly in the ?-phase.

Mohamed, Adel M. A.; Jafari, Reza; Farzaneh, Masoud

2014-01-01

388

Nanostructuring of Silicon Surfaces Using Selective Photodesorption  

NASA Astrophysics Data System (ADS)

The role of electronic point defects induced by substitutional doping in semiconductors can profoundly influence both their surface chemistry and morphology on an atomic scale. This results from a convolution of atomic site-specific photodesorption processes and the quantum mechanical enhancement of surface chemical reactions induced by uv-photon radation as a function of laser fluence. Substantial alterations of the surface nano-scale structure occurs by selective photodesorption from the chlorinated surface.Creation of hot holes and electrons coupled with field-induced charge transport and field build- up at the surface produces new chemical reaction channels which result in specific nano-scale structural effects, New film compositional measurements are correlated with previously reported results on chemisorption kinetics, reaction energetics and STM observations to produce models and mechanisms for the interpretation of the unique atomic-scale morphology resulting from selective photodesorption from well-defined chlorinated Si(111) and Si(100) surfaces. Supported: NSF-DMR-87-05680 & MSC-DMR-88-18558-A02. ("Overview on Surface Microstructuring by Photodesorption Etching of Chlorinated Silicon".Prog.Surf.Sci.54(1997)287-314.) THIS SECTION IS FOR APS USE ONLY

Rhodin, Thor; Paulsen-Boaz, Carlotta

1998-03-01

389

Tribology and Superhydrophobicity of Laser-Controlled-Melted Alumina Surfaces with Hard Particles  

NASA Astrophysics Data System (ADS)

Laser-controlled melting of alumina surface with a carbon film of about 40- ?m thickness formed prior to the laser treatment process is carried out to improve its hardness, durability, and superhydrophocity. The carbon film consisted of a uniformly distributed mixture of hard particles of WC, SiC, and B4C. The presence of carbon film improves the absorption of the laser beam during the treatment process. The morphology and hydrophobicity of the laser-treated surface were evaluated using optical microscopy, atomic force microscopy, and the contact angle measurement, respectively. The chemical changes of the treated layer were examined using scanning electron microscopy and energy-dispersive spectroscopy. The structure of the nitride compound formed at the surface was characterized using x-ray diffraction, which was also used to determine the residual stress at the surface. Both microhardness and fracture toughness of the laser-treated surface were determined using indentation tests. Scratch tests were conducted to measure the friction coefficient and scratch resistance of the laser-treated surface. Laser treatment produces micropoles, nanopoles, and small size cavities at the surface, which enhance hydrophobicity of the surface. The microhardness of the laser-treated surface increases almost 50% because of the dense layer formed at the surface and the residual stress is in the order of -2 GPa, which is compressive. The scratch resistance and friction coefficient of the laser-treated surface is superior.

Yilbas, Bekir Sami; Bhushan, Bharat; Abdul Aleem, B. J.; Gaseem, Zuhair

2014-06-01

390

Tribology and Superhydrophobicity of Laser-Controlled-Melted Alumina Surfaces with Hard Particles  

NASA Astrophysics Data System (ADS)

Laser-controlled melting of alumina surface with a carbon film of about 40-?m thickness formed prior to the laser treatment process is carried out to improve its hardness, durability, and superhydrophocity. The carbon film consisted of a uniformly distributed mixture of hard particles of WC, SiC, and B4C. The presence of carbon film improves the absorption of the laser beam during the treatment process. The morphology and hydrophobicity of the laser-treated surface were evaluated using optical microscopy, atomic force microscopy, and the contact angle measurement, respectively. The chemical changes of the treated layer were examined using scanning electron microscopy and energy-dispersive spectroscopy. The structure of the nitride compound formed at the surface was characterized using x-ray diffraction, which was also used to determine the residual stress at the surface. Both microhardness and fracture toughness of the laser-treated surface were determined using indentation tests. Scratch tests were conducted to measure the friction coefficient and scratch resistance of the laser-treated surface. Laser treatment produces micropoles, nanopoles, and small size cavities at the surface, which enhance hydrophobicity of the surface. The microhardness of the laser-treated surface increases almost 50% because of the dense layer formed at the surface and the residual stress is in the order of -2 GPa, which is compressive. The scratch resistance and friction coefficient of the laser-treated surface is superior.

Yilbas, Bekir Sami; Bhushan, Bharat; Abdul Aleem, B. J.; Gaseem, Zuhair

2014-04-01

391

The impalement of water drops impinging onto hydrophobic/superhydrophobic graphite surfaces: the role of dynamic pressure, hammer pressure and liquid penetration time  

NASA Astrophysics Data System (ADS)

Droplet impingement experiments at low Weber numbers were conducted by digitizing silhouettes of impacting water drops onto unlike graphite substrates, typified by different advancing water contact angles (?a): 140 and 160°. The relaxation of wetting diameter, dynamic contact angle, and drop shapes were measured. The purpose was to carefully investigate the phenomenology and possible causes of the failure of the superhydrophobicity. During impact and spreading phases, all the drops impinging onto both graphite substrates showed a similar behavior. Then, after an initial free recoil, drops impinging at lower impact velocities onto graphite substrates characterized by ?a = 140° clearly exhibited time intervals in which the wetting diameter appeared to be almost constant. The duration of this pinned phase was observed decreasing with increasing the impact height and almost completely disappearing for drops impinging at higher impact velocities. This behavior has never been reported before, and, contrariwise, water droplets impinging at lower impact velocities onto hydrophobic and superhydrophobic surfaces have been generally observed more freely retracting, and ultimately rebounding, compared to drops impacting at higher velocities. In the present study, this latter behavior was recorded just for drops impinging onto graphite surfaces characterized by ?a = 160°. A theoretical description of the experimental results was proposed, specifically investigating the role of dynamic pressure, hammer pressure and liquid penetration time during the impact, spreading and recoil stages.

Pittoni, Paola G.; Lin, Ya-Chi; Lin, Shi-Yow

2014-05-01

392

Multilayer liquid spreading on superhydrophilic nanostructured surfaces  

NASA Astrophysics Data System (ADS)

A phenomenon is presented where a propagating liquid on an array of nanopillars with scalloped features can separate into multiple layers of liquid films. The scallops were found to act as energy barriers that favor liquid separation into several layers over spreading in a uniform film. An analytical model based on surface energy was developed to explain the phenomenon. Additional tailored pillar geometries were fabricated and tested to validate the theory and model. The results provide design guidelines for geometries that promote multiple layer separation and offer opportunities to control liquid film thickness on superhydrophilic surfaces.

Xiao, Rong; Chu, Kuang-Han; Wang, Evelyn N.

2009-05-01

393

Gold-decorated block copolymer microspheres with controlled surface nanostructures.  

PubMed

Gold-decorated block copolymer microspheres (BCP-microspheres) displaying various surface morphologies were prepared by the infiltration of Au precursors into polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) microspheres. The microspheres were fabricated by emulsifying the PS-b-P4VP polymers in chloroform into a surfactant solution in water, followed by the evaporation of chloroform. The selective swelling of the P4VP domains in the microspheres by the Au precursor under acidic conditions resulted in the formation of Au-decorated BCP-microspheres with various surface nanostructures. As evidenced by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) measurements, dotted surface patterns were formed when microspheres smaller than 800 nm were synthesized, whereas fingerprint-like surface patterns were observed with microspheres larger than 800 nm. Au nanoparticles (NPs) were located inside P4VP domains near the surfaces of the prepared microspheres, as confirmed by TEM. The optical properties of the BCP-microspheres were characterized using UV-vis absorption spectroscopy and fluorescence lifetime measurements. A maximum absorption peak was observed at approximately 580 nm, indicating that Au NPs are densely packed into P4VP domains on the microspheres. Our approach for creating Au-NP-hybrid BCP-microspheres can be extended to other NP systems such as iron-oxide or platinum NPs. These precursors can also be selectively incorporated into P4VP domains and induce the formation of hybrid BCP-microspheres with controlled surface nanostructures. PMID:22352689

Kim, Minsoo P; Kang, Dong Jin; Jung, Dae-Woong; Kannan, Aravindaraj G; Kim, Ki-Hyun; Ku, Kang Hee; Jang, Se Gyu; Chae, Weon-Sik; Yi, Gi-Ra; Kim, Bumjoon J

2012-03-27

394

Sensitive And Selective Chemical Sensor With Nanostructured Surfaces.  

DOEpatents

A chemical sensor is provided which includes an optical resonator including a nanostructured surface comprising a plurality of nanoparticles bound to one or more surfaces of the resonator. The nanoparticles provide optical absorption and the sensor further comprises a detector for detecting the optical absorption of the nanoparticles or their environment. In particular, a selective chemical interaction is provided which modifies the optical absorption of the nanoparticles or their environment, and an analyte is detected based on the modified optical absorption. A light pulse is generated which enters the resonator to interrogate the modified optical absorption and the exiting light pulse is detected by the detector.

Pipino, Andrew C. R. (Gaithersburg, MD)

2003-02-04

395

Tunable reflection minima of nanostructured antireflective surfaces  

NASA Astrophysics Data System (ADS)

Broadband antireflection schemes for silicon surfaces based on the moth-eye principle and comprising arrays of subwavelength-scale pillars are applicable to solar cells, photodetectors, and stealth technologies and can exhibit very low reflectances. We show that rigorous coupled wave analysis can be used to accurately model the intricate reflectance behavior of these surfaces and so can be used to explore the effects of variations in pillar height, period, and shape. Low reflectance regions are identified, the extent of which are determined by the shape of the pillars. The wavelengths over which these low reflectance regions operate can be shifted by altering the period of the array. Thus the subtle features of the reflectance spectrum of a moth-eye array can be tailored for optimum performance for the input spectrum of a specific application.

Boden, S. A.; Bagnall, D. M.

2008-09-01

396

Superhydrophobic coating deposited directly on aluminum  

NASA Astrophysics Data System (ADS)

This study develops an alternative method for enhancing superhydrophobicity on aluminum surfaces with an amphiphilic reagent such as the dodecanoic acid. The goal is to induce superhydrophobicity directly through a simple process on pure (99.9 wt%) commercial aluminum. The initial surface activation leading to the formation of the superhydrophobic coating is studied using confocal microscopy. Superhydrophobic behavior is analyzed by contact angle measurements, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The highest contact angle (approaching 153°) was obtained after forming hierarchical structures with a particular roughness obtained by grinding and polishing microgrooves on the aluminum surface together with the simultaneous action of HCl and dodecanoic acid. The results also showed that after immersion in the ethanol-acidic-fatty acid solutions, they reacted chemically through the action of the fatty acid, on the aluminum surface. The mechanism is analyzed by TOF-SIMS and XPS in order to determine the molecules involved in the reaction. The TOF-SIMS analysis revealed that the metal and its oxides seem to be necessary, and that free-aluminum is anchored to the fatty acid molecules and to the alumina molecules present in the medium. Consequently, both metallic aluminum and aluminum oxides are necessary in order to form the compound responsible for superhydrophobicity.

Escobar, Ana M.; Llorca-Isern, Nuria

2014-06-01

397

Facile preparation of superhydrophobic copper surface by HNO 3 etching technique with the assistance of CTAB and ultrasonication  

NASA Astrophysics Data System (ADS)

Superhydrophobic rough structure was prepared on copper wafer via HNO 3 etching technique with the assistance of Cetyltrimethyl Ammonium Bromide (CTAB) and ultrasonication. After modification of 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane (FDTES), the copper wafer showed stable superhydrophobicity. The morphologies, chemical compositions and hydrophobicity of the substrates were analyzed by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and water contact angle measurement. Dense and spherical micropits appeared on copper wafer after it was etched by 5 M nitric acid with 1.2 mM CTAB under ultrasonication for 20 min. The SEM results indicated that the joint action of CTAB and ultrasonication caused the formation of dense and spherical micropits.

Pan, Lining; Dong, Huiru; Bi, Pengyu

2010-12-01

398

Nitrocellulose strip array assembled on superhydrophobic surface: An aqueous solution diffusion-localized platform for multianalyte immunogold staining assays  

Microsoft Academic Search

In this paper, an aqueous solution diffusion-localized platform (ASDLP) for multianalyte immunogold staining assays has been developed for the first time by assembling nitrocellulose (NC) strips onto a superhydrophobic polycarbonate (PC) coating with a water contact angle (CA) up to 160°. In the concept-of-proof experiments, the ASDLP was used for colorimetric detection of a human IgG model antigen based on

Yun Zhang; Hua Wang; Jianping Li; Jinfang Nie; Yuwei Zhang; Guoli Shen; Ruqin Yu

2011-01-01

399

Dry in the Water: The Superhydrophobic Water Fern Salvinia – a Model for Biomimetic Surfaces  

Microsoft Academic Search

Over millions of years plant surfaces evolved optimized complex multifunctional interfaces. They fulfill different functions\\u000a in terrestrial plants such as limitation of uncontrolled water loss, protection against various biotic and abiotic influences,\\u000a and they play a role in the attachment of insects. A recent overview on plant surface functions is presented by Jeffree (in\\u000a Riederer, 2006). One of the most

Zdenek Cerman; Boris F. Striffler; Wilhelm Barthlott

400

A lattice Boltzmann code for direct numerical simulation of skin-friction drag reduction by superhydrophobic surfaces in turbulent channel flow  

NASA Astrophysics Data System (ADS)

A lattice Boltzmann code for direct numerical simulation of flow over superhydrophobic surfaces has been developed. The code solves the Boltzmann equation for two different sets of particle distribution functions based on the Shan and Chen model [1], to account for the gas-liquid interactions. The immiscibility and inter-phase interactions are controlled through an interaction body force between the distribution functions. The recently proposed model of Hunag et al. [2] is used to set the contact angle in the simulations, in which by tuning the values of the interaction force, one can control the contact angle at the interfaces, simulating hydrophobicity or superhydrophobicity on the solid walls. Test results in channel flow will be presented and discussed.[4pt] [1] X.Shan and H.Chen, Phys. Rev. E, 47(3):1815 (1993)[0pt] [2] H.Huang, D.T.Throne, M.G.Schaap, and M.C.Sukop, Phys. Rev. E, 76:066701 (2007)

Rastegari, Amirreza; Akhavan, Rayhaneh

2010-11-01

401

Superhydrophobic silicone fiber mats fabricated by electrospinning from solution  

NASA Astrophysics Data System (ADS)

Fine silicone fibers of 1 -- 20 ?m diameter were fabricated from solution via electrospinning. These are the first examples of fine fibers prepared from silicone homopolymers. Fiber morphology (beaded, ribbon-like, smooth) and diameter were controlled. The nanoscale surface roughness of nonwoven fiber mats created with silicone fibers produced a superhydrophobic surface that had a water contact angle of ˜160^o. The superhydrophobic surface was made reversibly hydrophilic with exposure to oxygen plasma. The combination of high surface area and superhydrophobicity suggests potential applications in the areas of water-repellent textiles, filtration, adsorption and chemical separations, wound dressings, and fuel cells.

Ludwig, Bonnie; Clark, Aneta; Snow, Steven; Hill, Randal; Schmidt, Randall; Fogg, Brad; Lo, Peter

2007-03-01

402

Titanium nanostructural surface processing for improved biocompatibility  

SciTech Connect

X-ray photoelectron spectroscopy, grazing incident x-ray diffraction, transmission electron microscopy, and scanning electron microscopy were conducted to evaluate the effect of titanium hydride on the formation of nanoporous TiO{sub 2} on Ti during anodization. Nano-titanium-hydride was formed cathodically before anodizing and served as a sacrificial nanoprecipitate during anodization. Surface oxidation occurred and a multinanoporous structure formed after cathodic pretreatments followed by anodization treatment. The sacrificial nanoprecipitate is directly dissolved and the Ti transformed to nanoporous TiO{sub 2} by anodization. The formation of sacrificial nanoprecipitates by cathodic pretreatment and of the multinanostructure by anodization is believed to improve biocompatibility, thereby promoting osseointegration.

Cheng, H.-C.; Lee, S.-Y.; Chen, C.-C.; Shyng, Y.-C.; Ou, K.-L. [School of Dentistry, College of Oral Medicine, Taipei Medical University, Taipei 110, Taiwan (China)and Department of Dentistry, Taipei Medical University Hospital, Taipei 110, Taiwan (China); School of Dentistry, College of Oral Medicine, Taipei Medical University, Taipei 110, Taiwan (China); School of Dentistry, College of Oral Medicine, Taipei Medical University, Taipei 110, Taiwan (China) and Department of Emergency Medicine, Mackay Memorial Hospital, Taipei 110, Taiwan (China); Division of Oral and Maxillofacial Surgery, Kaohsiung Military General Hospital, Kaohsiung 807, Taiwan (China); Graduate Institute of Oral Sciences, College of Oral Medicine, Taipei Medical University, Taipei 110, Taiwan (China)

2006-10-23

403

Salinity Effects on Superhydrophobic Coatings  

NASA Astrophysics Data System (ADS)

Experiments are carried out to investigate the effect of NaCl concentrations on degree of hydrophobicity and longevity of polystyrene fibrous coating. A rheological study using salt water as a test fluid is performed to observe the generated drag reduction from the coating with increasing salt concentration compared to deionized water. Contact-angle measurements of droplets of solutions on the surface are used to validate the results from the rheometer. In situ noninvasive optical spectroscopy system is used to measure the time-dependent loss of entrapped air within the submerged fibrous coating. water for comparison. The superhydrophobic coating used is made of polystyrene fibers that are deposited using DC-biased AC-electrospinning. Such fabrication methods are far less expensive than ordered-microstructured fabrications, bringing the technology closer to large-scale submerged bodies such as submarines and ships. The present study sheds some light on how properties of a superhydrophobic coating could be influenced by water salinity.

Ochanda, F. O.; Samaha, M. A.; Vahedi Tafreshi, H.; Tepper, G. C.; Gad-El-Hak, M.

2011-11-01

404

Optimizing geometrical design of superhydrophobic surfaces for prevention of microelectromechanical system (MEMS) stiction  

Microsoft Academic Search

Due to the surface smoothness of micromachined structures, strong adhesion forces between these fabricated structures and the substrate can be developed. The major adhesion mechanisms include capillary forces, hydrogen bonding, electrostatic forces and van der Waals forces. Once contact is made, the magnitude of these forces is in some cases sufficient to deform and pin these structures to the substrate,

Lingbo Zhu; Yonghao Xiu; Jianwen Xu; Dennis W. Hess; C. P. Wong

2006-01-01