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1

Jumping-Droplet-Enhanced Condensation on Scalable Superhydrophobic Nanostructured Surfaces  

E-print Network

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 ...

Miljkovic, Nenad

2

Electric-Field-Enhanced Condensation on Superhydrophobic Nanostructured Surfaces  

E-print Network

When condensed droplets coalesce on a superhydrophobic nanostructured surface, the resulting droplet can jump due to the conversion of excess surface energy into kinetic energy. This phenomenon has been shown to enhance ...

Miljkovic, Nenad

3

Effect of Droplet Morphology on Growth Dynamics and Heat Transfer during Condensation on Superhydrophobic Nanostructured Surfaces  

E-print Network

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 ...

Miljkovic, Nenad

4

Condensation on superhydrophobic copper oxide nanostructures  

E-print Network

Condensation is an important process in many power generation and water desalination technologies. Superhydrophobic nanostructured surfaces have unique condensation properties that may enhance heat transfer through a ...

Dou, Nicholas (Nicholas Gang)

2012-01-01

5

Superhydrophobic Transparent Surface of Nanostructured Poly(Methyl Methacrylate)  

E-print Network

hydrolysis process with water immersion. During the CF4 plasma treatment, nanoscale pillar structures were hydrophobic coating, a superhydrophobic surface was achieved showing robust anti-wetting and anti wileyonlinelibrary.com DOI: 10.1002/ppap.201200131 481 #12;hydrophobic surfaces on PMMA have been developed

Kim, Ho-Young

6

Fabrication of surface micro- and nanostructures for superhydrophobic surfaces in electric and electronic applications  

NASA Astrophysics Data System (ADS)

In our study, the superhydrophobic surface based on biomimetic lotus leave is explored to maintain the desired properties for self-cleaning. Parameters in controlling bead-up and roll-off characteristics of water droplets were investigated on different model surfaces. The governing equations were proposed. Heuristic study is performed. First, the fundamental understanding of the effect of roughness on superhydrophobicity is performed. The effect of hierarchical roughness, i.e., two scale roughness effect on roughness is investigated using systems of (1) monodisperse colloidal silica sphere (submicron) arrays and Au nanoparticle on top and (2) Si micrometer pyramids and Si nanostructures on top from KOH etching and metal assisted etching of Si. The relation between the contact area fraction and water droplet contact angles are derived based on Wenzel and Cassie-Baxter equation for the systems and the two scale effect is explained regarding the synergistic combination of two scales. Previously the microscopic three-phase-contact line is thought to be the key factor in determining contact angles and hystereses. In our study, Laplace pressure was brought up and related to the three-phase-contact line and taken as a key figure of merit in determining superhydrophobicity. In addition, we are one of the first to study the effect of tapered structures (wall inclination). Combining with a second scale roughness on the tapered structures, stable Cassie state for both water and low surface energy oil may be achieved. This is of great significance for designing both superhydrophobicity and superoleophobicity. Regarding the origin of contact angle hysteresis, study of superhydrophobicity on micrometer Si pillars was performed. The relation between the interface work of function and contact angle hysteresis was proposed and derived mathematically based on the Young-Dupre equation. The three-phase-contact line was further related to a secondary scale roughness induced. Based on our understanding of the roughness effect on superhydrophobicity (both contact angle and hysteresis), structured surfaces from polybutadiene, polyurethane, silica, and Si etc. were successfully prepared. For engineering applications of superhydrophobic surfaces, stability issues regarding UV, mechanical robustness and humid environment need to be investigated. Among these factors, UV stability is the first one to be studied. However, most polymer surfaces we prepared failed the purpose. Silica surfaces with excellent UV stability were prepared. This method consists of preparation of rough silica surfaces, thermal treatment and the following surface hydrophobization by fluoroalkyl silane treatment. Fluoroalkyl groups are UV stable and the underlying species are silica which is also UV stable (UV transparent). UV stability on the surface currently is 5,500 h according the standard test method of ASTM D 4329. No degradation on surface superhydrophobicity was observed. New methods for preparing superhydrophobic and transparent silica surfaces were investigated using urea-choline chloride eutectic liquid to generate fine roughness and reduce the cost for preparation of surface structures. Another possible application for self-cleaning in photovoltaic panels was investigated on Si surfaces by construction of the two-scale rough structures followed by fluoroalkyl silane treatment. Metal (Au) assisted etching was employed to fabricate nanostructures on micrometer pyramid surfaces. The light reflection on the prepared surfaces was investigated. After surface texturing using KOH etching for micrometer pyramids and the following nanostructure using metal assisted etching, surface light reflection reduced to a minimum value which shows that this surface texturing technique is highly promising for improving the photovoltaic efficiency while imparting photovoltaics the self-cleaning feature. This surface is also expected to be UV stable due to the same fluoroalkyl silane used. Regarding the mechanical robustness, epoxy-silica superhydrophobic surfaces were prepared by O2 plas

Xiu, Yonghao

7

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

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

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

NASA Astrophysics Data System (ADS)

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.

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

10

Superhydrophobic and colorful copper surfaces fabricated by picosecond laser induced periodic nanostructures  

NASA Astrophysics Data System (ADS)

In this study, functional copper surfaces combined with vivid structural colors and superhydrophobicity were fabricated by picosecond laser. Laser-induced periodic surface structures (LIPSS), i.e. ripples, were fabricated by picosecond laser nanostructuring to induce rainbow-like structural colors which are uniquely caused by the grating - type structure. The effects of laser processing parameters on the formation of ripples were investigated. We also discussed the formation mechanism of ripples. With different combinations of the laser processing parameters, ripples with various morphologies were fabricated. After the modification with triethoxyoctylsilane, different types of ripples exhibited different levels of wettability. The fine ripples with minimal redeposited nanoparticles exhibited high adhesive force to water. The increased amount of nanoscale structures decreased the adhesive force to water and increased the contact angle simultaneously. In particular, a specific type of ripples exhibited superhydrophobicity with a large contact angle of 153.9 ± 3.2° and a low sliding angle of 11 ± 3°.

Long, Jiangyou; Fan, Peixun; Zhong, Minlin; Zhang, Hongjun; Xie, Yongde; Lin, Chen

2014-08-01

11

Microscopic droplet formation and energy transport analysis of condensation on scalable superhydrophobic nanostructured copper oxide surfaces.  

PubMed

Utilization of nanotechnologies in condensation has been recognized as one opportunity to improve the efficiency of large-scale thermal power and desalination systems. High-performance and stable dropwise condensation in widely-used copper heat exchangers is appealing for energy and water industries. In this work, a scalable and low-cost nanofabrication approach was developed to fabricate superhydrophobic copper oxide (CuO) nanoneedle surfaces to promote dropwise condensation and even jumping-droplet condensation. By conducting systematic surface characterization and in situ environmental scanning electron microscope (ESEM) condensation experiments, we were able to probe the microscopic formation physics of droplets on irregular nanostructured surfaces. At the early stages of condensation process, the interfacial surface tensions at the edge of CuO nanoneedles were found to influence both the local energy barriers for microdroplet growth and the advancing contact angles when droplets undergo depinning. Local surface roughness also has a significant impact on the volume of the condensate within the nanostructures and overall heat transfer from the vapor to substrate. Both our theoretical analysis and in situ ESEM experiments have revealed that the liquid condensate within the nanostructures determines the amount of the work of adhesion and kinetic energy associated with droplet coalescence and jumping. Local and global droplet growth models were also proposed to predict how the microdroplet morphology within nanostructures affects the heat transfer performance of early-stage condensation. Our quantitative analysis of microdroplet formation and growth within irregular nanostructures provides the insight to guide the anodization-based nanofabrication for enhancing dropwise and jumping-droplet condensation performance. PMID:25419845

Li, GuanQiu; Alhosani, Mohamed H; Yuan, ShaoJun; Liu, HaoRan; Ghaferi, Amal Al; Zhang, TieJun

2014-12-01

12

Corrosion resistance and durability of superhydrophobic surface formed on magnesium alloy coated with nanostructured cerium oxide film and fluoroalkylsilane molecules in corrosive NaCl aqueous solution.  

PubMed

The corrosion resistant performance and durability of the superhydrophobic surface on magnesium alloy coated with nanostructured cerium oxide film and fluoroalkylsilane molecules in corrosive NaCl aqueous solution were investigated using electrochemical and contact angle measurements. The durability of the superhydrophobic surface in corrosive 5 wt% NaCl aqueous solution was elucidated. The corrosion resistant performance of the superhydrophobic surface formed on magnesium alloy was estimated by electrochemical impedance spectroscopy (EIS) measurements. The EIS measurements and appropriate equivalent circuit models revealed that the superhydrophobic surface considerably improved the corrosion resistant performance of magnesium alloy AZ31. American Society for Testing and Materials (ASTM) standard D 3359-02 cross cut tape test was performed to investigate the adhesion of the superhydrophobic film to the magnesium alloy surface. The corrosion formation mechanism of the superhydrophobic surface formed on the magnesium alloy was also proposed. PMID:21417352

Ishizaki, Takahiro; Masuda, Yoshitake; Sakamoto, Michiru

2011-04-19

13

Multiscale effect of hierarchical self-assembled nanostructures on superhydrophobic surface.  

PubMed

In this work, we describe self-assembled surfaces with a peculiar multiscale organization, from the nanoscale to the microscale, exhibiting the Cassie-Baxter wetting regime with extremely low water adhesion: floating drops regime with roll-off angles < 5°. These surfaces comprise bundles of hierarchical, quasi-one-dimensional (1D) TiO2 nanostructures functionalized with a fluorinated molecule (PFNA). While the hierarchical nanostructures are the result of a gas-phase self-assembly process, their bundles are the result of the capillary forces acting between them when the PFNA solvent evaporates. Nanometric features are found to influence the hydrophobic behavior of the surface, which is enhanced by the micrometric structures up to the achievement of the superhydrophobic Cassie-Baxter state (contact angle (CA) ? 150°). Thanks to their high total and diffuse transmittance and their self-cleaning properties, these surfaces could be interesting for several applications such as smart windows and photovoltaics where light management and surface cleanliness play a crucial role. Moreover, the multiscale analysis performed in this work contributes to the understanding of the basic mechanisms behind extreme wetting behaviors. PMID:25346328

Passoni, Luca; Bonvini, Giacomo; Luzio, Alessandro; Facibeni, Anna; Bottani, Carlo E; Di Fonzo, Fabio

2014-11-18

14

Fabrication of Superhydrophobic Surfaces  

Microsoft Academic Search

Superhydrophobicity has recently drawn a great deal of attention from both fundamental and practical application points of view. This paper summarizes the basic principles involved in creation of superhydrophobicity and reviews the diverse methods recently developed to make superhydrophobic surfaces and coatings. The hydrophobic property of materials can be amplified through the surface roughness. This was first addressed theoretically in

Seong H. Kim

2008-01-01

15

Condensation on Superhydrophobic Copper Oxide Nanostructures  

E-print Network

Condensation is an important process in both emerging and traditional power generation and water desalination technologies. Superhydrophobic nanostructures promise enhanced condensation heat transfer by reducing the ...

Enright, Ryan

16

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

17

Nanostructured metal surfaces and their passivation for superhydrophobic and anti-icing applications  

NASA Astrophysics Data System (ADS)

Many systems and infrastructures developed by human beings frequently encounter deficiencies, stop functioning or even fail during severe weather conditions due to ice accumulation. One of the common methods to prevent snow and ice accumulation on exposed surfaces is the use of chemicals such as freezing point depressants. They should be applied during storms or just before ice accumulation which is practically difficult. Also these chemicals adversely affect the environment. New environment-friendly methods are necessary to be developed. An ideal solution can be covering the structures with a coating capable of inhibiting or reducing the bonding between snow or ice and solid surfaces. A solid surface with a water contact angle greater than 150° is called superhydrophobic. Desiring superhydrophobicity, a surface should satisfy two criteria, nano/micrometer scale roughness as well as low surface energy. Many applications in industry and in everyday-life can be benefited from this extreme water-repellence if one can develop a durable, environment-friendly superhydrophobic coating. In the present study, the hydrophobicity of the surfaces with submicron roughness prepared by spin-coating of metallic nanoparticle colloids on aluminum and copper substrates was studied. Three colloids of silver nanoparticles and two colloids of copper nanoparticles with different size distributions were synthesized by chemical reduction methods. Silver particles were found to be stable enough to make the model surfaces but copper particles were unstable and not suitable for this application. Regardless of nanoparticle type, hydrophobic surfaces could not be achieved by making rough surfaces by only one layer of coating. By adding a second layer of coating, all three types of silver nanoparticles resulted in coatings with high degree of superhydrophobicity on metallic substrates. Due to the similar shapes of nanoparticles, the difference in observed contact angles could be related to the particles sizes. The particles with the average size of ˜263 nm had the highest contact angles whereas the particles with average size of ˜195 nm or ˜360 nm showed lower values. The anti-icing behaviour of these superhydrophobic films was studied under atmospheric icing conditions. On aluminum, two layer coating of 263 nm particles could reduce the ice adhesion up to 8.1 times. This value was equal to 4 on copper substrates with similar coating. The copper based samples could keep their ice adhesion reduction even after five ice removal test.

Safaee, Alireza

18

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

19

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. PMID:22194987

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

2011-01-01

20

Condensation on Hydrophilic, Hydrophobic, Nanostructured Superhydrophobic and Oil-Infused Surfaces  

E-print Network

Color images of steady state water vapor condensing on smooth and nanostructured hydrophobic surfaces are presented. Figure 1a shows a snapshot of classical filmwise condensation on hydrophilic copper. A thin liquid film ...

Nenad, Miljkovic

21

Modeling & simulation of nanostructures for superhydrophobic coatings  

Microsoft Academic Search

Materials with surfaces that are difficult to wet with water are called hydrophobic. Hydrophobic molecules tend to be nonpolar and thus prefer other neutral molecules and nonpolar solvents. Hydrophobic molecules in water often cluster together. Superhydrophobic surfaces are generally made by additionally controlling the surface chemistry and surface roughness of various hydrophobic materials. Superhydrophobic surfaces can be caused by protrusions

Ronald Pirich; John Weir; Dennis Leyble; Steven Chu

2012-01-01

22

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.

23

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. PMID:21718023

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

2011-01-01

24

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

25

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

26

Superhydrophobic surfaces from various polypropylenes.  

PubMed

Superhydrophobic surfaces were prepared from solutions of isotactic polypropylenes of various molecular weights using soft chemistry. Varying the conditions of the experiments (polymer concentration and initial amount of the coated solution) allowed us to optimize the superhydrophobic behavior of the polymer film. Results show that decreasing the concentration and/or film thicknesses decreases the probability to get superhydrophobicity for all polypropylenes tested. Measurement and analysis of advancing and receding contact angles as well as estimation of surface homogeneity were performed. Similar results were obtained with syndio- as well as atactic polypropylenes. PMID:18646781

Rioboo, R; Voué, M; Vaillant, A; Seveno, D; Conti, J; Bondar, A I; Ivanov, D A; De Coninck, J

2008-09-01

27

Antibacterial fluorinated silica colloid superhydrophobic surfaces.  

PubMed

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, scanning electron microscopy (SEM), and atomic force microscopy (AFM). Quantitative bacterial adhesion studies performed using a parallel plate flow cell demonstrated that the adhesion of Staphylococcus aureus and Pseudomonas aeruginosa was 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. PMID:21718023

Privett, Benjamin J; Youn, Jonghae; Hong, Sung A; Lee, Jiyeon; Han, Junhee; Shin, Jae Ho; Schoenfisch, Mark H

2011-08-01

28

Nanostructured metal surfaces and their passivation for superhydrophobic and anti-icing applications  

Microsoft Academic Search

Many systems and infrastructures developed by human beings frequently encounter deficiencies, stop functioning or even fail during severe weather conditions due to ice accumulation. One of the common methods to prevent snow and ice accumulation on exposed surfaces is the use of chemicals such as freezing point depressants. They should be applied during storms or just before ice accumulation which

Alireza Safaee

2008-01-01

29

Robust biomimetic-structural superhydrophobic surface on aluminum alloy.  

PubMed

The following facile approach has been developed to prepare a biomimetic-structural superhydrophobic surface with high stabilities and strong resistances on 2024 Al alloy that are robust to harsh environments. First, a simple hydrothermal treatment in a La(NO3)3 aqueous solution was used to fabricate ginkgo-leaf like nanostructures, resulting in a superhydrophilic surface on 2024 Al. Then a low-surface-energy compound, dodecafluoroheptyl-propyl-trimethoxylsilane (Actyflon-G502), was used to modify the superhydrophilic 2024 Al, changing the surface character from superhydrophilicity to superhydrophobicity. The water contact angle (WCA) of such a superhydrophobic surface reaches up to 160°, demonstrating excellent superhydrophobicity. Moreover, the as-prepared superhydrophobic surface shows high stabilities in air-storage, chemical and thermal environments, and has strong resistances to UV irradiation, corrosion, and abrasion. The WCAs of such a surface almost remain unchanged (160°) after storage in air for 80 days, exposure in 250 °C atmosphere for 24 h, and being exposed under UV irradiation for 24 h, are more than 144° whether in acidic or alkali medium, and are more than 150° after 48 h corrosion and after abrasion under 0.98 kPa for 1000 mm length. The remarkable durability of the as-prepared superhydrophobic surface can be attributed to its stable structure and composition, which are due to the existence of lanthanum (hydr)oxides in surface layer. The robustness of the as-prepared superhydrophobic surface to harsh environments will open their much wider applications. The fabricating approach for such robust superhydrophobic surface can be easily extended to other metals and alloys. PMID:25545550

Li, Lingjie; Huang, Tao; Lei, Jinglei; He, Jianxin; Qu, Linfeng; Huang, Peiling; Zhou, Wei; Li, Nianbing; Pan, Fusheng

2015-01-28

30

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

31

A facile approach to fabricate superhydrophobic and corrosion resistant surface  

NASA Astrophysics Data System (ADS)

In the present study, we have fabricated superhydrophobic CuO nanostructured surfaces by a simple solution-immersion process and a subsequent chemical modification with various thiol groups. The morphology of the CuO nanostructures on the copper foil could be easily controlled by simply changing the reaction time. The influences of reaction time and the thiol groups on hydrophobic properties have been discussed in detail. It is shown that the chemically modified CuO nanostructured surfaces present remarkable superhydrophobic performance and non-sticking behaviour. Furthermore, a lower corrosion current density (icorr) and a higher corrosion potential (Ecorr) of the prepared superhydrophobic surface was observed in comparison with the bare Cu foil by immersing in a 3.5 wt% NaCl solution, indicating a good corrosion resistance capability. Our work provides a general, facile and low-cost route towards the preparation of superhydrophobic surface, which has potential applications in the fields of self-cleaning, anti-corrosion, and oil–water separation.

Wei, Guijuan; Wang, Zhaojie; Zhao, Xixia; Feng, Juan; Wang, Shutao; Zhang, Jun; An, Changhua

2015-01-01

32

Insights into the superhydrophobicity of metallic surfaces prepared by electrodeposition involving spontaneous adsorption of airborne hydrocarbons  

NASA Astrophysics Data System (ADS)

Electrochemical fabrication of micro/nanostructured metallic surfaces with superhydrophobicity has recently aroused great attention. However, the origin still remains unclear why smooth hydrophilic metal surfaces become superhydrophobic by making micro/nanostructures without additional surface modifications. In this work, several superhydrophobic micro/nanostructured metal surfaces were prepared by a facile one-step electrodeposition process, including non-noble and noble metals such as copper, nickel, cadmium, zinc, gold, and palladium with (e.g. Cu) or without (e.g. Au) surface oxide films. We demonstrated by SEM and XPS that both hierarchical micro/nanostructures and spontaneous adsorption of airborne hydrocarbons endowed these surfaces with excellent superhydrophobicity. We revealed by XPS that the adsorption of airborne hydrocarbons at the Ar+-etched clean Au surface was rather quick, such that organic contamination can hardly be prevented in practical operation of surface wetting investigation. We also confirmed by XPS that ultraviolet-O3 treatment of the superhydrophobic metal surfaces did not remove the adsorbed hydrocarbons completely, but mainly oxidized them into hydrophilic oxygen-containing organic substances. We hope our findings here shed new light on deeper understanding of superhydrophobicity for micro/nanostructured metal surfaces with and without surface oxide films.

Liu, Peng; Cao, Ling; Zhao, Wei; Xia, Yue; Huang, Wei; Li, Zelin

2015-01-01

33

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

34

Dynamic contact angle measurements on superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

In this paper, the dynamic advancing and receding contact angles of a series of aqueous solutions were measured on a number of hydrophobic and superhydrophobic surfaces using a modified Wilhelmy plate technique. Superhydrophobic surfaces are hydrophobic surfaces with micron or nanometer sized surface roughness. These surfaces have very large static advancing contact angles and little static contact angle hysteresis. In this study, the dynamic advancing and dynamic receding contact angles on superhydrophobic surfaces were measured as a function of plate velocity and capillary number. The dynamic contact angles measured on a smooth hydrophobic Teflon surface were found to obey the scaling with capillary number predicted by the Cox-Voinov-Tanner law, ?D3 ? Ca. The response of the dynamic contact angle on the superhydrophobic surfaces, however, did not follow the same scaling law. The advancing contact angle was found to remain constant at ?A = 160?, independent of capillary number. The dynamic receding contact angle measurements on superhydrophobic surfaces were found to decrease with increasing capillary number; however, the presence of slip on the superhydrophobic surface was found to result in a shift in the onset of dynamic contact angle variation to larger capillary numbers. In addition, a much weaker dependence of the dynamic contact angle on capillary number was observed for some of the superhydrophobic surfaces tested.

Kim, Jeong-Hyun; Kavehpour, H. Pirouz; Rothstein, Jonathan P.

2015-03-01

35

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

36

Superhydrophobic porous surfaces: dissolved oxygen sensing.  

PubMed

Porous polymer films are necessary for dissolved gas sensor applications that combine high sensitivity with selectivity. This report describes a greatly enhanced dissolved oxygen sensor system consisting of amphiphilic acrylamide-based polymers: poly(N-(1H, 1H-pentadecafluorooctyl)-methacrylamide) (pC7F15MAA) and poly(N-dodecylacrylamide-co-5- [4-(2-methacryloyloxyethoxy-carbonyl)phenyl]-10,15,20-triphenylporphinato platinum(II)) (p(DDA/PtTPP)). The nanoparticle formation capability ensures both superhydrophobicity with a water contact angle greater than 160° and gas permeability so that molecular oxygen enters the film from water. The film was prepared by casting a mixed solution of pC7F15MAA and p(DDA/PtTPP) with AK-225 and acetic acid onto a solid substrate. The film has a porous structure comprising nanoparticle assemblies with diameters of several hundred nanometers. The film shows exceptional performance as the oxygen sensitivity reaches 126: the intensity ratio at two oxygen concentrations (I0/I40) respectively corresponding to dissolved oxygen concentration 0 and 40 (mg L(-1)). Understanding and controlling porous nanostructures are expected to provide opportunities for making selective penetration/separation of molecules occurring at the superhydrophobic surface. PMID:25659178

Gao, Yu; Chen, Tao; Yamamoto, Shunsuke; Miyashita, Tokuji; Mitsuishi, Masaya

2015-02-18

37

Pancake bouncing on superhydrophobic surfaces  

E-print Network

Engineering surfaces that promote rapid drop detachment is of importance to a wide range of applications including anti-icing, dropwise condensation6, and self-cleaning. Here we show how superhydrophobic surfaces patterned with lattices of submillimetre-scale posts decorated with nano-textures can generate a counter-intuitive bouncing regime: drops spread on impact and then leave the surface in a flattened, pancake shape without retracting. This allows for a four-fold reduction in contact time compared to conventional complete rebound. We demonstrate that the pancake bouncing results from the rectification of capillary energy stored in the penetrated liquid into upward motion adequate to lift the drop. Moreover, the timescales for lateral drop spreading over the surface and for vertical motion must be comparable. In particular, by designing surfaces with tapered micro/nanotextures which behave as harmonic springs, the timescales become independent of the impact velocity, allowing the occurrence of pancake bou...

Liu, Yahua; Xu, Xinpeng; Qian, Tiezheng; Yeomans, Julia M; Wang, Zuankai

2014-01-01

38

Pancake bouncing on superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

Engineering surfaces that promote rapid drop detachment is of importance to a wide range of applications including anti-icing, dropwise condensation and self-cleaning. Here we show how superhydrophobic surfaces patterned with lattices of submillimetre-scale posts decorated with nanotextures can generate a counter-intuitive bouncing regime: drops spread on impact and then leave the surface in a flattened, pancake shape without retracting. This allows a fourfold reduction in contact time compared with conventional complete rebound . We demonstrate that the pancake bouncing results from the rectification of capillary energy stored in the penetrated liquid into upward motion adequate to lift the drop. Moreover, the timescales for lateral drop spreading over the surface and for vertical motion must be comparable. In particular, by designing surfaces with tapered micro/nanotextures that behave as harmonic springs, the timescales become independent of the impact velocity, allowing the occurrence of pancake bouncing and rapid drop detachment over a wide range of impact velocities.

Liu, Yahua; Moevius, Lisa; Xu, Xinpeng; Qian, Tiezheng; Yeomans, Julia M.; Wang, Zuankai

2014-07-01

39

Marangoni convection in droplets on superhydrophobic surfaces  

E-print Network

We consider a small droplet of water sitting on top of a heated superhydrophobic surface. A toroidal convection pattern develops in which fluid is observed to rise along the surface of the spherical droplet and to accelerate ...

Tam, Daniel

40

Optimum conditions for fabricating superhydrophobic surface on copper plates via controlled surface oxidation and dehydration processes  

NASA Astrophysics Data System (ADS)

The superhydrophobic surfaces on copper substrate were fabricated by direct oxidation and dehydration processes, and the reaction and modification conditions were optimized. Firstly, the oxidation conditions including the concentrations of K2S2O8 and NaOH, the oxidation time were studied. It is found that the superhydrophobicity would be better if the copper plates were oxidized in 0.06 M K2S2O8 and 3.0 M NaOH solution at 65 °C for 35 min. Then, the modification conditions including modifier concentration and modification time were investigated. The results showed that 5 wt% lauric acid and 1 h modification time were suitable modification conditions for preparing copper-based superhydrophobic surfaces. The surface fabricated under optimized conditions displayed excellent superhydrophobicity of high water contact angle of 161.1° and a low contact angle hysteresis of 2.5°. The surface microstructure and composition of the superhydrophobic surfaces were also characterized by SEM and FT-IR. It is found that the highly concentrated micro/nanostructured sheets and the low surface energy materials on the surface should be responsible for the high superhydrophobicity.

Zhang, Yan; Li, Wen; Ma, Fumin; Yu, Zhanlong; Ruan, Min; Ding, Yigang; Deng, Xiangyi

2013-09-01

41

Mechanically durable superhydrophobic surfaces prepared by abrading  

NASA Astrophysics Data System (ADS)

Superhydrophobic surfaces with both excellent mechanical durability and easy reparability based on polytetrafluoroethylene/room temperature vulcanized silicone rubber (PTFE/RTVSR) composites were prepared by a simple abrading method. The surface energy of RTVSR matrix decreased with the increasing volume fraction of PTFE particles, and the surface rough microstructures of the composites were created by abrading. A water droplet on the surface exhibited a contact angle of about 165° ± 3.4° and a sliding angle of about 7.3° ± 1.9°. Such superhydrophobic surfaces showed strong mechanical durability against sandpaper because the surfaces were prepared in the way of mechanical abrasion, and the fresh exposed surfaces were still superhydrophobic. In addition, the micro-structures on the elastic surface of the composite will be compressed by elastic deformation to avoid being broken during the friction cycles when cotton fabric was used as an abrasion surface. The deformation will rebound to renew the original surface structures when the load is withdrawn. Therefore, the elastic PTFE/RTVSR composites are of advantage to construct superhydrophobic surfaces with better abrasion resistance. More importantly, such superhydrophobicity can be repaired by a simple abrading regeneration process within a few minutes when the surface is damaged or polluted by organic contaminant.

Wang, Fajun; Yu, Shan; Ou, Junfei; Xue, Mingshan; Li, Wen

2013-09-01

42

Functional superhydrophobic surfaces made of Janus micropillars  

PubMed Central

We demonstrate the fabrication of superhydrophobic surfaces consisting of micropillars with hydrophobic sidewalls and hydrophilic tops, referred to as Janus micropillars. Therefore we first coat a micropillar array with a mono- or bilayer of polymeric particles, and merge the particles together to shield the top faces while hydrophobizing the walls. After removing the polymer film, the top faces of the micropillar arrays can be selectively chemically functionalised with hydrophilic groups. The Janus arrays remain superhydrophobic even after functionalisation as verified by laser scanning confocal microscopy. The robustness of the superhydrophobic behaviour proves that the stability of the entrapped air cushion is determined by the forces acting at the rim of the micropillars. This insight should stimulate a new way of designing super liquid-repellent surfaces with tunable liquid adhesion. In particular, combining superhydrophobicity with the functionalisation of the top faces of the protrusions with hydrophilic groups may have exciting new applications, including high-density microarrays for high-throughput screening of bioactive molecules, cells, or enzymes or efficient water condensation. However, so far chemical attachment of hydrophilic molecules has been accompanied with complete wetting of the surface underneath. The fabrication of superhydrophobic surfaces where the top faces of the protrusions can be selectively chemically post-functionalised with hydrophilic molecules, while retaining their superhydrophobic properties, is both promising and challenging. PMID:25415839

Mammen, Lena; Bley, Karina; Papadopoulos, Periklis; Schellenberger, Frank; Encinas, Noemí; Butt, Hans-Jürgen; Weiss, Clemens K.

2015-01-01

43

Functional superhydrophobic surfaces made of Janus micropillars.  

PubMed

We demonstrate the fabrication of superhydrophobic surfaces consisting of micropillars with hydrophobic sidewalls and hydrophilic tops, referred to as Janus micropillars. Therefore we first coat a micropillar array with a mono- or bilayer of polymeric particles, and merge the particles together to shield the top faces while hydrophobizing the walls. After removing the polymer film, the top faces of the micropillar arrays can be selectively chemically functionalised with hydrophilic groups. The Janus arrays remain superhydrophobic even after functionalisation as verified by laser scanning confocal microscopy. The robustness of the superhydrophobic behaviour proves that the stability of the entrapped air cushion is determined by the forces acting at the rim of the micropillars. This insight should stimulate a new way of designing super liquid-repellent surfaces with tunable liquid adhesion. In particular, combining superhydrophobicity with the functionalisation of the top faces of the protrusions with hydrophilic groups may have exciting new applications, including high-density microarrays for high-throughput screening of bioactive molecules, cells, or enzymes or efficient water condensation. However, so far chemical attachment of hydrophilic molecules has been accompanied with complete wetting of the surface underneath. The fabrication of superhydrophobic surfaces where the top faces of the protrusions can be selectively chemically post-functionalised with hydrophilic molecules, while retaining their superhydrophobic properties, is both promising and challenging. PMID:25415839

Mammen, Lena; Bley, Karina; Papadopoulos, Periklis; Schellenberger, Frank; Encinas, Noemí; Butt, Hans-Jürgen; Weiss, Clemens K; Vollmer, Doris

2015-01-21

44

Water drop friction on superhydrophobic surfaces.  

PubMed

To investigate water drop friction on superhydrophobic surfaces, the motion of water drops on three different superhydrophobic surfaces has been studied by allowing drops to slide down an incline and capturing their motion using high-speed video. Two surfaces were prepared using crystallization of an alkyl ketene dimer (AKD) wax, and the third surface was the leaf of a Lotus (Nelumbo Nucifera). The acceleration of the water droplets on these superhydrophobic surfaces was measured as a function of droplet size and inclination of the surface. For small capillary numbers, we propose that the energy dissipation is dominated by intermittent pinning-depinning transitions at microscopic pinning sites along the trailing contact line of the drop, while at capillary numbers exceeding a critical value, energy dissipation is dominated by circulatory flow in the vicinity of the contacting disc between the droplet and the surface. By combining the results of the droplet acceleration with a theoretical model based on energy dissipation, we have introduced a material-specific coefficient called the superhydrophobic sliding resistance, b(sh). Once determined, this parameter is sufficient for predicting the motion of water drops on superhydrophobic surfaces of a general macroscopic topography. This theory also infers the existence of an equilibrium sliding angle, ?(eq), at which the drop acceleration is zero. This angle is decreasing with the radius of the drop and is in quantitative agreement with the measured tilt angles required for a stationary drop to start sliding down an incline. PMID:23721176

Olin, Pontus; Lindström, Stefan B; Pettersson, Torbjörn; Wågberg, Lars

2013-07-23

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

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

47

Superhydrophobic nanocomposite surface topography and ice adhesion.  

PubMed

A method to reduce the surface roughness of a spray-casted polyurethane/silica/fluoroacrylic superhydrophobic nanocomposite coating was demonstrated. By changing the main slurry carrier fluid, fluoropolymer medium, surface pretreatment, and spray parameters, we achieved arithmetic surface roughness values of 8.7, 2.7, and 1.6 ?m on three test surfaces. The three surfaces displayed superhydrophobic performance with modest variations in skewness and kurtosis. The arithmetic roughness level of 1.6 ?m is the smoothest superhydrophobic surface yet produced with these spray-based techniques. These three nanocomposite surfaces, along with a polished aluminum surface, were impacted with a supercooled water spray in icing conditions, and after ice accretion occurred, each was subjected to a pressurized tensile test to measure ice-adhesion. All three superhydrophobic surfaces showed lower ice adhesion than that of the polished aluminum surface. Interestingly, the intermediate roughness surface yielded the best performance, which suggests that high kurtosis and shorter autocorrelation lengths improve performance. The most ice-phobic nanocomposite showed a 60% reduction in ice-adhesion strength when compared to polished aluminum. PMID:24914617

Davis, Alexander; Yeong, Yong Han; Steele, Adam; Bayer, Ilker S; Loth, Eric

2014-06-25

48

Hierarchically nanotextured surfaces maintaining superhydrophobicity under severely adverse conditions  

NASA Astrophysics Data System (ADS)

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.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. Electronic supplementary information (ESI) available: Contact angles on intermediate surfaces; changes in PDMS film thickness with n-hexane immersion; the chemical stability of surfaces with (C3) and without PDMS film (C2) and the impalement pressure balance. See DOI: 10.1039/c4nr01368a

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

2014-07-01

49

Fabrication and characterization of superhydrophobic surfaces on aluminum alloy substrates  

NASA Astrophysics Data System (ADS)

Superhydrophobic surfaces have potential anti-icing applications in industries and daily life. In the present study, we combine the methods of chemical etching and surface modification with 1H,1H,2H,2H-perfluorooctyltriethoxysilane (POTS) which has very low surface energy to simplify the fabrication procedures for superhydrophobic surfaces on aluminum alloy substrates. The results show that the contact angle (CA), rolling angle (RA) and contact angle hysteresis (CAH) of superhydrophobic surfaces etched with 8.0 wt% HCl aqueous solutions are 162.5°, 1.9° and 1.1°, respectively; the apparent surface free energies (ASFEs) of superhydrophobic surfaces increase with the decrease in surface temperature; the freezing time of water droplets on superhydrophobic surfaces is retarded by 1568s, and the temperature drops to as low as -11.9 ?C. The results indicate that superhydrophobic surfaces exhibit excellent anti-icing properties.

Lv, F. Y.; Zhang, P.

2014-12-01

50

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

51

Preparation of superhydrophobic surfaces on cotton textiles  

NASA Astrophysics Data System (ADS)

Superhydrophobic surfaces were fabricated by the complex coating of silica nanoparticles with functional groups onto cotton textiles to generate a dual-size surface roughness, followed by hydrophobization with stearic acid, 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane or their combination. The wettability and morphology of the as-fabricated surfaces were investigated by contact angle measurement and scanning electron microscopy. Characterizations by transmission electron microscopy, Fourier transformation infrared spectroscopy, and thermal gravimetric analysis were also conducted.

Xue, Chao-Hua; Jia, Shun-Tian; Zhang, Jing; Tian, Li-Qiang; Chen, Hong-Zheng; Wang, Mang

2008-07-01

52

Facile fabrication of nano-structured silica hybrid film with superhydrophobicity by one-step VAFS approach  

NASA Astrophysics Data System (ADS)

Here we report a novel one-step vapor-fed aerosol flame synthesis (VAFS) method to attain silica hybrid film with superhydrophobicity on normal glass and other engineering material substrates using hexamethyldisiloxane (HMDSO) as precursor. The deposited nano-structured silica films represent excellent superhydrophobicity with contact angle larger than 150° and sliding angle below 5°, without any surface modification or other post treatments. SEM photographs proved that flame-made SiO2 nanoparticles formed dual-scale surface roughness on the substrates. It was confirmed by FTIR and XPS that the in situ formed organic fragments on the particle surface as species like (CH3)xSiO2-x/2 (x = 1, 2, 3) which progressively lowered the surface energy of fabricated films. Thus, these combined dual-scale roughness and lowered surface energy cooperatively produced superhydrophobic films. IR camera had been used to monitor the real-time flame temperature. It is found that the inert dilution gas inflow played a critical role in attaining superhydrophobicity due to its cooling and anti-oxidation effect. This method is facile and scalable for diverse substrates, without any requirement of complex equipments and multiple processing steps. It may contribute to the industrial fabrication of superhydrophobic films.

Jia, Yi; Yue, Renliang; Liu, Gang; Yang, Jie; Ni, Yong; Wu, Xiaofeng; Chen, Yunfa

2013-01-01

53

Composite, nanostructured, super-hydrophobic material  

DOEpatents

A hydrophobic disordered composite material having a protrusive surface feature includes a recessive phase and a protrusive phase, the recessive phase having a higher susceptibility to a preselected etchant than the protrusive phase, the composite material having an etched surface wherein the protrusive phase protrudes from the surface to form a protrusive surface feature, the protrusive feature being hydrophobic.

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

2007-08-21

54

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

55

Superhydrophobic cuprous oxide nanostructures on phosphor-copper meshes and their oil-water separation and oil spill cleanup.  

PubMed

A simple aqueous solution-immersion process was established to fabricate highly dense ordered Cu2O nanorods on commercial phosphor-copper mesh, with which the preparation was accomplished in distilled water. The present method, with the advantages of simple operation, low cost, short reaction time, and environmental friendliness, can be well adopted to fabricate desired Cu2O nanostructures on the phosphor-copper mesh under mild conditions. After surface modification with 1-dodecanethiol, the Cu2O nanostructure obtained on the phosphor-copper mesh exhibits excellent superhydrophobicity and superoleophilicity. Besides, a "mini boat" made from the as-prepared superhydrophobic phosphor-copper mesh can float freely on water surface and in situ collect oil from water surface. This demonstrates that the present approach, being facile, inexpensive, and environmentally friendly, could find promising application in oil-water separation and off shore oil spill cleanup. PMID:25590434

Kong, Ling-Hao; Chen, Xin-Hua; Yu, Lai-Gui; Wu, Zhi-Shen; Zhang, Ping-Yu

2015-02-01

56

Effect of superhydrophobic surface morphology on evaporative deposition patterns  

NASA Astrophysics Data System (ADS)

Prediction and active control of the spatial distribution of particulate deposits obtained from sessile droplet evaporation are vital in printing, nanostructure assembly, biotechnology, and other applications that require localized deposits. This Letter presents surface wettability-based localization of evaporation-driven particulate deposition and the effect of superhydrophobic surface morphology on the distribution of deposits. Sessile water droplets containing suspended latex particles are evaporated on non-wetting textured surfaces with varying microstructure geometry at ambient conditions. The droplets are visualized throughout the evaporation process to track the temporal evolution of contact radius and apparent contact angle. The resulting particle deposits on the substrates are quantitatively characterized. The experimental results show that superhydrophobic surfaces suppress contact-line deposition during droplet evaporation, thereby providing an effective means of localizing the deposition of suspended particles. A correlation between deposit size and surface morphology, explained in terms of the interface pressure balance at the transition between wetting states, reveals an optimum surface morphology for minimizing the deposit coverage area.

Dicuangco, Mercy; Dash, Susmita; Weibel, Justin A.; Garimella, Suresh V.

2014-05-01

57

Drop impact on porous superhydrophobic polymer surfaces.  

PubMed

Water drop impacts are performed on porous-like superhydrophobic surfaces. We investigate the influence of the drop size and of the impact velocity on the event. The Cassie-Baxter/Wenzel transition is observed to be a function of the drop size, as well as the outcomes of the impact or deposition process, which can be deposition, rebound, sticking, or fragmentation. A quantitative analysis on the experimental conditions required to observe rebound is provided. Our analysis shows that the wettability hysteresis controls the limit between deposition and rebound events. This limit corresponds to a constant Weber number. A survey of literature results on impact over patterned superhydrophobic surfaces is provided as a comparison. PMID:19360957

Rioboo, R; Voué, M; Vaillant, A; De Coninck, J

2008-12-16

58

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. PMID:24198490

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

2011-01-01

59

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

60

Topology optimization of robust superhydrophobic surfaces  

E-print Network

In this paper we apply topology optimization to micro-structured superhydrophobic surfaces for the first time. It has been experimentally observed that a droplet suspended on a brush of micrometric posts shows a high static contact angle and low roll-off angle. To keep the fluid from penetrating the space between the posts, we search for an optimal post cross section, that minimizes the vertical displacement of the liquid-air interface at the base of the drop when a pressure difference is applied. Topology optimisation proves effective in this framework, showing that posts with a branching cross-section are optimal, which is consistent with several biologic strategies to achieve superhydrophobicity. Through a filtering technique, we can also control the characteristic length scale of the optimal design, thus obtaining feasible geometries

A. Cavalli; P. Bøggild; F. Okkels

2013-02-27

61

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

62

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

63

Dynamic wetting on superhydrophobic surfaces: Droplet impact and wetting hysteresis  

E-print Network

We study the wetting energetics and wetting hysteresis of sessile and impacting water droplets on superhydrophobic surfaces as a function of surface texture and surface energy. For sessile drops, we find three wetting ...

Smyth, Katherine M.

64

Preparation of polymeric superhydrophobic surfaces and analysis of their wettability  

NASA Astrophysics Data System (ADS)

In this paper, we presented three simple, facile and low-cost manufacturing methods—template method, nanoparticle filling method and extrusion stamping forming method—to fabricate the polymeric superhydrophobic surfaces. The stainless steel wire mesh as the template and glass beads was investigated in this study for the first time and low-cost hollow glass beads were rarely used as particles for fabricating the superhydrophobic surface. The water contact angle measurement of polymeric surfaces was used to investigate the effect of mesh count, glass beads and PTFE on fabricating polymeric superhydrophobic surface. It was found that the mesh count significantly affected the hydrophobicity of polymer surface in template method. The addition of glass beads improved the hydrophobicity by nanoparticle filling method. The addition of PTFE was of importance to fabricate the superhydrophobic surface by extrusion stamping forming method. The surface microstructure was also observed by scanning electron microscope.

Zhuang, Jian; Huang, Manling; Zhang, Yajun; Wu, Daming; Kuang, Tairong; Xu, Hong; Zhang, Xiaoxu

2015-02-01

65

Fabrication of superhydrophobic copper surface with excellent corrosion resistance  

NASA Astrophysics Data System (ADS)

This article presents an effective and facile method for preparing the superhydrophobic copper surface with excellent corrosion resistance. The superhydrophobic copper surfaces were fabricated by oxidizing, heat-treating, and alkyl chains' grafting. The resulting copper plates take on the binary structure which is composed of a great deal of nanosheets and needle-like/rod-like fibers. Just grounded on both the micro- and nanoscale hierarchical surface and the grafted long alkyl chains, the resulting copper plates are endued with the excellent water repellence, while the water contact angle and sliding angle can reach 157.3° and 5°, respectively. As a result, the superhydrophobic copper plates get the outstanding corrosion resistance.

Feng, Libang; Zhao, Libin; Qiang, Xiaohu; Liu, Yanhua; Sun, Zhiqiang; Wang, Bei

2014-12-01

66

Fabrication of superhydrophobic copper surface with excellent corrosion resistance  

NASA Astrophysics Data System (ADS)

This article presents an effective and facile method for preparing the superhydrophobic copper surface with excellent corrosion resistance. The superhydrophobic copper surfaces were fabricated by oxidizing, heat-treating, and alkyl chains' grafting. The resulting copper plates take on the binary structure which is composed of a great deal of nanosheets and needle-like/rod-like fibers. Just grounded on both the micro- and nanoscale hierarchical surface and the grafted long alkyl chains, the resulting copper plates are endued with the excellent water repellence, while the water contact angle and sliding angle can reach 157.3° and 5°, respectively. As a result, the superhydrophobic copper plates get the outstanding corrosion resistance.

Feng, Libang; Zhao, Libin; Qiang, Xiaohu; Liu, Yanhua; Sun, Zhiqiang; Wang, Bei

2015-04-01

67

Superhydrophobic alumina surface based on stearic acid modification  

NASA Astrophysics Data System (ADS)

A novel superhydrophobic alumina surface is fabricated by grafting stearic acid layer onto the porous and roughened aluminum film. The chemical and phase structure, morphology, and the chemical state of the atoms at the superhydrophobic surface were investigated by techniques as FTIR, XRD, FE-SEM, and XPS, respectively. Results show that a super water-repellent surface with a contact angle of 154.2° is generated. The superhydrophobic alumina surface takes on an uneven flowerlike structure with many nanometer-scale hollows distribute in the nipple-shaped protrusions, and which is composed of boehmite crystal and ?-Al2O3. Furthermore, the roughened and porous alumina surface is coated with a layer of hydrophobic alkyl chains which come from stearic acid molecules. Therefore, both the roughened structure and the hydrophobic layer endue the alumina surface with the superhydrophobic behavior.

Feng, Libang; Zhang, Hongxia; Mao, Pengzhi; Wang, Yanping; Ge, Yang

2011-02-01

68

Delayed Frost Growth on Jumping-Drop Superhydrophobic Surfaces  

SciTech Connect

Self-propelled jumping drops are continuously removed from a condensing superhydrophobic surface to enable a micrometric steady-state drop size. Here, we report that subcooled condensate on a chilled superhydrophobic surface are able to repeatedly jump off the surface before heterogeneous ice nucleation occurs. Frost still forms on the superhydrophobic surface due to ice nucleation at neighboring edge defects, which eventually spreads over the entire surface via an inter-drop frost wave. The growth of this inter-drop frost front is shown to be up to three times slower on the superhydrophobic surface compared to a control hydrophobic surface, due to the jumping-drop effect dynamically minimizing the average drop size and surface coverage of the condensate. A simple scaling model is developed to relate the success and speed of inter-drop ice bridging to the drop size distribution. While other reports of condensation frosting on superhydrophobic surfaces have focused exclusively on liquid-solid ice nucleation for isolated drops, these findings reveal that the growth of frost is an inter-drop phenomenon that is strongly coupled to the wettability and drop size distribution of the surface. A jumping-drop superhydrophobic condenser was found to be superior to a conventional dropwise condenser in two respects: preventing heterogeneous ice nucleation by continuously removing subcooled condensate, and delaying frost growth by minimizing the success of interdrop ice bridge formation.

Boreyko, Jonathan B [ORNL; Collier, Pat [ORNL

2013-01-01

69

Effects of Contact Angle Hysteresis on Ice Adhesion and Growth over Superhydrophobic Surfaces under Dynamic Flow Conditions  

SciTech Connect

In this paper, the iceophobic properties of superhydrophobic surfaces are investigated under dynamic flow conditions by using a closed loop low-temperature wind tunnel. Superhydrophobic surfaces were prepared by coating the substrates of aluminum and steel plates with nano-structured hydrophobic particles. The superhydrophobic plates along with uncoated control ones were exposed to an air flow of 12 m/s and 20 F accompanying micron-sized water droplets in the icing wind tunnel and the ice formation and accretion were probed by high-resolution CCD cameras. Results show that the superhydrophobic coatings significantly delay the ice formation and accretion even under the dynamic flow condition of the highly energetic impingement of accelerated super-cooled water droplets. It is found that there is a time scale for this phenomenon (delay of the ice formation) which has a clear correlation with the contact angle hysteresis and the length scale of surface roughness of the superhydrophobic surface samples, being the highest for the plate with the lowest contact angle hysteresis and finer surface roughness. The results suggest that the key parameter for designing iceophobic surfaces is to retain a low contact angle hysteresis (dynamic property) and the non-wetting superhydrophobic state under the hydrodynamic pressure of impinging droplets, rather than to only have a high contact angle (static property), in order to result in efficient anti-icing properties under dynamic conditions such as forced flows.

Sarshar, Mohammad Amin [Stevens Institute of Technology, Hoboken, New Jersey; Swarctz, Christopher [Stevens Institute of Technology, Hoboken, New Jersey; Hunter, Scott Robert [ORNL; Simpson, John T [ORNL; Choi, Chang-Hwan [Stevens Institute of Technology, Hoboken, New Jersey

2012-01-01

70

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

71

Fabrication of superhydrophobic and highly oleophobic silicon-based surfaces via electroless etching method  

NASA Astrophysics Data System (ADS)

This study reports on a simple method for the preparation of superhydrophobic and highly oleophobic nanostructured silicon surfaces. The technique relies on metal-assisted electroless etching of silicon in sodium tetrafluoroborate (NaBF4) aqueous solution. Then, silver particles were deposited on the obtained surfaces, changing their overall physical morphology. Finally, the surfaces were coated by either C4F8, a fluoropolymer deposited by plasma, or by SiOx overlayers chemically modified with 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFTS) through silanization reaction. All these surfaces exhibit a superhydrophobic character (large apparent contact angle and low hysteresis with respect to water). In addition, they present high oleophobic properties, i.e. a high repellency to low surface energy liquids with various contact angle hysteresis, both depending on the morphology and type of coating.

Nguyen, Thi Phuong Nhung; Dufour, Renaud; Thomy, Vincent; Senez, Vincent; Boukherroub, Rabah; Coffinier, Yannick

2014-03-01

72

Topographical length scales of hierarchical superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

The morphology of hydrophobic CF4 plasma fluorinated polybutadiene surfaces has been characterised using atomic force microscopy (AFM). Judicious choice of the plasma power and exposure duration leads to formation of three different surface morphologies (Micro, Nano, and Micro + Nano). Scaling theory analysis shows that for all three surface topographies, there is an initial increase in roughness with length scale followed by a levelling-off to a saturation level. At length scales around 500 nm, it is found that the roughness is very similar for all three types of surfaces, and the saturation roughness value for the Micro + Nano morphology is found to be intermediate between those for the Micro and Nano surfaces. Fast Fourier Transform (FFT) analysis has shown that the Micro + Nano topography comprises a hierarchical superposition of Micro and Nano morphologies. Furthermore, the Micro + Nano surfaces display the highest local roughness (roughness exponent ? = 0.42 for length scales shorter than ?500 nm), which helps to explain their superhydrophobic behaviour (large water contact angle (>170°) and low hysteresis (<1°)).

Dhillon, P. K.; Brown, P. S.; Bain, C. D.; Badyal, J. P. S.; Sarkar, S.

2014-10-01

73

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

74

Low temperature self-cleaning properties of superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

Outdoor surfaces are usually dirty surfaces. Ice accretion on outdoor surfaces could lead to serious accidents. In the present work, the superhydrophobic surface based on 1H, 1H, 2H, 2H-Perfluorodecanethiol (PFDT) modified Ag/PDMS composite was prepared to investigate the anti-icing property and self-cleaning property at temperatures below freezing point. The superhydrophobic surface was deliberately polluted with activated carbon before testing. It was observed that water droplet picked up dusts on the cold superhydrophobic surface and took it away without freezing at a measuring temperature of -10 °C. While on a smooth PFDT surface and a rough surface base on Ag/PDMS composite without PFDT modification, water droplets accumulated and then froze quickly at the same temperature. However, at even lower temperature of -12 °C, the superhydrophobic surface could not prevent the surface water from icing. In addition, it was observed that the frost layer condensed from the moisture pay an important role in determining the low temperature self-cleaning properties of a superhydrophobic surface.

Wang, Fajun; Shen, Taohua; Li, Changquan; Li, Wen; Yan, Guilong

2014-10-01

75

Nanotextured silica surfaces with robust superhydrophobicity and omnidirectional broadband supertransmissivity.  

PubMed

Designing multifunctional surfaces that have user-specified interactions with impacting liquids and with incident light is a topic of both fundamental and practical significance. Taking cues from nature, we use tapered conical nanotextures to fabricate the multifunctional surfaces; the slender conical features result in large topographic roughness, while the axial gradient in the effective refractive index minimizes reflection through adiabatic index-matching between air and the substrate. Precise geometric control of the conical shape and slenderness of the features as well as periodicity at the nanoscale are all keys to optimizing the multifunctionality of the textured surface, but at the same time, these demands pose the toughest fabrication challenges. Here we report a systematic approach to concurrent design of optimal structures in the fluidic and optical domains and a fabrication procedure that achieves the desired aspect ratios and periodicities with few defects and large pattern area. Our fabricated nanostructures demonstrate structural superhydrophilicity or, in combination with a suitable chemical coating, robust superhydrophobicity. Enhanced polarization-independent optical transmission exceeding 98% has also been achieved over a broad range of bandwidth and incident angles. These nanotextured surfaces are also robustly antifogging or self-cleaning, offering potential benefits for applications such as photovoltaic solar cells. PMID:22482937

Park, Kyoo-Chul; Choi, Hyungryul J; Chang, Chih-Hao; Cohen, Robert E; McKinley, Gareth H; Barbastathis, George

2012-05-22

76

Boiling Heat Transfer on Superhydrophilic, Superhydrophobic, and Superbiphilic Surfaces  

E-print Network

With recent advances in micro- and nanofabrication, superhydrophilic and superhydrophobic surfaces have been developed. The statics and dynamics of fluids on these surfaces have been well characterized. However, few investigations have been made into the potential of these surfaces to control and enhance other transport phenomena. In this article, we characterize pool boiling on surfaces with wettabilities varied from superhydrophobic to superhydrophilic, and provide nucleation measurements. The most interesting result of our measurements is that the largest heat transfer coefficients are reached not on surfaces with spatially uniform wettability, but on biphilic surfaces, which juxtapose hydrophilic and hydrophobic regions. We develop an analytical model that describes how biphilic surfaces effectively manage the vapor and liquid transport, delaying critical heat flux and maximizing the heat transfer coefficient. Finally, we manufacture and test the first superbiphilic surfaces (juxtaposing superhydrophobic ...

Betz, Amy Rachel; Kim, Chang-Jin 'CJ'; Attinger, Daniel

2012-01-01

77

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

PubMed

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. PMID:24045766

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

2013-10-18

78

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

79

Wetting of soap bubbles on hydrophilic, hydrophobic and superhydrophobic surfaces  

E-print Network

Wetting of sessile bubbles on solid and liquid surfaces has been studied. A model is presented for the contact angle of a sessile bubble based on a modified Young equation - the experimental results agree with the model. A hydrophilic surface results in a bubble contact angle of 90 deg whereas on a superhydrophobic surface one observes 134 deg. 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

2013-01-01

80

Wetting of soap bubbles on hydrophilic, hydrophobic and superhydrophobic surfaces  

E-print Network

Wetting of sessile bubbles on solid and liquid surfaces has been studied. A model is presented for the contact angle of a sessile bubble based on a modified Young equation - the experimental results agree with the model. A hydrophilic surface results in a bubble contact angle of 90 deg whereas on a superhydrophobic surface one observes 134 deg. 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.

Steve Arscott

2013-03-26

81

Transparent superhydrophobic surfaces for applications of controlled reflectance.  

PubMed

This work involves a new optical application for transparent superhydrophobic materials, which enables low-energy optical contact between a liquid and solid surface. The new technique described here uses this surface property to control the reflectance of a surface using frustration of total internal reflection. Surface chemistry and appropriate micro-scale and nano-scale geometries are combined to produce interfaces with low adhesion to water and the degree to which incident light is reflected at this interface is controlled by the movement of water, thereby modifying the optical characteristics at the interface. The low adhesion of water to superhydrophobic surfaces is particularly advantageous in imaging applications where power use must be minimized. This paper describes the general approach, as well as a proof-of-principle experiment in which the reflectance was controlled by moving a water drop into and out of contact with a superhydrophobic surface by variation of applied electrostatic pressure. PMID:22505153

Gou, Steven; Mossman, Michele; Whitehead, Lorne

2012-04-10

82

Transparent surface with reversibly switchable wettability between superhydrophobicity and superhydrophilicity.  

PubMed

In the present work, we have successfully fabricated a polyelectrolyte-tethered transparent surface on which superhydrophobicity and superhydrophilicity can be reversibly switched via counterion exchange between the chloride ion (Cl(-)) and perfluorooctanoate ion (PFO(-)). The stable superhydrophobic state can be obtained only when a certain extent of fluorine is chemically incorporated into the grafted polyelectrolyte. The counterion exchange does not have any influence on the transmittance of the transparent surface. The superhydrophobicity and superhydrophilicity can be reversibly switched on the surface for many cycles without any apparent damage to the wetting properties. Additionally, the transparent surface can be applied to prepare smart glass displays to hide and convey information by patterning the counterion distribution on the surface on the basis of the different antifogging properties between superphydrophobic and superhydrophilic surfaces. PMID:23915149

Hua, Zan; Yang, Jun; Wang, Tao; Liu, Guangming; Zhang, Guangzhao

2013-08-20

83

Fabrication of superhydrophobic surface by hierarchical growth of lotus-leaf-like boehmite on aluminum foil.  

PubMed

Hierarchical growth of boehmite film on the aluminum foil was carried out via a facile solution-phase synthesis route. The resultant film is composed of three-dimensional microprotrusions assembled from well aligned nanoneedles. Such dual scale micro-/nanostructures are highly similar with those of lotus leaves. The resultant surface after hydrophobization exhibits a water contact angle of 169° and a sliding angle of ?4° for a 5 ?L droplet, which is ascribed to the combination of the dual scale roughness at the micro- and nanometer scale and the low surface energy of stearic acid coating. The obtained film possesses relatively good adhesion to the aluminum substrate and keeps superhydrophobicity after the ultrasonic treatment or long-term storage in spite of the partial loss of it superhydrophobic ability after abrasion test. PMID:21419417

Liu, Lijun; Zhao, Jiashou; Zhang, Yi; Zhao, Fan; Zhang, Yanbo

2011-06-01

84

Optimal design of superhydrophobic surfaces using a paraboloid microtexture.  

PubMed

Due to the crucial role of surface roughness, it has been recently proposed to design optimal and extract geometrical microstructures for practical fabrications of superhydrophobic surfaces. In this work, a paraboloid microtexture is employed as a typical example to theoretically establish a relationship between surface geometry and superhydrophobic behavior for a final optimal design. In particular, based on a thermodynamic approach, the effects of all the geometrical parameters for such a paraboloid microtexture on free energy (FE) and free energy barrier (FEB) as well as equilibrium contact angle (ECA) and contact angle hysteresis (CAH) of a superhydrophobic surface have been systematically investigated in detail. It is interestingly noted that the droplet position for metastable state is closely related to the intrinsic CA of the surface. Furthermore, the paraboloid base steepness plays a significant important role in ECA and CAH, and a critical steepness is necessary for the transition from noncomposite to composite states, which can be judged using a proposed criterion. Moreover, the superhydrophobicity depends strongly the surface geometrical dimension for noncomposite state, while it is not sensitive for composite state. Additionally, both vibrational energy and geometrical dimension affect the transition from noncomposite to composite wetting states, and a comprehensive criterion for such transition can be obtained. Finally, using such criterion, it is revealed that the paraboloidal protrusion is the most optimal geometry among the three typical microtextures for ideal superhydrophobicity. PMID:25265581

Tie, Lu; Guo, Zhiguang; Li, Wen

2014-12-15

85

Fabrication of superhydrophobic ZnO/Zn surface with nanowires and nanobelts structures using novel plasma assisted thermal vapor deposition  

NASA Astrophysics Data System (ADS)

Superhydrophobic ZnO surfaces with a contact angle of about 157° and a tilt angle lower than 9° were fabricated on commercial glass substrates via novel plasma assisted thermal vapor deposition method. Interconnected ZnO nanobelts and nanowires were constructed on the glass surfaces by Ar plasma activated Zn vapor deposition and then followed by a low-pressure-air (5 Pa) thermal oxidation at 350 °C. The resulting glass slides uniformly covered with nano-structured ZnO exhibited excellent superhydrophobic properties without any additional chemical modification. Moreover, the transparency and conductivity of the ZnO glass slides could be regulated easily by varying the oxidation parameters. The results of this study might pave a new pathway to the fabrication of superhydrophobic transparent conducting surface used in engineering fields.

Li, Guoxing; Wang, Bo; Liu, Yi; Tan, Tian; Song, Xuemei; Yan, Hui

2008-12-01

86

Fabrication of Robust and Antifouling Superhydrophobic Surfaces via Surface-Initiated Atom Transfer Radical Polymerization.  

PubMed

Superhydrophobic surfaces were fabricated via surface-initiated atom transfer radical polymerization of fluorinated methacrylates on poly(ethylene terephthalate) (PET) fabrics. The hydrophobicity of the PET fabric was systematically tunable by controlling the polymerization time. The obtained superhydrophobic fabrics showed excellent chemical robustness even after exposure to different chemicals, such as acid, base, salt, acetone, and toluene. Importantly, the fabrics maintained superhydrophobicity after 2500 abrasion cycles, 100 laundering cycles, and long time exposure to UV irradiation. Also, the surface of the superhydrophobic fabrics showed excellent antifouling properties. PMID:25832484

Xue, Chao-Hua; Guo, Xiao-Jing; Ma, Jian-Zhong; Jia, Shun-Tian

2015-04-22

87

Modeling and Optimization of Superhydrophobic Condensation  

E-print Network

Superhydrophobic micro/nanostructured surfaces for dropwise condensation have recently received significant attention due to their potential to enhance heat transfer performance by shedding water droplets via coalescence-induced ...

Miljkovic, Nenad

88

Mechanical stability of surface architecture--consequences for superhydrophobicity.  

PubMed

Wet chemistry methods such as sol-gel provide a facile means of preparing coatings with controlled surface chemistry and architecture. The manipulation of colloidal "building blocks," film constituents, and reaction conditions makes it a promising method for simple, scalable, and routine production of superhydrophobic coatings. Despite all of this, the practical application of superhydrophobic coatings remains limited by low mechanical durability. The translation of chemistry to mechanical strength within superhydrophobic films is severely hindered by the requisite physical structure. More specifically, porosity and the surface architecture of roughness in sol-gel-derived films contribute significantly to poor mechanical properties. These physical effects emphasize that collective structure and chemistry-based strategies are required. This challenge is not unique to superhydrophobics, and there are many principles that can be drawn upon to greatly improve performance. The delicate interplay between chemistry and physical structure has been highlighted through theory and characterization of porous and rough interfaces within and outside the framework of superhydrophobics. Insights can further be drawn from biology. Nature's capacity for self-repair remains extremely challenging to mimic in materials. However, nature does demonstrate strategies for structuring nano- and microbuilding blocks to achieve generally mutually exclusive properties. Difficulties with characterization and example mechanical characterization methods have also been emphasized. PMID:25318076

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

2014-11-12

89

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

90

Dropwise condensation on superhydrophobic surfaces with two-tier roughness  

E-print Network

. This letter reports continuous dropwise condensation on a superhydrophobic surface with short carbon nanotubes, mimicking that on the surface of lotus leaves,11 was prepared by depositing carbon nanotubes CNTs° Philips XL30 . The dry substrate was held assisted by a thin film of water on a copper plate cooled

Chen, Chuan-Hua

91

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

92

Free-standing, flexible, multifunctional, and environmentally stable superhydrophobic composite film made of self-assembled organic micro/super-nanostructures through solution process.  

PubMed

A free-standing, flexible, transparent, and fluorescent superhydrophobic composite film is fabricated by drop-casting a layer of organic self-assembled flowerlike micro/super-nanostructures on top of a hydrophobic polyimide film. The solution process to grow the organic super-nanostructures, fabricate the composite film, and lift-off the film from the mother substrate, ensures the process simplicity, low-cost, and scalability. The water contact angle (CA) of the superhydrophobic composite films reaches as high as 159.6°, and the sliding angle (SA) is less than 2° without any further low surface energy treatment. The as-prepared film shows superhydrophobicity with a CA above 150° covering the entire pH range. Moreover, the composite film exhibits good environmental stability against both organic solvent treatment and being exposed to acidic and aqueous solutions. The fluorescence from the composite film extends the potential application of the film into the optoelectronic field. The results may open up an avenue to prepare smart and intelligent superhydrophobic films for application. PMID:25618240

Dong, Ting; Zhou, Yan; Hu, Diangang; Xiao, Peng; Wang, Qing; Wang, Jian; Pei, Jian; Cao, Yong

2015-05-01

93

Ag dendrites with rod-like tips: synthesis, characterization and fabrication of superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

A facile, low-cost and templateless wet-chemical method was reported for the mass synthesis of Ag dendrites with rod-like tips which were characterized by various methods. The columniform tips protruded in random directions, of which the diameters were similar. A series of experiments were carried out to explore the effect of sodium citrate on the morphology of the obtained Ag nanostructures, and it was demonstrated that the concentration of sodium citrate was important for the formation of the cylindrical tips on the Ag dendrites. A possible mechanism was proposed to explain the role of sodium citrate in the synthesis of Ag dendrites with rod-like tips. Based on the roughness caused by the Ag dendrites, a superhydrophobic surface was fabricated in a simple procedure on a glass substrate, and the contact angle of the surface was as high as 156.4°. According to similar procedures, superhydrophobic surfaces were easily attained on a DVD disc and commercial aluminium foil, indicating the as-prepared Ag dendrites can be used to fabricate superhydrophobic surfaces on various smooth substrates.

Ren, Wen; Guo, Shaojun; Dong, Shaojun; Wang, Erkang

2011-05-01

94

Fabrication of "Roll-off" and "Sticky" Superhydrophobic Cellulose Surfaces via Plasma Processing  

E-print Network

their potential applications. In contrast, cellulose, a biodegradable, renewable, flexible, inexpensiveFabrication of "Roll-off" and "Sticky" Superhydrophobic Cellulose Surfaces via Plasma Processing, but it is not superhydrophobic. Superhydrophobicity on cellulose paper was obtained by domain- selective etching of amorphous

Breedveld, Victor

95

Superhydrophobic Aluminum Surfaces: Preparation routes, properties and artificial weathering impact  

Microsoft Academic Search

Among the materials that can show superhydrophobic properties are hydrophilic metals which must undergo a sequential treatment, including roughening and hydrophobic coating. This contribution presents various preparation routes along with characterization work employing dynamic contact angle measurements (CA), scanning electron microscopy (SEM) and spec- trometric techniques (FT-IRRAS, XPS, EIS). Micro-rough surfaces of pure and alloyed aluminum were generated most easily

M. Thieme; C. Blank; A. Pereira de Oliveira; H. Worch; R. Frenzel; S. Höhne

96

Water condensation on a super-hydrophobic spike surface  

Microsoft Academic Search

Condensation-induced water drop growth was studied on a super-hydrophobic spike surface. The dynamics are described by three main stages depending on the size of the drop with respect to the different spike pattern length scales. The initial stage is characterized by nucleation of the drops at the bottom (cavities) of the spikes. During the intermediate stage, large drops are surrounded

R. D. Narhe; D. A. Beysens

2006-01-01

97

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

98

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

99

Studies of drag on the nanocomposite superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

The nanocomposite thin films of stearic acid (SA)-functionalized ZnO nanoparticles incorporated in epoxy polymer matrix have been achieved. The X-ray diffraction (XRD) studies show the formation of zinc stearate on ZnO nanoparticles as the confirmation of SA-functionalization of ZnO nanoparticles in the thin films. Morphological analyses reveal the presence of micro-holes with the presence of irregular nanoparticles. The measured root mean square (rms) roughness of the thin film is found to be 12 ± 1 ?m with the adhesion of 5B on both glass and aluminum substrates. The wetting property shows that the surface of the film is superhydrophobic with the contact angle of water of 156 ± 4° having contact angle hysteresis (CAH) of 4 ± 2°. The average terminal velocity in the water of the as-received glass spheres and superhydrophobic spheres were found to be 0.66 ± 0.01 m/s and 0.72 ± 0.01 m/s respectively. Consequently, the calculated average coefficients of the surface drag of the as-received glass sphere and superhydrophobic glass sphere were 2.30 ± 0.01 and 1.93 ± 0.03, respectively. Hence, the drag reduction on the surface of superhydrophobic glass sphere is found to be approximately 16% lower than as-received glass sphere.

Brassard, Jean-Denis; Sarkar, D. K.; Perron, Jean

2015-01-01

100

Design of a superhydrophobic surface using woven structures.  

PubMed

The relationship between surface tension and roughness is reviewed. The Cassie-Baxter model is restated in its original form, which better describes the most general cases of surface roughness. Using mechanical and chemical surface modification of nylon 6,6 woven fabric, an artificial superhydrophobic surface was prepared. A plain woven fabric mimicking the Lotus leaf was created by further grafting 1H,1H-perfluorooctylamine or octadecylamine to poly(acrylic acid) chains which had previously been grafted onto a nylon 6,6 woven fabric surface. Water contact angles as high as 168 degrees were achieved. Good agreement between the predictions based on the original Cassie-Baxter model and experiments was obtained. The version of the Cassie-Baxter model in current use could not be applied to this problem since the surface area fractions in this form is valid only when the liquid is in contact with a flat, porous surface. The angle at which a water droplet rolls off the surface has also been used to define a superhydrophobic surface. It is shown that the roll-off angle is highly dependent on droplet size. The roll-off angles of these superhydrophobic surfaces were less than 5 degrees when a 0.5 mL water droplet was applied. PMID:17465576

Michielsen, Stephen; Lee, Hoon J

2007-05-22

101

Micro to nano: Surface size scale and superhydrophobicity  

PubMed Central

Summary 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

2011-01-01

102

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

103

Superhydrophobic zinc oxide surface by differential etching and hydrophobic modification  

Microsoft Academic Search

A superhydrophobic ZnO nanorod films on zinc substrate were fabricated by natural oxidation of zinc metal and subsequent modification with a monolayer of n-octadecyl thiol (ODT). The surface morphology and composition were studied using SEM, XRD, and XPS, respectively. The surface of ZnO films directly grown on zinc substrate was hydrophilic with a water contact angle (CA) of 40±2°, whereas

Xianming Hou; Feng Zhou; Bo Yu; Weimin Liu

2007-01-01

104

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

105

Electro-osmosis on anisotropic super-hydrophobic surfaces  

E-print Network

We give a general theoretical description of electro-osmotic flow at striped super-hydrophobic 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 case of uncharged liquid-gas interface, the flow is the same or inhibited relative to flow in homogeneously charged channel with 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 a possibility of huge electro-osmotic slip even for electro-neutral surfaces. On the basis of these observations we suggest strategies for practical microfluidic mixing devices. These results provide a framework for the rational design of super-hydrophobic surfaces.

Belyaev, Aleksey V

2011-01-01

106

Electro-osmosis on anisotropic super-hydrophobic surfaces  

E-print Network

We give a general theoretical description of electro-osmotic flow at striped super-hydrophobic 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 case of uncharged liquid-gas interface, the flow is the same or inhibited relative to flow in homogeneous channel with 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 a possibility of huge electro-osmotic slip even for electro-neutral surfaces. On the basis of these observations we suggest strategies for practical microfluidic mixing devices. These results provide a framework for the rational design of super-hydrophobic surfaces.

Aleksey V. Belyaev; Olga I. Vinogradova

2011-07-20

107

Droplet detachment by air flow for microstructured superhydrophobic surfaces.  

PubMed

Quantitative correlation between critical air velocity and roughness of microstructured surface has still not been established systematically until the present; the dynamics of water droplet detachment by air flow from micropillar-like superhydrophobic surfaces is investigated by combining experiments and simulation comparisons. Experimental evidence demonstrates that the onset of water droplet detachment from horizontal micropillar-like superhydrophobic surfaces under air flow always starts with detachment of the rear contact lines of the droplets from the pillar tops, which exhibits a similar dynamic mechanism for water droplet motion under a gravity field. On the basis of theoretical analysis and numerical simulation, an explicit analytical model is proposed for investigating the detaching mechanism, in which the critical air velocity can be fully determined by several intrinsic parameters: water-solid interface area fraction, droplet volume, and Young's contact angle. This model gives predictions of the critical detachment velocity of air flow that agree well with the experimental measurements. PMID:23557076

Hao, Pengfei; Lv, Cunjing; Yao, Zhaohui

2013-04-30

108

Induced detachment of coalescing droplets on superhydrophobic surfaces.  

PubMed

Coalescence of a falling droplet with a stationary sessile droplet on a superhydrophobic surface is investigated by a combined experimental and numerical study. In the experiments, the droplet diameter, the impact velocity, and the distance between the impacting droplets were controlled. The evolution of surface shape during the coalescence of two droplets on the superhydrophobic surface is captured using high speed imaging and compared with numerical results. A two-phase volume of fluid (VOF) method is used to determine the dynamics of droplet coalescence, shape evaluation, and contact line movement. The spread length of two coalesced droplets along their original center is also predicted by the model and compared well with the experimental results. The effect of different parameters such as impact velocity, center to center distance, and droplet size on contact time and restitution coefficient are studied and compared to the experimental results. Finally, the wetting and the self-cleaning properties of superhydrophobic surfaces have been investigated. It has been found that impinging water drops with very small amount of kinetic impact energy were able to thoroughly clean these surfaces. PMID:22171956

Farhangi, Mehran M; Graham, Percival J; Choudhury, N Roy; Dolatabadi, Ali

2012-01-17

109

Shrink-induced superhydrophobic and antibacterial surfaces in consumer plastics.  

PubMed

Structurally modified superhydrophobic surfaces have become particularly desirable as stable antibacterial surfaces. Because their self-cleaning and water resistant properties prohibit bacteria growth, structurally modified superhydrophobic surfaces obviate bacterial resistance common with chemical agents, and therefore a robust and stable means to prevent bacteria growth is possible. In this study, we present a rapid fabrication method for creating such superhydrophobic surfaces in consumer hard plastic materials with resulting antibacterial effects. To replace complex fabrication materials and techniques, the initial mold is made with commodity shrink-wrap film and is compatible with large plastic roll-to-roll manufacturing and scale-up techniques. This method involves a purely structural modification free of chemical additives leading to its inherent consistency over time and successive recasting from the same molds. Finally, antibacterial properties are demonstrated in polystyrene (PS), polycarbonate (PC), and polyethylene (PE) by demonstrating the prevention of gram-negative Escherichia coli (E. coli) bacteria growth on our structured plastic surfaces. PMID:22916100

Freschauf, Lauren R; McLane, Jolie; Sharma, Himanshu; Khine, Michelle

2012-01-01

110

Shrink-Induced Superhydrophobic and Antibacterial Surfaces in Consumer Plastics  

PubMed Central

Structurally modified superhydrophobic surfaces have become particularly desirable as stable antibacterial surfaces. Because their self-cleaning and water resistant properties prohibit bacteria growth, structurally modified superhydrophobic surfaces obviate bacterial resistance common with chemical agents, and therefore a robust and stable means to prevent bacteria growth is possible. In this study, we present a rapid fabrication method for creating such superhydrophobic surfaces in consumer hard plastic materials with resulting antibacterial effects. To replace complex fabrication materials and techniques, the initial mold is made with commodity shrink-wrap film and is compatible with large plastic roll-to-roll manufacturing and scale-up techniques. This method involves a purely structural modification free of chemical additives leading to its inherent consistency over time and successive recasting from the same molds. Finally, antibacterial properties are demonstrated in polystyrene (PS), polycarbonate (PC), and polyethylene (PE) by demonstrating the prevention of gram-negative Escherichia coli (E. coli) bacteria growth on our structured plastic surfaces. PMID:22916100

Freschauf, Lauren R.; McLane, Jolie; Sharma, Himanshu; Khine, Michelle

2012-01-01

111

Deposition and tuning of nanostructured hydrocarbon deposits: From superhydrophobic to superhydrophilic and back  

SciTech Connect

Carbonaceous fluorine free nanoparticles synthesized in a low temperature acetylene discharge are used in a first step for the production of (super)hydrophobic coatings. In a second step, the influence of different plasma and UV induced functionalizations on the wetting characteristics of these materials is investigated. The experiments show that the superhydrophobic surfaces can be turned continuously and reversibly into hydrophilic (superhydrophilic) surfaces by means of the different treatment methods. The reversibility of these processes is studied in a third step. It is shown that the changes of the surface which are induced by the plasma treatment can be undone by means of EUV irradiation. The switchability of the surface due to external stimuli can be easily used for the controlled production of patterned surfaces. This is demonstrated by means of one simple example.

Berndt, J.; Acid, H.; Kovacevic, E.; Cachoncinlle, C.; Boufendi, L. [GREMI, Universite d'Orleans, Polytech'Orleans, F-45067 Orleans Cedex 2 (France); Strunskus, Th. [Christian-Albrechts-Universitaet zu Kiel, Institut fuer Materialwissenschaft-Materialverbunde, D-24143 Kiel (Germany)

2013-02-14

112

One step preparation of superhydrophobic polymeric surface with polystyrene under ambient atmosphere.  

PubMed

Brassica oleracea-like polymer surface is facilely fabricated by one-step casting process using amorphous polystyrene (PS) under ambient atmosphere. The obtained coatings show excellent superhydrophobicity and only possess unitary micro-scale structure, similar to the natural brassica leaf. In addition, a simple topography analysis also roughly verifies superhydrophobic structure of branched and intermingled sticks and bumps. This process provides a fairly easy procedure for preparing superhydrophobic surface from common plastics. Moreover, it demonstrates that the micro/nano-binary structure is not necessary for superhydrophobicity, while unitary micro-scale structure for a polymer surface can exhibit outstanding water repellency as natural lotus. PMID:18384802

Tan, Shuaixia; Xie, Qiongdan; Lu, Xiaoying; Zhao, Ning; Zhang, Xiaoli; Xu, Jian

2008-06-01

113

Super-hydrophobic bandages and method of making the same  

SciTech Connect

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

114

PREFACE: Nanostructured surfaces  

NASA Astrophysics Data System (ADS)

We can define nanostructured surfaces as well-defined surfaces which contain lateral features of size 1-100 nm. This length range lies well below the micron regime but equally above the Ångstrom regime, which corresponds to the interatomic distances on single-crystal surfaces. This special issue of Journal of Physics: Condensed Matter presents a collection of twelve papers which together address the fabrication, characterization, properties and applications of such nanostructured surfaces. Taken together they represent, in effect, a status report on the rapid progress taking place in this burgeoning area. The first four papers in this special issue have been contributed by members of the European Research Training Network ‘NanoCluster’, which is concerned with the deposition, growth and characterization of nanometre-scale clusters on solid surfaces—prototypical examples of nanoscale surface features. The paper by Vandamme is concerned with the fundamentals of the cluster-surface interaction; the papers by Gonzalo and Moisala address, respectively, the optical and catalytic properties of deposited clusters; and the paper by van Tendeloo reports the application of transmission electron microscopy (TEM) to elucidate the surface structure of spherical particles in a catalyst support. The fifth paper, by Mendes, is also the fruit of a European Research Training Network (‘Micro-Nano’) and is jointly contributed by three research groups; it reviews the creation of nanostructured surface architectures from chemically-synthesized nanoparticles. The next five papers in this special issue are all concerned with the characterization of nanostructured surfaces with scanning tunnelling microscopy (STM) and atomic force microscopy (AFM). The papers by Bolotov, Hamilton and Dunstan demonstrate that the STM can be employed for local electrical measurements as well as imaging, as illustrated by the examples of deposited clusters, model semiconductor structures and real devices, respectively, while the papers by Ledieu and Guo report the structural characterization of novel surface systems—quasicrystal surfaces and supramolecular monolayers, respectively. The final two papers, by Bennett and Smith, demonstrate the positive interplay between experimental measurements and theoretical modelling in the investigation of nanostructured surfaces. The examples discussed include, respectively, the growth of metal clusters on oxide surfaces and the deposition of fullerenes and energetic clusters from the gas phase. We note finally that the last six papers in this special issue have been contributed by members of the Committee of the newly-formed Nanoscale Physics and Technology Group of the Institute of Physics. The Group shares with this special issue the aim of promoting and disseminating exciting advances in the flourishing field of nanoscale physics.

Palmer, Richard E.

2003-10-01

115

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

116

Design of Superhydrophobic Paper/Cellulose Surfaces via Plasma Enhanced Etching and Deposition  

E-print Network

Design of Superhydrophobic Paper/Cellulose Surfaces via Plasma Enhanced Etching and Deposition established by selective etching of the amorphous domains in cellulose. Despite different fiber types of superhydrophobic paper or cellulose surfaces with specific adhesion properties are described. The significance

Breedveld, Victor

117

Water-collecting behavior of nanostructured surfaces with special wettability  

NASA Astrophysics Data System (ADS)

Dew is commonly formed even in dry regions, and we examined the suitability of surfaces with superhydrophilic patterns on a superhydrophobic background as a dew-harvesting system. Nanostructured surfaces with mixed wettability were fabricated by ZnO and TiO2 nanorods. The condensation properties were investigated by environmental scanning electron microscopy (ESEM), and the water-collecting function of the patterned surfaces in an artificial environment was confirmed. Condensation and water-collecting behavior were evaluated as a function of surface inclination angle and pattern shape. We examined the collecting efficiency among the different wettabilities at various inclination angles and observed the condensation behavior for various superhydrophilic shapes.

Choo, Soyoung; Choi, Hak-Jong; Lee, Heon

2015-01-01

118

Learning from superhydrophobic plants: the use of hydrophilic areas on superhydrophobic surfaces for droplet control.  

PubMed

In many countries, the mornings in spring are graced with spectacular displays of dew drops hanging on spiders' webs and on leaves. Some leaves, in particular, sport particularly large droplets that last well into the morning. In this paper, we study a group of plants that show this effect on their superhydrophobic leaves to try to discover how and why they do it. We describe the structures they use to gather droplets and suggest that these droplets are used as a damper to absorb kinetic energy allowing water to be redirected from sideways motion into vertical motion. Model surfaces in the shape of leaves and as more general flat sheets show that this principle can be used to manipulate water passively, such as on the covers of solar panels, and could also be used in parts of microfluidic devices. The mode of transport can be switched between rolling droplets and rivulets to maximize control. PMID:20560556

Shirtcliffe, N J; McHale, G; Newton, M I

2009-12-15

119

Fabrication and characterization of a cotton candy like surface with superhydrophobicity  

NASA Astrophysics Data System (ADS)

Superhydrophobic thin films were prepared on glass by air-brushing the in situ polymerization compositions of D 5/SiO 2. The wettability and morphology were investigated by contact angle measurement and scanning electron microscopy. The most superhydrophobic samples prepared had a static water contact angle of 157° for a 5 ?l droplet and a sliding angle of ˜1° for 10 ?l droplet. Thermal stability analysis showed that the surface maintained superhydrophobic at temperature up to 450 °C. Air trapping and capillary force on superhydrophobic behavior were evaluated.

Hu, You; Huang, Chengya; Su, Dong; Jiang, Qiangwei; Zhu, Yunfeng

2011-05-01

120

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

121

Drop shedding by shear flow for hydrophilic to superhydrophobic surfaces.  

PubMed

A balance of surface science and aerodynamic knowledge is brought to bear to elucidate the fundamental parameters determining the incipient motion (runback) for a drop exposed to shearing airflow. It was found that wetting parameters such as contact angle are very influential in determining the minimum required air velocity for drop shedding. On the basis of experimental results for drops of water and hexadecane (0.5-100 microL) on PMMA, Teflon, and a superhydrophobic aluminum surface, an exponential function is proposed that relates the critical air velocity for shedding to the ratio of drop base length to projected area. The results for all of the water systems can be collapsed to self-similar curves by normalization. Results from other researchers also conform to the exponential self-similar functional form proposed. It was shown that the data for hexadecane drops can be matched relatively well to those for water drops by means of a corrective factor based on fluid properties and contact angles. Also, the critical air velocity for shedding from the superhydrophobic surface is seen to be more constant over a range of volumes than for the other surfaces. Finally, contact angle measurements from airflow shedding experiments are compared to measurements made by tilted plate and quasi-static advancing and receding tests. The observed differences between contact angles from different measurement methods show that the transfer of contact angle data among various applications must be done with care. PMID:19685896

Milne, A J B; Amirfazli, A

2009-12-15

122

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

SciTech Connect

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 morphology. Prior to and after wind tunnel testing, apparent contact angles of water sessile droplets on samples were measured by a contact angle meter to check degradation of surface superhydrophobicity. A simple peel test was also performed to estimate adhesion of ice on the surfaces. When compared to an untreated sample, superhydrophobic surfaces inhibited initial ice formation. After a period of time, random droplet strikes attached to the superhydrophobic surfaces and started to coalesce with previously deposited ice droplets. These sites appear as mounds of accreted ice across the surface. The appearance of the ice formations on the superhydrophobic samples is white rather than transparent, and is due to trapped air. These ice formations resemble soft rime ice rather than the transparent glaze ice seen on the untreated sample. Compared to untreated surfaces, the icing film formed on superhydrophobic surfaces was easy to peel off by shear flows.

Swarctz, Christopher [Stevens Institute of Technology, Hoboken, New Jersey; Alijallis, Elias [Stevens Institute of Technology, Hoboken, New Jersey; Hunter, Scott Robert [ORNL; Simpson, John T [ORNL; Choi, Chang-Hwan [Stevens Institute of Technology, Hoboken, New Jersey

2010-01-01

123

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

124

Stable superhydrophobic surface of hierarchical carbon nanotubes on Si micropillar arrays  

NASA Astrophysics Data System (ADS)

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.

He, Shaoqing; Wei, Jinquan; Wang, Haifan; Sun, Deshun; Yao, Zhaohui; Fu, Chengsong; Xu, Ruiqiao; Jia, Yi; Zhu, Hongwei; Wang, Kunlin; Wu, Dehai

2013-10-01

125

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. PMID:24098965

2013-01-01

126

Stable superhydrophobic surface of hierarchical carbon nanotubes on Si micropillar arrays.  

PubMed

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. PMID:24098965

He, Shaoqing; Wei, Jinquan; Wang, Haifan; Sun, Deshun; Yao, Zhaohui; Fu, Chengsong; Xu, Ruiqiao; Jia, Yi; Zhu, Hongwei; Wang, Kunlin; Wu, Dehai

2013-01-01

127

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

128

Shear driven droplet shedding and coalescence on a superhydrophobic surface  

NASA Astrophysics Data System (ADS)

The interest on shedding and coalescence of sessile droplets arises from the importance of these phenomena in various scientific problems and industrial applications such as ice formation on wind turbine blades, power lines, nacelles, and aircraft wings. It is shown recently that one of the ways to reduce the probability of ice accretion on industrial components is using superhydrophobic coatings due to their low adhesion to water droplets. In this study, a combined experimental and numerical approach is used to investigate droplet shedding and coalescence phenomena under the influence of air shear flow on a superhydrophobic surface. Droplets with a size of 2 mm are subjected to various air speeds ranging from 5 to 90 m/s. A numerical simulation based on the Volume of Fluid method coupled with the Large Eddy Simulation turbulent model is carried out in conjunction with the validating experiments to shed more light on the coalescence of droplets and detachment phenomena through a detailed analysis of the aerodynamics forces and velocity vectors on the droplet and the streamlines around it. The results indicate a contrast in the mechanism of two-droplet coalescence and subsequent detachment with those related to the case of a single droplet shedding. At lower speeds, the two droplets coalesce by attracting each other with successive rebounds of the merged droplet on the substrate, while at higher speeds, the detachment occurs almost instantly after coalescence, with a detachment time decreasing exponentially with the air speed. It is shown that coalescence phenomenon assists droplet detachment from the superhydrophobic substrate at lower air speeds.

Moghtadernejad, S.; Tembely, M.; Jadidi, M.; Esmail, N.; Dolatabadi, A.

2015-03-01

129

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

130

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

131

Design of a robust superhydrophobic surface: thermodynamic and kinetic analysis  

E-print Network

The design of a robust superhydrophobic surface is a widely pursued topic.While many investigations are limited to applications with high impact velocities (for raindrops of the order of a few m/s), the essence of robustness is yet to be analyzed for applications involving quasi-static liquid transfer.To achieve robustness with high impact velocities, the surface parameters (geometrical details, chemistry) have to be selected from a narrow range of permissible values, which often entail additional manufacturing costs.From the dual perspectives of thermodynamics and mechanics, we analyze the significance of robustness for quasi-static drop impact, and present the range of permissible surface characteristics.For surfaces with a Youngs contact angle greater than 90{\\deg} and square micropillar geometry, we show that robustness can be enforced when an intermediate wetting state (sagged state) impedes transition to a wetted state (Wenzel state).From the standpoint of mechanics, we use available scientific data to ...

Sarkar, Anjishnu

2014-01-01

132

Verification of icephobic/anti-icing properties of a superhydrophobic surface.  

PubMed

Four aluminum surfaces with wettability varied from superhydrophilic to superhydrophobic were prepared by combining an etching and a coating process. The surface wettability was checked in terms of water contact angle (CA) and sliding angle (SA) under different humidity at -10 °C. High-speed photography was applied to study water droplet impact dynamics on these surfaces. It was found that single and successive water droplets could rebound on the superhydrophobic surface and roll off at a tilt angle larger than 30° under an extremely condensing weather condition (-10 °C and relative humidity of 85-90%). In addition, the superhydrophobic surface showed a strong icephobic property, the ice adhesion on this surface was only 13% of that on the superhydrophilic surface, though they had a similar nano/microtopological structure. Moreover, this superhydrophobic surface displayed an excellent durability of the icephobic property. The ice adhesion only increased to 20% and 16% of that on the superhydrophobic surface after the surface was undergone 20 icing/ice-breaking cycles and 40 icing/ice-melting cycles, respectively. Surface profile and XPS studies on these surfaces indicated a minor damage of the surface nano/microstructure and the coating layer upon these multiple ice-breaking and ice-melting processes. Therefore, this superhydrophobic surface could be a good candidate for icephobic applications. PMID:23537106

Wang, Yuanyi; Xue, Jian; Wang, Qingjun; Chen, Qingmin; Ding, Jianfu

2013-04-24

133

Superhydrophobic Zr-based metallic glass surface with high adhesive force  

NASA Astrophysics Data System (ADS)

Micro/nano hierarchical structures were constructed on Zr35Ti30Be26.75Cu8.25 metallic glass surface by silicon moulding and subsequently chemical etching. The as-formed surface exhibited both superhydrophobicity and high adhesive force towards water. The superhydrophobicity is rationalized based on the modified Cassie-Baxter model [A. B. D. Cassie and S. Baxter, Trans. Faraday Soc. 40, 546 (1944)]. The origin of the robust adhesion is described in terms of intermolecular capillary forces. The present results not only provide a method to fabricate superhydrophobic metallic glasses surface but also explore an important industrial application as dry adhesives and transport of liquid microdroplets.

Li, Ning; Xia, Ting; Heng, Liping; Liu, Lin

2013-06-01

134

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

135

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. PMID:21977425

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

2011-01-01

136

Simple Approach to Superhydrophobic Nanostructured Al for Practical Antifrosting Application Based on Enhanced Self-propelled Jumping Droplets.  

PubMed

Frost formation can cause operational difficulty and efficiency loss for many facilities such as aircraft, wind turbines, and outdoor heat exchangers. Self-propelled jumping by condensate droplets on superhydrophobic surfaces delays frost formation, so many attempts have been made to exploit this phenomenon. However, practical application of this phenomenon is currently unfeasible because many processes to fabricate the superhydrophobic surfaces are inefficient and because self-propelled jumping is difficult to be achieved in a humid and low-temperature environment because superhydrophobicity is degraded in these conditions. Here, we achieved significantly effective anti-icing superhydrophobic aluminum. Its extremely low adhesive properties allow self-propelled jumping under highly supersaturated conditions of high humidity or low surface temperature. As a result, this surface helps retard frost formation at that condition. The aluminum was made superhydrophobic by a simple and cost-effective process that is adaptable to any shape. Therefore, it has promise for use in practical and industrial applications. PMID:25782028

Kim, Aeree; Lee, Chan; Kim, Hyungmo; Kim, Joonwon

2015-04-01

137

Self-Propelled Dropwise Condensate on Superhydrophobic Surfaces Jonathan B. Boreyko and Chuan-Hua Chen*  

E-print Network

surfaces [8­10]. A superhydrophobic substrate, composed of two-tier roughness with carbon nanotubes used. The substrates were placed on a horizontally oriented copper plate controlled at 5:5 � 0:5 C

Chen, Chuan-Hua

138

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

PubMed

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. PMID:23630277

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

2013-05-14

139

Reactive superhydrophobic surface and its photoinduced disulfide-ene and thiol-ene (bio)functionalization.  

PubMed

Reactive superhydrophobic surfaces are highly promising for biotechnological, analytical, sensor, or diagnostic applications but are difficult to realize due to their chemical inertness. In this communication, we report on a photoactive, inscribable, nonwettable, and transparent surface (PAINTS), prepared by polycondensation of trichlorovinylsilane to form thin transparent reactive porous nanofilament on a solid substrate. The PAINTS shows superhydrophobicity and can be conveniently functionalized with the photoclick thiol-ene reaction. In addition, we show for the first time that the PAINTS bearing vinyl groups can be easily modified with disulfides under UV irradiation. The effect of superhydrophobicity of PAINTS on the formation of high-resolution surface patterns has been investigated. The developed reactive superhydrophobic coating can find applications for surface biofunctionalization using abundant thiol or disulfide bearing biomolecules, such as peptides, proteins, or antibodies. PMID:25486338

Li, Junsheng; Li, Linxian; Du, Xin; Feng, Wenqian; Welle, Alexander; Trapp, Oliver; Grunze, Michael; Hirtz, Michael; Levkin, Pavel A

2015-01-14

140

One-step electrodeposition process to fabricate corrosion-resistant superhydrophobic surface on magnesium alloy.  

PubMed

A simple, one-step method has been developed to construct a superhydrophobic surface by electrodepositing Mg-Mn-Ce magnesium plate in an ethanol solution containing cerium nitrate hexahydrate and myristic acid. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy were employed to characterize the surfaces. The shortest electrodeposition time to obtain a superhydrophobic surface was about 1 min, and the as-prepared superhydrophobic surfaces had a maximum contact angle of 159.8° and a sliding angle of less than 2°. Potentiodynamic polarization and electrochemical impedance spectroscopy measurements demonstrated that the superhydrophobic surface greatly improved the corrosion properties of magnesium alloy in 3.5 wt % aqueous solutions of NaCl, Na2SO4, NaClO3, and NaNO3. Besides, the chemical stability and mechanical durability of the as-prepared superhydrophobic surface were also examined. The presented method is rapid, low-cost, and environmentally friendly and thus should be of significant value for the industrial fabrication of anticorrosive superhydrophobic surfaces and should have a promising future in expanding the applications of magnesium alloys. PMID:25559356

Liu, Qin; Chen, Dexin; Kang, Zhixin

2015-01-28

141

Evaporating behaviors of water droplet on superhydrophobic surface  

NASA Astrophysics Data System (ADS)

We investigated the dynamic evaporating behaviors of water droplet on superhydrophobic surfaces with micropillars. Our experimental data showed that receding contact angles of the water droplet increased with the decreasing of the scale of the micropillars during evaporation, even though the solid area fractions of the microstructured substrates remained constant. We also experimentally found that the critical contact diameters of the transition between the Cassie-Baxter and Wenzel states are affected not only by the geometrical parameters of the microstructures, but also by the initial volume of the water droplet. The measured critical pressure is consistent with the theoretical model, which validated the pressure-induced impalement mechanism for the wetting state transition.

Hao, PengFei; Lv, CunJing; He, Feng

2012-12-01

142

Using Superhydrophobic Surfaces and Optical Caustics to Detect Nanoparticle Aggregation  

NASA Astrophysics Data System (ADS)

A 3-D envelope of refracted light known as an optical caustic, can be formed by shaping an aqueous drop on a superhydrophobic surface which is used to generate a signal that is very sensitive to changes in particle size. When the sample being detected is suspended in the drop, slow evaporation induces movement that segregates smaller from larger particles, enhancing the speed of detection via induced aggregation. While the unique properties of optical caustics have been used in engineering science to evaluate stress distributions and contact between material components, they have not been widely used in diagnostics or biological analyses. This paper demonstrates how this method can track aggregation of gold nanoparticles for rapid detection of molecular disease markers using immunoassays.

Garcia, Antonio; Lindsay, James; Gilmore, Eric

2012-02-01

143

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

144

Directional motion of water drop on ratchet-like superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

In this article, directional movements of drops on the ratchet-like superhydrophobic surfaces were observed. High-speed CCD images showed the caterpillar-like crawl of a drop on the inclined superhydrophobic surfaces as it rolled along the ridge of ratchet. In contrast, along the opposite direction, the movement of the drop only depended on the end of triple phase contact line while the front of contact line was pinned. The sliding angle (SA) measurements indicated that the ratchet-like superhydrophobic surfaces had directional drop retention traits. Moreover, the reduction of the rise angle ?1, the height d of the ratchet's ridge and the volume V of the drop can greatly enhance the directional difference of drop retention on the ratchet-like superhydrophobic surfaces. Therefore, it was concluded that the superhydrophobicity and the periodic ratchet-like microstructures were the keys to the directional drop sliding at one-dimensional level. We believe that these findings would be helpful to better understand the ratchet-like effect on the superhydrophobic surfaces and guide some novel engineering applications.

Sheng, Xianliang; Zhang, Jihua

2011-05-01

145

Design of a robust superhydrophobic surface: thermodynamic and kinetic analysis.  

PubMed

The design of a robust superhydrophobic surface is a widely pursued topic. While many investigations are limited to applications with high impact velocities (for raindrops of the order of a few meters per second), the essence of robustness is yet to be analyzed for applications involving quasi-static liquid transfer. To achieve robustness with high impact velocities, the surface parameters (geometrical details, chemistry) have to be selected from a narrow range of permissible values, which often entail additional manufacturing costs. From the dual perspectives of thermodynamics and mechanics, we analyze the significance of robustness for quasi-static drop impact, and present the range of permissible surface characteristics. For surfaces with a Young's contact angle greater than 90° and square micropillar geometry, we show that robustness can be enforced when an intermediate wetting state (sagged state) impedes transition to a wetted state (Wenzel state). From the standpoint of mechanics, we use available scientific data to prove that a surface with any topology must withstand a pressure of 117 Pa to be robust. Finally, permissible values of surface characteristics are determined, which ensure robustness with thermodynamics (formation of a sagged state) and mechanics (withstanding 117 Pa). PMID:25627327

Sarkar, Anjishnu; Kietzig, Anne-Marie

2015-03-14

146

Design of a robust superhydrophobic surface: thermodynamic and kinetic analysis  

E-print Network

The design of a robust superhydrophobic surface is a widely pursued topic.While many investigations are limited to applications with high impact velocities (for raindrops of the order of a few m/s), the essence of robustness is yet to be analyzed for applications involving quasi-static liquid transfer.To achieve robustness with high impact velocities, the surface parameters (geometrical details, chemistry) have to be selected from a narrow range of permissible values, which often entail additional manufacturing costs.From the dual perspectives of thermodynamics and mechanics, we analyze the significance of robustness for quasi-static drop impact, and present the range of permissible surface characteristics.For surfaces with a Youngs contact angle greater than 90{\\deg} and square micropillar geometry, we show that robustness can be enforced when an intermediate wetting state (sagged state) impedes transition to a wetted state (Wenzel state).From the standpoint of mechanics, we use available scientific data to prove that a surface with any topology must withstand a pressure of 117 Pa to be robust.Finally, permissible values of surface characteristics are determined, which ensure robustness with thermodynamics (formation of sagged state) and mechanics (withstanding 117 Pa).

Anjishnu Sarkar; Anne-Marie Kietzig

2014-12-17

147

Surface morphology control of polymer films by electron irradiation and its application to superhydrophobic surfaces.  

PubMed

A simple and controllable one-step method to fabricate superhydrophobic surfaces on poly(tetrafluoroethylene) (PTFE) films is developed on the base of electron irradiation. When the thickness of PTFE films is higher than the penetration depth of electron beams, electrical charging occurs at the surface of the films because of the imbalance between the accumulation of incident electrons and the emission of secondary electrons. Local inhomogeneity of charge distribution due to this electrical charging results in the nonuniform decomposition of PTFE molecular bonds. As electron fluence increases, surface morphology and surface roughness of the films are dramatically changed. An extremely rough surface with micrometer-sized pores is produced on the surface of PTFE films by electron irradiation at a fluence higher than 2.5 × 10(17) cm(-2).Because of high surface roughness, the irradiated PTFE films exhibit superhydrophobic property with a water contact angle (CA) greater than 150° at fluences ranging from 4 × 10(17) to 1 × 10(18) cm(-2). The surface morphology and corresponding water CA can be controlled by simply changing the electron fluence. This electron irradiation method can be applicable to the fabrication of superhydrophobic surfaces using other low-surface-energy materials including various fluoropolymers. PMID:21776956

Lee, Eun Je; Jung, Chan-Hee; Hwang, In-Tae; Choi, Jae-Hak; Cho, Sung Oh; Nho, Young-Chang

2011-08-01

148

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

149

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

SciTech Connect

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 [Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry and Environment, Beihang University, Beijing 100191 (China); Wang Weihua [Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Jiang Lei [Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry and Environment, Beihang University, Beijing 100191 (China); Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 (China)

2011-12-26

150

Facile fabrication of superhydrophobic nanostructures on aluminum foils with controlled-condensation and delayed-icing effects  

NASA Astrophysics Data System (ADS)

Superhydrophobic alumina films with a 2D close-packed array of nanospheres have been successfully fabricated on industrial aluminum foils by a simple anodization method and following modification. The water contact angle of the resultant surfaces is about 154.6° ± 1.4° and the adhesion of water droplets is very weak. Moreover, spherical droplets grow sparsely on the as-prepared superhydrophobic foils during cooling and can be liquid without ice formation for more than 30 min after being continuously cooled to 0 °C. Such foils have significant application prospects in high-efficient heat exchangers and products operating under low temperature.

Zhang, Youfa; Yu, Xinquan; Wu, Hao; Wu, Jie

2012-08-01

151

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

152

The preparation of lotus-like super-hydrophobic copper surfaces by electroplating  

NASA Astrophysics Data System (ADS)

The preparation of super-hydrophobic metal surfaces had to combine rough structures and the surface modifications with low surface energy materials. Although there were different views on it, no experiment was done to prove it yet. In this paper, the structure of natural lotus leaf was observed and the lotus-like surfaces on hydrophilic copper substrates were fabricated via electroplating in large current density. These surfaces were super-hydrophobic without any chemical modification. The hydrophobic mechanism was analyzed. It is believed that this was a meta-stable state in Cassie model. As long as the surface structure was suitable, hydrophobic surface, even super-hydrophobic surface, could be got on hydrophilic substrate.

Xi, Wenjun; Qiao, Zhenmei; Zhu, Chunlei; Jia, Ao; Li, Ming

2009-02-01

153

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

154

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

155

Nanoparticle-Based Surface Modifications for Microtribology Control and Superhydrophobicity  

NASA Astrophysics Data System (ADS)

The emergence of miniaturization techniques for consumer electronics has brought forth the relatively new and exciting field of microelectromechanical systems (MEMS). However, due to the inherent forces that exist between surfaces at the micro- and nanoscale, scientists and semiconductor manufacturers are still struggling to improve the lifetime and reliability of complex microdevices. Due to the extremely large surface area-to-volume ratio of typical MEMS and microstructured surfaces, dominant interfacial forces exist which can be detrimental to their operational lifetime. In particular, van der Waals, capillary, and electrostatic forces contribute to the permanent adhesion, or stiction , of microfabricated surfaces. This strong adhesion force also contributes to the friction and wear of these silicon-based systems. The scope of this work was to examine the effect of utilizing nanoparticles as the basis for roughening surfaces for the purpose of creating films with anti-adhesive and/or superhydrophobic properties. All of the studies presented in this work are focused around a gas-expanded liquid (GXL) process that promotes the deposition of colloidal gold nanoparticles (AuNPs) into conformal thin films. The GXL particle deposition process is finalized by a critical point drying step which is advantageous to the microelectromechanical systems and semiconductor (IC) industries. In fact, preliminary results illustrated that the GXL particle deposition process can easily be integrated into current MEMS microfabrication processes. Thin films of AuNPs deposited onto the surfaces of silicon-based MEMS and tribology test devices were shown to have a dramatic effect on the adhesion of microstructures. In the various investigations, the apparent work of adhesion between surfaces was reduced by 2-4 orders of magnitude. This effect is greatly attributed to the roughening of the typically smooth silicon oxide surfaces which, in turn, dramatically decreases the "real are of contact" between two contacting surfaces. The studies found that AuNP thin films produced using the lowest initial concentrations of nanoparticles in solution produced estimated real contact areas of around 1%, reducing the adhesion of oxidized Si (100) surfaces from about 37 mJ/m2 down to 0.02 mJ/m 2. In addition, the reducing in real contact area effectively reduced the coefficient of static friction between silicon-based surfaces due to the extremely high dependence of stiction on friction and wear at the microscale. This work also investigated methods of permanently immobilizing AuNP-based films on the silicon surfaces of microstructures in order to create more mechanically robust coatings. The use of organic self-assembled monolayers (SAMs) functionalized with tail-groups known to bond to metallic surfaces were effective in producing much more durable coatings as opposed to non-immobilized AuNP films. Chemical vapor deposition (CVD) techniques were also used to coat rough AuNP films with very thin films of silica (SiO2) to create a robust, rough surface. This method was also very effective in creating a durable coating which is capable of reducing the adhesion energy and friction between two microscale surfaces for extended periods of time. Similar CVD techniques were also used to begin investigating the production of alumina nanoparticle-based superhydrophobic films for use in consumer electronics. Overall, the work presented in this dissertation illustrates that engineered nanoparticle-based surface modifications can be extremely effective in the reduction of the inherent interfacial phenomena that exist on microfabricated systems. This work is can potentially lead us into a new age of the miniaturization of mechanical and electronic devices.

Hurst, Kendall Matthew

2010-11-01

156

Hydrophobic to superhydrophobic surface modification using impacting particulate sprays  

NASA Astrophysics Data System (ADS)

The roughening or structuring of inherently hydrophobic surfaces to possess microscopic and nanoscopic features can transform them to exhibit superhydrophobicity. The use of impacting particulate sprays here eschews specialized reagents and equipments; is simple, inexpensive, and rapid to implement; creates highly repeatable outcomes; and permits selective region transformation via simple masking. With PTFE, the contact angle transforms from 90° to 150°, in which SEM examination reveals erosive wear mechanisms that are dependent on the impingement angle. The process tends to cause the sample to bulge upwards from the treated surface due to elongation there, and can be mitigated by using lower impingement angles in the particulate spray. A finite element model created enables this characteristic to be related to the action of locked-in surface traction forces. The use of adhesive bonding to a rigid base is shown to be an alternative method to reduce the bulging. A second finite model developed allows knowledge of the right adhesive needed for this. In developing substrates for biochemical analysis, the approach offers very small possibilities for unintended synergistic interactions.

Lau, Chun Yat; Vuong, Thach; Wang, Jingming; Muradoglu, Murat; Liew, Oi Wah; Ng, Tuck Wah

2014-08-01

157

Preparation of superhydrophobic nanodiamond and cubic boron nitride films  

SciTech Connect

Superhydrophobic surfaces were achieved on the hardest and the second hardest materials, diamond and cubic boron nitride (cBN) films. Various surface nanostructures of nanocrystalline diamond (ND) and cBN films were constructed by carrying out bias-assisted reactive ion etching in hydrogen/argon plasmas; and it is shown that surface nanostructuring may enhance dramatically the hydrophobicity of ND and cBN films. Together with surface fluorination, superhydrophobic ND and cBN surfaces with a contact angle greater than 150 deg. and a sliding angle smaller than 10 deg. were demonstrated. The origin of hydrophobicity enhancement is discussed based on the Cassie model.

Zhou, Y. B.; Liu, W. M.; Wang, P. F. [Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Yang, Y.; Ye, Q.; He, B.; Pan, X. J.; Zhang, W. J.; Bello, I.; Lee, S. T. [Department of Physics and Materials Sciences, Center of Super-Diamond and Advanced Films (COSDAF), City University of Hong Kong (Hong Kong); Zou, Y. S. [Department of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094 (China)

2010-09-27

158

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

159

Irradiation of poly(tetrafluoroethylene) surfaces by CF4 plasma to achieve robust superhydrophobic and enhanced oleophilic properties for biological applications.  

PubMed

Poly(tetrafluoroethylene) (PTFE) was irradiated by CF4 plasma produced in the gas discharge ion source facility to produce stable and robust superhydrophobic surfaces and to enhance the materials' oleophilic property for biological applications. The characterizations employed on the samples are contact angle measurements, analysis of the surface morphology (scanning electron microscopy), surface roughness measurements (atomic force microscopy) and analysis of the surface chemistry (Fourier transform infrared spectroscopy). Superhydrophobic behavior with water contact angles as high as 156° was observed. The wettability of all the treated samples was found to be stable in time as evidenced by the statistically insignificant differences in the hysteresis contact angles. The level of enhanced hydrophobicity depended on the plasma energies (i.e. irradiation times, discharge current, and discharge voltage); higher plasma energies produced surfaces with high hydrophobicity. The plasma treatment also enhanced the oleophilic property of the materials' surface as evidenced by the decrease in the PDMS-oil contact angle from 33° to as low as 10°. The superhydrophobicity of the modified PTFE and the enhancement of its oleophilic property were due to (1) the changes in the roughness of the surface, (2) the formation of nanoparticles or nanostructures on the surface, and (3) the changes in the surface chemistry. PMID:25491987

Salapare, Hernando S; Suarez, Beverly Anne T; Cosiñero, Hannah Shamina O; Bacaoco, Miguel Y; Ramos, Henry J

2015-01-01

160

Simple and cost-effective fabrication of highly flexible, transparent superhydrophobic films with hierarchical surface design.  

PubMed

Optical transparency and mechanical flexibility are both of great importance for significantly expanding the applicability of superhydrophobic surfaces. Such features make it possible for functional surfaces to be applied to various glass-based products with different curvatures. In this work, we report on the simple and potentially cost-effective fabrication of highly flexible and transparent superhydrophobic films based on hierarchical surface design. The hierarchical surface morphology was easily fabricated by the simple transfer of a porous alumina membrane to the top surface of UV-imprinted polymeric micropillar arrays and subsequent chemical treatments. Through optimization of the hierarchical surface design, the resultant superhydrophobic films showed superior surface wetting properties (with a static contact angle of >170° and contact angle hysteresis of <3.5°) in the Cassie-Baxter wetting regime, considerable dynamic water repellency (with perfect bouncing of a water droplet dropped from an impact height of 30 mm), and good optical transparency (>82% at 550 nm wavelength). The superhydrophobic films were also experimentally found to be robust without significant degradation in the superhydrophobicity, even under repetitive bending and pressing for up to 2000 cycles. Finally, the practical usability of the proposed superhydorphobic films was clearly demonstrated by examining the antiwetting performance in real time while pouring water on the film and submerging the film in water. PMID:25688451

Kim, Tae-Hyun; Ha, Sung-Hun; Jang, Nam-Su; Kim, Jeonghyo; Kim, Ji Hoon; Park, Jong-Kweon; Lee, Deug-Woo; Lee, Jaebeom; Kim, Soo-Hyung; Kim, Jong-Man

2015-03-11

161

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

162

Effect of ionizing radiation on the properties of superhydrophobic silicone surfaces  

NASA Astrophysics Data System (ADS)

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 development of cost-effective processes that are compatible with non-planar optical substrates as well as the identification of material systems that exhibit longterm reliability. We have developed a 3D printing technology to create superhydrophobic surfaces by dispensing arrays of high aspect ratio polymeric features onto optical substrates. In this paper, superhydrophobic surfaces were prepared by dispensing silicone elastomers into arrays of features on glass substrates. These samples were exposed to either Cobalt 60 gammarays or 63.8 MeV protons to simulate ionization-induced total dose environments that could be experienced in some space orbits. In addition exposure to other harsh environments, including salt water and 125°C temperatures were evaluated. The effects of these exposure conditions on superhydrophobic properties, as measured by slip angles, are reported. Near-term potential space applications will be discussed.

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

2010-09-01

163

Fabrication of superhydrophobic surface on zinc substrate by 3-trifluoromethylbenzene diazonium tetrafluoroborate salts  

NASA Astrophysics Data System (ADS)

In this study we report a new and efficient method of fabricating superhydrophobic surface on zinc plate modified with 3-trifluoromethylbenzene diazonium tetrafluoroborate salts (CF3BD), which shows a water contact angle of 160° for a 4 ?l water droplet and a low sliding angle of about 1°. The morphology and chemical composition of as-prepared superhydrophobic zinc surfaces are investigated by means of scanning electron microscopy (SEM), electron probe microanalyzer (EPMA) and FT-IR spectrum. The results show that the organic layers formed on zinc plate surface are provided with the special hierarchical porous microstructure and the low surface energy, which lead to the superhydrophobicity surface on the modified zinc.

Li, Hong; Huang, Chengya; Zhang, Long; Lou, Wanqiu

2014-09-01

164

Surface Plasmons of Metal Nanostructure Arrays  

E-print Network

Surface Plasmons of Metal Nanostructure Arrays: From Nanoengineering to Active Plasmonics Yue Bing substrates. Surface plasmons of these nanostructure arrays were investigated both experimentally and theoretically. We systematically studied the effects of different parameters on the localized surface plasmon

165

Fabrication of super-hydrophobic surfaces on aluminum alloy substrates by RF-sputtered polytetrafluoroethylene coatings  

SciTech Connect

In this work, we present a method of fabricating super-hydrophobic surface on aluminum alloy substrate. The etching of aluminum surfaces has been performed using Beck's dislocation etchant for different time to create micrometer-sized irregular steps. An optimised etching time of 50 s is found to be essential before polytetrafluoroethylene (PTFE) coating, to obtain a highest water contact angle of 165±2° with a lowest contact angle hysteresis as low as 5±2°. The presence of patterned microstructure as revealed by scanning electron microscopy (SEM) together with the low surface energy ultrathin RF-sputtered PTFE films renders the aluminum alloy surfaces highly super-hydrophobic.

Wang, Yang; Liu, Xiao Wei; Zhang, Hai Feng, E-mail: wy3121685@163.com; Zhou, Zhi Ping [Department of Microelectronics, Harbin Institute of Technology, Harbin, Heilongjiang, 150001 (China)] [Department of Microelectronics, Harbin Institute of Technology, Harbin, Heilongjiang, 150001 (China)

2014-03-15

166

Fabrication of a superhydrophobic surface from porous polymer using phase separation  

NASA Astrophysics Data System (ADS)

The present work reports a simple method to fabricate superhydrophobic porous polymeric surfaces by a phase separation process. The method involves the in situ polymerization of butyl methacrylate (BMA) and ethylene dimethacrylate (EDMA) in the presence of co-porogens of 1,4-butanediol (BDO) and N-methyl-2-pyrrolidone (NMP) to afford superhydrophobic surfaces with the micro/nano roughness structure. The influences of the polymerization mixture on the morphology and hydrophobicity were investigated by adjusting the composition of the co-porogens and the mass ratio of monomers to co-porogens, respectively. And a precise description of the underlying mechanism of the microstructure formation was presented. The as-prepared surface shows a superhydrophobicity with water contact angle (WCA) of 159.5° and low sliding angle (SA) of 3.1°. Moreover, the superhydrophobic surface shows good chemical stability with better resistance to acid, alkali or salt aqueous solutions and excellent thermal stability. The method is simple and low-cost and can be used for the preparation of the self-cleaning superhydrophobic surfaces.

Liu, Jianfeng; Xiao, Xinyan; Shi, Yinlong; Wan, Caixia

2014-04-01

167

Fabrication of superhydrophobic surfaces on flexible fluorinated foils by using dual-scale patterning  

NASA Astrophysics Data System (ADS)

This paper investigates the interest of combining NanoImprint Lithography with plasma treatment in order to easily create dual-scale superhydrophobic surfaces on flexible fluorinated foils. The studies were led on FEP and PCTFE materials with conditions compatible with standard NIL equipments. Different pattern geometries, densities and aspect ratio have been investigated and we show that patterning at a nanometer scale improves hydrophobic behaviour compared to microstructuration. Water-contact angle (WCA) of 154° (and water contact angle hysteresis of 11 ± 2°) were measured, which corresponds to a superhydrophobic surface. However, patterning large surfaces at nanoscale with a high aspect ratio is more difficult to achieve and limits the use of such a process for industrial applications. So, we have decided to induce a nanopatterning on microstructures previously printed using plasma etching. This plasma roughening leads to a highly superhydrophobic surface and WCA values as high as 170°.

Ferchichi, A. K.; Panabière, M.; Desplats, O.; Gourgon, C.

2014-04-01

168

From Sticky to Slippery Droplets: Dynamics of Contact Line Depinning on Superhydrophobic Surfaces  

NASA Astrophysics Data System (ADS)

This study explores how surface morphology affects the dynamics of contact line depinning of an evaporating sessile droplet on micropillared superhydrophobic surfaces. The result shows that neither a liquid-solid contact area nor an apparent contact line is a critical physical parameter to determine the depinning force. The configuration of a contact line on a superhydrophobic surface is multimodal, composed of both two phases (liquid and air) and three phases (liquid, solid, and air). The multimodal state is dynamically altered when a droplet recedes. The maximal three-phase contact line attainable along the actual droplet boundary is found to be a direct and linear parameter that decides the depinning force on the superhydrophobic surface.

Xu, Wei; Choi, Chang-Hwan

2012-07-01

169

Fabrication of biomimetic superhydrophobic surfaces inspired by lotus leaf and silver ragwort leaf  

NASA Astrophysics Data System (ADS)

Inspired by the self-cleaning lotus leaf and silver ragwort leaf, here we demonstrate the fabrication of biomimetic superhydrophobic fibrous mats via electrospinning polystyrene (PS) solution in the presence of silica nanoparticles. The resultant electrospun fiber surfaces exhibited a fascinating structure with the combination of nano-protrusions and numerous grooves due to the rapid phase separation in electrospinning. The content of silica nanoparticles incorporated into the fibers proved to be the key factor affecting the fiber surface morphology and hydrophobicity. The PS fibrous mats containing 14.3 wt% silica nanoparticles showed a stable superhydrophobicity with a water contact angle as high as 157.2°, exceeding that (147°) of the silver ragwort leaf and approaching that (160°) of the lotus leaf. The superhydrophobicity was explained by the hierarchical surfaces increasing the surface roughness which trapped more air under the water droplets that fell on the fibers.Inspired by the self-cleaning lotus leaf and silver ragwort leaf, here we demonstrate the fabrication of biomimetic superhydrophobic fibrous mats via electrospinning polystyrene (PS) solution in the presence of silica nanoparticles. The resultant electrospun fiber surfaces exhibited a fascinating structure with the combination of nano-protrusions and numerous grooves due to the rapid phase separation in electrospinning. The content of silica nanoparticles incorporated into the fibers proved to be the key factor affecting the fiber surface morphology and hydrophobicity. The PS fibrous mats containing 14.3 wt% silica nanoparticles showed a stable superhydrophobicity with a water contact angle as high as 157.2°, exceeding that (147°) of the silver ragwort leaf and approaching that (160°) of the lotus leaf. The superhydrophobicity was explained by the hierarchical surfaces increasing the surface roughness which trapped more air under the water droplets that fell on the fibers. Electronic supplementary information (ESI) available: Preparation procedure and characterization of microfibrous polystyrene mats. See DOI: 10.1039/c0nr00812e

Lin, Jinyou; Cai, Yu; Wang, Xianfeng; Ding, Bin; Yu, Jianyong; Wang, Moran

2011-03-01

170

Super-hydrophobic surfaces of SiO?-coated SiC nanowires: fabrication, mechanism and ultraviolet-durable super-hydrophobicity.  

PubMed

The interest in highly water-repellent surfaces of SiO2-coated SiC nanowires has grown in recent years due to the desire for self-cleaning and anticorrosive surfaces. It is imperative that a simple chemical treatment with fluoroalkylsilane (FAS, CF3(CF2)7CH2CH2Si(OC2H5)3) in ethanol solution at room temperature resulted in super-hydrophobic surfaces of SiO2-coated SiC nanowires. The static water contact angle of SiO2-coated SiC nanowires surfaces was changed from 0° to 153° and the morphology, microstructure and crystal phase of the products were almost no transformation before and after super-hydrophobic treatment. Moreover, a mechanism was expounded reasonably, which could elucidate the reasons for their super-hydrophobic behavior. It is important that the super-hydrophobic surfaces of SiO2-coated SiC nanowires possessed ultraviolet-durable (UV-durable) super-hydrophobicity. PMID:25585284

Zhao, Jian; Li, Zhenjiang; Zhang, Meng; Meng, Alan

2015-04-15

171

Nonfunctionalized Polydimethyl Siloxane Superhydrophobic Surfaces Based on Hydrophobic-Hydrophilic Interactions  

SciTech Connect

Superhydrophobic surfaces based on polydimethyl siloxane (PDMS) were fabricated using a 50:50 PDM-poly(ethylene glycol) (PEG) blend. PDMS was mixed with PEG, and incomplete phase separation yielded a hierarchic structure. The phase-separated mixture was annealed at a temperature close to the crystallization temperature of the PEG. The PEG crystals were formed isothermally at the PDMS/PEG interface, leading to an engineered surface with PDMS spherulites. The resulting roughness of the surface was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The PDMS spherulites, a few micrometers in diameter observed from SEM images, were found to have an undulated (rippled) surface with nanometer-sized features. The combination of micrometer- and nanometer-sized surface features created a fractal surface and increased the water contact angle (WCA) of PDMS more than 60, resulting in a superhydrophobic PDMS surface with WCA of >160 degrees. The active surface layer for the superhydrophobicity was approximately 100 mu m thick, illustrating that the material had bulk superhydrophobicity compared to conventional fluorocarbon or fluorinated coated rough surfaces. Theoretical analysis of the fractal surface indicates that the constructed surface has a fractal dimension of 2.5, which corresponds to the Apollonian sphere packing.

Polizos, Georgios [Oak Ridge National Laboratory (ORNL); Tuncer, Enis [ORNL; Qiu, Xiaofeng [ORNL; Aytug, Tolga [ORNL; Kidder, Michelle [ORNL; Messman, Jamie M [ORNL; Sauers, Isidor [ORNL

2011-01-01

172

Fabrication of "roll-off" and "sticky" superhydrophobic cellulose surfaces via plasma processing.  

PubMed

Most of the artificial superhydrophobic surfaces that have been fabricated to date are not biodegradable, renewable, or mechanically flexible and are often expensive, which limits their potential applications. In contrast, cellulose, a biodegradable, renewable, flexible, inexpensive, biopolymer which is abundantly present in nature, satisfies all the above requirements, but it is not superhydrophobic. Superhydrophobicity on cellulose paper was obtained by domain-selective etching of amorphous portions of the cellulose in an oxygen plasma and subsequently coating the etched surface with a thin fluorocarbon film deposited via plasma-enhanced chemical vapor deposition using pentafluoroethane as a precursor. Variation of plasma treatment yielded two types of superhydrophobicity : "roll-off" (contact angle (CA), 166.7 degrees +/- 0.9 degrees ; CA hysteresis, 3.4 degrees +/- 0.1 degrees ) and "sticky" (CA, 144.8 degrees +/- 5.7 degrees ; CA hysteresis, 79.1 degrees +/- 15.8 degrees ) near superhydrophobicity. The nanometer scale roughness obtained by delineating the internal roughness of each fiber and the micrometer scale roughness which is inherent to a cellulose paper surface are robust when compared to roughened structures created by traditional polymer grafting, nanoparticle deposition, or other artificial means. PMID:18315020

Balu, Balamurali; Breedveld, Victor; Hess, Dennis W

2008-05-01

173

Optimal conditions for the preparation of superhydrophobic surfaces on al substrates using a simple etching approach  

NASA Astrophysics Data System (ADS)

Many methods have been proposed to develop the fabrication techniques for superhydrophobic surfaces. However, such techniques are still at their infant stage and suffer many shortcomings. In this paper, the superhydrophobic surfaces on an Al substrate were prepared by a simple etching method. Effects of etching time, modifiers, and modification concentration and time were investigated, and optimal conditions for the best superhydrophobicity were studied. It was demonstrated that for etching the aluminum plate in Beck's dislocation, if the etching time was 15 s, modifier was Lauric acid-ethanol solution, and modification concentration and time was 5% and 1.5 h, respectively, the surface exhibited a water contact angle as high as 167.5° and a contact angle hysteresis as low as 2.3°.

Ruan, Min; Li, Wen; Wang, Baoshan; Luo, Qiang; Ma, Fumin; Yu, Zhanlong

2012-07-01

174

Facile fabrication of large-scale stable superhydrophobic surfaces with carbon sphere films by burning rapeseed oil  

NASA Astrophysics Data System (ADS)

Stable anti-corrosive superhydrophobic surfaces were successfully prepared with the carbon nanosphere films by means of depositing the soot of burning rapeseed oil. The method is extremely cheap, facile, time-saving and avoided any of the special equipments, special reagents and complex process control. The method is suitable for the large-scale preparation of superhydrophobic surface and the substrate can be easily changed. The as-prepared surfaces showed stable superhydrophobicity and anti-corrosive property even in many corrosive solutions, such as acidic or basic solutions over a wide pH range. The as-prepared superhydrophobic surface was carefully characterized by the field emission scanning electron microscopy and transmission electron microscope to confirm the synergistic binary geometric structures at micro- and nanometer scale. This result will open a new avenue in the superhydrophobic paint research with these easily obtained carbon nanospheres in the near future.

Qu, Mengnan; He, Jinmei; Cao, Biyun

2010-10-01

175

Electrostatic powder spraying process for the fabrication of stable superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

Nano-sized Al2O3 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 Al2O3 particles in the coating. As the Al2O3 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

176

Optically transparent superhydrophobic surfaces with enhanced mechanical abrasion resistance enabled by mesh structure.  

PubMed

Inspired by naturally occurring superhydrophobic surfaces such as "lotus leaves", a number of approaches have been attempted to create specific surfaces having nano/microscale rough structures and a low surface free energy. Most importantly, much attention has been paid in recent years to the improvement of the durability of highly transparent superhydrophobic surfaces. In this report, superhydrophobic surfaces are fabricated using three steps. First, chemical and morphological changes are generated in the polyester mesh by alkaline treatment of NaOH. Second, alkaline treatment causes hydrophobic molecules of 1H,1H,2H,2H-perfluorodecyltrichlorosilane to react with the hydroxyl groups on the fiber surfaces forming covalent bonds by using the chemical vapor deposition method. Third, hydrophobicity is enhanced by treating the mesh with SiO2 nanoparticles modified with 1H,1H,2H,2H-perfluorooctyltriethoxysilane using a spray method. The transmittance of the fabricated superhydrophobic mesh is approximately 80% in the spectral range of 400-1000 nm. The water contact angle and the water sliding angle remain greater than 150° and lower than 25°, respectively, and the transmittance remains approximately 79% after 100 cycles of abrasion under approximately 10 kPa of pressure. The mesh surface exhibits a good resistance to acidic and basic solutions over a wide range of pH values (pH 2-14), and the surface can also be used as an oil/water separation material because of its mesh structure. PMID:25625787

Yokoi, Naoyuki; Manabe, Kengo; Tenjimbayashi, Mizuki; Shiratori, Seimei

2015-03-01

177

A Novel General Chemistry Laboratory: Creation of Biomimetic Superhydrophobic Surfaces through Replica Molding  

ERIC Educational Resources Information Center

Biomimetic replicas of superhydrophobic lotus and taro leaf surfaces can be made using polydimethylsiloxane. These replicas faithfully reproduce the microstructures of the leaves' surface and can be analyzed using contact angle goniometry, self-cleaning experiments, and optical microscopy. These simple and adaptable experiments were used to…

Verbanic, Samuel; Brady, Owen; Sanda, Ahmed; Gustafson, Carolina; Donhauser, Zachary J.

2014-01-01

178

Mechanically Robust Superhydrophobic Steel Surface with Anti-Icing, UV-Durability, and Corrosion Resistance Properties.  

PubMed

A superhydrophobic steel surface was prepared through a facile method: combining hydrogen peroxide and an acid (hydrochloric acid or nitric acid) to obtain hierarchical structures on steel, followed by a surface modification treatment. Empirical grid maps based on different volumes of H2O2/acid were presented, revealing a wettability gradient from "hydrophobic" to "rose effect" and finally to "lotus effect". Surface grafting has been demonstrated to be realized only on the oxidized area. As-prepared superhydrophobic surfaces exhibited excellent anti-icing properties according to the water-dripping test under overcooled conditions and the artificial "steam-freezing" (from 50 °C with 90% humidity to the -20 °C condition) test. In addition, the surfaces could withstand peeling with 3M adhesive tape at least 70 times with an applied pressure of 31.2 kPa, abrasion by 400 grid SiC sandpaper for 110 cm under 16 kPa, or water impacting for 3 h without losing superhydrophobicity, suggesting superior mechanical durability. Moreover, outstanding corrosion resistance and UV-durability were obtained on the prepared surface. This successful fabrication of a robust, anti-icing, UV-durable, and anticorrosion superhydrophobic surface could yield a prospective candidate for various practical applications. PMID:25749123

Wang, Nan; Xiong, Dangsheng; Deng, Yaling; Shi, Yan; Wang, Kun

2015-03-25

179

Wetting on fractal superhydrophobic surfaces from "core-shell" particles: a comparison of theory and experiment.  

PubMed

We report an experimental and theoretical investigation of the wetting behavior of different model polar and nonpolar liquids and their mixtures on superhydrophobic fractal surfaces made of polymer- or silane-coated "core-shell" particles. We compared the experimental results with the theoretical predictions made according to the theories of Onda-Shibuichi (describes wetting on fractal surfaces) and Cassie-Baxter (describes wetting on generic rough composite surfaces). We found that the experimental findings deviate from the behavior predicted by the Onda-Shibuichi model. On the other hand, the wetting properties were found to be close to the predictions made by the Cassie-Baxter model in the hydrophobic region (the intrinsic contact angle on the flat surface is larger than 90 degrees). However, the wetting behavior in the hydrophilic region (the intrinsic contact angle is less than 90 degrees) could not be described by the Onda-Shibuichi or Cassie-Baxter model. The observed inconsistency between the experimental results and theoretical predictions was explained by the formation of metastable states of a liquid droplet on a fabricated fractal surface according to the theory developed by Johnson and Dettre for generic rough surfaces. The entrapments of the liquid droplets in metastable states resulted in superhydrophobic behavior on fractal surfaces as well, made from nonfluorinated material such as polystyrene with a surface free energy of about 30 mJ/m2. This finding is very promising for real industrial applications where fluorinated compounds are willing to be reduced. It can be concluded that employing a texture with fractal geometry is necessary for the design of superhydrophobic coatings. Thereby, extremely lowering the surface free energy of materials by fluorination is not an obligatory factor for the generation of liquid-repellent superhydrophobic materials. We believe that the results we presented in the paper give new insight into the understanding of wetting not only on general superhydrophobic rough surfaces but also on fractal surfaces. PMID:19437778

Synytska, Alla; Ionov, Leonid; Grundke, Karina; Stamm, Manfred

2009-03-01

180

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

181

Thermoresponsive PNIPAAm-modified cotton fabric surfaces that switch between superhydrophilicity and superhydrophobicity  

NASA Astrophysics Data System (ADS)

Thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) was grafted onto the cotton fabric by atom transfer radical polymerization (ATRP). Introducing 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDTS) onto the surface, the density of PNIPAAm chains can be adjusted because of the competitive reactions of (3-aminopropyl) triethoxysilane (APS) and PFDTS. With the appropriate ratio of APS and PFDTS, the cotton fabric can be switched from superhydrophilic to superhydrophobic by controlling temperature. The prepared cotton fabric may find application in functional textiles, soft and folding superhydrophobic materials.

Jiang, Cheng; Wang, Qihua; Wang, Tingmei

2012-03-01

182

The termiticidal properties of superhydrophobic wood surfaces treated with ZnO nanorods  

Microsoft Academic Search

ZnO is a cost-effective and more environmentally friendly wood preservative than other metallic-based formulations. ZnO-stearate\\u000a treatment imparts superhydrophobicity to wood surfaces, thereby providing triple protection to wood products, i.e., superhydrophobicity,\\u000a inhibition to insects and microorganisms, and UV radiation protection. The objective of this study was to evaluate ZnO-stearate\\u000a hydrophobic treatments of southern pine sapwood for resistance to Formosan subterranean termites.

Todd Shupe; Cheng Piao; Cran Lucas

183

Superhydrophobicity — 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,

184

Role of water vapor desublimation in the adhesion of an iced droplet to a superhydrophobic surface.  

PubMed

The study of the adhesion of solid and liquid aqueous phases to superhydrophobic surfaces has become an attractive topic for researchers in various fields as a vital step in the design of icephobic coatings. The analysis of the available results shows that the experimentally measured values of adhesion strength for superhydrophobic substrates, which in some cases are quite small, are still essentially higher than might be expected from the portion of the actual wetted area. In this study we have considered the peculiarities of the three-phase contact zone between sessile supercooled water or ice droplets and a superhydrophobic coating at negative temperatures (below 0 °C) and during the water-ice phase transition. Two types of superhydrophobic coatings with very different textures were used to analyze the evolution of shape parameters of a sessile water droplet during droplet cooling and freezing. It was shown that the evolution of the contact angle and droplet contact diameter of a water droplet deposited on a superhydrophobic surface does not undergo essential changes when the droplet is cooled simultaneously with the substrate and the surrounding environment, and the humidity is maintained close to 100% during the cooling process. However, the phase transition from supercooled water to ice droplets leads to the growth of a metastable iced meniscus and a frost halo in the vicinity of the three-phase contact zone. The meniscus effectively increases the area of adhesive contact between the droplet and the substrate. This phenomenon is intrinsically related to the release of the heat of crystallization and is responsible for the enhancement of adhesion to a superhydrophobic substrate upon droplet transition from supercooled water to ice. At the same time, it was shown that the metastable state of the above meniscus leads to its spontaneous sublimation during exposure at negative temperatures. PMID:25286023

Boinovich, Ludmila; Emelyanenko, Alexandre M

2014-10-28

185

SERS optrode as a "fishing rod" to direct pre-concentrate analytes from superhydrophobic surfaces.  

PubMed

SERS optrodes were used to "fish" aqueous drops from superhydrophobic surfaces. The technique led to an improvement of 2-3 orders of magnitude in the lowest detectable amount of the Raman probe nile blue A, reaching 25 fg (34 attomoles). Further tests run on samples containing pesticide revealed that 20 pg of triazophos could be clearly detected from a single drop. PMID:25531897

Fan, Meikun; Cheng, Fansheng; Wang, Cong; Gong, Zhengjun; Tang, Changyu; Man, Changzhen; Brolo, Alexandre G

2015-02-01

186

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

E-print Network

Edited by Xiao Cheng Zeng, University of Nebraska, Lincoln, NE, and accepted by the Editorial Board April the superhydrophobic surface is powered by the sur- face energy released upon coalescence of the condensed water phase, or wind flow. Our findings offer insights for the development of self-cleaning materials. particle

Chen, Chuan-Hua

187

The freezing process of continuously sprayed water droplets on the superhydrophobic silicone acrylate resin coating surface  

NASA Astrophysics Data System (ADS)

This study conducted experiments on freezing process of water droplets on glass slides covered with superhydrophobic coatings under the continuous water spray condition in the artificial climatic chamber which could simulate low temperature and high humidity environments. The freezing mechanism and freezing time of water droplets under the condition of continuous spray were observed by the microscope and were compared with those of the single static droplet. Then, differences of freezing process between continuously sprayed droplets and single static droplet were analyzed. Furthermore, the effects of static contact angle (CA), contact angle hysteresis (CAH) and roughness of the superhydrophobic coating surface on the freezing time of continuously sprayed droplets were explored. Results show that the freezing process of the continuously sprayed droplets on the superhydrophobic coating started with the homogeneous nucleation at gas-liquid interfaces. In addition, the temperature difference between the location near the solid-liquid interface and the location near the gas-liquid interface was the key factor that influenced the ice crystallization mechanism of water droplets. Moreover, with the larger CA, the smaller CAH and the greater roughness of the surface, droplets were more likely to roll down the surface and the freezing duration on the surface was delayed. Based on the findings, continuous water spray is suggested in the anti-icing superhydrophobic coatings research.

Hu, Jianlin; Xu, Ke; Wu, Yao; Lan, Binhuan; Jiang, Xingliang; Shu, Lichun

2014-10-01

188

Superhydrophobic TiO2-polymer nanocomposite surface with UV-induced reversible wettability and self-cleaning properties.  

PubMed

Multifunctional superhydrophobic nanocomposite surfaces based on photocatalytic materials, such as fluorosilane modified TiO2, have generated significant research interest. However, there are two challenges to forming such multifunctional surfaces with stable superhydrophobic properties: the photocatalytic oxidation of the hydrophobic functional groups, which leads to the permanent loss of superhydrophobicity, as well as the photoinduced reversible hydrolysis of the catalytic particle surface. Herein, we report a simple and inexpensive template lamination method to fabricate multifunctional TiO2-high-density polyethylene (HDPE) nanocomposite surfaces exhibiting superhydrophobicity, UV-induced reversible wettability, and self-cleaning properties. The laminated surface possesses a hierarchical roughness spanning the micro- to nanoscale range. This was achieved by using a wire mesh template to emboss the HDPE surface creating an array of polymeric posts while partially embedding untreated TiO2 nanoparticles selectively into the top surface of these features. The surface exhibits excellent superhydrophobic properties immediately after lamination without any chemical surface modification to the TiO2 nanoparticles. Exposure to UV light causes the surface to become hydrophilic. This change in wettability can be reversed by heating the surface to restore superhydrophobicity. The effect of TiO2 nanoparticle surface coverage and chemical composition on the mechanism and magnitude of wettability changes was studied by EDX and XPS. In addition, the ability of the surface to shed impacting water droplets as well as the ability of such droplets to clean away particulate contaminants was demonstrated. PMID:23889192

Xu, Qian Feng; Liu, Yang; Lin, Fang-Ju; Mondal, Bikash; Lyons, Alan M

2013-09-25

189

Hemocompatibility of Polymeric Nanostructured Surfaces  

PubMed Central

Tissue integration is an important property when inducing transplant tolerance, however, the hemocompatibility of the biomaterial surface also plays an important role in the ultimate success of the implant. Therefore, in order to induce transplant tolerance, it is critical to understand the interaction of blood components with the material surfaces. In this study, we have investigated the adsorption of key blood serum proteins, in vitro adhesion and activation of platelets and clotting kinetics of whole blood on flat polycaprolactone (PCL) surfaces, nanowire (NW) surfaces and nanofiber (NF) surfaces. Previous studies have shown that polymeric nanostructured surfaces improve cell adhesion, proliferation and viability; however it is unclear how these polymeric nanostructured surfaces interact with the blood and its components. Protein adsorption results indicate that while there were no significant differences in total albumin adsorption on PCL, NW and NF surfaces, NW surfaces had higher total fibrinogen and immunoglobulin-G adsorption compared to NF and PCL surfaces. In contrast, NF surfaces had higher surface FIB and IgG adsorption compared to PCL and NW surfaces. Platelet adhesion and viability studies show more adhesion and clustering of platelets on the NF surfaces as compared to PCL and NW surfaces. Platelet activation studies reveal that NW surfaces have the highest percentage of unactivated platelets, whereas NF surfaces have the highest percentage of fully activated platelets. Whole blood clotting results indicate that NW surfaces maintain an increased amount of free hemoglobin during the clotting process compared to PCL and NF surface, indicating less clotting and slower rate of clotting on their surfaces. PMID:23848447

Leszczak, Victoria; Smith, Barbara S.; Popat, Ketul C.

2013-01-01

190

Synthesis of superhydrophobic SiO{sub 2} layers via combination of surface roughness and fluorination  

SciTech Connect

We describe the preparation of superhydrophobic SiO{sub 2} layers through a combination of surface roughness and fluorination. Electrospraying SiO{sub 2} precursor solutions that were prepared by a sol-gel route and included trichloro(1H,1H,2H,2H-perfluorooctyl)silane as a fluorination source produced highly rough, fluorinated SiO{sub 2} layers. In sharp contrast to the fluorinated flat SiO{sub 2} layer, the fluorinated rough SiO{sub 2} layer showed much enhanced repellency toward liquid droplets of different surface tensions. The surface fraction and the work of adhesion of the superhydrophobic SiO{sub 2} layers were determined, respectively, based on Cassie-Baxter and Young-Dupre equations. The satisfactory long-term stability for 30 days, the ultraviolet resistance and the thermal stability up to 400 {sup o}C of the superhydrophobic SiO{sub 2} layers prepared in this work confirm a promising practical application. - Graphical abstract: A schematic illustration of the electrospray deposition used for preparing SiO{sub 2} layers. Shapes of liquid droplets of water, glycerol, coffee, juice and milk created on the fluorinated rough SiO{sub 2} layer deposited on a silicon wafer. Highlights: Black-Right-Pointing-Pointer Superhydrophobic SiO{sub 2} layers are realized by a combination of surface roughness and fluorination. Black-Right-Pointing-Pointer The fluorinated rough SiO{sub 2} layer shows enhanced repellency toward various liquid droplets. Black-Right-Pointing-Pointer The wetting behavior is explained based on Cassie-Baxter and Young-Dupre equations. Black-Right-Pointing-Pointer The superhydrophobic SiO{sub 2} layers confirm a promising practical application.

Kim, Eun-Kyeong; Yeong Kim, Ji [School of Materials Science and Engineering, Inha University, Incheon 402-751 (Korea, Republic of); Sub Kim, Sang, E-mail: sangsub@inha.ac.kr [School of Materials Science and Engineering, Inha University, Incheon 402-751 (Korea, Republic of)

2013-01-15

191

Super-hydrophobic surface treatment as corrosion protection for aluminum in seawater  

Microsoft Academic Search

“Underwater super-hydrophobicsurface applied in the corrosion protection was prepared by melting myristic acid (CH3(CH2)12COOH) adsorbed onto the anodized aluminum. The static contact angle for seawater on the surface was measured to be 154°. The surface structure and composition were then characterized by means of scanning electron microscopy (SEM) with energy dispersive X-ray spectrum (EDS) and atomic force microscope (AFM).

Tian He; Yuanchao Wang; Yijian Zhang; Qun lv; Tugen Xu; Tao Liu

2009-01-01

192

Microscopic receding contact line dynamics on pillar and irregular superhydrophobic surfaces.  

PubMed

Receding angles have been shown to have great significance when designing a superhydrophobic surface for applications involving self-cleaning. Although apparent receding angles under dynamic conditions have been well studied, the microscopic receding contact line dynamics are not well understood. Therefore, experiments were performed to measure these dynamics on textured square pillar and irregular superhydrophobic surfaces at micron length scales and at micro-second temporal scales. Results revealed a consistent "slide-snap" motion of the microscopic receding line as compared to the "stick-slip" dynamics reported in previous studies. Interface angles between 40-60° were measured for the pre-snap receding lines on all pillar surfaces. Similar "slide-snap" dynamics were also observed on an irregular nanocomposite surface. However, the sharper features of the surface asperities resulted in a higher pre-snap receding line interface angle (~90°). PMID:25670630

Yeong, Yong Han; Milionis, Athanasios; Loth, Eric; Bayer, Ilker S

2015-01-01

193

Experimental evidence of slippage breakdown for a superhydrophobic surface in a microfluidic device  

E-print Network

A full characterization of the water flow past a silicon superhydrophobic surface with longitudinal micro-grooves enclosed in a microfluidic device is presented. Fluorescence microscopy images of the flow seeded with fluorescent passive tracers were digitally processed to measure both the velocity field and the position and shape of the liquid-air interfaces at the superhydrophobic surface. The simultaneous access to the meniscus and velocity profiles allows us to put under a strict test the no-shear boundary condition at the liquid-air interface. Surprisingly, our measurements show that air pockets in the surface cavities can sustain non-zero interfacial shear stresses, thereby hampering the friction reduction capabilities of the surface. The effects of the meniscus position and shape as well as of the liquid-air interfacial friction on the surface performances are separately assessed and quantified.

Guido Bolognesi; Cecile Cottin-Bizonne; Christophe Pirat

2014-06-12

194

Design of an outstanding super-hydrophobic surface by electro-spinning  

NASA Astrophysics Data System (ADS)

A duel-layer super-hydrophobic surface, comprising polyvinylidene fluoride (PVDF) and fluorinated silane molecules (FSM), was engineered using electro-spinning a coating onto the glass. Scanning electron microscopy was used to confirm that, by reducing the percentage of PVDF in the spraying solution, the aspect ratio of the nano-beads could be changed and a sharp bead profile obtained. Energy dispersive spectroscopy was employed to ensure the maximum amount of FSM was present on the surface, which assists in achieving a high Water Contact Angle. Using a two-step process, involving PVDF and FSM, nano-beads, with high aspect ratio, were formed on a rough surface which produced a super-hydrophobic surface with a Water Contact Angle of 170.2° and a very low Water Roll-off Angle (<1°). Such a coating facilitates the speedy run-off of water drops from a surface and has many potential applications in buildings and other areas.

Sarkar, Manas K.; Bal, Kausik; He, Fuen; Fan, Jintu

2011-05-01

195

Microscopic Receding Contact Line Dynamics on Pillar and Irregular Superhydrophobic Surfaces  

NASA Astrophysics Data System (ADS)

Receding angles have been shown to have great significance when designing a superhydrophobic surface for applications involving self-cleaning. Although apparent receding angles under dynamic conditions have been well studied, the microscopic receding contact line dynamics are not well understood. Therefore, experiments were performed to measure these dynamics on textured square pillar and irregular superhydrophobic surfaces at micron length scales and at micro-second temporal scales. Results revealed a consistent ``slide-snap'' motion of the microscopic receding line as compared to the ``stick-slip'' dynamics reported in previous studies. Interface angles between 40-60° were measured for the pre-snap receding lines on all pillar surfaces. Similar ``slide-snap'' dynamics were also observed on an irregular nanocomposite surface. However, the sharper features of the surface asperities resulted in a higher pre-snap receding line interface angle (~90°).

Yeong, Yong Han; Milionis, Athanasios; Loth, Eric; Bayer, Ilker S.

2015-02-01

196

Microscopic Receding Contact Line Dynamics on Pillar and Irregular Superhydrophobic Surfaces  

PubMed Central

Receding angles have been shown to have great significance when designing a superhydrophobic surface for applications involving self-cleaning. Although apparent receding angles under dynamic conditions have been well studied, the microscopic receding contact line dynamics are not well understood. Therefore, experiments were performed to measure these dynamics on textured square pillar and irregular superhydrophobic surfaces at micron length scales and at micro-second temporal scales. Results revealed a consistent “slide-snap” motion of the microscopic receding line as compared to the “stick-slip” dynamics reported in previous studies. Interface angles between 40–60° were measured for the pre-snap receding lines on all pillar surfaces. Similar “slide-snap” dynamics were also observed on an irregular nanocomposite surface. However, the sharper features of the surface asperities resulted in a higher pre-snap receding line interface angle (~90°). PMID:25670630

Yeong, Yong Han; Milionis, Athanasios; Loth, Eric; Bayer, Ilker S.

2015-01-01

197

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

198

Transferrable superhydrophobic TiO2 nanorods on reduced graphene oxide films using block copolymer templates.  

PubMed

Superhydrophobic surfaces are normally fixed on the chosen materials. Here, we report transferrable superhydrophobicity which was enabled by fabricating TiO2 nanorods on a reduced graphene oxide (rGO) film. Superhydrophobic TiO2 nanorods were first synthesized from a nanoporous template of block copolymers (BCPs). The controllability over the dimension and shape of nanopores of the BCP template allowed for the adjustment of TiO2 nanostructures for superhydrophobicity. Since the rGO film provided effective transferring, TiO2 nanorods were conveyed onto a flexible polymer film and a metal substrate. Thus, the surface of the designated substrate was successfully changed to a superhydrophobic surface without alteration of its inherent characteristics. PMID:25824622

Seo, Myung-Seok; Kim, Jin-Hyung; Kim, Sung-Soo; Kang, Heejung; Sohn, Byeong-Hyeok

2015-04-24

199

Superhydrophobic functionalized graphene aerogels.  

PubMed

Carbon-based nanomaterials such as carbon nanotubes and graphene are excellent candidates for superhydrophobic surfaces because of their intrinsically high surface area and nonpolar carbon structure. This paper demonstrates that graphene aerogels with a silane surface modification can provide superhydrophobicity. Graphene aerogels of various concentrations were synthesized and the receding contact angle of a water droplet was measured. It is shown that graphene aerogels are hydrophobic and become superhydrophobic following the application of a fluorinated surfactant. The aerogels produced for this experiment outperform previous carbon nanomaterials in creating superhydrophobic surfaces and offer a more scalable synthetic procedure for production. PMID:21714511

Lin, Yirong; Ehlert, Gregory J; Bukowsky, Colton; Sodano, Henry A

2011-07-01

200

A new method for preparing bionic multi scale superhydrophobic functional surface on X70 pipeline steel  

NASA Astrophysics Data System (ADS)

The hydrophobic property of a rough surface with a low free energy coating was theoretically analyzed in this paper. In order to obtain a superhydrophobic surface, a rough surface morphology must be formed in addition to the low free energy coating on the surface. Through the shot blasting, chemical etching with concentrated hydrochloric acid, and low free energy modification with myristic acid ethanol solution, the superhydrophobic surface was obtained on X70 pipeline steel. The better process parameters for preparing superhydrophobic surface on X70 pipeline steel were obtained. The diameter of the stainless steel shot used in the shot blasting was 0.8-1.0 mm. The concentration of hydrochloric acid was 6 mol/L. The chemical etching time was 320 min. The concentration of myristic acid ethanol solution was 0.1 mol/L. The soaking time in myristic acid ethanol solution was 72 h. After X70 pipeline steel surface was treated using the process parameters mentioned above, the biggest contact angle between the specimen surface and distilled water was 153.5°, and the sliding angle was less than 5°.

Yu, Sirong; Wang, Xiaolong; Wang, Wei; Yao, Qiang; Xu, Jun; Xiong, Wei

2013-04-01

201

High-adhesive superhydrophobic 3D nanostructured silver films applied as sensitive, long-lived, reproducible and recyclable SERS substrates  

NASA Astrophysics Data System (ADS)

Silver films with different morphologies were chemically deposited by controlling the bath composition. It is found that the wettability and surface enhanced Raman scattering (SERS) properties were closely connected with the surface morphology. Due to the perfect 3D morphology and the 3D electromagnetic field enhanced by three types of nanogaps distributed uniformly, the 3D microball/nanosheet (MN) silver film shows better SERS properties than those of 2D nanosheets (NSs) and nanoparticles (NPs). The MN silver film showed high adhesive superhydrophobic properties after an oxidation process without any functionalization. It can hold the liquid droplet and trace the target molecules in a rather small volume. The SERS properties of the oxidized MN substrate were enhanced remarkably compared to those of the freshly prepared substrate because of the concentrating effect of the superhydrophobicity. The as-prepared 3D MN silver substrate has also exhibited good performances in reproducibility and reutilization which makes it a promising substrate for molecule tracing.Silver films with different morphologies were chemically deposited by controlling the bath composition. It is found that the wettability and surface enhanced Raman scattering (SERS) properties were closely connected with the surface morphology. Due to the perfect 3D morphology and the 3D electromagnetic field enhanced by three types of nanogaps distributed uniformly, the 3D microball/nanosheet (MN) silver film shows better SERS properties than those of 2D nanosheets (NSs) and nanoparticles (NPs). The MN silver film showed high adhesive superhydrophobic properties after an oxidation process without any functionalization. It can hold the liquid droplet and trace the target molecules in a rather small volume. The SERS properties of the oxidized MN substrate were enhanced remarkably compared to those of the freshly prepared substrate because of the concentrating effect of the superhydrophobicity. The as-prepared 3D MN silver substrate has also exhibited good performances in reproducibility and reutilization which makes it a promising substrate for molecule tracing. Electronic supplementary information (ESI) available: XRD patterns of three different substrates. XPS spectra of the MN silver film after modification. Raman spectra collected from 5 random points in the NP silver film. SERS spectra of 1 ?M 4-Mpy absorbed on different substrates. XPS O 1s spectra of the MN surface before and after storage. SERS spectra of 4 ?L 10-12 R6G absorbed onto the freshly prepared MN substrate. Raman spectra obtained on the solid R6G. SERS spectra obtained on the surface of the oxidized MN substrate after rinsing with deionized water. See DOI: 10.1039/c4nr02198c

Wu, Yunwen; Hang, Tao; Komadina, Jason; Ling, Huiqin; Li, Ming

2014-07-01

202

Development of super-hydrophobic PTFE and PET surfaces by means of plasma processes  

NASA Astrophysics Data System (ADS)

In this work, Poly(tetrafluoroethylene) and Poly(ethylene terephtalate) substrates were modified by means of plasma techniques for the creation of super-hydrophobic surfaces. Both the materials were etched with an O2 plasma, thus increasing their surface roughness which was investigated by means of Atomic Force Microscopy analysis. Plasma etching of PTFE surfaces under appropriate conditions results in the creation of super-hydrophobic surfaces, as assessed by measurements of dynamic contact angles and sliding angles. Chemical modifications of the PTFE surfaces was investigated with Attenuated Total Reflectance Fourier Transform Infrared spectroscopy and X-ray Photoelectron Spectroscopy analysis. The realization of super-hydrophobic PET surfaces needs the deposition of a hydrophobic top coating, which was realized through an hexamethyldisiloxane (HMDSO) plasma. The thickness of this top layer was varied by changing the plasma deposition time and the effects on the hydrophobic performances of the modified PET were investigated. Micro-nano structures created by plasma on PTFE and PET surfaces were characterized and correlated with the wettability.

Zanini, S.; Bami, R.; Della Pergola, R.; Riccardi, C.

2014-11-01

203

Superhydrophobic Surface Enhanced Raman Scattering Sensing using Janus Particle Arrays Realized by Site-Specific Electrochemical Growth  

PubMed Central

Site-specific electrochemical deposition is used to prepare polystyrene (PS)-Ag Janus particle arrays with superhydrophobic properties. The analyte molecules can be significantly enriched using the superhydrophobic property of the PS-Ag Janus particle array before SERS detections, enabling an extremely sensitive detection of molecules in a highly diluted solution (e.g., femtomolar level). This superhydrophobic surface enhanced Raman scattering sensing concept described here is of critical significance in biosensing and bioanalysis. Most importantly, the site-specific electrochemical growth method we developed here is a versatile approach that can be used to prepare Janus particle arrays with different properties for various applications. PMID:24748991

Hricko, Patrick John; Huang, Po-Hsun; Li, Sixing; Zhao, Yanhui; Xie, Yuliang; Guo, Feng; Wang, Lin

2014-01-01

204

Superhydrophobic Surface Enhanced Raman Scattering Sensing using Janus Particle Arrays Realized by Site-Specific Electrochemical Growth.  

PubMed

Site-specific electrochemical deposition is used to prepare polystyrene (PS)-Ag Janus particle arrays with superhydrophobic properties. The analyte molecules can be significantly enriched using the superhydrophobic property of the PS-Ag Janus particle array before SERS detections, enabling an extremely sensitive detection of molecules in a highly diluted solution (e.g., femtomolar level). This superhydrophobic surface enhanced Raman scattering sensing concept described here is of critical significance in biosensing and bioanalysis. Most importantly, the site-specific electrochemical growth method we developed here is a versatile approach that can be used to prepare Janus particle arrays with different properties for various applications. PMID:24748991

Yang, Shikuan; Hricko, Patrick John; Huang, Po-Hsun; Li, Sixing; Zhao, Yanhui; Xie, Yuliang; Guo, Feng; Wang, Lin; Huang, Tony Jun

2014-01-21

205

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

206

Controllable fabrication of lotus-leaf-like superhydrophobic surface on copper foil by self-assembly  

NASA Astrophysics Data System (ADS)

A novel approach was developed to fabricate a lotus-leaf-like superhydrophobic surface on a copper foil by simple self-assembly method with the assistance of the porous PDMS template which was used to adjust the oxidized parts of the copper foil surface before self-assembly. The results showed a series of beautiful flower-like microstructures resulting from the self-assembly of cupric stearate that were distributed at regular intervals on the as-prepared copper foil surface similar to the papillae of lotus leaf surface. The water contact angle of the as-prepared copper surface was up to 161° and its sliding angle was only 3°. Its great superhydrophobicity could be kept unchanged after 6 months in air. The formation mechanism of the lotus-leaf-like structure was discussed. This simple and low-cost method is expected to be applied to design and prepare complicated superhydrophobic surfaces with beautiful regular microstructures on different substrates such as stainless steel, zinc, and so on.

Yuan, Zhiqing; Wang, Xian; Bin, Jiping; Wang, Menglei; Peng, Chaoyi; Xing, Suli; Xiao, Jiayu; Zeng, Jingcheng; Chen, Hong

2014-09-01

207

Geometric study of transparent superhydrophobic surfaces of molded and grid patterned polydimethylsiloxane (PDMS)  

NASA Astrophysics Data System (ADS)

Herein we describe an economical method to fabricate a transparent superhydrophobic surface that uses grid patterning, and we report on the effects of grid geometry in determining the wettability and transparency of the fabricated surfaces. A polymer casting method was utilized because of its applicability to economical manufacturing and mass production; the material polydimethylsiloxane (PDMS) was selected because of its moldability and transparency. PDMS was replicated from a laser textured mold fabricated by a UV nanosecond pulsed laser. Sapphire wafer was used for the mold because it has very low surface roughness (Ra ?0.3 nm) and adequate mechanical properties. To study geometric effects, grid patterns of a series of step sizes were fabricated. The maximum water droplet contact angle (WDCA) observed was 171°. WDCAs depended on the wetting area and the wetting state. The experimental results of WDCA were analyzed with Wenzel and Cassie-Baxter equations. The designed grid pattern was suitably transparent and structurally stable. Transmittance of the optimal transparent superhydrophobic surface was measured by using a spectrophotometer. Transmittance loss due to the presence of the grid was around 2-4% over the wavelength region measured (300-1000 nm); the minimum transmittance observed was 83.1% at 300 nm. This study also demonstrates the possibility of using a nanosecond pulsed laser for the surface texturing of a superhydrophobic surface.

Davaasuren, Gaasuren; Ngo, Chi-Vinh; Oh, Hyun-Seok; Chun, Doo-Man

2014-09-01

208

A novel simple approach to preparation of superhydrophobic surfaces of aluminum alloys  

NASA Astrophysics Data System (ADS)

A novel two-step methodology is successfully developed to fabricate superhydrophobic surfaces of aluminum alloys. The essential procedure is that samples are first immersed and etched in a boiling aqueous solution of NaOH for 5 min without preprocessing, and then they are modified for 30 min in an ethanol solution of lauric acid, cheaper and more efficient than the fluorinated silane frequently adopted by other researchers. If the concentration of NaOH solution is larger than 5 g/L, the contact angle of the prepared surfaces will be larger than 150° with a negligible hysteresis. Such a fast, low-cost, and reliable method for superhydrophobic surfaces implies significant promising industrial applications.

Xie, Degang; Li, Wen

2011-11-01

209

Preparation of self-cleaning surfaces with a dual functionality of superhydrophobicity and photocatalytic activity  

NASA Astrophysics Data System (ADS)

Thin film of polydimethylsiloxane (PDMS) was deposited on SiO2 nanoparticles by chemical vapor deposition, and SiO2 became completely hydrophobic after PDMS coating. Mixtures of TiO2 and PDMS-coated SiO2 nanoparticles with various relative ratios were prepared, and distributed on glass surfaces, and water contact angles and photocatalytic activities of these surfaces were studied. Samples consisting of TiO2 and PDMS-coated SiO2 with a ratio of 7:3 showed a highly stable superhydrophobicity under UV irradiation with a water contact angle of 165° and UV-driven photocatalytic activity for decomposition of methylene blue and phenol in aqueous solution. Our process can be exploited for fabricating self-cleaning surfaces with dual functionality of superhydrophobicity and photocatalytic activity at the same time.

Park, Eun Ji; Yoon, Hye Soo; Kim, Dae Han; Kim, Yong Ho; Kim, Young Dok

2014-11-01

210

Preparation and properties of ZnS superhydrophobic surface with hierarchical structure  

NASA Astrophysics Data System (ADS)

A novel ZnS hierarchical structure composed of nanorod arrays with branched nanosheets and nanowires grown on their upside walls, was synthesized over Au-coated silicon substrate via chemical vapor deposition technique. Contact angle and sliding angle of this hierarchical film with no surface modification were measured to be about 153.8° and 9.1° for 5 ?l water droplets. Self-cleaning behavior and dynamic water-repelling performance were clearly demonstrated. In addition, electrowetting transition phenomenon from superhydrophobic to hydrophilic state happened when a critical bias ?7.0 V was applied. Below this threshold voltage, the contact angle change is little. This work for the first time reports the creation of ZnS superhydrophobic surface and could enrich its research field as surface functional materials.

Yao, Lujun; Zheng, Maojun; He, Shuanghu; Ma, Li; Li, Mei; Shen, Wenzhong

2011-01-01

211

Fabrication of self-healing super-hydrophobic surfaces on aluminium alloy substrates  

NASA Astrophysics Data System (ADS)

We present a method to fabricate a super-hydrophobic surface with a self-healing ability on an aluminium alloy substrate. The coatings are obtained by combining a two-step process (first, the substrate is immersed in a solution of HCl, HF and H2O, and then in boiling water) and succeeding surface fluorination with a solution of poly(vinylidene-fluoride-co-hexafluoropropylene) and a fluoroalkyl silane. The morphological features and chemical composition were studied by scanning electron micrometry and energy-dispersive X-ray spectroscopy. The prepared super-hydrophobic aluminium surfaces showed hierarchical structures forming pores, petals and particles with a contact angle of 161° and a sliding angle of 3°.

Wang, Yang; Wei Liu, Xiao; Zhang, Hai Feng; Zhou, Zhi Ping

2015-04-01

212

Durable superhydrophobic and antireflective surfaces by trimethylsilanized silica nanoparticles-based sol-gel processing.  

PubMed

We present a robust and cost-effective coating method to fabricate long-term durable superhydrophobic andsimultaneouslyantireflective surfaces by a double-layer coating comprising trimethylsiloxane (TMS) surface-functionalized silica nanoparticles partially embedded into an organosilica binder matrix produced through a sol-gel process. A dense and homogeneous organosilica gel layer was first coated onto a glass substrate, and then, a trimethylsilanized nanospheres-based superhydrophobic layer was deposited onto it. After thermal curing, the two layers turned into a monolithic film, and the hydrophobic nanoparticles were permanently fixed to the glass substrate. Such treated surfaces showed a tremendous water repellency (contact angle = 168 degrees ) and stable self-cleaning effect during 2000 h of outdoor exposure. Besides this, nanotextured topology generated by the self-assembled nanoparticles-based top layer produced a fair antireflection effect consisting of more than a 3% increase in optical transmittance. PMID:19466786

Manca, Michele; Cannavale, Alessandro; De Marco, Luisa; Aricò, Antonino S; Cingolani, Roberto; Gigli, Giuseppe

2009-06-01

213

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

214

Facile fabrication of superhydrophobic surfaces with low roughness on Ti-6Al-4V substrates via anodization  

NASA Astrophysics Data System (ADS)

The combination of suitable micro-scale structures and low surface energy modification plays a vital role in fabricating superhydrophobic surfaces on hydrophilic metal substrates. This work proposes a simple, facile and efficient method of fabricating superhydrophobic titanium alloy surfaces with low surface roughness. Complex micro-pore structures are generated on titanium alloy surfaces by anodic oxidation in the NaOH and H2O2 mixed solution. Fluoroalkylsilane (FAS) is used to reduce the surface energy of the electrochemically oxidized surface. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Zygogpi-xp6 (ZYGO) and contact angle measurements are performed to determine the morphological features, chemical composition, surface roughness and wettability. The formation mechanism of micro-scale rough structures, wettability of the superhydrophobic surfaces and the relationship between reaction time with wettability and roughness of the superhydrophobic surfaces are also analyzed in detail. The as-prepared titanium alloy surfaces not only show low roughness Ra = 0.669 ?m and good superhydrophobicity with a water contact angle of 158.5° ± 1.9° as well as a water tilting angle of 5.3° ± 1.1°, but also possess good long-term stability and abrasion resistance.

Gao, Yuze; Sun, Yuwen; Guo, Dongming

2014-09-01

215

Superhydrophobic aluminum surfaces by deposition of micelles of fluorinated block copolymers.  

PubMed

Superhydrophobic surfaces are generated by chemisorption on aluminum substrates of fluorinated block copolymers synthesized by reversible addition-fragmentation chain transfer in supercritical carbon dioxide. In an appropriate solvent, those block copolymers can form micelles with a fluorinated corona, which are grafted on the aluminum substrate thanks to the presence of carboxylic acid groups in the corona. Water contact angle and drop impact analysis were used to characterize the wettability of the films at the macroscale, and atomic force microscopy measurements provided morphological information at the micro- and nanoscale. The simple solvent casting of the polymer solution on a hydroxylated aluminum surface results in a coating with multiscale roughness, which is fully superhydrophobic over areas up to 4 cm(2). PMID:19761260

Desbief, Simon; Grignard, Bruno; Detrembleur, Christophe; Rioboo, Romain; Vaillant, Alexandre; Seveno, David; Voué, Michel; De Coninck, Joel; Jonas, Alain M; Jérôme, Christine; Damman, Pascal; Lazzaroni, Roberto

2010-02-01

216

Fabrication of superhydrophobic copper surface on various substrates for roll-off, self-cleaning, and water/oil separation.  

PubMed

Superhydrophobic surfaces prevent percolation of water droplets and thus render roll-off, self-cleaning, corrosion protection, etc., which find day-to-day and industrial applications. In this work, we developed a facile, cost-effective, and free-standing method for direct fabrication of copper nanoparticles to engender superhydrophobicity for various flat and irregular surfaces such as glass, transparency sheet (plastic), cotton wool, textile, and silicon substrates. The fabrication of as-prepared superhydrophobic surfaces was accomplished using a simple chemical reduction of copper acetate by hydrazine hydrate at room temperature. The surface morphological studies demonstrate that the as-prepared surfaces are rough and display superhydrophobic character on wetting due to generation of air pockets (The Cassie-Baxter state). Because of the low adhesion of water droplets on the as-prepared surfaces, the surfaces exhibited not only high water contact angle (164 ± 2°, 5 ?L droplets) but also superb roll-off and self-cleaning properties. Superhydrophobic copper nanoparticle coated glass surface uniquely withstands water (10 min), mild alkali (5 min in saturated aqueous NaHCO3 of pH ? 9), acids (10 s in dilute HNO3, H2SO4 of pH ? 5) and thiol (10 s in neat 1-octanethiol) at room temperature (25-35 °C). Again as-prepared surface (cotton wool) was also found to be very effective for water-kerosene separation due to its superhydrophobic and oleophilic character. Additionally, the superhydrophobic copper nanoparticle (deposited on glass surface) was found to exhibit antibacterial activity against both Gram-negative and Gram-positive bacteria. PMID:25419984

Sasmal, Anup Kumar; Mondal, Chanchal; Sinha, Arun Kumar; Gauri, Samiran Sona; Pal, Jaya; Aditya, Teresa; Ganguly, Mainak; Dey, Satyahari; Pal, Tarasankar

2014-12-24

217

Fabrication of a super-hydrophobic nanofibrous zinc oxide film surface by electrospinning  

Microsoft Academic Search

We report a new approach for fabricating a super-hydrophobic nanofibrous zinc oxide (ZnO) film surface. The pure poly(vinyl alcohol) (PVA) and composite PVA\\/ZnO nanofibrous films can be obtained by electrospinning the PVA and PVA\\/zinc acetate solutions, respectively. After the calcination of composite fibrous films, the inorganic fibrous ZnO films with a reduced fiber diameter were fabricated. The wettability of three

Bin Ding; Tasuku Ogawa; Jinho Kim; Kouji Fujimoto; Seimei Shiratori

2008-01-01

218

Highly transparent superhydrophobic surfaces from the coassembly of nanoparticles (?100 nm).  

PubMed

We report a simple and versatile approach to creating a highly transparent superhydrophobic surface with dual-scale roughness on the nanoscale. 3-Aminopropyltrimethoxysilane (APTS)-functionalized silica nanoparticles of two different sizes (100 and 20 nm) were sequentially dip coated onto different substrates, followed by thermal annealing. After hydrophobilization of the nanoparticle film with (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trichlorosilane for 30 min or longer, the surface became superhydrophobic with an advancing water contact angle of greater than 160° and a water droplet (10 ?L) roll-off angle of less than 5°. The order of nanoparticles dip coated onto the silicon wafer (i.e., 100 nm first and 20 nm second or vice versa) did not seem to have a significant effect on the resulting apparent water contact angle. In contrast, when the substrate was dip coated with monoscale nanoparticles (20, 50, and 100 nm), a highly hydrophobic surface (with an advancing water contact angle of up to 143°) was obtained, and the degree of hydrophobicity was found to be dependent on the particle size and concentration of the dip-coating solution. UV-vis spectra showed nearly 100% transmission in the visible region from the glass coated with dual-scale nanoparticles, similar to the bare one. The coating strategy was versatile, and superhydrophobicity was obtained on various substrates, including Si, glass, epoxy resin, and fabrics. Thermal annealing enhanced the stability of the nanoparticle coating, and superhydrophobicity was maintained against prolonged exposure to UV light under ambient conditions. PMID:21355577

Karunakaran, Raghuraman G; Lu, Cheng-Hsin; Zhang, Zanhe; Yang, Shu

2011-04-19

219

Sustainable Drag Reduction in Turbulent Taylor-Couette Flows by Depositing Sprayable Superhydrophobic Surfaces  

NASA Astrophysics Data System (ADS)

We demonstrate a reduction in the measured inner wall shear stress in moderately turbulent Taylor-Couette flows by depositing sprayable superhydrophobic microstructures on the inner rotor surface. The magnitude of reduction becomes progressively larger as the Reynolds number increases up to a value of 22% at Re =8.0 ×1 04 . We show that the mean skin friction coefficient Cf in the presence of the superhydrophobic coating can be fitted to a modified Prandtl-von Kármán-type relationship of the form (Cf/2 )-1 /2=M ln (Re (Cf/2 )1 /2) +N +(b /? r )Re (Cf/2 )1 /2 from which we extract an effective slip length of b ?19 ? m . The dimensionless effective slip length b+=b /??, where ?? is the viscous length scale, is the key parameter that governs the drag reduction and is shown to scale as b+˜Re1 /2 in the limit of high Re.

Srinivasan, Siddarth; Kleingartner, Justin A.; Gilbert, Jonathan B.; Cohen, Robert E.; Milne, Andrew J. B.; McKinley, Gareth H.

2015-01-01

220

The evaluation of hierarchical structured superhydrophobic coatings for the alleviation of insect residue to aircraft laminar flow surfaces  

NASA Astrophysics Data System (ADS)

Surface contamination caused by insects on laminar flow wing surfaces causes a disruption of the flow, resulting in an increase in drag and fuel consumption. Consequently, the use of superhydrophobic coatings to mitigate insect residue adhesion was investigated. A range of hierarchical superhydrophobic coatings with different surface chemistry and topography was examined. Candidate coatings were characterized in terms of their morphology and hydrophobic properties by scanning electron microscopy (SEM) and static and dynamic contact angle measurements, respectively. Arithmetic mean surface roughness (Ra) values were measured using profilometry. Only superhydrophobic coatings with a specific topography showed complete mitigation against insect residue adhesion. A surface which exhibited a specific microstructure (Ra = 5.26 ?m) combined with a low sliding angle (SA = 7.6°) showed the best anti-contamination properties. The dynamics of an insect impact event and its influence on the wetting and adhesion mechanisms of insect residue to a surface were discussed.

Kok, Mariana; Young, Trevor M.

2014-09-01

221

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

222

Wetting and phase-change phenomena on micro/nanostructures for enhanced heat transfer  

E-print Network

Micro/nanostructures have been extensively studied to amplify the intrinsic wettability of materials to create superhydrophilic or superhydrophobic surfaces. Such extreme wetting properties can influence the heat transfer ...

Xiao, Rong, Ph. D. Massachusetts Institute of Technology

2013-01-01

223

General formulations for predicting longevity of submerged superhydrophobic surfaces composed of pores or posts.  

PubMed

Superhydrophobicity can arise from the ability of a submerged rough hydrophobic surface to trap air in its surface pores, and thereby reduce the contact area between the water and the frictional solid walls. A submerged surface can only remain superhydrophobic (SHP) as long as it retains the air in its pores. SHP surfaces have a short underwater life, and their longevity depends strongly on the hydrostatic pressure at which they operate. In this work, a comprehensive mathematical framework is developed to predict the mechanical stability and the longevity of submerged SHP surfaces with arbitrary pore or post geometries. We start by deriving an integro-partial differential equation for the 3-D shape of the air-water interface, and use this information to predict the rate of dissolution of the entrapped air into the ambient water under different hydrostatic pressures. For the special case of circular pores, the above integro-partial differential equation is reduced to easy-to-solve ordinary differential equations. In addition, approximate nonlinear algebraic solutions are also obtained for surfaces with circular pores or posts. The effects of geometrical parameters and hydrostatic conditions on surface stability and longevity are discussed in detail. Moreover, a simple equivalent pore diameter method is developed for SHP surfaces composed of posts with ordered or random configuration--an otherwise complicated task requiring the solution of an integro-partial differential equation. PMID:25109908

Hemeda, A A; Tafreshi, H Vahedi

2014-09-01

224

Designing heterogeneous chemical composition on hierarchical structured copper substrates for the fabrication of superhydrophobic surfaces with controlled adhesion.  

PubMed

Controlling water adhesion is important for superhydrophobic surfaces in many applications. Compared with numerous researches about the effect of microstructures on the surface adhesion, research relating to the influence of surface chemical composition on the surface adhesion is extremely rare. Herein, a new strategy for preparation of tunable adhesive superhydrophobic surfaces through designing heterogeneous chemical composition (hydrophobic/hydrophilic) on the rough substrate is reported, and the influence of surface chemical composition on the surface adhesion are examined. The surfaces were prepared through self-assembling of mixed thiol (containing both HS(CH2)9CH3 and HS(CH2)11OH) on the hierarchical structured copper substrates. By simply controlling the concentration of HS(CH2)11OH in the modified solution, tunable adhesive superhydrophobic surfaces can be obtained. The adhesive force of the surfaces can be increased from extreme low (about 8 ?N) to very high (about 65 ?N). The following two reasons can be used to explain the tunable effect: one is the number of hydrogen bond for the variation of surface chemical composition; and the other is the variation of contact area between the water droplet and surface because of the capillary effect that results from the combined effect of hydrophilic hydroxyl groups and microstructures on the surface. Noticeably, water droplets with different pH (2-12) have similar contact angles and adhesive forces on the surfaces, indicating that these surfaces are chemical resistant to acid and alkali. Moreover, the as-prepared surfaces were also used as the reaction substrates and applied in the droplet-based microreactor for the detection of vitamin C. This report provides a new method for preparation of superhydrophobic surfaces with tunable adhesion, which could not only help us further understand the principle for the fabrication of tunable adhesive superhydrophobic surfaces, but also potentially be used in many important applications, such as microfluidic devices and chemical microreactors. PMID:23919678

Cheng, Zhongjun; Hou, Rui; Du, Ying; Lai, Hua; Fu, Kewei; Zhang, Naiqing; Sun, Kening

2013-09-11

225

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

226

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

227

Bioinspired uniform illumination by vibrated sessile droplet pinned by a hydrophilic/superhydrophobic heterogeneous surface.  

PubMed

We introduce a strategy to generate uniform illumination. The droplet pinned by a hydrophilic/superhydrophobic heterogeneous surface is oscillated, driven by a laterally placed loudspeaker. The vibrated droplet can be considered as a tunable lens, whose focus and focus length can be real-time tuned. The tunable "lens" is presented as a device for uniform illumination by mechanical manipulation. The incident light is scattered by the vibrated droplet during oscillation, and the irradiance distribution on the image plane becomes larger and more homogenous when the droplet is at resonance. PMID:23903122

Zhu, Shuya; Jiang, Weitao; Liu, Hongzhong; Yin, Lei; Shi, Yongsheng; Chen, Bangdao; Ding, Yucheng; An, Ningli

2013-08-01

228

Durable, superhydrophobic, superoleophobic and corrosion resistant coating on the stainless steel surface using a scalable method  

NASA Astrophysics Data System (ADS)

In this study, superamphiphobic coating was produced using low surface energy materials and fabrication of hierarchical structures on stainless steel surface. Hierarchical structure was fabricated by silica multilayer coatings and adequate control of particles size in each layer. The surface energy was decreased by fluoropolymer compounds. The maximum static contact angle of DI water, ethylene glycol and fuel oil droplets on the prepared surface increased from 64° to 166°, from 33° to 157° and from 0° to 116°, respectively. Also, the minimum sliding angles of DI water, ethylene glycol and fuel oil droplets on the prepared surface were less than 2°, 5° and 12°, respectively. These results confirmed the superhydrophobicity and superoleophobicity of coated surfaces. These films maintained their superamphiphobicity after 16 days of immersion in water. In electrochemical corrosion evaluation, the highest protection efficiency of fabricated films reached as high as 97.33%. These satisfied results confirmed that this simple method can be used to fabricate large scale samples.

Valipour Motlagh, N.; Birjandi, F. Ch.; Sargolzaei, J.; Shahtahmassebi, N.

2013-10-01

229

Replication of butterfly wing and natural lotus leaf nanostructures by nanoimprint on Silica Sol-gel films.  

E-print Network

1 Replication of butterfly wing and natural lotus leaf nanostructures by nanoimprint on Silica Sol applications are the lotus leaves and butterfly wings with their specific structure given a superhydrophobicity have chosen to imprint the lotus leaf and butterfly wings in order to obtain superhydrophobic surfaces

230

A novel method to fabricate superhydrophobic surfaces based on well-defined mulberry-like particles and self-assembly of polydimethylsiloxane  

NASA Astrophysics Data System (ADS)

A superhydrophobic surface was obtained by combining application of CaCO 3/SiO 2 mulberry-like composite particles, which originated from violent stirring and surface modification, and self-assembly of polydimethylsiloxane. Water contact angle and sliding angle of the superhydrophobic surface were measured to be about 164 ± 2.5° and 5°, respectively. The excellent hydrophobicity is attributed to the synergistic effect of micro-submicro-nano-meter scale roughness (fabricated by composite particles) and the low surface energy (provided by polydimethylsiloxane). This procedure makes it possible for widespread applications of superhydrophobic film due to its simplicity and practicability.

Yang, Jinxin; Pi, Pihui; Wen, Xiufang; Zheng, Dafeng; Xu, Mengyi; Cheng, Jiang; Yang, Zhuoru

2009-01-01

231

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

232

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

233

Fabrication of superhydrophobic surfaces via CaCO3 mineralization mediated by poly(glutamic acid)  

NASA Astrophysics Data System (ADS)

Surfaces with micrometer and nanometer sized hierarchical structures were fabricated by an one-step in situ additive controlled CaCO3 mineralization method. After chemical modification, the surfaces with various morphologies showed superhydrophobicity in different states, which could be easily adjusted by the initial supersaturation of the mineralization solution (concentration of calcium ion and poly(glutamic acid)). Generally, the "lotus state" surface which was covered by a thick layer of tetrahedron-shaped CaCO3 particles to exhibit a contact angle (CA) of 157±1° and a very low contact angle hysteresis (CAH) (roll-off angle=1°) was produced under high supersaturation. On the other hands, the petal-like surface with flower-shaped calcite spherulites was obtained in a relative low supersaturation, which showed both high CA (156±2°) and CAH (180°) in a "Cassie impregnating wetting state".

Cao, Heng; Yao, Jinrong; Shao, Zhengzhong

2013-03-01

234

Fabrication and analysis of PMMA, ABS, PS, and PC superhydrophobic surfaces using the spray method  

NASA Astrophysics Data System (ADS)

In this study, superhydrophobic surfaces were fabricated using a facile spraying technique with poly(methyl methacrylate) (PMMA), acrylonitrile butadiene styrene (ABS), polystyrene (PS) and polycarbonate (PC). Also, the surface energy was qualitatively analyzed via the water contact angle with respect to the spraying time and the sprayed position. Firstly, PMMA, ABS, PS and PC were dissolved by using solvents such as methyl chloride, methanol, THF (tetrahydrofuran), and methanol, respectively. After that, the dissolved polymer was sprayed onto a thin film of the same polymer for various spraying times. Nozzle size, pressure and spraying distance were fixed as 0.2 mm, 0.1 bar, and 100 mm, respectively, after several feasibility experiments. For the sprayed surfaces, the topology was analyzed with scanning electron microscopy (SEM) and confocal microscopy, and the surface energy was qualitatively analyzed using the water-contactangle measurement. According to a quantitative analysis using the roughness factor and he Wenzel equation, all specimens could be assumed to be in a Wenzel state. To convert the Wenzel state into a Cassie-Baxster state by decreasing the surface energy of polymer-sprayed specimen, we treated the polymer-sprayed surfaces by using trichloro (1H, 1H, 2H, 2H-perfluorooctyl) silane. Consequently, non-sticky superhydrophobic surfaces having water contact angles greater than 155° and water sliding angles lower than 8° were fabricated. The water contact angle and the water sliding angle were measured by using a contact-angle-measuring device. In addition, a brief qualitative analysis of the effect of surface topology on the water sliding angle was conducted for the polymer-sprayed specimens.

Cho, Young-Sam; Ahn, Sang Hyun; Lee, Se-Hwan

2013-07-01

235

Superhydrophobic, antiadhesive, and antireflective surfaces mediated by hybrid biomimetic salvinia leaf with moth-eye structures  

NASA Astrophysics Data System (ADS)

In this paper, we successfully demonstrate multifunctional surfaces based on scaffolding biomimetic structures, namely, hybrid salvinia leaves with moth-eye structures (HSMSs). The novel fabrication process employs scalable polystyrene nanosphere lithography and a lift-off process. Systematic characterizations show the biomimetic HSMS exhibiting superhydrophobic, self-cleaning, antiadhesive, and antireflective properties. Furthermore, the resulting surface tension gradient (known as the Marangoni effect) leads to a superior air retention characteristic in the HSMS under water droplet impact, compared with the traditional hybrid lotus leaf with a moth-eye structure (HLMS). Such results and learnings pave the way towards the attainment and mass deployment of dielectric surfaces with multiple functionalities for versatile biological and optoelectronic applications.

Yang, Cho-Yun; Tsai, Yu-Lin; Yang, Cho-Yu; Sung, Cheng-Kuo; Yu, Peichen; Kuo, Hao-Chung

2014-08-01

236

Superhydrophobic surface directly created by electrospinning based on hydrophilic material  

Microsoft Academic Search

We describe a method to form hydrophobic surfaces using PHBV (Poly (hydroxybutyrate-co-hydroxyvalerate))—a kind of intrinsically\\u000a hydrophilic material. The concentration of polymer solutions was varied to control the surface morphology and resultant wetting\\u000a property. The as-prepared films were characterized by micro-scale valley-and-hill structure, which was formed by aggregating\\u000a of electrospun beads. The bead morphology changed from smooth to porous and popcorn-like

Meifang Zhu; Weiwei Zuo; Hao Yu; Wen Yang; Yanmo Chen

2006-01-01

237

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. PMID:23703091

Kiraly, Brian; Yang, Shikuan

2014-01-01

238

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

239

Boiling heat transfer on superhydrophilic, superhydrophobic, and superbiphilic surfaces  

E-print Network

that describes how biphilic surfaces effectively manage the vapor and liquid transport, delaying critical heat flux and maximizing the heat transfer coef- ficient. Finally, we manufacture and test the first, with the exception of experiments involving single nucleation [14] or condensation [15]. The high heat transfer rates

Attinger, Daniel

240

Creation of microstructured surfaces using Cu-Ni composite electrodeposition and their application to superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

This research analyzed the influence of the electrodeposition ratio of Cu-Ni on the creation of microstructure in Cu-Ni composite electrodeposition, and identified the microstructure generation mechanism with respect to the Cu-Ni electrodeposition ratio. The concentration of CuSO4 in the electrodeposition solution was varied to 0.00, 0.02, 0.04 M to control the electrodeposition ratio of Cu, and the applied voltage was varied to voltages of -0.9, -1.2, -1.5 V, which were applied to control the electrodeposition ratio of Ni. In the composite electrodeposition, Cu ions precipitated intensively at the top of the structure with a short ion diffusion length, and the Ni ions precipitated regularly throughout the entire area charge transferred. Therefore, the structure showed vertically oriented growth when Cu electrodeposition was dominant, and the structure showed isotropic growth when Ni electrodeposition was dominant. On the other hand, Cu ions precipitation concentration at the tip of the grown structure intensified as the height of the structure increased. Therefore, when a structure grows above a certain height, the excess Cu ions precipitate at the top of the grown structure and a cluster structure composed of spherical Cu particles develops. The microstructure produced in the electrodeposition solution with the CuSO4 concentration of 0.04 M had such a high structure generation density and aspect ratio that it was modified to a superhydrophobic surface with a contact angle higher than 150°, and it manifested an excellent self-cleaning ability.

Lee, Jae Min; Bae, Kong Myeong; Jung, Kyung Kuk; Jeong, Ji Hwan; Ko, Jong Soo

2014-01-01

241

Water desorption from nanostructured graphite surfaces.  

PubMed

Water interaction with nanostructured graphite surfaces is strongly dependent on the surface morphology. In this work, temperature programmed desorption (TPD) in combination with quadrupole mass spectrometry (QMS) has been used to study water ice desorption from a nanostructured graphite surface. This model surface was fabricated by hole-mask colloidal lithography (HCL) along with oxygen plasma etching and consists of a rough carbon surface covered by well defined structures of highly oriented pyrolytic graphite (HOPG). The results are compared with those from pristine HOPG and a rough (oxygen plasma etched) carbon surface without graphite nanostructures. The samples were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The TPD experiments were conducted for H2O coverages obtained after exposures between 0.2 and 55 langmuir (L) and reveal a complex desorption behaviour. The spectra from the nanostructured surface show additional, coverage dependent desorption peaks. They are assigned to water bound in two-dimensional (2D) and three-dimensional (3D) hydrogen-bonded networks, defect-bound water, and to water intercalated into the graphite structures. The intercalation is more pronounced for the nanostructured graphite surface in comparison to HOPG surfaces because of a higher concentration of intersheet openings. From the TPD spectra, the desorption energies for water bound in 2D and 3D (multilayer) networks were determined to be 0.32 ± 0.06 and 0.41 ± 0.03 eV per molecule, respectively. An upper limit for the desorption energy for defect-bound water was estimated to be 1 eV per molecule. PMID:24018989

Clemens, Anna; Hellberg, Lars; Grönbeck, Henrik; Chakarov, Dinko

2013-12-21

242

Superhydrophobic aluminium-based surfaces: Wetting and wear properties of different CVD-generated coating types  

NASA Astrophysics Data System (ADS)

In view of generating superhydrophobic aluminium-based surfaces, this work presents further results for the combination of anodic oxidation as the primary pretreatment method and chemical vapour deposition (CVD) variants for chemical modification producing coatings of 250-1000 nm thickness. In detail, CVD involved the utilisation of i - hexafluoropropylene oxide as precursor within the hot filament CVD process for the deposition of poly(tetrafluoroethylene) coatings at alternative conditions (PTFE-AC) and ii - 1,3,5-trivinyltrimethylcyclotrisiloxane for the deposition of polysiloxane coatings (PSi) by initiated CVD. The substrate material was Al Mg1 subjected to usual or intensified sulphuric acid anodisation pretreatments (SAAu, SAAi, respectively) affording various degrees of surface micro-roughness (SAAu < SAAi) to the oxidic layers. Performance characteristics were evaluated in the original as-coated states and after standardised artificial weathering and/or mild wear testing. Superhydrophobicity (SH) was observed with the system SAAi + PTFE-AC similarly to former findings with the standard hot filament CVD PTFE coating variant (SAAi + PTFE-SC). The results indicated that the specific coating morphology made an important contribution to the water-repellency, because even some of the SAAu-based samples tended to reveal SH. Subjecting samples to weathering treatment resulted in a general worsening of the wetting behaviour, primarily limited to the receding contact angles. These tendencies were correlated with the chemical composition of the sample surfaces as analysed by X-ray photoelectron spectroscopy. The wear tests showed, as evaluated by scanning electron microscopy and contact angle measurement, that the PTFE coatings were relatively sensitive to friction. This was connected with a dramatic deterioration of the water-repelling properties. PSi-coated surfaces generally showed rather poor water-repellency, but this coating type was surprisingly resistant towards the applied friction test. From these findings it may be concluded that the combination of hydrophobic fluorine containing structure elements and cross-linking of the polymeric chains would likely afford highly durable SH.

Thieme, M.; Streller, F.; Simon, F.; Frenzel, R.; White, A. J.

2013-10-01

243

Decorated Electrospun Fibers Exhibiting Superhydrophobicity  

Microsoft Academic Search

Superhydrophobicity, water repellency, and self-cleaning properties of materials have recently attracted tremendous at- tention.(1-3) Superhydrophobic surfaces exhibit extraordinarily high water contact angles, by convention greater than 150°, and extraordinarily low contact-angle hysteresis (i.e., a low difference between advancing and receding contact angles), typically less than 5°-10°. Studies of superhydrophobicity re- alized by insects(4) and many plants,(5,6) particularly the lotus leaf,(6)

Minglin Ma; Malancha Gupta; Zhi Li; Lei Zhai; Karen K. Gleason; Robert E. Cohen; Michael F. Rubner; Gregory C. Rutledge

2007-01-01

244

Catalytic, self-cleaning surface with stable superhydrophobic properties: printed polydimethylsiloxane (PDMS) arrays embedded with TiO2 nanoparticles.  

PubMed

Maintaining the long-term stability of superhydrophobic surfaces is challenging because of contamination from organic molecules and proteins that render the surface hydrophilic. Reactive oxygen species generated on a photocatalyst, such as TiO2, could mitigate this effect by oxidizing these contaminants. However, incorporation of such catalyst particles into a superhydrophobic surface is challenging because the particles become hydrophilic under UV exposure, causing the surface to transition to the Wenzel state. Here we show that a high concentration of hydrophilic TiO2 catalytic nanoparticles can be incorporated into a superhydrophobic surface by partially embedding the particles into a printed array of high aspect ratio polydimethylsiloxane posts. A stable Cassie state was maintained on these surfaces, even under UV irradiation, because of the significant degree of hierarchical roughness. By printing the surface on a porous support, oxygen could be flowed through the plastron, resulting in higher photooxidation rates relative to a static ambient. Rhodamine B and bovine serum albumin were photooxidized both in solution and after drying onto these TiO2-containing surfaces, and the effects of particle location and plastron gas composition were studied in static and flowing gas environments. This approach may prove useful for water purification, medical devices, and other applications where Cassie stability is required in the presence of organic compounds. PMID:25525836

Zhao, Yuanyuan; Liu, Yang; Xu, Qianfeng; Barahman, Mark; Lyons, Alan M

2015-02-01

245

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

246

Nano-TiO2 Modified Super-hydrophobic Surface Coating for Anti-ice and Anti-flashover of Insulating Layer  

Microsoft Academic Search

This paper focus on the development of the antipollution-flashover, anti-ice-flashover materials, analyzing the excellent characteristics of super-hydrophobic surface based on nano-TiO2 modified RTV coatings. The super-hydrophobic surface could be adopted to enhancing the performance of anti-ice, anti-ice-flashover and anti-pollution-flashover of the power transmission and distribution system, overcome the effect of environmental pollution, and tropical climate. The results suggested the application

Wei Li; Yalou Li; Xingwei Wang

2010-01-01

247

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

248

Temperature-Induced Coalescence of Colliding Binary Droplets on Superhydrophobic Surface  

PubMed Central

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

249

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

250

Temperature-Induced Coalescence of Colliding Binary Droplets on Superhydrophobic Surface  

NASA Astrophysics Data System (ADS)

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.

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

2014-03-01

251

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

PubMed Central

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

2011-01-01

252

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

NASA Astrophysics Data System (ADS)

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.

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

2011-08-01

253

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. PMID:24991518

Reker, Meike; Barthlott, Wilhelm

2014-01-01

254

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

255

Hierarchically structured re-entrant microstructures for superhydrophobic surfaces with extremely low hysteresis  

NASA Astrophysics Data System (ADS)

This paper reports a new type of hierarchically structured surface consisting of re-entrant silicon micropillars with silicon nanowires atop for superhydrophobic surface with extremely low hysteresis. Re-entrant microstructures were fabricated on a silicon substrate through a customized one-mask microfabrication process while silicon nanopillars were created on the entire surface of microstructures, including sidewalls, by a metal-assisted-chemical etching process. The strategy of constructing hierarchical surfaces aims to reduce the actual contact area between liquid and top part of solid surface, thereby increasing the contact angle and reducing the sliding angle. The strategy of using re-entrant profile of the microstructure aims to prevent a liquid droplet from falling into cavities of roughened structures and decrease the actual contact area between the liquid droplet and sidewalls of solid structures, therefore reducing adhesion forces acting on the liquid droplet. Our measurement shows that the surface incorporating both hierarchical and re-entrant strategies exhibits a sliding angle as low as 0.5°, much lower than sliding angles of surfaces only incorporating either one of the strategies.

Hu, Huan; Swaminathan, Vikhram V.; Zamani Farahani, Mahmoud Reza; Mensing, Glennys; Yeom, Junghoon; Shannon, Mark A.; Zhu, Likun

2014-09-01

256

A durable, superhydrophobic, superoleophobic and corrosion-resistant coating with rose-like ZnO nanoflowers on a bamboo surface  

NASA Astrophysics Data System (ADS)

Bamboo remains a vital component of modern-day society; however, its use is severely limited in certain applications because of its hydrophilic and oleophilic properties. In this work, we present a method to render bamboo surfaces superamphiphobic by combining control of ZnO nanostructures and fluoropolymer deposition while maintaining their corrosion resistance. Large-scale rose-like ZnO nanoflowers (RZN) were planted on the bamboo surface by a hydrothermal method. After fluoroalkylsilane (FAS) film deposition to lower the surface energy, the resulting surface showed superamphiphobicity toward water, oil, and even certain corrosive liquids, including salt solutions and acidic and basic solutions at all pH values. The as-prepared superamphiphobic bamboo surface was durable and maintained its superhydrophobic property with water contact angles >150° when stored under ambient condition for two months or immersed in a hydrochloric acid solution of pH 1 and a sodium hydroxide solution of pH 14 for 3 h at 50 °C.

Jin, Chunde; Li, Jingpeng; Han, Shenjie; Wang, Jin; Sun, Qingfeng

2014-11-01

257

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

258

Super-hydrophobic transparent surface by femtosecond laser micro-patterned catalyst thin film for carbon nanotube cluster growth  

Microsoft Academic Search

In this work, super-hydrophobic surfaces were fabricated by femtosecond laser micro-machining and chemical vapor deposition to constitute hybrid scale micro\\/nano-structures formed by carbon nanotube (CNT) clusters. Nickel thin-film microstructures, functioning as CNT growth catalyst, precisely control the distribution of the CNT clusters. To obtain minimal heat-affected zones, femtosecond laser was used to trim the nickel thin-film coating. Plasma treatment was

M. Tang; M. H. Hong; Y. S. Choo; Z. Tang; Daniel H. C. Chua

2010-01-01

259

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

260

Superhydrophobic perfluoropolymer surfaces having heterogeneous roughness created by dip-coating from solutions containing a nonsolvent  

NASA Astrophysics Data System (ADS)

Superhydrophobic and oleophobic rough copolymer surfaces containing micro- and nano-hierarchical ball-like islands having diameters between 100 nm and 7 ?m were formed using styrene-perfluoromethacrylate random copolymers which were dip-coated on glass slides from THF and MEK mixture containing methanol as nonsolvent. These copolymers were synthesized in a CO2-expanded monomer medium at 250 bar pressure and 80 °C. The sizes of the micro-islands can be controlled by varying the copolymer composition; and the degree of phase separation by adjusting the solvent/non-solvent ratio. Flat and lotus-like hierarchical surfaces of the copolymers were characterized using contact angle measurements and SEM. The increase in the perfluoromethacrylate content of the flat copolymers resulted in a decrease of the total surface free energy of the flat copolymer surfaces from 18.3 down to 14.2 mJ/m2. The increase in the methanol non-solvent fraction resulted in decrease of the micro-island diameter from 7 ?m down to 100 nm and the water contact angle increased from 117° up to 160° and hexadecane from 65° up to 90°.

Cengiz, Ugur; Erbil, H. Yildirim

2014-02-01

261

Multipurpose ultra and superhydrophobic surfaces based on oligodimethylsiloxane-modified nanosilica.  

PubMed

Nonfluorinated hydrophobic surfaces are of interest for reduced cost, toxicity, and environmental problems. Searching for such surfaces together with versatile processing, A200 silica nanoparticles are modified with an oligodimethylsiloxane and used by themselves or with a polymer matrix. The goal of the surface modification is controlled aggregate size and stable suspensions. Characterization is done by NMR, microanalysis, nitrogen adsorption, and dynamic light scattering. The feasibility of the concept is then demonstrated. The silica aggregates are sprayed in a scalable process to form ultrahydrophobic and imperceptible coatings with surface topographies of controlled nanoscale roughness onto different supports, including nanofibrillated cellulose. To improve adhesion and wear properties, the organosilica was mixed with polymers. The resulting composite coatings are characterized by FE-SEM, AFM, and contact angle measurements. Depending on the nature of the polymer, different functionalities can be developed. Poly(methyl methacrylate) leads to almost superhydrophobic and highly transparent coatings. Composites based on commercial acrylic car paint show "pearl-bouncing" droplet behavior. A light-emitting polyfluorene is synthesized to prepare luminescent and water repellent coatings on different supports. The interactions between polymers and the organosilica influence coating roughness and are critical for wetting behavior. In summary, the feasibility of a facile, rapid, and fluorine-free hydrophobization concept was successfully demonstrated in multipurpose antiwetting applications. PMID:25275966

de Francisco, Raquel; Tiemblo, Pilar; Hoyos, Mario; González-Arellano, Camino; García, Nuria; Berglund, Lars; Synytska, Alla

2014-11-12

262

Superhydrophobic and oleophobic surface from fluoropolymer-SiO2 hybrid nanocomposites.  

PubMed

The fluoropolymer-SiO2 hybrid nanocomposite consisting of core-corona fluoropolymer-grafted SiO2 nanoparticle (NP) and poly(dodecafluoroheptyl methacrylate) (PDFHM) was obtained by radical solution polymerization of the vinyl trimethoxy silane (VTMS)-treated SiO2 NP with DFHM in this work. In H2O/tetrahydrofuran (THF) solution, PDFHM self-assembles into dendritic micelle and the increase in H2O volume is favorable for fluoropolymer-grafted SiO2 NPs to create dense fluoropolymer corona layer. It also shows that the addition of H2O to the THF suspension of fluoropolymer-SiO2 nanocomposite could cause a transfer for surface morphology of cast film from smooth film-covered aggregation to bare-exposed flaky aggregation and microsphere aggregation, which results in an increase in surface RMS roughness of cast film and induces a superhydrophobicity. Oleophobicity of cast film can be improved by thermal annealing, because strong surface self-segregation of PDFHM chains during thermal annealing process arouses a marked increase in surface fluorine content. PMID:25218050

Wang, Li; Liang, Junyan; He, Ling

2014-12-01

263

Preparation and anti-icing behavior of superhydrophobic surfaces on aluminum alloy substrates.  

PubMed

It has been expected that superhydrophobic (SHP) surfaces could have potential anti-icing applications due to their excellent water-repellence properties. However, a thorough understanding on the anti-icing performance of such surfaces has never been reported; even systematic characterizations on icing behavior of various surfaces are still rare because of the lack of powerful instrumentations. In this study, we employed the electrochemical anodic oxidation and chemical etching methods to simplify the fabrication procedures for SHP surfaces on the aluminum alloy substrates, aiming at the anti-icing properties of SHP surfaces of various engineering materials. We found that the one-step chemical etching with FeCl3 and HCl as the etchants was the most effective for ideal SHP surfaces with a large contact angle (CA, 159.1°) and a small contact angle hysteresis (CAH, 4.0°). To systematically investigate the anti-icing behavior of the prepared SHP surfaces, we designed a robust apparatus with a real-time control system based on the two stage refrigerating method. This system can monitor the humidity, pressure, and temperature during the icing process on the surfaces. We demonstrated that the SHP surfaces exhibited excellent anti-icing properties, i.e., from the room temperature of 16.0 °C, the icing time on SHP surfaces can be postponed from 406s to 676s compared to the normal aluminum alloy surface if the surfaces were put horizontally, and the icing temperature can be decreased from -2.2 °C to -6.1 °C. If such surfaces were tilted, the sprayed water droplets on the normal surfaces iced up at the temperature of -3.9 °C, but bounced off the SHP surface even as the temperature reached as low as -8.0 °C. The present study therefore suggests a general, simple, and low-cost methodology for the promising anti-icing applications in various engineering materials and different fields (e.g., power lines and aircrafts). PMID:23718719

Ruan, Min; Li, Wen; Wang, Baoshan; Deng, Binwei; Ma, Fumin; Yu, Zhanlong

2013-07-01

264

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. PMID:24941969

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

2014-01-01

265

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

266

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. PMID:21204982

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

2014-01-01

267

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

268

Superhydrophobicity - Magic Sand - Presentation  

NSDL National Science Digital Library

This pdf from the Midwest Regional Center for Nanotechnology Education (NANO-LINK) introduces the forces and interactions central to understanding nanotechnology. The presentation explores how surfaces respond to water by explaining hydrophobic, hydrophilic, and super-hydrophobic surfaces. Visitors must complete a quick and free registration to access materials.

269

Shear shedding of drops and the use of superhydrophobic surfaces in microgravity: PFC and ground based results  

NASA Astrophysics Data System (ADS)

In free fall, the absence of gravity poses many challenges for fluid handling systems. One such example of this is condensers. On earth, the condensed liquid is removed from the tilted condenser plate by gravity forced shedding. In microgravity, proposed solutions include the use of surfaces with gradients in wettability [1], the use of electrowetting [2], and shearing airflow [3]. In this talk, shear shedding results for a variety of surface (hydrophilic to superhydrophobic (extremely water repelling)) will be presented. Surface science and aerodynamics are used to reveal fundamental parameters controlling incipient motion for drops exposed to shearing airflow. It is found that wetting parameters such as contact angle and surface tension are very influential in determining the minimum required air velocity for drop shedding. Based on experimental results for drops of water and hexadecane (0.5-100 l) on PMMA, Teflon, and a superhydrophobic aluminum surface, an exponential function is proposed that relates the critical air velocity for shedding to the ratio of drop base length to projected area. The results for the water systems can be collapsed to a self similar curve by normalization, which also explains results from other researchers. Since shedding from superhydrophobic surfaces (SHS) is seen to be easier compared to other surfaces, the behaviour of SHS is also probed in this talk. SHS have space-based applications to shedding, self cleaning, anti-icing (spacecraft launch/re-entry), anti-fouling, fluid actuation, and decreased fluid friction. The mechanism for SHS is understood to be the existence of an air layer between large portions of the drop and solid. The first concrete visual evidence of this was gained performing a parabolic flight experiment with the ESA. Results of this experi-ment will be discussed, showing the extreme water repelling potential of SHS in microgravity, and demonstrating how the wetting behaviours seen (partial penetration, transition of wetting states, unpredicted contact angle behaviour) affect models of superhydrophobicity and the use of SHS to both space and Earth based applications. 1) Darhuber, A. A.; Troian, S. M. Annual Review of Fluid Mechanics 2005, 425-455. 2) Berthier, J.; Dubois, P.; Clementz, P.; Claustre, P.; Peponnet, C.; Fouillet, Y. Sensors and Actuators A: Physical 2007, 134, 471-479. 3) Milne, A. J. B.; Amirfazli, A. Langmuir 2009, 25, 14155-14164.

Milne, Andrew; Amirfazli, Alidad

270

A bioinspired planar superhydrophobic microboat  

NASA Astrophysics Data System (ADS)

In nature, a frog can easily rest on a lotus leaf even though the frog's weight is several times the weight of the lotus leaf. Inspired by the lotus leaf, we fabricated a planar superhydrophobic microboat (SMB) with a superhydrophobic upper surface on a PDMS sheet which was irradiated by a focused femtosecond laser. The SMB can not only float effortlessly over the water surface but can also hold up some heavy objects, exhibiting an excellent loading capacity. The water surface is curved near the edge of the upper surface and the SMB's upper edge is below the water level, greatly enhancing the displacement. Experimental results and theoretical analysis demonstrate that the superhydrophobicity on the edge of the upper surface is responsible for the SMB's large loading capacity. Here, we call it the ‘superhydrophobic edge effect’.

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

2014-03-01

271

On the possibility of superhydrophobic behavior for hydrophilic materials  

Microsoft Academic Search

It has been recognized well that it is necessary to achieve superhydrophobic surfaces on intrinsically hydrophobic materials. However, recently experiments have demonstrated that it is possible to fabricate superhydrophobic surfaces on intrinsically hydrophilic materials by creating adequate roughness. In this study, such a possibility for superhydrophobicity on a hydrophilic surface with an intrinsic contact angle (CA) of 80°, with a

X. S. Cui; W. Li

2010-01-01

272

Nanostructured Surface by Self-Assembly of Carbon Nanotubes for Bio-Analysis  

NASA Astrophysics Data System (ADS)

A nanostructured surface was designed and created by synthesizing Carbon Nanotubes (CNTs) on a plane substrate. Multi-walled carbon nanotubes (MWNTs) were synthesized on a Si/SiO2 substrate by alcohol catalytic chemical vapor deposition (ACCVD). The MWNTs were vertically synthesized on the surface, and the structure and characteristics of the surface, such as wettability, were evaluated. The surface with the MWNTs was also treated by coating with Au and subsequent plasma irradiation, in order to change the wettability from hydrophobic to hydrophilic. The results of wettability tests show that the surface with the MWNT film behaved as a super-hydrophobic surface before coating with Au and plasma irradiation, but behaved as a super-hydrophilic surface after coating with Au and plasma irradiation. Furthermore, experiments using water droplets on the MWNTs and subsequent drying was carried out, and the resulting changes in the structure and characteristics of the MWNTs were evaluated using scanning electron microscopy (SEM). The MWNTs subjected to plasma irradiation were found to clump together forming bundles after dropping water and drying; we found that the CNTs moved after the water was dropped on them. These results show that highly dense CNTs with self-assembled structures can be realized for potential applications as microreactors.

Kobayashi, Ryuichi; Yang, Ming

273

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

274

Super-hydrophobic transparent surface by femtosecond laser micro-patterned catalyst thin film for carbon nanotube cluster growth  

Microsoft Academic Search

In this work, super-hydrophobic surfaces were fabricated by femtosecond laser micro-machining and chemical vapor deposition\\u000a to constitute hybrid scale micro\\/nano-structures formed by carbon nanotube (CNT) clusters. Nickel thin-film microstructures,\\u000a functioning as CNT growth catalyst, precisely control the distribution of the CNT clusters. To obtain minimal heat-affected\\u000a zones, femtosecond laser was used to trim the nickel thin-film coating. Plasma treatment was

M. Tang; M. H. Hong; Y. S. Choo; Z. Tang; Daniel H. C. Chua

2010-01-01

275

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

276

Facile preparation of super durable superhydrophobic materials.  

PubMed

The low stability, complicated and expensive fabrication procedures seriously hinder practical applications of superhydrophobic materials. Here we report an extremely simple method for preparing super durable superhydrophobic materials, e.g., textiles and sponges, by dip coating in fluoropolymers (FPs). The morphology, surface chemical composition, mechanical, chemical and environmental stabilities of the superhydrophobic textiles were investigated. The results show how simple the preparation of super durable superhydrophobic textiles can be! The superhydrophobic textiles outperform their natural counterparts and most of the state-of-the-art synthetic superhydrophobic materials in stability. The intensive mechanical abrasion, long time immersion in various liquids and repeated washing have no obvious influence on the superhydrophobicity. Water drops are spherical in shape on the samples and could easily roll off after these harsh stability tests. In addition, this simple dip coating approach is applicable to various synthetic and natural textiles and can be easily scaled up. Furthermore, the results prove that a two-tier roughness is helpful but not essential with regard to the creation of super durable superhydrophobic textiles. The combination of microscale roughness of textiles and materials with very low surface tension is enough to form super durable superhydrophobic textiles. According to the same procedure, superhydrophobic polyurethane sponges can be prepared, which show high oil absorbency, oil/water separation efficiency and stability. PMID:25069050

Wu, Lei; Zhang, Junping; Li, Bucheng; Fan, Ling; Li, Lingxiao; Wang, Aiqin

2014-10-15

277

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

278

Superhydrophobic surfaces allow probing of exosome self organization using X-ray scattering  

NASA Astrophysics Data System (ADS)

Drops of exosome dispersions from healthy epithelial colon cell line and colorectal cancer cells were dried on a superhydrophobic PMMA substrate. The residues were studied by small- and wide-angle X-ray scattering using both a synchrotron radiation micrometric beam and a high-flux table-top X-ray source. Structural differences between healthy and cancerous cells were detected in the lamellar lattices of the exosome macro-aggregates.Drops of exosome dispersions from healthy epithelial colon cell line and colorectal cancer cells were dried on a superhydrophobic PMMA substrate. The residues were studied by small- and wide-angle X-ray scattering using both a synchrotron radiation micrometric beam and a high-flux table-top X-ray source. Structural differences between healthy and cancerous cells were detected in the lamellar lattices of the exosome macro-aggregates. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr34032e

Accardo, Angelo; Tirinato, Luca; Altamura, Davide; Sibillano, Teresa; Giannini, Cinzia; Riekel, Christian; di Fabrizio, Enzo

2013-02-01

279

Superhydrophobic conductive carbon nanotube coatings for steel.  

PubMed

We report the synthesis of superhydrophobic coatings for steel using carbon nanotube (CNT)-mesh structures. The CNT coating maintains its structural integrity and superhydrophobicity even after exposure to extreme thermal stresses and has excellent thermal and electrical properties. The coating can also be reinforced by optimally impregnating the CNT-mesh structure with cross-linked polymers without significantly compromising on superhydrophobicity and electrical conductivity. These superhydrophobic conductive coatings on steel, which is an important structural material, open up possibilities for many new applications in the areas of heat transfer, solar panels, transport of fluids, nonwetting and nonfouling surfaces, temperature resilient coatings, composites, water-walking robots, and naval applications. PMID:19281157

Sethi, Sunny; Dhinojwala, Ali

2009-04-21

280

Superhydrophobicity of a material made from multiwalled carbon nanotubes  

Microsoft Academic Search

Superhydrophobic carbon nanotubes (CNTs) were prepared by low-pressure CF4 glow plasma to provide roughness and fluorination in CNTs. The water droplet falling freely on the superhydrophobic CNT powders bounced dynamically. The superhydrophobicity resulted from the combined effects of the chemical modification and surface roughness. Using the contact angles obtained from the capillary rise method based on the Washburn equation, the

Yong Cheol Hong; Han Sup Uhm

2006-01-01

281

Design of superhydrophobic porous coordination polymers through the introduction of external surface corrugation by the use of an aromatic hydrocarbon building unit.  

PubMed

We demonstrate a new approach to superhydrophobic porous coordination polymers by incorporating an anisotropic crystal morphology featuring a predominant surface that is highly corrugated and terminated by aromatic hydrocarbon moieties. The resulting low-energy surface provides particularly promising hydrophobic properties without the need for postsynthetic modifications or surface processing that would block the porosity of the framework. Consequently, hydrophobic organic molecules and water vapor are able to penetrate the surface and be densely accommodated within the pores, whereas bulk water is repelled as a result of the exterior surface corrugation derived from the aromatic surface groups. This study provides a new strategy for the design and development of superhydrophobic porous materials. PMID:24975561

Rao, Koya Prabhakara; Higuchi, Masakazu; Sumida, Kenji; Furukawa, Shuhei; Duan, Jingui; Kitagawa, Susumu

2014-07-28

282

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

283

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

284

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

285

Lattice Boltzmann modeling of droplet condensation on superhydrophobic nanoarrays.  

PubMed

Droplet nucleation and growth on superhydrophobic nanoarrays is simulated by employing a multiphase, multicomponent lattice Boltzmann (LB) model. Three typical preferential nucleation modes of condensate droplets are observed through LB simulations with various geometrical parameters of nanoarrays, which are found to influence the wetting properties of nanostructured surfaces significantly. The droplets nucleated at the top of posts (top nucleation) or in the upside interpost space of nanoarrays (side nucleation) will generate a nonwetting Cassie state, while the ones nucleated at the bottom corners between the posts of nanoarrays (bottom nucleation) produce a wetting Wenzel state. The simulated time evolutions of droplet pressures at different locations are analyzed, which offers insight into the underlying physics governing the motion of droplets growing from different nucleation modes. It is demonstrated that the nanostructures with taller posts and a high ratio of post height to interpost space (H/S) are beneficial to produce the top- and side-nucleation modes. The simulated wetting states of condensate droplets on the nanostructures, having various geometrical configurations, compare reasonably well with experimental observations. The established relationship between the geometrical parameters of nanoarrays and the preferential nucleation modes of condensate droplets provides guidance for the design of nanoarrays with desirable anticondensation superhydrophobic properties. PMID:25275954

Zhang, Qingyu; Sun, Dongke; Zhang, Youfa; Zhu, Mingfang

2014-10-28

286

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; Gumowski, Konrad; Zhou, Feng; Liu, Weimin

2012-10-01

287

Wetting, superhydrophobicity, and icephobicity in biomimetic composite materials  

NASA Astrophysics Data System (ADS)

Recent developments in nano- and bio-technology require new materials. Among these new classes of materials which have emerged in the recent years are biomimetic materials, which mimic structure and properties of materials found in living nature. There are a large number of biological objects including bacteria, animals and plants with properties of interest for engineers. Among these properties is the ability of the lotus leaf and other natural materials to repel water, which has inspired researchers to prepare similar surfaces. The Lotus effect involving roughness-induced superhydrophobicity is a way to design nonwetting, self-cleaning, omniphobic, icephobic, and antifouling surfaces. The range of actual and potential applications of superhydrophobic surfaces is diverse including optical, building and architecture, textiles, solar panels, lab-on-a-chip, microfluidic devices, and applications requiring antifouling from biological and organic contaminants. In this thesis, in chapter one, we introduce the general concepts and definitions regarding the wetting properties of the surfaces. In chapter two, we develop novel models and conduct experiments on wetting of composite materials. To design sustainable superhydrophobic metal matrix composite (MMC) surfaces, we suggest using hydrophobic reinforcement in the bulk of the material, rather than only at its surface. We experimentally study the wetting properties of graphite-reinforced Al- and Cu-based composites and conclude that the Cu-based MMCs have the potential to be used in the future for the applications where the wear-resistant superhydrophobicity is required. In chapter three, we introduce hydrophobic coating at the surface of concrete materials making them waterproof to prevent material failure, because concretes and ceramics cannot stop water from seeping through them and forming cracks. We create water-repellant concretes with CA close to 160o using superhydrophobic coating. In chapter four, experimental data are collected in terms of oleophobicity especially when underwater applications are of interest. We develop models for four-phase rough interface of underwater oleophobicity and develop a novel approach to predict the CA of organic liquid on the rough surfaces immersed in water. We investigate wetting transition on a patterned surface in underwater systems, using a phase field model. We demonstrated that roughening on an immersed solid surface can drive the transition from Wenzel to Cassie-Baxter state. This discovery improves our understanding of underwater systems and their surface interactions during the wetting phenomenon and can be applied for the development of underwater oil-repellent materials which are of interest for various applications in the water industry, and marine devices. In chapter five, we experimentally and theoretically investigate the icephobicity of composite materials. A novel comprehensive definition of icephobicity, broad enough to cover a variety of situations including low adhesion strength, delayed ice crystallization, and bouncing is determined. Wetting behavior and ice adhesion properties of various samples are theoretically and experimentally compared. We conclude superhydrophobic surfaces are not necessarily icephobic. The models are tested against the experimental data to verify the good agreement between them. The models can be used for the design of novel superhydrophobic, oleophobic, omniphobic and icephobic composite materials. Finally we conclude that creating surface micro/nanostructures using mechanical abrasion or chemical etching as well as applying low energy materials are the most simple, inexpensive, and durable techniques to create superhydrophobic, oleophobic, and icephobic materials.

Hejazi, Vahid

288

Superhydrophobic materials for drug delivery  

NASA Astrophysics Data System (ADS)

Superhydrophobicity is a property of material surfaces reflecting the ability to maintain air at the solid-liquid interface when in contact with water. These surfaces have characteristically high apparent contact angles, by definition exceeding 150°, as a result of the composite material-air surface formed under an applied water droplet. Superhydrophobic surfaces were first discovered on naturally occurring substrates, and have subsequently been fabricated in the last several decades to harness these favorable surface properties for a number of emerging applications, including their use in biomedical settings. This work describes fabrication and characterization of superhydrophobic 3D materials, as well as their use as drug delivery devices. Superhydrophobic 3D materials are distinct from 2D superhydrophobic surfaces in that air is maintained not just at the surface of the material, but also within the bulk. When the superhydrophobic 3D materials are submerged in water, water infiltrates slowly and continuously as a new water-air-material interface is formed with controlled displacement of air. Electrospinning and electrospraying are used to fabricate superhydrophobic 3D materials utilizing blends of the biocompatible polymers poly(epsilon-caprolactone) and poly(caprolactone-co-glycerol monostearate) (PGC-C18). PGC-C18 is significantly more hydrophobic than PCL (contact angle of 116° versus 83° for flat materials), and further additions of PGC-C18 into electrospun meshes and electrosprayed coatings affords increased stability of the entrapped air layer. For example, PCL meshes alone (500 mum thick) take 10 days to fully wet, and with 10% or 30% PGC-C18 addition wetting rates are dramatically slowed to 60% wetted by 77 days and 4% by 75 days, respectively. Stability of the superhydrophobic materials can be further probed with a variety of physio-chemical techniques, including pressure, surfactant containing solutions, and solvents of varying surface tension. Superhydrophobicity is shown to be enhanced with further increases in PGC-C18 content and surface roughness (a decrease in fiber size). We demonstrate the utility of superhydrophobicity as a method for drug delivery. When the camptothecin derivatives SN-38 and CPT-11 are encapsulated within electrospun meshes, changes in air layer stability (due to changes in PGC-C18 content) dictate the rate of drug release by controlling the rate in which water can permeate into the porous 3D electrospun structure. Drug release can be tuned from 2 weeks to >10 weeks from 300 mum meshes, and meshes effectively kill a variety of cancer cell lines (lung, colon, breast) when utilized in a cytotoxicity assay. After determining that air could be used to control the rate of drug release, superhydrophobic 3D materials are explored for three applications. First, meshes are considered as a potential combination reinforcement-drug delivery device for use in resectable colorectal cancer. Second, removal of the air layer in superhydrophobic meshes is used as a method to trigger drug release. The pressure generated from high-intensity focused ultrasound (0.75-4.25 MPa) can remove the air layer spatially and temporally, allowing drug release to be controlled with application of a sufficient treatment. Third, "connective" electrosprayed coatings are deposited on chemically distinct material surfaces, which are both three-dimensional and mechanically robust. In summary, superhydrophobic 3D materials are fabricated and characterized, and are utilized as drug delivery devices. Controlled air removal from these materials offers an entirely new strategy for drug delivery, and is promising for the applications considered in this work as well as many others.

Yohe, Stefan Thomas

289

Towards design rules for covalent nanostructures on metal surfaces.  

PubMed

The covalent molecular assembly on metal surfaces is explored, outlining the different types of applicable reactions. Density functional calculations for on-surface reactions are shown to yield valuable insights into specific reaction mechanisms and trends across the periodic table. Finally, it is shown how design rules could be derived for nanostructures on metal surfaces. PMID:24338925

Björk, Jonas; Hanke, Felix

2014-01-20

290

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

291

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

NASA Astrophysics Data System (ADS)

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.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. Electronic supplementary information (ESI) available: Experimental details for the fabrication of ball-like structured Cu(OH)2; XRD of Cu(OH)2; SEM images of the surfaces after reaction in an ethanol solution of n-octyl mercaptan with different concentrations; dependence of the contact angles on the chain length of the thiols; contact angle on the flat copper surface and the discussion of the super-hydrophobicity of the as-prepared surfaces; SEM images of the surfaces after reaction with different thiols at a constant time. See DOI: 10.1039/c3nr34256e

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

2013-03-01

292

Effect of the size of silica nanoparticles on wettability and surface chemistry of sol-gel superhydrophobic and oleophobic nanocomposite coatings  

NASA Astrophysics Data System (ADS)

Superhydrophobic sol-gel nanocomposite coatings have been fabricated by incorporating silica nanoparticles with different particle sizes separately in an acid-catalyzed sol of methyltriethoxysilane (MTEOS). Water contact angle (WCA) of the coatings increased with increase in the concentration of silica nanoparticles in both the cases. The coatings became superhydrophobic at an optimum silica concentration. The water repellency was further improved by the addition of fluoroalkylsilane (FAS). The optimum silica concentration was found to depend on the size of silica nanoparticles and FAS content and the coatings exhibited WCA of about 160° and water sliding angle (WSA) of <2°. FAS addition also improved the oleophobicity of the coatings. The coatings exhibited oil-repellency with a lubricant oil contact angle of 126° and ethylene glycol contact angle of 153.3°. Surface morphology of the coatings analyzed using field emission scanning electron microscopy (FESEM) showed a rough surface with microscale bumps and nanoscale pores. XPS was used to study the surface composition of the coatings. The superhydrophobic property of the coatings was due to the synergistic effect of surface chemistry and surface microstructure and can be explained using Cassie-Baxter model.

Lakshmi, R. V.; Bera, Parthasarathi; Anandan, C.; Basu, Bharathibai J.

2014-11-01

293

Super-Hydrophobic Multi-Walled Carbon Nanotube Coatings for Stainless Steel  

E-print Network

We have taken advantage of the native surface roughness and the iron content of AISI 316 stainless steel to direct grow multi-walled carbon nanotube (MWCNT) random networks by chemical vapor deposition (CVD) at low-temperature ($treatments. In this way, super-hydrophobic MWCNT films on stainless steel sheets were obtained, exhibiting high contact angle values ($154^{\\circ}$) and high adhesion force (high contact angle hysteresis). Furthermore, the investigation of MWCNT films at scanning electron microscopy (SEM) reveals a two-fold hierarchical morphology of the MWCNT random networks made of hydrophilic carbonaceous nanostructures on the tip of hydrophobic MWCNTs. Owing to the Salvinia effect, the hydrophobic and hydrophilic composite surface of the MWCNT films supplies a stationary super-hydrophobic coating for conductive stainless steel. This biomimetical inspired surface not only may prevent corrosion and fouling but also could provide low-friction and drag-reduction.

Francesco De Nicola; Paola Castrucci; Manuela Scarselli; Francesca Nanni; Ilaria Cacciotti; Maurizio De Crescenzi

2015-03-18

294

Using sharp transitions in contact angle hysteresis to move, deflect, and sort droplets on a superhydrophobic surface  

NASA Astrophysics Data System (ADS)

In order to make an effective droplet-based microfluidic device, one must be able to precisely control a number of key processes including droplet positioning, motion, coalescence, mixing, and sorting. In a typical three-dimensional device, these processes are well understood. However, for planar or open microfluidic devices, many of these processes have yet to be demonstrated. In this paper, a series of superhydrophobic surfaces created by sanding Teflon are used as the microfluidics platform. The superhydrophobic surfaces used in this study all have advancing contact angles of 150° but have contact angle hysteresis that were varied smoothly from 3° to 30° as the grit size of the sandpaper is changed. Drop motion was initiated by placing the surface on an inclined plane. To deflect and move droplets along the surface, single and multiple transition lines in receding contact angle were created by spatially varying the surface roughness of the Teflon. The degree of droplet deflection was studied as a function of droplet size, droplet speed, and the angle that the transition line in contact angle hysteresis made with the principle direction of droplet motion. Droplet deflections across a single transition as large as 140% the droplet diameter were observed. The droplet deflection was found to increase with increasing difference in contact angle hysteresis across the transition and increasing transition angles up to about 40°. The largest deflections were observed over a very narrow range of droplet velocities corresponding to a range in Weber numbers between 0.1 and 0.2. This narrow range in Weber number suggests that transitions in receding contact angle can be used to sort drops based on velocity, size or wetting properties with a strong degree of selectivity. The direction of deflection was observed to change depending on whether the drops transitioned from a region of low to high or high to low contact angle hysteresis. In a transition from low to high hysteresis, a large portion of the drop's kinetic energy is converted into interfacial energy as the receding contact line of the drop is deformed. Alternatively, a transition from high to low hysteresis results in some of the drop's interfacial energy converted into kinetic energy as the deformation of the droplet is reduced. The result is either a reduction or increase in the droplet's velocity normal to the line of transition depending on the sign of the transition in contact angle hysteresis. Finally, single and multiple stripes of different contact angle hysteresis are also shown to be effective at deflecting droplets.

Nilsson, Michael A.; Rothstein, Jonathan P.

2012-06-01

295

Molecular imaging with surface-enhanced CARS on nanostructures  

NASA Astrophysics Data System (ADS)

Strongly localized electromagnetic fields in the vicinity of nanoparticles and nanogaps greatly enhance spectroscopic signals near them such as in surface-enhanced Raman spectroscopy (SERS). In this work we combine this plasmonic surface enhancement with coherent anti-Stokes Raman spectroscopy (CARS) on reproducible nanostructured surfaces. Surface-enhanced CARS (SECARS) gives rise to very strong enhancements and we find that an enhancement of ~105 can be obtained over standard CARS. Using our nanostructured surfaces, we demonstrate strong correlation between plasmon resonances and surface-enhanced CARS intensities. Furthermore, fast imaging of molecular monolayers is performed. Our work paves the way for reliable single molecule Raman spectroscopy and fast molecular imaging on plasmonic surfaces.

Steuwe, Christian; Kaminski, Clemens F.; Baumberg, Jeremy J.; Mahajan, Sumeet

2012-03-01

296

Fabrication of Co3O4 hierarchically superhydrophobic boat-like hollow cages at the silicon surface  

NASA Astrophysics Data System (ADS)

By employing a simple bottom-up method for the first time and using ideas learned from nature, especially from the lotus leaf, we fabricated unique Co3O4 hierarchical boat-like hollow cages about 30 µm in length and 8 µm in width at the middle constituted of many nanorods and nanoparticles. The various morphologies of the products can be tailored from nanoparticles to nanorods and to microcages by tuning the concentration of Co(NO3)2·6H2O. We believe that ammonia employed in this method plays not only the role of ligand to ensure the oxidation of Co2+ to Co3+ but also helps with the variation of concentration for the final morphologies. The products, which might be used as catalysts and microreactors, show superhydrophobic properties after chemical modification with poly(dimethylsiloxane) vinyl-terminated (PDMSVT) compound. It is confirmed that the synergic effect of the surface morphology and the surface free energy contribute to this unique surface water repellence.

Guo, Zhiguang; Liu, Weimin; Su, Bao-Lian

2008-11-01

297

Superhydrophilicity to superhydrophobicity transition of picosecond laser microstructured aluminum in ambient air.  

PubMed

Studies regarding the wettability transition of micro- and nano-structured metal surfaces over time are frequently reported, but there seems to be no generally accepted theory that explains this phenomenon. In this paper, we aim to clarify the mechanism underlying the transition of picosecond laser microstructured aluminum surfaces from a superhydrophilic nature to a superhydrophobic one under ambient conditions. The aluminum surface studied exhibited superhydrophilicity immediately after being irradiated by a picosecond laser. However, the contact angles on the surface increased over time, eventually becoming large enough to classify the surface as superhydrophobic. The storage conditions significantly affected this process. When the samples were stored in CO2, O2 and N2 atmospheres, the wettability transition was restrained. However, the transition was accelerated in atmosphere that was rich with organic compounds. Moreover, the superhydrophobic surface could recover their original superhydrophilicity by low temperature annealing. A detailed XPS analysis indicated that this wettability transition process was mainly caused by the adsorption of organic compounds from the surrounding atmosphere onto the oxide surface. PMID:25481645

Long, Jiangyou; Zhong, Minlin; Zhang, Hongjun; Fan, Peixun

2015-03-01

298

Nanostructured surfaces for surface plasmon resonance spectroscopy and imaging  

NASA Astrophysics Data System (ADS)

Surface plasmon resonance (SPR) has achieved widespread recognition as a sensitive, label-free, and versatile optical method for monitoring changes in refractive index at a metal-dielectric interface. Refractive index deviations of 10-6 RIU are resolvable using SPR, and the method can be used in real-time or ex-situ. Instruments based on carboxymethyl dextran coated SPR chips have achieved commercial success in biological detection, while SPR sensors can also be found in other fields as varied as food safety and gas sensing. Chapter 1 provides a physical background of SPR sensing. A brief history of the technology is presented, and publication data are included that demonstrate the large and growing interest in surface plasmons. Numerous applications of SPR sensors are listed to illustrate the broad appeal of the method. Surface plasmons (SPs) and surface plasmon polaritions (SPPs) are formally defined, and important parameters governing their spatial behavior are derived from Maxwell's equations and appropriate boundary conditions. Physical requirements for exciting SPs with incident light are discussed, and SPR imaging is used to illustrate the operating principle of SPR-based detection. Angle-tunable surface enhanced infrared absorption (SEIRA) of polymer vibrational modes via grating-coupled SPR is demonstrated in Chapter 2. Over 10-fold enhancement of C-H stretching modes was found relative to the absorbance of the same film in the absence of plasmon excitation. Modeling results are used to support and explain experimental observations. Improvements to the grating coupler SEIRA platform in Chapter 2 are explored in Chapters 3 and 4. Chapter 3 displays data for two sets of multipitch gratings: one set with broadly distributed resonances with the potential for multiband IR enhancement and the other with finely spaced, overlapping resonances to form a broadband IR enhancement device. Diffraction gratings having multiple periods were fabricated using a Lloyd's mirror interferometer to perform multiple exposures at multiple angles before developing. Precise control of the resonance position is shown by locating three SPR dips at predetermined wavenumbers of 5000, 4000, and 3000 cm-1, respectively. A set of three gratings, each having four closely spaced resonances is employed to show how the sensor response could be broadened. The work in Chapter 3 shows potential for simultaneous enhancement of multiple vibrational modes; the multiband approach might find application for modes at disparate locations within the IR spectrum, while the broadband approach may allow concurrent probing of broad single modes or clusters of narrow modes within a particular neighborhood of the spectrum. Chapter 4 uses the rigorous coupled-wave analysis (RCWA) method to numerically explore another facet of the nanostructure-based tunability of grating-baed SPR sensing. The work in this chapter illustrates how infrared signal enhancement could be tailored by through adjustment of the grating amplitude. Modeled infrared reflection absorption (IRRAS) spectra and electric field distributions were generated for several nanostructured grating configurations. It was found that there exists a critical amplitude value for a given grating pitch where the plasmon response achieves a maximum. Amplitudes greater than this critical value produce a broader and attenuated plasmon peak, while smaller amplitudes produce a plasmon resonance that is not as intense. Field simulations show how amplitudes nearer the critical amplitude resulted in large increases in the electric field within an analyte film atop the sensor surface, and the relative strength of the increased field is predictable based on the appearance of the IRRAS spectra. It is believed that these larger fields are the cause of observed enhanced absorption. Published reports pertaining to interactions of SPs with molecular resonance and to diffraction-based tracking of plasmons without a spectrometer are included in the Appendix to this thesis. In the first of the two reports, it is shown that plasmons

Petefish, Joseph W.

299

Table of Contents Superhydrophilic and Superhydrophobic Nanostructured Surfaces for Microfluidics and Thermal Management 4-1  

E-print Network

for Microfluidics and Thermal Management 4-1 Design of a Micro-breather for Venting Vapor Slugs in Two-phase Microchannels 4-2 Microfluidic Patterning of P-Selectin for Cell Separation through Rolling 4-3 Electrical Membranes in Thermoplastic Microfluidic Devices 4-5 Teflon Films for Chemically-inert Microfluidic Valves

Voldman, Joel

300

Electrostatic charging of jumping droplets on superhydrophobic nanostructured surfaces : fundamental study and applications  

E-print Network

Condensation is a ubiquitous process often observed in nature and harnessed in many industrial processes such as power generation, desalination, thermal management, and building environmental control. Recent advancements ...

Preston, Daniel J. (Daniel John)

2014-01-01

301

Emerging applications of superhydrophilic-superhydrophobic micropatterns.  

PubMed

Water on superhydrophilic surfaces spreads or is absorbed very quickly, and exhibits water contact angles close to zero. We encounter superhydrophilic materials in our daily life (e.g., paper, sponges, textiles) and they are also ubiquitous in nature (e.g., plant and tree leaves, Nepenthes pitcher plant). On the other hand, water on completely non-wettable, superhydrophobic surfaces forms spherical droplets and rolls off the surface easily. One of the most well-known examples of a superhydrophobic surface is the lotus leaf. Creating novel superhydrophobic surfaces has led to exciting new properties such as complete water repellency, self-cleaning, separation of oil and water, and antibiofouling. However, combining these two extreme states of superhydrophilicity and superhydrophobicity on the same surface in precise two-dimensional micropatterns opens exciting new functionalities and possibilities in a wide variety of applications from cell, droplet, and hydrogel microarrays for screening to surface tension confined microchannels for separation and diagnostic devices. In this Progress Report, we briefly describe the methods for fabricating superhydrophilic-superhydrophobic patterns and highlight some of the newer and emerging applications of these patterned substrates that are currently being explored. We also give an outlook on current and future applications that would benefit from using such superhydrophilic-superhydrophobic micropatterns. PMID:23345109

Ueda, Erica; Levkin, Pavel A

2013-03-01

302

Near-infrared light responsive multi-compartmental hydrogel particles synthesized through droplets assembly induced by superhydrophobic surface.  

PubMed

Light-responsive hydrogel particles with multi-compartmental structure are useful for applications in microreactors, drug delivery and tissue engineering because of their remotely-triggerable releasing ability and combinational functionalities. The current methods of synthesizing multi-compartmental hydrogel particles typically involve multi-step interrupted gelation of polysaccharides or complicated microfluidic procedures with limited throughput. In this study, a two-step sequential gelation process is developed to produce agarose/alginate double network multi-compartmental hydrogel particles using droplets assemblies induced by superhydrophobic surface as templates. The agarose/alginate double network multi-compartmental hydrogel particles can be formed with diverse hierarchical structures showing combinational functionalities. The synthesized hydrogel particles, when loaded with polypyrrole (PPy) nanoparticles that act as photothermal nanotransducers, are demonstrated to function as near-infrared (NIR) light triggerable and deformation-free hydrogel materials. Periodic NIR laser switching is applied to stimulate these hydrogel particles, and pulsatile release profiles are collected. Compared with massive reagents released from single-compartmental hydrogel particles, more regulated release profiles of the multi-compartmental hydrogel particles are observed. PMID:25059988

Luo, Rongcong; Cao, Ye; Shi, Peng; Chen, Chia-Hung

2014-12-10

303

An effective medium approach to predict the apparent contact angle of drops on super-hydrophobic randomly rough surfaces  

NASA Astrophysics Data System (ADS)

The apparent contact angle of large 2D drops with randomly rough self-affine profiles is numerically investigated. The numerical approach is based upon the assumption of large separation of length scales, i.e. it is assumed that the roughness length scales are much smaller than the drop size, thus making it possible to treat the problem through a mean-field like approach relying on the large-separation of scales. The apparent contact angle at equilibrium is calculated in all wetting regimes from full wetting (Wenzel state) to partial wetting (Cassie state). It was found that for very large values of the roughness Wenzel parameter (rW > ?1/?cos??Y, where ?Y is the Young's contact angle), the interface approaches the perfect non-wetting condition and the apparent contact angle is almost equal to 180°. The results are compared with the case of roughness on one single scale (sinusoidal surface) and it is found that, given the same value of the Wenzel roughness parameter rW, the apparent contact angle is much larger for the case of a randomly rough surface, proving that the multi-scale character of randomly rough surfaces is a key factor to enhance superhydrophobicity. Moreover, it is shown that for millimetre-sized drops, the actual drop pressure at static equilibrium weakly affects the wetting regime, which instead seems to be dominated by the roughness parameter. For this reason a methodology to estimate the apparent contact angle is proposed, which relies only upon the micro-scale properties of the rough surface.

Bottiglione, F.; Carbone, G.

2015-01-01

304

Superhydrophobicity in perfection: the outstanding properties of the lotus leaf  

PubMed Central

Summary Lotus leaves have become an icon for superhydrophobicity and self-cleaning surfaces, and have led to the concept of the ‘Lotus effect’. Although many other plants have superhydrophobic surfaces with almost similar contact angles, the lotus shows better stability and perfection of its water repellency. Here, we compare the relevant properties such as the micro- and nano-structure, the chemical composition of the waxes and the mechanical properties of lotus with its competitors. It soon becomes obvious that the upper epidermis of the lotus leaf has developed some unrivaled optimizations. The extraordinary shape and the density of the papillae are the basis for the extremely reduced contact area between surface and water drops. The exceptional dense layer of very small epicuticular wax tubules is a result of their unique chemical composition. The mechanical robustness of the papillae and the wax tubules reduce damage and are the basis for the perfection and durability of the water repellency. A reason for the optimization, particularly of the upper side of the lotus leaf, can be deduced from the fact that the stomata are located in the upper epidermis. Here, the impact of rain and contamination is higher than on the lower epidermis. The lotus plant has successfully developed an excellent protection for this delicate epistomatic surface of its leaves. PMID:21977427

Ditsche-Kuru, Petra; Neinhuis, Christoph; Barthlott, Wilhelm

2011-01-01

305

Development and characterization of nanostructured-perlite-cementitious surface compounds  

Microsoft Academic Search

The effect of perlite loading on the thermal resistivity, solar reflectance and indirect tensile strength of Nanostructured\\u000a Cementitious Binder is studied. The main objective of this research is to constitute structural lightweight surface compounds\\u000a and to improve their thermal resistivity and reflectivity with suitable mechanical performances as a surface compound. Portland\\u000a White Cement (PWC) was partially substituted by nano clay.

M. S. Morsy; H. A. Aglan

2007-01-01

306

Electrodynamics simulations of surface plasmon behavior in metallic nanostructures  

Microsoft Academic Search

Realistic finite-difference time-domain simulations are carried to learn how to understand and control localized surface plasmons (LSP's) and traveling surface plasmon polaritons (SPP's) in metallic nanostructures. We show how to control the spatio-temporal behavior of LSP hot spots in cone-shaped metal nanoparticles. We discuss how to intensify and lengthen SPP's in thin metallic films. Finally, we discuss the relative roles

Stephen K. Gray; Tae-Woo Lee; Shih-Hui Chang; George C. Schatz

2005-01-01

307

Effects of long pulse width and high pulsing frequency on surface superhydrophobicity of polytetrafluoroethylene in quasi-direct-current plasma immersion ion implantation  

SciTech Connect

Long pulse, high frequency quasi-direct-current (dc) oxygen plasma immersion ion implantation (PIII) is utilized to create a superhydrophobic polytetrafluoroethylene (PTFE) surface with a water contact angle of over 150 deg. This technique allows the use of a high duty cycle without deleterious effects such as extensive sample heating encountered in conventional PIII. Scanning electron microscopy images review submicrometer-nanometer structures on the PTFE surface after long pulse, high frequency PIII indicative of ion implantation. On the other hand, plasma modification is the dominant effect in short pulse, low frequency PIII. Quasi-dc PIII is demonstrated to offer adjustable synergistic plasma and ion beam effects.

Kwok, Dixon T. K.; Wang Huaiyu; Yeung, Kelvin W. K.; Chu, Paul K. [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China); Zhang Yumei [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China); Department of Prosthodontics, School of Stomatology, Fourth Military Medical University, 145 Changle Xi Road, Xi'an 710032 (China)

2009-03-01

308

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. PMID:24717682

Schmidt, Franz-Philipp; Ditlbacher, Harald; Hohenester, Ulrich; Hohenau, Andreas; Hofer, Ferdinand; Krenn, Joachim R.

2014-01-01

309

Rational nanostructuring of surfaces for extraordinary icephobicity  

E-print Network

, also for anti-icing applications.25,26 Clearly, a rational approach to the design of surface texturing versus icing is needed to generate surfaces with extraordinary delay in ice formation.17,27 The anti-icing/surface/surrounding gas system is cooled in a slow, quasi-steady manner. The average nucleation delay time refers

Daraio, Chiara

310

Enantioselectivity on Surfaces with Chiral Nanostructures  

E-print Network

of chiral surfaces: surfaces modified by chiral organic adsorbates, surfaces of any naturally chiral bulk of amino acids that form proteins, the building blocks of life, and of DNA, which encodes the genetic by living organisms. As a result, it is necessary to produce many chiral compounds in enantiomerically pure

Gellman, Andrew J.

311

Surface-enhanced Raman spectroscopy of CdSe quantum dots on nanostructured plasmonic surfaces  

E-print Network

Surface-enhanced Raman spectroscopy of CdSe quantum dots on nanostructured plasmonic surfaces James they have not so far been used as Raman labels. Here we demonstrate resonant surface-enhanced Raman-16 cm2 molecule-1 .5 However in surface-enhanced Raman scattering SERS , plasmonic sur- faces enhance

Steiner, Ullrich

312

Nanostructured surfaces for microfluidics and sensing applications.  

SciTech Connect

The present work demonstrates the use of light to move liquids on a photoresponsive monolayer, providing a new method for delivering analyses in lab-on-chip environments for microfluidic systems. The light-driven motion of liquids was achieved on photoresponsive azobenzene modified surfaces. The surface energy components of azobenzene modified surfaces were calculated by Van Oss theory. The motion of the liquid was achieved by generation of a surface tension gradient by isomerization of azobenzene monolayers using UV and Visible light, thereby establishing a surface energy heterogeneity on the edge of the droplet. Contact angle measurements of various solvents were used to demonstrate the requirement for fluid motion.

Picraux, Samuel Thomas (Arizona State University); Piech, Marcin (United Technologies Corp.); Schneider, John F.; Vail, Sean (Arizona State University); Hayes, Mark A. (Arizona State University); Garcia, Anthony A.; Bell, Nelson Simmons; Gust, D (Arizona State University); Yang, Dongqing (Arizona State University)

2007-01-01

313

Dual responsive nanostructured surfaces for biomedical applications.  

PubMed

In this paper, we describe the construction and characteristics of thermoresponsive, thin nanostructured films prepared by layer-by-layer sequential assembly of chitosan-graft-NIPAAm and alginate. FTIR and (1)H NMR spectra have confirmed the introduction of NIPAAm moieties onto the chitosan backbone. The LCST of the synthesized copolymer was found to be around 31-33 °C. The formation of the polyelectrolyte multilayers containing the copolymer and alginate was followed in situ by quartz crystal microbalance with dissipation monitoring technique and ex situ by UV-vis measurements. Our results revealed the linear increase of the multilayer film growth and the influence of the presence of salt. Moreover, AFM analysis has confirmed that PNIPAAm is able to reconform upon temperature swaps even when combined with other layers in a polyelectrolyte multilayer, demonstrating that the nanoassemblies are thermoresponsive. Preliminary results showed that, upon reducing culture temperature below PNIPAAm LCST, a gradual detachment of cell sheets from these PNIPAAm-based coatings has occurred. PMID:21639130

Martins, Gabriela V; Mano, João F; Alves, Natália M

2011-07-01

314

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

315

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

316

Fabrics coated with lubricated nanostructures display robust omniphobicity.  

PubMed

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. PMID:24334333

Shillingford, Cicely; MacCallum, Noah; Wong, Tak-Sing; Kim, Philseok; Aizenberg, Joanna

2014-01-10

317

Nanostructured substrates for surface plasmon resonance sensors  

Microsoft Academic Search

Surface Plasmon Resonance (SPR) sensors are usually based on continuous thin metallic films and coupling of propagative plasmon (PP) modes using high index prism or grating. The quantitative monitoring of the surface evolution is performed by measuring either shift in angular or spectral dip position, or by reflectivity variation in the slope of the angulo- spectral coupling curve. Such sensors

Aurelien Duval; Mohamed Nakkach; Alain Bellemain; Julien Moreau; Michael Canva; Anuj Dhawan; Tuan Vo-Dinh

2011-01-01

318

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

319

Increasing the efficiency of photoelectric cells by nanostructuring their surface  

Microsoft Academic Search

A method of fabrication of nanostructured objects, which increases the efficiency of the photo-electric system used in the\\u000a conversion of energy of electromagnetic radiation into electric energy is suggested. The method is based on the formation\\u000a of metal nanodots on the basis of the surface layer of porous silicon, which concentrates the energy of electromagnetic radiation\\u000a due to localized plasmon

E. I. Vaganova; A. A. Mironenko; V. A. Paporkov; N. A. Rud; A. S. Rudyi; A. V. Prokaznikov

2011-01-01

320

Superhydrophobicity of polyvinylidene fluoride membrane fabricated by chemical vapor deposition from solution  

NASA Astrophysics Data System (ADS)

Due to the chemical stability and flexibility, polyvinylidene fluoride (PVDF) membranes are widely used as the topcoat of architectural membrane structures, roof materials of vehicle, tent fabrics, and so on. Further modified PVDF membrane with superhydrophobic property may be even superior as the coating layer surface. The lotus flower is always considered to be a sacred plant, which can protect itself against water, dirt, and dust. The superhydrophobic surface of lotus leaf is rough, showing the micro- and nanometer scale morphology. In this work, the microreliefs of lotus leaf were mimicked using PVDF membrane and the nanometer scale peaks on the top of the microreliefs were obtained by the method of chemical vapor deposition from solution. The surface morphology of PVDF membrane was investigated by scanning electronic microscopy (SEM) and atomic force microscope (AFM). Elemental composition analysis by X-ray photoelectron spectroscopy (XPS) revealed that the material of the nanostructure of PVDF membrane was polymethylsiloxane. On the lotus-leaf-like PVDF membrane, the water contact angle and sliding angle were 155° and 4°, respectively, exhibiting superhydrophobic property.

Zheng, Zhenrong; Gu, Zhenya; Huo, Ruiting; Ye, Yonghong

2009-05-01

321

Femtosecond surface plasmon interferometry with gold nanostructures  

E-print Network

We measure the ultrafast electron dynamics in gold via ultrafast surface plasmon interferometry. A new plasmonic microinterferometer with tilted slit-groove pair is used to unambiguously determine changes of real and ...

Temnov, Vasily V.

322

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

323

Nanostructured surface layer on metallic materials induced by surface mechanical attrition treatment  

Microsoft Academic Search

In terms of the grain refinement mechanism induced by plastic straining, a novel surface mechanical attrition treatment (SMAT) was developed for synthesizing a nanostructured surface layer on metallic materials in order to upgrade the overall properties and performance. In this paper, the SMAT technique and the microstructure of the SMAT surface layer will be described. The grain refinement mechanism of

K. Lu; J. Lu

2004-01-01

324

Engineering atomic and molecular nanostructures at surfaces  

Microsoft Academic Search

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,

Johannes V. Barth; Giovanni Costantini; Klaus Kern

2005-01-01

325

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

326

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

327

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

328

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

329

Superomniphobic, transparent, and antireflection surfaces based on hierarchical nanostructures.  

PubMed

Optical surfaces that can repel both water and oil have much potential for applications in a diverse array of technologies including self-cleaning solar panels, anti-icing windows and windshields for automobiles and aircrafts, low-drag surfaces, and antismudge touch screens. By exploiting a hierarchical geometry made of two-tier nanostructures, primary nanopillars of length scale ? 100-200 nm superposed with secondary branching nanostructures made of nanoparticles of length scale ? 10-30 nm, we have achieved static contact angles of more than 170° and 160° for water and oil, respectively, while the sliding angles were lower than 4°. At the same time, with respect to the initial flat bare glass, the nanotextured surface presented significantly reduced reflection (<0.5%), increased transmission (93.8% average over the 400 to 700 nm wavelength range), and very low scattering values (about 1% haze). To the authors' knowledge, these are the highest optical performances in conjunction with superomniphobicity reported to date in the literature. The primary nanopillars are monolithically integrated in the glass surface using lithography-free metal dewetting followed by reactive ion etching,1 while the smaller and higher surface area branching structure made of secondary nanoparticles are deposited by the NanoSpray2 combustion chemical vapor deposition (CCVD). PMID:24988148

Mazumder, Prantik; Jiang, Yongdong; Baker, David; Carrilero, Albert; Tulli, Domenico; Infante, Daniel; Hunt, Andrew T; Pruneri, Valerio

2014-08-13

330

Drag Reduction in Turbulent Flows over Super-hydrophobic Micro/nano Structured Biomimetic Surfaces  

E-print Network

of channel DH ­ Hydraulic diameter Understanding the influence of the surface on the drag designing the channel: · Set Bench Mark with Other Researches Similar DH (hydraulic diameter) sought Lengths manipulated to give same DH · Surfaces Geometrics Limitations Stages allow a 5 x 5 mm x-y range Time

Barthelat, Francois

331

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

E-print Network

with dimensions on the single-nanometer scale. Both Raman spectroscopy and photoluminescence data were used surface-enhanced Raman scattering (SERS) substrates by depositing metal onto the pillars. The SERS, photoluminescence, and surface-enhanced Raman scattering This article has been downloaded from IOPscience. Please

332

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

333

Wetting hysteresis and droplet roll off behavior on superhydrophobic surfaces by Katherine Marie Smyth.  

E-print Network

Various states of hydrophobic wetting and hysteresis are observed when water droplets are deposited on micro-post surfaces of different post densities. Hysteresis is commonly defined as the difference between the advancing ...

Smyth, Katherine Marie

2010-01-01

334

Electronic relaxation at a photoexcited nanostructured Si(111) surface  

NASA Astrophysics Data System (ADS)

A combination of time dependent density matrix and ab initio electronic structure methods provide details of the relaxation pathways of photo-induced charge redistribution at nanostructured semiconductor surfaces, giving their changes in energy and space over time. They are applied to a Ag3 cluster on a Si(111) surface, initially photoexcited by a short pulse, and show how surface-localized states added by the Ag cluster enhance electron transfer. Population density distributions in energy and in space, for valence and conduction bands, explore the energy band landscape of a Si slab, with various relaxation pathways ending up in a charge-separated state, with a hole in the Si slab and an electron in the adsorbed Ag cluster. Calculated electronic relaxation times for Si(111):H are of the same order as experimental values for similar semiconductor systems. Results from a reduced density matrix propagation over time, with Hamiltonian and rates parametrized from ab initio electronic structure calculations, give new insight on electronic dynamics at nanostructured surfaces.

Kilin, Dimitri; Micha, David A.

2010-03-01

335

Manufacturing a durable superhydrophobic polypropylene coating on aluminum alloy substrate by adding nano-titania nanoparticles.  

PubMed

A superhydrophobic polypropylene (PP) coating on the surface of aluminum alloy coupons is unstable because of the existence of metastable state in curing process. Nano-titania particles were added into PP solution to form hierarchical micro- and nano-structures of PP coatings on the surface of aluminum alloy coupons. The morphology of the coatings was observed with Scanning Electron Microscopy (SEM), and the corresponding structure and components were investigated with Energy Dispersive Spectrometer (EDS) and X-ray diffractometer (XRD), respectively. The results indicated that nano-TiO2 particles are the main nucleation cores in the curing of the coatings; PP in solution is enclosed in these cores and crystallizes gradually. The coatings can preserve the stable micro- and nano-structure on six months due to the nucleation action of nano-TiO2 particles, and its durable water contact angle (WCA) is about 164 +/- 1.5 degrees. PMID:24758042

Jiang, Haiyun; Wu, Ruomei; Hu, Zhongliang; Yuan, Zhiqing; Zhao, Xuehui; Liu, Qilong

2014-07-01

336

Selective bactericidal activity of nanopatterned superhydrophobic cicada Psaltoda claripennis wing surfaces.  

PubMed

The nanopattern on the surface of Clanger cicada (Psaltoda claripennis) wings represents the first example of a new class of biomaterials that can kill bacteria on contact based solely on its physical surface structure. As such, they provide a model for the development of novel functional surfaces that possess an increased resistance to bacterial contamination and infection. Their effectiveness against a wide spectrum of bacteria, however, is yet to be established. Here, the bactericidal properties of the wings were tested against several bacterial species, possessing a range of combinations of morphology and cell wall type. The tested species were primarily pathogens, and included Bacillus subtilis, Branhamella catarrhalis, Escherichia coli, Planococcus maritimus, Pseudomonas aeruginosa, Pseudomonas fluorescens, and Staphylococcus aureus. The wings were found to consistently kill Gram-negative cells (i.e., B. catarrhalis, E. coli, P. aeruginosa, and P. fluorescens), while Gram-positive cells (B. subtilis, P. maritimus, and S. aureus) remained resistant. The morphology of the cells did not appear to play any role in determining cell susceptibility. The bactericidal activity of the wing was also found to be quite efficient; 6.1?±?1.5?×?10(6) P. aeruginosa cells in suspension were inactivated per square centimeter of wing surface after 30-min incubation. These findings demonstrate the potential for the development of selective bactericidal surfaces incorporating cicada wing nanopatterns into the design. PMID:23250225

Hasan, Jafar; Webb, Hayden K; Truong, Vi Khanh; Pogodin, Sergey; Baulin, Vladimir A; Watson, Gregory S; Watson, Jolanta A; Crawford, Russell J; Ivanova, Elena P

2013-10-01

337

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

338

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

339

Superhydrophobic films from raspberry-like particles.  

PubMed

We report a robust procedure for preparing superhydrophobic hybrid films on which the advancing contact angle for water is about 165 degrees and the roll-off angle of a 10-muL water droplet is 3 +/- 1 degrees . Dual-size surface roughness, which mimics the surface topology of self-cleaning plant leaves, originates from well-defined silica-based raspberry-like particles that are covalently bonded to an epoxy-based polymer matrix. The roughened surface is chemically modified with a layer of poly(dimethylsiloxane) (PDMS). The robustness and simplicity of this procedure may make widespread applications of so-prepared superhydrophobic films possible. PMID:16277471

Ming, W; Wu, D; van Benthem, R; de With, G

2005-11-01

340

Origin of hydrophobicity in FIB-nanostructured Si surfaces.  

PubMed

Surface morphology has been demonstrated to influence the tribological properties at different scales, but the phenomena which occur at the nanoscale have not been completely understood. The present study reports on the effect of focused ion beam nanopatterning on coefficient of friction (CoF) and adhesion of Si(001) surface covered by native oxide. Regular arrays of nanogrooves reduce both CoF and adhesion, related to a hydrophobic character of the patterned surface, but this effect disappears as soon as the separation among the nanostructures approaches the microscopic scale. The dependence of this hydrophobic effect on the pitch is not linked to the corresponding contact area. It has been found that each nanostructure is surrounded by a low-friction region which extends some hundreds of nanometers from it. For pitches of 125 and 250 nm these low-friction regions completely overlap, generating a consistent decrease in CoF and adhesion, while for pitches of 500 and 1000 nm their effect is negligible. The low-friction regions were not observed in humidity-free ambient, indicating that they are the origin of patterns of hydrophobicity. PMID:23556503

Rota, Alberto; Tripathi, Manoj; Gazzadi, GianCarlo; Valeri, Sergio

2013-04-30

341

Nanostructuring of molybdenum and tungsten surfaces by low-energy helium ions  

SciTech Connect

The formation of metallic nanostructures by exposure of molybdenum and tungsten surfaces to high fluxes of low energy helium ions is studied as a function of the ion energy, plasma exposure time, and surface temperature. Helium plasma exposure leads to the formation of nanoscopic filaments on the surface of both metals. The size of the helium-induced nanostructure increases with increasing surface temperature while the thickness of the modified layer increases with time. In addition, the growth rate of the nanostructured layer also depends on the surface temperature. The size of the nanostructure appears linked with the size of the near-surface voids induced by the low energy ions. The results presented here thus demonstrate that surface processing by low-energy helium ions provides an efficient route for the formation of porous metallic nanostructures.

De Temmerman, Gregory; Bystrov, Kirill; Zielinski, Jakub J.; Balden, Martin; Matern, Gabriele; Arnas, Cecile; Marot, Laurent [FOM Institute DIFFER, Ducth Institute For Fundamental Energy Research, Association EURATOM-FOM, Trilateral Euregio Cluster, P.O. Box 1207, 3430 BE Nieuwegein (Netherlands); Max Planck Institute for Plasma Physics, EURATOM Association, 85748 Garching (Germany); Laboratoire PIIM, CNRS/Aix-Marseille Universit, 13397 Marseille (France); Department of Physics, University of Basel, Basel, CH-4056 (Switzerland)

2012-07-15

342

Impact of picolitre droplets on superhydrophobic surfaces with ultra-low spreading ratios  

E-print Network

for over a century.1 Important technological applications include: rapid cooling,2,3,4 delayed freezing,5,6,7,8 crop spraying,9 and inkjet printing. In recent years, work has been carried out to assess the feasibility of inkjet printing technology... of the drop towards its equilibrium diameter. Whilst liquid properties are important during drop impact,22 there exists strong evidence suggesting that surface properties not only affect the final static diameter of the droplet, but other key aspects...

Brown, P.S.; Berson, A.; Talbot, E.L.; Wood, T.J.; Schofield, W.C.E.; Bain, C.D.; Badyal, J.P.S.

2011-01-01

343

Strong Casimir force reduction through metallic surface nanostructuring  

PubMed Central

The Casimir force between bodies in vacuum can be understood as arising from their interaction with an infinite number of fluctuating electromagnetic quantum vacuum modes, resulting in a complex dependence on the shape and material of the interacting objects. Becoming dominant at small separations, the force has a significant role in nanomechanics and object manipulation at the nanoscale, leading to a considerable interest in identifying structures where the Casimir interaction behaves significantly different from the well-known attractive force between parallel plates. Here we experimentally demonstrate that by nanostructuring one of the interacting metal surfaces at scales below the plasma wavelength, an unexpected regime in the Casimir force can be observed. Replacing a flat surface with a deep metallic lamellar grating with sub-100?nm features strongly suppresses the Casimir force and for large inter-surfaces separations reduces it beyond what would be expected by any existing theoretical prediction. PMID:24071657

Intravaia, Francesco; Koev, Stephan; Jung, Il Woong; Talin, A. Alec; Davids, Paul S.; Decca, Ricardo S.; Aksyuk, Vladimir A.; Dalvit, Diego A. R.; López, Daniel

2013-01-01

344

Time-resolved imaging and immobilization study of biomaterials on hydrophobic and superhydrophobic surfaces by means of laser-induced forward transfer  

NASA Astrophysics Data System (ADS)

In this work, we present the generation of high velocity liquid jets of a photosynthetic biomaterial in buffer solution (i.e. thylakoid membranes) and a test solution, using the laser-induced forward transfer (LIFT) technique. The high impact pressure of the collision of the jets on solid substrates, ranging from 0.045?MPa–35?MPa, resulted in strong physical immobilization of the photosynthetic biomaterial on superhydrophobic (SH) poly(methyl methacrylate) (PMMA) surfaces and hydrophobic gold surfaces. The immobilization efficiency was evaluated by fluorescence microscopy, while time-resolved imaging of the LIFT process was carried out to study the corresponding LIFT dynamics. The results show that this simple, direct and chemical-linkers-free immobilization technique is valuable for several biosensors and microfluidic applications since it can be applied to a variety of hydrophobic and SH substrates, leading to the selective immobilization of the biomaterials, due to the high spatial printing resolution of the LIFT technique.

Boutopoulos, Christos; Chatzipetrou, Marianneza; Papathanasiou, Athanasios G.; Zergioti, Ioanna

2014-10-01

345

Durability of Hydrophobic Coatings for Superhydrophobic Aluminum Oxide  

SciTech Connect

Robust and easily produced Superhydrophobic surfaces are of great interest for mechanical applications, including drag reduction and MEMS. We produce novel superhydrophobic surfaces with several different coatings and tested the durability of each of these coatings with respect to long term immersion in water in order to determine the most long-lasting surface preparation. A pair of combinations of spin on polymers, surface features, and adhesion promoters was found that provide long term durability.

Jenner, Elliot [University of Pittsburgh; Barbier, Charlotte N [ORNL; D'Urso, Brian R [ORNL

2013-01-01

346

Cotton fabrics with single-faced superhydrophobicity.  

PubMed

This article reports on the fabrication of cotton fabrics with single-faced superhydrophobicity using a simple foam finishing process. Unlike most commonly reported superhydrophobic fabrics, the fabrics developed in this study exhibit asymmetric wettability on their two faces: one face showing superhydrophobic behavior (highly nonwetting or water-repellent characteristics) and the other face retaining the inherent hydrophilic nature of cotton. The superhydrophobic face exhibits a low contact angle hysteresis of ?(a)/?(r) = 151°/144° (?(a), advancing contact angle; ?(r), receding contact angle), which enables water drops to roll off the surface easily so as to endow the surface with well-known self-cleaning properties. The untreated hydrophilic face preserves its water-absorbing capability, resulting in 44% of the water-absorbing capacity compared to that of the original cotton samples with both sides untreated (hydrophilic). The single-faced superhydrophobic fabrics also retain moisture transmissibility that is as good as that of the original untreated cotton fabrics. They also show robust washing fastness with the chemical cross-linking process of hydrophobic fluoropolymer to fabric fibers. Fabric materials with such asymmetric or gradient wettability will be of great use in many applications such as unidirectional liquid transporting, moisture management, microfluidic systems, desalination of seawater, flow management in fuel cells, and water/oil separation. PMID:23186211

Liu, Yuyang; Xin, J H; Choi, Chang-Hwan

2012-12-18

347

Electrowetting of superhydrophobic ZnO nanorods.  

PubMed

This paper reports the electrowetting properties of ZnO nanorods. These nanorods were grown on indium tin oxide (ITO) substrates using different liquid-phase deposition techniques and hydrophobized with sputtered Teflon. The surfaces display superhydrophobic properties. When the applied voltages are less than 35 V, the contact angle change is small and exhibits instant reversibility. For higher voltages, larger contact angle changes were observed. However, the surface was not reversible after removing the applied voltage and required mechanical agitation to return to its initial superhydrophobic state. PMID:18373379

Campbell, Jos Laurie; Breedon, Michael; Latham, Kay; Kalantar-zadeh, Kourosh

2008-05-01

348

Control of Superhydrophilic and Superhydrophobic Graphene Interface  

PubMed Central

Superhydrophobic and superhydrophilic properties of chemically-modified graphene have been achieved in larger-area vertically aligned few-layer graphene nanosheets (FLGs), prepared on Si (111) substrate by microwave plasma chemical vapor deposition (MPCVD). Furthermore, in order to enhance wettability, silicon wafers with microstructures were fabricated, on which graphene nanosheets were grown and modified by a chemical method to form hydrophilic and hydrophobic structures. A superhydrophilic graphene surface (contact angle 0°) and a superhydrophobic graphene surface (contact angle 152.0°) were obtained. The results indicate that the microstructured silicon enhances the hydrophilic and hydrophobic wettabilities significantly.

Dong, Jing; Yao, Zhaohui; Yang, Tianzhong; Jiang, Lili; Shen, Chengmin

2013-01-01

349

Two-silane chemical vapor deposition treatment of polymer (nylon) and oxide surfaces that yields hydrophobic (and superhydrophobic), abrasion-resistant thin films  

SciTech Connect

This article describes a two-silane, chemical vapor deposition (CVD) approach to creating hydrophobic (or even superhydrophobic), abrasion-resistant coatings on silicon oxide and polymer (nylon) substrates. This multistep approach employs only reagents delivered in the gas phase, as follows: (i) plasma cleaning/oxidation of the substrate, (ii) CVD of 3-isocyanatopropyltriethoxysilane, which is used as an adhesion promoter for the substrate, (iii) hydrolysis with water vapor, and (iv) CVD of (tridecafluoro-1,1,2,2-tetrahydrooctyl)trichlorosilane (the 'R{sub f}-Cl silane'). Surfaces are characterized by wetting, spectroscopic ellipsometry, x-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). This work has the following unique features. First, the authors explore an all gas phase deposition of a new silane coating that is scientifically interesting and technologically useful. Second, the authors show that the presence of an adhesion promoter in the process leads to thinner films that are more robust in abrasion testing. Third, results obtained using plasma/deposition equipment that is relatively inexpensive and/or available in most laboratories are compared to those obtained with a much more sophisticated, commercially available plasma/CVD system (the YES-1224P). The entire deposition process can be completed in only {approx}1 h using the industrial equipment (the 1224P). It is of significance that the polymer surfaces modified using the 1224P are superhydrophobic. Fourth, the thickness of the R{sub f}-Cl silane layer deposited by CVD correlates well with the thickness of the underlying spin coated nylon surface, suggesting that the nylon film acts as a reservoir of water for the hydrolysis and condensation of the R{sub f}-Cl silane.

Saini, Gaurav; Sautter, Ken; Hild, Frank E.; Pauley, Jerry; Linford, Matthew R. [Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602 (United States); Yield Engineering Systems, Livermore, California 94551 (United States); TriStar Plastics Corp., Yorba Linda, California 92887 (United States); Sonic Innovations, Inc., Salt Lake City, Utah 84121 (United States); Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602 (United States)

2008-09-15

350

Superhydrophobic RTV silicone rubber insulator coatings  

NASA Astrophysics Data System (ADS)

On wet days, environmental contamination of outdoor insulation surfaces can reduce the reliability of electrical transmission systems and lead to flashover and arcing over the entire insulator. The use of superhydrophobic coatings would resolve this problem due to their self-cleaning effect. Water droplets can pick up dirt particles and remove contamination from the surfaces of insulators. This paper reports on a study to make a superhydrophobic RTV silicone rubber coating that has contact angles of higher than 145° and good UV durability. The Inclined Plane Test, water durability test and adhesion test are presented to show the effectiveness of this coating and the best formulations. The results of tracking and erosion resistance test (Inclined Plane Test) showed that formulations with at least 35 wt% ATH can be used for superhydrophobic RTV insulator coatings.

Seyedmehdi, Seyed Amirhossein; Zhang, Hui; Zhu, Jesse

2012-01-01

351

Au-coated ZnO nanostructures for surface enhanced Raman spectroscopy applications  

SciTech Connect

Thin ZnO nanostructured films were produced by pulsed laser deposition (PLD) for surface enhanced Raman spectroscopy (SERS) studies. The experimental conditions used for preparation of the samples were chosen to obtain different types of ZnO nanostructures. The Raman spectra of rhodamine 6G (R6G) were measured at an excitation wavelength of 785 nm after coating the ZnO nanostructures with a thin Au layer. The influence of the surface morphology on the Raman signal obtained from the samples was investigated. High SERS signal enhancement was observed from all Au-coated ZnO nanostructures.

Dikovska, A O; Nedyalkov, N N; Imamova, S E; Atanasova, G B; Atanasov, P A

2012-03-31

352

Engineering metallic nanostructures for surface plasmon resonance sensing  

NASA Astrophysics Data System (ADS)

A change in almost any characteristic of a given material can be detected by one or more beams of light. Optical sensors are extremely sensitive, non-destructive, and immune to electromagnetic interference, offering many significant advantages. Being able to harness this enormous potential within the realm of nanotechnology, however, requires manipulation and control of an optical field on scales well below its wavelength. Dielectric structures cannot achieve this due to diffraction. However, metallic nanostructures which support evanescent surface plasmon resonances can provide a solution. Thin gold or silver films, when patterned with nanometer-scale holes, grooves or bumps can efficiently capture incident light and launch an oscillatory motion of the electrons at the film surface, known as a surface plasmon. Using state of the art nanofabrication techniques, we have engineered these plasmonic structures to exhibit unusual optical properties not found in natural materials. Such novel materials are broadly applicable and useful, in particular, for sensing. In this dissertation, patterned metallic nanostructures are used to demonstrate high-resolution sensing of complex biomolecular interactions in a quantitative and high-throughput manner. Additionally, efficient chemical sensing via surface enhanced Raman spectroscopy, and proximity sensing with structures suitable for scanning probe microscopy are also presented. The structures are rigorously analyzed with theoretical computer simulations based on finite-difference time-domain methods. Using a newly developed high-throughput fabrication method based on template stripping of patterned metals, this work may open up avenues for the realization of practical plasmonic devices in a wide variety of disciplines.

Lindquist, Nathan Charles

353

Surface integral formulations for the design of plasmonic nanostructures.  

PubMed

Numerical formulations based on surface integral equations (SIEs) provide an accurate and efficient framework for the solution of the electromagnetic scattering problem by three-dimensional plasmonic nanostructures in the frequency domain. In this paper, we present a unified description of SIE formulations with both singular and nonsingular kernel and we study their accuracy in solving the scattering problem by metallic nanoparticles with spherical and nonspherical shape. In fact, the accuracy of the numerical solution, especially in the near zone, is of great importance in the analysis and design of plasmonic nanostructures, whose operation critically depends on the manipulation of electromagnetic hot spots. Four formulation types are considered: the N-combined region integral equations, the T-combined region integral equations, the combined field integral equations and the null field integral equations. A detailed comparison between their numerical solutions obtained for several nanoparticle shapes is performed by examining convergence rate and accuracy in both the far and near zone of the scatterer as a function of the number of degrees of freedom. A rigorous analysis of SIE formulations and their limitations can have a high impact on the engineering of numerous nano-scale optical devices such as plasmon-enhanced light emitters, biosensors, photodetectors, and nanoantennas. PMID:23201792

Forestiere, Carlo; Iadarola, Giovanni; Rubinacci, Guglielmo; Tamburrino, Antonello; Dal Negro, Luca; Miano, Giovanni

2012-11-01

354

Surface Integral Formulations for the Design of Plasmonic Nanostructures  

NASA Astrophysics Data System (ADS)

Numerical formulations based on surface integral equations (SIEs) provide an accurate and efficient framework for the solution of the electromagnetic scattering problem by three-dimensional plasmonic nanostructures in the frequency domain. In this work, we present a unified description of SIE formulations with both singular and nonsingular kernel and we study their accuracy in solving the scattering problem by metallic nanoparticles with spherical and nonspherical shape. In fact, the accuracy of the numerical solution, especially in the near zone, is of great importance in the analysis and design of plasmonic nanostructures, whose operation critically depends on the manipulation of electromagnetic hot spots. Four formulation types are considered: the N-combined region integral equations, the T-combined region integral equations, the combined field integral equations and the null field integral equations. A detailed comparison between their numerical solutions obtained for several nanoparticle shapes is performed by examining convergence rate and accuracy in both the far and near zone of the scatterer as a function of the number of degrees of freedom. A rigorous analysis of SIE formulations can have a high impact on the engineering of numerous nano-scale optical devices.

Forestiere, Carlo; Iadarola, Giovanni; Rubinacci, Guglielmo; Tamburrino, Antonello; Dal Negro, Luca; Miano, Giovanni

2013-03-01

355

Preparation of Nanostructured Film Arrays for Transmission Localized Surface Plasmon Sensing  

Microsoft Academic Search

This article presents a concise review of preparation methods for transparent nanostructured films, with an emphasis on their\\u000a current applications in transmission-localized surface plasmon resonance (T-LSPR) sensing. One of the first methods used for\\u000a the fabrication of transparent nanostructured metal films is a direct vacuum evaporation of thin gold films. Self-induced\\u000a formations of small gold islands result in transparent nanostructured

Young-Seok Shon; Hyung Y. Choi; Michael S. Guerrero; Chuhee Kwon

2009-01-01

356

Superamphiphobic surface by nanotransfer molding and isotropic etching.  

PubMed

We present a novel method of fabricating superhydrophobic and superoleophobic surfaces with nanoscale reentrant curvature by nanotransfer molding and controlled wet etching of the facile undercut. This method produces completely ordered re-entrant nanostructures and prevents capillary-induced bundling effects. The mushroom-like, re-entrant, overhanging structure demonstrates superhydrophobic and superoleophobic characteristics, as tested by water droplet bouncing and contact angle measurements, and has high transparency on a flexible substrate. Widespread use as self-cleaning surfaces is expected in the near future. PMID:23701230

Lee, Sang Eon; Kim, Han-Jung; Lee, Su-Han; Choi, Dae-Geun

2013-06-25

357

Development of Methods for Surface Modification of Nanostructured Materials  

NASA Astrophysics Data System (ADS)

The surfaces of a material become increasingly more influential when the dimensions are reduced, because a larger percentage of the atoms are exposed on the surface. The surface environment of nanostructured materials dictates both physical properties and function, but is synthetically challenging to control. Although the desired functionality is commonly introduced via post-synthetic modification, it would be advantageous to minimize the number of synthetic steps by having specific function installed in the precursor. This work describes efforts to investigate new precursor complexes for the synthesis of nanoparticles, in addition to electrochemical studies on single monolayer films for electrocatalysis. Chapter 2 focuses on the preparation of magnetic nanoaparticles, and the synthesis of a polymerizable surfactant, stacac, to be used to generate composite materials. Although an iron complex of stacac could be used as a precursor for magnetic nanoparticles, favorable composite materials could only be produced by introduction of stacac after isolation of magnetic nanoparticles. Chapter 3 describes the synthesis of Au(I) complexes with various thiourea-based ligands, to be used as precursors for gold nanoparticles. The experimental conditions were varied and parameters were found where addition of a reducing agent generated solution-stable gold nanoparticles in a reproducible manner. It was determined that only aggregated gold nanoparticles were produced when Au(I) complexes were generated in situ and the use of crystalline precursors resulted in soluble gold nanoparticles. Chapter 4 discusses the preparation of electrocatalysts for the oxidation of water with a focus on accurately determining the active surface area. A monolayer of cobalt was prepared on a gold electrode by underpotential deposition and used as an electrocatalyst for water oxidation. Because the surface area of gold can be measured directly, deposition of a single monolayer produced negligible roughening of the surface and so the active surface area was based on the surface area of gold. The catalytic efficiency was enhanced in the presence of external anions, highlighting the importance of the surface environment on function.

Marsh, David A.

358

Is superhydrophobicity robust with respect to disorder?  

PubMed

We consider theoretically the Cassie-Baxter and Wenzel states describing the wetting contact angles for rough substrates. More precisely, we consider different types of periodic geometries such as square protrusions and disks in 2D, grooves and nanoparticles in 3D and derive explicitly the contact angle formulas. We also show how to introduce the concept of surface disorder within the problem and, inspired by biomimetism, study its effect on superhydrophobicity. Our results, quite generally, prove that introducing disorder, at fixed given roughness, will lower the contact angle: a disordered substrate will have a lower contact angle than a corresponding periodic substrate. We also show that there are some choices of disorder for which the loss of superhydrophobicity can be made small, making superhydrophobicity robust. PMID:24072468

De Coninck, Joël; Dunlop, François; Huillet, Thierry

2013-09-01

359

Colour centres and nanostructures on the surface of laser crystals  

SciTech Connect

This paper presents a study of structural and radiationinduced colour centres in the bulk and ordered nanostructures on the surface of doped laser crystals: sapphire, yttrium aluminium garnet and strontium titanate. The influence of thermal annealing, ionising radiation and plasma exposure on the spectroscopic properties of high-purity materials and crystals containing Ti, V and Cr impurities is examined. Colour centres resulting from changes in the electronic state of impurities and plasma-induced surface modification of the crystals are studied by optical, EPR and X-ray spectroscopies, scanning electron microscopy and atomic force microscopy. X-ray line valence shift measurements are used to assess changes in the electronic state of some impurity and host ions in the bulk and on the surface of oxide crystals. Conditions are examined for the formation of one- and two-level arrays of ordered crystallites 10{sup -10} to 10{sup -7} m in size on the surface of crystals doped with irongroup and lanthanoid ions. The spectroscopic properties of the crystals are analysed using ab initio self-consistent field calculations for Me{sup n+} : [O{sup 2-}]{sub k} clusters. (interaction of laser radiation with matter. laser plasma)

Kulagin, N A [Firma SIFA Ukraine - Germany Joint Venture, ul. Shekspira 6-48, 61045 Kharkiv (Ukraine)

2012-11-30

360

Fast-response no-bias-bend liquid crystal displays using nanostructured surfaces  

E-print Network

liquid crystal LC response is a still one of the major problems for LCD in video applications.1 TimeFast-response no-bias-bend liquid crystal displays using nanostructured surfaces Fion Sze-Yan Yeung-bias-bend NBB liquid crystal display, made possible by using a nanostructured alignment layer. Such alignment

361

The role of new particle surfaces in synthesizing bulk nanostructured metallic materials by powder metallurgy  

Microsoft Academic Search

The role of new particle surfaces in synthesizing bulk nanostructured metallic materials by consolidation of nanostructured powders and nanopowders is analysed by developing three simple mathematical equations for calculating the ? factor for different thermomechanical powder consolidation processes such as hot pressing, high pressure torsion and extrusion. The ? factor is the fraction of the area of the powder particle

D. L. Zhang; C. C. Koch; R. O. Scattergood

2009-01-01

362

Nanostructures  

NSDL National Science Digital Library

This page from Foothill-De Anza Community College provides a list of nanostructures. For each structure, its properties, structure, process, and application are detailed. Additionally, most pages include a picture, video, and references. The structures include aerogels, biomolecules, carbon, composite materials, ferrofluids, and many others.

363

On the possibility of superhydrophobic behavior for hydrophilic materials.  

PubMed

It has been recognized well that it is necessary to achieve superhydrophobic surfaces on intrinsically hydrophobic materials. However, recently experiments have demonstrated that it is possible to fabricate superhydrophobic surfaces on intrinsically hydrophilic materials by creating adequate roughness. In this study, such a possibility for superhydrophobicity on a hydrophilic surface with an intrinsic contact angle (CA) of 80 degrees, with a comparison to a hydrophobic surface with an intrinsic CA of 120 degrees, is thermodynamically analyzed using a pillared microtexture. Based on the calculations of free energy (FE) and free energy barrier (FEB), it is found that for such hydrophilic materials, generally, the FE for noncomposite or Wenzel's state is lower than that composite or Cassie's state for various geometrical wetting systems. Furthermore, even if pillar height or roughness is adequately large, it is hard to realize superhydrophobic behavior because of the surface wicking resulted from its special FE state. In addition, due to the negative FEB of the noncomposite state, there is no transition between noncomposite and composite states no matter how surface geometry varies. The above results also indicates that once noncomposite state is formed, it can hardly be become composite state, or in other words, even if superhydrophobic behavior is possible, it could be temporary and unstable. The present theoretical investigation therefore keeps a reservation on the practicability of superhydrophobic surfaces built on hydrophilic materials. PMID:20417521

Cui, X S; Li, W

2010-07-01

364

Surface antireflection properties of GaN nanostructures with various effective refractive index profiles.  

PubMed

GaN nanostructures with various effective refractive index profiles (Linear, Cubic, and Quintic functions) were numerically studied as broadband omnidirectional antireflection structures for concentrator photovoltaics by using three-dimensional finite difference time domain (3D-FDTD) method. Effective medium theory was used to design the surface structures corresponding to different refractive index profiles. Surface antireflection properties were calculated and analyzed for incident light with wavelength, polarization and angle dependences. The surface antireflection properties of GaN nanostructures based on six-sided pyramid with both uniform and non-uniform patterns were also investigated. Results indicate a significant dependence of the surface antireflection on the refractive index profiles of surface nanostructures as well as their pattern uniformity. The GaN nanostructures with linear refractive index profile show the best performance to be used as broadband omnidirectional antireflection structures. PMID:25607159

Han, Lu; Zhao, Hongping

2014-12-29

365

Plastron induced drag reduction and increased slip on a superhydrophobic G. McHale,*a  

E-print Network

of hydrophobic surface chemistry to create superhydrophobic surfaces.1 Methods for creating such surfaces In the modern era of super- hydrophobicity, the ability of superhydrophobic materials to perform the same. It is intuitively appealing, but less obvious, that when such material is immersed in water, the liquid will flow

Flynn, Morris R.

366

Nanostructuring steel for injection molding tools  

NASA Astrophysics Data System (ADS)

The production of nanostructured plastic items by injection molding with ridges down to 400 nm in width, which is the smallest line width replicated from nanostructured steel shims, is presented. Here we detail a micro-fabrication method where electron beam lithography, nano-imprint lithography and ion beam etching are combined to nanostructure the planar surface of a steel wafer. Injection molded plastic parts with enhanced surface properties, like anti-reflective, superhydrophobic and structural colors can be achieved by micro- and nanostructuring the surface of the steel molds. We investigate the minimum line width that can be realized by our fabrication method and the influence of etching angle on the structure profile during the ion beam etching process. Trenches down to 400 nm in width have been successfully fabricated into a 316 type electro-polished steel wafer. Afterward a plastic replica has been produced by injection molding with good structure transfer fidelity. Thus we have demonstrated that by utilizing well-established fabrication techniques, nanostructured steel shims that are used in injection molding, a technique that allows low cost mass fabrication of plastic items, are produced.

Al-Azawi, A.; Smistrup, K.; Kristensen, A.

2014-05-01

367

In situ surface-enhanced Raman spectroelectrochemical analysis system with a hemin modified nanostructured gold surface.  

PubMed

An integrated surface-enhanced Raman scattering (SERS) spectroelectrochemical (SEC) analysis system is presented that combines a small volume microfluidic sample chamber (<100 ?L) with a compact three-electrode configuration for in situ surface-enhanced Raman spectroelectrochemistry. The SEC system includes a nanostructured Au surface that serves dual roles as the electrochemical working electrode (WE) and SERS substrate, a microfabricated Pt counter electrode (CE), and an external Ag/AgCl reference electrode (RE). The nanostructured Au WE enables highly sensitive in situ SERS spectroscopy through large and reproducible SERS enhancements, which eliminates the need for resonant wavelength matching of the laser excitation source with the electronic absorption of the target molecule. The new SEC analysis system has the merits of wide applicability to target molecules, small sample volume, and a low detection limit. We demonstrate in situ SERS spectroelectrochemistry measurements of the metalloporphyrin hemin showing shifts of the iron oxidation marker band ?4 with the nanostructured Au working electrode under precise potential control. PMID:25643066

Yuan, Tao; Le Thi Ngoc, Loan; van Nieuwkasteele, Jan; Odijk, Mathieu; van den Berg, Albert; Permentier, Hjalmar; Bischoff, Rainer; Carlen, Edwin T

2015-03-01

368

Nanosilver on nanostructured silica: Antibacterial activity and Ag surface area  

PubMed Central

Nanosilver is one of the first nanomaterials to be closely monitored by regulatory agencies worldwide motivating research to better understand the relationship between Ag characteristics and antibacterial activity. Nanosilver immobilized on nanostructured silica facilitates such investigations as the SiO2 support hinders the growth of nanosilver during its synthesis and, most importantly, its flocculation in bacterial suspensions. Here, such composite Ag/silica nanoparticles were made by flame spray pyrolysis of appropriate solutions of Ag-acetate or Ag-nitrate and hexamethyldisiloxane or tetraethylorthosilicate in ethanol, propanol, diethylene glucolmonobutyl ether, acetonitrile or ethylhexanoic acid. The effect of solution composition on nanosilver characteristics and antibacterial activity against the Gram negative Escherichia coli was investigated by monitoring their recombinantly synthesized green fluorescent protein. Suspensions with identical Ag mass concentration exhibited drastically different antibacterial activity pointing out that the nanosilver surface area concentration rather than its mass or molar or number concentration determine best its antibacterial activity. Nanosilver made from Ag-acetate showed a unimodal size distribution, while that made from inexpensive Ag-nitrate exhibited a bimodal one. Regardless of precursor composition or nanosilver size distribution, the antibacterial activity of nanosilver was correlated best with its surface area concentration in solution. PMID:23730198

Sotiriou, Georgios A.; Teleki, Alexandra; Camenzind, Adrian; Krumeich, Frank; Meyer, Andreas; Panke, Sven; Pratsinis, Sotiris E.

2013-01-01

369

Underwater drag-reducing effect of superhydrophobic submarine model.  

PubMed

To address the debates on whether superhydrophobic coatings can reduce fluid drag for underwater motions, we have achieved an underwater drag-reducing effect of large superhydrophobic submarine models with a feature size of 3.5 cm × 3.7 cm × 33.0 cm through sailing experiments of submarine models, modified with and without superhydrophobic surface under similar power supply and experimental conditions. The drag reduction rate reached as high as 15%. The fabrication of superhydrophobic coatings on a large area of submarine model surfaces was realized by immobilizing hydrophobic copper particles onto a precross-linked polydimethylsiloxane (PDMS) surface. The pre-cross-linking time was optimized at 20 min to obtain good superhydrophobicity for the underwater drag reduction effect by investigating the effect of pre-cross-linking on surface wettability and water adhesive property. We do believe that superhydrophobic coatings may provide a promising application in the field of drag-reducing of vehicle motions on or under the water surface. PMID:25496725

Zhang, Songsong; Ouyang, Xiao; Li, Jie; Gao, Shan; Han, Shihui; Liu, Lianhe; Wei, Hao

2015-01-13

370

Excitation and Far field Spectroscopy of surface plasmons in Gold nanostructures  

E-print Network

The properties of surface plasmons (SPs) and their excitation by a light wave are considered. The interaction of light with a metal nanostructure resulted in transmission, reflection and diffraction of light. The spectra of light obtained from...

Peng, Siying

2011-08-08

371

Controlling the Wettability and Adhesion of Nanostructured Poly-(p-xylylene) Films  

E-print Network

of wall-climbing robots. The methods of preparing superhydrophobic and adhesive surfaces include chemical surfaces to robotics. Introduction Superhydrophobic surfaces (water contact angle w > 150°) have been

Demirel, Melik C.

372

Super-hydrophobic multi-walled carbon nanotube coatings for stainless steel  

NASA Astrophysics Data System (ADS)

We have taken advantage of the native surface roughness and the iron content of AISI 316 stainless steel to directly grow multi-walled carbon nanotube (MWCNT) random networks by chemical vapor deposition (CVD) at low-temperature (\\lt 1000{}^\\circ C) without the addition of any external catalysts or time-consuming pre-treatments. In this way, super-hydrophobic MWCNT films on stainless steel sheets were obtained, exhibiting high contact angle values (154{}^\\circ ) and high adhesion force (high contact angle hysteresis). Furthermore, the investigation of MWCNT films with scanning electron microscopy (SEM) reveals a two-fold hierarchical morphology of the MWCNT random networks made of hydrophilic carbonaceous nanostructures on the tip of hydrophobic MWCNTs. Owing to the Salvinia effect, the hydrophobic and hydrophilic composite surface of the MWCNT films supplies a stationary super-hydrophobic coating for conductive stainless steel. This biomimetical inspired surface not only may prevent corrosion and fouling, but also could provide low friction and drag reduction.

De Nicola, Francesco; Castrucci, Paola; Scarselli, Manuela; Nanni, Francesca; Cacciotti, Ilaria; De Crescenzi, Maurizio

2015-04-01

373

Super-hydrophobic multi-walled carbon nanotube coatings for stainless steel.  

PubMed

We have taken advantage of the native surface roughness and the iron content of AISI 316 stainless steel to directly grow multi-walled carbon nanotube (MWCNT) random networks by chemical vapor deposition (CVD) at low-temperature ([Formula: see text]) without the addition of any external catalysts or time-consuming pre-treatments. In this way, super-hydrophobic MWCNT films on stainless steel sheets were obtained, exhibiting high contact angle values ([Formula: see text]) and high adhesion force (high contact angle hysteresis). Furthermore, the investigation of MWCNT films with scanning electron microscopy (SEM) reveals a two-fold hierarchical morphology of the MWCNT random networks made of hydrophilic carbonaceous nanostructures on the tip of hydrophobic MWCNTs. Owing to the Salvinia effect, the hydrophobic and hydrophilic composite surface of the MWCNT films supplies a stationary super-hydrophobic coating for conductive stainless steel. This biomimetical inspired surface not only may prevent corrosion and fouling, but also could provide low friction and drag reduction. PMID:25772497

Nicola, Francesco De; Castrucci, Paola; Scarselli, Manuela; Nanni, Francesca; Cacciotti, Ilaria; Crescenzi, Maurizio De

2015-04-01

374

Reusable three-dimensional nanostructured substrates for surface-enhanced Raman scattering  

PubMed Central

To date, fabricating three-dimensional (3D) nanostructured substrate with small nanogap was a laborious challenge by conventional fabrication techniques. In this article, we address a simple, low-cost, large-area, and spatially controllable method to fabricate 3D nanostructures, involving hemisphere, hemiellipsoid, and pyramidal pits based on nanosphere lithography (NSL). These 3D nanostructures were used as surface-enhanced Raman scattering (SERS) substrates of single Rhodamine 6G (R6G) molecule. The average SERS enhancement factor achieved up to 1011. The inevitably negative influence of the adhesion-promoting intermediate layer of Cr or Ti was resolved by using such kind of 3D nanostructures. The nanostructured quartz substrate is a free platform as a SERS substrate and is nondestructive when altering with different metal films and is recyclable, which avoids the laborious and complicated fabricating procedures. PMID:24417892

2014-01-01

375

Investigations of the Band Structure and Morphology of Nanostructured Surfaces  

NASA Astrophysics Data System (ADS)

In this dissertation, I examine the electronic structure of two very different types of two-dimensional systems: valence band electrons in single layer graphene and electronic states created at the vacuum interface of single crystal copper surfaces. The characteristics of both electronic systems depend intimately on the morphology of the surfaces they inhabit. Thus, in addition to discussing the respective band structures of these systems, a significant portion of this dissertation will be devoted to measurements of the surface morphology of these systems. Free-standing exfoliated monolayer graphene is an ultra-thin flexible membrane and, as such, is known to exhibit large out-of-plane deformation due to substrate and adsorbate interaction as well as thermal vibrations and, possibly, intrinsic buckling. Such crystal deformation is known to limit mobility and increase local chemical reactivity. Additionally, deformations present a measurement challenge to researchers wishing to determine the band structure by angle-resolved photoemission since they limit electron coherence in such measurements. In this dissertation, I present low energy electron microscopy and micro probe diffraction measurements, which are used to image and characterize corrugation in SiO2-supported and suspended exfoliated graphene at nanometer length scales. Diffraction line-shape analysis reveals quantitative differences in surface roughness on length scales below 20 nm which depend on film thickness and interaction with the substrate. Corrugation decreases with increasing film thickness, reflecting the increased stiffness of multilayer films. Specifically, single-layer graphene shows a markedly larger short range roughness than multilayer graphene. Due to the absence of interactions with the substrate, suspended graphene displays a smoother morphology and texture than supported graphene. A specific feature of suspended single-layer films is the dependence of corrugation on both adsorbate load and temperature, which is manifested by variations in the diffraction lineshape. The effects of both intrinsic and extrinsic corrugation factors will be discussed. Through a carefully coordinated study I show how these surface morphology measurements can be combined with angle resolved photoemission measurements to understand the role of surface corrugation in the ARPES measurement process. The measurements described here rely on the development of an analytical formulation for relating the crystal corrugation to the photoemission linewidth. I present ARPES measurements that show that, despite significant deviation from planarity of the crystal, the electronic structure of exfoliated suspended graphene is nearly that of ideal, undoped graphene; the Dirac point is measured to be within 25 meV of EF. Further, I show that suspended graphene behaves as a marginal Fermi-liquid, with a quasiparticle lifetime which scales as (E -- EF)--1 ; comparison with other graphene and graphite data is discussed. In contrast to graphene, which must be treated as a flexible membrane with continuous height variation, roughness in clean single crystal surfaces arises from lattice dislocations, which introduce discrete height variations. Such height variations can be exploited to generate a self assembled nano-structured surface. In particular, by making a vicinal cut on a single crystal surface, a nanoscale step array can be formed. A model system for such nanoscale self assembly is Cu(111). Cu(775) is formed by making an 8.5° viscinal cut of Cu(111) along the [112¯] axis. The electronic states formed on the surface of this system, with a nanoscale step array of 14 A terraces, shows markedly different behavior those formed on Cu(111). In this dissertation, I show that the tunability of a femtosecond optical parametric oscillator, combined with its high-repetition rate and short pulse length, provides a powerful tool for resonant band mapping of the sp surface and image states on flat and vicinal Cu(111)-Cu (775) surfaces, over the photon energy range from 3.9 to 5 eV. Since the tim

Knox, Kevin R.

2011-12-01

376

Functional surface chemistry of carbon-based nanostructures  

NASA Astrophysics Data System (ADS)

The recently discovered abilities to synthesize single-walled carbon nanotubes and prepare single layer graphene have spurred interest in these sp2-bonded carbon nanostructures. In particular, studies of their potential use in electronic devices are many as silicon integrated circuits are encountering processing limitations, quantum effects, and thermal management issues due to rapid device scaling. Nanotube and graphene implementation in devices does come with significant hurdles itself. Among these issues are the ability to dope these materials and understanding what influences defects have on expected properties. Because these nanostructures are entirely all-surface, with every atom exposed to ambient, introduction of defects and doping by chemical means is expected to be an effective route for addressing these issues. Raman spectroscopy has been a proven characterization method for understanding vibrational and even electronic structure of graphene, nanotubes, and graphite, especially when combined with electrical measurements, due to a wealth of information contained in each spectrum. In Chapter 1, a discussion of the electronic structure of graphene is presented. This outlines the foundation for all sp2-bonded carbon electronic properties and is easily extended to carbon nanotubes. Motivation for why these materials are of interest is readily gained. Chapter 2 presents various synthesis/preparation methods for both nanotubes and graphene, discusses fabrication techniques for making devices, and describes characterization methods such as electrical measurements as well as static and time-resolved Raman spectroscopy. Chapter 3 outlines changes in the Raman spectra of individual metallic single-walled carbon nantoubes (SWNTs) upon sidewall covalent bond formation. It is observed that the initial degree of disorder has a strong influence on covalent sidewall functionalization which has implications on developing electronically selective covalent chemistries and assessing their selectivity in separating metallic and semiconducting SWNTs. Chapter 4 describes how optical phonon population extinction lifetime is affected by covalent functionalization and doping and includes discussions on static Raman linewidths. Increasing defect concentration is shown to decrease G-band phonon population lifetime and increase G-band linewidth. Doping only increases G-band linewidth, leaving non-equilibrium population decay rate unaffected. Phonon mediated electron scattering is especially strong in nanotubes making optical phonon decay of interest for device applications. Optical phonon decay also has implications on device thermal management. Chapter 5 treats doping of graphene showing ambient air can lead to inadvertent Fermi level shifts which exemplifies the sensitivity that sp2-bonded carbon nanostructures have to chemical doping through sidewall adsorption. Removal of this doping allows for an investigation of electron-phonon coupling dependence on temperature, also of interest for devices operating above room temperature. Finally, in Chapter 6, utilizing the information obtained in previous chapters, single carbon nanotube diodes are fabricated and characterized. Electrical performance shows these diodes are nearly ideal and photovoltaic response yields 1.4 nA and 205 mV of short circuit current and open circuit voltage from a single nanotube device. A summary and discussion of future directions in Chapter 7 concludes my work.

Abdula, Daner

377

Chondrocyte behavior on nanostructured micropillar polypropylene and polystyrene surfaces.  

PubMed

This study was aimed to investigate whether patterned polypropylene (PP) or polystyrene (PS) could enhance the chondrocytes' extracellular matrix (ECM) production and phenotype maintenance. Bovine primary chondrocytes were cultured on smooth PP and PS, as well as on nanostructured micropillar PP (patterned PP) and PS (patterned PS) for 2 weeks. Subsequently, the samples were collected for fluorescein diacetate-based cell viability tests, for immunocytochemical assays of types I and II collagen, actin and vinculin, for scanning electronic microscopic analysis of cell morphology and distribution, and for gene expression assays of Sox9, aggrecan, procollagen ?1(II), procollagen ?1(X), and procollagen ?2(I) using quantitative RT-PCR assays. After two weeks of culture, the bovine primary chondrocytes had attached on both patterned PP and PS, while practically no adhesion was observed on smooth PP. However, the best adhesion of the cells was on smooth PS. The cells, which attached on patterned PP and PS surfaces synthesized types I and II collagen. The chondrocytes' morphology was extended, and an abundant ECM network formed around the attached chondrocytes on both patterned PP and PS. Upon passaging, no significant differences on the chondrocyte-specific gene expression were observed, although the highest expression level of aggrecan was observed on the patterned PS in passage 1 chondrocytes, and the expression level of procollagen ?1(II) appeared to decrease in passaged chondrocytes. However, the expressions of procollagen ?2(I) were increased in all passaged cell cultures. In conclusion, the bovine primary chondrocytes could be grown on patterned PS and PP surfaces, and they produced extracellular matrix network around the adhered cells. However, neither the patterned PS nor PP could prevent the dedifferentiation of chondrocytes. PMID:25175232

Prittinen, Juha; Jiang, Yu; Ylärinne, Janne H; Pakkanen, Tapani A; Lammi, Mikko J; Qu, Chengjuan

2014-10-01

378

Multifunctional superhydrophobic coatings for large area applications  

NASA Astrophysics Data System (ADS)

Formulation of flexible superhydrophobic coatings (water droplet contact angles above 150 deg and roll-off angles below 10 deg) with high durability and electrical conductivity, and their fabrication using scalable techniques is a major challenge. The current work lays their foundation using solution processed polymer nanocomposites. Carefully selected polymer(s) are used to disperse filler particles and the dispersions are applied by spraying process. The filler particle size, surface energy and other functionalities are varied to produce the coatings. Sub-micron poly(tetrafluoroethylene) (PTFE) particles and carbon black or other nanoparticles are jointly used to obtain hierarchical morphology (micro-to-nanoscale roughness) and superhydrophobicity. As examples, firstly, acrylonitrile-co-butadiene rubber based nanocomposites are shown to maintain superhydrophobicity up to 200% linear and for 100 cycles of reversible 0 to 100% uniaxial stretching. Secondly, poly(vinylidene fluoride) and poly(methyl methacrylate) blend based nanocomposites containing carbon nanofibers are demonstrated as superhydrophobic coatings with electrical conductivity up to 300 S/m.

Megaridis, Constantine; Schutzius, Thomas; Das, Arindam; Tiwari, Manish; Bayer, Ilker

2009-11-01

379

A facile method to fabricate superhydrophobic cotton fabrics  

NASA Astrophysics Data System (ADS)

A facile and novel method for fabricating superhydrophobic cotton fabrics is described in the present work. The superhydrophobic surface has been prepared by utilizing cationic poly (dimethyldiallylammonium chloride) and silica particles together with subsequent modification of (heptadecafluoro-1,1,2,2-tetradecyl) trimethoxysilane. The size distribution of silica particles was measured by Particle Size Analyzer. The cotton textiles before and after treatment were characterized by using scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The wetting behavior of cotton samples was investigated by water contact angle measurement. Moreover, the superhydrophobic durability of coated cotton textiles has been evaluated by exposure, immersion and washing tests. The results show that the treated cotton fabrics exhibited excellent chemical stability and outstanding non-wettability with the WCA of 155 ± 2°, which offers an opportunity to accelerate the large-scale production of superhydrophobic textiles materials for new industrial applications.

Zhang, Ming; Wang, Shuliang; Wang, Chengyu; Li, Jian

2012-11-01

380

Surface and interface magnetism in nanostructures and thin films  

NASA Astrophysics Data System (ADS)

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 sensors and devices, increasing storage density for magnetic media, as well as for biomedical applications such as drug delivery, MRI contrast enhancement, and hyperthermia treatment for cancer. In this project we have examined the surface and interface magnetism of composite nanoparticles and multilayer thin films by using conventional DC magnetization and AC susceptibility as well as transverse susceptibility, a method for directly probing the magnetic anisotropy of materials. Au and Fe3O4 synthesized together into three different nanoparticle configurations and ranging in size for 60 nm down to 9nm are used to study how the size, shape, and interfaces affect the most fundamental properties of magnetism in the Au-Fe3O 4 system. The findings have revealed ways in which the magnetic properties can be enhanced by tuning these parameters. We have shown that by changing the configurations of the Au and Fe3O4 particles, exotic behavior can be observed such as a large increase in anisotropy field (H K ranging from 435 Oe to 1650 Oe) and the presence of exchange bias. Multilayer thin films have been studied as well which combine the important classes of ferromagnetic and ferroelectric materials. In one case, barium hexaferrite/barium strontium titanate thin films, the anisotropic behavior of the ferromagnet is shown to change due to the introduction of the secondary material. In the other example, CrO2/Cr2O3 bilayers, exchange coupling is observed as Cr2O3 is an antiferromagnet as well as a ferroelectric. This coupling is manifest as a uniaxial anisotropy rather than the unidirectional anisotropy associated with exchange biased bilayers. Not only will such multifunctional structures will be useful for technological applications, but the materials properties and configurations can be chosen and tuned to further enhance the desired functional properties.

Frey, Natalie A.

381

Role of nanostructured gold surfaces on monocyte activation and Staphylococcus epidermidis biofilm formation  

PubMed Central

The role of material surface properties in the direct interaction with bacteria and the indirect route via host defense cells is not fully understood. Recently, it was suggested that nanostructured implant surfaces possess antimicrobial properties. In the current study, the adhesion and biofilm formation of Staphylococcus epidermidis and human monocyte adhesion and activation were studied separately and in coculture in different in vitro models using smooth gold and well-defined nanostructured gold surfaces. Two polystyrene surfaces were used as controls in the monocyte experiments. Fluorescent viability staining demonstrated a reduction in the viability of S. epidermidis close to the nanostructured gold surface, whereas the smooth gold correlated with more live biofilm. The results were supported by scanning electron microscopy observations, showing higher biofilm tower formations and more mature biofilms on smooth gold compared with nanostructured gold. Unstimulated monocytes on the different substrates demonstrated low activation, reduced gene expression of pro- and anti-inflammatory cytokines, and low cytokine secretion. In contrast, stimulation with opsonized zymosan or opsonized live S. epidermidis for 1 hour significantly increased the production of reactive oxygen species, the gene expression of tumor necrosis factor-? (TNF-?), interleukin-1? (IL-1?), IL-6, and IL-10, as well as the secretion of TNF-?, demonstrating the ability of the cells to elicit a response and actively phagocytose prey. In addition, cells cultured on the smooth gold and the nanostructured gold displayed a different adhesion pattern and a more rapid oxidative burst than those cultured on polystyrene upon stimulation. We conclude that S. epidermidis decreased its viability initially when adhering to nanostructured surfaces compared with smooth gold surfaces, especially in the bacterial cell layers closest to the surface. In contrast, material surface properties neither strongly promoted nor attenuated the activity of monocytes when exposed to zymosan particles or S. epidermidis. PMID:24550671

Svensson, Sara; Forsberg, Magnus; Hulander, Mats; Vazirisani, Forugh; Palmquist, Anders; Lausmaa, Jukka; Thomsen, Peter; Trobos, Margarita

2014-01-01

382

Localized surface resonances of J-aggregate nanostructures  

E-print Network

Metallic nanostructures are able to concentrate light into volumes far below the diffraction limit. Here we show, by accurate scattering calculations, that nanostructures obtained from thin films of J-aggregate dyes, concentrate the electromagnetic field at optical frequencies. Moreover, in contrast to metal nanoparticles, these molecular aggregates display highly attractive nonlinear optical properties that can be exploited for the realization of ultracompact devices for switching light by light on the nanoscale without the need of additional nonlinear materials. These results open new perspectives in plasmonic based nanophotonics.

Triolo, Claudia; Di Stefano, Omar; Genco, Armando; Mazzeo, Marco; Patanè, Salvatore; Saija, Rosalba; Savasta, Salvatore

2015-01-01

383

Superhydrophobic silicone\\/PTFE films for biocompatible application in encapsulation of implantable microelectronics devices  

Microsoft Academic Search

In this paper, the novel biocompatible materials were created on the basis of creation of the bio-inert superhydrophobic surfaces using a heat curable polydimethylsiloxane (PDMS, Sylgard 184, a product of Dow Corning) and polytetrafluoroethylene (PTFE) particles. The incorporation of PTFE nanoparticles in the PDMS matrix allows the formulation of superhydrophobic films with contact angles of ~160deg. Evaluation of the effect

Yonghao Xiu; Lingbo Zhu; Dennis Hess; C. P. Wong

2006-01-01

384

Nanostructured zonolite–cementitious surface compounds for thermal insulation  

Microsoft Academic Search

This paper investigates the effect of zonolite loadings on the thermal resistivity and indirect tensile strength of nanostructured cementitious compounds. The main objective of this research is to develop a structural lightweight compound that can be used on building skins and cores for pre fabricated structural insulated panels (SIPs). The application of this compound is intended to improve the thermal

M. S. Morsy; H. A. Aglan; M. M. Abd El Razek

2009-01-01

385

Nano-structured poly-lactic-co-glycolic acid polymer surface features increase cell functions  

Microsoft Academic Search

Polymers currently utilized for tissue engineering applications do not possess surfaces with nanostructured features. In contrast, the tissue that the polymers will regenerate is composed of proteins that have nanometer dimensions. Undoubtedly, the presence of proteins in natural tissue provide for surface roughness values in the nanometer regime. For this reason, the objective of the present study was to design,

D. C. Miller; A. Thapa; K. M. Haberstroh; T. J. Webster

2002-01-01

386

Structure-related antibacterial activity of a titanium nanostructured surface fabricated by glancing angle sputter deposition  

NASA Astrophysics Data System (ADS)

The aim of this study was to reproduce the physico-mechanical antibacterial effect of the nanocolumnar cicada wing surface for metallic biomaterials by fabrication of titanium (Ti) nanocolumnar surfaces using glancing angle sputter deposition (GLAD). Nanocolumnar Ti thin films were fabricated by GLAD on silicon substrates. S. aureus as well as E. coli were incubated with nanostructured or reference dense Ti thin film test samples for one or three hours at 37 °C. Bacterial adherence, morphology, and viability were analyzed by fluorescence staining and scanning electron microscopy and compared to human mesenchymal stem cells (hMSCs). Bacterial adherence was not significantly different after short (1 h) incubation on the dense or the nanostructured Ti surface. In contrast to S. aureus the viability of E. coli was significantly decreased after 3 h on the nanostructured film compared to the dense film and was accompanied by an irregular morphology and a cell wall deformation. Cell adherence, spreading and viability of hMSCs were not altered on the nanostructured surface. The results show that the selective antibacterial effect of the cicada wing could be transferred to a nanostructured metallic biomaterial by mimicking the natural nanocolumnar topography.

Sengstock, Christina; Lopian, Michael; Motemani, Yahya; Borgmann, Anna; Khare, Chinmay; Buenconsejo, Pio John S.; Schildhauer, Thomas A.; Ludwig, Alfred; Köller, Manfred

2014-05-01

387

Ultranarrow band absorbers based on surface lattice resonances in nanostructured metal surfaces.  

PubMed

Nanostructured metals have received a significant amount of attention in recent years due to their exciting plasmonic and photonic properties enabling strong field localization, light concentration, and strong absorption and scattering at their resonance frequencies. Resonant plasmonic and metamaterial absorbers are of particular interest for applications in a wide variety of technologies including photothermal therapy, thermophotovoltaics, heat-assisted magnetic recording, hot-electron collection, and biosensing. However, it is rather challenging to realize ultranarrow absorption bands using plasmonic materials due to large optical losses in metals that decrease the quality factor of optical resonators. Here, we theoretically and experimentally demonstrate an ultranarrow band absorber based on the surface lattice resonances (SLRs) in periodic nanowire and nanoring arrays on optically thick, reflecting metallic films. In experiments, we observed ultranarrow band resonant absorption peaks with a bandwidth of 12 nm and absorption amplitude exceeding 90% at visible frequencies. We demonstrate that the resonance absorption wavelength, amplitude of the absorption peak, and the bandwidth can be controlled by tuning the periodicity and the thickness of nanoring and nanowire arrays. Unlike conventional plasmonic absorbers utilizing common metal–insulator–metal stacks, our narrow band absorber consists solely of metals, facilitating stronger optical interaction between the SLR of periodic nanostructures and the highly reflective film. Moreover, by introducing asymmetry to the nanoring/nanowire hybrid system, we observe the spectral evolution of resonance splitting enabled by strong coupling between two individual SLRs arising from nanoring and nanowire arrays. Designing such all-metallic nanostructure arrays is a promising route for achieving ultranarrow band absorbers which can be used as absorption filters, narrow band thermal emitters in thermophotovoltaics, and plasmonic biosensors. PMID:25072803

Li, Zhongyang; Butun, Serkan; Aydin, Koray

2014-08-26

388

Self-organisation and magnetic properties of Co nanostructures embedded in a Cu(100) surface  

NASA Astrophysics Data System (ADS)

Using a self-learning kinetic Monte-Carlo method, the formation of embedded Co nanostructures is investigated on an atomic scale. The atomic processes responsible for the formation of the simplest types of nanostructures are identified. We demonstrate that the time evolution of the Cu(100) surface with the embedded Co atoms can be divided into three stages. The surface morphology is observed during these three stages at substrate temperatures of 300-400 K and low concentrations of Co atoms. The magnetic properties of the structures forming in the first two stages are calculated using density functional theory. The spin and orbital magnetic moments and the magnetic anisotropy energy of these embedded nanostructures are obtained. In this way, the time evolution of the structural and magnetic properties of a Cu(100) surface with embedded Co atoms is investigated.

Kolesnikov, S. V.; Klavsyuk, A. L.; Saletsky, A. M.

2013-06-01

389

One-step fabrication of nanostructures by femtosecond laser for surface-enhanced Raman scattering.  

PubMed

This paper reports an efficient fabrication of nanostructures on silicon substrates for surface-enhanced Raman scattering (SERS). Silicon wafer substrates in the aqueous solution of silver nitrate were machined by the femtosecond laser direct writing to achieve simultaneously in one-step the generation of grating-like nanostructures on the surface of the substrate and the formation of silver nanoparticles on the surface of the nanostructures via the laser-induced photoreduction effect. Parametric studies were conducted for the different concentrations of aqueous silver nitrate solutions and scanning speeds. The enhancement factor of the SERS is found to be higher than 10(9). The patterning technique provides an opportunity to incorporate the SERS capability in a functional microchip. PMID:19997399

Lin, Cheng-Hsiang; Jiang, Lan; Chai, Yen-Hsin; Xiao, Hai; Chen, Shean-Jen; Tsai, Hai-Lung

2009-11-23

390

Nanostructured surface enhanced Raman scattering sensor platform with integrated waveguide core  

NASA Astrophysics Data System (ADS)

We present a planar waveguide based sensor capable of simultaneous surface enhanced Raman scattering (SERS)/surface plasmon resonance (SPR) sensing methodologies. The sensor consists of a nanostructured area etched into a low loss planar waveguide fabricated from silicon oxynitride. The selective deposition of the 25 nm thick gold film on the nanostructured features was applied to create the SERS/SPR active sites. In this work, we adapt the SPR approach, coupling light propagating along the slab waveguide to the nano-textured area from underneath. The shapes of the nanostructures, thickness, and morphology of the gold coating are chosen to be suitable for SERS and SPR. Effects of geometric parameters associated with the nanostructured features such as diameters, length, and pitch were investigated. Detection of Benzyl Mercaptan was accomplished using a 785 nm laser in a SERS configuration excited from the underlying waveguide core. The detection of the analyte was confirmed by normal incident SERS measurements using an InVia Raman spectrometer. The surface enhanced Raman scattering signal from the 25 nm thick Au coated nanostructures provided a maximum intensity signal of 104. Using the same device in the SPR sensing arrangement provided a wavelength shift of 25 nm and an average signal to noise ratio of 10 dB to Benzyl Mercaptan. The fabricated sensor can easily be fabricated using nano imprinting into cheap polymer substrates and would provide disposable real-world remote sensing capabilities.

Pearce, S. J.; Pollard, M. E.; Oo, S. Z.; Chen, R.; Charlton, M. D. B.

2014-11-01

391

Physicochemical characteristics and droplet impact dynamics of superhydrophobic carbon nanotube arrays.  

PubMed

The physicochemical and droplet impact dynamics of superhydrophobic carbon nanotube arrays are investigated. These superhydrophobic arrays are fabricated simply by exposing the as-grown carbon nanotube arrays to a vacuum annealing treatment at a moderate temperature. This treatment, which allows a significant removal of oxygen adsorbates, leads to a dramatic change in wettability of the arrays, from mildly hydrophobic to superhydrophobic. Such change in wettability is also accompanied by a substantial change in surface charge and electrochemical properties. Here, the droplet impact dynamics are characterized in terms of critical Weber number, coefficient of restitution, spreading factor, and contact time. Based on these characteristics, it is found that superhydrophobic carbon nanotube arrays are among the best water-repellent surfaces ever reported. The results presented herein may pave a way for the utilization of superhydrophobic carbon nanotube arrays in numerous industrial and practical applications, including inkjet printing, direct injection engines, steam turbines, and microelectronic fabrication. PMID:24866696

Aria, Adrianus I; Gharib, Morteza

2014-06-17

392

Extreme wettability of nanostructured glass fabricated by non-lithographic, anisotropic etching  

PubMed Central

Functional glass surfaces with the properties of superhydrophobicity/or superhydrohydrophilicity, anti-condensation or low reflectance require nano- or micro-scale roughness, which is difficult to fabricate directly on glass surfaces. Here, we report a novel non-lithographic method for the fabrication of nanostructures on glass; this method introduces a sacrificial SiO2 layer for anisotropic plasma etching. The first step was to form nanopillars on SiO2 layer-coated glass by using preferential CF4 plasma etching. With continuous plasma etching, the SiO2 pillars become etch-resistant masks on the glass; thus, the glass regions covered by the SiO2 pillars are etched slowly, and the regions with no SiO2 pillars are etched rapidly, resulting in nanopatterned glass. The glass surface that is etched with CF4 plasma becomes superhydrophilic because of its high surface energy, as well as its nano-scale roughness and high aspect ratio. Upon applying a subsequent hydrophobic coating to the nanostructured glass, a superhydrophobic surface was achieved. The light transmission of the glass was relatively unaffected by the nanostructures, whereas the reflectance was significantly reduced by the increase in nanopattern roughness on the glass. PMID:25791414

Yu, Eusun; Kim, Seul-Cham; Lee, Heon Ju; Oh, Kyu Hwan; Moon, Myoung-Woon

2015-01-01

393

Extreme wettability of nanostructured glass fabricated by non-lithographic, anisotropic etching.  

PubMed

Functional glass surfaces with the properties of superhydrophobicity/or superhydrohydrophilicity, anti-condensation or low reflectance require nano- or micro-scale roughness, which is difficult to fabricate directly on glass surfaces. Here, we report a novel non-lithographic method for the fabrication of nanostructures on glass; this method introduces a sacrificial SiO2 layer for anisotropic plasma etching. The first step was to form nanopillars on SiO2 layer-coated glass by using preferential CF4 plasma etching. With continuous plasma etching, the SiO2 pillars become etch-resistant masks on the glass; thus, the glass regions covered by the SiO2 pillars are etched slowly, and the regions with no SiO2 pillars are etched rapidly, resulting in nanopatterned glass. The glass surface that is etched with CF4 plasma becomes superhydrophilic because of its high surface energy, as well as its nano-scale roughness and high aspect ratio. Upon applying a subsequent hydrophobic coating to the nanostructured glass, a superhydrophobic surface was achieved. The light transmission of the glass was relatively unaffected by the nanostructures, whereas the reflectance was significantly reduced by the increase in nanopattern roughness on the glass. PMID:25791414

Yu, Eusun; Kim, Seul-Cham; Lee, Heon Ju; Oh, Kyu Hwan; Moon, Myoung-Woon

2015-01-01

394

Superhydrophobic silanized melamine sponges as high efficiency oil absorbent materials.  

PubMed

Superhydrophobic sponges and sponge-like materials have attracted great attention recently as potential sorbent materials for oil spill cleanup due to their excellent sorption capacity and high selectivity. A major challenge to their broad use is the fabrication of superhydrophobic sponges with superior recyclability, good mechanical strength, low cost, and manufacture scalability. In this study, we demonstrate a facile, cost-effective, and scalable method to fabricate robust, superhydrophobic sponges through the silanization of commercial melamine sponges via a solution-immersion process. The silanization was achieved through secondary amine groups on the surface of the sponge skeletons with alkylsilane compounds, forming self-assembled monolayers on the surface of sponge skeletons. This resulted in our ability to tune the surface properties of the sponges from being hydrophilic to superhydrophobic with a water contact angle of 151.0°. The superhydrophobic silanized melamine sponge exhibited excellent sorption capacity for a wide range of organic solvents and oils, from 82 to 163 times its own weight, depending on the polarity and density of the employed organic solvents and oils, and high selectivity and outstanding recyclability with an absorption capacity retention greater than 90% after 1000 cycles. These findings offer an effective approach for oil spill containment and environmental remediation. PMID:25039789

Pham, Viet Hung; Dickerson, James H

2014-08-27

395

Localized surface plasmon resonance induced structure-property relationships of metal nanostructures  

NASA Astrophysics Data System (ADS)

The confluence of nanotechnology and plasmonics has led to new and interesting phenomena. The industrial need for fast, efficient and miniature devices which constantly push the boundaries on device performance tap into the happy marriage between these diverse fields. Designing devices for real life application that give superior performance when compared with existing ones are enabled by a better understanding of their structure-property relationships. Among all the design constraints, without doubt, the shape and size of the nanostructure along with the dielectric medium surrounding it has the maximum influence on the response and thereby the performance of the device. Hence a careful study of the above mentioned parameters is of utmost importance in designing efficient devices. In this dissertation, we synthesize and study the optical properties of nanostructures of different shapes and size. In particular, we estimated the plasmonic near field enhancement via surface-enhanced Raman scattering (SERS) and 2-photon Photoemission electron microscopy (2P-PEEM). We synthesized the nanostructures using four different techniques. One synthesis technique, the thermal growth method was employed to grow interesting Ag and Au nanostructures on Si. The absence of toxic chemicals during nanostructure synthesis via the thermal growth technique opens up myriad possibilities for applications in the fields of biomedical science, bioengineering, drug delivery among others along with the huge advantage of being environment friendly. The other three synthesis techniques (ion implantation, Electrodeposition and FIB lithography) were chosen with the specific goal of designing novel plasmonic metal, metal hybrid nanostructures as photocathode materials in next generation light sources. The synthesis techniques for these novel nanostructures were dictated by the requirement of high quantum efficiency, robustness under constant irradiation and coherent unidirectional electron emission. Two designs, (i) partially exposed metal nanostructures in an oxide matrix (ii) metal nanorod arrays, couple with incoming light at particular wavelengths which leads to plasmonic near field enhancement from the nanostructures. This plasmonic response is expected to lead to enhanced photoemission and thereby enhanced quantum efficiency. Moreover, the plasmonic enhancement and the shape of the nanostructure enable coherent unidirectional electron emission. Such an in depth study of the structure-property relationship, particularly the near field enhancement of novel metal, metal-metal oxide nanostructures will lead to applications as photocathode materials in next generation light sources.

Vilayurganapathy, Subramanian

396

From hydrophobic to superhydrophobic and superhydrophilic siloxanes by thermal treatment.  

PubMed

The cross-influence effects of treatment temperature and time on the wettability of a siloxane elastomer is investigated in detail, through static and tilt contact angle measurements. The material is heated at 400, 500, 600, 650, 700, and 800 °C for various periods, ranging from 1 to 300 s. The siloxane surface is subjected to multiple wettability transitions with treatment time: from intrinsic hydrophobicity to superhydrophobicity (and water repellency) and then through intermediate stages (hydrophobicity and hydrophilicity) to superhydrophilicity. For the time scale used herein (1-300 s), this scenario is recorded for treatment at 650, 700, and 800 °C. For treatment at lower temperatures (400, 500, and 600 °C) only the first transition, from intrinsic hydrophobicity to superhydrophobicity, is recorded. Scanning electron microscopy, micro-Fourier transform infrared (micro-FTIR), and micro-Raman spectroscopies are employed to correlate the aforementioned wettability transitions with structural and chemical changes of the siloxane surface, developed during thermal treatment. It is shown that the first transition from intrinsic hydrophobicity to superhydrophobicity is accompanied by a severe surface-structure evolution that increases surface roughness. Once superhydrophobicity is achieved, the surface structure reaches a saturation point and it is not subjected to any other change with further thermal treatment. FTIR spectroscopy shows that the intensity of the O-H/C-H peaks increases/decreases with treatment time, and Raman measurements show that the C-Si-C vibrations gradually disappear with treatment time. The evaporation of a droplet resting on a superhydrophobic, water-repellent siloxane surface, which was produced after appropriate thermal treatment, is monitored. It is shown that droplet evaporation initially follows the constant contact area mode. At later evaporation stages, a transition to the constant contact angle mode is recorded. Finally, it is demonstrated that the superhydrophobic and water-repellent siloxane surfaces exhibit self-cleaning properties, good durability, and furthermore do not practically affect the optical transparency of glass substrates. PMID:25313653

Karapanagiotis, Ioannis; Manoudis, Panagiotis N; Zurba, Andreea; Lampakis, Dimitrios

2014-11-11

397

Surface properties and biocompatibility of nanostructured TiO2 film deposited by RF magnetron sputtering.  

PubMed

Nanostructured TiO2 films are deposited on a silicon substrate using 150-W power from the RF magnetron sputtering at working pressures of 3 to 5 Pa, with no substrate bias, and at 3 Pa with a substrate bias of -50 V. X-ray diffraction (XRD) analysis reveals that TiO2 films deposited on unbiased as well as biased substrates are all amorphous. Surface properties such as surface roughness and wettability of TiO2 films, grown in a plasma environment, under biased and unbiased substrate conditions are reported according to the said parameters of RF power and the working pressures. Primary rat osteoblasts (MC3T3-E1) cells have been cultured on nanostructured TiO2 films fabricated at different conditions of substrate bias and working pressures. The effects of roughness and hydrophilicity of nanostructured TiO2 films on cell density and cell spreading have been discussed. PMID:25852353

Majeed, Asif; He, Jie; Jiao, Lingrui; Zhong, Xiaoxia; Sheng, Zhengming