Exploring an expedient IMDA reaction approach to construct the guanacastepene core

Construction of the [5-7-6] tricyclic core of guanacastepenes was attempted by using the intramolecular Diels-Alder (IMDA) reaction and Me(3)Al-mediated ring opening of the oxabridge as key synthetic steps. The illustrated chemistry demonstrated a synthetic feasibility to build up the framework of guanacastepenes by the IMDA reaction. [reaction: see text]     

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

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

Pendant bubble method for an accurate characterization of superhydrophobic surfaces

The commonly used sessile drop method for measuring contact angles and surface tension suffers from errors on superhydrophobic surfaces. This occurs from unavoidable experimental error in determining the vertical location of the liquid-solid-vapor interface due to a camera's finite pixel resolution, thereby necessitating the development and application of subpixel algorithms. We demonstrate here the advantage of a pendant bubble in decreasing the resulting error prior to the application of additional algorithms. For sessile drops to attain an equivalent accuracy, the pixel count would have to be increased by 2 orders of magnitude.     

Palladium catalyzed fragmentation reaction as an approach to vitamin A ester

A novel C₁₀ + C₁₀ approach to retinoids employing a palladium induced decarboxylative elimination is described.     

Diverse access to artificial superhydrophobic surfaces using block copolymers

The creation of an artificial superhydrophobic surface with micro- and nanostructures has been demonstrated using a block copolymer micelle solution and silica nanoparticles. The unique technique of a nanoparticle-supported micelle stabilization together with changes in the solvent power guarantees the precise morphology control of certain block copolymer-mediated surfaces. The approaches presented here provide a new strategy for the fabrication of a wettability-controlled organic-inorganic hybrid or organic coatings.     

Water and ice in contact with octadecyl-trichlorosilane functionalized surfaces: a high resolution x-ray reflectivity study

We present a high energy x-ray reflectivity study of the density profiles of water and ice at hydrophobic and hydrophilic substrates. At the hydrophobic water/octadecyl-trichlorosilane (water-OTS) interface, we find clear evidence for a thin density depletion layer with an integrated density deficit corresponding to approximately 40% of a monolayer of water molecules. We discuss the experimental results in terms of a simple model of hydrophobic/hydrophilic solid-liquid interfaces. Our results also exclude the presence of nanobubbles. A detailed study of possible radiation damage induced by the intense x-ray beam at the dry OTS surface and at the ice-OTS, as well as at water-OTS interfaces, discloses that noticeable damage is only induced at the water-OTS interface, and thus points to the dominant role of highly mobile radicals formed in bulk water close to the interface.     

UVO-tunable superhydrophobic to superhydrophilic wetting transition on biomimetic nanostructured surfaces

A novel strategy for a tunable sigmoidal wetting transition from superhydrophobicity to superhydrophilicity on a continuous nanostructured hybrid film via gradient UV-ozone (UVO) exposure is presented. Along a single wetting gradient surface (40 mm), we could visualize the superhydrophobic (thetaH2O > 165 degrees and low contact angle hysteresis) transition (165 degrees > thetaH2O > 10 degrees ) and superhydrophilic (thetaH2O < 10 degrees within 1 s) regions simply through the optical images of water droplets on the surface. The film is prepared through layer-by-layer assembly of negatively charged silica nanoparticles (11 nm) and positively charged poly(allylamine hydrochloride) with an initial deposition in a fractal manner. The extraordinary wetting transition on chemically modified nanoparticle layered surfaces with submicrometer- to micrometer-scale pores represents a competition between the chemical wettability and hierarchical roughness of surfaces as often occurs in nature (e.g., lotus leaves, insect wings, etc).     

Facile method to fabricate raspberry-like particulate films for superhydrophobic surfaces

A facile method using layer-by-layer assembly of silica particles is proposed to prepare raspberry-like particulate films for the fabrication of superhydrophobic surfaces. Silica particles 0.5 microm in diameter were used to prepare a surface with a microscale roughness. Nanosized silica particles were then assembled on the particulate film to construct a finer structure on top of the coarse one. After surface modification with dodecyltrichlorosilane, the advancing and receding contact angles of water on the dual-sized structured surface were 169 and 165 degrees , respectively. The scale ratio of the micro/nano surface structure and the regularity of the particulate films on the superhydrophobic surface performance are discussed.     

A nonlithographic top-down electrochemical approach for creating hierarchical (micro-nano) superhydrophobic silicon surfaces

Superhydrophobic surfaces are biomimetic structures with potential applications in several key technological areas. In the past decade, several top-down and bottom-up fabrication methods have been developed to create such surfaces. These typically combine a hierarchical structure and low surface energy coatings to increase the contact angle and decrease the rolling angles. Silicon-based superhydrophobic surfaces are particularly attractive since they can be integrated with active electronics in order to protect them from the detrimental effects of environmental water and moisture. In this work, we introduce a simple and inexpensive process incorporating electrochemical surface modification (to create a fractal shape micro-nano topography) in combination with a final wet etching step to fabricate a superhydrophobic silicon surface with a contact angle of 160 degrees and a sliding angle of less than 1 degree.     

A facial approach to fabricate superhydrophobic aluminum surface

A facial chemical etching method was developed for fabricating superhydrophobic aluminum surfaces. The resultant surfaces were characterized by scanning electron microscopy, water contact angle (WCA) measurement, and optical methods. The surfaces of the modified aluminum substrates exhibit superhydrophobicity, with a WCA of 154.8° ± 1.6° and a water sliding angle of about 5°. The etched surfaces have binary structure consisting of the irregular microscale plateaus and caves in which there are the nanoscale block‐like convexes and hollows. The superhydrophobicity of aluminum substrates occurs only in some structures in which the plateaus and caves are appropriately ordered. The resulted surfaces have good self‐cleaning properties. The results demonstrate that it is possible to construct superhydrophobic surface on hydrophilic substrates by tailoring the surface structure to providing more spaces to trap air. Copyright © 2009 John Wiley & Sons, Ltd.     

Droplet motion on designed microtextured superhydrophobic surfaces with tunable wettability

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

Investigating the interface of superhydrophobic surfaces in contact with water

Neutron reflectivity (NR) is used to probe the solid, liquid, vapor interface of a porous superhydrophobic (SH) surface submerged in water. A low-temperature, low-pressure technique was used to prepare a rough, highly porous organosilica aerogel-like film. UV/ozone treatments were used to control the surface coverage of hydrophobic organic ligands on the silica framework, allowing the contact angle with water to be continuously varied over the range of 160 degrees (superhydrophobic) to <10 degrees (hydrophilic). NR shows that the superhydrophobic nature of the surface prevents infiltration of water into the porous film. Atomic force microscopy and density functional theory simulations are used in combination to interpret the NR results and help establish the location, width, and nature of the SH film-water interface.     

A general route to transform normal hydrophilic cloths into superhydrophobic surfaces

Herein, we describe a simple and inexpensive method for forming superhydrophobic cloths with the highest water contact angle of close to 180 degrees , in which normal commercial cloths serving as pristine materials are modified with suitable gold micro/nanostructures.     

Reversible superhydrophobic to superhydrophilic conversion of Ag@TiO2 composite nanofiber surfaces

A new type of superhydrophobic material consisting of a surface with supported Ag@TiO(2) core-shell nanofibers has been prepared at low temperature by plasma-enhanced chemical vapor deposition (PECVD). The fibers are formed by an inner nanocrystalline silver thread which is covered by a TiO(2) overlayer. Water contact angles depend on the width of the fibers and on their surface concentration, reaching a maximum wetting angle close to 180 degrees for a surface concentration of approximately 15 fibers microm(-2) and a thickness of 200 nm. When irradiated with UV light, these surfaces become superhydrophilic (i.e., 0 degrees contact angle). The decrease rate of the contact angle depends on both the crystalline state of the titania and on the size of the individual TiO(2) domains covering the fibers. To the best of our knowledge, this is one of the few examples existing in the literature where a superhydrophobic surface transforms reversibly into a superhydrophilic one as an effect of light irradiation.     

Variability of silica surfaces as reaction media

The properties of nine silica surfaces as reaction media are compared.     

Electrochemical synthesis of silver polyhedrons and dendritic films with superhydrophobic surfaces

Single-crystalline Ag dendrites are grown on a Ni/Cu substrate by using a simple templateless, surfactantless electrochemical technique. Controlling only the applied potential causes a change in the deposited silver morphology from polyhedrons to dendrites. Microstructure characterization suggests that preferential growth along the 211 directions by the oriented attachment of Ag nanocrystals leads to the formation of Ag dendrites, which are composed of trunks, branches, and leaves. Modifying as-grown Ag dendritic film with a thickness of about 10 microm with a self-assembled monolayer of n-dodecanethiol yields a superhydrophobic surface with a contact angle of 154.5 +/- 1.0 degrees and a tilt angle lower than 2 degrees.     

Impact of picoliter droplets on superhydrophobic surfaces with ultralow spreading ratios

The impact of picoliter-sized water droplets on superhydrophobic CF(4) plasma fluorinated polybutadiene surfaces is investigated with high-speed imaging. Variation of the surface topography by plasmachemical modification enables the dynamics of wetting to be precisely controlled. Final spreading ratios as low as 0.63 can be achieved. A comparison of the maximum spreading ratio and droplet oscillation frequencies to models described in the literature shows that both are found to be much lower than theoretically predicted.     

Simultaneous fabrication of superhydrophobic and superhydrophilic polyimide surfaces with low hysteresis

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

In situ infrared approach to unravel reaction intermediates and pathways on catalyst surfaces

Research on Chemical Intermediates - Reaction intermediates on catalyst surfaces have often been elucidated on the basis of ex situ observation of adsorbed species and theoretical computations...