Shock-induced transformation of liquid deuterium into a metallic fluid

Simultaneous measurements of shock velocity and optical reflectance at 1064, 808, and 404 nm of a high pressure shock front propagating through liquid deuterium show a continuous increase in reflectance from below 10% and saturating at approximately (40-60)% in the range of shock velocities from 12 to 20 &mgr;m/ns (pressure range 17-50 GPa). The high optical reflectance is evidence that the shocked deuterium reaches a conducting state characteristic of a metallic fluid. Above 20 &mgr;m/ns shock velocity (50 GPa pressure) reflectance is constant indicating that the transformation is substantially complete.     

Wetting behavior of pentane on water. The analysis of temperature dependence

The temperature dependence of wetting behavior for pentane on water is analyzed from the standpoint of the Derjaguin-Frumkin theory. The joint action of two mechanisms of surface forces, the van der Waals and the image charge interactions, are considered to calculate the isotherms of the disjoining pressure. To analyze the temperature influence on the magnitude of van der Waals forces, we have used the exact Dzyaloshinsky, Lifshitz, and Pitaevsky equation. It is shown that image forces, arising due to the restricted solubility of water in pentane, decay much faster with increasing the film thickness and can be considered as short ranged in comparison to the van der Waals forces. The competitive action of the image charge and the van der Waals forces provides the plausible explanation of the temperature dependence of wetting in the system under consideration.     

Preparation of Stable Superhydrophobic Coatings on a Paint Surface with the Use of Laser Treatment Followed by Hydrophobizer Deposition

Colloid Journal - Several superhydrophobic coatings have been created with the use of laser treatment of a paint surface followed by the chemisorption of a hydrophobic agent. Surfaces with...     

The influence of the surface on conformational equilibrium in thin layers of nematic liquid crystal

Changes in the conformational equilibrium in thin layers of the nematic liquid crystal 5CB between fluorite plates were studied by IR spectroscopy. A decrease in the thickness of the liquid crystalline layer symmetrically confined by poorly wettable fluorite surfaces is accompanied by the shift of conformational equilibrium toward rotamers characterized by a higher energy and the spatial structure preventing dense packing of molecules in the interlayer.     

Shift of triple point in confined systems with curved interfaces

The unified thermodynamic approach to the analysis of melting/freezing phenomena in confined systems is proposed. The approach relates the shift of the triple point in a confined system in comparison with the bulk system with the physico-chemical parameters of the bulk system and the boundary layer. The application of general equations to particular types of confinement is illustrated for small particles and substance embedded inside porous matrices. The analysis of equations derived indicates that for the systems considered the shift of triple point in the boundary layers and in the uniform core part of the system in the general case differ from each other. The shift of triple point may be either positive or negative and may be controlled for paricles by variation of the interfacial energy, and for the pores by variation of interfacial energy and/or pore walls wettability.     

Origins of thermodynamically stable superhydrophobicity of boron nitride nanotubes coatings

Superhydrophobic surfaces are attractive as self-cleaning protective coatings in harsh environments with extreme temperatures and pH levels. Hexagonal phase boron nitride (h-BN) films are promising protective coatings due to their extraordinary chemical and thermal stability. However, their high surface energy makes them hydrophilic and thus not applicable as water repelling coatings. Our recent discovery on the superhydrophobicity of boron nitride nanotubes (BNNTs) is thus contradicting with the fact that BN materials would not be hydrophobic. To resolve this contradiction, we have investigated BNNT coatings by time-dependent contact angle measurement, thermogravimetry, IR spectroscopy, and electron microscopy. We found that the wettability of BNNTs is determined by the packing density, orientation, length of nanotubes, and the environmental condition. The origins of superhydrophobicity of these BNNT coatings are identified as (1) surface morphology and (2) hydrocarbon adsorbates on BNNTs. Hydrocarbon molecules adsorb spontaneously on the curved surfaces of nanotubes more intensively than on flat surfaces of BN films. This means the surface energy of BNNTs was enhanced by their large curvatures and thus increased the affinity of BNNTs to adsorb airborne molecules, which in turn would reduce the surface energy of BNNTs and make them hydrophobic. Our study revealed that both high-temperature and UV-ozone treatments can remove these adsorbates and lead to restitution of hydrophilic BN surface. However, nanotubes have a unique capability in building a hydrophobic layer of adsorbates after a few hours of exposure to ambient air.