Fabrication of Novel Superhydrophobic Surfaces and Water Droplet Bouncing Behavior - Part 1: Stable ZnO-PDMS Superhydrophobic Surface with Low Hysteresis Constructed Using ZnO Nanoparticles

A superhydrophobic surface has many advantages in micro/nanomechanical applications, such as low adhesion, low friction and high restitution coefficient, etc. In this paper, we introduce a novel and simple route to fabricate superhydrophobic surfaces using ZnO nanocrystals. First, tetrapod-like ZnO nanocrystals were prepared via a one-step, direct chemical vapor deposition (CVD) approach. The nanostructured ZnO material was characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD) and the surface functionalized by aminopropyltriethoxysilane (APS) was found to be hydrophobic. Then the superhydrophobic surface was constructed by depositing uniformly ZnO hydrophobic nanoparticles (HNPs) on the Poly(dimethylsiloxane) (PDMS) film substrate. Water wettability study revealed a contact angle of 155.4 +/- 2 degrees for the superhydrophobic surface while about 110 degrees for pure smooth PDMS films. The hysteresis was quite low, only 3.1 +/- 0.3 degrees. Microscopic observations showed that the surface was covered by micro- and nano-scale ZnO particles. Compared to other approaches, this method is rather convenient and can be used to obtain a large area superhydrophobic surface. The high contact angle and low hysteresis could be attributed to the micro/nano structures of ZnO material; besides, the superhydrophobic property of the as-constructed ZnO-PDMS surface could be maintained for at least 6 months. (C) Koninklijke Brill NV, Leiden, 2010

Theoretical foundation of Zisman's empirical equation for wetting of liquids on solid surfaces

Theories of wetting of liquids on solid surfaces under the condition that van der Waals force is dominant are briefly reviewed. We show theoretically that Zisman's empirical equation for wetting of liquids on solid surfaces is a linear approximation of the Young-van der Waals equation in the wetting region, and we express the two parameters in Zisman's empirical equation in terms of the dielectric polarizabilities of the solid and liquids. The materials contained in this paper are suitable for physics teaching of wetting phenomena for undergraduate, graduate, general physicist, etc.

Evaporation of Ethanol Drops on a Heated Substrate Under Microgravity Conditions

We present in this paper results obtained from a parabolic flight campaign regarding ethanol sessile drop evaporation under reduced gravity conditions. Drops are created using a syringe pump by means of injection through a PTFE (polytetrafluoroethylene) substrate. The drops are recorded using a video camera and an infrared camera to observe the thermal motion inside the drop and on the heating substrate. The experimental set-up presented in this paper enables the simultaneous visualization and access to the heat flux density that is transferred to the drop using a heat flux meter placed between the heating block and the PTFE substrate. We evidence original thermal spreading phenomena during the ethanol drop creation on a heated PTFE substrate. The drop exhibits specific behaviour which is discussed here. This work is performed in the frame of a French-Chinese collaboration (project IMPACHT) for future experiments in a Chinese scientific satellite.

Near infrared lights emission of Ar-40(16+) impacting on metal surfaces

The highly charged ion Ar-40(16+) with the velocity (kinetic energy E (K)=150 keV, velocity V=8.5x10(5) m/s) smaller than Bohr velocity (V (Bohr)=2.9x10(6) m/s) was found to hove impacts on the surfaces of metals Ni, Mo, Au and Al, and the Ar atomic infrared light lines and X-rays spectra were simultaneously measured. The experimental results show that the highly charged ion that captures electrons is neutralized, and the multiply-excited hollow atom forms. The hollow atom cascade decay radiates lights from infrared to X-ray spectrum. The intensity of infrared lights shows that the metallic work functions play an important role in the neutralization process of highly charged ions during their interaction with metallic surfaces, which verifies the classical over-the-barrier model.

Slow highly charged ion O4+ induced electron emission from clean solid surfaces

The. total electron emission yields following the interaction of slow highly charged ions (SHCI) O4+ with different material surfaces (W, Au, Si and SiO2) have been measured. It is found that the electron emission yield gamma increases proportionally with the projectile velocity v ranging from 5.36 x 10(5)m/s to 10.7 x 10(5)m/s. The total emission yield is dependent on the target materials, and it turns out to follow the relationship gamma(Au) > gamma(Si)> gamma(W). The result shows that the electron emission yields are mainly determined by the electron stopping power of the target when the projectile potential energy is taken as a constant, which is in good agreement with the former studies