296 research outputs found
A simple method to create superhydrophobic aluminium surfaces
Superhydrophobic surfaces were prepared using a very simple and low-cost method by spray coating. A high static water contact angle of about 154° was obtained by deposition of stearic acid on an aluminium alloy. However, this coating demonstrated a high contact angle hysteresis (~ 30Âș). On the other hand, superhydrophobic surfaces with a static contact angle of about 162Âș and 158Âș, and a low contact angle hysteresis of about 3Âș and 5Âș were respectively obtained by incorporating nanoparticles of SiO2 and CaCO3 in stearic acid. The excellent resulting hydrophobicity is attributed to the synergistic effects of micro/nanoroughness and low surface energy. A study of the wettability of these surfaces at temperatures ranging from 20 to-10 ÂșC showed that the superhydrophobic surface becomes rather hydrophobic at supercooled temperatures
Fabrication of PECVD-grown fluorinated hydrocarbon nanoparticles and circular nanoring arrays using nanosphere lithography
Nanosphere lithography (NSL) masks were created by spin-coating of polystyrene particles onto silicon surfaces. Fluorinated hydrocarbon films were coated on the nanosphere lithography masks using plasma-enhanced chemical vapor deposition (PECVD) to obtain ordered arrays of fluorinated hydrocarbon. Atomic force microscope images show hexagonally ordered nanodots of dimension 225 ± 11 nm with a height of 23 ± 4 nm. Every hexagon encloses a circular ring of diameter 540 ± 24 nm having a height and width of 13.5 ± 0.6 nm and 203 ± 16 nm, respectively. FTIR analysis shows two distinct zones of atomic bonding of CHx and CFx in the plasma coated ordered fluorinated hydrocarbon films
Superhydrophobic coatings with reduced ice adhesion
A brief description of how superhydrophobicity can help mitigate the ice accretion problem on power network equipment and other exposed structures by reducing ice-to-surface adhesion is presented. Basic models, namely the Wenzel and CassieâBaxter models, accounting for the contact angle of water on solid surfaces relating to the influence of surface roughness on hydrophobicity are discussed. The results on superhydrophobic aluminum surfaces, superhydrophobic nanostructured silver thin films, superhydrophobic nanostructured zinc oxide as well as superhydrophobic nanofibres are also discussed. Some of the superhydrophobic surfaces were tested for ice adhesion and a reduced ice adhesion was obtained
Superhydrophobic and icephobic surfaces prepared by RF-sputtered polytetrafluoroethylene coatings
A superhydrophobic and icephobic surface were investigated on aluminum alloy substrate. Anodizing was used first to create a micro-nanostructured aluminum oxide underlayer on the alloy substrate. In a second step, the rough surface was coated with RF-sputtered polytetrafluoroethylene (PTFE or TeflonÂź). Scanning electron microscopy images showed a âbird's nestâ-like structure on the anodized surface. The RF-sputtered PTFE coating exhibited a high static contact angle of ~165° with a very low contact angle hysteresis of ~3°. X-ray photoelectron spectroscopy (XPS) results showed high quantities of CF3 and CF2 groups, which are responsible for the hydrophobic behavior of the coatings. The performance of this superhydrophobic film was studied under atmospheric icing conditions. These results showed that on superhydrophobic surfaces ice-adhesion strength was 3.5 times lower than on the polished aluminum substrate
Morphological instability of the solid-liquid interface in crystal growth under supercooled liquid film flow and natural convection airflow
Ring-like ripples on the surface of icicles are an example of morphological
instability of the ice-water interface during ice growth under supercooled
water film flow. The surface of icicles is typically covered with ripples of
about 1 cm in wavelength, and the wavelength appears to be almost independent
of external temperature, icicle radius, and volumetric water flow rate. One
side of the water layer consists of the water-air surface and growing ice is
the other. This is one of the more complicated moving phase boundary problems
with two interfaces. A recent theoretical work [K. Ueno, Phys. Rev. E 68,
(2003) 021603] to address the underlying instability that produces ripples is
based on the assumption of the absence of airflow around icicles. In this
paper, we extend the previous theoretical framework to include a natural
convection airflow ahead of the water-air surface and consider whether the
effect of natural convection airflow on the wavelength of ripples produced on
an ice surface is essential or not.Comment: 19 pages, 5 figure
Risk assessment of failure of outdoor high voltage polluted insulators under combined stresses near shoreline
The aim of this paper is to investigate the various effects of climate conditions on outdoor insulators in coastal areas as a result of saline contamination under acidic and normal cold fog, determining significant electrical and physico-chemical changes on the insulator surface and considering the effect of discharge current, electric field distribution and surface roughness. To replicate similar conditions near the shoreline, experimental investigations have been carried out on insulation materials with the combined application of saline contamination and acidic or normal cold fog. The test samples included silicone rubber (SiR), ethylene propylene diene monomer (EPDM) and high-density polyethylene (HDPE), which were used as reference. The materials are of the same composition as those used in real-life outdoor high voltage insulators. All samples were aged separately in an environmental chamber for 150 h for various saline contaminations combined with acidic and normal cold fog, and were generated by means of the adopted experimental setup. This analysis represented conditions similar to those existing near the shoreline exposed to saline and acid spray during winter and early spring. Electric field and discharge current along polymeric samples were examined under acidic and normal cold fog. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopic (SEM) were used to probe the physico-chemical changes on the samples surface and investigate the hydrophobicity recovery property after aging tests. Finally, a comparative study was carried out on polymeric samples before and after being exposed to the acidic and normal cold fog based on the results obtained from the experiment. Research data may provide references for the better prediction of surface degradation as well as for the better material coating and design of external insulation
Superhydrophobic properties of silver-coated films on copper surface by galvanic exchange reaction
Hydrophobic properties of thin nanostructured silver films produced by galvanic exchange reaction on a copper surface were studied after passivation with stearic acid.
The morphology of the silver films was controlled by varying the concentration of silver nitrate in the solution. Water contact angle as high as 156° and contact angle hystérésis as low as 5° were achieved for samples obtained with initial silver ion concentration of
24.75 mM in the solution. However, a strong dependence of contact angle and contact angle hysteresis on the fractal-like morphology of the silver films was observed with the
variation of silver ion concentration
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