Application of hydrophobic fluorinated silicon oxide nanoparticle coating on electrodynamic screen (EDS) films for enhancing self-cleaning function of solar collectors

Optical surfaces, which are exposed to outdoor environmental conditions, are susceptible to dust deposition. Sunlight incident on the surface of photovoltaic (PV) modules is attenuated by the dust layer accumulation on the front surface of the modules. Energy-yield decrease by dust layer accumulation, called soiling losses, can be 5 to 40 percent annually unless the modules are cleaned frequently. Cleaning the optical surface with water is generally used in solar plants, which causes an unsustainable demand for freshwater in semi arid and desert areas. Adhesion of soil on the front surface of solar collectors plays a major role in the cleaning process. For low water cleaning, the module surface is often coated with an anti-soiling coating. If the surface is made hydrophilic, water can wet the surface most effectively making the cleaning process efficient, but requiring a low amount of water. If the surface is made hydrophobic, the surface energy is decreased reducing the adhesion force; the cleaning can be performed even with a lesser amount of water or with an application of an external removal force, such as wind. Major problems with the application of anti-soiling coatings are their environmental durability, poor adhesion of the coating on the surface and low resistance to abrasion. Since the removal of dust still requires spraying of water to the PV modules, the coatings get removed within a short period. Similarly, another dust removal method that does not require water for cleaning PV modules, is the Electrodynamic Screen (EDS) film, which consists of series of parallel transparent electrodes embedded within two transparent dielectric films and laminated on the surface of the solar collectors. When the electrodes are activated film by applied voltage pulses there will be a traveling electric field on the EDS surface, then the dust particles on the film surface gets charged electrostatically and are removed by Coulomb forces applied by the electric field. The EDS film application is an elective removal of the dust particles from the PV module surface without requiring any water or mechanical forces. However, the applied Coulomb force cannot overcome the dust adhesion force when the particles are smaller than 2 m in diameter or if the capillary adhesion forces are present because of the high humidity environment. The objective of the thesis is to decrease the particle adhesion forces of the EDS film surface by the application of a hydrophobic coating so that the dust removal efficiency is enhanced for moving small particles. To improve EDS film based dust-removal performance it is necessary to have the coating non-conductive and optically transparent and hydrophobic for the effective application electrostatic removal mechanisms. The hydrophobic coating would reduce the surface energy and hence the dust adhesion force, assisting the self-cleaning effect, which would not require any water consumption. Since water-based cleaning is no longer needed for dust removal when the EDS film surface is modified with hydrophobic surface properties, the durability of the coating would improve. We describe here a synthesis of a hydrophobic fluorinated silicon oxide nanoparticle coating on the EDS films for enhancing the self-cleaning function of solar collectors. We used dip-coating method to apply a single-layer hydrophobic silicon oxide nanoparticle film with a large static water contact angle on the EDS film surface. silicon oxide was prepared by the sol-gel method using Tetraethylorthosilicate (TEOS) and ammonium hydroxide as a precursor anda catalyst. The suspension was treated with 3-aminopropyltriethoxysilane (APS) and 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FAS-17) to modify the surface of the coating, which greatly improved the hydrophobicity, and thus gave the coating the desired self-cleaning property. We used polyurethane (PU) as a binder between the substrate and coating to enhance the durability of the lm in outdoors applications. Experimental data on the optical transmittance, adhesion of the hydrophobic film on the glass surface of the EDS lm, and the dust removal efficiency are presented. The average optical transmission efficiency (TE) decreased from 93.43 to 89.78 percent and the output power restoration (OPR) of the solar panels laminated with EDS film with SH coating increased from 98.3 to 99.19 percent. Possible improvements to the hydrophobic coating process and its durability and future research needs are discussed

The influence of surface treatment of PVD coating on its quality and wear resistant

The article deals with a determination of the influence of a cutting edge preparation on the quality and wear resistance of coated cutting tools. Cutting inserts made from a sintered carbide with a deposited layer of PVD coating were selected for measurement. Non-homogeneity caused by the creation of droplets arises in the application layer during the process of applying the coating by the PVD method. These droplets make the surface roughness of the PVD coating worse, increase the friction and thereby the thermal load of the cutting tool as well. Also, the droplets could be the cause of the creation and propagation of droplets in the coating and they can cause quick cutting tool wear during machining. Cutting edge preparations were suggested for the improvement of the surface integrity of deposited layers of PVD coating, namely the technology of drag finishing and abrasive jet machining. After their application, the areal surface roughness was measured on the surface of coated cutting inserts, the occurrence of droplets was tracked and the surface structure was explored. A tool-life test of cutting inserts was carried out for verification of the influence of surface treatment on the wear resistance of cutting inserts during the milling process. The cutting inserts with a layer of PVD coatings termed as samples A, B, and C were used for the tool-life test. The first sample, A, represented the coating before the application of cutting edge preparations and samples B and C were after the application of the cutting edge preparation. A carbon steel termed C45 was used for the milling process and cutting conditions were suggested. The visual control of surface of cutting inserts, intensity of wear and occurrence of thermal cracks in deposited PVD layers were the criterion for the evaluation of the individual tests.Web of Science97art. no. 43

Controlling Marangoni induced instabilities in spin-cast polymer films: how to prepare uniform films

In both research and industrial settings spin coating is extensively used to prepare highly uniform thin polymer films. However, under certain conditions, spin coating results in films with non-uniform surface morphologies. Although the spin coating process has been extensively studied, the origin of these morphologies is not fully understood and the formation of non-uniform spincast films remains a practical problem. Here we report on experiments demonstrating that the formation of surface instabilities during spin coating is dependent on temperature. Our results suggest that non-uniform spincast films form as a result of the Marangoni effect, which describes flow due to surface tension gradients. We find that both the wavelength and amplitude of the pattern increase with temperature. Finally, and most important from a practical viewpoint, the non-uniformities in the film thickness can be entirely avoided simply by lowering the spin coating temperature.Comment: 8 pages, 6 figures. electronic supplementary material: 3 pages, 4 figure

A starch edible surface coating delays banana fruit ripening

A rice starch edible coating blended with sucrose esters was developed for controlling the postharvest physiological activity of Cavendish banana to extend postharvest quality during ripening at 20 ± 2 °C. Coating effectiveness was assessed against changes in fruit physiochemical parameters such as weight loss, titratable acidity, total soluble solids, flesh fruit firmness, ion leakage, colour change, respiration, ethylene production, chlorophyll degradation and starch conversion were determined. The topography of coating material on the fruit surface was evaluated by scanning electron microscope (SEM). Surface morphology studies highlighted the binding compatibility of the coating matrix with the fruit peel character and formed a continuous uniform layer over the fruit surface. The results showed that the coating was effective in delaying ethylene biosynthesis and reducing respiration rate. Other factors impacting included delayed chlorophyll degradation, reduced weight loss and retention of fruit firmness for the first six days, all of which improved the commercial value of the fruit. The shelf life of coated fruit was prolonged for 12 days in comparison with the untreated control which ripened within seven days and lost marketability after Day 6. The pilot study demonstrates the effectiveness of a starch-based edible coating formulation for improving the ambient storage capacity of banana fruit

Reusable Surface Insulation (RSI) Material Samples

Test specimen data sheets are presented for 48 high temperature and 40 low temperature reusable surface insulation tiles. Tabular data show dimensions, density, coating weight, and final tile weight. Codes indicate basic material, surface coating, and hydrophobic treatment

Thermodynamical fluctuations in optical mirror coatings

Thermodynamical fluctuations of temperature in mirrors may produce surface fluctuations not only through thermal expansion in mirror body but also through thermal expansion in mirror coating. We analyze the last "surface" effect which can be larger than the first "volume" one due to larger thermal expansion coefficient of coating material and smaller effective volume. In particular, these fluctuations may be important in laser interferometric gravitational antennae.Comment: 12 pages, LaTex, 3 figure

Structure and wear mechanisms of nano-structured TiAlCN/VCN multilayer coatings

Dry sliding wear of transition metal nitride coatings usually results in a dense and strongly adhered tribofilm on the worn surface. This paper presents detailed electron microscopy and Raman spectroscopy characterizations of the microstructure, a newly developed multilayer coating TiAlCN/VCN and its worn surface after pin-on-disc sliding wear against an alumina ball. The friction coefficient in a range of 0.38–0.6 was determined to be related to the environmental humidity, which resulted in a wear coefficient of the coating varying between 1017 and 1016 m3 N1 m1. TEM observation of worn surfaces showed that, when carbon was incorporated in the nitride coating, the formation of dense tribofilm was inhibited

Development and application of rice starch based edible coating to improve the postharvest storage potential and quality of plum fruit (<i>Prunus salicina</i>)

The study investigated the possibility of enhancing the shelf life of plum fruit coated with rice starch-ι-carrageenan (RS-ι-car) composite coating blended with sucrose fatty acid esters (FAEs). Film solution (starch 3%, carrageenan 1.5% and FAEs 2%) was prepared by mixing the ingredients and properties of stand-alone films (physical, mechanical, barrier and surface morphology) were studied before applying the coating on fruit surface. Fruit were stored at 20 °C for 3 weeks and analyzed for weight loss, ethylene production, respiration rate, color change, firmness, and titratable acidity (TA) and soluble solid content (SSC). Surface morphology of stand-alone film and fruit surface (after applying on the plum fruit) was studied using scanning electron microscopy (SEM). Phytochemical analysis was performed during the storage period and total phenolic content (TPC), total antioxidant capacity (TAC), flavonoid content (FC) and free radical scavenging activity were determined. The rice starch composite coating was shown to be effective in reducing both weight loss (WL) and respiration rate and inhibiting the endogenous ethylene production when compared to the uncoated control fruit stored at room temperature (p &lt; 0.05). TPC, TAC, FC and free radical scavenging activity was unaffected in the coated fruit throughout the storage period (p &lt; 0.05). The findings reported in this study indicate that the RS-ι-car-FAEs coating prolongs the shelf life and maintains the overall quality of plum fruit during storage and could potentially be commercialized as a new edible coating for the plum fruit industry

Adsorption and release of BMP-2 on nanocrystalline apatite-coated and uncoated hydroxyapatite/b-tricalcium phosphate porous ceramics

The association of bone morphogenetic proteins (BMPs) with calcium phosphate bioceramics is known to confer them osteoinductive properties. The aim of this study was to evaluate the surface properties, especially regarding recombinant human BMP-2 (rhBMP-2) adsorption and release, of commercial sintered biphasic calcium phosphate ceramics after coating with biomimetic nanocrystalline apatite. The raw and coated ceramics exhibited similar macroporous structures but different nanometer-sized pores contents. Both types of ceramics showed Langmuir-type adsorption isotherms of rhBMP-2. The coating noticeably increased the rate of adsorption and the total amount of growth factor taken up, but the maximum coverage per surface area unit as well as the affinity constant appeared lower for coated ceramics compared with raw ceramic surfaces. The limited advantage gained by coating the ceramics can be assigned to a lower accessibility of the surface adsorption sites compared with the raw ceramics. The quantity of rhBMP-2 spontaneously released in cell culture medium during the first weeks was lower for coated samples than for uncoated ceramics and represented a minor fraction of the total adsorbed amount. In conclusion, the nanocrystalline apatite coating was found to favor the adsorption of rhBMP-2 while providing a mean to fine tune the release of the growth factor

Effect of surface modification on single-walled carbon nanotube retention and transport in saturated and unsaturated porous media

This work investigated the effect of different surface modification methods, including oxidization, surfactant coating, and humic acid coating, on single-walled carbon nanotube (SWNT) stability and their mobility in granular porous media under various conditions. Characterization and stability studies demonstrated that the three surface modification methods were all effective in solubilizing and stabilizing the SWNTs in aqueous solutions. Packed sand column experiments showed that although the three surface medication methods showed different effect on the retention and transport of SWNTs in the columns, all the modified SWNTs were highly mobile. Compared with the other two surface modification methods, the humic acid coating method introduced the highest mobility to the SWNTs. While reductions in moisture content in the porous media could promote the retention of the surface modified SWNTs in some sand columns, results from bubble column experiment suggested that only oxidized SWNTs were retention in unsaturated porous media through attachment on air–water interfaces. Other mechanisms such as grain surface attachment and thin-water film straining could also be responsible for the retention of the SWNTs in unsaturated porous media. An advection–dispersion model was successfully applied to simulate the experimental data of surface modified SWNT retention and transport in porous media