With acidic etching and fluorination treatment, super-hydrophobic surface is successfully fabricated on aluminous sheet. Water contact angle on the surface is larger than 150°and contact angle hysteresis is about 4°(5μL droplet) . The resultant surfaces are analyzed by means of scanning electron microscopy (SEM). It is shown that a “labyrinthic” structure with mass cuboid plateaus and caves is formed on the surface of aluminous sheet. Surface microstructures are the key to the preparation of super-hydrophobic surfaces.Water-repellency of the super-hydrophobic surface is studied in some aspects, such as the droplet’s behaviors on the super-hydrophobic surface, the effects of the organic compound content in water on the wettability of the surface, the phase transformation process on the super-hydrophobic surface. It is shown that the super-hydrophobic surface has the characters of no-droplet adherence, oleophilic and dropwise condensation.Based on above research, super-hydrophobic aluminous micro-channels are successfully fabricated by reasonable ameliorating preparation techniques and experiment conditions. Heat transfer and fluid flow of deionized water flowing laminarly in the super-hydrophobic/hydrophilic microchannel are studied experimentally. The results show that the pressure drop and f·Re in super-hydrophobic micro-channels are lower than that of super-hydrophilic micro-channels, dimensionless pressure drop is fluctuating and the heat transfer coefficient and Nu in super-hydrophobic micro-channels are lower than that of super-hydrophilic micro-channels. The analysis result is that the air-layer existing in the micro – nano structures of the super-hydrophobic surface decreases flow resistance evidently and , in the same time, blocks heat transfer to a certain extent.The apparent heat transfer coefficient of super-hydrophobic micro-channels is computed in which the heat conduction of a stationary air-layer in no-slip boundary is considered. It is found that the apparent heat transfer coefficient is lower than experimental data and the difference increases with air-layer’s thickness. It is supposed that eddy flow is generated in the micro-nano bubbles by the slip flow of water at the wall, which enhances the heat transfer.
Post about "super-hydrophobicity"
Polytetrafluoroethylene(PTFE)-polyphenylene sulfide(PPS) composite coating mesh film was successfully prepared by a spray-plasticizing method on the stainless steel mesh. These composite coating mesh films show super-hydrophobic and super-oleophilic properties. Contact angle of this mesh film is 156.3°for water,and close to 0°for diesel oil and kerosene. The contact angle hysteresis is about 4.3°(5μL droplet) for water.The surfaces of the prepared PTFE-PPS composite coating mesh films were analyzed through scanning electron microscopy(SEM).It is shown that lots of particles with microscale accumulate on the surface of the mesh film and on these particles find reseaus of nanometer scale.It was analyzed by Wenzel model that the micro- and nanostructures on the surface of mesh film could enhance hydrophobicity and oleophilicity of the surface.Surface micro- and nanostructures is the key to PTFE-PPS composite coating mesh films with super-hydrophobicity and super-oleophilicity.Performance of PTFE-PPS composite coating mesh films was studied in some aspects, such as the water and oil droplets’ behaviors on the mesh films,the effects of the mesh films being immerged in different solutions on the super-hydrophobicity and super-oleophilicity, the pencil hardness,flexility and the adhesive force of the mesh films.It is shown that PTFE-PPS composite coating mesh films have the characters of super-hydrophobic, super-oleophilic,high hardness,strong adhesive force,better flexility and corrosion resistance, which lay a foundation for application of these mesh films.According to the two extreme properties of super-hydrophobicity and super-oleophilicity, PTFE-PPS composite coating mesh films were used to separate oil and water.A simple oil/water separation device with many stages was designed to investigate the separation ability of the prepared mesh films.The retentate separated by the mesh film was analyzed through extraction-uv spectrophotometer.In the experiment,the effects of the state of oil in the water,initial oil content,pore diameter of the stainless steel mesh substrate and separation stages of the mesh film on the separation effect were studied.The results show that PTFE-PPS composite coating mesh films are only used for the separation of the floating oil at present.The more initial oil content,the higher oil removal rate;the smaller pore diameter of the stainless steel substrate,with the increase of separation stages of the mesh film,the less oil content in the retentate and higher oil removal rate. PTFE-PPS composite coating mesh films on the 400 meshes/inch(0.038 mm) stainless steel mesh were used to design two oil/water separation devices respectively.And the separation effect of the two oil/water separation devices was investigated.The results show that the separation effect of the improved device is stabler than that of the initial device;the smaller flow rate,the less oil content in the retentate and higher oil removal rate.The oily feed containing 16.9 wt%(about 163.7 g/L) is separated by the improved device to 20 mg/L.
According to the characteristics of super-hydrophobic films in the process of separation, a suit of oil/water separation device has been designed so that the super-hydrophobic/super-oleophilicity films can be applied to the filed of oil/water separation. The device has advantages of high space utility and convenient operation.A problem of the separation device has been analyzed by experiment and solved by inclining the oil/water separator. The influence of incline angle on separation effects has been analyzed and studied. Experiments have been performed by changing the connection (series and parallel) of the three separation units. It is indicated that the separation device can handle oil/water mixture with large flow rate when the three single separators are connected in parallel. However, owing to the resistance between separation units, the separation device only can handle oil/water mixture with small flow rate when connected in series, and three single separators connected in series are not as good as in parallel on the disposing capacity.Factors, such as pressure difference on both sides of film, oil/water mixture flow rate and oil initial content have been studied on the separation effect on condition that the device be inclined (the obliquity is 4.12°) and connected in parallel. It is shown that oil content in outlet water with the increases of oil/water mixture flow rate and oil initial content, and the greater the flow rate, the effects is more significant; while the influence of pressure difference is small; These factors influence one another, Through reasonable control of these factors, the separator can handle oil/water mixture with large flow rate or a wide range of oil initial content. According to the Karl Fischer principle, a set of titration equipment which can be used to measure the trace water in oil has been set up and tested. Water content in oil in different pressure and oil initial content has been measured. It is indicated that water content in oil is small and little change when separating films are operated under 14.72kpa (equal to 150cm water column). While operated over 15.70kpa (equal to 160cm water column), the quantity of water permeating from separating films will increase with pressure difference and decline with oil initial content. The oil permeating velocity of separating films is measured, indicating that the oil permeating velocity of separating films and pressure difference on both sides of film have a linear relation.
Super-hydrophobic surface of polypropylene sheet is successfully prepared via acombination of micro-molding method and photo-grafting method. In this method, PPsheets with a roughness surface were firstly prepared by micro-molding, and thenphoto grafting method was employed to prepare a low energy layer on the roughsurface. With the advantages of roughness and low-energy layer, the modified PPsurface became super-hydrophobic, and the contact angle (CA) was 170o.To prepare a PP surface with roughness, a stainless steel sheet corroded by FeCl3solution is used as the template. Because of the well- distribution of micro-scale pit onthe metal surface, the topography of surface of PP sheet is shaped as a kind of roughstructure which consists of abundant of micro-convex. The metallographicmicroscope was used to observe the template surface, scanning electron microscope(SEM) was used to observe the PP surface, WAC measurement instrument was usedto characterized the hydrophobicity of PP surface. The results indicated that extendingthe etching time and rising the etching temperature could contribute to increase theroughness of PP surface and the WAC arrived at 135 o.UV-induced photo-grafting polymerization was employed to make one kind offluorinated acrylate monomer graft on to the rough surface of PP substrate. Thehydrophobicity of the surface before and after modified was investigated by watercontact angle measurement. SEM was used to observe the microstructure ofsurface．The existence of a fluorinated polymer layer and its linkage with the PPsubstrate through chemical bonds were confirmed by FT-IR, surface elementalanalysis (EDS) and DSC measurements on the extracted grafted films. The influenceof experimental factors on the grafting yield (GY) was studied systematically whichwas including plasma treatment conditions, the concentration of initiator and monomer, and UV-grafting conditions. The results show that GY could be promotedby increasing the power and extending the time of plasma treatment, increasing theconcentration of initiator and monomer and raising the temperature of graftingreaction. In this study, the WAC of prepared PP surface is 155 o under optimalconditions.Finally, the micro-molding method and UV-induced photo-grafting were combinedto modify PP surface. Fluorinated groups were grafted onto the rough PP surface,which result in many micro- and nano- scale binary convexities distributed on thesurface. SEM, X-ray photoelectron spectroscopy (XPS) and WAC measurements wereused to characterize the effect of modification. The results indicated that this kind ofcomposite structure and low surface energy together endowed the surface excellentsuper-hydrophobic ability.
Micro- and nano-structure’s special wettability (such as superhydrophobic) has attracted much attention for their promising applications in self-cleaning, biomedical, micro-flowing, anti-corrosion and new-type drag reduction material. Surface wettability is governed by the microstructure and surface energy of a solid. In the present dissertation, several surfaces with special wettability have been prepared and constructed by manipulating composition and roughness. By using several methods, super-hydrophobic surfaces modified with four different micro-nanostructures have been successfully prepared. As follows:1. The oriented ZnO nanostructure was synthesized by mild two-step solution(﹤100℃) method. We have modified ZnO nanostructures on the surfaces of different substrates, such as brocade, Wound-paste and metal mesh. The obtained surfaces exhibit contact angles larger than 150°, with a rolling angle of 6°. Meanwhile, ZnO nanoneedles have been synthesized, because the contact area between a water droplet and a nanoneedle was reduced, the roughness of the surface has improved, thus the resulting surface shows great water-repellency, with a contact angle of 163°.2. On the basic of solution method of fabricating Ag leaf-like crystalloids, we provide an Ag~+ solution with low concentration and stable property to prepare superhydrophobic surface. In this way, the resulting surface exhibits superhydrophobicity, with a contact angle of 163°. The obtained surface can resist solution(pH=3~12), the static contact angle can also reach to 157°. Superhydrophobic film has been successfully used as fliter for separating oil-water liquid, the separating rate is high, and the ratio can reach 90%, therefore, has practical application.3. We assembled different super-hydrophobic nanostructures on different substrates by oxidation method. Including: (1) Preparing CuO nanosheets on brass; (2) Fabricating nanoneedles on copper. The obtained surfaces show high roughness, especially for copper mesh with nanoneedles, with a contact angle of 167°, water droplets hardly sticked to the resulting surface. Importantly, nanostructures firmly stick to the substrate, liquid and gas can go through mesh freely, thus, the superhydrophobic film has practical application prospects in oil-water separation.