Influence of N-alkanes on contact angle and flotability of quartz

Measurements of time dependence of the contact angle were carried out for water drops on a quartz surface in the presence of saturated hydrocarbon vapour as well as on a quartz surface previously wetted with a hydrocarbon. The results obtained were compared with theoretically calculated values on the basis of the modified Young equation and the literature data for the surface free energy components of quartz covered with a monolayer water film. On the basis of the measurements and calculations it was found that the values of the contact angle in the studied systems depend on the kind and thickness of hydrocarbon film present on the quartz surface, as well as on the thickness of water film present on this surface. Changes of the contact angle with the hydrocarbon film thickness are characterized by the maximum and minimum values. This allows previously obtained results of the quartz flotation activity changes in the presence of the aliphatic hydrocarbon films to be explained.     

Superhydrophobic polymer films via aerosol assisted deposition — Taking a leaf out of nature's book

Aerosol assisted deposition of three sets of polymer films based on commercially available resins was achieved on various substrates. The films were characterised using a range of methods, including water contact and slip angle to determine water repellent properties. The aerosol assisted deposition inside the chemical vapour deposition reactor was unique in generating a highly rough superhydrophobic surface with water contact angles up to 170°. During the deposition process, two of the polymers were cured resulting in the development of high surface morphology. It was observed that the polymer that did not cure did not develop such a rough surface resulting in a lower water contact angle (∼ 99°). The superhydrophobic films had a Cassie-Baxter type wetting with water failing to penetrate the surface porosity, water spraying on the surface would bounce off. These films had exceptionally low slide angles of ca 1-2° from the horizontal.     

Surface energy and chemical characteristics of interfaces of adhesively bonded aluminium joints

The deleterious effects of water on the physico-chemical aspects of the durability of adhesively bonded aluminium joints has been investigated. Emphasis was placed on analytical techniques that lead to the better understanding of changes induced at the metal/epoxy interface by the presence of water. Analytical techniques such as contact angle measurements, X-ray photoelectron spectroscopy and X-ray diffraction were practical in obtaining information on the chemical composition and structure of the samples. Chemical conversion-coated samples were found to be much more stable in wet conditions compared to samples without conversion coating. The surface structure on the adherend, after extensive immersion times, was found to consist of a compact layer of bayerite with traces of gibbsite. The calculations of interfacial energy, _sl, and work of adhesion in dry and wet conditions, W _A and W _Al were carried out to evaluate the maximum bond strength. It was found that the durability of the bond in the presence of water was quite high for the XD4300/6061-T6 joint systems.     

动态毛吸法测定纤维及粉末料的接触角研究

本文用动态毛吸法研究了表面处理对纤维浸润性的影响,结果表明碳纤维及聚酯纤维表面经冷等离子体氧处理,浸润性有很大的改善,碳纤维约提高四倍,这是因为等离子氧表面处理过程,将含氧基团羧基,羟基及羰基等引入到表面所致。同时从测得的浸润过程表面自由能改变值△γ,计算出水对纤维的接触角,它与采用接触角测定仪倾斜法所测得的结果基本上一致。从所测得的接触角值也可以看出表面经处理之后,浸润性得以改善。如碳纤维由77°降为63°,聚酯纤维由77°降为52°。此外我们还研究了煤粉和玻璃粉体系对水的浸润性,发现水对玻璃粉的浸润性优于煤粉,前者的浸润接触角为47°、后者则为90°,此接触角值也与采用接触角测定仪由静滴法测得水对片材的接触角相一致。由此可见动态毛吸法可以用于研究纤维及粉末体系的浸润性,而且操作简单易行,测试周期短。      

THE LINE/PSEUDO-LINE TENSION IN THREE-PHASE SYSTEMS

The effect of drop (bubble) size on contact angle was examined over a wide range of drop (bubble) sizes for the CCl₄-toluene solution/NaCl aqueous solution/quartz, ethylene gtycol/CCI₄-toluene solution/quartz, bitumen/ Na₅P₃O₁₀ aqueous solution/quartz, water/kerosene/quartz, heptane/water/quartz, and air bubble/water/polyethylene systems. For most systems, a nonlinear relationship between cosine of the contact angle and reciprocal of drop (bubble) base radius was obtained. All known factors affecting the contact angle/drop size relationship are discussed. It was found that the effect of gravitational forces as well as solid strain in the vicinity of the three-phase contact line are not responsible for the contact angle/drop size relationship for the systems examined. It appears that surface heterogeneities (contaminants) have the greatest effect on the contact angle/drop size relationship as is evident for these results from our laboratory. Also, surface roughness can contribute to the effect of drop size on contact angle. A theoretical background is presented and modifications of both the Cassie Equation and Wenzel Equation are derived.

A linear correlation of cosine of the contact angle vs. reciprocal of drop base radius was obtained for the heptane/waler/quartz systems, when high purity single-component liquids and a smooth, chemically cleaned, quartz plate were used. The line tension was determined for this system to be (5.1 ± 4.3) 10 ^- 9N.     

Oxidation of silicon nitride in a wet atmosphere

The effect of water vapour on oxidation was studied with hot-pressed silicon nitride containing both yttria and alumina as sintering aids in wet air flow with 10, 20, 30, and 40 vol% H₂O at 1300°C for 100 h. The oxidation kinetics were determined in a wet air flow with 20 vol% H₂O and in a dry air flow at 1300°C for oxidation times up to 360 h. The water vapour in the atmosphere slightly influenced the oxidation and accelerated the reaction, and the weight gained on oxidation in a wet atmosphere had an increasing tendency with increasing water vapour content. The oxidation proceeded in a diffusion-controlled manner in both wet and dry atmospheres. The values of weight gained in wet oxidation varied to a greater degree than in dry oxidation. Water vapour had a strong effect on the devitrification of the amorphous oxide. This process was presumed to promote the rate of oxidation more than in dry atmosphere. The water vapour also had a strong roughening effect on the surface oxide layer grown during oxidation. The flexural strength at room temperature was degraded by oxidation in a wet atmosphere and it is presumed to be degraded by wet oxidation slightly and consecutively with time.     

柔印网纹辊油墨转移特性研究

目的研究网纹辊向印版进行油墨转移的特性。方法将网纹辊结构简化为轴对称的梯形槽,使用有限元法对网纹辊油墨转移过程进行数值模拟,即模拟油墨从网纹辊向印版进行转移,并且加入网纹辊和印版滚筒的运动情况,研究了接触角、梯形槽高宽比和角速度对油墨转移的影响。结果分析了油墨从网纹辊转移到印版的影响因素,油墨转移率随着上板接触角的增加而减小,随着梯形槽接触角的增大而增大,梯形槽高宽比越小和角速度越大,油墨转移率越高。结论通过对柔印网纹辊油墨转移情况进行数值模拟,得到了接触角、梯形槽高宽比及角速度对油墨转移情况的影响规律,为柔印生产实践提供了理论参考。     

Aerosol assisted deposition of melamine-formaldehyde resin: Hydrophobic thin films from a hydrophilic material

An intrinsically hydrophilic melamine-formaldehyde thin film (water contact angle of 34° for a cast flat surface) was deposited on a glass substrate using aerosol assisted chemical vapour deposition. The resultant resin films showed a highly developed microstructure consisting of spherical structures that were agglomerated into towers. The surface wetted via a Cassie-Baxter mechanism with air trapped underneath the water droplets and resultant water contact angles as high as 135°. Film thickness and coverage were crucial in determining the wetting properties. Films with limited deposition gave hydrophilic results, whereas thicker films greater than 4 μm were superhydrophilic. This behaviour could be explained by the ease of trapping air under the coating. It is shown that the water wetting properties of a single material can be altered from superhydrophilic to near superhydrophobic by controlling the surface microstructure in a single-step aerosol route.     

含氟成膜聚合物应用于文物的表面保护

含氟聚合物具有稳定性高、耐氧化性及耐化学侵袭性良好等特点，适用于器物表面的防护处理．在分析了含氟聚合物及其共混物的成膜性能、接触角、玻璃化转变温度、耐酸碱性能等研究结果的基础上，将含氟聚合物应用于土质及石质类文物表面的防护处理．通过文物样块表面颜色、接触角、透气性的测定表评估含氟聚合物在文物表面防护应用的效果．并用电子显微镜分析技术对膜的表面特征及与文物表面结合情况进行了表征．     

An experimental modeling of gravity effect on rupture of a locally heated liquid film

This study deals with the formation of dry patches in a subcooled liquid film flowing over a locally heated plate at small positive and negative plate inclination angles with respect to the horizon. Prior to film rupture appreciable thermocapillary deformations of the film surface appear, growing with the heat flux. Upon reaching a threshold heat flux the film rupture occurs. By means of high speed imaging it is found that the process of rupture involves two stages: 1) abrupt film thinning down to a thin residual film on the heater; 2) rupture and dryout of the residual film. As the plate inclination angle is reduced the threshold heat flux required for film rupture weakly decreases, however when the angle becomes negative the threshold heat flux begins to rise dramatically, which is associated with an increase of the stabilizing hydrostatic effect due to the growth of the film thickness. The characteristic time of rupture decreases as the threshold heat flux increases. At nucleation of the dry patch the speed of contact line can be as high as 220 mm/s. The results obtained, apart from their intrinsic importance for ground-based applications, can also be of interest for microgravity research as a film flow with different relative contribution of inertia, hydrostatic and thermocapillary forces is considered.     

具有不同浸润性功能有机表面薄膜的制备

通过开发的有机镀膜技术,选用具有不同功能基团的有机镀液对不锈钢表面进行改性.借助于红外光谱、接触角和表面自由能等测试对有机镀膜处理的不锈钢表面薄膜进行了表征.实验结果表明,经过TTN溶液有机镀膜后,不锈钢表面自由能升高、蒸馏水接触角减小,具有了亲水功能特性;而经过DHN和AF17N溶液有机镀膜处理后,其表面自由能降低、蒸馏水接触角增大,具有良好的疏水功能特性;其中经过AF17N镀液处理后表面自由能最小而接触角最大,即疏水效果最佳.该技术实现了不锈钢表面的亲/疏水表面改性,提供了一种制备具有不同浸润性的有机表面薄膜材料的方法.     

Impact of Device Technology Processes on the Surface Properties and Biocompatibility of Group III Nitride Based Sensors

In this work we have investigated the impact of typical device processing steps on the surface properties (roughness, chemical composition, contact angle to water) of group III‐nitride based chemical sensors with emphasis on the electrical performance of the sensor and the biocompatibility. Basic sensing device is an AlGaN/GaN high electron mobility transistor. The widely distributed mammalian cell cultures HEK 293FT and CHO‐K1 served as biological model systems. The processing of the devices had only little influence on the cell growth onto the sensor. In all cases it was superior to silicon surfaces. Fluorine dry etching smoothes the surface and forms an oxide, which improves the electrical properties of the AlGaN/GaN sensor. In contrast, autoclave treatment enhances the carbon contamination with negative impact on the sensor properties and increased the contact angle to water. For all other treatments the contact angle recaptures a value of about 50 ± 5° after exposure to air or water droplets for some hours due to the contamination by hydrocarbons.     

MB8镁合金超疏水表面的制备和润湿性

通过激光加工在MB8镁合金表面构造具有规则结构的纹理,再制备1H,1H,2H,2H-全氟葵烷基三氯硅烷(FDTS)自组装分子膜,从而构建了MB8镁合金超疏水表面。用扫描电子显微镜和接触角测量仪观察和测量试样表面的形貌和润湿性。结果表明,激光加工在试样表面构造的粗糙结构和低表面能物质FDTS自组装分子膜使该试样具有超疏水性;经激光加工和沉积自组装分子膜后,MB8镁合金试样表面对水的接触角显著增大(达到150°以上)。将MB8镁合金超疏水表面加工成漂浮平台,承载能力的测试结果表明,超疏水平台的漂浮承载能力明显比非超疏水性平台的大,平台的承载能力与接触角的数值成正比。理论计算结果和"气垫"的存在表明,该超疏水表面符合Cassie-Baxter。状态模型,对接触角理论值与测量值的分析表明分级粗糙结构对超疏水表面构建有重要作用。     

Antibacterial Performance of a Cu-bearing Stainless Steel against Microorganisms in Tap Water

Tap water is one of the most commonly used water resources in our daily life. However, the increasing water contamination and the health risk caused by pathogenic bacteria, such as Staphylococcus aureus and Escherichia coli have attracted more attention. The mutualism of different pathogenic bacteria may diminish antibacterial effect of antibacterial agents. It was found that materials used for making pipe and tap played one of the most important roles in promoting bacterial growth. This paper is to report the performance of an innovative type 304 Cu-bearing stainless steel(304Cu SS) against microbes in tap water. The investigation methodologies involved were means of heterotrophic plate count, contact angle measurements, scanning electron microscopy for observing the cell and subtract surface morphology,atomic absorption spectrometry for copper ions release study, and confocal laser scanning microscopy used for examining live/dead bacteria on normal 304 stainless steel and 304 Cu SS. It was found that the surface free energy varied after being immersed in tap water with polar component and Cu ions release.The results showed 304 Cu SS could effectively kill most of the planktonic bacteria(max 95.9% antibacterial rate), and consequently inhibit bacterial biofilms formation on the surface, contributing to the reduction of pathogenic risk to the surrounding environments.     

Excitation of plate waves in thickness measurements of layers deposited on thin plates

Layer thickness measurements with an acoustic micrometer using pseudo-Sezawa waves in which ultrasonic waves are obliquely applied to a layered surface of a specimen have been proposed. A case in which the plate thickness of the specimen is so thin that it cannot be regarded as a half space is studied. A number of modes of plate waves are then excited in addition to pseudo-Sezawa waves. The plate waves, giving rise to the appearance of extra dips in the power spectrum of reflected waves, cause difficulties in the measurements. To prevent the excitation of plate waves, it is proposed that a mask of a sound-insulating material with a slit aperture should be placed on the layered surface of the specimen. Experiments and theoretical calculations, using lead frames of LSI chips as typical test specimens with thin substrates, were performed to demonstrate the effectiveness of the present method in preventing the excitation of plate waves.     

Thermophysical Analysis of Gioia Marble in Dry and Water-Saturated States by the Pulse Transient Method

Measurements of the thermophysical properties of Gioia marble in the temperature range from −20 to 60°C are presented. Thermophysical properties, namely, thermal diffusivity, thermal conductivity, and specific heat, were measured by the pulse transient technique. The data were compared for dry and water-saturated states. Despite the very low porosity of marble of about 0.6 vol%, an increase of the transport property parameters (thermal diffusivity and thermal conductivity) up to 20% after water saturation was found. To verify the differences in the transport parameters, the ultrasonic pulse velocity method was employed. A detailed analysis of thermophysical property data during the freeze/thaw process for dry and water-saturated marble was carried out in the temperature range from −8 to 1°C, where an anomaly in the water freezing process was observed. In order to study artificial aging of Gioia marble, up to 60 freeze/thaw cycles were performed. No significant changes in the thermophysical properties of Gioia marble were observed during the artificial aging process. Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.     

Components of surface free energy of galena

Measurements of the contact angle for water, diiodomethane, bromoform and 1,1,2,2-tetrabromoethane on non-oxidized and oxidized surfaces of galena were made. Using the results obtained, the geometric mean approach, and the long-range and short-range interactions approaches, the dispersion and non-dispersion, and Lifshitz-van der Waals and acid-base components of the surface free energy of galena were determined and compared with those calculated from adsorption isotherms ofn-octane andn-propanol. On the basis of the measurements and calculations it was found that the surface free energy of galena depends on its degree of oxidation and arise mainly from London's and acid-base intermolecular interactions. It was also found that values of the dispersion and non-dispersion components of galena surface free energy determined from the contact angle assuming that a film is present around the water and diiodomethane drops, are close to those obtained from adsorption isotherms ofn-octane andn-propanol.     

Contact angle hysteresis on smooth and homogenous surfaces in gravitational fields

In an experiment conducted on a space shuttle flight, contact angle hysteresis was observed for the water-glass system. Surface heterogeneities have usually been taken as the cause of the observed hysteresis. In order to examine if other factors such as adsorption could be the cause of the observed hysteresis, contact angles on homogenous, smooth surfaces of glass were examined in ground-based experiments. Ten glass cylinders with different inside diameters were constructed with a capillary tube in the centre of each cylinder. The cylinders were filled with prepared water and the meniscus heights inside the capillary tube and in the glass cylinder were measured. Using the values of these parameters, the pressure in the vapour and the contact angle at the three-phase line of each interface were calculated from the equilibrium conditions. In each of the cylinders, a difference in the contact angle at the three-phase line of the capillary and the three-phase line of the cylinder was observed. This contact angle hysteresis cannot be explained by surface heterogeneity or line tension effect. The observed contact angle hysteresis is predicted to be the result of the pressure profile in the system. This suggests adsorption and its extraordinary sensitivity to vapour-phase pressure as the source of the contact angle hysteresis.     

A study on the components of surface free energy of quartz from contact angle measurements

Measurements of the contact angle for water, glycerol, formamide, diiodomethane and 1,1,2,2-tetrabromoethane on a quartz surface were made. Using the results obtained, the geometric mean approach and long-range and acid-base interaction approach, the dispersion, non-dispersion, Lifshitz-van der Waals and acid-base components of the surface free energy of quartz were determined and compared with those determined in different ways. On the basis of the measurements and calculations it was found that the surface free energy of quartz depends largely on the amounts of silanol groups and physically adsorbed water molecules on its surface. It was also found that the two tested approaches to surface free energy of solids and liquids gave similar results, and it is suggested that the surface free energy of quartz results mainly from dispersion and hydrogen-bond intermolecular interactions.