Physico-chemical and dynamic study of oil-drop removal from bare and coated stainless-steel surfaces

We have studied the removal of sessile oil drops from stainless-steel surfaces under the action of water flow. A shear-flow cell is used to compare bare and polysiloxane-coated stainless-steel surfaces. We consider a rectangular channel where initially deposited drops are subjected to drag, gravity and pressure gradient forces. Our results indicate that a drop detachment mode is observed for the bare steel, whereas a sliding mode is observed for the coated steel. The removal of large drops, which requires low critical shear flows, is essentially dominated by the combined action of the lift and gravity forces. However, for small drops with a large critical shear flow, the capillary forces are the key factor. The detachment was also studied with surfactants added to water. It was found that the detachment mode exhibits a 'depinning effect', which results in drops sliding. Due to low pressure near the triple line, an accumulation of the surfactant induces surface tension gradients along the interface (Marangoni effect), which, in turn, facilitates depinning of the contact line. These results underline the crucial role of the capillary forces governed by the physico-chemical nature of stainless steels, a key factor for understanding the cleanability processes of these materials.     

Effects of Electrostatic and Capillary Forces and Surface Deformation on Particle Detachment in Turbulent Flows

In this work the rolling detachment of particles from surfaces in the presence of electrostatic and capillary forces based on the maximum adhesion resistance was studied. The effective thermodynamic work of adhesion, including the effects of electrostatic and capillary forces, was used in the analysis. The Johnson, Kendall and Roberts (JKR) and Derjaguin, Muller and Toporov (DMT) models for elastic interface deformations and the Maugis–Pollock model for plastic deformation were extended to include the effect of electrostatic and capillary forces. Under turbulent flow conditions, the criteria for incipient rolling detachment were evaluated. The turbulence burst model was used to evaluate the airflow velocity near the substrate. The critical shear velocities for removal of particles of different sizes were evaluated, and the results were compared with those without electrostatic and capillary forces. The model predictions were compared with the available experimental data and good agreement was observed.     

Effects of capillary force and surface deformation on particle removal in turbulent flows

A new rolling detachment model for particle removal in the presence of capillary forces based on the maximum adhesion resistance was developed. The new model uses an effective thermodynamic work of adhesion model that includes the effects of capillary forces generated by the formation of liquid meniscus at the interface. The JKR and DMT models for elastic particle and surface deformations and the Maugis and Pollock model for the plastic deformation were extended to include the effect of capillary forces. Under turbulent flow conditions, the criteria for incipient rolling detachments were evaluated. The turbulence burst model was used to evaluate the air velocity near the substrate. The critical shear velocities for resuspension of particles of different sizes were evaluated and the results were compared with those without capillary force. The model predictions were compared with the available experimental data and good agreement was found.     

Role of Interfacial Interactions in the Deposition of Colloidal Clay Particles in Porous Media

Colloidal clay particle transport under saturated conditions is believed to be controlled by its interactions with the surrounding environment. The dominating forces among these interactions are electrostatic forces that are determined by colloidal clay particle and porous medium surface charge density and Lifshitz–van der Waals forces that are determined by colloidal clay particle and porous medium surface thermodynamic properties. Electrostatic forces are greatly affected by solution chemistry in terms of solution ionic strength and pH. In this research, electrostatic and Lifshitz–van der Waals forces of natural colloidal clay particles with a model porous medium of silica sand were quantified at different ionic strength and pH conditions. At the same time, colloidal clay particle transport in the model medium of silica sand was conducted in a laboratory column. The maximum electrostatic forces, F ^EL (max), which occurred when the separation distance between colloidal clay particles and the porous medium was in the range of the sum of the double layer thicknesses of the colloidal clay particles and the porous medium, was found to be the determinant factor for colloidal clay particle deposition in the porous medium. Colloidal clay particle desorption in the porous media was related to the net effect of attractive Lifshitz–van der Waals forces and repulsive electrostatic forces, evaluated at the equilibrium distance where physical contact between the colloidal clay particle and silica sand actually occurred (i.e., affix force). Higher colloidal clay particle desorption was found to coincide with smaller affix force values.     

Mapping of adhesion forces on soil minerals in air and water by atomic force spectroscopy (AFS)

The adhesion force between an atomic force microscope (AFM) tip and sample surfaces, mica and quartz substrates, was measured in air and water. The force curves show that the adhesion has a strong dependence on both the surface roughness and the environmental conditions surrounding the sample. The variability of the adhesion force was examined in a series of measurements taken at the same point, as well as at different places on the sample surface. The adhesion maps obtained from the distribution of the measured forces indicated regions contaminated by either organic compounds or adsorbed water. Using simple mathematical expressions we could quantitatively predict the adhesion force behavior in both air and water. The experimental results are in good agreement with theoretical calculations, where the adhesion forces in air and water were mostly associated with capillary and van der Waals forces, respectively. A small long-range repulsive force is also observed in water due to the overlapping electrical double-layers formed on both the tip and sample surfaces.     

Impact of the Charge-Regulated Nature of the Bacterial Cell Surface on the Activity of Adhered Cells

Since the first reported observations by Zobell in 1943, it has been recognized that the metabolic activity of adhered bacteria can differ from that of their planktonic counterparts. Many studies have been performed and the overwhelming evidence is that bacterial adhesion to surfaces can result in changes to cellular metabolic activity and that the changes are a function of the surface properties of both the bacterial and adhering surfaces. However, the mechanism that results in these observations has remained elusive. The authors have approached this problem by focusing on cellular bioenergetics, which describes how bacteria obtain, store and use energy, and how adhesion can affect this process. In a series of experimental and numerical studies, the authors developed a hypothesis linking cellular bioenergetics to the physicochemical charge-regulation effect, which causes variations in surface electrostatic properties as a surface containing acid/base functional groups (e.g., the bacterial cell surface) approaches another surface. The purpose of this paper is to synthesize these prior studies and provide a cohesive presentation of the hypothesis. If this hypothesis is ultimately shown to be true, it will provide a fundamental basis for the engineered design of surface materials and coatings that can enhance or inhibit bacterial activity and colonization, depending on the requirements of the system at hand.     

Determination of the attachment and detachment forces in a coal grain/liquid/coal grain system by detachment experiments

On the basis of measurements of the destruction time of a coal sediment column structure, which were described earlier, a further and more detailed analysis of the results of these measurements was carried out. The radius of the contact plane between coal particles in the studied liquids was calculated. The values of the radius decreased with increasing length of the hydrocarbon chain of both alkanes and alcohols. Next, the values of the attachment force of two coal particles through a liquid were calculated and they increased with increasing length of the hydrocarbon chain of both liquids. We have found a linear relationship between reciprocal of the destruction time and the difference in the detachment and attachment forces. From this relationship we concluded that the work of adhesion of the liquid to the coal surface also influenced the attachment force between coal particles through the liquid.     

Effects of Nanoparticle Coating on the Adhesion of Emulsion Aggregation Toner Particles

Toner is a key material for the xerographic printing and copying industry. Compared to conventional pulverized toner particles, emulsion aggregation (EA) toner particles could adhere more strongly to substrates and their property distributions are narrower because of their near-perfect spherical shape and higher surface free energy. However, in general, uncoated EA toner is more difficult to transfer and clean during printing/copying processes for the same reasons. Nanoparticle additives could be used as control agents to reduce the toner particle–substrate adhesion. In order to optimize their adhesion and handling performances, an accurate adhesion characterization of the toner particles coated with different levels of additives is required. In current study, two non-contact adhesion characterization techniques based on acoustic air-coupled excitation and ultrasonic base excitation are presented. Their use for the adhesion characterization of individual bare toner particles with an average diameter of 6.0 μm on silicon substrates, and their silica nanoparticle coated variants with a surface area coverage (SAC) of 50% is demonstrated. The techniques are based on the detection of the resonance frequencies of rocking motion of micro-spheres. The out-of-plane transient displacement responses of the rocking particles are captured by a laser interferometer, and the natural frequencies of particle rocking motion obtained from transient displacements at the top of particles and the substrate are related to the strength of the adhesion bond. It is reported that the work of adhesion values of the 50% SAC-coated toner on silicon substrates are almost an order of magnitude lower than those for the bare ones.     

利用空气净化器去除甲醛的研究进展

针对当前市场空气净化器净化甲醛的应用现状,按照净化原理和常用材料介绍了净化器的分类,并介绍了新标准下了评价净化器效能的关键因子,综合分析了吸附、催化、负离子、等离子的效果优劣,对空气净化器未来的研究热点进行了阐述。     

Removal of Moisture from the Ultra Fine Particles Using Both High Centrifugal Force and Air Pressure

Abstract

A newly developed centrifugal batch dewatering unit was developed and used to remove the moisture contents of ultra fine particles (e.g., kaolin clay, silica, talc, and precipitated calcium carbonate). In the present method, air pressure was applied into the vessel of a conventional centrifuge to improve the efficiency of the dewatering. The experimental results showed that the moisture reductions of the samples could be enhanced more than 50% depending on dewatering conditions (i.e., G-force, spin time, applied pressure, cake thickness, particle size, surface hydrophobicity, and particle agglomeration). As a result, when the new centrifuge modification is used for the fine particle dewatering, cost and environmental concerns of thermal dryers could be considerably reduced and the handleability of the filter cakes could be significantly increased.     

对新BP公司战略的几点体会

分析了重组后的新BP公司的战略特点和发展动向,并结合中国石化集团公司的本情况提出了进一步研究的课题。     

粉末活性炭除臭工艺的影响因素

对粉末活性炭除臭工艺的若干影响因素（预处理参数、背景有机物、预氯化、pH值等）进行了较为深人的分析和探讨,得到了一些对实际生产具有较强指导意义的结论：①当混凝过程中生成的絮体尺寸与粉末活性炭尺寸相当时,粉末活性炭除臭效果最佳;（萤去除水中的背景有机物可以大幅度提高粉末活性炭的除臭效率：③取消预氯化可以提高粉末活性炭的除臭效率;（D调节原水的pH至弱酸性,对提高粉末活性炭的除臭效果有重要的意义。     

活性炭纤维负载纳米TiO2在光反应器中降解空气中微量甲醛的研究

以活性炭纤维为载体,用浸涂法制备了TiO2/ACF(活性炭纤维)光催化剂,设计了栅式光反应器用于空气中微量甲醛的净化,研究了ACF/TiO2的组成和光反应器构造对甲醛净化量的影响。结果表明,TiO2/ACF对空气中微量甲醛有较高的光催化降解活性,催化剂m(TiO2)/m(ACF)=0.082 1,光反应器催化层厚度为2 mm,各催化层间隔为20 mm时,甲醛净化量较大。TiO2/ACF催化剂稳定性好,累计运行45 h,甲醛的净化速率仍保持在0.150μg/(g.m in)左右。     

导流装置对含油雾颗粒气流影响的数值模拟

使用数值模拟分析的方法,探究在加装角钢和百叶这两种导流装置的情况下,静电式油雾净化器箱体内气流的变化。结果显示,在含油雾颗粒气流质量流量相同的前提下,角钢对箱体四周漩涡具有抑制作用,因而减少了漩涡区对气流造成的能量损耗。     

Temperature Effect on Removal of Sulfur Dioxide and Benzene in Humid Air by DC Corona Discharge

A DC corona discharge reactor was applied to remove sulfur dioxide (SO₂) and benzene (C₆H₆) from N₂‐O₂‐H₂O mixed gas in the temperature range from room temperature to 400 °C. When SO₂ was removed, the temperature elevation caused the decrease of the removal efficiency of SO₂. On the other hand, the removal efficiency of C₆H₆ was not significantly influenced by the temperature elevation. In the simultaneous removal of SO₂ and C₆H₆ in the relatively low temperature range below 200 °C, the removal efficiency of SO₂ is significantly inhibited by coexisting C₆H₆. When the simultaneous removal was conducted in the high temperature range, the removal efficiency of SO₂ was not sensitive against the coexisting C₆H₆. On the other hand, the removal efficiency of C₆H₆ was almost independent of coexisting SO₂ at all temperatures. A hypothesis of reaction mechanism was discussed based on radical reactions with SO₂ and C₆H₆ to explain the trend observed in the experiment.     

Studies of the Mechanical Properties and Practical Coating Adhesion on PP Modified by Oxidized Wax

In this study, the influences of polarity and the amount of oxidized polypropylene wax (OPPW) in blends with polypropylene (PP) were investigated by studying their surface properties. OPPW was completely miscible with PP up to 10 wt%. The adhesive strength of a acrylic-based primer coating on PP sheets, containing different wt% of OPPWs, was evaluated by using a direct 'pull off' test method. The results showed that the adhesive strength of the coating improved with an increase of the amount of OPPW in the blend. However, the degree of polarity in the OPPW did not have a significant impact on its adhesive properties. These observations were also supported by the results of ATR–FT-IR spectroscopy and surface energy measurements of the substrate. Furthermore, the results of adhesion test on the coating panels showed a significant enhancement after exposing to heat in an oven prior to the application of coating, e.g., about 230% increase for the blend containing 8 wt% of OPPW. The TGA curves showed a maximum drop of about 10% in thermal stability in comparison with that of the unblended PP. The changes in the mechanical properties of the blends were explained by considering the morphology of the blends and were supported by the changes in blend crystalinity and melting behavior. The elastic modulus remained almost unchanged while elongation and stress to breakpoint experienced a sharp reduction at concentrations of wax content higher than 6 wt%. The study showed a good balance of substrate coatability with its bulk properties at a blend concentration of about 6 wt% of OPPW.     

Some Remarks on the Classification of Water Vapor Sorption Isotherms and Blahovec and Yanniotis Isotherm Equation

Mathematical analysis was performed on equations describing water vapor sorption isotherms. It was shown that an identity exists between the Blahovec and Yanniotis (BY), D'Arcy and Watt (DW), and generalized D'Arcy and Watt (GDW) models. The original BY model has been modified to account for temperature dependence of the model parameters. This modification enables the application of this model to describe sorption data obtained at different temperatures. A new method for classification of sorption isotherms has been proposed that is much simpler than the classification established by Blahovec and Yanniotis.     

Influence of surface chemistry on particle-particle aggregation as measured by a Coulter Counter in the low concentration regime

The link between particle concentration, surface properties, and particle aggregation has been investigated for polystyrene latex in the low particle concentration regime, volume fractions less than 1 × 10^-6. The particles used in this model study were 9.14-μm diameter polystyrene beads, approximately the same size as red blood cells, using a Coulter Counter with a 100-μm aperture as a gauge of clustering. The lower concentrations of beads displayed the same trend as reported in other publications. Albumin and fibrinogen were then attached to the beads and the effect of non-specific binding by the proteins on particle agglomeration was studied. Albumin showed little effect on the number of aggregates encountered whereas fibrinogen increased the number of aggregates, indicating that stronger particle interactions occurred between the fibrinogen coated particles. The addition of stearic acid had no marked effect on the aggregation properties of the beads, coated or uncoated. The addition of sodium stearate, however, increased the number of doublets, triplets, and multiplets formed. These results may be relevant to adhesion of cells. Our approach is a plausible way to consider the roles that proteins and fatty acid molecules have on the relative binding potential without the constraints of using live cells.     

Effect of grafting of acrylic acid onto PET film surfaces by UV irradiation on the adhesion of PSAs

To improve the peel strength between a pressure-sensitive adhesive (PSA) and its substrate, grafting of acrylic acid (AA) onto the surface of poly(ethylene terephthalate) (PET) film was carried out. After AA was coated onto the surface of PET films using a spin coater, the coated PET films were irradiated by UV. To investigate the surface chemistry and topography of the PET-g-AA films, the grafted surface of the PET films was characterized by FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS) and scanning probe microscopy (SPM). From these investigations, the effects of grafting of AA at the surface of PET by UV irradiation were discussed. In addition, to determine the effect of grafting on the adhesion between PSA polymer and PET-g-AA films, peel strength was measured after the PSA/PET-g-AA system was cured at various temperatures. As the esterification between PSA polymer and PET-g-AA films occurred in the interfacial region, the peel strength of the PSA/PET-g-AA system generally increased with increasing curing temperature.