Dynamic Contact Angles of Water in Ultrathin Capillaries

Velocities of motion V of advancing meniscus of water in quartz capillaries with radii from 45 to 270 nm was directly measured using an optical microscope. In the case, when the meniscus advanced over the wetting film that is remained after the previous meniscus receding, hysteresis was not observed, and the wetting was complete. When the meniscus advanced over the yet unwetted surface, the dynamic contact angle _d greatly depended on V, this dependence was the more pronounced, the smaller the r value. As the velocity V increases to 10^–3 cm s^–1, the value of _d rises to 60°–70° reaching the plateau. Preliminary adsorption of water vapors on the capillary surface markedly decreases the values of _d. The results obtained cannot be explained in terms of hydrodynamic and barrier theories of the contact angle. It was assumed that the controlling factor is the kinetics of vapor adsorption on the capillary surface in front of advancing meniscus.     

接触角法研究氨丙基硅烷化石英表面

利用接触角法研究了氨丙基硅烷化石英表面的基团浓度及单分子层中单个分子的截面积。提出了氨丙基硅烷化的模型。     

Electrokinetic Properties of the Methylated Surface of Quartz Capillaries

The surface charge and electrokinetic potential of quartz capillaries with hydrophobized (methylated) surface are measured. It is shown that, during the flow of an electrolyte solution through the capillary, the potential lowers with time due to formation of gas bubbles on the surface screening the surface charge. In a certain period of time, drastic jump of the potential to its initial value is observed, which is interpreted as a detachment of bubbles by the flowing solution. The formation of bubbles is provoked by the roughness of the methylated surface with asperities of up to 20 nm in height. The profiles of the methylated surface were obtained by the atomic force microscopy. An addition of a nonionic surfactant hydrophilizing the hydrophobic surface to the electrolyte solution lowers the -potential, which could be caused by the suppression of the slip effect. Estimations made on the basis of an earlier developed theory lead to the values of slip coefficient that are close to those measured for micron-sized hydrophobic capillaries.     

On the Problem of the Relationship between the Contact Angle and Surface Roughness Coefficient: Quartz Wettability with Melted Germanium

Equilibrium contact angles of melted geranium have been measured at fused quartz surfaces. The surfaces were preliminarily grinded, polished, and, in some cases, etched. Then, the roughness coefficients are determined for the relief profile and the surface itself by optical interferometry using a NanoMap 1000 WLI profilometer. The contact angle has been found to vary in a range of 147°–164° depending on the method of surface pretreatment. The measured values of the contact angles agree with the data of other researchers. At the same time, the analysis of the obtained data has led to the conclusion that Wenzel’s equation, which relates the contact angles at smooth and rough surfaces, is not valid for germanium droplets on quartz surface.     

Computer Simulation of Thin Water Films in Nonwettable Capillaries. The Laplace Pressure and Disjoining Pressure

The behavior of water in flat unwettable microcapillaries was studied as a function of their width by the methods of Monte Carlo and molecular dynamics. The conditions of the coexistence of liquid–vapor phases in capillaries were found, and the values of the coefficient of isothermal compressibility were determined by the calculated supercritical and subcritical adsorption isotherms. The profiles of local density and energy were calculated. The Laplace pressure and disjoining pressure, whose values and signs manifest strong hydrophobic attraction of solid surfaces, were estimated.     

Spontaneous Polarization of Thin Water Films in Nonwettable Capillaries by the Data of Numerical Experiment

Abstract–Water films in the flat capillaries with ideal walls were simulated by molecular dynamics method. The profiles of local density and distribution functions of the dipole moment orientations, the directions of valence and H-H bonds were obtained. Profiles of local electric field and electric potential were calculated. Potential jumps at the water–vapor interface were estimated.     

Dynamic Surface Tension and Adsorption Mechanism of Surfactant Benzyltrimethylammonium Bromide at the Air/Water Interface

The air‐solution equilibrium tension, γ_c and dynamic surface tension, γ_t, of aqueous solutions of a novel ionic surfactant benzyltrimethylammonium bromide (BTAB) were measured by Wilhelmy method and Maximum bubble pressure method (MBPM), respectively. Adsorption equilibrium and mechanism of BTAB at the air‐solution interface were studied. The CMC was determined to be 0.11 mol/L. The results show that at the start, the adsorption process is controlled by a diffusion step. Toward the end, it changes to a mixed kinetic‐diffusion controlled mechanism with the adsorption activation energy of about 11.0 KJ/mol. Effects of temperature, inorganic salts, and alcohols on adsorption kinetics also are discussed.     

一种磺酸聚醚型表面活性剂的制备及动态表面张力

通过3-氯-2-羟基丙磺酸钠(NaCHPS)和1-氯-3-丁氧基-2-丙醇(CBP)之间溶液共缩聚,合成了一种新型磺酸聚醚表面活性剂—环氧丙磺酸缩水甘油丁基醚共聚物。采用红外、核磁等测试技术对其结构进行了表征。测定了不同质量浓度、不同结构的磺酸聚醚水溶液的动态表面张力(DST),并用Rosen经验方程对DST进行了分析。结果表明,磺酸聚醚的数均分子量为900～1 600,其溶液浓度越高,DST达到介平衡越快,则DST分析曲线越低;当质量浓度从56．4 mg/L增大到3 611 mg/L时,R_(1/2)值从11．04 mN/(m·min)增大到7 662．5 mN/(m·min);磺酸聚醚的动态表面活性随着磺酸聚醚中CBP含量的增加而增强。     

采用XPS与接触角法研究氟聚合物表面结构与性能

本文采用接触角和变角XPS方法对FA共聚物的表面能、 表面微相结构做了进一步的研究.     

双子表面活性剂Dynol-604溶液的动态表面张力研究

通过测定双子表面活性剂Dynol-604的动态表面张力(DST),研究了温度和浓度等对其DST的影响,详细表征了DST随时间的变化过程,计算了动态表面张力的各种参数(t_i,t^*,t_m,R_1/2).结果表明,其表面张力降低迅速,γ_m值也很低.探讨了上述参数的物理意义和变化规律.     

Dynamic Surface Tension and Adsorption Kinetics of Sodium Lignosulfonate Aqueous Solutions

In the article, the dynamic surface tension of sodium lignosulfonate (SL) aqueous solutions are investigated using an axisymmetric drop shape analysis-profile method. The data are analyzed by the Langmuir, Frumkin, modified Frumkin, and modified Flory-Huggins equations. The results indicate that the Langmuir model's results with two adjustable parameters are comparable to that of other models with three or four adjustable parameters. Based on the simplicity of simulation, the Langmuir adsorption equation is used to correlate the dynamic adsorption processing. The aggregation between SL molecules and the variation of adsorption configuration are proposed to interpret the results of dynamic surface tension.      

Effects of Dissipation on Contact Angle Measurements Using a Dynamic Method

We report studies of the effect of hydrothermal treatment on physical properties such as crystalline phase, size, and morphology of nanosized cadmium sulfide (CdS) particles. CdS precipitates have been synthesized by the reaction of Cd(NO(3))(2) with Na(2)S at room temperature. These CdS precipitates have been hydrothermally treated in the range 120-240 degrees C with variation of the treatment time. The effects of acid catalysts and other additives were also investigated. The particles prepared were characterized by XRD, TEM, and BET methods. With increased hydrothermal treatment temperature and time, crystallization from amorphous to crystalline form, cubic or hexagonal, and an increase of particle size occurred. CdS particles of well-developed hexagonal form were obtained at a hydrothermal treatment temperature of 240 degrees C; the primary hexagonal grain size was on the order of 20-30 nm. The addition of an acid catalyst, HCl, or of Cd(NO(3))(2) into the precipitate sol promoted crystal growth and phase transformation during the hydrothermal treatment, but another additive, Na(2)S, showed the opposite trend. It appears that hydrothermal treatment combined with proper additives could be an effective method for preparation of nanosize crystalline CdS particles. Copyright 2001 Academic Press.     

表面活性剂溶液的动表面张力研究

用振荡射流法分别测定了不同温度下全氟辛酸、十二烷基硫酸钠、二聚氯乙烯正辛醇醚溶液(浓度低于CMC)的动表面张力,讨论了它们的表面吸附动力学,研究结果表明都是扩散控制。     

Equilibrium and Dynamic Surface Tension of Carboxymethylchitosan and Alkyl Trimethylammonium Bromide Mixtures

A water-soluble derivative of chitosan, carboxymethylchitosan (CMCH), was mixed with alkyltrimethylammoniumbromides (C_mTAB) and was studied on the adsorption at air/water interface using equilibrium and dynamic surface tension method. The effects of surfactant and polymer concentrations, surfactant chain length, as well as pH of solution were investigated. Addition of the surfactants remarkably promotes the polymer adsorption. Increasing any one of surfactant concentration, surfactant chain length, and pH will facilitate the adsorption of the mixture whereas little effects of polymer concentration were observed. The results are explained in terms of the interaction between CMCH and C_mTAB under different conditions.     

Study of Interfacial Tension Between Glass and Polyethylene Capillaries in Highly Concentrated Electrolyte Solutions

Abstract

The polyethylene capillary used for dropping mercury electrodes (D.M.E.) has permitted the study of interfacial tension by a drop time method in highly concentrated solutions. The electrocapillary curves were obtained for the aqueous solutions of KF, NaOH and KCL. The measurements evince that there is a difference between results obtained using glass and polyethylene capaillaries. The difference increases with the concentration of the electrolyte. We attribute that fact to wetting of the polyethylene capillary by mercury.     

Aqueous Solutions of Sodium Deoxycholate and Hydroxypropylmethylcellulose: Dynamic Surface Tension Measurements

Interfacial tension changes and interaction between sodium deoxycholate (DOC) and a nonionic polymer hydroxypropylmethylcellulose (HPMC) were studied by the Wilhelmy plate method. The concentration of HPMC was fixed at 8x10(-5), 2x10(-4), and 1x10(-3)% (w/v) while DOC ranged form 0 to 8x10(-2) M, i.e., concentrations below and above the critical micellar concentration (cmc) for DOC. Emphasis was placed on the highly diluted solutions of the polymer in order to lessen possible contributions of the effects of the bulk phase on the observed surface behavior. The dynamics of the surface tension was investigated in the presence and absence of DOC. The kinetics of the interfacial tension changes were explained in terms of adsorption of the polymer molecules and conformational changes of already adsorbed molecules at the interface. The molecules above a critical DOC aggregation concentration (cac) formed clusters, which was evidenced by these surface tension measurements. A synergism in surface activity was observed below that cac. The cmc of DOC remained unchanged by the presence of HPMC. Copyright 2000 Academic Press.     

不同结构烷基苯磺酸钠水溶液的泡沫性能及动态表面张力

研究了一系列直链三取代和支链双取代烷基苯磺酸钠水溶液的动态表面张力(DST)和泡沫性能, 考察了分子结构变化对烷基苯磺酸钠水溶液的DST和泡沫性能的影响. 探讨了动态表面张力参数(t*, n, R1/2)的变化规律及其与泡沫性能的关系. 结果表明, 随着取代烷基链长度增加, t*和n值增大, R1/2减小, 动态表面活性降低. 由于双取代支链烷基苯磺酸钠分子具有特殊的柔性长支链, 使得吸附膜排列紧密、膜弹性增大, 因而其泡沫稳定性明显优于多取代直链烷基苯磺酸钠的稳定性. 在气流法产生泡沫的过程中, 动态表面张力是控制起泡高度的关键因素.     

Experimental Study on Contact Angle Patterns: Liquid Surface Tensions Less Than Solid Surface Tensions

The interpretation of contact angles in terms of solid surface tensions is not trivial. In the past, we and others have postulated that contact angles should be measured with liquid of surface tension larger than the anticipated solid surface tension, i.e., gamma(lv)>gamma(sv). This has recently been disputed. It is also not entirely obvious how to proceed experimentally since gamma(sv) is not known initially. Typically, one starts with a liquid of high gamma(lv) (such as water) and goes lower. We have stopped in the past when the contact angles became small. A question arises as to what would happen if we would go on. Contact angles of liquids with gamma(lv) less than or near gamma(sv) were measured on eight polymer-coated solid surfaces. The experimental contact angle patterns for gamma(lv)gamma(sv) were compared. Results suggest that contact angle interpretation in terms of solid surface tensions requires contact angles to be measured for gamma(lv)>gamma(sv) because the Young equation is not applicable for gamma(lv)相似文献   

Flow-Induced Precipitation in Thin Capillaries Creates Helices,Lamellae, and Tubes

Precipitation reactions under flow in confined media are relevant to the control of pathological biomineralization, processes affecting aquifers, and challenges in the petroleum industry. Here we show that for a simple geometry, such conditions create macroscopic structures including helices, tubes, lamellae, slugs, and disordered patterns. All structures emerge when salt solution is slowly injected into thin capillaries filled with hydroxide solution. For the helices, the pitch is proportional to the pump rate revealing a constant period of 0.63 s. Different morphologies of the insoluble metal hydroxide can co-exist causing random transitions along the capillary. On average, 15 % of the final system contains residual hydroxide solution. While mechanically stable for flow speeds above 25 mm min⁻¹, structures collapse and sediment for slower injection speeds. Some of the observed features share similarities with precipitate tubes in chemical gardens and the dynamics of liquid–liquid pipe flow.     

Study on Foaming Properties and Dynamic Surface Tension of Sodium Branched-alkyl Benzene Sulfonates

Foaming properties and the dynamic surface tension (DST) were carried out with aqueous solutions of sodium branched-alkyl benzene sulfonates to elucidate the relationship between foaming properties and surfactant structures. The parameters of the DST (t*, n, R _1/2 ) are correlated with the foaming ability for alkyl benzene sulfonates with benzene ring substituting at positions 2, 4, and 8 of hexadecane. The parameters of the DST (t*, n, R _1/2 ) are correlated with the foaming ability of the same surfactant solutions. The results indicated that the molecular diffusion in the solution, adsorption, and arrangement at the air/water interface were changed with different molecular structures: changing the substituted position of benzene ring from 2 to 8 of hexadecane, the value of t* and n decrease, and the value of R _1/2 increases, which lead to the high dynamic surface activity and high foam volume. The foam stability is correlated with the high surface dilational elasticity and the strength of surface monolayer: changing the substituted position of benzene ring from 2 to 8 of hexadecane, the branched-alkyl chain becomes more flexible, which is characterized by densely packed adsorbed molecules and high film elasticity of the adsorption film. Therefore, the foam stability increases.