DIFFUSION AND ADSORPTION KINETICS OF A WATER-SOLUBLE NONIONIC SURFACTANT TO THE INTERFACE BETWEEN TWO VISCOUS IMMISCIBLE LIQUIDS

The kinetics of diffusion and adsorption of a water-soluble nonionic surfactant, polyoxyethylene sorbitan monolaurate (Tween-20), to the interface between two viscous immiscible liquids relevant to many applications is experimentally investigated using drop volume tensiometry. The measured variation in dynamic interfacial tension with contact time at different bulk concentrations of the surfactant in the viscous aqueous phase indicates that the equilibrium is slowly attained at low concentrations. As the bulk surfactant concentration is increased by two orders of magnitude, the contact time needed to reach equilibrium decreased by about an order of magnitude. The corresponding values of diffusion coefficient in the viscous liquid, determined using existing theoretical equations, are found to be almost constant. These are about two orders of magnitude smaller than those for the data available in literature for similar surfactants in much less viscous water at the air interface. The molecular area of Tween-20 determined in the present work is found to be very close to the value reported by other authors.     

纳米NaY分子筛的合成

在合成NaY分子筛时，向合成体系中添加少量的吐温系列表面活性剂(吐温20,吐温40,吐温60)可以显著地降低分子筛的晶粒尺寸。这是由于吐温系列表面活性剂在体系的强碱作用下发生皂化反应，生成聚氧乙烯山梨酸糖醇酐和酸钠皂，有利于降低NaY分子筛的表面能。但棕榈酸钠和硬脂酸钠在高含量Al³⁺的合成体系中，会形成不溶于水的棕榈酸铝和硬脂酸铝, 因此，吐温40和吐温60在合成纳米分子筛中的作用不如吐温20。在添加吐温20合成纳米分子筛时，较适宜的合成条件为：晶化温度90 ℃，晶化时间17 h，吐温20的添加量n(吐温20)/n(Al₂O₃)=0.2%。产品的粒度约75 nm，产率≥92%，硅铝比为3.46。     

Oxidation of linoleic acid in emulsions: Effect of substrate, emulsifier, and sugar concentration

Linoleic acid oxidation in oil-in-water emulsions stabilized by a nonionic surfactant (Tween-20) was studied. The emulsion composition was varied at a constant oil droplet size. Lipid oxidation was measured as a function of time in the presence of a catalyst (FeSO₄ corbic acid) by two methods: gas chromatographic determination of residual substrate and ultraviolet-visible spectrophotometric determination of conjugated dienes. Rate of oxidation was influenced by the emulsion composition (relative concentrations of substrate and emulsifier) and especially by the partition of the emulsifier between the interface and water phase. Concentrations of emulsifier exceeding the critical micelle concentration protected the fatty acid against oxidation. Excess surfactant formed micelles and mixed micelles with linoleic acid, which retarded oxidation by diluting the substrate or perhaps by replacing linoleic acid at the interface, making it less accessible to radical attack. The addition of sucrose also had a protective effect, but only up to a certain concentration, indicating the effect may involve factors other than viscosity.     

The effect of mixed micelle formation on the dynamics of phase partitioning for a polydisperse ethoxylated nonionic surfactant

Mixed surfactants are common in practical applications, and their behaviors are often observed to deviate from the behaviors of pure surfactants with similar average properties in striking, and sometimes unexpected ways. The focus of this work was on exploring the role of mixed micelle formation in a mixed ethoxylated nonionic surfactant on the dynamics of partitioning between immiscible phases. The work examined partitioning of an ethoxylated nonylphenol surfactant between water and tetrachloroethylene (PCE) in a stagnant system at two different phase volume ratios. A model describing partitioning rate was developed and calibrated to experimental data, and then used to predict the long-term dynamic approach to equilibrium in mixed and pure systems. The work suggests that micelle formation slows partitioning time by limiting the concentration of monomers in water; in pure systems, time to approach equilibrium increases with increasing concentration, but then reaches a maximum. However, in mixed systems, time to approach equilibrium continues to increase with increasing concentration over the physically-possible concentration range. For the mixed system studied here, partitioning could be expected to take two orders of magnitude longer at very high concentrations than a similar pure system. Because of the similarity of the mathematics, this result might be expected for any monomer-driven interaction, such as adsorption or interfacial tension reduction.     

Adsorption Behavior of Nonionic Surfactants Studied by Drop Volume Technique

This study shows that the drop volume technique can be used to determine the adsorption behavior and interfacial adsorption kinetics of surfactants at fluid interfaces. Using this tensiometric method, one can determine not only the interfacial tension of the pure phases, but also the critical concentration for the formation of micelles (CMC) in a surfactant system, the quasi‐static (equilibrium) interfacial tension, the diffusion coefficient as a function of surfactant concentration, and the maximum adsorption density at the interface. The determination of the dynamic interfacial tension allows to indirectly characterize the kinetics of surfactant adsorption. The time dependence of the interfacial coverage resulting from this adsorption process is well described by two approximation solutions (for short and long adsorption times), with the result that the diffusion coefficients calculated as a function of surfactant concentration using these two methods show good agreement. The droplet formation and dripping process of a surfactant solution in a capillary was found to be quite different depending on whether the process occurred in gaseous or fluid surroundings. In particular, the formation of satellite droplets was different for the two different media, in terms of both the volume and shape of the satellite droplets.     

Effect of speciation on the apparent diffusion coefficient in nonreactive porous systems

A combined theoretical and experimental study of the effect that concentration and ionic speciation have on the apparent diffusion coefficient is performed using a nonreactive porous material in a divided cell diffusion apparatus. Varying the ionic species concentration over two orders of magnitude changes the apparent diffusion coefficient by no more than 20% for the systems studied. By contrast, at fixed ionic concentration, varying the ionic species changes the initial apparent diffusion coefficient by a factor of two. Over longer periods of time, the apparent diffusion coefficient varies in time, increasing by a factor of ten or more. For one system, the macroscopic diffusion potential across the specimen induces a transient negative apparent diffusion coefficient; iodide ions are transported from regions of low iodide concentration to regions of high iodide concentration. The theoretical analysis shows that, in nonreactive porous systems, the behavior of all the concentrations and species studied can be completely characterized by an electro-diffusion system of equations that contain two time-independent constants: the porosity and the formation factor. The relationship between these results and the prediction of concrete performance in the field is discussed.     

结合图像数字化技术用悬滴法测动态界面张力——动态界面张力与表面活性剂浓度的关系

引　言从微观机理上讲 ,能否制得稳定乳状液与乳化剂扩散速度、界面层吸附速度和成膜分子间协同作用等因素有关 ,而这些信息可以通过测动态界面张力反映出来 ,因此测动态界面张力是研究乳状液稳定性微观机理的一条重要途径 .测动态界面张力的方法[1] 很多 ,其中悬滴法 (滴外形法的一种 )有独特的优点[1] .目前 ,在国外已利用该法展开了许多卓有成效的研究工作[2～ 6 ] ;国内李佟茗[7] 等已报道采用计算机图像采集技术实时记录气泡长大过程测动态表面张力的工作 ;田宜灵[8] 等则报道了用数字化摄像仪拍摄悬滴 ,以选面法[9] 计算静态界面张力…     

Analysis of the solvent diffusion in glassy polymer films using a set inversion method

Within the framework of solvent diffusion in glassy polymers, this paper concerns an experimental study of toluene sorption and desorption in P(MMA/nBMA) copolymer films. Gravimetric experiments (quartz microbalance) are performed in a pressure and temperature controlled chamber. Coupling between solvent diffusion and viscoelastic relaxation is taken into account through the time-dependent solubility model, based on the Fick diffusion equation inside the film and a time variable boundary condition at the film/vapor interface. Viscoelastic relaxation is described by a first order model or by a stretched exponential. In the present paper, a special focus is given on the set inversion method used to analyze the data and to derive well-defined uncertainty intervals upon each determined quantity, taking all the uncertainties on the weight measurements into account. We find that the mutual diffusion coefficient strongly decreases in the glassy state, of about two orders of magnitude for a 0.05 decrease in the solvent weight fraction.     

Surface remobilization of buoyancy-driven surfactant-laden drops at low reynolds and capillary numbers

It is well known that the terminal velocity of a drop settling in a viscous fluid is impacted by surface tension gradients. These gradients can develop because of nonuniform accumulation of surfactant on the surface as a result of a number of transport mechanisms. Here, a surfactant transport model based on a sorption-limited Frumkin framework is used to describe surfactant transport in the presence of both surface convection and diffusion at low Reynolds and capillary numbers. Constants characterizing surfactant transport in the Frumkin framework are experimentally determined and used to predict aqueous drop velocities with varying surfactant concentrations and volumes. Computation is carried out by satisfying equations governing mass, momentum, and interface species conservation. Experiments demonstrate qualitative and quantitative agreement between predicted and measured drop velocities. It is shown that surface remobilization explains some observed trends in measured velocity as the drop size decreases. © 2018 American Institute of Chemical Engineers AIChE J, 65: 294–304, 2019     

Tritium Diffusion in A12O3 and BeO

Tritium diffusion in aluminum and beryllium oxides was studied by recoiling tritium into specimens and measuring the time rate of tritium release during postirradiation heating. Results were consistent with classical diffusion solutions and gave single values for the diffusion activation energy over the temperature range of measurement for single-crystal, sintered, and powdered specimens. Varying amounts of tritium were released as tritiated water even after attempts to remove most of the water absorbed by the specimens. Condensable amounts of tritium ranged from <20% for single-crystal specimens to as high as 90% for some powders. Alumina containing 0.2% MgO gave tritium diffusion coefficients 4 to 5 orders of magnitude higher than those for undoped A1₂O₃, implying a significant impurity effect on tritium diffusion. Measured diffusion coefficients were many orders of magnitude lower than hydrogen diffusion coefficients in metals. When a simple equilibrium permeation model was used which neglected tritium partition effects at interfaces and enhanced diffusion along grain boundaries, it was shown that thin coatings of beryllium or aluminum oxides on metal substrates could markedly reduce tritium permeation rates through metals. The present results may be applied in the future to fusion reactors where tritium inventories will be high and tritium diffusion within the blanket region undesirable.     

Wetting of hydrophobic substrates by nanodroplets of aqueous trisiloxane and alkyl polyethoxylate surfactant solutions

Trisiloxane surfactants at low concentrations promote the complete and rapid wetting of aqueous droplets on very hydrophobic (hydrocarbon) substrates. This behavior has not been demonstrated by any other surfactant which explains why the trisiloxanes are referred to as superspreaders. Despite many experimental and theoretical investigations the mechanism of superspreading is not fully understood. Molecular dynamics simulations using all-atom force fields have been conducted to attempt to elucidate the mechanism of superspreading. Spherical nanodroplets containing approximately 10,000 water molecules in the bulk and 475 surfactant molecules at the liquid-vapor interface were placed in the vicinity of a graphite substrate and allowed to spread freely at room temperature. In the trisiloxane case the droplet was found to spread very little, although randomly removing 175 surfactant molecules lowered the final contact angle from 110^° to 80^°. In contrast, an alkyl polyethoxylate surfactant-laden droplet was found to spread significantly further, with the equilibrium contact angle reaching 55^°. Similar results for the two surfactant systems were found for cylindrical nanodroplets spreading on a self-assembled monolayer (SAM). The reasons for the lack of spreading in the trisiloxane case and the simulation challenges associated with these systems are discussed. In support of our arguments we demonstrate that the surfactant molecules of an initially uniform aqueous trisiloxane solution self-assemble into a bilayer in tens of nanoseconds on a graphite substrate. Lastly, in a final set of simulations, neat trisiloxane droplets at 450 K are found to arrange into a layered structure on a methyl-terminated SAM and to form a sand pile-shape on a hydroxyl-terminated SAM.     

Drop coalescence in planar extensional flow and gravity

A film drainage model, which allowed for the effect of the ratio of the viscosities of the drop and liquid film on the interfacial mobility, is found to represent reasonably well the published experimental data on the coalescence times of drops in two different flow fields at a constant force. The data of Yang et al. [2001. The coalescence of two equal-sized drops in a two-dimensional linear flow. Physics of Fluids 13, 1087-1106] on the head-on collision of two equisized drops at the center of the inflow axis under planar extensional hyberbolic flow in a four-roll mill, and the data of several authors on the coalescence time of a single drop with its bulk homophase at a deformable interface under gravity are considered. The scaled coalescence time increased linearly with the product of the viscosity ratio and the applied external to interfacial tension forces ratio over three orders of magnitude. Higher applied external forces resulted in larger film areas while more viscous drops reduced the interfacial mobility thereby increasing the coalescence times.     

Investigation of concentration‐dependent diffusion on frontal instabilities and mass transfer in homogeneous porous media

Mass transfer plays an important role in influencing the efficiency of miscible displacements in solvent‐based processes in enhanced oil recovery. The mass transfer rate because of the pure molecular diffusion is very slow. However, this process can be greatly enhanced by the appearance of frontal instabilities called viscous fingering mechanisms, which are beneficial for improving the mixing and mass transfer between the injected solvent and oil. Instead of a piston‐like displacement, the interface between solvent and oil is very convoluted with intricate finger‐like patterns of the less viscous solvent intruding into the highly viscous oil. This intrusion significantly increases the surface area of contact of the two fluids and leads to more efficient mass transfer and mixing. Experimental measurements on the diffusion coefficients of two miscible fluids indicate that, instead of a constant diffusion coefficient (CDC), a concentration‐dependent diffusion coefficient (CDDC) is more realistic. In the present study, a CDDC relation in which the diffusion coefficient is exponentially proportional to concentration is adopted. Its effect on the development of frontal instabilities is examined through highly accurate nonlinear numerical simulations. The differences between the CDDC case and the widely assumed CDC case are discussed. Furthermore, the enhancement of frontal instabilities on mass transfer when the CDDC is considered is investigated at various mobility ratios and Peclet numbers. The special characteristics for the CDDC case indicate its important role in miscible displacements. Eventually, the relation of breakthrough time to parameters is correlated to accurately predict the breakthrough time in any CDDC scenario.     

Influence du dodecyl sulfate de sodium sur la tension interfaciale du système biphasé butanol-eau

Interfacial tension between the two phases formed by the partially miscible system composed of butanol-1 and water has been investigated. Using the method of drop volume tensiometry, the effect of a surface-active agent, sodium dodecyl sulfate, on interfacial tension was investigated. Addition of surfactant to the butanol-rich phase, which forms the droplet, has been found to bring about a decrease in interfacial tension the magnitude of which was influenced by the time of contact. When the surfactant was added to the aqueous (bulk) phase, the decrease in interfacial tension was greater and it was equal to that observed when the surfactant was added to both phases. It is concluded that the orientation of phases in the instrument has an important effect on the apparent interfacial tension observed.     

Suspension Polymerization of Styrene with Pickering Emulsifiers

The suspension polymerization of styrene in water with hydroxyapatite and calcium carbonate as Pickering emulsifiers and sodium dodecylbenzenesulfonate (NaDDBS) and poly(vinylpyrrolidone) (PVP) as surfactants was investigated. The adsorption of NaDDBS and PVP at the surface of the solids, the surface tensions of the aqueous solutions, the interfacial tensions between the aqueous solutions and styrene and the contact angles versus water and styrene, respectively, were measured in dependence of the surfactant and the solids concentrations. In contrast to assumptions in literature, the adsorption equilibrium was found to be far on the side of desorption. The decrease of surface and interfacial tensions with increasing surfactant concentrations especially in the case of NaDDBS were stronger than expected due to an enhanced dissolution of the solids caused by the surfactant. The contact angles of the binary systems were measured by the Washburn method. Surprisingly their absolute values depended on the packing densities of the solids. The theory of Good and Girifalco was used to calculate the interfacial tensions and the contact angle between solids and water in the ternary system solid/water/styrene. For NaDDBS, the contact angle was higher than 90° even at very low surfactant concentrations, causing unstable suspensions. Therefore, the modulation effect of NaDDBS seems to be very low and developing very slowly due to the slow adsorption process. Also for PVP the contact angle was higher than 90°, however, stable suspensions were obtained. This may be due to the fact that PVP stabilizes polymer suspensions also without any solids and that in such a system the stabilizing effect of solids is of minor importance. In the case of PVP the particle size of polystyrene could be controlled by the PVP concentration and the length of the contact time between PVP and solid.     

Disintegration of granules made from pure nonionic surfactants and surfactant mixtures

Dissolution in water of pure liquid nonionic surfactants and some of their mixtures was studied in previous research in this laboratory. In the work described here, a hanging drop slide was used to study disintegration behavior in water of corresponding granules consisting of many zeolite particles bound together with a liquid nonionic surfactant. Granules disintegrated below the cloud point of the nonionic surfactant or mixture. Few differences in disintegration time were seen for various systems. However, disintegration did not occur when the neat surfactant developed viscous myelinic figures upon contact with water. Nor was it observed when a dilute aqueous phase coexisted with a surfactant-rich L₁ phase or L₃ (sponge) phase at equilibrium.     

Effects of branching in hexadecylbenzene sulfonate isomers on interfacial tension behavior in oil/alkali systems

This paper is concerned with the study of the effect of the molecular structure of surfactant on the reduction of interfacial tension of Enhanced Oil Recovery (EOR). The interfacial tension behavior of nonane and crude oil with three hexadecylbenzene sulfonate isomers (with benzene rings located at different positions along the alkyl chains) were investigated. It was found that the interfacial tensions could be reduced to ultra-low values at low alkali concentrations by using a surfactant molecule with a phenyl group located near the center of the alkyl chain. Molecular structures of this kind were considered to be the most ideal for surfactant flooding. Moreover, the transient low interfacial tensions in crude oil/alkali system were caused by the synergistic effects between surfactant and the active species generated at interface, but surfactant molecules played the dominant role at equilibrium.     

Wettability alteration and reducing water blockage in tight gas sandstone reservoirs using mixed cationic Gemini/nonionic fluorosurfactant mixtures

The unrecovered hydraulic fracturing fluid will invade the matrix and induce water blockage, creating formation damage and hindering the oil or gas production rate. First, the synergistic effect of cationic Gemini surfactant (MQAS) and nonionic fluorosurfactant (N-2821) mixtures on reducing the surface tension and wettability alteration was investigated in this paper. The critical micelle concentration (CMC) of the surfactant mixture is one or two orders of magnitude lower than that of N-2821 and MQAS, indicating that the MQAS/N-2821 mixtures exhibit an apparent synergistic effect in reducing surface tension. Moreover, the maximal contact angle of MQAS/N-2821 mixtures reached 83.55° at α_N-2821 = 0.5, and the total surfactant concentration of 1 × 10⁻⁴ mol/L due to the adsorption of surfactant. The adsorption mechanism of surfactants on the surface of quartz sand was then examined. The adsorption kinetics is consistent with the pseudo-second-order model at different surfactant concentrations, while the Freundlich model is suitable for describing the adsorption behavior of surfactants on the sandstone surface. This finding indicates that surfactant adsorption is multilayered. The MQAS/N-2821 surfactant mixtures have excellent surfactant activity due to the relationship of the capillary pressure to the surface tension, pore radius, and contact angle; thus, the addition of surfactant mixtures can reduce the liquid saturation effectively. Furthermore, the sequential imbibition experiments indicate that MQAS/N-2821 mixtures alter the wettability of the core plug, which results from the adsorption of surfactants. Compared with brine water, the MQAS/N-2821 mixtures decreased the liquid saturation and increased the permeability recovery ratios of the core plug.     

Interactions between fat crystal networks and sodium caseinate at the sunflower oil-water interface

A Couette-type torsion wire surface shear viscometer was used to measure the apparent interfacial shear viscosity of pH 7 (I=0.05 M) buffered solutions of sodium caseinate in contact with sunflower oil. The sunflower oil contained 1% fat crystals in either the β or β′ polymorphic form, or was crystal free. In all cases, the fat crystals increased the interfacial shear viscosity synergistically, with the β′ crystals causing the biggest increase. Substituting the protein for a small-molecule surfactant (Tween-40) showed that this was not simply due to the protein lowering the interfacial tension. Sedimentation studies of the different fat crystal slurries suggested that the extent of the interfacial shear viscosity increase was related to the strength of crystal-crystal interactions in the oil phase. It seems likely that when protein is present at the interface, it fixes the adsorbed layer of fat crystals to the cross-linked protein film at the interface. When this film was sheared, the strength of the crystal-crystal interactions in the oil phase became important. However, when Tween-40 was in the aqueous phase instead of the protein, the crystal-crystal interactions were not relevant, presumably because the Tween-40 interfacial film simply flowed around the adsorbed crystals     

Highly efficient[C8mim][Cl] ionic liquid accompanied with magnetite nanoparticles and different salts for interfacial tension reduction

The 1-octyl-3-methylimidazolium chloride, [C_8 mim][Cl] ionic liquid(IL) was used as a novel surfactant in n-heptane/water system. The interfacial tensions(IFT) were measured and corresponding variations were investigated. An IFT reduction of 80.8% was appropriate under the IL CMC of about 0.1 mol·L~(-1) and stronger effects were achieved when magnetite nanoparticles and salts were present profoundly under alkaline p Hs.The equilibrium IFT data were accurately simulated with the Frumkin adsorption model. Hereafter, the saturated surface concentration, equilibrium constant and interaction parameter were obtained and their variations were demonstrated. Further, emulsion stability and contact angle of oil/water interface over quartz surface were studied. The oil/water emulsion stability was hardly changed with nanoparticles; however, the stability of oil/water + IL emulsions was significantly improved. It was also revealed that the presence of sodium and calcium chloride electrolytes fortifies the IL impact, whereas sodium sulfate weakens. From dynamic IFT data and fitting with kinetic models, it was found that the IL migration toward interface follows the mixed diffusion–kinetic control model. Consequently, the IL diffusion coefficient and the appropriate activation energy were determined.