Dynamic surface tension of micellar solutions studied by the maximum bubble pressure method

A theoretical model for the dynamic surface tension of an air bubble expanding in surfactant solution is proposed. The model accounts for the effect of convection on the surfactant diffusion and the effect of expansion of the bubble surface during the adsorption of surfactant molecules. Assuming small deviation from equilibrium and constant rate of expansion, an analytical solution for the surface tension and the subsurface concentration as a function of time is derived. The parameters of the model are computed from experimental data for sodium dodecyl sulfate obtained by the maximum bubble pressure method.     

Dynamic surface tension of micellar solutions studied by the maximum bubble pressure method

A theoretical model for the dynamic surface tension of an air bubble expanding in micellar surfactant solution is proposed. The model accounts for the effect of expansion of the bubble surface during the adsorption of surfactant molecules (monomers) and the effect of disintegration of polydisperse micelles on the surfactant diffusion. Assuming small deviations from equilibrium and constant rate of expansion analytical expression for the surface tension and the subsurface concentration of monomers as a function of time is derived. The characteristic time of micellization is computed from the experimental data for two surfactants (sodium dodecyl sulfate and nonylphenol polyglycol ether) obtained by the maximum bubble pressure method.     

The measurement of dynamic surface tension by the maximum bubble pressure method

The principle of maximum pressure in a bubble for measurements of dynamic surface tension is realized in a fully automatically operating apparatus. The set-up yields data in the time interval from 1 ms up to several seconds and can be temperature controlled from 5° to 80°C. Experimental data obtained for different surfactants and gelatine in water and/or water/glycerine mixtures at different temperatures are discussed. A direct comparison with results from oscillating jet and inclined plate experiments shows excellent agreement.     

Dynamic surface tension of micellar solutions studied by the maximum bubble pressure method. 1. Experiment

The effect of the micelles on the dynamic surface tension of micellar surfactant solutions is studied experimentally by means of the maximum bubble pressure method. Different frequencies of bubbling ranging approximately between 1 and 30 s^–1 are applied. The time dependence of the surface tension is calculated using a dead time correction. Water solutions of two types of surfactants with different concentrations are investigated: sodium dodecyl sulfate and nonylphenol polyglycol ether. The surface tension relaxes more quickly in the presence of micelles. The characteristic times of relaxation of the surface tension seem to be in the millisecond range. The time constants observed experimentally are explained in terms of the theory of surfactant diffusion affected by micellization kinetics.     

Adsorption kinetics at air/solution interface studied by maximum bubble pressure method

A general dynamic surface adsorption equation (t) for maximum bubble pressure method was derived by solving Ficks diffusion equation for the bubbles under different initial and boundary conditions. Different from the planar surface adsorption(Ward-Tordai equation), the derived dynamic surface adsorption (t) for the short time consists of two terms, one of them reflects the geometric effect caused by the spherical bubble surface. This kind of effect was discussed.The equilibrium surface tension _eq and the dynamic surface tension (t) of aqueous C₁₀E₈ (CH₃(CH₂)₉(OCH₂CH₂)₈OH) solution at temperature 25 °C were measured by means of Wilhelmy plate method and maximal bubble pressure method respectively. In the region of t0 (short time limits) a good agreement of experimental results with the theory was reached and the adsorption was controlled by diffusion. However, for the long time limits, a mixed diffusion-kinetics controlled process was proved.     

Dynamic surface tensions of micellar Triton X-100 solutions

Considering surfactant solutions at concentrations exceeding the CMC, another relaxation process besides diffusion occurs, also affecting the dynamic surface tension. The latter equilibration process concerns a micellisation/demicellisation process, representing the disintegration of micelles into monomers. The micellisation kinetics are accounted for by adding a single source term to the diffusion equation of the free monomers.

In the present paper the integration of the diffusion equation is avoided by using the concept of the diffusion penetration depth. Nevertheless, when this approximation is made, good agreement is achieved between experiment and theory for micellar Triton X-100 solutions. Moreover, it follows that diffusion of micelles may not be neglected.     

A model for simulating the dynamic surface tension behavior of aqueous surfactant dispersions

A dynamic adsorption model for surface-active materials at air/liquid interfaces with the consideration of aggregate dissolution effect was developed to investigate the dynamic surface tension behavior of aqueous surfactant dispersions. Two catanionic surfactants, cetylpyridinium dodecylsulfate (CP-DS) and dodecyltrimethylammonium dodecylsulfate (DTMA-DS), with low critical aggregation concentrations were chosen as model systems. Dynamic surface tensions of aqueous CP-DS and DTMA-DS systems were measured by a drop volume tensiometer. A model with diffusion-controlled or mixed-kinetic dynamic adsorption mechanisms considering the dissolution effect of dispersed aggregates was developed to simulate the dynamic surface tension data. An analysis by comparing the model predictions with experimental data demonstrated that the dynamic surface tension behavior of aqueous CP-DS and DTMA-DS dispersions could be described with a diffusion-controlled dynamic adsorption model taking the aggregate dissolution effect into account.     

On the solution of diffusion controlled adsorption kinetics by means of orthogonal collocation

The problem of diffusion controlled adsorption kinetics is solved by orthogonal collocation for the Henry and the Langmuir isotherms. The dependence of the surface concentration of a surfactant on time is described by explicit formulae for the whole range of time. The results are compared with those obtained by power series expansions and finite difference methods and have a high accuracy for any time value. The method of orthogonal collocation has been shown to be very effective. It is suitable for applications to similar problems.     

Adsorption kinetics of nonionic surfactants using the drop volume method

The kinetic results obtained for the nonionic surfactantsn-octyl,n-decyl, andn-dodecyl dimethyl andn-octyl, andn-decyl diethyl phosphine oxide show purely diffusion controlled adsorption. The drop volume technique applied in a static and dynamic version proves to be useful to measure the adsorption kinetics in the form of surface tensions in function of time. Comparisons of the results obtained from both the static and the dynamic measuring procedure confirm the validity of a theory applied to interpret the kinetic data.Nomenclature a Langmuir parameter - c ₀ surfactant bulk concentration - D diffusion coefficient - surface concentration - ₀ equilibrium surface concentration - ¯ (t)/ ₀ reduced surface concentration - maximum value of - R gas law constant - surface tension - ₀ surface tension of pure water - t time - T absolute temperature     

Low-rate dynamic contact angles on poly(n-butyl methacrylate) and the determination of solid surface tensions

 Low-rate dynamic contact angles of 22 liquids on a poly(n-butyl methacrylate) (PnBMA) polymer are measured by an automated axisymmetric drop shape analysis-profile (ADSA-P). It is found that 16 liquids yielded non-constant contact angles, and/or dissolved the polymer on contact. From the experimental contact angles of the remaining 6 liquids, it is found that the liquid–vapor surface tension times cosine of the contact angle changes smoothly with the liquid–vapor surface tension, i.e. γ_lv cos θ depends only on γ_lv for a given solid surface (or solid surface tension). This contact angle pattern is in harmony with those from other inert and non-inert (polar and non-polar) surfaces [34–37, 45–47]. The solid–vapor surface tension calculated from the equation-of-state approach for solid-liquid interfacial tensions [14] is found to be 28.8 mJ/m², with a 95% confidence limit of ±0.5 mJ/m², from the experimental contact angles of the 6 liquids. Received: 12 September 1997 Accepted: 22 January 1998     

Low‐rate dynamic contact angles on poly(methyl methacrylate/ethyl methacrylate, 30/70) and the determination of solid surface tensions

Low‐rate dynamic contact angles of 12 liquids on a poly(methyl methacrylate/ethyl methacrylate, 30/70) P(MMA/EMA, 30/70) copolymer were measured by an automated axisymmetric drop shape analysis‐profile (ADSA‐P). It was found that five liquids yield nonconstant contact angles, and/or dissolve the polymer on contact. From the experimental contact angles of the remaining seven liquids, it is found that the liquid–vapor surface tension times cosine of the contact angle changes smoothly with the liquid–vapor surface tension (i.e., γ_l|Kv cos θ depends only on γ_l|Kv for a given solid surface or solid surface tension). This contact angle pattern is in harmony with those from other methacrylate polymer surfaces previously studied.^45,50 The solid–vapor surface tension calculated from the equation‐of‐state approach for solid–liquid interfacial tensions¹⁴ is found to be 35.1 mJ/m², with a 95% confidence limit of ± 0.3 mJ/m², from the experimental contact angles of the seven liquids. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2039–2051, 1999     

Multidimensional analysis of denatured milk proteins by hydrophobic interaction chromatography coupled to a dynamic surface tension detector

Multidimensional analysis of denatured milk proteins is reported using high-performance liquid chromatography (HPLC) combined with dynamic surface tension detection (DSTD). A hydrophobic interaction chromatography (HIC) column (a TSK-Gel Phenyl-5PW column, TosoBiosep), in the presence of 3.0 M guanidine hydrochloride (GdmHCl) as denaturing agent is employed as the mobile phase. Dynamic surface tension is measured through the differential pressure across the liquid-air interface of repeatedly growing and detaching drops. Continuous surface tension measurement throughout the entire drop growth (50 ms to 4 s) is achieved, for each eluting drop of 4 s length, providing insight into both the kinetic and thermodynamic behavior of molecular orientation processes at the liquid-air interface. An automated calibration procedure and data analysis method is applied with the DSTD system, which allows two unique solvents to be used, the HIC mobile phase for the sample and a second solvent (water for example) for the standard, permitting real-time dynamic surface tension data to be obtained. Three-dimensional data is obtained, with surface tension as a function of drop time first converted to surface pressure, which is plotted as a function of the chromatographic elution time axis. Experiments were initially performed using flow injection analysis (FIA) with the DSTD system for investigating commercial single standard milk proteins (alpha-lactalbumin, beta-lactoglobulin, alpha-, beta-, kappa-casein and a casein mixture) denatured by GdmHCl. These FIA-DSTD experiments allowed the separation and detection conditions to be optimized for the HIC-DSTD experiments. Thus, the HIC-DSTD system has been optimized and successfully applied to the selective analysis of surface-active casein fractions (alpha s1- and beta-casein) in a commercial casein mixture, raw milk samples (cow's, ewe's and goat's milk) and other diary products (yogurt, stracchino, mozzarella, parmesan cheese and chocolate cream). The different samples were readily distinguished based upon the selectivity provided by the HIC-DSTD method. The selectivity advantage of using DSTD relative to absorbance detection is also demonstrated.     

等离子体改性聚合物表面动力学的动态接触角法研究

不同聚合物经CF~4/CH~4等离子体处理后,在浸水过程中表面动力学衰减常数对温度通过Arrhenius关系作图,对于所研究的聚合物都有一个明显的转折点。转折点处的温度称作表面构型转变温度(T~s),大约为15℃,与表面邻近水的Drost-Hansen温度一致。T~s以上及以下的活化能数值较小,说明表面构型变化的本质可看作是由于基团的翻转运动,而不需要整个大分子或链段的迁移运动。在浸水过程中,接触角滞后Δθ在表面构型转变温度T~s附近有转变,并有极小值,此后随着温度的升高出现极大值,继续升高温度接触角滞后Δθ又反而下降。     

Sequential injection analysis with dynamic surface tension detection High throughput analysis of the interfacial properties of surface-active samples

A sequential injection analysis (SIA) system is coupled with dynamic surface tension detection (DSTD) for the purpose of studying the interfacial properties of surface-active samples. DSTD is a novel analyzer based upon a growing drop method, utilizing a pressure sensor measurement of drop pressure. The pressure signal depends on the surface tension properties of sample solution drops that grow and detach at the end of a capillary tip. In this work, SIA was used for creating a reagent concentration gradient, and for blending the reagent gradient with a steady-state sample. The sample, consisting of either sodium dodecyl sulfate (SDS) or poly(ethylene glycol) at 1470 g mol⁻¹ (PEG 1470), elutes with a steady-state concentration at the center of the sample plug. Reagents such as Brij®35, tetrabutylammonium (TBA) hydroxide and β-cyclodextrin were introduced as a concentration gradient that begins after the sample plug has reached the steady-state concentration. By blending the reagent concentration gradient with the sample plug using SIA/DSTD, the kinetic surface pressure signal of samples mixed with various reagent concentrations is observed and evaluated in a high throughput fashion. It was found that the SIA/DSTD method consumes lesser reagent and required significantly less analysis time than traditional FIA/DSTD. Four unique chemical systems were studied with regard to how surface activity is influenced, as observed through the surface tension signal: surface activity addition, surface activity reduction due to competition, surface activity enhancement due to ion-pair formation, and surface activity reduction due to bulk phase binding chemistry.     

Theory of diffusion-controlled adsorption kinetics at the expanding planar surface with a constant area rate

The diffusion equation for the expanding surface was solved and a corresponding general expression of dynamic surface adsorption was derived. For the short-time adsorption, a special factor 1/3, which reflected the effect of the expanding surface on the adsorption, appeared in the equation. In addition, the effects of the surface expansion on subsurface concentration (ϕ(t)), dynamic surface adsorption (Γ(t)), dynamic surface tension (γ(t)) and the adsorption mechanism were discussed. In contrast to the adsorption on a still planar surface, ϕ(t) and Γ(t) are smaller, but γ(t) increased. The adsorption mechanism will be the same as long as the corresponding theories are used.     

Dynamic surface tension behavior of aqueous solutions ofN-dodecyl-N,N dimethyl aminobetaine chlorohydrate

The adsorption behavior ofN-dodecyl-N,N dimethyl aminobetaine chlorohydrate (DDAB·HCl) at the air/aqueous interface was studied for solutions in pure water and phosphate buffer (pH=7.4). The equilibrium surface tension versus concentration curves were used to estimate the equilibrium adsorption parameters and CMCs. The buffer solution has a lower CMC and shows higher surface activity below the CMC than the pure water solution. Data and calculations of the dynamic tension behavior at constant-area conditions showed that the adsorption processes of DDAB·HCl solutions are about 10 to 300 times slower than those predicted by a diffusion-controlled model. A mixed kinetics adsorption model with a modified Langmuir-Hinshelwood kinetic equation, which considers an activation energy barrier for adsorption, was applied to find the kinetic adsorption parameters. The dynamic tension behavior at pulsating-area conditions with large amplitude was also examined for frequencies up to 90 cycles/min. The tension amplitude responses depended strongly on the concentration and frequency. Comparisons of diffusion-controlled model predictions and pulsating area tension data confirmed the need to use a mixed kinetics model. The latter model can improve the fit over the diffusion-controlled model, but it does not quantitatively match the observed tensions.     

Study on the Surface Property of Surfactant Ionic Liquids Solutions

The surfactant TX-100 can be dissolved in ionic liquid bmimPF6 and decrease the surface tension of 1-buty1-3-methylimidazolium hexafluorophosphate (bmimPF6) solutions. Here, we confirmed that in this new system, the pure solvents need rearrangement at the air-wate rinterface at the initial stage. The dynamic surface tension (DST) study shows that at the initial adsorption stage, the adsorption model of surfactant accords with the diffusion-controlled adsorption mechanism, and the dilute ionic liquids solutions is further close to the diffusion-controlled adsorption.     

Effect of surfactant structure on the adsorption of carboxybetaines at the air–water interface

In order to study the effect of charge on the adsorption of surfactants at the air–water interface, two carboxybetaines have been synthesized with different number of separation methylenes between their charged groups. After purification and structure confirmation, the equilibrium and dynamic surface tensions were measured as a function of surfactant concentration for both the cationic and neutral forms of the surfactant molecules. The effect of ionic strength on the adsorption process was also studied. The equilibrium surface tension values were interpreted according to the Langmuir model and the dynamic surface tension data, converted to surface concentration by the Langmuir parameters, are consistent with the assumption of diffusion control over the range of surfactant concentrations studied. The diffusion coefficients show a progressive decrease in the rate of adsorption when the number of methylene units between the betaine charged groups increase.     

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.     

气-液界面上十六烷基溴化吡啶水溶液动态表面张力的研究

滴体积法测定了十六烷基溴化吡啶溶液的动态表面张力。考察了浓度、温度对动态表面张力的影响。讨论了十六烷基溴化吡啶分子在气／液界面上的吸附动力学,发现吸附遵从扩散-动力学控制机理．从表观扩散系数计算了吸附能垒,分析了吸附能垒存在的原因。