Studies of dynamic surface tension of polyoxyethylene alkylphenols at the air–water interface

This paper presents the study of dynamic surface tension of polyoxyethylene alkylphenol surfactants (Igepals) at the air–solution interface. The experimental investigation of the surface tension dynamics are carried out using a pendant drop method for two of the representative alkylphenols (Igepal-630 and Igepal-720) nonionic surfactants. The general trend of the dynamic surface tension for the two surfactants appears to be similar. However, the absolute surface activities are different. Between the two poloxyethylene alkylphenol surfactants, it was found that Igepal-C0-630 has a higher surface activity and a lower critical micelle concentration (CMC) value. This agreed well with their reported hydrophile–lipophile balance (HLB). The equilibrium adsorption parameters for these surfactant systems have been estimation using two different methods and are in good agreement. The theoretical model developed for the surface tension dynamics based on the Statistical Rate Theory (SRT) in our earlier (J. Colloid Interface Sci., 286, 2005, 14–27) work satisfactorily predicted the experimental results for the present systems.     

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.     

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.     

蓖麻油酸甲酯乙氧基化物水溶液的动态表面张力

用最大气泡压力法分别测定了不同环氧乙烷(EO)加合数(10、12、14、16、20)的蓖麻油酸甲酯乙氧基化物(ECAME)水溶液的动态表面张力(DST)。考察了浓度、温度和无机电解质对DST的影响,探讨了不同浓度时DST参数(动态表面张力特性参数n,平衡时间t^*,曲线最大斜率R_1/2)的变化规律。结果表明,随着EO数由10增加到20,DST不断增大;随着浓度由0.5×10^-5 mol/L增加到10×10^-5 mol/L,n由3.02减小到1.05,t^*值由14.45减小到2.29,R_1/2由0.43增大到6.44,则动态表面活性增大,DST降低;随着温度由25 ℃升高至45 ℃,DST降低;吸附初期DST曲线随无机电解质浓度的增大而升高,吸附后期DST曲线随无机电解质浓度的增大而降低。和常规的脂肪酸甲酯乙氧基化物(FMEE)相比,ECAME的动态表面活性更加优异,这为开拓ECAME的应用指明了新的方向。     

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.     

Importance of dynamic surface tension to the residual water content of fabrics

At the end of the final spin cycle of the laundry process, the residual moisture content (RMC) of fabric is directly related to the dynamic surface tension of the residual water in the fabric. The LaPlace equation for capillary rise predicts that the capillary rise of solutions in a capillary is proportional to the surface tension at the air-liquid interface. If fabric can be considered to be a large ensemble of capillaries due to interfiber spacing, then the RMC of fabrics will be directly related to the surface tension of residual solution in the fabric. The use of a tailored rinse additive has the potential to decrease the surface tension of solution significantly, thus leading to a decrease in the residual water content of the fabric. It is expected that as the surfactant concentration increases the surface tension decreases. Hence, the RMC of fabrics must decrease with increasing surfactant concentration. However, a peak is observed in the RMC of fabrics before the critical micelle concentration (CMC) is reached. Prior to the CMC, it is proposed that a sudden adsorption of surfactant is occurring on the fabric surface leading to a decrease in bulk monomer concentration. The decrease in free monomer concentration should result in an increase in the equilibrium surface tension of the residual solution leading to a concomitant increase in RMC. Because the dynamic surface tension is measured on a short time scale (on the order of milliseconds), there will be less adsorption of monomer onto the newly created air-liquid interface of the bubbles during the measurement process. This decrease in adsorption should lead to a pronounced increase in the dynamic surface tension. This indeed was observed. The RMC correlates very well with the dynamic surface tension of the residual solution.     

Dynamic surface tension of polyelectrolyte/surfactant systems with opposite charges: two states for the surfactant at the interface

The molecular reorientation model of Fainerman et al. is conceptually adapted to explain the dynamic surface tension behavior in polyelectrolyte/surfactant systems with opposite charges. The equilibrium surface tension curves and the adsorption dynamics may be explained by assuming that there are two different states for surfactant molecules at the interface. One of these states corresponds to the adsorption of the surfactant as monomers, and the other to the formation of a mixed complex at the surface. The model also explains the plateaus that appear in the dynamic surface tension curves and gives a picture of the adsorption process.     

Application of the maximum bubble pressure technique for dynamic surface tension studies of surfactant solutions using the Sugden two-capillary method

Exact knowledge of the dead time as part of the bubble lifetime in the maximum bubble pressure method is an important prerequisite for accurate dynamic surface tension measurements. The duration of the dead time depends essentially on the capillary geometry and affects significantly the measured surface tensions of concentrated surfactant solutions. Increase of the dead time leads to a significant surface tension decrease of a freshly formed bubble surface due to the significantly higher residual adsorption of the surfactant molecules. It is shown that correct dynamic surface tensions are obtained with the experimental procedure of Sugden's method only when in addition to the fixed frequency of bubble formation, also the dead time values for the two capillaries are kept constant.     

Studies on the application of dynamic surface tensiometry of serum and cerebrospinal liquid for diagnostics and monitoring of treatment in patients who have rheumatic, neurological or oncological diseases

Human biological liquids comprise various surfactants, which adsorb at liquid interfaces and lead to a variation in surface tension. The adsorption processes involving low molecular weight surfactants, proteins and phospholipids play a vital role in the physiological functions of the human organism, especially if large surfaces are involved (e.g., gas exchange in lungs, metabolism of kidneys, liver and brain). Dynamic surface tensiometric studies of biological liquids like serum and cerebrospinal fluid provide surrogate parameters that reflect surface tension phenomena. We provide dynamic surface tension data of serum and cerebrospinal fluid that were collected from healthy volunteers and patients with rheumatic, neurological or oncological diseases. Our studies indicate that dynamic surface tension data are helpful for diagnostic purposes and for monitoring of therapeutic interventions.     

Contact angle interpretation in terms of solid surface tension

Recent experimental (low-rate) dynamic contact angles for 14 solid surfaces are interpreted in terms of their solid surface tensions. Universality of these experimental contact angle patterns is illustrated; other reasons that can cause data to deviate from the patterns are discussed. It is found that surface tension component approaches do not reflect physical reality. Assuming solid surface tension is constant for one and the same solid surface, experimental contact angle patterns are employed to deduce a functional relationship to be used in conjunction with the Young equation to determine solid surface tensions. The explicit form of such a relation is obtained by modifying Berthelot’s rule together with experimental data; essentially constant solid surface tension values are obtained, independent of liquid surface tension and molecular structure. A new combining rule is also derived based on an expression similar to one used in molecular theory; such a combining rule should allow a better understanding of the molecular interactions between unlike solid–liquid pairs.     

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 tensions of Athabasca bitumen vacuum residue including the effect of dissolved air

The pendant drop technique was used to measure the equilibrium and dynamic surface tensions of Athabasca bitumen vacuum residue (500 degrees C+) (AVR) between 150 and 280 degrees C. A significant (16%) slow (over hours) decrease from initial to equilibrium values was found. In addition, the effect of dissolved air on surface tension was studied at 150 degrees C by comparing dynamic surface tensions of air- or nitrogen-saturated AVR in contact with air or nitrogen. It was found that the presence of dissolved air significantly decreases the dynamic change in surface tension (from 16 to 5%). In order to perform the surface tension studies, the density of AVR was required. Archimedes method was used to measure the density of AVR from 98 to 335.8 degrees C.     

Synthesis and surface properties of anionic gemini surfactants with amide groups

Novel anionic gemini surfactants, 1,2-bis(N-beta-carboxypropanoyl-N-alkylamino)ethane (2CnenAm; n is hydrocarbon chain length of 6, 8, 10, 12, or 14), with two hydrocarbon chains, two carboxylate groups, and two amide groups, were synthesized by three-step reactions. Their solution properties were characterized by equilibrium and dynamic surface tension, steady-state fluorescence spectroscopy of pyrene, and dynamic light-scattering techniques. The surface tension measurements of 2CnenAm give low critical micelle concentrations (cmc), great efficiency in lowering the surface tension, and strong adsorption at air/water interface. Gemini surfactants behave normally with the logarithm of cmc decrease linearly with the chain length. In addition, adsorption and micellization behavior of 2CnenAm was estimated by parameter of pC20, cmc/C20, and standard free energy (DeltaG(0)mic and DeltaG(0)ads); they are significantly influenced by hydrocarbon chain length, and the adsorption is promoted more than the micellization as chain length becomes longer. The results of dynamic light-scattering and fluorescence quenching indicate that small micelles of 2CnenAm are observed at the concentrations above the cmc, and further large particles are also seen. Further, from the dynamic surface tension measurements, it is found that the shorter hydrocarbon chain length of 2CnenAm, the faster the rate of decrease of surface tension.     

Dynamic Behavior of Surfactants in Solution

Adsorption of various surfactants at the gas liquid interface is studied with equilibrium and dynamic surface tension measurements. The Wilhelmey plate method and maximum bubble pressure method are used for this study. Dynamic surface tension of solutions of different surfactants, sodium lauryl sulfate (SLS), polyoxyethylene glycol 4‐tert‐octyl phenyl ether (Triton X 100), poly‐oxyethylene(20) cetyl ether (Brij 58), and tetraethylene glycol mono‐n‐dodecyl ether (Brij 30), is measured at different concentrations. Adsorption of different surfactants is compared on the basis of equilibrium and dynamic behavior. Effectiveness and efficiency of different surfactants is found from equilibrium surface tension measurement. A new parameter is defined to quantify the dynamic behavior of adsorption, which gives the concentration of surfactant needed to reduce surface tension to half of its maximum reduction within a defined time available for adsorption. The dynamics of surfactant solution is quantified by using this parameter.     

Dynamic adsorption and surface tension of aqueous dilauroylphosphatidylcholine dispersions under physiological conditions

The dynamic surface tension and equilibrium adsorption behavior of DLPC dispersions in phosphate buffer saline at 37 and 25 degrees C was studied with tensiometry, infrared reflection--absorption spectroscopy (IRRAS), and ellipsometry. The results are compared with those in water (Pinazo et al. Langmuir 2002, 18, 8888). Even though the pH and salinity have no apparent effect on the equilibrium surface tension and the surface pressure--area isotherm, they affect the dynamic surface tension by decreasing the adsorption rate and increasing the dynamic tension minima at a pulsating area of 20 or 80 cycles per minute. Moreover, IRRAS and ellipsometry results show that the adsorbed layers and the spread monolayers have larger area per molecule, or looser packing, in buffer than in water. A new hypothesis is proposed to elucidate the effect of pH/salinity on this zwitterionic surfactant: there is some specific interaction or binding between the ions from the buffer saline with the polar headgroups of DLPC. This interaction induces stronger intermolecular repulsions of the surfactant layer in buffer than that in water, despite the expected electrostatic screening effect, and causes higher dynamic surface tensions. The results have implications in designing lung surfactant replacement formulations.     

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.     

聚二甲基二烯丙基氯化铵及其与CTAB混合物水溶液 的吸附动力学

用最大泡压法分别测定了聚二甲基二烯丙基氯化铵,十六烷基三甲基溴化铵以及两者混合物水溶液的动表面张力。十六烷基三甲基溴化铵的吸附服从扩散-动力学控制机理。发现聚二甲基二烯丙基氯化铵水溶液的表面张力具有独特的时间相关性。吸附的前期服从扩散控制机理,而在吸附的后期,即接近吸附平衡时服从扩散-动力学控制机理。混合物水溶液的整个吸附过程受扩散控制。     

Surface energy and surface tension of condensed matter and the principle of minimum potential energy of systems (revised)

We consider the essence and relation of the surface energy and surface tension of condensed matter: which is which … and (most important question here)—when? For the first time, this consideration is based not on reversible thermodynamics but, as an approximation, on the Principle of Minimum Potential Energy, given two factors: (1) the time-dependent dynamic transformation of the potential energy of the system into the surface energy and into the surface tension (stress); (2) elasticity of structured surface layers of the liquids.     

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.      

Effect of counterions on surface and foaming properties of dodecyl sulfate

The influence of counterions of surfactant on interfacial properties is studied by measuring foamability, foam stability, equilibrium and dynamic surface tension, and surface viscosity. The surfactant chosen is anionic dodecyl sulfate with various counterions, Li(+), Na(+), Cs(+), and Mg(++). Surface tension measurements show a decrease in the following order: LiDS > NaDS > CsDS > Mg(DS)(2). Foamability done using shaking method shows similar order as surface tension, i.e., LiDS > NaDS > CsDS > Mg(DS)(2). This has been explained in terms of the differences in micellar stability and diffusion of monomers. This is further confirmed by our dynamic surface tension results, which show the same order as equilibrium surface tension (i.e., LiDS > NaDS > CsDS > Mg(DS)(2)) at low bubble frequencies but the order is LiDS > NaDS = Mg(DS)(2) > CsDS at high bubble frequencies. Foam stability measurements were done at concentrations below and above cmc to elucidate the role of micelles. It was found that there is no significant change in foam stability when counterions are changed for surfactant concentration values below the cmc, but at concentration above cmc the foam stability of CsDS and Mg(DS)(2) are much greater than LiDS and NaDS indicating presence of stable micelles are essential to high foam stabilities. Surface viscosity measurements correlated well with the foam stability trends and gave the following order LiDS < NaDS < CsDS < Mg(DS)(2), indicating that the molecules of CsDS and Mg(DS)(2) are tightly packed at the air/water interface.