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.     

Dynamic adsorption and characterization of phospholipid and mixed phospholipid/protein layers at liquid/liquid interfaces

Drop profile analysis tensiometry is applied to study the adsorption dynamics of phospholipids, proteins and phospholipid/protein mixtures at liquid/liquid interfaces. Measurements of the dynamic interfacial tension of phospholipid layers give information on the adsorption mechanism and the structure of the adsorption layer. The equilibrium and dynamic adsorption of pure protein solutions, i.e. human serum album (HSA), beta-lactoglobulin (beta-LG), beta-casein (beta-CA), can be explained well by the thermodynamic model of Frumkin and the diffusion-controlled adsorption theory. The adsorption behavior from mixed phospholipid/protein solutions was also investigated in terms of dynamic interfacial tensions. Interestingly, a "skin-like" folded film of pure protein or phospholipid/protein complex layers can be observed at curved surfaces at the water/oil interfaces. The addition of phospholipids accelerates the formation of the folded structure at the drop surface through co-adsorption of proteins.     

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.     

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.     

Kinetics of adsorption from micellar solutions

Previous studies on surfactant adsorption mostly deal with dilute systems without aggregation in the bulk phase. At the same time, micellar solutions can be more important from the point of view of applications. If one attempts to estimate the equilibrium adsorption, neglecting the influence of micelles can lead to reasonable results. The situation differs for non-equilibrium systems when the adsorption rate can increase by an order of magnitude at the increase of the surfactant concentration beyond the CMC. A critical survey of various models describing the influence of micelles on adsorption kinetics at the liquid-gas interface is given and the theoretical results are compared with existing experimental data. The theories proposed for the case of large deviations from the equilibrium are usually based on some unjustifiable assumptions and can describe the kinetic dependencies of adsorption in only a limited number of situations. Consequently, only rough estimates of the kinetic coefficients of micellization can be obtained from experimental data on dynamic surface tension. More rigorous equations can be derived if the system only deviates slightly from equilibrium. In the latter case, the agreement between theoretical and experimental results is essentially better and measurements of the dynamic surface elasticity of micellar solutions allow us to study the micellization kinetics.     

New methodology to determine the rate-limiting adsorption kinetics mechanism from experimental dynamic surface tension data

We present a new methodology to determine the rate-limiting adsorption kinetics mechanism (diffusion-controlled vs mixed diffusion-barrier controlled), including deducing the kinetics parameters (the diffusion coefficient, D, and the energy-barrier parameter, beta), from the experimental short-time dynamic surface tension (DST) data. The new methodology has the following advantages over the existing procedure used to analyze the experimental DST data: (a) it does not require using a model for the equilibrium adsorption isotherm, and (b) it only requires using the experimental short-time DST data measured at two initial surfactant bulk solution concentrations. We apply the new methodology to analyze the experimental short-time DST data of the following alkyl poly(ethylene oxide), CiEj, nonionic surfactants: C12E4, C12E6, C12E8, and C10E8 measured using the pendant-bubble apparatus. We find that for C12E4 and C12E6, the effect of the energy barrier on the overall rate of surfactant adsorption can be neglected for surfactant bulk solution concentrations below their respective critical micelle concentrations (CMCs), and therefore, that the rate-limiting adsorption kinetics mechanism for C12E4 and C12E6 is diffusion-controlled at any of their premicellar surfactant bulk solution concentrations. On the other hand, for C12E8 and C10E8, we find that their respective CMC values are large enough to observe a significant effect of the energy barrier on the overall rate of surfactant adsorption. In other words, for C12E8 and C10E8, the rate-limiting adsorption kinetics mechanism shifts from diffusion-controlled to mixed diffusion-barrier controlled as their premicellar surfactant bulk solution concentrations increase. We test the new methodology by predicting the short-time DST profiles at other initial surfactant bulk solution concentrations, and then comparing the predicted DST profiles with those measured experimentally. Very good agreement is obtained for the four CiEj nonionic surfactants considered. We also compare the results of implementing the new methodology with those of implementing the existing procedure, and conclude that using a model for the equilibrium adsorption isotherm can lead not only to different values of D and beta, but it can also lead to a completely different determination of the rate-limiting adsorption kinetics mechanism. Since the new methodology proposed here does not require using a model for the equilibrium adsorption isotherm, we conclude that it should provide a more reliable determination of the rate-limiting adsorption kinetics mechanism, including the deduced kinetics parameters, D and beta.     

Equilibrium and dynamic aspects of dodecyltrimethylammonium bromide adsorption at the air/water interface in the presence of lambda-carrageenan

In this work we present equilibrium and dynamic surface tension together with dilational elasticity data for dodecyltrimethylammonium bromide in the presence of lambda-carrageenan, a sulfated polysaccharide extracted from algae. The critical aggregation concentration and (CAC) and critical micellar concentration CMC of the mixed system were determined and shown to have a direct influence on the elasticity modulus. The behavior of the adsorption kinetics was shown to be dependent on the surfactant to polyelectrolyte charge ratio or excess species in the bulk solution.     

Short-time behavior of mixed diffusion-barrier controlled adsorption

This paper focuses on the short-time adsorption kinetics of nonionic surfactants onto water/air surfaces, analyzed in the context of the mixed diffusion-barrier controlled adsorption modeling framework. Specifically, we reconcile the apparent contradiction between theoretical prediction and experimental observations on the adsorption kinetics mechanism at short times: while the mixed diffusion-barrier controlled model predicts a barrier-controlled adsorption, as well as the impossibility of a diffusion-controlled adsorption at asymptotic short times, the short-time experimental dynamic surface tension (DST) behavior of many nonionic surfactants has been interpreted to result from diffusion-controlled adsorption at asymptotic short times. This is because the short-time experimental DST of these surfactants displays a t variation, which is considered as a fingerprint for the existence of diffusion-controlled adsorption, based on the short-time asymptotic behavior of the diffusion-controlled adsorption model. As a result of this interpretation, the fundamental physical nature of the energy barrier has been proposed to be associated with high surfactant surface concentrations. In this paper, we derive a new nonasymptotic short-time formalism of the mixed diffusion-barrier controlled model to describe surfactant adsorption onto a spherical pendant-bubble surface, including determining the ranges of time and surfactant surface concentration values where the short-time formalism is applicable. Based on this formalism, we find that one can expect to observe an apparent t variation of the DST at short times even for the mixed diffusion-barrier controlled adsorption model. We analyze the consequence of this finding by re-evaluating the existing notions of the energy barrier. We conclude that the energy barrier is associated with the adsorption of a single surfactant molecule onto a clean surface.     

Lipophilic counterion effect on aggregation and adsorption behavior of quaternary ammonium surfactants

The obvious different aggregation and adsorption behavior of six newly quaternary ammonium surfactants with different lipophilic counterions has been discoverd by measurements of equilibrium and dynamic surface tension, fluorescence and conductivity. Interestingly, the critical micelle concentration (CMC) and its surface tension γ_CMC decrease with the increasing counterion chain length. However, three methods have confirmed that an exception of CMC increases slightly from C₁₆NC₁ to C₁₆NC₂. According to experimental results, a balanced mechanism between hydrophobicity and electrostatic of counterion is proposed. Besides, the dynamic surface tension results show the diffusion coefficient increases with the increasing counterion length both at a short time (D_t?→?0) and long time (D_t?→?∞), which indicates a faster adsorption process. Unlike the inorganic counterion, the diffusion coefficient decreases with the increase of hydrophobic chain length. This is attributed to the strong electrostatic interactions between counterions and cationic headgroups.     

Surface tension and adsorption behavior of mixtures of diacyl glycerol arginine-based surfactants with DPPC and DMPC phospholipids

The binary surface interactions of some novel cationic diacyl glycerol arginine-based surfactants with model phospholipids, which are often used as model membrane components, are studied at 25 °C in aqueous solutions of 0.1 M sodium chloride. The surfactants are 1,2-dimyristoyl-rac-glycero-3-O-(N^α-acetyl-l-arginine) hydrochloride (1414RAc) and 1,2-dilauroyl-rac-glycero-3-O-(N^α-acetyl-l-arginine) hydrochloride (1212RAc), and they are important as potential antimicrobial agents which are biodegradable and with less toxicity than other cationic surfactants. The phospholipids are 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC). The equilibrium and dynamic surface tension of each surfactant, each phospholipid, and some of their binary mixtures are studied using the bubble surfactometry method at constant area or pulsating area conditions. In addition, the surface densities of pure and mixed monolayers of these compounds at the air/water interface are probed with infrared reflection–absorption spectroscopy (IRRAS). Steady state and dynamic surface tension synergism, or antisynergism in one case, and synergistic adsorption effects are detected for the mixed dispersions studied. The enhanced adsorption detected with IRRAS, and the enhanced dynamic and steady state surface tension lowering indicate strong miscibility and net attractive interactions between the compounds in the adsorbed mixed monolayers.     

不同锌铝比水滑石的合成及其吸附脱除水中邻苯二甲酸性能

采用共沉淀法合成一系列具有不同锌铝比的水滑石,并利用X射线衍射(XRD)、扫描电镜(SEM)、热重(TG)、氮气吸脱附及电感耦合等离子体质谱(ICP-MS)等表征手段对其结构与组成进行了测试。将上述水滑石材料用于吸附脱除水中邻苯二甲酸污染物,考察了不同锌铝比水滑石吸附邻苯二甲酸性能的差异。结果表明,在较低锌铝比时,随着水滑石锌铝比的增加,其对邻苯二甲酸的吸附量逐渐增大;当锌铝比较大时(6),随着锌铝比的增加,水滑石的吸附量基本保持不变。进一步选取锌铝比为6的水滑石,分别对其吸附邻苯二甲酸的动力学和热力学进行了研究,发现其吸附等温线和吸附动力学数据分别符合Freundlich等温吸附模型和准二级动力学模型,且循环吸附性能较好。     

不同锌铝比水滑石的合成及吸附脱除水中邻苯二甲酸性能的研究

采用共沉淀法合成一系列具有不同锌铝比的水滑石,并利用X射线衍射（XRD）、扫描电镜（SEM）、热重（TG）、氮气吸脱附及电感耦合等离子体质谱（ICP-MS）等表征手段对其结构与组成进行了测试。将上述水滑石材料用于吸附脱除水中邻苯二甲酸污染物,考察了不同锌铝比水滑石吸附邻苯二甲酸性能的差异。结果表明,在较低锌铝比时,随着水滑石锌铝比的增加,其对邻苯二甲酸的吸附量逐渐增大;当锌铝比较大时（>6）,随着锌铝比的增加,水滑石的吸附量基本保持不变。进一步选取锌铝比为6的水滑石,分别对其吸附邻苯二甲酸的动力学和热力学进行了研究,发现其吸附等温线和吸附动力学数据分别符合Freundlich等温吸附模型和准二级动力学模型,且循环吸附性能较好。     

Dynamic surface tension and its diffusional decay of dodecyl ethoxylates with different homologue distribution

Dynamic surface tension and its diffusional decay have been studied with four different polydisperse C12E7 at different temperatures and different concentrations. The CMC and the headgroup area from equilibrium surface tension were shown with polydispersity and temperature. The chain length of oxyethylene on the surface was derived from comparison between the headgroup area of monodisperse dodecyl ethoxylates and that of polydisperse C12E7. The values for (Deff/D) were deduced with a diffusion-controlled adsorption model using parameters obtained from equilibrium surface tension. It was shown at short adsorption time that molecules were really adsorbed onto the surface in a diffusion-controlled manner. At a comparably long adsorption time, the ratios (Deff/D) were calculated by assuming the selective adsorption onto the surface. The modified Arrhenius-type equation was proposed by putting a concentration term in front of the exponential terms. The modified Arrhenius-type equation gave Ea=30 kJ/mole for this system. Ea directly derived without an Arrhenius plot was between 9 to 11 kJ/mole. It was an indication that the activation energy alone was not enough to explain the decay of dynamic surface tensions.     

Nonequilibrium surface tension for mixed adsorption kinetics

Experimental nonequilibrium surface tension measurements of 1–9 nonanediol solutions obtained by the oscillating-jet method have been interpreted in terms of our theoretical predictions derived for a mixed-controlled adsorption kinetics of the surfactant. The surface tension values have been calculated from the Szyszkowski equation using the Langmuir model of surfactant adsorption. Our theoretical results, obtained by a numerical solution of the adsorption equations, agree well with experimental data giving a value of the kinetics Szyszkowski constant very similar to the thermodynamic equilibrium value determined from experimental measurements of the static surface tension of 1–9 nonanediol solutions of various concentration. The approximate kinetic equation derived by P. Joos, G. Bleys, and G. Petre (J. Chim. Phys.79, 387 (1982)) for purely barrier-controlled adsorption proved to be less accurate.     

卤化钠对一种新型阳离子表面活性剂动态表面张力的影响

The equilibrium and dynamic surface tension （DST） of the novel cationic surfactant, 3-（p-nonylphenoxy）-2-hydroxylpropyl trimethyl ammonium bromide, abbreviated as RTAB, were studied. The effect of sodium halide such as NaCl, NaBr and NaI on the DST behavior of the RTAB solution below its CMC was studied in detail. Due to the preferential adsorption, the effect of hydration and salting out, the ability to reduce the DST values at the same concentration was in the order of NaI〉NaBr〉NaCl. Attributed to its high surface activity, the equilibrium time of the DST of the surfactant solution was insensitive to the ionic strength.     

羧甲基纤维素与丙烯酸接枝共聚凝胶的溶胀动力学及过溶胀平衡特性的研究

采用接枝共聚合成了羧甲基纤维素钠、丙烯酸与N,N′-亚甲基双丙烯酰胺的交联凝胶, 研究了这类凝胶在不同pH值的缓冲溶液中的溶胀行为, 发现在酸性介质中凝胶的溶胀动力学行为表现出过溶胀平衡特性(overshooting effect), 即凝胶先发生溶胀到最大值, 然后再逐渐消溶胀到平衡. 这种现象可归因于凝胶溶胀过程中羧基之间通过氢键所产生的协同物理交联. 较之凝胶的组成, 缓冲溶液的pH值对过溶胀平衡现象的影响更为显著. 前者是因为凝胶羧基的总摩尔分数并不随两组分结构单元摩尔数的改变而改变, 羧基之间通过氢键形成的物理交联程度在交联剂摩尔分数接近的条件下变化不大; 后者是由于溶液的pH值显著影响凝胶羧基的质子化程度, 进而影响羧基之间通过氢键形成的物理交联程度. 凝胶在酸性介质中的溶胀过程符合E. Díez-Peña等提出的溶胀动力学定量模型, 理论曲线与实验数据有较好的相关性. 凝胶在pH≥5.0的缓冲溶液中的溶胀不产生过溶胀平衡现象, 这一现象归因于完全离子化的羧基之间不能形成物理交联. 凝胶的溶胀过程遵循Schott二级溶胀动力学.     

On the adsorption kinetics of surface-chemically pure n-dodecanoic acid at the air/water interface

The dynamic surface tension data for n-dodecanoic acid in 0.005 M hydrochloric acid, for as-received as well as for surface-chemically pure solutions, show the presence of a prolonged induction period, clearly indicating that the adsorption of this nonionic surfactant is not simply diffusion-controlled. A kinetic model for the reversible formation of monolayer islands, long known in the field of electrochemistry, is shown to also apply to the adsorption of n-dodecanoic acid at the air/water interface. The rate constant increases linearly with increasing bulk concentration, while the induction time decreases exponentially. The phenomenon of nucleation at the air/water interface is consistent with the direct experimental observation of the formation of solid-like patches as the interfacial region is drastically compressed.     

Adsorption Kinetics of Octanoyl-<Emphasis Type="Italic">N</Emphasis>-Methylglucamine at Air/Solution Interface

By means of maximal bubble pressure method, the dynamic surface tensions of aqueous octanoyl-N-methylglucamine (Mega-8) solutions at 25°C were measured. On the base of the experimental data, the adsorption kinetics of Mega-8 at air/solution interface was studied. In the short time range, the adsorption was diffusion-controlled and the diffusion coefficient was calculated. However, for the long time limit there was an adsorption barrier and the mixed diffusion-activation mechanism was proved.__________From Kolloidnyi Zhurnal, Vol. 67, No. 3, 2005, pp. 377–380.Original English Text Copyright © 2005 by Liu, Zhang, Yang, Messow.This article was submitted by the authors in English.     

Removal of Copper(II) in the Presence of Sodium Dodecylobenzene Sulfonate from Acidic Effluents Using Adsorption on Ion Exchangers and Micellar-Enhanced Ultrafiltration Methods

The selective removal of Cu(II) in the presence of sodium dodecylobenzene sulfonate from acidic effluents was made using the adsorption and micellar-enhanced ultrafiltration methods. Lewatit MonoPlus TP220 showed the best adsorption behavior in the systems containing Cu(II) in the presence of ABSNa50 surfactant compared to the other adsorbents (removal efficiency ≈ 100%, sorption capacity ≈ 10 mg/g). The kinetics followed the pseudo-second order kinetic equation. The Langmuir adsorption capacities were 110 mg/g (the system with ABSNa50 above CMC) and 130.38 mg/g (the system with ABSNa50 below CMC). The working ion exchange capacities were C_w = 0.0216 g/mL and C_w = 0.0135 g/mL. The copper removal by the micellar-enhanced ultrafiltration method was 76.46% (0.1 mol/L HCl).     

Surfactant adsorption onto interfaces: measuring the surface excess in time

We propose a direct method to measure the equilibrium and dynamic surface properties of surfactant solutions with very low critical micellar concentrations (CMC) using a pendant drop tensiometer. We studied solutions of the nonionic surfactant hexaethylene glycol monododecyl ether (C(12)E(6)) and of the ionic surfactant hexadecyl trimethyl ammonium bromide (CTAB) with concentrated sodium bromide (NaBr). The variation of the surface tension as a function of surface concentration is obtained easily without the need for complex models and compares well with the result obtained using the Gibbs adsorption equation. The time-dependent surface concentration of each surfactant was also measured, and the adsorption process was found to be diffusion-controlled. The diffusion coefficients of the two surfactants can be extracted from the data and were found in very good agreement with literature values, further validating the method.