Determination of critical micelle concentrations of some surfactants by keto-enol tautomerism of benzoylacetone

Benzoylacetone, keto-enol tautomer, was dissolved in aqueous solutions of sodium dodecyl sulfate, dodecyl trimethyl ammonium chloride, hexaethyleneglycol dodecyl ether, polyoxyethylene tert-octyl phenyl ether, and polyoxyethylene nonyl phenyl ether, respectively. The effect of surfactants on this keto-enol equilibrium was examined by measuring the intensity of two spectral bands at ca. 250 nm and 315 nm due to ketonic and enolic form of this compound. The existence of keto-enol equilibrium of the benzoylacetone was indicated by an isosbestic point among the two bands. The absorbances of the two bands showed hardly any change in the range of surfactant concentrations below the critical micelle concentration (cmc) but, in the concentration range above the cmc, the absorbance of the enolic form increased and that of the ketonic form decreased abruptly. These changes at cmc were very noticeable in the case of ionic surfactant solution. The concentrations corresponding to abrupt change of the spectra used for the determination of cmc were in fair agreement with data obtained by other methods. However, in the case of nonionic surfactant solutions, the absorbance due to the enolic form increased gradually with increase of the surfactant concentration, and the distinct break point was not observed at cmc.     

On the measurement of critical micelle concentrations of pure and technical-grade nonionic surfactants

The critical micelle concentrations (CMC) of nine commercial nonionic surfactants (Tween 20, 22, 40, 60, and 80; Triton X-100; Brij 35, 58, and 78) and two pure nonionics [C₁₂(EO)₅ and C₁₂(EO)₈] were determined by surface tension and dye micellization methods. Commercially available nonionic surfactants (technical grade) usually contain impurities and have a broad molecular weight distribution owing to the degree of ethoxylation. It was shown that the surface tension method (Wilhelmy plate) is very sensitive to the presence of impurities. Much lower CMC values were obtained with the surface tension method than with the dye micellization method (up to 6.5 times for Tween 22). In the presence of highly surfaceactive impurities, the air/liquid interface is already saturated at concentrations well below the true CMC, leading to a wrong interpretation of the break in the curve of surface tension (γ) vs. concentration of nonionic surfactant (log C). The actual onset of micellization happens at higher concentrations, as measured by the dye micellization method. Furthermore, it was shown that when a commercial surfactant sample (Tween 20) is subjected to foam fractionation, thereby removing species with higher surface activity, the sample yields almost the same CMC values as measured by surface tension and dye micellization methods. It was found that for monodisperse pure nonionic surfactants, both CMC determination methods yield the same results. Therefore, this study indicates that precaution should be taken when determining the CMC of commercial nonionic surfactants by the surface tension method, as it indicates the surface concentration of all surface-active species at the surface only, whereas the dye method indicates the presence of micelles in the bulk solution.     

一种表面活性剂临界胶束浓度测定方法研究

测量吖啶化合物作为发光剂在系列浓度的表面活性剂溶液的化学发光值,根据所得发光值的对数值与其对应的表面活性剂溶液中表面活性剂浓度的对数值进行线性拟合得出若干条拟合直线,相邻两条拟合直线的交点对应的表面活性剂浓度中的最小值即为该表面活性剂的临界胶束浓度.由测定结果可知,十二烷基三甲基氯化铵的临界胶束浓度是11.5 mmol...     

Effect of additives on the critical micelle concentration of some polyethoxylated nonionic detergents

The effect of electrolytes and other additives influencing water structure, viz., urea and formamide, has been studied on the micelle formation of polyethoxylated nonionic detergents in their aqueous solutions. The decrease in critical micelle concentration (c.m.c.) by electrolytes has been interpreted in terms of salting out mechanism and evidence has been obtained in support of the contention that micelles of polyethoxylated nonionic detergents are weakly positively charged. Effect of urea and formamide on the c.m.c. values of these nonionic detergents indicate that hydrophobic bonding is loosened in their presence with a consequent increase in the c.m.c. of these detergents.     

Determination of critical micelle concentration (CMC) of nonionic surfactants by donor-acceptor interaction with lodine and correlation of CMC with hydrophile-lipophile balance and other parameters of the surfactants

The nonionic surfactants form donor-acceptor complexes with iodine in aqueous medium. The spectral absorption and the shift in the λ_max of l₂ upon complexation have been exploited to determine the critical micelle concentration (CMC) of Tweens, Brijs, and Triton X-100. The CMC values obtained closely agree with those determined by other methods, including measurements of static surface tension, differential refractive index, and iodine solubilization. The spectral characteristics of the complex salt Kl₃ can be utilized as well to derive similar information. The CMC and the spectral shift can be correlated with the weight fraction of the polyoxyethylene groups and the hydrophile-lipophile balance (HLB) in various ways, with the parameters in these relationships depending on the series to which the surfactant belong. Because both CMC and HLB depend on temperature, the results and the relations obtained are temperature-dependent; those presented are with reference to 298 K.     

Quantitative-structure-effect relationship for some technical nonionic surfactants

The detergency effect has been examined for a series of technical nonionic surfactants with the use of statistical experimental designs and revealed a plateau in each of the response surfaces obtained. The surfactant concentrations and washing temperatures, needed to reach the edge of each detergency effect plateau, were also determined. These conditions, which define the edge of the plateau, could be well modeled from the physicochemical properties of the surfactants with the use of partial least squares of latent structures. It was also possible to point out the importance of the different physicochemical properties. If an experimental design has been utilized, the detergency effect of a nonionic surfactant can be modeled from multiple linear regression as a function of surfactant concentration, washing time, and washing temperature. We have shown how these regression coefficients can be modeled from the physicochemical properties of the surfactants. Partial least squares of latent structures were used to estimate these models as well. We also demonstrated how these models can be used to predict the regression coefficients of a surfactant not included in the model estimations. The resultant regression coefficients can then be used to predict the detergency effects of this surfactant at different variable settings. The detergency effects thus obtained are in good agreement with measured data acquired under corresponding conditions.     

Determination of cloud points of nonionic surfactants

By use of a specially adapted fluorometer attached to a strip chart recorder, a spectrum or cloud-o-gram can be obtained from various types of ethylene oxide condensates (nonionic surfactants). A cloud-point reproducible to ±0.2C can be determined from the cloud-o-gram. The cloud-o-gram is unique for each classification, and differences can be detected within classifications.     

Mixed monolayer and mixed micelle formation in binary mixture of surfactants—Systems for trioxyethylenated dodecyl sulfonate and some polyoxyethylenated fatty alcohol ether nonionic surfactants

The interaction and synergism of some polyoxyethylenated fatty alcohol ether (POE) nonionic surfactants (C₁₂E₂, C₁₂E₃, C₁₀E₅, C₁₀E₇, where C_x indicates number of carbon atoms in the chain and E_y indicates number of oxyethylene glycol ethers) with trioxyethylenated dodecyl sulfonate (C₁₂E₃S) in mixed monolayer formation at the surface and in mixed micelle formation in aqueous solutions were studied at 25 and 40°C by calculating interaction parameters (β_α, β_M) from surface tension-concentration data by use of Rosen's equations based on the nonideal solution theory. All the systems investigated adapt reasonably well to the nonideal model, with negative values of β_σ and β_M (where M means micelle and σ refers to the air-liquid interface) indicating a favorable interaction between the mixed surfactants. Either at a monolayer or in a mixed micelle, the attractive interaction becomes stronger when the alkyl chain in the POE surfactant is longer, i.e., when the POE becomes more hydrophobic. The interaction increases in the order C₁₀E₇<C₁₀E₅<C₁₂E₃, C₁₂E₂. For the two C₁₀E _n (n= 5,7)/C₁₂E₃S systems, as temperature increases from 25 to 40°C, the interaction increases in a mixed micelle, but it decreases in a mixed monolayer. Synergism in mixed micelle formation exists for C₁₂E₃S/C₁₀E _n mixtures when X₁ ^M , the mole fraction of POE in a mixed micelle, is ≈0.4–0.8, whereas synergism does not occur in the systems of C₁₂E₃S/C₁₂E _m due to the large difference between CMC₁ and CMC₂, i.e., large |In(C ₁ ^M /C ₂ ^M )| value (where CMC=critical micelle concentration). The degree of synergism in mixed micelle formation is temperature independent and is 0.23, 0.18, and close to zero for C₁₀E₅/C₁₂E₃S, C₁₀E₇/C₁₂E₃S, and C₁₂E _m (m=2,3)/C₁₂E₃S systems, respectively. Synergism in surface tension reduction effectiveness occurs in C₁₂E₃S/C₁₂E₂ and C₁₂E₃S/C₁₂E₃ systems. The mole fractions of POE in the solution phase are 0.302 and 0.333 for the two mixtures at the point of maximum synergism.     

Determination of the degree of ethoxylation of nonionic surfactants by elemental analysis

This report presents a fast, accurate analytical method for the determination of the degree of ethoxylation of nonionic ethoxylated surfactants based on the indirect determination of the oxygen content of the surfactant using a C,H,N elemental analyzer. The weight percent oxygen is then easily translated into ethylene oxide (EO) content. This method was found to be fairly accurate in determining the EO content of surfactants containing up to 20 mol EO, which is equivalent to about 80% EO content in most common nonionic surfactant ethoxylates. A comparison of the results obtained with this procedure versus hydroxyl value and HI cleavage methods is also presented in this paper.     

The effect of glycols on the hydrophile-lipophile balance and the micelle formation of nonionic surfactants

The empirical hydrophile-liophile balance (HLB) value of nonionic surfactants is an important parameter used to predict performance as, e.g., emulsifiers, solubilizers and wetting agents. However, the HLB value is based on an original molecular structure and does not take into account all the factors affecting the performance of nonionics, such as presence of additives, type of solvent, temperature, degree of hydration, structural modifications of the surfactant molecule and decomposition of surfactants. On a performance basis, where these factors come into play, a given nonionic surfactant may exhibit a multiplicity of apparent HLB values. Accordingly, we recently introduced the term “effective HLB value” which is a performance value which incorporates into the HLB the parameters listed above. The HLB value thus becomes a variable depending on the physical and chemical conditions at the time of the measurement. In this work, we investigated the effect of adding glycols and diglycols on the HLB using 3 different methods: cloud point, phenol index and critical micelle concentration (cmc). We found that this type of additive increases the cloud point, phenol index, cmc and the “effective HLB” of a polyoxyethylated nonionic surfactant. The effectiveness of the glycols in causing these increases was in the following order; dipropylene glycol > 1,4-butanediol > 1,2-propanediol > diethylene glycol > ethylene glycol. The solvent effect of glycols and diglycols on the hydrophobic and hydrophilic portions of the surfactant molecule are discussed. On the hydrocarbon part of the surfactant molecule, the solvents cause a weakening of the hydrophobic bond and an increase in the cmc. On the polyoxyethylene part of the molecule, the solvent may cause either an increase or a decrease in the cmc. The effect on the hydro-philic portion is related to hydrogen bonding exhibited by the additives. The results obtained again suggest that the effective HLB value, which is a measure of the HLB under operative conditions, may be of greater practical significance than calculated HLB.     

Precipitation of nonionic surfactants by polymeric acid

Nonionic surfactants of the polyethylene oxide type are precipitated by carboxy vinyl polymer (CVP) in its acid form. While the reduced viscosity of the CVP solution is affected more markedly by a surfactant with a longer polyethylene oxide chain, the binding to CVP of the nonionic surfactants with the same hydrophobic parts occurs more effectively with shortening of the polyethylene oxide chain or with lowering of the critical micelle concentration. The structure of the complexes formed is discussed.     

吸附伏安法测定阳离子表面活性剂的临界胶束浓度

以中性红为探针,用吸附伏安法测定了溴化十六烷基三甲铵的临界胶束浓度。     

Determination of critical micelle concentration of surfactant by ultraviolet absorption spectra

A method was investigated for determining the critical micelle concentration (CMC) by the shift of absorption maxima when an organic compound (I) with ultraviolet absorption was added to an aqueous solution of a surfactant. When I was added to the surfactant solution at higher concentrations (above the CMC), λ_max of I approached the value inn-octane, since I was solubilized in the hydrocarbon atmosphere of the inner part of the surfactant micelle. At lower concentrations (below the CMC), however, I was present in the water phase and λ_max approached the value in water. The curve of λ_max vs. surfactant concentration declined from the high concentration values as the CMC was approached and at the CMC, the curve broke upward sharply. Then, it rose for some time and approached the value in water. N,N′-diethylaniline was used because it exhibited larger shifts of λ_max. The standard amount used was 0.002 ml/3–10 ml of aqueous solution of the surfactant. The CMC values obtained agreed with those obtained by the electric conductivity method, dye adsorption method and light scattering method, for surfactants such as tetradecyldimethylbenzylammonium chloride, sodium dodecyl sulfate and polyoxyethylene cetyl ether.     

Determining the critical micelle concentration of surfactants using a binary mixing system

A simple method is described for measuring the critical micelle concentration (CMC) of surfactants using a computer-driven mixing system and a variable wavelength spectrophotometer. Analyses using this method were typically done in 15 min. Detergents that were analyzed included sodium dodecyl sulfate (SDS), sodium cholate, Lubrol-PX and Triton X-100. Lubrol PX showed two phase transitions; other detergents appeared to have only one near their CMC. For sodium cholate, the CMC was more difficult to analyze than the others. This may have been due to its low aggregation number (≤ 4). Since this method successfully identified the CMC of these four detergents, it is likely that most, if not all, surfactants can be analyzed in the same manner.     

The characterization of nonionic surfactants by NMR

The methods currently reported in the literature for the characterization of nonionic surfactants are usually applied to one portion of the molecule and require a knowledge of the other portion for complete identification. This indirect approach leaves much to be desired. A simple, rapid, and more direct method of characterization is to measure the proton signal intensity in high resolution nuclear magnetic resonance (NMR) spectra. This method determines the hydrophile to hydrophobe ratio without requiring standard samples for calibration or a prior knowledge of the hydrophobe. In addition, this method will frequently give much valuable information about the identity of the hydrophobe, such as the average chain length, the degree of branching, and the type of aromatic substitution, if any. This method has been applied to the characterization of the common types of commercial polyethylene oxide condensates. The application of NMR to the analysis of formulated detergent products is also discussed. Presented at the AOCS meeting in New Orleans, La., 1962.     

Biodegradation of nonionic surfactants

This paper discusses the biodegradability of alcohol-based nonionics measured by the recommended legislative test procedures and how the results obtained are affected by the chemical structure of the surfactant, and thus provides guidance on the selection of materials. More detailed studies on the biodegradation of alcohol ethoxylates during the activated sludge sewage treatment process are also reported. Examination of a wide range of alcohol ethoxylates in the legislative tests shows that the majority of those nonionics of practical importance will be extensively biodegraded. Although the mathematical model used to design the treatability test is very simple and has frequently come under criticism, the predictions seem to be upheld and the results obtained appear to provide a reliable guide to what is likely to happen in practice. The sludge residence time, which has long been regarded as of particular importance by those involved in the field of sewage treatment, is clearly demonstrated to be a highly significant factor whose influence should be taken into account in any detailed laboratory study of treatability. The study of alcohol ethoxylates indicates that extensive primary biodegradation will occur even in overloaded treatment plants where sludge retention times (SRT) are likely to be short. The effect of temperature on the biodegradation is small and suggests that effective treatment will be achieved in such plants even at the lower temperatures experienced during winter. Ultimate biodegradation of alcohol ethoxylates was shown to be extensive under practical conditions and levels of “polyethylene glycol” intermediates discharged to surface waters will be low. Although alcohol ethoxylates are rapidly and extensively absorbed on activated sludge, this does not play a significant role in the removal process which is essentially one of biodegradation.     

Fluorescence technique for the determination of low critical micelle concentrations

A technique for determining low critical micelle concentrations (CMC) by means of a hydrophobic fluorescence probe has been developed. The amount of the fluorescent probe at the CMC is so small that the effect of the probe on micelle formation is negligible. The fluorescence intensity was measured at fixed dye/surfactant ratios, and it decreased with concentration. A quantity proportional to fluorescent quantum yield was calculated and found to be high for concentrations of surfactant above the CMC and almost zero below the CMC, giving a distinct break in the quantum yield vs. the concentration curve.     

Use of alizarin red S for determining critical micelle concentration of cationic surfactants

The critical micelle concentrations of cetyl trimethyl ammonium bromide and cetyl pyridinium bromide have been calculated by a spectral-dye method. Alizarin red S at pH 9.12 was found to be suitable for these two cationics. Two shifts in the dye maximum, one due to complex formation (500 mॖ or 525 mॖ) and the other due to the dye-surfactant complex solubilized in the micelles of the cationics were realized. The critical micelle concentration was represented by the point of intersection of two curves at wavelength 500 mॖ and 550 mॖ for cetyl pyridinium bromide and 525 mॖ and 550 mॖ for cetyl trimethyl ammonium bromide.