Hydrolyzable nonionic surfactants: stability and physicochemical properties of surfactants containing carbonate, ester, and amide bonds

A linear and a branched nonionic cleavable surfactants containing a carbonate bond have been prepared from tetra(ethylene glycol) and an alkylchloroformate. The stability of these carbonate surfactants was determined by investigating their hydrolysis and biodegradability characteristics. The hydrolysis was catalyzed by alkali or enzymes (esterase from porcine liver and lipases from Mucor miehei and Candida antarctica B) and was monitored using 1H NMR. It was found that the stability toward alkali was higher for a carbonate surfactant than for a corresponding surfactant with an ester as weak bond. Biodegradation tests resulted in more than 60% degradation after 28 days for both carbonate surfactants. Physicochemical properties, such as critical micelle concentration (CMC), cloud point, area per molecule, and surface tension at the CMC, were determined and compared to those obtained from similar surfactants containing ester, amide, or ether bonds. It was found that the carbonate linkage is hydrophobic and that the oxycarbonyl part of the carbonate group is equivalent, in a formal sense, to an extra methylene group in the alkyl chain of the surfactant.     

Kinetics of horseradish peroxidase reactions in aqueous and reverse micelles composed of nonionic, polyoxyethylene alkyl ether surfactants

Differences between the rates of oxidation of substrates by horseradish peroxidase in buffer, aqueous micellar solution of Brij 35 and in reverse micelles formed of Brij 30 in several hydrocarbons are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Simultaneous determination of cationic surfactants and nonionic surfactants by ion-association titration.

A simultaneous determination of cationic and nonionic surfactants has been developed using ion-association titration. Tetrabromophenolphthalein ethyl ester (TBPE) was used as an indicator. Benzalkonium reacted with TBPE to form a blue ion-associate in the organic phase. When tetrakis(4-fluorophenyl)borate was added dropwise to the solution, the color of the organic phase turned to yellow at the equivalence point. In addition, when a large amount of potassium ion was added to a solution including Triton X-100, Triton X-100 could be determined by the same technique as described above because of formation of the K+-Triton X-100 cation. The proposed method is available for the stepwise determination of cationic and nonionic surfactants in mixtures.     

Simple determination of nonionic surfactants in highly-polluted aqueous samples

This study examined the direct spectrometric method for determining non-ionic surfactants in highly-polluted samples (i.e., soil leachates) containing high concentrations of humic acids. Meso-tetra-(3,5-dibromo-4-hydrooxyphenyl)-porphyrin served as a coloration agent. The method was tested by use of two polyethoxylate/polypropoxylate — based non-ionic surfactants: Triton CF-21 containing aromatic groups in the structure and Novanik 1047A containing only linear hydrocarbon chains. The main goal was to quantify the influence of interfering species to the results. A test for coincidence of regression lines was employed for objective evaluation of the humic acid influence on the determination. It was observed that for linear surfactant Novanik 1047 A the method provides reliable result and thus, can serve for routine analyses. Regarding Triton CF-21, an interfering effect of humic acids was observed; however, after sufficient dilution of the samples, the method can be used as well. Finally, the method can be used for simple analyses of problematic samples without complicated sample-pretreatment.      

The use of nonionic polymerizable surfactants in latexes and paints

In combination with anionic surfactants nonionic polymerizable surfactants lead to stable dispersions, which can be used as binders for paints. Generally the obtained results are worse than with a nonpolymerizable ethoxylated fatty alcohol. However the properties can be optimized through the right choice of the anionic surfactant. This further work is in progress.     

Flow-injection system for determination of critical micelle concentrations of ionic and nonionic surfactants

A practical technique is presented for the rapid, accurate determination of the critical micelle concentrations (CMCs) of ionic and nonionic surfactants. The precision, speed and instrumental simplicity of a flow-injection system are combined with a gradient chamber and flow-through conductance and absorbance detection to produce a system capable of determining the CMC of surfactant solutions in less than 30 min. The exponential response gradients from the resulting system are monitored by a chart recorder and simple manual calculations yield the CMC. The validity of the technique is verified by determination of the CMC values for both ionic (cetyltrimethylammonium bromide and chloride and sodium dodecyl sulfate) and nonionic (Brij-35, Brij-56, Brij-99, Triton X-100) surfactants. The proposed technique does not require the extensive solution preparation, repetitive measurements, complex instrumentation and data manipulation typical of other methods for determining CMCs.     

Preparation and dilute solution properties of model gemini nonionic surfactants

Dimeric poly(ethylene oxide) surfactants (or nonionic gemini surfactants) with the structure (Cn-2H2n-3CHCH2O(CH2CH2O)mH)2(CH2)6 (or GemnEm), where n is the alkyl length and m is the average number of ethylene oxides per head group, were synthesized. Surfactants were synthesized with alkyl chain lengths n = 12, 14, and 20 and m = 5, 10, 15, 20, and 30. Water solubilities and cloud temperatures at 1 wt% were determined by measuring turbidity as a function of temperature. Cloud temperatures increase with m and decrease with n, as observed for conventional surfactants. For large m the cloud temperatures were all above 100 degrees C. Surfactants with small m (i.e., n = 12, 14, m = 5 and n = 20, m = 10) were insoluble at room temperature, forming two-phase mixtures. Critical micelle concentrations (CMCs) were measured using a pyrene fluorescence method and are all in the range of 10(-7) to 10(-6) M, with the lowest values from the surfactants with large n and small m. CMCs of mixtures with both anionic and nonionic conventional (monomeric) surfactants were well described by an ideal mixing model.     

Surface and micellar properties of new nonionic gemini aldonamide-type surfactants

A new group of gemini aldonamide-type surfactants-N,N'-bisalkyl-N,N'-bis[(3-gluconylamide)propyl]ethylenediamines, N,N'-bisdodecyl-N,N'-bis[(3-glucoheptonylamide)propyl]ethylenediamine, and N,N'-bisalkyl-N,N'-bis[(3-lactobionylamide)propyl]ethylenediamines, (alkyl: n-C(8)H(17), n-C(12)H(25)), were synthesized and characterized. The surface properties, such as surface excess concentration, Gamma(cmc), surface area demand per molecule, A(min), efficiency in surface tension reduction, pC(20), the effectiveness of surface tension reduction, gamma(cmc), critical micelle concentration, cmc, and a measure of the tendency of the surfactant to adsorb at the aqueous/air interface relative to its tendency to form micelles in the bulk surfactant solution, cmc/C(20), and standard free energy of micellization, DeltaG(mic)(0), have been obtained by means of surface tension measurements. The standard fluorescence shift technique using PRODAN as a probe provide confirmation of the cmc values by an alternative method. Additionally, the micellar properties for the concentration near above the cmc have been characterized by the aggregation number, N(agg). The presence of the dimeric segments with the aldonamide hydrophilic units in the surfactant molecule is found to be the source of their unusual physicochemical behavior. They are very efficient at adsorbing at the free surface and at forming micelles in water. Their critical micelle concentration values are remarkably low. They reveal remarkably low A(min) values in relation to conventional nonionic surfactants, which is unexpected from the molecular dimensions for the molecule but which is possible if one assumes some type of multilayer structure or a coherent interfacial film.     

Mixed micellization of anionic–nonionic surfactants in aqueous media: a physicochemical study with theoretical consideration

Mixed micellization of binary and ternary mixtures of anionic and nonionic surfactants, such as lithium dodecyl sulfate, polyoxyethylene(23)laurylether, and polyoxyethylene-tert-octylphenylether, is studied in aqueous solution using tensiometric, conductometric, and spectrophotometric methods. Although tensiometry and conductometry complement each other closely, the spectroscopic critical micellar concentration (cmc) is far from agreement with tensiometric study. Several parameters, e.g., cmc, degree of counterion binding, free energies of micellization, and interfacial adsorption, have been evaluated. Established theories of Clint, Rosen, Rubingh, Motomura, Georgiev, Maeda, and Blankschtein were applied to evaluate the mole fraction of different components in the self-aggregated phase, the interaction parameter, free energy contributions, and expected cmc.     

Simultaneous potentiometric determination of cationic and ethoxylated nonionic surfactants in liquid cleaners and disinfectants

A sensitive potentiometric surfactant sensor based on a highly lipophilic 1,3-didecyl-2-methyl-imidazolium cation and a tetraphenylborate (TPB) antagonist ion was used as the end-point detector in ion-pair potentiometric surfactant titrations using sodium TPB as a titrant. Several analytical and technical grade cationic and ethoxylated nonionic surfactants (EONS) and mixtures of both were potentiometrically titrated.The sensor showed satisfactory analytical performances within a pH range of 3-10 and exhibited satisfactory selectivity for all CS and EONS investigated. Ionic strength did not influence the titration except at 0.1 M NaCl, in which a slight distortion of the second inflexion corresponded with the nonionic surfactant.Two-component combinations of four CS and three EONS were potentiometrically titrated using the sensor previously mentioned as the end-point detector. The quantities of the surfactants varied between 2 and 6 μmol for CS and 2.50 and 7.50 μmol for EONS. The known addition methodology was used for determination of the surfactant with considerably lower concentration in the mixture.Three commercial products containing cationic surfactants as disinfectants and nonionic surfactants were potentiometrically titrated, and the results for both type of surfactants were compared with those obtained with standard conventional methods.     

Tools to discover anionic and nonionic polyfluorinated alkyl surfactants by liquid chromatography electrospray ionisation mass spectrometry

A tiered approach is proposed for the discovery of unknown anionic and nonionic polyfluorinated alkyl surfactants (PFASs) by reversed phase ultra high performance liquid chromatography (UHPLC)--negative electrospray ionisation--quadrupole time of flight mass spectrometry (UHPLC-ESI(-)-QTOF-MS). The chromatographic separation, ionisation and detection of PFASs mixtures, was achieved at high pH (pH=9.7) with NH(4)OH as additive. To distinguish PFASs from other chemicals we used the characteristic negative mass defects of PFASs, their specific losses of 20 Da (HF) and the presence of series of chromatographic peaks, belonging to homologues series with m/z of n×50 Da (CF(2)) or n×100 Da (CF(2)CF(2)). The elemental composition of the precursor ions were deducted from the accurate m/z values of the deprotonated molecules [M-H](-). In case of in-source fragmentation, the presence of dimers, e.g. [M(2)-H](-) and adduct ions such as [M-H+solvent](-) and [(M-H)(M-H+Na)(n)](-) were used to confirm the identity of the precursor ions. In relation to quantification of PFASs, we discuss how their surfactancy influence the ESI processes, challenge their handling in solution and choices of precursor-to-product ions for MSMS of e.g., structural PFAS isomers. The method has been used to discover PFASs in industrial blends and in extracts from food contact materials.     

Influence of temperature and alkyl chain length on phase behavior in Langmuir monolayers of some oxyethylenated nonionic surfactants

We study the surface phase behavior in Langmuir monolayers of a series of nonionic surfactants of the general formula CnE1 with n=14, 16, and 18 by film balance and Brewster angle microscopy (BAM) over a wide range of temperatures. A cusp point followed by a pronounced plateau region in the pressure-area (pi-A) isotherms indicates a first-order phase transition in the coexisting state between a lower density liquid expanded (LE) phase and a higher density liquid condensed (LC) phase at the air-water interface. The formation of bright two-dimensional (2D) LC domains in a dark background visualized by BAM further confirms this observation. In addition to the cusp point at the onset of the LE-LC coexistence state, another cusp point followed by a small plateau is observed for the C14E1 and C18E1 monolayers, indicating a second phase transition between two condensed phases of different compressibility and tilt orientation of the molecules. This unusual two-step phase transition is explained by the Ostwald step rule. The C16E1 and C18E1 monolayers show a kink in their respective isotherms, after which the surface pressure increases steeply with only a little decrease in the molecular area, suggesting that the molecules undergo a transition from a tilted to an almost vertical orientation with respect to the water surface. The thermodynamic parameters for the condensation of the molecules in the LE-LC coexistence state were calculated by employing the 2D Clapeyron equation. The temperature coefficient of the critical surface pressure dpi(c)/dT values shows a decreasing trend from C14E1 to C18E1, suggesting that the condensation process becomes less and less prone to thermal perturbation as the chain length increases. For all the amphiphiles, the DeltaH values are found to be negative, suggesting an exothermic nature of condensation. The negative DeltaS values obtained from the relation DeltaH/T probably come from the restriction on the rotational and translational motion of the molecules constrained in a confined area in the LE-LC transition region.     

Spectrophotometric determination of cationic and anionic surfactants with anionic dyes in the presence of nonionic surfactants,part I: A general aspect

The behavior of color development of anionic azo dyes, methyl orange and its analogues, was examined in aqueous media by changing the microenvironment of the dyes. The addition of alcohols, organic onium ions, anionic surfactants and nonionic surfactants brought about a decrease of the band at wavelengths near 480 nm and an increase of the band at wavelengths near 420 nm. Such a shift toward the shorter wavelengths in spectra was attributed to the change of the micro-environment around the dyes from a polar field to a less polar field; that is, the shift is caused by the change of the contribution of the following resonance forms, On the basis of the color change phenomena, the spectrophotometric methods for the determination of organic onium ions and anionic surfactants were proposed.     

Tetrabutylammonium alkyl carboxylate surfactants in aqueous solution: self-association behavior, solution nanostructure, and comparison with tetrabutylammonium alkyl sulfate surfactants

A series of long and ultralong chain tetrabutylammonium alkyl carboxylate (TBACm, TBA = tetrabutylammonium ion; Cm = carboxylate ion C(m-1)H(2)(m-1)CO(2)(-) of total carbon number m) surfactants have been obtained by direct neutralization of the fatty acids with m = 12, 14, 18, 22, and 24 by tetrabutylammonium hydroxide. Time-resolved fluorescence quenching has been used to determine the micelle aggregation number (N) of the surfactants with m = 12, 14, and 18 in the temperature range 10-50 degrees C and of the surfactants with m = 22 and 24 in the temperature range 25-60 degrees C. In all instances the values of N were well below those that can be calculated for the maximum spherical micelle formed by surfactants with the same alkyl chain as the investigated surfactants on the basis of the oil drop model for the micelle core. The microstructure of selected solutions of TBAC22 was examined using transmission electron microscopy at cryogenic temperature and compared to the microstructure of solutions of TBA dodecyl and tetradecyl sulfates. These observations generally confirmed the findings of TRFQ. The self-association behavior of these anionic surfactants with TBA counterions is explained on the basis of the large size and the hydrophobicity of the tetrabutylammonium ions. The important differences in behavior that have been evidenced between tetrabutylammonium alkyl carboxylates and alkyl sulfates are discussed in terms of differences in distribution of the surfactant electrical charge on the headgroup and alkyl chain predicted by quantum chemical calculations (Langmuir 1999, 15, 7546).     

Preparation of water-in-diesel oil nano-emulsion using nonionic surfactants with enhanced stability and flow properties

Formation of water-in-diesel oil (w/o) nano-emulsion has been achieved by a low-energy emulsification method by stabilizing a new combination of nonionic sorbitan esters surfactants, that is PEG20-sorbitan monostearate and sorbitan monooleate in mixed proportions. Different combinations of the surfactants (T6?+?S8) have been tested and the best possible combination of mixed surfactants is found at a surfactants ratio of 35:65 (wt/wt) for T6:S8 at hydrophile–lipophile balance (HLB)?=?8.01, which resulted in smaller droplet size of 44.87?nm. A phase diagram study is performed to identify the zones of formation of transparent, translucent, and opaque emulsions (44?nm??27?m³?·?s^?1. Comparison of Ostwald ripening rate with other sets of surfactants obtained by different authors showed the lowest rate among them, indicative of enhanced stability. A rheological study of the tested set of nano-emulsions depicts the Newtonian behavior (1.0371?≤?n?≤?1.0826) over a wider range of shear rates (10–1000?s^?1) at different temperatures (25–40°C).     

Effect of nature of support and impregnating agent on lipophilicity determination for nonionic surfactants by reversed-phase thin-layer chromatography

Summary The retention of 9 nonylphenyl ethylene oxide oligomers was determined in 15 reversed-phase chromatographic systems using silicone oils of various molecular mass as impregnating agents and silica, cellulose and alumina supports. The data were evaluated with principal component analysis carried out on the covariance and the correlation matrices. The R_M values did not follow the additivity rule and they did not change linearly with increasing length of the ethylene oxide chain. This is probably due to the folded state of the chain in the eluent. The molecular mass of the silicone oils had a negligible effect on the retention whereas the retention increased with increasing level of impregnation. The support considerably influenced the lipophilicity values of these nonionic surfactants and cellulose seemed to be the most appropriate support. Calculations proved that the application of a correlation matrix may cause data distortion; therefore, the use of a covariance matrix is strongly proposed.     

Mixtures of nonionic and anionic surfactants: interactions with low-molecular-mass homopeptides

The interaction between low molecular-mass homopeptides and mixtures of nonionic and anionic surfactants has been assessed by using reversed-phase thin-layer chromatography. The relative strength of interaction for mixtures of sodium dodecylsulfate and tridecylalcohol diglycolate (GNX) at the molar ratios of 8:2, 6:4, 4:6 and 2:8 has been calculated and its relationship with the physicochemical parameters (number of amino acid units, hydrophobicity, side chain bulkiness, electronic characteristics) of peptides has been computed by stepwise regression analysis. Each peptide interacted with each surfactant mixture the strength of interaction markedly depending on both the character of the peptide and the composition of the surfactant mixture. The hydrophobicity and electronic properties of the amino acid units exerted the highest influence on the strength of interaction at the highest concentration of the nonionic surfactant (GNX) whereas the number of amino acid units in the peptide molecule and the bulkiness of the amino acid side chain governed the strength of interaction at the lowest concentration of GNX.     

Adsorption relaxation for nonionic surfactants under mixed barrier-diffusion and micellization-diffusion control

Relaxation processes of surfactant adsorption and surface tension, which are characterized by two specific relaxation times, are theoretically investigated. We are dealing with fluid interfaces and small initial deviations from equilibrium. For surfactant concentrations below the critical micellization concentration (CMC), we consider adsorption under mixed barrier-diffusion control. General analytical expressions are derived, which are convenient for both numerical computations and asymptotic analysis. Series expansions for the short- and long-time limit are derived. The results imply that the short-time asymptotics is controlled by the adsorption barrier, whereas the long-time asymptotics is always dominated by diffusion. Furthermore, for surfactant concentrations above the CMC, adsorption under mixed micellization-diffusion control is considered. Again, a general analytical expression is derived for the relaxation of surfactant adsorption and surface tension, whose long- and short-time asymptotics are deduced. The derived equations show that at the short times the relaxation is completely controlled by the diffusion, whereas the long-time asymptotics is affected by both demicellization and diffusion. The micellar effect is manifested as an exponential (rather than square-root) decay of the perturbation. The derived expressions are applied to process available experimental data for the nonionic surfactant Triton X-100 and to determine the respective demicellization rate constant.     

Forces between silica surfaces with adsorbed cationic surfactants: influence of salt and added nonionic surfactants

Forces have been measured between silica surfaces with adsorbed surfactants by means of a bimorph surface force apparatus. The surfactants used are the cationic surfactant tetradecyltrimethylammonium bromide (TTAB) and the nonionic surfactant hexakis(ethylene glycol) mono-n-tetradecyl ether (C(14)E(6)) as well as mixtures of these two surfactants. The measurements were made at elevated pH, and the effect of salt was studied. At high pH the glass surface is highly charged, which increases the adsorption of TTAB. Despite the low adsorption generally seen for nonionic surfactants on silica at high pH, addition of C(14)E(6) has a considerable effect on the surface forces between two glass surfaces in a TTAB solution. The barrier force is hardly affected, but the adhesion is reduced remarkably. Also, addition of salt decreases the adhesion, but increases the barrier force. In the presence of salt, addition of C(14)E(6) also increases the thickness of the adsorbed layer. The force barrier height is also shown to be related to literature values for surface pressure data in these systems.