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.     

Clouding of nonionic surfactants

Nonionic surfactants have broad applications such as cleaning and dispersion stabilization, which frequently are hampered by strong temperature sensitivities. As manifested by clouding and decreased solubility with increasing temperature, the interaction between water and the oligo(oxyethylene) head-groups is becoming less favorable. Different aspects of surfactant self-assembly, like the critical micelle concentration, micelle size and shape, intermicellar interactions and phase separation phenomena are reviewed as well as suggested underlying causes of the temperature dependence. Furthermore, the effect of cosolutes on clouding and the behavior of related systems, non-aqueous solutions and nonionic polymers, are examined.     

Novel nonionic siloxane surfactants

A new method for ethoxylation without application of pressure is described. Butynediololigo(oxyethylene) [H(OCH₂CH₂)_n? OCH₂? C?C? CH₂O(CH₂CH₂O)_nH with n=1–16] has been prepared in the presence of an electrophilic catalyst in a specially developed reciruculating apparatus. The products have been characterized by NMR and IR spectroscopy. New nonionic silicone surfactants have been synthesized by hydrosilylation of these butynediololigo(oxyethylenes) with defined siloxanes and polysiloxanes. Protection of the hydroxyl group before hydrosilylation was not necessary. Hydrosilylation was carried out in the presence of a solvent. It has been possible to obtain surfactants with a surface tension of about 21-22 mN m^?1 and an interfacial tension of 2 mN m^?1.     

Solubilization of unilamellar phospholipid bilayers by nonionic surfactants

The mechanisms governing the solubilization of neutral or electrically charged unilamellar liposomes by a series of octylphenol polyethoxylated surfactants (average of ethylene oxide units between 8.5 and 20.0) were investigated. Solubilization was detected as a decrease in light-scattering of liposome suspensions. To this end, in accordance with the nomenclature adopted by Lichtenberg, three parameters were considered as corresponding to the effective surfactant/lipid molar ratios (Re) at which the surfactant (a) saturated the liposomesRe _sat; (b) resulted in a 50% solubilization of vesiclesRe _50% and (c) led to a total solubilization of liposomesRe _sol. These parameters, corresponded to theRe at which light scattering starts to decrease, reaches 50% of the original value and shows no further decrease.It is noteworthy that theRe _sat parameter decreases as the EO contents or the surfactant critical micellar concentration (CMC) increases. However, theRe _50% and theRe _sol parameters show the lowest values for the surfactant with 12.5 EO units in its molecular structure regardless of the electrical charge of the lipid bilayers. As a consequence, these last parameters are not linearly correlated with the CMC of these surfactants. The CMC values of the surfactant/lipid systems at 0.5 mM lipid concentration corresponded in all cases to the surfactant concentration at which liposomes were saturated by surfactants (S _sat).     

Oxidation of self-organized nonionic surfactants

Nonionic surfactants containing a polyoxyethylene headgroup are known to slowly undergo oxidative degradation when exposed to air. The oxidation, which starts by abstraction of a hydrogen atom from a methylene group in alpha-position to an ether oxygen, is accelerated by metal ions. Silver ion mediated oxidation of a technical grade surfactant of this type, Brij 30, was investigated in two types of self-assembled systems, a water-in-oil microemulsion and a liquid crystalline phase. It was found that in both systems the longer homologues, i.e., the surfactant homologues that carry a longer polyoxyethylene chain, decompose faster than the shorter homologues. This trend was found to be more pronounced when the surfactant is present in a liquid crystal than in a microemulsion. The difference is explained in terms of differences in accessibility of the polyoxyethylene chains to the silver ions.     

Hydrogen ion titration of alkyldimethylamine oxides by 13C and 1H NMR and conventional methods

In the hydrogen ion titration of micelles, the degree of ionization of the micelle at a given pH has to be evaluated to obtain a pKa value of micelles (Ka being the proton dissociation constant) at the pH. We compared the degree of ionization obtained from 13C and 1H NMR spectra with that obtained from the stoichiometric method. We used dodecyldimethylamine oxide (C12DMAO) and hexyldimethylamine oxide (C6DMAO) to examine the titration behavior of micelles and monomers, respectively. We determined pKa values of amine oxides both in H2O and D2O. As to the monomer (C6DMAO), the degree of ionization from NMR, alpha(NMR), coincided with that from the conventional stoichiometric method alpha. The difference of pK1 of amine oxide monomer between D2O and H2O was about 0.5: pK1(D) approximately pK1(H) + 0.5. The difference was about the same as that for carboxylic acids. As to the C12DMAO micelle, alphaNMR did not coincide with alpha over a considerable range of alpha. The NMR chemical shift might be influenced by micellar structure changes induced by the ionization, such as the sphere-to-rod transition. The intrinsic logarithmic dissociation constants of the micelle were 5.9+/-0.1 for H2O, and 6.5+/-0.1 for D2O.     

Modification of ion chromatographic separations by ionic and nonionic surfactants

New findings are reported on simple ways to modify an ordinary HPLC column to obtain efficient ion chromatographic (IC) separations. Permanently coating a column with an ionic surfactant is known to produce an effective column for IC. We now show that incorporation of a nonionic surfactant in the coating, or coating in separate layers, results in a dramatic reduction of ion retention times and gives sharper peaks. Dynamic coating by incorporating a small amount of an alcohol, diol or zwitterion in the aqueous mobile phase permits good separations of alkanecarboxylic acids. A mobile phase containing a quaternary ammonium cation and a zwitterion anion provides excellent separations of common anions on a silica C18 column. An aqueous eluent containing a mixture of a zwitterion 4-(2-hydroxyethyl) acid and methanesulfonic acid can be used in conjunction with a standard cation exchange column. After passing through a membrane suppressor, the mobile phase has a slightly acidic pH, permitting divalent transition metal ions (as well as others) to be detected by conductivity.     

Effects of protonation of alkyldimethylamine oxides on the dissolution temperature in aqueous media

The effects of protonation (ionization) of hexadecyldimethylamine oxides on the dissolution temperature in aqueous media were investigated by differential scanning calorimetry. Only one endothermic peak was reproducibly observed at all the degrees of ionization alpha examined that were assigned to the transition from the solid (the gel phase) to the solution containing micelles. The dissolution temperature versus alpha curves showed a maximum at alpha=0.5, strongly suggesting the formation of a stable complex of 1-to-1 composition of the nonionic and cationic species through the proposed hydrogen bond. From the shape of the dissolution curve as well as the composition analysis of the solid phase, the solid solution was found to be formed over all alpha values. Effects of alkylchain length on the dissolution temperature for a homologous series of octadecyl- (C18DAO), hexadecyl- (C16DAO), and tetradecyldimethylamine oxide (C14DAO) were also examined for alpha=0.5 and alpha=1. Both the transition temperature and the associated thermodynamic quantities DeltaH and DeltaS increased systematically with the chain length, but for alpha=0.5 smaller increases in DeltaH and DeltaS values with the chain length were observed [DeltaH/CH2 (kJ mol(-1))=7.2+/-0.2 and 2.2+/-0.5 for alpha=1 and alpha=0.5, respectively, and DeltaS/CH2 (J mol(-1) K(-1))=21.9+/-1.8 for alpha=1 and 4.6+/-1.9 for alpha=0.5]. By annealing procedures, the metastable nature of the gel phase was demonstrated for the C16DAO (alpha=1) solid.     

Adsorption kinetics measurements of some nonionic surfactants

Dynamic surface tension values of aqueous surfactant solutions were measured by using the ring and plate method. The mean diffusion coefficients calculated on the basis of the purely diffusion controlled adsorption model vary between 2 · 10^–6 to 7 · 10^–6 cm²/s for all surfactants studied:n-alkanols,n-alkanoic acids, dimethyl and diethyln-alkyl phosphine oxides. That means the surfactants investigated adsorb with a purely diffusion controlled adsorption mechanism and no barriers excist to hinder sorption processes.Nomenclature c ₀ surfactant bulk concentration - D diffusion coefficient - surface concentration - ₀ equilibrium surface concentration - ¯ (t)/ ₀ reduced surface concentration - maximum surface concentration - K ₀/c₀ - surface tension - t time - Dt/K ² reduced time - a _L coefficient of the Langmuir isotherm     

Effects of nonionic surfactants on seeded polymerizations

The rate of polymerization of vinyl acetate in systems containing poly(vinyl acetate) seed particles was investigated. A significant reduction in rate was observed when nonionic surfactants were adsorbed onto the particles prior to polymerization. The molecular weight of the poly(ethylene oxide) moieties in the surfactants was varied over two decades. The diminution in rate was relatively insensitive to this molecular weight variation, at least for higher molecular weights (≥20,000). A minimum in the rate was apparent at lower molecular weights. No new nucleation was detectable in any of these systems. The results have been interpreted in terms of two properties of the dissolved poly(ethylene oxide) layers through which the oligomeric free radicals must diffuse in order to reach the major loci of polymerization inside the particles. These two properties, the effective thickness of the dissolved poly(ethylene oxide) layer and its average microscopic viscosity, are expected theoretically to be approximately self-compensating when the molecular weight is varied.     

Oxidation of nonionic surfactants with molecular oxygen

Kinetic regularities are studied for the air oxidation of surfactants that are widely used in the food industry, such as natural phosphatidylcholine (egg lecithin, PC) and synthetic nonionic surfactants Triton X-100 (ТХ-100), Tween 65, and Pluronic F68. Azobis(amidinopropane)-dichloride-initiated oxidation of these surfactants in an aqueous medium at 37°C develops via the chain free-radical mechanism. The chain length is equal to 5–10 units, depending on the initiator-to-surfactant concentration ratio. The rate of surfactant oxidation in an aqueous medium is proportional to the rate of radical initiation. At the same mass concentrations of the reagents, the rate of PC oxidation is several times higher than the oxidation rates of the other surfactants. The addition of TX-100 to PC liposomes decelerates the oxidation; i.e., TX-100 plays the role of an antioxidant for PC. The superposition of the oxidation rates of individual and mixed PC and TX-100 with the sizes of the microaggregates formed in their aqueous solutions shows that the antioxidation action of TX-100 is realized via the formation of a protective layer composed of its ethylene oxide groups, which shields PC liposomes from radicals, which are initiated in the bulk of an aqueous phase due to the decomposition of azobis(amidinopropane) dichloride.     

Separation of nonionic surfactants of the polyoxyethylene type by capillary electrophoresis

 Nonionic surfactants are widely used in commercial formulations as complex mixtures requiring efficient and selective separation methods. Capillary electrophoretic separations were carried out in electrolytes containing high amounts of organic solvents and anionic surfactants based on the formation of association complexes between analytes and anionic surfactants without micelle formation. Octyl- and nonylphenol polyethoxylates were separated as their ethoxylate homologues. Influences of the electrophoretic conditions like electrolyte concentration and pH, type and content of anionic surfactant and organic solvents were investigated. Received: 12 February 1996/Revised: 21 May 1996/Accepted: 5 June 1996     

Protonation-induced structural change of lyotropic liquid crystals in oley- and alkyldimethylamine oxides/water systems

Lyotropic phase behavior of the nonionic and the half-ionized oleyldimethylamine oxide (OlDMAO)/water systems was investigated using polarized light microscopy, small-angle X-ray diffraction, and differential scanning calorimetry. Nonionic OlDMAO formed isotropic micellar solution, nematic, hexagonal, cubic, and lamellar liquid crystalline phases as the surfactant concentration increased. In contrast, half-ionized OlDMAO (i.e., 1:1 mixture of the nonionic and the protonated species) had a greater tendency to form bilayer structures, and the phase diagram became quite similar to those of double-chained ionic surfactants rather than single-chained ones, despite the introduction of positive charges to the nonionic one. The preference of the bilayer structures in the half-ionized OlDMAO was interpreted in terms of the dimers stabilized by the hydrogen bond between the nonionic and protonated species. For alkyldimethylamine oxides with a saturated hydrocarbon chain (CnDMAO, chain length: n = 14, 16, and 18), the phase sequence of lyotropic liquid crystals was hardly affected by the protonation, but an elongation of the cylinders of the hexagonal phase was observed for the half-ionized C14DMAO. Consequently, it can be considered that the dominant bilayer formation of the half-ionized OlDMAO is attributed to the combined effect of the hydrogen-bonded dimer formation and the cis-double-bond configuration of the alkyl chain.     

C12 hydroxyester ethoxylates as nonionic surfactants

A series of ethoxylates of 2,2,4-trimethyl-1,3-pentanediol mono-isobutyrate representing a synthetic C12 hydroxyester hydrophobe was obtained. The solubility parameters, surface tension and critical micelle concentrations for model solutions were investigated. The new surfactants were found to produce extremely low foam levels and a non-standard surface interfacial behavior was determined. It was observed that the ethoxylates of the C12 hydroxyester formed an oriented monolayer at the interface regardless of their average polyaddition degree. Such behavior is different from the surface activities of commonly known linear nonionic surfactants and it indicates self organization of the surfactants at the interface. This feature offers possibility for application of these surfactants in nanotechnology as well as in the conventional cleaning processes.     

一种非离子型含氟聚氨酯表面活性剂的合成及性能

以甲苯-2,4-二异氰酸酯(2,4-TDI)、2-甲氧基-3-全氟壬烯氧基丙醇和聚乙二醇(PEG)等为主要原料,通过分布缩合得到一种非离子型含氟聚氨酯表面活性剂,并利用红外光谱对其进行了表征。讨论了加料方式、亲水单体相对分子质量、聚乙二醇用量等因素对产品性能的影响。实验结果表明,当n(2,4-TDI):n(氟醇):n(PEG)=1:1:1.1时,采用先加入TDI和氟醇,反应一段时间后滴加PEG的加料方式,能够合成得到综合性能较好的非离子型含氟聚氨酯表面活性剂。对该表面活性剂在水相中的表面活性进行了测试,所制得的非离子型含氟聚氨酯表面活性剂(FPU-1)的相对分子质量为1310,其临界胶束浓度约为9.54×10-5mol/L,水溶液的最低表面张力为20.88mN/m。     

Hydrophilic-lipophilic balance and surface film state of nonionic surfactants

Summary The polarographic study on the effect of nonionic surfactants on the damping of oxygen maximum confirms the validity ofVan Voorst Vader's rule and a major part which play the hydrophilic-lipophilic balance of surfactant molecules in surface phenomena. On this basis the simple relationships are presented between the molecular area in surface film (A) andGriffin's andDavies' HLB. It is shown that at a specific pressure theA increases with increasing HLB values for homologous series of nonionic surfactants. The limitations of the validity of the relations derived with respect to the specific surface pressure chosen are also considered.

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Zusammenfassung Polarographische Studien über die Wirkung nichtionogener Tenside auf die Dämpfung des Sauerstoff maximums bestätigen die Gültigkeit der Regel vonVan Voorst Vader und den überwiegenden Einfluß, welchen der Anteil hydrophil-lipophil in den Tensidmolekülen für Grenzflächenphänomene spielt. Auf dieser Basis wird eine einfache Beziehung erhalten zwischen dem Flächenbedarf eines Moleküls im Grenzflächenfilm (A) undGriffin's undDavies HLB-Werten. Es wird gezeigt, daß bei einem spezifischen Oberflächendruck dieA-Werte mit steigenden HLB-Werten in homologen Reihen nichtionogener Tenside ansteigen. Die Grenzen der Gültigkeit dieser Regel werden diskutiert.

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With 2 tables     

Sequential injection chemiluminescence immunoassay for nonionic surfactants by using magnetic microbeads

A rapid and sensitive immunoassay based on a sequential injection analysis (SIA) using magnetic microbeads for the determination of alkylphenol polyethoxylates (APnEOs) is described. An SIA system was constructed from a syringe pump, a switching valve, a flow-through type immunoreaction cell equipped with a photon counting unit and a neodymium magnet. Magnetic beads, to which an anti-APnEOs monoclonal antibody was immobilized, were used as a solid support in an immunoassay. The introduction, trapping and release of the magnetic beads in and from the immunoreaction cell were controlled by means of a neodymium magnet and adjusting the flow of a carrier solution. The immunoassay was based on an indirect competitive immunoreaction of an anti-APnEOs monoclonal antibody immobilized on the magnetic beads with a sample APnEOs and a horseradish peroxidase (HRP)-labeled APnEOs in the same sample solution, and was based on the subsequent chemiluminscence reaction of HRP on the magnetic microbeads with a luminol solution containing hydrogen peroxide and p-iodophenol. The anti-APnEOs antibody was immobilized on the magnetic microbeads by coupling the antibody with the magnetic beads after activation of a carboxylate moiety on the surface of the magnetic beads that had been coated with a polylactic acid film. The antibody immobilized magnetic beads were introduced in the immunoreaction cell and trapped in it by the neodymium magnet, which was equipped beneath the immunoreaction cell. An APnEOs sample solution containing the HRP-labeled APnEOs at a constant concentration, and a luminol solution containing hydrogen peroxide and p-iodophenol were sequentially introduced into the immunoreaction cell, according to an SIA programmed sequence. Chemiluminescence emission was monitored by means of a photon counting unit located at the upper side of the immunoreaction cell by collecting the emitted light with a lens. A typical sigmoidal calibration curve was obtained, when the logarithm of the concentration of APnEOs was plotted against the chemiluminescence intensity as the number of photons in 100 ms using standard APnEOs sample solutions at various concentrations (0–1000 ppb) under optimum conditions. The lower detection limit defined as IC₈₀ is ca 10 ppb. The time required for analysis is less than 15 min per a sample. The present method was successfully applied to the determination of APnEOs in river water.