Solubilization of model polycyclic aromatic hydrocarbons by nonionic surfactants

Solubilization of model polycyclic aromatic hydrocarbons (PAHs) by the readily biodegradable nonionic surfactants, Tergitol 15-S-X (X=7,9 and 12), consisting of mixtures of secondary ethoxylated alcohols was investigated at temperatures below their cloud points. Their solubilization capacities for phenanthrene were compared to those of three other commonly used surfactants, e.g. Triton X-100 and Tween 20 as well as Tween 80. Correlation between the micelle-water partition coefficients and the octanol-water partition coefficients in Tergitol 15-S-7 solutions indicated that the hydrophobicity of PAHs, i.e., their octanol-water partition coefficients, could be used in predicting the solubilization efficiency of PAHs by this nonionic surfactant. Effects of temperature and salinity on solubilization capacity of Tergitol 15-S-7 surfactant for phenanthrene were also investigated along with the micellar properties. The change in hydrodynamic radius and aggregation number of micelles with temperature was measured by the dynamic and static laser light scattering techniques. Results showed that increasing aggregation number and micellar size at higher temperature when cloud point is approached gives rise to the higher solubilization capacity of this surfactant. Effect of salinity on the enhancement of phenanthrene solubility was also discussed in terms of conformation changes in the micelles due to the possible coordination of sodium cations and oxygen atoms on the ethylene oxide groups of the surfactant.     

Osmometric study of commercial surfactants

The micellar weights of Tergitol 15-S-9 (Union Carbide) and of Neodol 25-9 (Shell Chemical Co.) were determined by membrane osmometry in water as 98,000 and 82,000, respectively (36.5 C). Both surfactants contained a small amount of a nonassociating component. The micelles were found to be extremely stable. The micellar weight of Aerosol OT (American Cyanamid) was determined as <5,900 (toluene, 34 C). The results of this investigation indicate the usefulness of membrane osmometry in the determination of micellar weights of surfactants. Information with respect to the stability of the micelles and the dialytic behavior of surfactants in general can be obtained from the osmotic pressure-time curve.     

Study of the Interaction Between Methyl Orange and Mono and Bis-Quaternary Ammonium Surfactants

The solubilization and interaction of an azo-dye (methyl orange) with dodecyl trimethyl ammonium bromide and cationic gemini surfactants in the series of alkanediyl α,ω-bis[(dimethyl alkyl ammonium)bromide)] referred to as (m-s-m), m = 10, 12, 14 and s = 2, 3, 4 were investigated by means of UV–Vis spectroscopy. Aggregation with the anionic dye was reflected by a hypsochromic shift with a decrease in the intensity of the absorption band. The results also show a bathochromic shift followed by a sharp increase in the intensity of the maximum absorption band λ_max after the critical micellar concentration (CMC). This indicates that the dye solubility increased with increasing surfactant concentration. It was also observed that the aggregation of surfactant and dye takes place at a surfactant concentration far below the CMC of the individual surfactant. The effects of the chain length as well as the spacer length of gemini surfactants on the critical aggregation concentration and CMC were also examined. Moreover, the partition coefficients between the bulk water and surfactant micelles K _S and K _X as well as the Gibbs energies of distribution of dye between the bulk water and surfactant micelles were determined using the pseudo-phase model. The effect of the hydrophobic chain length and spacer of gemini surfactants on the distribution parameters is also reported.     

Partitioning and Localization of Fragrances in Surfactant Mixed Micelles

The localization and dynamics of fragrance compounds in surfactant micelles are studied systematically in dependence on the hydrophobicity and chemical structure of the molecules. A broad range of fragrance molecules varying in octanol/water partition coefficients P _ow is employed as probe molecules in an aqueous micellar solution, containing anionic and nonionic surfactants. Diffusion coefficients of surfactants and fragrances obtained by Pulsed Field Gradient (PFG)-NMR yield the micelle/water distribution equilibrium. Three distinct regions along the log(P _ow) axis are identified: hydrophilic fragrances (log(P _ow) < 2) distribute almost equally between micellar and aqueous phases whereas hydrophobic fragrances (log(P _ow) > 3.5) are fully solubilized in the micelles. A steep increase of the incorporated fraction occurs in the intermediate log(P _ow) region. Here, distinct micelle swelling is found, while the incorporation of very hydrophobic fragrances does not lead to swelling. The chemical structure of the probe molecules, in addition to hydrophobicity, influences fragrance partitioning and micelle swelling. Structural criteria causing a decrease of the aggregate curvature (flattening) are identified. ²H-NMR spin relaxation experiments of selectively deuterated fragrances are performed monitoring local mobility of fragrance and leading to conclusions about their incorporation into either micellar interface or micelle core. The tendencies of different fragrance molecules (i) to cause interfacial incorporation, (ii) to lead to a flattening of the micellar curvature and (iii) to incorporate into micelles are shown to be correlated.     

Mass spectrometric study of nonylphenol-ethylene oxide adducts

Individual ethylene oxide adducts of high purity have been separated chromatographically from commercial grade nonylphenoxypoly (oxyethylene)-ethanol (TERGITOL nonionic NP surfactants) and studied by time-of-flight mass spectrometric techniques. The 1–9 mole ethylene oxide adducts of nonylphenol produced clearcut spectra with a small number of fragment ions. Four groups of different ion types have been established and some remarks concerning their formation are given. Molecular ions for the nine adducts, through mass 616, were observed in good abundances because of the low-energy and high-speed capabilities of the instrument. However, no single structure for an adduct can be proposed because the nonyl portions of the compounds are isomeric mixtures. The ionization characteristics of the NPE_n compounds reveal that the aromatic and alkyl portions of the molecules are easily activated. Tergitol nonionic NP surfactants have branched alkyl substituents and are not completely biodegradable. Therefore it is speculated that the biodegradation process leads to exposure of the highly branched alkylaromatic portions of the molecules in a manner comparable to mass spectral fragmentation processes.     

Partition Coefficients for Continuous Micellar Reaction Processes

The micelle‐water partition coefficients of reactants, products, and catalyst ligands are predicted using UNIFAC‐IF and COSMO‐RS. It is demonstrated that both models represent a reasonable tool for preliminary screening of the micellar systems for a specific continuous reaction process supported by micellar enhanced ultrafiltration (MEUF). The model reaction is the hydrogenation of itaconic acid and its derivatives (dialkyl esters) in the presence of a rhodium‐based catalyst. The effect of the size and nature of the surfactant head group and tail is explored for nonionic and ionic surfactants. The high partition coefficients of the catalyst ligands indicate that no catalyst leakage is expected in MEUF. Based on the concentration dependence of the calculated partition coefficients, the solubilization capacity of micelles is estimated.     

Emulsion polymerization initiated by alkylcobalt–tridentate Schiff base complexes in relation to kinetics and mechanism of their decomposition

Summary Former studies of decomposition of the title alkylcobalt(III)–tridentate Schiff base complexes (RCo) in acidic media have been extended to neutral and alkaline aqueous solutions including micellar ones. In combination, results of both the works indicate a common reaction mechanism, with homolysis of the Co–C bond preceded by substitution of extra ligand(s) with water molecules. Both protons and hydroxyl ions catalyze the latter aquation step after the conventional pattern of acid–base catalysis. Effect of surfactants on the reaction rate has been explained by electrostatic and hydrophilic/hydrophobic interactions between the cationic complexes and other components of micelles formed. On these bases, the use of RCo, which had been formerly proved to be advanced pH-dependent initiators of emulsion polymerization in acidic to neutral media, was extended to alkaline ones. Namely, the emulsion polymerization of styrene was shown to proceed at pH 7 to 13 in the presence of surfactants of any type up to high conversions, but did so, ceteris paribus, much slower than in acidic media. Polystyrene with molecular mass as high as 12 × 10⁶ was thus obtained at pH 9–10. The effect of pH on the rate of emulsion polymerization as well as on characteristics of its products was related to the corresponding rates of decomposition of RCo as well as to stability of emulsion systems and polar interactions in the adsorption layer.     

Catalytic effect of dipotassium glycyrrhizinate on the hydrolysis of nonionic ester surfactants

The family of dipotassium glycyrrhizinate (GK2) catalyzes the hydrolysis of nonionic ester surfactants (NES), such as hydrogenated castor oil with 60 oxyethylene units attached (HCO-60) and monostearate with 25 oxyethylene units attached (SA-25), even in the pH range of 3–6, where NES are generally stable in the absence of GK2. Long-chain fatty acids also accelerate the hydrolysis reaction. Analyses, based on circular dichroism spectroscopy, and empirical force field calculations suggest that a GK2 and an NES molecule form an energetically stable complexvia hydrophobic interactions in which the ester carbonyl is in close contact with either one of the three different carboxyl groups in GK2, acting as an acid catalyst.     

Synergistic Behavior of a Triblock Copolymer with Anionic and Cationic Surfactants in Aqueous Solution

The synergistic behavior of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer in aqueous solution with the synthesized anionic surfactants [decyl sulfonate (A10), myristyl sulfonate (A14) and cetyl sulfonate (A16)] and cationic surfactants [decyl pyridinium bromide (C10), myristyl peridinium bromide (C14) and cetyl pyridinium bromide (C16)] was investigated using a surface tension technique at 25 °C. The results show that the CMC values of binary mixtures for anionic and cationic surfactants with the triblock copolymer are lower than that of single surfactants. The synergistic interaction between surfactant molecules and copolymer molecules in binary mixed solution enhance the adsorption of surfactant molecules at the interface. The micellar mole fractions (X _m) and the interaction parameter (β) of these surfactants in mixed micelles were determined.

Mixed Micellization and Interfacial Properties of Polyoxyethylene Sorbitan Esters with Cetylpyridinium Chloride: A Tensiometric Study

In this work a surface tensiometric method was used to study the effect of the chain length of non-ionic surfactants, viz. ethoxylated sorbitan esters, on micellar composition, critical micellar concentration, mutual interaction parameter (β ₁₂), and activity coefficients of the mixed micelles formed with the cationic surfactant cetylpyridinium chloride at 25 °C. The micellar characteristics evaluated using the Clint, Rubingh, and Blankschtein models deviated significantly from ideality, and were used to ascertain the validity of these theories. Thermodynamic stability in terms of Maeda’s approach and interfacial properties is also discussed.     

Synthesis and Surface-Active Properties of Uronic Amide Derivatives,Surfactants from Renewable Organic Raw Materials

Short chemical syntheses were developed to produce a new set of surfactants from uronic acids derived from widely available raw materials. Three different strategies were used to synthesize uronic amide derivatives, the structures of which were totally characterized by spectrometric methods (IR, MS, ¹H-RMN and ¹³C-RMN). The best one, using an acid chloride as the synthetic intermediate, furnished the expected amides as a mixture of anomers in 46–58% global yield. Surface-active properties (CMC, γ_cmc, Γ_max, A _min) of homologous series of uronic acid N-alkylamides from C8 to C18 were also assessed. In general, these sugar-based surfactants exhibited good surface-activities, and appeared as valuable nonionic surfactants compared to octylphenol 9–10 ethylene oxide condensate, the most well-known nonionic surfactant. Increasing the alkyl chain length influenced the CMC values for both glucuronic and galacturonic N-alkylamide derivatives. The galacturonic N-alkylamides decreased γ_cmc at slower values than their counterpart’s glucuronic N-alkylamides.     

Partition Coefficients of Alkyl Parabens and Ibuprofen in Micellar Systems

The partitioning of alkyl parabens and ibuprofen in aqueous solutions of nonionic and ionic surfactants is studied experimentally and via a priori predictions using the COSMO‐RS model. The effects of organic (Bu₄NBr) and inorganic (NaCl) electrolytes are examined. Addition of NaCl results in a slight increase in the partition coefficients of parabens in solutions of octylphenolpoly(ethyleneglycolether) and a more pronounced increase in the sodium dodecyl sulfate (SDS) system. The partition coefficients of ibuprofen increase on addition of NaCl to aqueous solutions of SDS and decrease if Bu₄NBr is added to dodecyl trimethyl ammonium bromide (DTAB) solutions. Good agreement between experimental and calculated data shows a high potential of COSMO‐RS in the prediction of micelle/water partition coefficients in the presence of electrolytes and makes it a valuable tool in drug and drug‐carrier design as well as in optimizing micellar reactions or micelle‐enhanced separation processes.     

Theoretical Approaches on the Synergistic Interaction between Double-Headed Anionic Amino Acid-Based Surfactants and Hexadecyltrimethylammonium Bromide

Theoretical investigations on the micellization of mixtures of (i) amino acid-based anionic surfactants [AAS: N-dodecyl derivatives of aminomalonate, −aspartate, and -glutamate] and (ii) hexadecyltrimethylammonium bromide (HTAB), were carried out at different mole ratios. Variation in the theoretical values of critical micelle concentration (CMC), mole fraction of surfactants in the micellar phase (X), at the interface (X^σ), interaction parameters at the bulk/interface (β^R/β^σ), ideality/nonideality of the mixing processes, and activity coefficients (f) were evaluated using Rubingh, Rosen, Motomora, and Sarmoria-Puvvada-Blankschtein models. CMC values significantly deviate from the theroretically calculated values, indicating associative interaction. With increasing mole fraction of AAS (α_AAS), the magnitude of the (β^R/β^σ) values gradually decreased, considered to attributable to hydrophobic interactions. With increasing α_AAS, the micellar mole fraction of HTAB (X₂) decreased insignificantly and X₂ values were higher than those compared to AAS for all combinations, due to the dominance of HTAB in micelles. Micellar mole fraction at the ideal state of AAS () differed from micellar mole fraction of AAS (X₁), indicating nonideality in the mixed micellization process. Gibbs free energy of micellization ( ∆G_m ) values are more negative than the free energy of micellization for ideal mixing (), indicating the micellization process is spontaneous. With increasing α_AAS, the enthalpy of micellization (ΔH_m) and entropy of micellization (ΔS_m) values gradually increased, which indicates micellization is exothermic. The different physicochemical parameters of the mixed micelles are correlated with the variation in the spacer length between the two carboxylate groups of AAS.     

Synthesis of Ethoxylated Alkyl Sulfosuccinate Surfactants and the Investigation of Mixed Solutions

A series of ethoxylated sodium monoalkyl sulfosuccinate (ESMASS) ester surfactants were prepared by reacting polyethylene glycol (molecular weight 600) with sodium monoalkyl sulfosuccinate (SMASS). The esters were prepared by reacting octyl, lauryl, or cetyl alcohol with sodium sulfosuccinate (SSS) to prepare E(14)SMOSS, E(14)SMLSS, and E(14)SMCSS. The chemical structures of the prepared surfactants were confirmed by Fourier transform infrared (FTIR) and ¹H-NMR spectroscopy. The surface tension of the synthesized surfactants was measured at 25 °C individually or mixing at different molar fractions with sodium dioctyl sulfosuccinate. The surface active properties were calculated and the micellization process of the mixture was investigated. The molar ratio of anionic (SDOSS) and anionic–nonionic surfactant moieties [E(14)SMOSS, E(14)SMLSS, and E(14)SMCSS] in the mixed aggregates were deduced using the regular solution approximation equations. Depending on the critical micelle concentration values measured for each surfactant individually, and as well as the mixed systems, the minimum surface tension was exhibited at a ratio of 0.6 SDOSS:0.4 E(14)SMCSS. The micellar composition of the mixed aggregates were explained and discussed based on the effect of their chemical structures. The activity coefficient (f ₁, f ₂), interaction parameter (β), and ideality of anionic–nonionic mixed aggregates were evaluated.

Partitioning of Carboxylic Acid between Oil and Water Phases. Experimental,Correlation, and Prediction

Partition coefficients for the carboxylic acids (A) acetic and formic acids between oil and water were measured, correlated, and predicted. The experiments were conducted by equilibrating the systems, soybean oil (SO)–H₂O–A and fatty acid methyl ester (FAME)–H₂O–A, at 40 °C employing different compositions. The partition coefficients were correlated using the UNIQUAC model and, also, predicted by calculating the activity coefficients of the carboxylic acid in the two phases using a group contribution method, the UNIFAC equation. Agreement of experimental partition coefficients values with those estimated by UNIFAC are fair. Other experimental data from literature were also correlated and are discussed.     

The adsorption behavior of dialkyl dimethyl ammonium chloride-nonionic surfactant binary systems

From the practical standpoint of fabric softener formulation, a comparative study was made on adsorption behavior toward fabrics of binary systems consisting of di(hydrogenated tallow) dimethyl ammonium chloride (purified Arquad 2HT) and typical polyoxyethylenated nonionic surfactants which are commonly used as auxiliary agents for softeners. Soxhlet extraction of treated fabrics and quantitative analysis by high-performance liquid chromatography (HPLC) gave significant results indicating many of these nonionic surfactants, assumed to be inherently unadsorbable in rinse-cycle treatment, were highly adsorbable even at a high bath ratio by being applied with the water-insoluble cationic surfactant. Moreover, it was also disclosed that the hydrophobic structure of nonionic surfactants is another factor, other than hydrophobicity, determining adsorption. Furthermore, the mechanism of this nonionic adsorption was elucidated on the basis of results of structural analyses of binary dispersions by differential scanning calorimetry (DSC), X-ray diffraction, electron spin resonance spectroscopy (ESR) and transmission electromicroscopy (TEM) in addition to partition measurements of the surfactants into the dispersed and the continuous aqueous phases. It was concluded that the primary driving force for this nonionic adsorption is an association with the lamellar of Arquad 2HT and that the cationic vesicles act as “anchors” in adsorption.     

Synthesis and Study of the Surface Properties of Alkylnaphthalene and Alkylphenanthrene Sulfonates

Some alkylnaphthalene and alkylphenanthrene sulfonates were synthesized by means of a Wurtz–Fittig reaction. The HLB values for the prepared compounds were calculated, and the basic properties were studied in water at different temperatures, namely, 25, 35 and 45 °C. Through surface tension measurements, the following values were determined: the critical micelle concentration (CMC) and the surface tension at the CMC (γ_CMC). The following values were calculated: area per molecule at the CMC (A_CMC), standard free energy change of micellization (ΔG _mic), standard free energy of adsorption (ΔG _ad), and the efficiency of a surfactant in reducing surface tension (pC20). Furthermore, the partition coefficients of the synthesized compounds were also measured. The results show that n-alkylnaphthalene and n-alkylphenanthrene surfactants studied exhibit desirable properties that may be of value in some fields such as detergency. To confirm the detergency power of the prepared surfactants, some foam studies were performed.     

Permeability changes of phospholipid vesicles caused by surfactants

The partition coefficient at equilibrium of different surfactants between the aqueous phase and the lipid bilayer of small unilamellar vesicle (SUV) liposome has been determined. The release of the fluorescent agent 5-(6) carboxyfluorescein from the interior of liposomes, induced by a nonionic surfactant octylphenol ethoxylated with 10 units of ethylene oxide (Triton X-100), by two anionic surfactants — sodium dodecyl sulphate and sodium dodecyl ether sulphate — and by an amphoteric surfactant dodecyl betaine was studied at sub-solubilizing concentrations. The following increasing order of the partition coefficients obtained for each surfactant can be observed: Triton X-100 > sodium dodecyl ether sulphate > sodium dodecyl sulphate > dodecyl betaine. There was a strong positive association between coefficient of partition and the ability of the different surfactants to modify the permeability of liposomes. The importance of the presence of ethylene oxide units in the molecular structure of the surfactant in relation to alter the partition coefficient in front of SUV liposomes is indicated.     

Solubilization of unilamellar liposomes by betaine-type zwitterionic/anionic surfactant systems

The mechanisms governing the solubilizing interactions between zwitterionic/anionic mixed surfactant systems at different molar fractions of the zwitterionic surfactant (X_zwitter) and neutral or electrically charged unilamellar liposomes were investigated. The mixed systems were formed by N-dodecyl-N,N-dimethylbetaine and sodium dodecyl sulfate in the presence of piperazine-1,4-bis-(2-ethanesulfonic acid) buffer at pH 7.20. Unilamellar liposomes formed by egg phosphatidylcholine, in some cases together with stearylamine or phosphatidic acid, were used. Solubilization was detected as a decrease in static light-scattering of liposomes. Two parameters were regarded as corresponding to the effective surfactant/lipid molar ratios (Re) at which the surfactant system (i) saturated the liposomes, Re_sat, and (ii) led to a total solubilization of liposomes, Re_sol. From these parameters the bilayer/aqueous medium surfactant partition coefficients for the saturation (K_sat) and complete bilayer solubilization (K_sol) were determined. When X_zwitter was 0.40, The Re and K parameters showed a maximum, whereas the critical micellar concentration (CMC) of these systems exhibited a minimum, regardless of the electrical charge of bilayers. Given that the ability of the surfactant systems to saturate or solubilize liposomes is inversely related to the Re_sat and Re_sol parameters, these capacities appear to be directly correlated with the CMC of the mixed systems. The similarity of both K_sat and K_sol (particularly for X_zwitter=0.2–0.8) suggests that a similar partition equilibrium governs both the saturation and the complete solubilization of bilayers, the free surfactant concentration (S_a,S_b), remaining almost constant with similar values to the CMC for each mixed system studied.     

Influence of added surfactant on particle flocculation in waterborne polymer–particle systems

Polymer–particle interactions can cause particle flocculation and phase separation problems in waterborne coatings. The problems can be the result of interactions that are either too weak or too strong. It is known by empirical work that addition of surfactants can minimize these problems. In this study, the authors have investigated how different types of surfactants influence the polymer–particle interactions. Both hydrophobic and hydrophilic particles were included in the study, and nonionic, anionic, and cationic surfactants were used. A simple model is suggested that can be used to predict the surfactant concentration needed to stabilize the system. The model considers the cmc (critical micelle concentration) of the surfactant, the adsorption to the polymer, and the adsorption to the particles.