Anionic–Nonionic Mixed Surfactant Systems: Micellar Interaction and Thermodynamic Behavior

The interactions between an anionic surfactant, viz., sodium dodecylbenzenesulfonate and nonionic surfactants with different secondary ethoxylated chain length, viz., Tergitol 15-S-12, Tergitol 15-S-9, and Tergitol 15-S-7 have been studied in the present article. An attempt has also been made to investigate the effect of ethoxylated chain length on the micellar and the thermodynamic properties of the mixed surfactant systems. The micellar properties like critical micelle concentration (CMC), micellar composition (X_A), interaction parameter (β), and the activity coefficients (f_A and f_NI) have been evaluated using Rubingh's regular solution theory. In addition to micellar studies, thermodynamic parameters like the surface pressure (Π_CMC), surface excess values (Γ_CMC), average area of the monomers at the air–water interface (A_avg), free energy of micellization (ΔG_m), minimum energy at the air–water interface (G_min), etc., have also been calculated. It has been found that in mixtures of anionic and nonionic secondary ethoxylated surfactants, a surfactant containing a smaller ethoxylated chain is favored thermodynamically. Additionally, the adsorption of nonionic species on air/water interface and micelle increases with decreasing secondary ethoxylated chain length. Dynamic light scattering and viscometric studies have also been performed to study the interactions between anionic and nonionic surfactants used.     

Cyclic voltammetry and viscosity measurements of aggregated assemblies of anionic surfactants with nonionic surfactants and triblock copolymers

Cyclic voltammetry (CV) and viscosity measurements have been employed to study the aggregation behavior of mixed micellar systems of anionic surfactant (dioctyl sulfosuccinate sodium salt, AOT) with conventional nonionic surfactants such as Brij 35/TritonX-100/Tween 20/Tween 80/Myrj 45 and two triblock copolymers (L64 and F68). Critical micelle concentration (cmc) values have been determined for various micellar systems from CV measurements using 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as an electroactive probe at 25 °C. Diffusion coefficient (D) has been evaluated from Randles–Sevcik equation which showed an overall decrease for most of the binary systems. The negative values of interaction parameters (β) obtained from regular solution theory suggest the synergistic behavior in all the binary systems except AOT + Tween 80 mixtures. The mixed systems of AOT with triblock copolymers showed stronger synergistic interactions than that of mixed systems of AOT with nonionic surfactants. A comparative evaluation of mixed systems of anionic surfactants AOT and sodium dodecyl sulfate with Myrj 45 and AOT + L64 and F68 has been made on the basis of different micellar parameters and structural properties of surfactants. Viscosity measurements also show similar type of interactions in the mixed micelles.     

Spectrophotometric studies of anionic dye-cationic surfactant interactions in mixture of cationic and nonionic surfactants

The interaction between an anionic dye C.I. Reactive Orange 16 (RO16) and a cationic surfactant dodecylpyridinium chloride (DPC) in mixtures of DPC and nonionic surfactants poly(oxyethylene)ethers (C(m)POE(n); m = 12, 16 and 18, n = 4, 10 and 23) are investigated spectrophotometrically in a certain micellar concentration range. The spectrophotometric measurements of dye-surfactant systems are carried out as function of mole fraction of surfactant at four different temperatures. For this reason, a typical system was occurred at 1.0 x 10(-2) mol l(-1) for surfactants and at 1.0 x 10(-4) mol l(-1) for dye concentrations. The formation of DPC-RO16 complex in the C(m)POE(n) solutions of different mole fractions in its micellar concentration range have been determined and compared to those obtained in the binary mixtures. From the spectrophotometric measurements has been observed that the addition of nonionic surfactant in to the mixture of DPC-RO16, causes a significant increase of the value of absorbance. This increase explains that the stability of DPC-RO16 complex is reduced in the presence of nonionic surfactant micelles. It can be seen from results; in mixed surfactant solutions, there are DPC-C(m)POE(n) and RO16-C(m)POE(n) interactions in addition to DPC-RO16 interaction. Since the solubilizaton of the DPC-RO16 complex has been appeared in the C(m)POE(n) solution, our results support the conclusion that adding C(m)POE(n) influences the hydrophobic-hydrophilic balance of the studied complex. Furthermore effect of the alkyl chain length and the number of poly(oxyethylene) in nonionic surfactant on values of absorbance have been investigated.     

Surfactant effect on the lower critical solution temperature of poly(organophosphazenes) with methoxy-poly(ethylene glycol) and amino acid esters as side groups

 The surfactant effect on the lower critical solution temperature (LCST) of thermosensitive poly(organophosphazenes) with methoxy-poly(ethylene glycol) and amino acid esters as side groups was examined in terms of molecular interactions between the polyphosphazenes and surfactants including various anionic, cationic, and nonionic surfactants in aqueous solution. Most of the anionic and cationic surfactants increased the LCST of the polymers: the LCST increased more sharply with increasing length and hydrophobicity of the hydrophobic part of the surfactant molecule. The ΔLCSTs (T _0.03M− T _0M), the change in the LCST by addition of 0 and 0.03 M sodium dodecyl sulfate (SDS), were found to be 7.0 and 14.5 °C for the polymers bearing ethyl esters of glycine and aspartic acid, respectively. The LCST increase of poly(organophosphazene) having a more hydrophobic aspartic acid ethyl ester was 2 times larger compared with that of the polymer having glycine ethyl ester as a side group. The binding behavior of SDS to the polymer bearing glycine ethyl ester as a hydrophobic group was explained from the results of titration of the polymer solutions containing SDS with tetrapropylammonium bromide. Graphic models for the molecular interactions of polymer/surfactant and polymer/surfactant/salt in aqueous solutions were proposed. Received: 17 February 2000/Accepted: 25 April 2000     

Spectroscopic Investigations on the Interaction of Crystal Violet with Nonionic Micelles of Brij and Igepal Surfactants in Aqueous Media

The behavior of the triphenylmethane dye crystal violet in aqueous solutions containing polyoxyethylene nonionic surfactants was investigated using absorption and fluorescence spectroscopic techniques. The interactions of the dye were examined in micellar media in order to prevent dye aggregation and to ensure maximum dye and surfactant interaction. The relative fluorescence enhancements and the binding constants of the dye to the surfactant micelles were determined. The micropolarities of the micellar environment sensed by the pyrene probe were estimated from the I ₁/I ₃ intensity ratios of the fluorescence spectra of pyrene. The fluorescence quenching of pyrene by hexadecylpyridinium chloride was investigated in aqueous surfactant mixtures at a fixed concentration of surfactant in order to determine the aggregation numbers. Attempts were made to correlate the binding constants obtained in this investigation to various micellar parameters.     

Role of the Surfactant Structure in the Behavior of Hydrophobic Ionic Liquids within Aqueous Micellar Solutions

The behavior of an ionic liquid (IL) within aqueous micellar solutions is governed by its unique property to act as both an electrolyte and a cosolvent. The influence of the surfactant structure on the properties of aqueous micellar solutions of zwitterionic SB‐12, nonionic Brij‐35 and TX‐100, and anionic sodium dodecyl sulfate (SDS) in the presence of the “hydrophobic” IL 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([bmim][PF₆]) is assessed along with the possibility of forming oil‐in‐water microemulsions in which the IL acts as the “oil” phase. The solubility of [bmim][PF₆] within aqueous micellar solutions increases with increasing surfactant concentration. In contrast to anionic SDS, the zwitterionic and nonionic surfactant solutions solubilize more [bmim][PF₆] at higher concentrations and the average aggregate size remains almost unchanged. The formation of IL‐in‐water microemulsions when the concentration of [bmim][PF₆] is above its aqueous solubility is suggested for nonionic Brij‐35 and TX‐100 aqueous surfactant solutions.     

Studies of Monolayer and Mixed Micelle Formation of Anionic and Nonionic Surfactants in the Presence of Adenosine-5-monophosphate

The interactions between the anionic surfactant di-(2-ethylhexyl) phosphate sodium salt (DEP) and two nonionic surfactants, dimethyldecyl phosphineoxide (DDPO) and dimethyltetradecyl phosphineoxide (DTPO), at the interface and in the micellar phases were investigated in the absence and presence of adenosine-5-monophosphoric acid disodium salt (AMP). The mixed systems were DEP–DDPO, DEP–DDPO/AMP (0.001 mol⋅L⁻¹), DEP–DTPO, and DEP–DTPO/AMP (0.001 mol⋅L⁻¹) at different bulk mole fractions of the anionic component (α ₁=0.9,0.8,0.6,0.4,0.2). The mixed systems studied were investigated based on the theoretical models of Rubingh and Clint. The results showed surface tension reduction efficiency. The adsorbed mixed monolayer demonstrated stronger interactions than the mixed micelles, whereas AMP increased the interfacial interactions more than those in the micellar phase. The Gibbs energy of mixing suggests that the stability of the mixed micellar phase is greater than that of the micellar phases of the individual components. The synergism that occurred in the different mixed phases is discussed.     

Microstructure of un-neutralized hydrophobically modified alkali-soluble emulsion latex in different surfactant solutions

At low pH conditions and in the presence of anionic, cationic, and nonionic surfactants, hydrophobically modified alkali-soluble emulsions (HASE) exhibit pronounced interaction that results in the solubilization of the latex. The interaction between HASE latex and surfactant was studied using various techniques, such as light transmittance, isothermal titration calorimetry, laser light scattering, and electrophoresis. For anionic surfactant, noncooperative hydrophobic binding dominates the interaction at concentrations lower than the critical aggregation concentration (CAC) (C < CAC). However, cooperative hydrophobic binding controls the formation of mixed micelles at high surfactant concentrations (C > or = CAC), where the cloudy solution becomes clear. For cross-linked HASE latex, anionic surfactant binds only noncooperatively to the latex and causes it to swell. For cationic surfactant, electrostatic interaction occurs at very low surfactant concentrations, resulting in phase separation. With further increase in surfactant concentration, noncooperative hydrophobic and cooperative hydrophobic interactions dominate the binding at low and high surfactant concentrations, respectively. For anionic and cationic surfactant systems, the CAC is lower than the critical micelle concentration (CMC) of surfactants in water. In addition, counterion condensation plays an important role during the binding interaction between HASE latex and ionic surfactants. In the case of nonionic surfactants, free surfactant micelles are formed in solution due to their relatively low CMC values, and HASE latexes are directly solubilized into the micellar core of nonionic surfactants.     

Steady-state fluorescence investigations of aqueous binary mixtures of myristyl alcohol based bis-sulfosuccinate anionic gemini surfactant and effect of different conventional surfactants therein

The present research work is associated with the fluorescence investigations of binary aqueous mixed surfactants solutions of anionic bis-sulfosuccinate gemini surfactant (BSGSMA_1,8) and three different conventional surfactants—anionic viz. sodium dodecyl sulfate (SDS), cationic viz. cetyl trimethyl ammonium bromide (CTAB), and nonionic surfactant viz. Triton X 100. Steady-state fluorescence spectroscopy technique has been utilized to examine the micellization behavior of aqueous solution of pure myristyl alcohol-based BSGSMA_1,8 having flexible methylene chain [(CH₂)₈] as spacer group. Critical micelle concentration (CMC), aggregation number (N), and micropolarity of pure and mixed surfactants systems were explored during the investigations. The results revealed the best synergism behavior of prepared gemini BSGSMA_1,8 with SDS as compared to CTAB and Triton X 100. The maximum reduction in the value of pyrene intensity ratio (I₁/I₃) was observed for gemini and SDS mixed surfactant solution. On the other hand, the increased I₁/I₃ value of mixed gemini with Triton X 100 exhibited that mixed surfactant system of anionic gemini BSGSMA_1,8 with non-ionic Triton X 100 is not as compact as other mixed surfactant systems. Aggregation number increased and micropolarity decreased with increased concentration of gemini surfactants.     

Effects of Salts on the Micellization of a Short-Tailed Nonionic Ethoxylated Surfactant: An Intradiffusion Study

In commercial formulations, surfactants are often co-formulated with inorganic electrolytes, which are included as inexpensive thickeners. Salts affect the surfactant’s aggregative and functional behavior. However, while the electrolyte effect on the self-aggregation of ionic surfactants can be rationalized in terms of electrostatic interactions, in the case of nonionic surfactants the molecular determinants are still unclear. In this work, we investigate the effects of alkali and alkaline–earth metal chlorides on the micellization of the nonionic surfactant hexyl penta(oxyethylene) ether, C₆E₅, in aqueous solution. To this aim, the C₆E₅ intradiffusion (also named self-diffusion) coefficient in aqueous mixtures of various alkali and alkaline–earth metal chlorides was measured by pulsed gradient spin-echo NMR. The results show that all the considered electrolytes cause a decrease of the surfactant critical micellar concentration, cmc, while the micellar size is almost unaffected. The experimental evidence can be interpreted in terms of de-hydration of the apolar alkyl tails with a minor contribution arising from the dehydration of the poly(ethylene oxide) headgroups. The order of effectiveness of the different cations follows the Hofmeister series, some aspects of which are briefly discussed.     

Rheological properties of the aqueous solution for fluorocarbon‐containing hydrophobically modified sodium polyacrylic acid with various surfactants

The interaction of fluorocarbon‐ containing hydrophobically modified sodium polyacrylic acid (FMPAANa) (0.5 wt%) with various surfactants (anionic, nonionic and cationic) has been investigated by rheological measurements. Different rheological behaviors are displayed for ionic surfactants and nonionic surfactants. Fluorinated surfactants have stronger affinity with polyelectrolyte hydrophobes comparing with hydrogenated surfactants. The hydrophobic association of FMPAANa with a cationic surfactant (CTAB) and a fluorinated nonionic surfactant (FC171) is much stronger than with a nonionic surfactant (NP7. 5) and an anionic surfactant (FC143). Further investigation of the effects of temperature on solution properties shows that the dissociation energy E_m is correlated to the strength of the aggregated junctions.     

Fluorocarbon polymerizable surfactants: viscometric behavior, micellar polymerization and interactions with associating polymers

 The micellar aggregation of two fluorocarbon surfactants bearing a polymerizable acrylamido group and differing only in the degree of amido substitution (CONH or CONC₂H₅) has been investigated by viscometry. The two surfactants exhibit distinct solution properties with a micellar growth occurring at a much lower concentration for the N-monosubstituted sample which shows in addition a shear thickening and rheopectic behavior. The ability of the latter surfactant to form hydrogen bonding is responsible for this difference in behavior. Micellar copolymerization of acrylamide with these surfactants or with a hydrocarbon analogue gives copolymers with a polysoap-like behavior. The copolymers in aqueous solution show a pronounced intramolecular hydrophobic aggregation expressed by relatively low-viscosity values when compared with those of other hydrophobically modified water-soluble polymers reported in the literature. Surfactant–polymer mixed systems do not show a strong incompatibility between fluorocarbon and hydrocarbon moieties. Received: 24 March 1998 Accepted: 30 June 1998     

Spectrophotometric Determination of Acidity Constants of 4‐(2‐Pyridylazo) Resorcinol in Various Micellar Media Solutions

Dissociation equilibria of 4‐(2‐pyridylazo) resorcinol (PAR) in aqueous micellar solutions were determined spectrophotometrically at 25 °C and at the constant ionic strength I = 0.1 M KNO₃. For this purpose, the effect of nonionic (Brij‐35, Triton X‐100, Triton X‐114, Triton X‐405), and anionic (SDS) surfactants on the absorption spectra of PAR at different pH values was studied. Results show that the pK_a values and pure spectra of each species of PAR are influenced by percentages of a neutral and an anionic surfactant such as Brij‐35, Triton X‐100, Triton X‐114, Triton X‐405 and SDS, respectively, added to the solution of this reagent.     

Investigation on the basic hydrolysis of crystal violet in mixed reverse micelles formed with AOT and nonionic surfactants

 The kinetics and thermodynamics of the basic hydrolysis of crystal violet (CV) in mixed reverse micelles formed with anionic surfactant AOT and nonionic surfactants have been investigated. It was found that the mixed reverse micelles had inhibitory effects on CV hydrolysis compared with the normal aqueous solution, and the equilibrium constant K of the reaction in mixed reverse micellar systems is smaller than that in pure water. The influence of water content and surfactant composition in reverse micelles on the second-order rate constant k ₁ of the positive reaction, on the first-order rate constant k _-1 of the reverse reaction, as well as on the equilibrium constant K of the reaction has been studied, and the results obtained were interpreted in terms of the nature of surfactants and the properties of microenvironment where the reaction took place. Received: 24 October 1997 Accepted: 18 March 1998     

Polymers as Hydrophobic Adsorbent Surface for Some Surfactants

Polyvinyl alcohol (PVA) and polyacrilic acid (PAA) were used as hydrophobic adsorbent surfaces at 25°C for two nonionic surfactants, namely, tetradecyl polyoxyethylenated monolaurate [La(EO)₁₄] and tetradecyl polyoxyethylenated monooleate [Ol(EO)₁₄], and two anionic surfactants, namely, sodium oleic sulfonate [OlSO₃Na] and sodium dodecyl benzene sulfonate [SDBS]. Surface tension measurements were performed to determine the critical micelle concentration (CMC) and the adsorption isotherms of the tested surfactants. All the tested surfactants display L-shape isotherms except that of OlSO₃Na onto PVA. No adsorption behavior has been shown for the anionic SDBS onto both PVA and PAA. The adsorption data show higher adsorption affinity for all the tested nonionic surfactants onto PAA than onto PVA while the investigated anionic surfactant OlSO₃Na possesses close values of Γ_max. The study reveals that the nature of the polymer surface as adsorbent besides the molecular structure of the surfactant defined the types and mechanisms of adsorption.     

Viscoelastic behavior of surfactants worm-like micellar solution in the presence of alkanolamide

A study of the phase and rheological behavior of anionic surfactant sodium dodecyl trioxyethylene sulfate (SDES) and nonionic polyoxyethylene sorbitan monooleate (Tween-80) with alkanoyl-N-methylethanolamide (C(12), NMEA-12; and C(16), NMEA-16) in aqueous system is presented. Upon addition of NMEA to the semi-dilute solution of SDES or Tween-80, induces micellar growth leading to the formation of a gel-like highly viscoelastic solution in the maximum viscosity region. These solutions obey the Maxwell model of a viscoelastic fluid. It was observed from rheological measurements that NMEA-16 is more effective than NMEA-12 to induce the micellar growth of surfactants. The relationship between the marked changes in viscosity with surfactant-cosurfactant mixing ratio based on the experimental observations is discussed.     

Mixed micellization of an anionic gemini surfactant (GA) with conventional polyethoxylated nonionic surfactants in brine solution at pH 5 and 298 K

The micellization behavior of an anionic gemini surfactant, GA with nonionic surfactants C₁₂E₈ and C₁₂E₅ in presence of 0.1 M NaCl at 298 K temperature, has been studied tensiometrically in pure and mixed states, and the related physicochemical parameters (cmc, γ _cmc, pC ₂₀, Γ _max, and A _min) have been evaluated. Tensiometric profile (γ vs log [surfactant]), for conventional surfactants, generally consists of a single point of intersection; a gradually decreasing line (normally linear, or with slight curvature) ultimately saturates in γ at a particular [surfactant], corresponding to complete monolayer saturation. The gemini, in this report, led to two unequivocal breaks in the tensiometric isotherm. An attempt to the interpretation of the two breaks from molecular point of view is provided, depending solely on the chemical structure of the surfactant. The gemini, even in mixed state with the conventional nonionic surfactants C₁₂E₅ and C₁₂E₈, manifested the dual breaks; of course, the dominance of the feature decreases with increasing mole fraction of the nonionics in the mixture. Theories of Clint, Rosen, Rubingh, Motomura, Georgiev, Maeda, and Nagarajan have been used to determine the interaction between surfactants at the interface and micellar state of aggregation, the composition of the aggregates, the theoretical cmc in pure and mixed states, and the structural parameters according to Tanford and Israelachvili. Several thermodynamic parameters have also been predicted from those theories.     

Micellization of monomeric and dimeric (gemini) surfactants in polar nonaqueous-water-mixed solvents

Dimeric or gemini surfactants are novel surfactants that are finding a great deal of discussion in the academic and industrial arena. They consist of two hydrophobic chains and two polar head groups covalently linked by a spacer. Data on critical micelle concentration (cmc) and degree of counterion dissociation (α) are reported on bis-cationic C₁₆H₃₃N⁺(CH₃)₂–(CH₂)_s–N⁺(CH₃)₂C₁₆H₃₃, 2Br⁻, referred to as 16-s-16, for spacer lengths s=4, 5, 6 in aqueous and in polar nonaqueous (1-propanol, 2-methoxyethanol or methyl cellosolve, dimethyl sulfoxide, acetonitrile)-water-mixed solvents. The behavior is compared with conventional monomeric surfactant cetyltrimethylammonium bromide (CTAB). Thermodynamic parameters are obtained from the temperature dependence of the cmc values. It is observed that micellization tendency of the surfactants decreases in the presence of polar nonaqueous solvents. However, detailed studies with dimethylsulfoxide (DMSO) show that the geminis nearly outclass the micellization-arresting property of this solvent. Also, within geminis, higher spacer length is found suitable for showing micellization even with high DMSO content (50% v/v). The implications of these results of gemini micellization may be useful in micellar catalysis in polar nonaqueous solvents.     

Interfacial and Thermodynamic Properties of Anionic‐Nonionic Mixed Surfactant System: Influence of Hydrophobic Chain Length of the Nonionic Surfactant

The influence of hydrophobic chain length in nonionic surfactants on interfacial and thermodynamics properties of a binary anionic‐nonionic mixed surfactant was investigated. In this study, nonionic surfactants lauric‐monoethanolamide (C₁₂ MEA) and myrisitic‐monoethanolamide (C₁₄ MEA) were mixed with an anionic surfactant, α‐olefin sulfonate (AOS). The critical micelle concentration (cmc), maximum surface excess (Γ_max), and minimum area per molecule (A_min) were obtained from surface tension isotherms at various temperatures. The thermodynamic parameters of micellization and adsorption were also computed. Micellar aggregation number (N_agg), micropolarity, and binding constant (K_sv) of pure and mixed surfactant system was calculated by fluorescence measurements. Rubingh's method was applied to calculate interaction parameters for the mixed surfactant systems.     

Effects of nonionic surfactant and sodium dodecyl sulfate layers on electroacoustics of hexadecane/water emulsions

Hexadecane-in-water emulsion droplets were formed in a homogeniser in the presence of a mixture of an anionic surfactant (sodium dodecyl sulfate, SDS) and nonionic surfactants of various chain lengths [nonylphenol ethoxylate (C₉φE_N, N=100, 40 and 30) or an alcohol ethoxylate (Brij35)]. The dynamic mobility of the oil droplets was then measured using a flow-through version of an AcoustoSizer. Large changes were observed in the dynamic mobility of the particles formed with the mixed surfactants compared to particles formed with SDS alone. O'Brien's “gel layer” model was employed to interpret the data. The characteristics of the adsorbed layer appeared to be similar whether the nonionic surfactant was adsorbed concurrently with the SDS as the emulsion formed or was merely added afterwards to the emulsion established. The particle size, the charge and the molar fraction of SDS had virtually no effect. The layers formed with the nonionic surfactants decreased in thickness with decreasing molecular weight as expected. Passage through the homogeniser itself had no effect on the properties of the largest nonionic surfactant and, hence, on the adsorption layer formed with it. Received: 4 October 2000 Accepted: 16 October 2000