Surfactant polymer interactions between strongly interacting cationic surfactants and anionic polyelectrolytes from conductivity and turbidity measurements

The interactions between oppositely charged surfactant/polymer mixtures have been studied using conductivity and turbidity measurements. The dependence of aggregation phenomenon on the chain length and head group modifications of conventional cationic surfactants, i.e., hexadecyl- (HTAB), tetradecyl- (TTAB), and dodecyltrimethylammonium bromides (DTAB) and dimeric cationic surfactants, i.e., decyl- (DeDGB) and dodecyldimethylgemini bromides (DDGB), is investigated. It was observed that cationic surfactants induce cooperative binding with anionic polyelectrolytes at critical aggregation concentration (cac). The cac values are considerably lower than the critical micelle concentration (cmc) values for the same surfactant. After the complete complexation, free micelles are formed at the apparent critical micelle concentration (acmc), which is slightly higher in aqueous polyelectrolyte than in pure water. Among the conventional and dimeric cationic surfactants, DTAB and DeDGB, respectively, have been found to have least interactions with oppositely charged polyelectrolytes.     

Benzylic and pyridinium head groups controlled surfactant-polymer aggregates of mixed cationic micelles and anionic polyelectrolytes

The oppositely charged electrostatic interactions between cationic single and mixed micelles of benzyldimethylhexadecylammonium chloride (BHDACl), hexadecylpyridinium bromide (HPyBr), hexadecylpyridinium chloride (HPyCl), and their mixtures with anionic polyelectrolytes, namely carboxymethylcellulose sodium salt (CMC) and polystyrene sulfonate sodium salt (PSS) were studied with the help of conductivity (), viscosity (), turbidity (), and NMR studies. showed single aggregation process, which was represented by apparent critical micelle concentration, acmc, of each surfactant in aqueous polyelectrolyte solution. Both and demonstrated strong electrostriction effects in the case of BHDACl-polyelectrolyte systems due to weak electrostatic interactions in view of steric hindrances created by benzylic group of BHDACl. ¹H NMR results showed that the head group proton resonances of BHDACl upon incorporation of HPyBr or HPyCl in the presence of CMC or PSS remained identical to that in pure water, which demonstrated very weak interactions between BHDACl and polyelectrolytes. A less shielding of pyridinium head group protons by BHDACl in the presence of polyelectrolytes in comparison to that in pure water indicated favorable electrostatic interactions between pyridinium head groups and anionic polyelectrolytes. HPyBr in comparison to HPyCl showed stronger interactions with polyelectrolytes.     

Interactions between cationic gemini/conventional surfactants with polyvinylpyrrolidone: Specific conductivity and dynamic light scattering studies

The interaction between bis(hexadecyldimethylammonium)hexane dibromide (16-6-16), bis(tetradecyldimethylammonium)hexane dibromide (14-6-14), their conventional counterparts cetyltrimethylammonium bromide (CTAB) and tetradecyltrimethylammonium bromide (TTAB) with polyvinylpyrrolidone (PVP) was investigated using the conductivity technique. The results show that gemini surfactants interact strongly with PVP as compared to conventional surfactants. The results also reveal that the surfactants with shorter hydrocarbon chain interact weakly as those of longer hydrocarbon chain. The interactions of 16-6-16 and 14-6-14 and their conventional counterparts with PVP were also studied using dynamic light scattering (DLS) measurements. We have also highlighted the effect of surfactant–polymer interactions on the dispersion force in the solution. Critical aggregation concentration (cac) and critical micelle concentration (cmc) were obtained using the conductivity data. The degrees of micelle ionization and free energies associated with aggregation, micellization, and transfer have also been evaluated and discussed.     

Interactions between cationic starch and anionic surfactants

The surface tensions and the phase equilibria of dilute aqueous cationic starch (CS)/surfactant systems were investigated. The degree of substitution of the CS varied from 0.014 to 0.772. The surfactants investigated were sodium dodecyl sulphate (SDS), potassium octanoate (KOct), potassium dodecanoate (KDod) and sodium oleate (NaOl). The concentrations of CS were 0.001, 0.01 and 0.1 w%.Critical association concentrations (cac) occur at surfactant concentrations well below the critical micelle concentrations of the surfactants, except for KOct, KDod and NaOl at the lowest CS concentrations investigated (0.001 w%). The surface tensions of CS/surfactant solutions decrease strongly already below the cac. This is attributed to the formation of surface active associates by ion condensation. Associative phase separation of gels formed by CS and surfactant takes place at extremely low concentrations when the surfactant/polymer charge ratio is somewhat larger than 1. The gel is higly viscous and contains 40–60% water, depending on the concentration of electrolyte, the surfactant hydrocarbon chain length and the nature of the polar head of the surfactant.The concentration at which the phase separation occurs decreases with increasing surfactant chain length and the concentration of simple electrolyte, factors that promote micelle formation. This indicates that the gels are formed by association of CS to surfactant micelles. When surfactant well in excess of charge equivalence is added, the gels dissolve because the CS/surfactant complexes acquire a high charge.     

Investigation of interactions between some anionic dyes and cationic surfactants by conductometric method

The interactions of cationic surfactants with anionic dyes were studied by conductometric method. Benzyltrimethylammonium chloride (BTMACl), benzyltriethylammonium chloride (BTEACl) and benzyltributylammonium chloride (BTBACl) were used as cationic surfactants and indigo carmine (IC) and amaranth (Amr) were chosen as anionic dyes. The specific conductance of dye–surfactant mixtures was measured at 25, 35 and 45 °C. A decrease in measured specific conductance values of dye–surfactant mixture was caused by the formation of non-conducting or less-conducting dye–surfactant complex. The equilibrium constants, K₁, the standard free energy changes, ΔG₁°$\mathrm{\Delta }{G}_1°$, the standard enthalpy changes, ΔH₁°$\mathrm{\Delta }{H}_1°$ and the standard entropy changes, ΔS₁°$\mathrm{\Delta }{S}_1°$ for the first association step of dye–surfactant complex formation were calculated by a theoretical model. The results showed that the equilibrium constants and the negative standard free energy change values for all systems decreased as temperature increased. Also these values decreased for all systems studied with increasing alkyl chains of surfactants due to the steric effect. When the equilibrium constant values, K₁, for the first association step of IC–surfactant and Amr–surfactant systems with the same surfactant were compared, the values of K₁ for IC–surfactant system were higher than that of Amr–surfactant system.     

Synthesis and comparative behaviour study of fluorocarbon and hydrocarbon cationic surfactants in aqueous media

A series of perfluorinated cationic surfactants and their corresponding hydrocarbon ones whose general formula is C_nX_2n+1-C(O)NH-(CH₂)₃-N⁺Me₃, I⁻, with X = F, H and n = 9, 11, have been synthesized via two steps. Their aggregative and surface-active properties were studied in aqueous solution using tensiometry and conductimetry. The critical micelle concentrations and the molecular areas at the air/water interface of fluorinated surfactants are lower than those of their hydrocarbon homologues. Micellar aggregation numbers and geometric packing parameters have been investigated. The results indicated that fluorocarbon surfactants tend to form lamellar aggregates while the hydrocarbon ones associate into spherical aggregates.     

Monomeric and dimeric anionic surfactants: A comparative study of self-aggregation and mineralization

A study on the phase behavior and structure of the alkanolamine salts of the dimeric amphiphile 3,4-bis-dodecyloxycarbonyl-hexanedioic acid (GS-H) is presented for the first time. Data are compared to those of the corresponding monomeric surfactant (lauric acid, LA). The alkanolamine salts of GS-H show very low Krafft points (<0 °C) and form hexagonal liquid crystals at concentrations lower than its monomeric counterpart, indicating that aggregation is favored for dimeric surfactants. The minimum concentration for liquid crystal formation increases for bulky alkanolamines with a structure-disrupting effect, such as triethanolamine (TEA). However, the specific surface areas per molecule in the liquid crystals derived from small-angle X-ray scattering (SAXS) are similar for monoethanolamine (MEA) and TEA salts; the same can be said when comparing monomeric (LA) and dimeric (GS-H) salts. GS-H can also form hexagonal and lamellar liquid crystals with organic aminosilanes acting as reactive counterions, as revealed by solvent penetration experiments with polarized optical microscopy (POM). Consequently, mineralization with silica and alumina was carried out by a sol–gel method using GS-H as a possible structure-directing agent. Both silica and alumina samples possessed a lamellar structure, which disappears on calcination; however, calcined alumina has indeed a high surface area coming mainly from micropores. It was found that the surfactant/aminosilane ratio is critical for obtaining structured silica before calcination.     

Mixed micelles of series of monomeric and dimeric cationic, zwitterionic, and unequal twin-tail cationic surfactants with sugar surfactants: a fluorescence study

Steady state fluorescence measurements have been carried out for binary mixtures of a series of monomeric cationic (MC), zwitterionic (ZI), dimeric cationic (DC), and twin-tail cationic (TC) surfactants with sugar (beta-C8G and beta-C12G) over the whole mole fraction range using pyrene as fluorescence probe. The cmc values thus determined for all the binary mixtures have been further evaluated using the regular solution theory. The various micellar parameters, such as micelle mole fraction (X1), regular solution interaction parameter (beta), micropolarity, and mean micelle aggregation number (Nagg), have been determined for all these series of mixtures. Variation in all these micellar parameters demonstrates that mixed micelles of these surfactants with beta-C8G are mostly synergistic in nature and the synergism increases with the increase in hydrophobicity of the cosurfactant in each case. The mixtures of beta-C12G with various cosurfactants do not show this behavior and instead of it, they show an increase in antagonism with the increase in hydrophobicity of cosurfactants. This discrepancy has been attributed to a large difference in hydrophobicity between beta-C8G and beta-C12G, and the chain folding of the latter is considered to be the reason for the antagonism.     

Mixed micellization and surface properties of non-ionic/cationic surfactants

We investigate the surface properties of aqueous binary mixtures of our cationic surfactant O-dodecyl-N,N′-diisopropylisourea hydrochloride (ISO-DIC C₁₂) with commercially available nonionic surfactant polyoxyethylene p-(1,1,3,3-tetramethylbutyl)phenyl ether (TritonX-100) at different temperatures (288 to 303?K). The micellization behavior of the binary systems is studied by determining the surface tension and other important physicochemical parameters, such as the critical micelle concentration (CMC), surface tension at the CMC(γ_cmc), Krafft Temperature (T_K), maximum excess concentration (Γ_max), minimum surface area per molecule (A_min), surface pressure at the CMC (П_cmc), and the adsorption efficiency (pC20) at the air/water interface. The study has additionally covered the calculation of thermodynamic parameters of micellization, including the standard Gibbs free energy, the standard enthalpy, the standard entropy, the free energy, and the Gibbs free energy of adsorption at air/water interface. The CMC values of the binary systems determined by experimental data are used to evaluate the micellar composition in the mixed micelle, the interaction parameter β and the activity coefficients f₁(ISO-DIC C₁₂) and f₂ (polyoxyethylene p-(1,1,3,3-tetramethylbutyl)phenyl ether) using the theoretical treatment proposed by Clint and Rubingh. Our results reveal that the proposed binary systems possess enhanced surface activity compared to those of the individual surfactants.     

Interactions of temperature-responsive anionic polyelectrolytes with a cationic surfactant

The interactions of temperature-responsive copolymers of sodium 2-acrylamido-2-methyl-1-propanesulfonate (AMPS) and N-isopropylacrylamide (NIPAM) with a cationic surfactant, dodecyltrimethylammonium chloride (DTAC), have been studied. The content of AMPS in the copolymers ranged from 1.1 to 9.6 mol%. The surface activity was higher for the polymers with lower AMPS content. It was found that DTAC undergoes association with the polymer chain, forming mixed polymer-surfactant micelles. The values of cac for the polymers were found in fluorescence studies using pyrene as the fluorescent probe. They were in the range 0.9-3.6x10(-3) M and were lower for polymers with higher AMPS content. An increase in DTAC concentration up to about its cmc results in a decrease of the LCST (lower critical solution temperature) of the copolymers, while further increase above the cmc results in an increase of the LCST. The minimum value of LCST in the presence of the surfactant is lower than the LCST of NIPAM homopolymer.     

Cloud point variation of amphiphilic drug promethazine hydrochloride with added surfactants

In this paper we report clouding phenomenon occurring in an amphiphilic phenothiazine drug promethazine hydrochloride (PMT) in presence of surfactants. Cationic and nonionic surfactants increase the CP of 75 mM PMT solutions (prepared in 10 mM sodium phosphate buffer). These surfactants form mixed micelles with PMT. Anionic surfactants also form mixed micelles with the drug but the CP behavior is different by showing a peaked behavior. At low concentrations, anionic surfactants hinder micelle formation by forming ion-pairs whereas the usual CP decreasing effect at higher concentrations is due to mixed micellization. The CP behavior of 75 mM PMT+50 mM TBAB+surfactant systems is also explored which is found similar to PMT+surfactant systems with the difference only in magnitude of the clouding temperature.     

Micellization and mixed micellization of cationic gemini (dimeric) surfactants and cationic conventional (monomeric) surfactants: Conductometric,dye solubilization,and surface tension studies

In the present study, we have investigated the self-association, mixed micellization, and thermodynamic studies of a cationic gemini (dimeric) surfactant, hexanediyl-1,6-bis(dimethylcetylammonium bromide (16-6-16)) and a cationic conventional (monomeric) surfactant, cetyltrimethylammonium bromide (CTAB). The critical micelle concentration (CMC) of pure (16-6-16 and CTAB) and mixed (16-6-16+CTAB) surfactants was measured by electrical conductivity, dye solubilization, and surface tension measurements. The surface properties (viz., C₂₀ (the surfactant concentration required to reduce the surface tension by 20 mN/m), Π_CMC (the surface pressure at the CMC), Γ_max (maximum surface excess concentration at the air/water interface), A_min (the minimum area per surfactant molecule at the air/water interface), etc.) of micellar (16-6-16 or CTAB) and mixed micellar (16-6-16+CTAB) surfactant systems were evaluated. The thermodynamic parameters of the micellar (16-6-16 and CTAB) and mixed micellar (16-6-16+CTAB) surfactant systems were also evaluated.     

A proton NMR study on aggregation of cationic surfactants in water: effects of the structure of the headgroup

 ¹H NMR chemical shifts of solutions of the following cationic surfactants in D₂O were determined as a function of their concentrations: cetyltrimethylammonium chloride, CTACl, a 1 : 1 molar mixture of CTACl and toluene, cetylpyridinium chloride, CPyCl, cetyldimethylphenylam-monium chloride, CDPhACl, cetyldimethylbenzylammonium chloride, CDBzACl, cetyldimethyl-2-phenylethylammonium chloride, CDPhEtACl, and cetyldimethyl-3-phenylpropylammonium chloride, CDPhPrACl. Plots of observed chemical shifts versus [surfactant] are sigmoidal, and were fitted to a model based on the mass-action law. Satisfactory fitting was obtained for the discrete protons of all surfactants. From these fits, we calculated the equilibrium constant for micelle formation, K, the critical micelle concentration, CMC and the chemical shifts of the monomer, δ_mon and the micelle δ_mic. ¹H NMR-based CMC values are in excellent agreement with those which we determined by surface tension measurements of surfactant solutions in H₂O, allowing for the difference in structure between D₂O and H₂O. Values of K increase as a function of increasing the size of the hydrophilic group, but the free energy of transfer per CH₂ group of the phenylalkyl moiety from bulk water to the micellar interface is approximately constant, 1.9±0.1 kJ mol^-1. Values of (δ_mic–δ_mon) for the surfactant groups at the interface, e.g., CH₃–(CH₂)₁₅–N+(CH₃)₂ and within the micellar core, e.g., CH₃–(CH₂)₁₅–N⁺ were used to probe the (average) conformation of the phenyl group in the interfacial region. The picture that emerges is that the aromatic ring is perpendicular to the interface in CDPhACl and is more or less parallel to it in CDBzACl, CDPhEtACl, and CDPhPrACl. Received: 23 February 1996 Accepted: 29 August 1996     

SAXS study on complexes formed by anionic poly(sodium methacrylate‐co‐N‐isopropylacrylamide) gels with cationic surfactants

Small‐angle X‐ray scattering (SAXS) has been used to study the nanostructures of complexes formed by slightly crosslinked anionic copolymer gels of poly(sodium methacrylate‐co‐N‐isopropylacrylamide) [P(MAA/NIPAM)] interacting with cetylpyridinium bromide (CPB), and alkyltrimethylammonium bromide (C_nTAB, 10 ≤n ≤ 18), respectively. Both the charge density of polyelectrolyte gels and the surfactant alkyl tail length could induce the phase structure transition from Pm3n space group cubic to hexagonal close packing of spheres (HCP), while the different polar groups of pyridinium and trimethylammonium with the same hydrophobic cetyl chain in surfactants had no significant effects on the structures of complexes formed with the same gels. The highly ordered structures were shown to be formed by the self‐assembly of ionic surfactants inside the anionic gel network, driven by both electrostatic and hydrophobic interactions. Freeze drying the water‐equilibrated complexes could collapse the formed ordered structures. However, the highly ordered structures could be restored after the dried complexes were reswollen by water under the same conditions, indicating that the highly ordered water‐equilibrated complexes were thermodynamically stable. Copyright © 2000 John Wiley & Sons, Ltd.     

Estimation of degree of counterion binding and related parameters of monomeric and dimeric cationic surfactants from cloud point measurements by using triblock polymer as probe

The cloud point (C _P) measurements of aqueous solutions of a triblock polymer (TBP) [(PEO)_2.5(PPO)₃₁(PEO)_2.5], in the presence of varying amounts of cationic surfactants (monomeric and dimeric alkylammoniumbromides) covering premicellar to postmicellar regions, have been carried out. A plot of C _P vs surfactant concentration allowed us to evaluate apparent critical micelle concentration (cmc*), which has been found to decrease with an increase in the amount of salt. The cmc* values thus obtained in the absence and presence of salt allowed us to evaluate counterion binding (β) by using the Corrin–Harkins method. β values have been further used to evaluate the thermodynamic parameters of these ionic surfactants. The results suggest that the β values evaluated using this method, especially at low [TBP], are in good agreement with those already reported in the literature.     

Interaction between anionic and cationic gemini surfactants at air/water interface and in aqueous bulk solution

The mixture of the anionic O,O′-bis(sodium 2-lauricate)-p-benzenediol (C₁₁pPHCNa) and cationic (oligoona)alkanediyl-α, ω-bis(dimethyldodecylammonium bromide) (C₁₂-2-E_x-C₁₂·2Br) gemini surfactants has been investigated by surface tension and pyrene fluorescence. The results show that the surface tension γ drops faster with total surfactant concentration C_T for α₁ = 0.1 or 0.3 than for α₁ = 0.7 or 0.9, where α₁ is the mole fraction of C₁₁pPHCNa in the bulk solution on a surfactant-only basis. The fast drop in γ for α₁ < 0.5 indicates strong adsorption at the air/water interface owing to the interaction between oppositely charged components, resulting in the formation of the adsorption double layers in the subsurface. The slow descent in γ for α₁ > 0.5 is attributed to the pre-aggregation in the solution before the critical micelle concentration cmc. A possible mechanism is proposed.     

离子缔合物-萃取荧光光度法测定水中阴离子表面活性剂

在 0 .2 5 mol/L H2 SO4 溶液中 ,罗丹明 B与阴离子表面活性剂形成离子缔合物 ,氯仿萃取后 ,于 5 5 0 nm处激发 ,荧光波长为 60 0 nm,对于十二烷基硫酸钠的线性范围为 0 .0 2 5～ 0 .4mg/L,RSD<2 .6%。方法可用于河水及生活废水中 1 0 -7～ 1 0 -6mol/L 阴离子表面活性剂的测定     

Surface-active properties of new cationic gemini surfactants with cyclic spacer

Three cationic gemini surface active compounds of the type (1r,4r)-1,4-dialkyl-1,4-dimethy-l-piperazine-1,4-diium bromide (Ia, Ib, and Ic), were synthesized. They were characterized using elemental analysis and ¹H-NMR spectra. Their surface-active properties were measured in aqueous solutions with different concentrations at different temperatures (25, 40, and 55°C). Various surface measurements of these gemini surfactants, (compared to the conventional one, 1-Dodecyl-1-methylpiperidinium bromide (a)) were estimated, specifically critical micelle concentration (CMC), effectiveness (π_CMC), efficiency (P_C20) as well as maximum surface excess (Γ_max) and minimum surface area (A_min). The measurements of the gemini compounds gave low CMC, high efficiency in reducing the surface tension, and intense adsorption at air/water interface. These surfactants have lower Krafft points and thus better solubility. Thermodynamic data, free energy, entropy, and enthalpy changes (ΔG°, ΔS°, and ΔH°) for micellization at the air/water interface and also for adsorption in the bulk of surface-active solutions were calculated.     

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.