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 properties of cationic surfactants with tuned hydrophylicity

A series of pyridinium-based cationic surfactants has been synthesised and their amphiphilic properties have been studied by conductivity and surface tension measurements. The modification of the substitution pattern on the pyridinium ring by hydrophobic moieties (methyl vs. hydrogen and presence or not of condensed benzene ring) gave the opportunity to investigate structure–activity relationships. Characterization by conductivity and surface tension measurements shed light on the behaviour at the air/water interface and in the micellar environment. In particular, the tendency to form ion pairs at very low concentration was evidenced for all the surfactants substituted on the ring, but not for the simple pyridinium ones. The formation of ion pairs affects both the conductivity and the surface tension plots, showing that a series of steps is involved during the adsorption to the air/water surface. An attempt was made to qualify the single steps in the adsorption at the surface layer. Those steps were attributed to different chemical species (free surfactant ions or ion pairs) and to different arrangements of the surfactant. This work also represents a contribution of investigation at very low surfactant concentrations and high surface tension values.     

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.     

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     

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.     

Separation of cationic analytes by nonionic micellar electrokinetic chromatography using polyoxyethylene lauryl ether surfactants with different polyoxyethylene length

Although nonionic micellar electrokinetic chromatography is used for the separation of charged compounds that are not easily separated by capillary zone electrophoresis, the effect of the hydrophilic moiety of the nonionic surfactant has not been studied well. In this study, the separation of ultraviolet‐absorbing amino acids was studied in electrokinetic chromatography using neutral polyoxyethylene lauryl ether surfactants (Adekatol) in the separation solution. The effect of the polyethylene moiety (the number of repeating units was from 6.5 to 50) of the hydrophobic test amino acids (methionine, tryptophan, and tysorine) was studied using a 10 cm effective length capillary. The separation mechanism was based on hydrophobic as well as hydrogen bonding interactions at the micellar surface, which was made of the polyoxyethylene moiety. The length of the polyoxyethylene moiety of the surfactants was not important in nonionic micellar electrokinetic chromatography mode.     

Interactions of monomeric and dimeric cationic surfactants with anionic polyelectrolytes: a fluorescence study

The interactions of conventional cationic, i.e. dodecyl-(DTAB), tetradecyl-(TTAB), and hexadecyltrimethylammonium bromides (HTAB), and dimeric cationic surfactants, i.e. dimethylene bis decyl-(10-2-10), and dodecyldimethylammonium bromides (12-2-12) with anionic polyelectrolytes, were studied by fluorescence measurements. The variation of I₁/I₃ ratio of the fluorescence of pyrene in aqueous solutions of polyelectrolytes was measured as a function of surfactant concentration. A three-step aggregation process involving the critical aggregation concentration (cac) and critical micelle concentration (cmc) was observed in each case. The cationic surfactants with lower hydrophobicity demonstrated higher degree of binding and vice versa.     

The effect of the nature of the head group on the micellar effects of functional/cationic co-micelles in acyl transfer reactions

The reactivity of co-micelles of functional/cationic surfactants [functional surfactants-1-cetyl-3-(2-hydroxyiminopropyl)-, 1-cetyl-3-(2-amino-2-hydroxyiminoethyl)-, and 1-cetyl-3-(2-hydroxyaminoethyl-2-onyl)imidazolium chlorides, cationic surfactants-1-cetyl-3-methylimidazolium and cetyltrimethyl-ammonium chlorides] toward the 4-nitrophenyl esters of diethylphosphoric, diethylphosphonic, and toluenesulfonic acids was investigated. It was shown that the nucleophilicity of the functional groups in the surfactant does not undergo substantial changes with variation in the nature of the head group of the cationic surfactant and the fraction of functional detergent in the co-micelle. This makes it possible to create systems that decompose organophosphorus substrates unusually quickly even with small contents of the functional surfactant. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 1, pp. 30–37, January–February, 2007.     

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     

The estimation of the hydrophobic and electrostatic contributions to the free energy change upon cationic surfactants binding to Jack bean urease

The binding of a homologous series of n-alkyltrimethyl ammonium bromides with Jack bean urease (JBU) have been studied previously. It has been suggested that both electrostatic and hydrophobic interactions are involved in the formation of surfactant-protein complexes, but there is not any quantities analyzing method for resolution of their contributions in the process. In the present study, at first, the intrinsic Gibbs free energy of binding, ΔG_b,ν, has been calculated for these systems and the trend of variation for both binding sets have been interpreted on basis of cooperativity and hydrophobicity of surfactants. Subsequently, a novel approach has been introduced for estimation of electrostatic and hydrophobic interactions in ΔG_b,ν, by considering of this fact that ΔG_b,ν is the summation of electrostatic, ΔG_b,ν(ele), and hydrophobic, ΔG_b,ν(hyd), parts and considering this fact that just ΔG_b,ν(hyd) is a function of hydrocarbon tail length of surfactant (C_n). The results represents the higher positive rule of electrostatic interactions in binding affinity of first set and inhibiting rule of this interaction in the second binding set. The predominate driving force in the second binding set is entropy statistical effect, which arises from numerous number of binding sites in this set. A binding mechanism on basis of structural changes in JBU due to its interaction with cationic surfactants has also been proposed.     

Rheological properties and structures of cationic surfactants and fatty alcohol emulsions: effect of surfactant chain length and concentration

 Rheological and optical properties of cetyltrimethylammonium chloride (CTAC)/fatty alcohol (FA), behenyltrimethylammonium chloride (BTAC)/FA and CTAC/FA/hydroxyethyl cellulose (HEC) emulsions have been studied with particular emphases on the effects of FA content, the difference in the chain length of the hydrophobic groups between CTAC and BTAC, and the addition of a water soluble polymer, HEC. The effects of the FA content are to accelerate the structure development during the aging period and to increase the storage modulus, the yield stress, and the zero-shear-rate viscosity in the three emulsion systems investigated. At a low FA content of 2% w/w, lamellar and vesicular aggregates and isolated multilamellar vesicles can be observed in the CTAC/FA and BTAC/FA emulsions, respectively. At a high FA content of 6% w/w or with an excess of FA present, networklike structures and sunflower-like structures form, respectively, instead, inducing a higher entanglement storage modulus and a higher yield stress relative to those emulsions with a low FA content. The effect of adding HEC to the CTAC/FA emulsion is to reduce the entanglement storage modulus and the yield stress, consistent with the optical observation that the presence of the polymer disrupts the formations of lamella and vesicular aggregates and network structures. Received: 27 July 2000 Accepted: 28 November 2000     

Effect of the alkyl chain of quaternary ammonium cationic surfactants on corrosion inhibition in hydrochloric acid solution

In this study, the effect of the alkyl chain of quaternary ammonium cationic surfactants on corrosion inhibition in hydrochloric acid (HCl) solution was investigated by using dodecyl trimethyl ammonium chloride (DTAC), tetradecyl trimethyl ammonium chloride (TTAC), cetyl trimethyl ammonium chloride (CTAC), and octadecyl trimethyl ammonium chloride (OTAC) as corrosion inhibitors to uncover their structure–efficiency relationships. The effect of the alkyl chain of quaternary ammonium cationic surfactants on corrosion inhibition in HCl solution was studied under different conditions, such as corrosion inhibitor concentration, temperature, and acidity, and this was done using the weightlessness method. The results obtained show that these inhibitors have high corrosion inhibition effect on A₃ steel, and the corrosion inhibition efficiency is dependent on the length of the alkyl chain. At the same concentration, the longer the alkyl chain, the weaker the corrosion inhibition effect. When the temperature was 50 °C and the concentration of corrosion inhibitor was 70 mg/L, the corrosion inhibition efficiency order of the four cationic surfactants was DTAC > TTAC > CTAC > OTAC. Besides, the experimental results obtained show that the adsorption of the inhibitor on the A₃ steel surface conforms to the Langmuir type isotherm, and then the corresponding adsorption thermodynamic parameters were obtained according to these parameters. It was observed that ΔH, ΔS, and E_a increased with increase in the length of the alkyl chain. The adsorption of the inhibitor on the steel surface is an exothermic, spontaneous, entropy process.     

Rheological study of the pH-dependence of interactions between gelatin and anionic surfactants: flow behaviour and gelation

The interactions between gelatin and two anionic surfactants (sodium di-sec-butylnaphthalenesulfonate and sodium dodecylbenzenesulfonate, respectively) were investigated using rheological methods, charge and surface tension measurements. Upon the addition of surfactants, the viscosity of aqueous gelatin solutions increases at pH values higher than the isoelectric point (IEP) of the gelatin, provided that a distinct surfactant concentration is exceeded. The increase in viscosity depends on the structure of the hydrophobic moiety of the surfactant. Surface tension measurements suggest the formation of gelatin-surfactant-complexes. If the surfactant is added in high concentration, the viscosity does not further increase, and free micelles are formed in the solution. Directly at the IEP and at pH values below, the addition of surfactants leads to flocculation because of electrostatic interactions. At all surfactant concentrations, the flow behaviour was strictly Newtonian. As a model of the structure of the complex, a modified bead and necklace-model is suggested. This model proposes the nucleation of micelles at the hydrophobic gelatin regions (micellar surfactant-gelatin complexes). The number of micelle moieties per gelatin chain could be estimated to be about three. The complex stability is dependent on the extent of hydrophobic interaction.The gelation behaviour of gelatin is strongly affected by the addition of the surfactant. The ratio between the attainable linear storage and loss moduli,G andG, decreases strongly. Gelation is generally hindered, but the effect is stronger at pH values below the IEP than above.     

Aqueous two-phase system of an anionic gemini surfactant and a cationic conventional surfactant mixture

The aqueous two-phase system formed by the mixture of dodecyltrimethylammonium bromide (DTAB) with a gemini surfactant O,O′-bis(sodium 2-lauricate)-p-benzenediol (C₁₁pPHCNa) has been studied. Two two-phase regions were observed, one was a wide region in the cationic surfactant-rich side and the other in the vicinity of R = 1:1, where R is the mixing mole ratio of DTAB to C₁₁pPHCNa in global solution. Multi-lamellar vesicles are formed in the concentrated upper phase of cationic surfactant-rich systems and spherical aggregates in the concentrated bottom phase at R = 1:1. The microstructure of the solution and the phase behavior of the aqueous two-phase system strongly depended on the total concentration and the composition of the system.     

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

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

Influence of cationic gemini surfactants on the electrochemical behavior of 2-thiouracil at silver electrodes

The voltammetric behavior of 2-thiouracil at a silver electrode is described. 2-Thiouracil can deposit or chemisorb anodically at silver surface; when the potential is made more negative the deposited 2-thiouracil undergoes reductive desorption-process, yielding a cathodic peak at about −1.2 V (vs. SCE) in basic phosphate buffer solution (pH 10.3). In the presence of cationic gemini surfactant C₄H₈–1,4-(C₁₆H₃₃N⁺ (CH₃)₂Br⁻)₂ (C₁₆–C₄–C₁₆) the deposition of 2-thiouracil is greatly improved and the cathodic peak is enhanced. Meanwhile, the peak shifts to more negative potential. The role of C₁₆–C₄–C₁₆ is thought to combine and coadsorb with 2-thiouracil at silver surface as well as reduce the electrostatic repulse in the deposited film, thus making it more easy to deposit and desorb at more negative potential. With C₁₆–C₄–C₁₆ the lateral interaction of deposits reduces, the reductive desorption becomes faster and the cathodic peak becomes sharper. For geminis with different spacer groups and alkyl chains, their influence is mainly determined by their hydrophobicity and adsorbability. It was found that increasing length of alkyl chain was favorable for obtaining a high and sharp desorption peak, whose peak potential is more negative. For comparison, surfactants with single alkyl-chain and double alkyl-chain, such as cetyltrimethyl ammonium bromide and dicetyldimethyl ammonium bromide were studied. They made the desorption peak shift less due to their weaker combination with 2-thiouracil.     

Effect of the nature of the counterion on the properties of anionic surfactants. 5. Self-association behavior and micellar properties of ammonium dodecyl sulfate

Micelles formed in water from ammonium dodecyl sulfate (AmDS) are characterized using time-resolved fluorescence quenching (TRFQ), electron paramagnetic resonance (EPR), conductivity, Krafft temperature, and density measurements. TRFQ was used to measure the aggregation number, N, and the quenching rate constant of pyrene by dodecylpyridinium chloride, k(Q). N depends only on the concentration (C(aq)) of ammonium ions in the aqueous phase whether these counterions are derived from the surfactant alone or from the surfactant plus added ammonium chloride as follows: N = N0(C(aq)/cmc0)(gamma), where N0 is the aggregation number at the critical micelle concentration in the absence of added salt, cmc0, and is equal to 77, 70, and 61 at 16, 25, and 35 degrees C, respectively. The exponent gamma = 0.22 is independent of temperature in the range 16 to 35 degrees C. The fact that N depends only on C(aq) permits the determination of the micelle ionization degree (alpha) by employing various experimental approaches to exploit a recent suggestion (J. Phys. Chem. B 2001, 105, 6798) that N depends only on C(aq). Utilizing various combinations of salt and surfactant, values of alpha were obtained by finding common curves as a function of C(aq) of the following experimental results: the Krafft temperature, N, k(Q), the microviscosity of the Stern layer determined from the rotational correlation time of a spin probe, 5-doxyl stearic acid methyl ester, and the spin-probe sensed hydration of the micelle surface. The values of alpha, determined from applying the aggregation number-based definition of alpha to all of these quantities, were within experimental uncertainty of the values alpha = 0.19, 0.20, and 0.21 derived from conductivity measurements at 16, 25, and 35 degrees C, respectively. The volume fraction of the Stern layer occupied by water decreases as N increases. For AmDS micelles, both the hydration and its decrease are predicted by a simple theory of micelle hydration by fixing the parameters of the theory for sodium dodecyl sulfate and employing no further adjustable parameters. For a given value of N, the hydration decreases as the temperature increases.     

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.