Sodium Alkylcarboxylates Research Articles

Self-Aggregation of New Alkylcarboxylate-Based Anionic Surface Active Ionic Liquids: Experimental and Theoretical Investigations

Halogen-free and low-cost alkylcarboxylate-based anionic surface active ionic liquids (SAILs), namely, 1-butyl-3-methylimidazolium alkylcarboxylates ([C4mim][C(n)H(2n-1)O2], n = 8, 10, 12), were first synthesized through the neutralization of imidazolium hydroxide by alkylcarboxylic acids. A systematic study of their self-aggregation behavior in water was investigated by surface tension, electrical conductivity, steady-state fluorescence quenching, and (1)H NMR. The micellar properties of this series of SAILs in ethylammonium nitrate (EAN) were also studied by surface tensiometry for comparison. A set of surface active parameters and thermodynamic parameters of these compounds in water and EAN was obtained. Surface tension results show that the surface activity of [C4mim][C(n)H(2n-1)O2] in EAN is inferior to that in water. They exhibit a higher ability to aggregate in water than the traditional anionic surfactants, sodium alkylcarboxylates (SAC), and anionic SAILs, 1-butyl-3-methylimidazolium alkylsulfates ([C4mim][C(n)H(2n+1)SO4]) with the same hydrocarbon chain length. This demonstrates that the incorporation of carboxylate group and [C4mim](+) cation favors micelle formation. To understand the discrepancy in the surface activity of alkylsulfate- and alkylcarboxylate-based SAILs, theoretical calculations were performed to give electrostatic potential of the corresponding anions. The higher surface activity of [C4mim][C12H23O2] mainly originates from the lower electronegativity of its anion. Density functional theory (DFT) calculations manifest that the interaction energy of binary combination SAILs-EAN is larger than that of SAILs-H2O, implying the stronger interaction of the former. Consequently, it is more difficult for [C4mim][C(n)H(2n-1)O2] to self-aggregate in EAN than in H2O. This work is expected to be of practical value for the environmentally friendly alkylcarboxylate-based SAILs in some potential applications, including nanomaterials synthesis and phase separation, among others.

The effect of steel modifying with zinc oxyethylidenediphosphonate on its passivation in solutions of certain inhibitors

It is shown that a solution of zinc complex of 1-hydroxyethane-1,1-diphosphonic acid can be used for modifying the surface of low-carbon steel in order to enhance its passivation by aqueous solutions of other inhibitors (1,2,3-benzotriazole, sodium alkylcarboxylate, and their mixture). The results of accelerated tests of protectability of nanosized passivating coatings are compared. To assess the efficiency of steel protection by electrochemical tests, the difference in pit formation potentials ΔE = Eptin − Eptsup are determined from polarization curves in borate buffer solutions containing NaCl in the absence (Eptsup) and in the presence (Eptin) of the inhibitor. The direct corrosion tests are carried out in cells and in the G-4 humidity chamber (GOST (State Standard) 9.054–75) where the time of the appearance of first indications of corrosion on samples τcor serves as the criterion of efficient protection. Three groups of coatings can be distinguished: with weak protectability characterized by ΔE 0.40 V where τcor can be even longer than 25 days.

THF hydrate crystal growth inhibition with small anionic organic compounds and their synergistic properties with the kinetic hydrate inhibitor poly(N-vinylcaprolactam)

Small, cationic tetraalkylammonium ions (particularly for alkyl=butyl or pentyl) are known to inhibit tetrahydrofuran (THF) and natural gas hydrate crystal growth and have been used as synergists for commercial kinetic hydrate inhibitor polymers (KHIs), such as N-vinylcaprolactam polymers, for a number of years. The ability for small, organic anionic molecules to inhibit (THF) hydrate crystal growth and their potential as KHI synergists in blends with poly(N-vinylcaprolactam) have been investigated. Several series of sodium alkyl carboxylates, sulphates and sulphonates were synthesised. It was found that none of these molecules were capable of inhibiting THF hydrate crystal growth as well as the best tetraalkylammonium salts. Alkyl carboxylates appeared to be more effective as inhibitors than the sulphonates or sulphates. The most effective anionic THF hydrate crystal growth inhibitors had butyl or pentyl groups, with alkyl branching at the tail (i.e. iso- rather than n-isomers) being advantageous. Anionic carboxylate molecules, particularly with isopentyl or isobutyl groups, showed some kinetic inhibition synergy with poly(N-vinylcaprolactam) lowering the onset and catastrophic hydrate formation temperatures in high pressure (78 bar) constant cooling experiments with Structure II hydrates by 1–2 °C when dosed at 2500 ppm compared with using 2500 ppm polymer alone. This synergism was however less than the best tetraalkylammonium salts (alkyl=n-butyl or n-pentyl) at the same test conditions. Sodium butyl sulphonate and sodium 4-methylpentanoate did not prevent hydrate agglomeration with 3.6% brine and decane at 25% water cut in stirred sapphire cells when dosed at 20,000 ppm based on the aqueous phase, whereas 10,000–20,000 ppm active material of several commercially available anti-agglomerants gave fine transportable slurries and no hydrate deposits at the same conditions.

Structure and physico-chemical properties in mixed aqueous solution of sodium alkylcarboxylate-alkyltrimethylammonium bromide

The physico-chemical properties of organized assemblies (micelle or vesicle) from sodium alkylcarboxylate - alkyltrimethyl -ammonium bromide mixture have been investigated systematically. In different mixed cationc-anionic surfactant systems, micelles and vesicles can coexist or be transformed into each other on different conditions. The experimental results are explained prelimilarily from the viewpoint of molecular packing geometry. The solubilization of organic compound in the mixed surfactant system was also studied in detail.

A study on organized assemblies in the sodium alkylcarboxylate/ fatty alcohol/water systems

The phase behavior and evolution of self-organized assembling structures in the sodium alkylcarboxylate/fatty alcohol systems were investigated by TEM. With increasing concentration of fatty alcohol, the micells transform into lamellar La phase, sponge L3 phase, multilamellar vesicle, and transform back to lamellar La phase. At higher alcohol concentration, a stable two aqueous phase coexisting region has been observed in this kind of systems after aged two months. Unilamellar vesicles were found both in two separated phases but the vesicle density of the upper phase is much higher than that of me bottom phase.

Effect of anionic surfactant molecular structure on bovine serum albumin (BSA) fluorescence

The interactions of BSA with different anionic surfactants, such as sodium alkyl sulfate (C n SO 4Na, n = 8, 10 and 12), sodium alkyl sulfonate (C n SO 3Na, n = 8, 10 and 12) and sodium alkyl carboxylate (C n COONa, n = 9 and 11) were investigated by fluorescence spectroscopy. The effect of molecular structure of anionic surfactants, such as the types of hydrophilic groups and the lengths of hydrophobic chain, on BSA intrinsic fluorescence was examined. It was shown that addition of anionic surfactants induced strong quenching of BSA fluorescence. The quenching of BSA fluorescence relied on the hydrophobic chain lengths of surfactant. The more hydrophobic surfactant had a greater capacity to quench BSA fluorescence. However, anionic surfactants with different headgroups did not show significant difference, e.g., C n SO 4 − and C n SO 3 − with same alkyl chain had similar quenching effect on BSA fluorescence.

Dependence of Alkyl Chain Asymmetry on the Phase Equilibria of Three Catanionic Surfactant Mixtures Containing Dodecyltrimethylammonium Chloride−Sodium Alkylcarboxylate−Water

The pseudoternary phase behavior of three aqueous systems with catanionic surfactant mixtures was studied at 20 °C, with emphasis on the effect of the level of asymmetry between the parent surfactants. The three mixtures all contain the cationic surfactant dodecyltrimethylammonium chloride (DoTAC), combined with one of the surfactants sodium hexanoate (SH), sodium octanoate (SO), or sodium decanoate (SD). As could be expected, all three systems form a variety of phases deriving from the binary DoTAC−water axis, and the extension of those phases vary with the anionic surfactant chain length. The binary sodium alkylcarboxylate/water systems do not show as rich phase behavior as DoTAC−water at this temperature, and the small hexagonal liquid crystalline phase present in the binary SO−water are destabilized by DoTAC in the pseudoternary system. This can be explained in terms of asymmetry between the surfactant chain lengths, which causes packing problems. Neither SH nor SD forms a hexagonal phase at room temperature, the former due to its short alkyl chain and the latter due to its high Krafft temperature. The DoTAC−SD−water phase diagram is dominated by a lamellar liquid crystalline phase, whereas the range of existence of the lamellar phases in the SO and SH systems are much more limited. The hexagonal phases deriving from the binary DoTAC system can incorporate varying amounts of alkyl carboxylate. The largest extension is found in the SO system, indicating a favorable level of asymmetry between the two surfactants. All three systems form a large isotropic solution phase with water. In the SD system, the solution phase has a discontinuity around the equimolar line at high water content. Up to 13 wt % of total surfactant, there is coacervation resulting in two translucent solutions, one dense and one dilute. In the most dilute region, the solutions within and close to the small two-phase area have a bluish appearance. All solution phases were studied by 1H self-diffusion NMR. The results show that all systems are most likely to form mixed aggregates at anionic/catanionic molar ratios <1. In the DoTAC−SH and −SO systems, there are indications of micelles and anionic surfactant monomers coexisting in the monophasic isotropic solutions at anionic/catanionic molar ratios ≥1. In the DoTAC−SD system, on the other hand, there seems to be coexistence of two different types of aggregates at the molar ratios larger than unity. The phase boundaries of the pseudoternary phase diagrams in this work were constructed on the basis of 2H NMR experiments and visual observations, and the microstructures of the one-phase regions were clarified by SAXS.

Interactions between Poly(ethylene oxide) and Sodium Alkylcarboxylates As Studied by Conductivity and Gel Permeation Chromatography

The interactions between PEO and sodium alkylcarboxylates (octyl, decyl, and dodecyl) have been investigated by conductivity measurements and gel permeation chromatography (GPC). Also included in the study was sodium dodecyl sulfate. From the conductivity measurements the critical aggregation concentration, ionization degree, and binding ratios were determined; the binding ratio was also determined from GPC. PEO–surfactant interactions were observed for all the studied surfactants, except sodium octanoate. For the polymer–surfactant complexes the ionization degree was in all cases observed to be about 0.2 higher than the ionization degree for the corresponding aqueous micelles. Further, the binding ratio decreased somewhat with decreasing chain length of the alkylcarboxylate. The Gibbs free energy showed that the polymer–surfactant interaction decreases with decreasing chain length of the alkylcarboxylates and is weaker for alkylcarboxylate compared to alkylsulfate of similar chain length.

Fluorescence probes study on the mixed cationic-anionic surfactant solutions

Pyrene andp-N,N-dimethylaminostyrylphenylmalononitrile are used as the fluorescence probes to study the micro environment and observe the excimer formation of pyrene in sodium alkylcarboxylate and alkyltrimethyl ammonium bromide mixed solutions. The micro polarity, micro-dielectric constants and micro viscosity of the self-organized assemblies in the mixed cationi-anionic surfactant solution were compared before and after sonication, which may form different organized assemblies (micelle or vesicle). The micelle and vesicles have almost the same polarity for the probing molecules whereas the microviscosity differs. The variation of fluorescence quenching curves also shows the different effect of the change of assembly forms (micelles to vesicles). Thus some novel physicochemical properties about the micro environment of the cationic-anionic surfactant assemblies were found from this report.

Formation and coexistence of the micelles and vesicles in mixed solution of cationic and anionic surfactant

In the aqueous mixtures of sodium alkylcarboxylate and alkyltrimethylammonium bromide, large unilamelar vesicles can be formed spontaneously or by sonication as the total carbon number in the HC chains is 19 (or larger). Vesicle formation can be influenced by changes of pH, molar ratio of the two surfactant components, and the polar head group of cationic surfactant. Micelles may coexist with the vesicles in these mixed systems. The larger hydrodynamic radius (∼200 nm) and aggregation number (∼800) illustrate that the shape of the micelle in 1:1 C9H19COONa−C10H21N(CH3)3Br is rod-like. In some mixed systems, the micelles can be transformed into stable vesicles by sonication — a phenomenon revealed for the first time. The surface-chemical properties of these catanionic surfactant solutions and the stabilities of vesicle have been studied systematically.

Micellar properties of ethoxylated sodium alkylcarboxylates

Some micellar properties of four ethoxylated sodium alkylcarboxylates have been investigated by means of electrical conductivity (critical micelle concentration, CMC, apparent micelle ionization degree) and time-resolved fluorescence probing (micelle aggregation number N) as a function of temperature and surfactant concentration. The CMCs are larger and the N values smaller than for the corresponding nonionic surfactants. The micelle ionization degrees are large.

Polarization Microscopy of Short Chain Sodium Carboxylate Mesophases

Abstract Polarization microscopy has been used to study the ionic mesophases of melts of short chain sodium alkyl carboxylates. The smectic A or neat structure is confirmed for all the sodium carboxylates studied: isovalerate, n-butyrate, n-valerate, n-hexanoate and n-heptanoate. The domain sizes and transition temperatures are reported and an empirical correlation between birefringence and the order parameter is observed. The birefringence is predicted to be negative for all the compounds studied. It is interesting to note that sodium isovalerate exhibits quite different properties from those found for the other n-alkyl carboxylates. Both the birefringence temperature coefficient and the average domain size (500 μm) are unusually large for sodium isovalerate.

Thermodynamics of micelle formation: Model calculations for alkyl carboxylates

A model for the calculation of the standard free energy of transfer of an amphiphilic monomer from the intermicellar solution to a spherical micelle that previously [9] was applied to solutions of sodium octanoate is shown to be applicable to the homologous series of straight-chain sodium alkyl carboxylates. This model is largely based on the previous works by Ruckenstein and Nagarajan [2], Israelachvili, Mitchell and Ninham [12] and Tanford [11]. The two main factors involved are: the standard free energy of transfer of the hydrocarbon chains from water to the liquid hydrocarbon interior of the micelle with the account taken to the residual hydrocarbon/water contact and the repulsion between the polar end groups. The model is shown to give good agreement with experimental data on mean aggregation numbers, apparent molar volumes and counter ion and water activities for all of the short-chain [C 5—C 6] carboxylates.

Partial molal volumes and compressibilities of the homologous series of long-chained sodium-alkylmalonates in aqueous solution at 25°c

The change in partial molal volume ( ΔV m ) and compressibility ( Δκ s m ) during micelle formation has been determined at 25°C for the homologous series of sodium alkylmalonates, CH 3(CH 2) 7CH-(COO −Na +) 2 to CH 3(CH 2) 11CH(COO −Na +) 2. ΔV m and ΔK s m have been determined from density measurements and ultrasound measurements, respectively. Both these quantities increase with increasing surfactant chain length. ΔV m has been found to be almost equal to ΔV m for sodium alkylcarboxylates of similar effective chain length, indicating that the ionic head group of the surfactant has a minor contribution to this quantity. ΔK s m is somewhat smaller for the alkylmalonates than for the corresponding alkylcarboxylates, indicating a small negative contribution from the surfactant head group to Δκ s m. The fraction of associated counterions to the micelles has been determined by emf measurements, and it was found that this quantity increases slightly with increasing surfactant chain length.

Partial molal volumes and compressibilities of n-alcohols in micellar solutions of sodium alkylcarboxylates

The partial molal volumes of n-alcohols (C 3C 10) in micellar solutions of sodium dodecanoate, sodium decanoate, and sodium octanoate have been determined at 25°C by density measurements. From ultrasound measurements the partial molal compressibilities of the alcohols in the micellar solutions have been determined. The partial molal volumes and compressibilities of the alcohols in micellar solutions are higher than those in water and are similar to the partial molal quantities for the liquid alcohol. The partial molal volumes and compressibilities decrease with increasing chain length of the surfactant and with increasing surfactant concentration. The same trend has been found for the corresponding quantities for liquid alcohols, and the results have been interpreted by comparing the interior of the micelles to liquid alcohols.

Partial molal volumes and compressibilities of the homologous series of sodium alkylcarboxylates, R 6COONaR 13COONa, in aqueous solution

The changes in partial molal volume (Δ V m) and compressibility (Δ κ m) in the formation of micelles have been determined at 25°C for the homologous series of sodium-alkylcarboxylates, R 6COONaR 13COONa. Δ V m has been determined by density measurements and by conductance measurements at different pressures. Δκ m has been evaluated from the conductance measurements and from ultrasound measurements. For each quantity the two independent methods of measurements gave consistent values. Δ V m and Δ κ m both increase with increasing chain length of the surfactant, but not in a linear manner. An analysis of the quantity Δ V m shows that the difference between successive values of Δ V m in the homologous series does not represent the group partial molal volume of the CH 2 group added to the micelle. The fraction of counterions associated with the micelles has been determined by EMF measurements, using a membrane electrode. This quantity was found to increase with increasing chain length.