Mixed Cationic-anionic Surfactants Research Articles

Application of dodecyl amine/dodium petroleum sulfonate mixed collector in quartz-feldspar flotation separation

It’s highly challenging to separate feldspar from quartz by flotation owing to their similar crystal structure and physicochemical properties. Using mixed collectors has become a promising method to improve the quartz-feldspar separation. In this study, mixed dodecyl amine (DDA) and sodium petroleum sulfonate (SPS) surfactants were used in the flotation separation of feldspar and quartz, and the adsorption mechanism of mixed collectors and depression mechanisms of two depressants were investigated through zeta potential, contact angle and Fourier transform infrared (FT-IR) spectra. When the pH reached 4.5, the separation of feldspar from quartz was more obvious. In the presence of DDA/SPS collector, the contact angle of feldspar was increased more obviously leading to enhance hydrophobicity. The infrared spectra revealed the interaction of collectors on feldspar surface involved physical and chemical adsorption, whereas the adsorption of collector on quartz was only physical interactions. The use of sodium hexametaphosphate resulted in a significantly enhanced separation performance. The weaker physical adsorption of mixed collector on quartz can be destroyed by sodium hexametaphosphate. This study is beneficial for understanding the collect mechanisms of mixed cationic-anionic surfactants on quartz and feldspar minerals, and promotes the development of advanced feldspar separation techniques.

Separation of silicon carbide and silicon powders in kerf loss slurry of loose abrasive sawing by means of phase transfer separation method with mixed cationic-anionic surfactant collectors addition

Kerf loss slurry generated from the slicing process of silicon wafer by using loose abrasive sawing method contains silicon carbide (SiC) and silicon (Si) powders. This study attempted to separate SiC and Si powders in kerf loss slurry through phase transfer separation method with mixed cationic-anionic surfactant collectors addition. Isooctane and water were employed as the two phases. Dodecylamine acetate (DAA) and sodium oleate (NaOL) was used as the cationic and anionic surfactant collector, respectively. The effects of single surfactant collector addition (DAA/NaOL) and mixed cationic-anionic surfactant collectors addition (DAA + NaOL) on the transfer of individual SiC and Si powders from the water phase to the isooctane phase, as well as on the separation of SiC and Si powders in kerf loss slurry, were investigated and compared.The results indicated that DAA could improve the transfer of both SiC and Si powders to the isooctane phase, and the improvement for SiC powder was higher than for Si powder. In contrast, NaOL could only improve the transfer of SiC powder to the isooctane phase, and the improvement for SiC powder was less than DAA did. Compared to single DAA/NaOL addition, mixed DAA + NaOL addition could improve the separation of SiC and Si powders in kerf loss slurry at lower surfactant collector dosages. In addition, the dosage of NaOL in mixed DAA + NaOL addition had more significant effect on improving their mutual separation than that of DAA did. The optimal separation results were obtained with mixed surfactant collectors addition of 0.01 kg/ton DAA and 0.05 kg/ton NaOL at pH 5. The purity and recovery of SiC powder recovered from the isooctane phase was 90.0% and 92.0%, respectively, and those of Si powder recovered from the water phase was 89.5% and 87.0%, respectively. The total dosage of surfactant collectors was 40% reduced.

Hybrid-Supported Bilayers Formed with Mixed-Charge Surfactants on C18-Functionalized Silica Surfaces.

Mixtures of cationic-anionic surfactants have been shown to spontaneously form ordered monolayers at hydrophobic-hydrophilic boundaries, including air-water and oil-water interfaces. In this work, confocal Raman microscopy is used to investigate the structure of hybrid-supported surfactant bilayers (HSSBs) formed by deposition of a distal leaflet of mixed cationic-anionic surfactants onto a proximal leaflet of n-alkane (C18) chains on the interior surfaces of chromatographic silica particles. The surface coverage of the two surfactants in a hybrid bilayer was determined from carbon analysis and the relative Raman scattering of their respective head-groups. Within the measurement uncertainty, the stoichiometric ratio of the two surfactants is one-to-one, equivalent to mixed-charge-surfactant monolayers at air-water and oil-water interfaces and consistent with the role of the head-group electrostatic interactions in their formation. When self-assembled on the hydrophobic surface, pairs of oppositely charged n-alkyl chain surfactants resemble a phospholipid (phosphatidylcholine) molecule, with its zwitterionic head-group and two hydrophobic acyl chain tails. Indeed, the structure of these hybrid-supported surfactant bilayers on C18-modified silica surfaces is similar to that of hybrid-supported lipid bilayers (HSLBs) on the same supports, but with denser and more-ordered n-alkyl chains. Hybrid-supported surfactant bilayers exhibit a melting phase transition (gel to liquid-crystalline phase) with structural and energetic characteristics similar to those of hybrid-supported bilayers prepared from a zwitterionic phospholipid of the same alkyl chain length. These mixed-charge surfactants on n-alkane-modified silica are stable in water over time (months), results that suggest the potential use of these hybrid bilayers for generating supported lipid-bilayer-like surfaces or for separation applications.

The significant effects of linear medium chain fatty alcohols on phase behavior of aqueous solution of mixed cationic–anionic surfactant

The effect of 1-hexanol on the phase behavior of aqueous solutions of sodium dodecyl sulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB) has been systematically studied. The phase ranges of vesicle and liquid crystal (LC) can be greatly extended with the addition of 1-hexanol. These specific structures distributed symmetrically on the two sides of the SDS/CTAB equimolar line in the pseudo ternary phase diagram. The aqueous two phase system (ATPS) contained vesicles that would transform into lamellar LC with the change of ratio of SDS/CTAB. The phase behaviors of SDS/CTAB system with addition of different alcohols (C5OH–C8OH) showed similar trends in structural transition except for phase span, demonstrating that the obstruction of electrostatic interaction between surfactant polar heads was affected by the insertion depth of the added alcohols.

Oil agglomeration of metal-bearing shale in the presence of mixed cationic-anionic surfactants

Oil agglomeration of metal-bearing shale in the presence of mixed cationic-anionic surfactants

Perfluorinated Alcohols Induce Complex Coacervation in Mixed Surfactants.

Recently, we reported a unique and nearly ubiquitous phenomenon of inducing simple and complex coacervation in solutions of a broad variety of individual and mixed amphiphiles and over a wide range of concentrations and mole fractions. This paper describes a novel type of biphasic separation in aqueous solutions of mixed cationic-anionic (catanionic) surfactants induced by hexafluoroisopropanol (HFIP). The test cases included mixtures of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) (surfactants with different carbon chain lengths) as well as dodecyltrimethylammonium bromide (DTAB) with SDS (surfactants with the same carbon chain lengths). The CTAB-SDS-HFIP coacervate systems can be produced at many different mole ratios of surfactant, but DTAB-SDS-HFIP formed only coacervates at equimolar (1:1) mole ratios of DTAB and SDS. The phase-transition behavior of both systems was studied over a wide range of surfactant and HFIP concentrations at the stoichiometric (1:1) mole ratio of cationic/anionic surfactants. The chemical compositions of each of the two phases (aqueous-rich and coacervate phases) were studied with regard to the concentrations of HFIP, water, and individual surfactants. It is revealed that the surfactant-rich phase (coacervate phase) contains a large percentage of fluoroalcohol relative to the aqueous phase and is enriched in both surfactants but contains a small percentage of water. Surprisingly, the concentration of water in the coacervate phase increases as the total HFIP concentration is increased while the concentration of HFIP in the coacervate phase remains relatively constant, which means a larger amount of water associated with HFIP molecules is extracted into the coacervate phase, which results in the growth of the phase. The volume of the coacervate phase increases with an increase in surfactant concentration and total HFIP %. The coacervate phase is highly enriched in the two amphiphilic ions (DTA(+) and DS(-)) whereas the two counterions (Br(-) and Na(+)) primarily reside in the aqueous-rich phase. The results suggest the formation of a catanionic complex in the coacervate phase through ion pairing with a concomitant release of the surfactant counterions (Na(+) and Br(-)) into the aqueous-rich phase. Finally, the fluorocarbon alcohol systems are contrasted with the effects of aliphatic alcohols in the mixed catanionic surfactant systems. Isopropanol does not have the same interactions as HFIP with respect to solubilization, aggregation, and phase separation of the oppositely charged surfactants.

Mixed Cationic and Anionic Surfactant Systems Achieve Ultra-Low Interfacial Tension in the Karamay Oil Field

Based on cationic and anionic surfactant mixed systems, ultra-low interfacial tension was achieved in the Karamay oil field systems. Upon the addition of a non-ionic third component, the solubility of the mixed cationic-anionic surfactant systems increased significantly. The mixed surfactant ratio and the concentration were determined by the application in the five areas of the Karamay oil field. The interfacial tension in some real systems was found to be around 10 mN∙m-1. These cationic and anionic surfactant mixed systems have a super-resistance adsorption capacity. The results show that after 72 h of quartz adsorption, these systems can still reduce the interfacial tension to an ultra-low level.

Synthesis of Al-substituted MCM-41 and MCM-48 solid acids with mixed cationic–anionic surfactants as templates

Al-substituted MCM-41 and MCM-48 (Al-MCMs in short) are potential solid acid catalysts for cracking long-chain alkanes to make lower-carbon alkenes. This work demonstrates the mixed cationic–anionic templating route as a low-cost method to make regular Al-MCMs with Al-enriched channel surface. Surface Al-enrichment is due to the interaction between Al3+ and COO− head group of anionic surfactant in mixed micelles during the formation of mesostructured precursors of Al-MCMs. Al-MCM-41 has a particularly higher amount of aluminum on its channel surface than Al-MCM-48. Therefore, Al-MCM-41 contains more and stronger acid sites and exhibits better activity in acid-catalyzed cracking of long-chain alkanes.

Charged nanoparticles as supramolecular surfactants for controlling the growth and stability of microcrystals

Microcrystals of desired sizes are important in a range of processes and materials, including controlled drug release, production of pharmaceutics and food, bio- and photocatalysis, thin-film solar cells and antibacterial fabrics. The growth of microcrystals can be controlled by a variety of agents, such as multivalent ions, charged small molecules, mixed cationic-anionic surfactants, polyelectrolytes and other polymers, micropatterned self-assembled monolayers, proteins and also biological organisms during biomineralization. However, the chief limitation of current approaches is that the growth-modifying agents are typically specific to the crystalizing material. Here, we show that oppositely charged nanoparticles can function as universal surfactants that control the growth and stability of microcrystals of monovalent or multivalent inorganic salts, and of charged organic molecules. We also show that the solubility of the microcrystals can be further tuned by varying the thickness of the nanoparticle surfactant layers and by reinforcing these layers with dithiol crosslinks.

Anomalous effects of concentrated salts on the equimolarly mixed cationic–anionic surfactant mixtures

Effects of alkali metal halides (NaX, X = F−, Cl−, Br−, I−; KX, X = Cl−, Br−, I−; and CsCl) on the morphology of the aggregates of decyltriethylammonium bromide and sodium decylsulfonate (C10NE–C10SO3) mixtures with equimolar ratios were studied by static/dynamic light scattering and viscosity measurements. The average hydrodynamic radii of the aggregates, the apparent aggregation number, and the relative viscosity as functions of both the concentrations of surfactants and added salts were investigated, respectively. It showed that the addition of a small amount of NaX (e.g., 0.1 M) had only small effects on the C10NE–C10SO3 vesicles. However, striking anion specificity, which differed anomalously with the anions of salts varying from F− to I−, was observed when large amounts of NaX (e.g., 1 M) were added. The size of the C10NE–C10SO3 aggregates was normally increased and then a liquid–liquid phase separation occurred with the addition of NaF; meanwhile, the addition of NaCl had little effect on the C10NE–C10SO3 aggregates under experimental conditions; however, the size of the C10NE–C10SO3 aggregates was abnormally decreased when high concentrations of NaBr or NaI (up to 2 M) were added, implying a vesicle-to-micelle transition which might be due to a decrease in the intramicellar attraction between oppositely charged headgroups by electrical shielding, and the mixtures still remained homogeneous. A cation specificity of added salts was also observed with the increase of the ionic radii from Na+ to Cs+. However, it was noted that the influence of increasing the ionic radii of cations on the aggregate size was not as pronounced as that of anions in the presence of high concentrations of salts. The aggregates of C10NE–C10SO3 became a little smaller when concentrated alkali metal halides with bigger cations were added into this homogeneous equimolar cationic–anionic surfactant mixture. Both the observed cation and anion specificities were consistent with the Hofmeister series.

Enhanced stabilization of vesicles formed in mixed cationic and anionic surfactant systems by compressed gases

Herein we investigated the effects of six hydrocarbon gases (methane, ethane, propane, ethylene, propylene and isobutene) on mixed cationic–anionic surfactant solutions by phase behavior observation, turbidity, conductivity, and fluorescence spectra. It was found that all these gases could enhance the stability of vesicles formed in the mixed surfactant solutions. The pressure for the stable vesicle formation is decreased with the increasing gas molecular chain length. The possible mechanism for the enhanced vesicle stability by compressed gases was discussed.

The influence of mixed cationic–anionic surfactants on the three-phase contact parameters in silica–solution systems

The formation of thin wetting films on silica surface from aqueous solution of (a) tetradecyltrimetilammonium bromide (C 14TAB) and (b) surfactant mixture of the cationic C 14TAB with the anionic sodium alkyl- (straight chain C 12–, C 14– and C 16–) sulfonates, was studied using the microscopic thin wetting film method developed by Platikanov. Film lifetimes, three-phase contact (TPC) expansion rates, receding contact angles and surface tension were measured. It was found that the mixed surfactants caused lower contact angles, lower rates of the thin aqueous film rupture and longer film lifetimes, as compared to the pure C 14TAB. This behavior was explained by the strong initial adsorption of interfacial complexes from the mixed surfactant system at the air/solution interface, followed by adsorption at the silica interface. The formation of the interfacial complexes at the air/solution interface was proved by means of the surface tension data. It was also shown, that the chain length compatibility between the anionic and cationic surfactants controls the strength of the interfacial complex and causes synergistic lowering in the surface tension. The film rupture mechanism was explained by the heterocoagulation mechanism between the positively charged air/solution interface and the solution/silica interface, which remained negatively charged.

Partitioning of biomaterials in aqueous two-phase systems of mixed cationic-anionic surfactants

Partitioning of biomaterials in aqueous two-phase systems of mixed cationic-anionic surfactants

Synergic Effect of the Mixed Cationic-Anionic Surfactants on the Interfacial Composition and Thermodynamics of W/O Microemulsions

The interfacial composition, the solubility of the alcohol in the oil phase, and the standard free energy change of transferring alcohol from the continuous oil phase to the interfacial layer in the W/O microemulsion stabilized by cationic-anionic surfactants sodium dodecyl sulfate and 1-hexadecyl-3-methylimidazolium bromide were studied with the dilution method. The synergic effect exists between cationic and anionic surfactants on the formation of W/O microemulsion. The effects of different alcohols, oils, and brine on the formation of W/O microemulsions stabilized by cationic-anionic surfactants were also investigated. The alcohols with longer chain length have higher efficiency to form the W/O microemulsion. Long-chain alcohol was easier to penetrate into the interfacial layer and less alcohol was needed to form the stable W/O microemulsion. The effects of decreasing the carbon chain length of the alkane molecules and increasing NaCl concentrations are equivalent to that of increasing the carbon chain length of the alcohol molecules.

New catanionic surfactants based on 1-alkyl-3-methylimidazolium alkylsulfonates, [CnH2n+1mim][CmH2m+1SO3]: mesomorphism and aggregation

Anionic and cationic alkyl-chain effects on the self-aggregation of both neat and aqueous solutions of 1-alkyl-3-methylimidazolium alkylsulfonate salts ([C(n)H(2n+1)mim][C(m)H(2m+1)SO(3)]; n = 8, 10 or 12; m = 1 and n = 4 or 8; m = 4 or 8) have been investigated. Some of these salts constitute a novel family of pure catanionic surfactants in aqueous solution. Examples of this class of materials are rare; they are distinct from both mixed cationic-anionic surfactants (obtained by mixing two salts) and gemini surfactants (with two or more amphiphilic groups bound by a covalent linker). Fluorescence spectroscopy and interfacial tension measurements have been used to determine critical micelle concentrations (CMCs), surface activity, and to compare the effects of the alkyl-substitution patterns in both the cation and anion on the surfactant properties of these salts. With relatively small methylsulfonate anions (n = 8, 10 and 12, m = 1), the salts behave as conventional single chain cationic surfactants, showing a decrease of the CMC upon increase of the alkyl chain length (n) in the cation. When the amphiphilic character is present in both the cation and anion (n = 4 and 8, m = 4 and 8), novel catanionic surfactants with CMC values lower than those of the corresponding cationic analogues, and which exhibited an unanticipated enhanced reduction of surface tension, were obtained. In addition, the thermotropic phase behaviour of [C(8)H(18)mim][C(8)H(18)SO(3)] (n = m = 8) was investigated using variable temperature X-ray scattering, polarising optical microscopy and differential scanning calorimetry; formation of a smectic liquid crystalline phase with a broad temperature range was observed.

Demicellization of a Mixture of Cationic−Anionic Hydrogenated/Fluorinated Surfactants through Selective Inclusion by α- and β-Cyclodextrin

The interactions between alpha- and beta-cyclodextrin (alpha-/beta-CD) and an equimolar mixture of octyltriethylammonium bromide (OTEAB) and sodium perfluorooctanoate (SPFO) were studied by 1H and 19F NMR, surface tension, conductivity, and dynamic light scattering. It was shown that beta-CD could destroy the mixed micelles of OTEAB-SPFO by selective inclusion of SPFO. As beta-CD was added, the system was observed to undergo a process like this: beta-CD preferentially included SPFO to form 1:1 beta-CD/SPFO complexes. As the inclusion of SPFO was almost saturated, the mixed micelles broke and all OTEAB was released and exposed to aqueous surroundings. Then 1:1 beta-CD/OTEAB and 2:1 beta-CD/SPFO complexes significantly formed simultaneously. Contrary to beta-CD, alpha-CD exhibited selective inclusion to OTEAB and only weak association with SPFO. alpha-CD could also destroy the mixed micelles of OTEAB-SPFO; however, the demicellization ability of alpha-CD is much smaller than that of beta-CD. These conclusions were also well supported by the calculations of binding constants and DeltaG degrees . Different from the complexes of CD/conventional surfactants, the complexes of beta-CD/SPFO or alpha-CD/OTEAB formed by selective inclusion of CD in the mixed cationic-anionic surfactants may have contributed to the surface activity of the aqueous mixtures. The complexes of alpha-CD/OTEAB showed much more significant contribution to the surface activity than that of the complexes of beta-CD/SPFO.

Phase behavior and morphology of equimolar mixed cationic–anionic surfactant monolayers at the air/water interface: Isotherm and Brewster angle microscopy analysis

The phase behavior and morphological characteristics of monolayers composed of equimolar mixed cationic–anionic surfactants at the air/water interface were investigated by measurements of surface pressure–area per alkyl chain ( π – A ) and surface potential–area per alkyl chain ( Δ V – A ) isotherms with Brewster angle microscope (BAM) observations. Cationic single-alkyl ammonium bromides and anionic sodium single-alkyl sulfates with alkyl chain length ranging from C 12 to C 16 were used to form mixed surfactant monolayers on the water subphase at 21 °C by a co-spreading approach. The results demonstrated that when the monolayers were at states with larger areas per alkyl chain during the monolayer compression process, the Δ V – A isotherms were generally more sensitive than the π – A isotherms to the molecular orientation variations. For the mixed monolayer components with longer alkyl chains, a close-packed monolayer with condensed monolayer characteristics resulted apparently due to the stronger dispersion interaction between the molecules. BAM images also revealed that with the increase in the alkyl chain length of the surfactants in the mixed monolayers, the condensed/collapse phase formation of the monolayers during the interface compression stage became pronounced. In addition, the variations in the condensed monolayer morphology of the equimolar mixed cationic–anionic surfactants were closely related to the alkyl chain lengths of the components.

Controlled Synthesis of Gold Nanobelts and Nanocombs in Aqueous Mixed Surfactant Solutions

Well-defined gold nanobelts as well as unique gold nanocombs made of nanobelts were readily synthesized by the reduction of HAuCl4 with ascorbic acid in aqueous mixed solutions of the cationic surfactant cetyltrimethylammonium bromide (CTAB) and the anionic surfactant sodium dodecylsulfonate (SDSn). Single-crystalline gold nanobelts grown along the <110> and <211> directions were prepared in mixed CTAB-SDSn solutions at 4 and 27 degrees C, respectively. Furthermore, single-crystalline gold nanocombs consisting of a <110>-oriented stem nanobelt and numerous <211>-oriented nanobelts grown perpendicularly on one side of the stem were fabricated by a two-step process with temperature changing from 4 to 27 degrees C. It was proposed that the mixed cationic-anionic surfactants exerted a subtle control on the growth of gold nanocrystals in solution due to the cooperative effect of mixed surfactants. This synthetic strategy may open a new route for the mild fabrication and hierarchical assembly of metal nanobelts in solution. The obtained gold nanobelts showed good electrocatalytic activity toward the oxidation of methanol in alkaline solution; in particular, the electrode modified with the nanobelts obtained at 27 degrees C exhibited an electrocatalytic activity considerably higher than normal polycrystalline gold electrode. Moreover, the gold nanobelts were used as the surface-enhanced Raman scattering (SERS) substrate for detecting the enhanced Raman spectra of p-aminothiophenol (PATP) molecules, and the gold nanobelts obtained at 4 degrees C exhibited an unusual larger enhancement of the b2 modes relative to the a1 modes for the adsorbed PATP molecules.

Enhancement of catansome formation by means of cosolvent effect: Semi-spontaneous preparation method

Some short-chained alcohols have been found to be good vesicle-promoting agents for both mixed cationic–anionic surfactant systems through spontaneous formation and ion-pair amphiphiles (IPAs) through classic mechanical dispersion preparation. The promotion is mainly due to the cosolvent effects based on the medium dielectric constant. Such prepared vesicle will be referred as “catansome” in this work. A semi-spontaneous method for preparing catansomes through a simple process, that is, dissolving the IPA in a liquid alcohol and then adding water with mixing by using of a homogenizer, is proposed here. This preparation method has the advantage over the preceding ones in purity and simplicity, in the sense that no counterions exist in the solution and no film preparation is needed, respectively. Effects of four homologous cosolvents (methanol, ethanol, 1-propanol, and 1-butanol) on the stability of catansomes formed from three IPAs (decyltrimethylammonium dodecylsulfate, DeTMA-DS; decyltrimethylammonium tetradecylsulfate, DeTMA-TS; dodecyltrimethylammonium dodecylsulfate, DTMA-DS) were systematically studied. Successful preparations of stable catansomes were established for both DeTMA-DS and DeTMA-TS with the four alcohols used and for DTMA-DS with 1-propanol and 1-butanol. An explanation of cosolvent effects based on the medium dielectric constant was found to be still appropriate.

Polymer effects on the equimolar mixed cationic–anionic surfactants

Interactions between poly(ethylene oxide) (PEO), and equimolar mixed sodium decylsulfonate and decyltriethylammonium bromide were studied using surface tension, fluorescence, dynamic light scattering and freeze-fracture transmission electron microscopy techniques. Below the cmc of the equimolar mixed cationic–anionic surfactants, no obvious interaction was observed under the experimental conditions. However, PEO had dramatic effects on the morphology of the aggregates of the equimolar mixed cationic–anionic surfactants. Spontaneous, stable and narrow distributed vesicles could be prepared by mixing PEO and equimolar mixed cationic–anionic surfactants. Furthermore, the size of the vesicles could be controlled by turning the total surfactant concentration, PEO concentration and PEO molecular weight. We found the effect of PEO on the vesicles could be explained by the Asakura–Oosawa model.