Aqueous Surfactant Two-phase System Research Articles

Investigation on the phase behaviors of aqueous surfactant two-phase systems containing Alkyl polyglucosides (APG) and alkyl polyglucoside sulfosuccinate (APGSS)

The surfactant aqueous two-phase systems have been widely attention because of their mild conditions and easy recovery. The phase behaviors and formation mechanism of an aqueous surfactant two-phase system (ATPS), which was composed of a nonionic surfactant Alkyl polyglucosides (APG) and an anionic surfactant sodium alkyl polyglucoside sulfosuccinate (APGSS), were studied. The phase diagram for APG/APGSS ATPS was illustrated. Merchuk relation was used to correlate the binodal experimental data. Indicating that top phase is APG enriched phase and the bottom phase is APGSS enriched. By measurements of surface tension, electrical conductivity, density, viscosity, transmission electron microscopy, and dynamic light scattering, micelle aggregation behaviors were explored. The formation mechanism of the ATPS was also proposed, which is attributed to the different aggregation behaviors between APG and APGSS molecules leads to different micelle size and morphology. The top phase flocculates due to the presence of asymmetric larger wormlike aggregates, lead to phase separation and the formation of the ATPS.

Enzyme-Responsive Aqueous Two-Phase Systems in a Cationic-Anionic Surfactant Mixture.

Enzyme-instructed self-assembly is an increasingly attractive topic owing to its broad applications in biomaterials and biomedicine. In this work, we report an approach to construct enzyme-responsive aqueous surfactant two-phase (ASTP) systems serving as enzyme substrates by using a cationic surfactant (myristoylcholine chloride) and a series of anionic surfactants. Driven by the hydrophobic interaction and electrostatic attraction, self-assemblies of cationic-anionic surfactant mixtures result in biphasic systems containing condensed lamellar structures and coexisting dilute solutions, which turn into homogeneous aqueous phases in the presence of hydrolase (cholinesterase). The enzyme-sensitive ASTP systems reported in this work highlight potential applications in the active control of biomolecular enrichment/release and visual detection of cholinesterase.

Endowing a Light-Inert Aqueous Surfactant Two-Phase System with Photoresponsiveness by Introducing a Trojan Horse.

The ability to modulate the phase behavior of an aqueous surfactant two-phase (ASTP) system reversibly with light is of great importance in both fundamental and applied science. Thus far, most of the light-responsive ASTP systems are based on covalent modification of the component molecules. In this article, we, for the first time, achieve photoresponsiveness in a light-inert ASTP system by physically introducing a phototrigger with the aid of a Trojan horse. The ASTP system formed from sodium laurate (SL) and dodecyltributylammonium bromide (DBAB) does not show light responsiveness by physically mixing a light-responsive azobenzene compound, 2-(4-(phenyldiazenyl)phenoxy)acetate sodium (Azo). However, in the presence of the host-guest complex SL@β-CD formed from β-CD and sodium laurate (SL), the ASTP turns quickly into a homogeneous suspension under visible light, which recovers to the original ASTP state again under 365 nm UV irradiation. Because the SL@β-CD complex exists harmonically with the ASTP system, it can be viewed as a "Trojan horse" that becomes fatal only when the encapsulated SL is triggered to release. In the presence of the Trojan horse, the photoresponsiveness of the ASTP system can be manipulated reversibly by alternatively exerting UV and visible light. Using this strategy, we are able to collect trace amounts of oily components from water. The current strategy points out that it is possible to achieve light responsiveness in light-inert systems with a physical method, which may have profound impact on both the fundamental and applied science.

Adjusting and Resetting of the Pre-determined Storage Temperature for O/W Emulsions

Adjusting and resetting the predetermined storage temperature of O/W miconazole cream from 20-24° to be 30° to coincide with the storage temperature of the Egyptian climatic ICH/WHO zone IVA was the objective of this work. Eight sets of miconazole cream were prepared by using different proportions of the oil phase ingredients while their ratios were fixed at 30 %. The calculated HLB values of the oil phases were 9.067, 9.134, 9.2, 9.267, 9.36, 9.46, 9.566 and 9.6. These eight sets have same optimum surfactants blend proportions equal to 0.5:0.5 and same effective surfactant blend concentration equal to 7 %. Sets which have storage temperature equal to 30±2° were assessed according to the acceptance criteria of the accelerating stability testing protocol for O/W emulsions stabilized by nonionic surfactants (aqueous surfactant two-phase systems) as previously reported. Only two sets, numbered 2 and 4 with storage temperature of 30.5 and 32°, respectively met the acceptance criteria of aqueous surfactant two-phase system. The applicability and validity of the method was confirmed by measuring zeta potential and particle size distribution of original miconazole cream set, set numbers 2 and 4. Zeta potential and particle size distribution of the three sets were measured on a Zetasizer with zeta potential results equal to -20, -30.7, -41.7 mV and particle size distribution results equal to 560.8, 387.6, 386.5 nm, respectively. Particle size distribution was also measured using a transmission electron microscope with results equal to 84.875, 49.168 and 46.05 nm, respectively. These results indicated that zeta potential defined the emulsion stability accurately and precisely whereas particle size distribution measurement gave unreliable and indefinite results. Zeta potential results revealed that the increase in the storage temperature of emulsion to 30° is accompanied by an increase in its stability. Increasing temperature beyond 30 is possible and would result in subsequent increase in stability due to the presence of liquid crystalline phase below 35°, which contributes significantly to emulsion stability while the destructive effect of the temperature starts at 35°. Unreliable and indefinite results of particle size measurement proved that the droplet diameter and droplet size measurement reported in many reports is more convenient. This work described a theory to determine the storage temperature of materials, pharmaceuticals, foods and cosmetics obeying non-Newtonian plastic flow.

Incorporation and recovery of SWNTs through phase behavior and aggregates transition induced by changes in pH in a catanionic surfactants system

The phase behavior and aggregates induced by changes in pH in a sodium N-tetradecyl-maleimidepimaric carboxylate (C14-MPA-Na)/cetyltrimethylammonium bromide (CTAB) system have been investigated using rheology and cryogenic transmission electron microscopy (cryo-TEM). Viscoelastic solutions at a pH between 6.40 and 1.41, opalescent blue solutions at a pH between 1.41 and 1.32 and aqueous surfactant two-phase systems (ASTPs) at a pH between 1.32 and 0.56 are formed sequentially. The microstructures in the viscoelastic solutions are wormlike micelles that partially transform to vesicles in the opalescent blue solutions. The aggregates in the upper phase of the ASTPs are vesicles and lamellar micelles, and in the lower phase are spherical micelles. Further, Single-walled carbon nanotubes (SWNTs) were successfully hybridized into the wormlike micellar viscoelastic solutions. cryo-TEM, UV–Vis-IR, near-infrared photoluminescence (NIR-PL) and UV–Vis spectroscopy were used to study the dispersion of SWNTs in the viscoelastic solutions, and the results showed SWNTs can remain dispersed for more than 6 months at pH 6.40. The results obtained from rheology showed that the hybridization of SWNTs will not affect the aggregates and viscoelasticity compared that to the native viscoelastic solution. Above more, the SWNTs could be recycled by the pH-switched phase behaviors between viscoelastic solutions and ASTPs.

Phase Behavior and Aggregation in a Catanionic System Dominated by an Anionic Surfactant Containing a Large Rigid Group.

The phase behavior and aggregates of a catanionic system have been investigated. The anionic surfactants in the mixed systems were sodium N-alkylmaleimidepimaric carboxylate (Cn -MPA-Na, n=12, 14, 16), which were prepared from rosin and contain a large rigid skeleton and a flexible alkane chain, and the cationic surfactant was cetyltrimethylammonium bromide (CTAB). The phase behavior of the C14 -MPA-Na/CTAB system transformed sequentially from a viscoelastic solution to an aqueous surfactant two-phase system (ASTP), an aqueous surfactant three-phase system (AS3P), and an anisotropic homogeneous phase as the concentration of C14 -MPA-Na was continuously increased from 10 to 35 mm. The C16 -MPA-Na/CTAB system showed similar phase behavior, whereas the C12 -MPA-Na/CTAB system did not form the AS3P system. The corresponding microstructures in the different phases were investigated by using rheology and cryogenic transmission electron microscopy (Cryo-TEM). The aggregates in the viscoelastic solutions are thread-like, annular, and worm-like micelles. The microstructures in the upper phase of the ASTP are worm-like micelles, and in the lower phase are spherical and rod-like micelles. The aggregates in the upper and lower phases of the AS3P are worm-like micelles and spherical and rod-like micelles, respectively. The aggregates in the middle phase of the AS3P and the anisotropic homogeneous phase are sponge-like micelles. The clear Cryo-TEM images of the sponge-like micelles are presented.

Influence of d-glucose as additive on thermodynamics and physical properties of aqueous surfactant two-phase systems for the continuous micellar extraction

Aqueous nonionic surfactants solutions can form two coexisting phases when heated beyond the so called cloud point temperature. Hence, these surfactants are potential solvents for extraction processes. In this work the effect of d-glucose on phase behavior of aqueous surfactant two-phase systems containing the nonionic surfactants Tergitol 15-S-7 or Triton X-114 was investigated in order to design micellar systems for liquid-liquid extraction. It was found that d-glucose can lead to an increased density difference if the surfactant-rich phase is the lighter one as well as an enhancement of the phase separation. Furthermore, the effect of d-glucose on the liquid-liquid equilibrium of aqueous Tergitol 15-S-7 solutions was studied. The partition behavior of three model solutes was determined and modeled with the combination of molecular dynamics simulations and the thermodynamic model COSMOmic. Based on these data an experiment in a continuous extraction column using an aqueous surfactant two-phase system containing d-glucose as additive was performed. The results demonstrate that sugars as additives can be used to tailor surfactant solutions in a beneficial way for separation processes.

Investigation on the phase behaviors of aqueous surfactant two-phase systems in a mixture of N-dodecyl-N-methylpiperidinium bromide (C12MDB) and sodium dodecyl sulfate (SDS)

Abstract To study the phase behavior and formation mechanism of an aqueous surfactant two-phase system (ASTP), which was composed of a cationic surfactant N-dodecyl-N-methylpiperidinium bromide (C12MDB) and an anionic surfactant sodium dodecyl sulfate (SDS), an investigation was conducted. The phase diagram for C12MDB/SDS aqueous solutions was mapped, indicating that the ASTP forms between the homogeneous and heterogeneous phase regions in a narrow concentration range. By measurements of surface tension, transmission electron microscopy, dynamic light scattering, and zeta potential, the formation mechanism of the ASTP was proposed, which is attributed to the aggregation of vesicles. Different aggregation behaviors of vesicles lead to phase separation and the formation of the ASTP.

Phase behavior and microstructures in a mixture of anionic Gemini and cationic surfactants.

We report in this work the phase behavior and microstructures in a mixture of an anionic Gemini surfactant, sodium dilauramino cystine (SDLC), and a conventional cationic surfactant, dodecyl trimethyl ammonium chloride (DTAC). Observation of the appearance shows that the phase behavior of the SDLC-DTAC mixed cationic surfactant system transforms from an isotropic homogeneous phase to an aqueous surfactant two-phase system (ASTP) and then to an anisotropic homogeneous phase with the continuous addition of DTAC. The corresponding aggregate microstructures are investigated by rheology, dynamic light scattering, transmission electron microscopy and polarization microscopy. It has been found that a wormlike micelle, in the isotropic homogeneous phase, occurs linear to the branch growth. The aggregate microstructures in the ASTP lower and upper phases are branched wormlike micelles and vesicles, respectively. The micelle transformed into a vesicle upon varying the phase volume percentage until a lamellar liquid crystal formed in the anisotropic homogeneous phase. The macroscopic phase behavior and microscopic aggregate structure are related to the understanding of the possible mechanisms for the above phenomena.

Extraction of Theanine from Waste Liquid of Tea Polyphenol Production in Aqueous Two-phase Systems with Cationic and Anionic Surfactants

Extraction of theanine from waste liquid of tea polyphenol production was studied in aqueous surfactant two-phase system (ASTP) with cationic surfactant (CTAB) and anionic surfactant (SDS). Results indicate that the region of ASTP is narrow and there is only a two-phase region of cationic surfactant. The increase in concentrations of NaBr and Na2SO4 are beneficial to the formation of ASTP. Theanine concentration in the bottom phase increases with increasing concentration of theanine, whereas the partition coefficient and extraction rate only change a little when the concentration of theanine is above 0.2 g·L−1. With the increase of SDS concentration, the phase ratio and the partition coefficient decrease, while the extraction efficiency of theanine increases and the concentration of theanine changes a little in the range from 2.4/7.5 to 2.8/7.2 for SDS/CTAB ratio. The temperature has a notable effect on the concentration of theanine in the bottom phase, partition coefficient and extraction rate of theanine. The increase of waste liquid decreases the phase ratio, increases the concentration and extraction rate of theanine in the bottom phase, since the protein and the saccharide enter the bottom phase with theanine.

Aqueous Surfactant Two‐Phase Systems for the Continuous Countercurrent Cloud Point Extraction

AbstractAqueous nonionic surfactant solutions split into two phases if the temperature is increased beyond a certain temperature, the so‐called cloud point temperature. Presently many different types of nonionic surfactants are produced commercially, out of these numerous have been considered as potential solvent for the cloud point extraction. In this work the crucial thermophysical properties of nonionic surfactants are investigated to determine the potential of surfactant systems for extraction processes. Phase equilibria of the binary system Triton X‐114/water and the ternary system Triton X‐114/water/phenol were measured. Based on these data the cloud point extraction was implemented in a continuous stirred extraction column. It was found, that increasing temperature within the column reduces the loss of surfactant and leads to an increasing enrichment factor. This work demonstrates that surfactant/water systems represent a suitable alternative to conventional solvents and can effectively be processed in continuous extraction columns.

An aqueous anonic/nonionic surfactant two-phase system in the presence of salt. 2. Partitioning of ice structuring proteins

Three ice structuring proteins (ISPs) with different molecular weights and net charges at pH 7.4 were partitioned in an aqueous anionic/nonionic surfactant two-phase system of SDS and Trition X-114 in the presence of 100 mM sodium chloride. The effects of temperature and SDS concentration on the protein partition coefficients were investigated. It is found that the protein partition coefficients increase with the increase of temperature and SDS concentration. Compared to the reported net dependence of protein partitioning in aqueous mixed surfactant two-phase systems, the observed protein partitioning behavior is driven primarily by excluded volume interactions between the proteins and the surfactant aggregates, rather than electrostatic interactions. Specifically, the ISPs partition preferentially to the micelle-poor phase, where they experience less excluded-volume interactions with the surfactant aggregates. The improvements in protein partitioning to the micelle-poor phase upon the SDS addition appear to result from the growth of the surfactant aggregates by forming mixed micelles, which enhances the excluded-volume interactions between the proteins and the surfactant aggregates.

Effect of Electrolyte and Temperature on Volatile Organic Compounds Removal from Wastewater Using Aqueous Surfactant Two-Phase System of Cationic and Anionic Surfactant Mixtures

Benzene, toluene, ethylbenzene, and xylene are frequently observed contaminants in industrial wastewaters causing concerns about environmental and health effects. An aqueous surfactant two-phase (ASTP) extraction system using mixtures of cationic and anionic surfactants have been shown to be a promising surfactant-based separation technique to concentrate solutes such as proteins and dyes from aqueous solution. A phase separation of a surfactant solution occurs at certain surfactant compositions and concentrations, forming two isotropic phases. One is rich in surfactant aggregates (surfactant-rich phase) and the other is lean in surfactant aggregates (surfactant-dilute phase). Most of the organic contaminants tend to solubilize and concentrate in the surfactant-rich phase, leaving the surfactant-dilute phase containing only small amounts of contaminants as remediated water. The effect of NaCl addition on the critical micelle concentration (CMC) and the extraction ability of ASTP formed by mixtures of cationic surfactant (dodecyltrimethylammonium bromide; DTAB) and anionic surfactant (alkyl diphenyloxide disulfonate; DPDS) at 50 mM total surfactant concentration with a 2:1 molar ratio of DTAB:DPDS was investigated; the CMC of the mixture slightly decreases with increasing NaCl concentration. The extraction and preconcentration of benzene are greatly enhanced by added NaCl. The higher the degree of hydrophobicity of contaminants, the greater the extraction into the surfactant-rich phases. At 1.0 M NaCl addition, about 95% of xylene, 92% of ethylbenzene, 90% of toluene, and 79% of benzene are extracted into the surfactant-rich phase within a single stage extraction and the contaminant partition ratios can be as high as 395 for xylene, 273 for ethylbenzene, 206 for toluene, and 84 for benzene, which are greater than those obtained from the conventional ASTP extraction system using nonionic surfactants.

Phase and self-assembly transition induced by glycerol–borax interaction in an aqueous surfactant two-phase system

We report that the phase and self-assembly transition in an aqueous surfactant two-phase (ASTP) system can be induced by a small amount of glycerol. The ASTP was formed from a cationic Gemini surfactant, C12C6C12(Et), and an anionic surfactant, sodium laureate (SL), in a borax solution. Upon addition of 0.3–2 vol% glycerol to the system, the ASTP system underwent a striking phase transition: three phases at 0.3–0.5% glycerol, a single birefringent phase at 0.7–1.2% glycerol, then again two phases, with the upper one like ice-cream. FF-TEM, CSLM and polarized microscopy revealed that the lamellae in the original upper phase were transformed into multilamellar vesicles. This phase and the microstructure transition were attributed to neutralization of sodium laureate to lauric acid by the formation of protons from the reaction of borax with glycerol. The variation of the charge density on the bilayer assemblies and the formation of LA were confirmed by fluorescence quenching and ATR-IR experiments. Our results demonstrate that a small amount of glycerol can be used to tailor the phases and microstructures in surfactant systems containing pH-sensitive components.

Aqueous Surfactant Two-Phase Systems in a Mixture of Cationic Gemini and Anionic Surfactants

The phase behavior as well as the microstructures of the cationic gemini surfactant and anionic conventional surfactant aqueous two-phase system (ASTP) have been studied. The ASTP formation can be attributed to the coexistence of different kinds of aggregates in the upper and lower phases. The effects of temperature, shearing, surfactant concentration and mixing molar ratio on the phase separation of the ASTP-forming systems are systematically investigated. The ASTP can be destroyed by applying shear and increasing temperature. In this process, the lamellar structures (flat bilayers) in the ASTP are transformed into vesicles. Variation of surfactant structure also affects the phase behavior and the aggregates transformation. Appropriate molecular packing is crucial for the formation of ASTP.

Temperature-Sensitive Aqueous Surfactant Two-Phase System Formation in Cationic−Anionic Surfactant Systems

Temperature-induced aqueous surfactant two-phase system (T-ASTP), which was found to be of generic importance, was investigated in a series of conventional mixed cationic-anionic surfactant systems. On the basis of the investigations of turbidity, dynamic light scattering, transmission electron microscopy, and fluorescence resonance energy transfer, the formation of T-ASTP can be attributed to temperature-induced vesicle aggregation. Aggregated vesicles existed in the upper part, while the separated vesicles existed in the lower part. The phase separation temperature can be regulated by varying the surfactant composition or adding additives, such as d-sorbitol, urea, or NaBr. The hydrophobic interaction and cooperative effect between cationic and anionic surfactants played a significant role in the formation of T-ASTP.

Two-Phase Region in the DTAB/SL Mixed Surfactant System

The phase behavior as well as the microstructures of the dodecyltrimethylammonium bromide (DTAB)/sodium laurate (SL) aqueous two-phase system has been studied. By using FF-TEM, dynamic light scattering (DLS), a viscosity meter, and polarization microscopy, the effects of surfactant concentration and mixing ratio, temperature, salt concentration, and additives (octanol and toluene) on the phase separation have been systematically investigated. The phase separation is found to be strongly dependent on the variation of the surfactant aggregates. The different kinds of aqueous surfactant two-phase system can transit between each other upon the variation of the mixing ratio, the change of the salt concentration, and the addition of toluene and octanol.

The Transition from Vesicles to Micelles Induced by Octane in Aqueous Surfactant Two-Phase Systems

The transition from vesicles to micelles by adding octane into the dodecyl-pyridinium chloride (DPCl)/sodium laurate (SL), and dodecyltrimethylammonium bromide (DTAB)/SL aqueous two-phase systems has been studied. The two-phase systems were transformed into single-phase isotropic solutions with the addition of a certain amount of octane. The results of dynamic light scattering (DLS) demonstrate the decrease of large aggregates (vesicles) and the increase of the small aggregates (spherical micelles) upon octane addition. Such transformation of the surfactant aggregates was also corroborated by the results of time-resolved fluorescence quenching (TRFQ) and viscometry. The change of the phase behavior was discussed on the basis of the interaggregate interactions influenced by the variation of organized assemblies.

Phase behavior and protein partitioning in aqueous two-phase systems of cationic–anionic surfactant mixtures

Cationic–anionic surfactant mixtures can form aqueous two-phase systems. Such aqueous surfactant two-phase systems (ASTP systems) can be used for separation and purification of biomaterials. In this work we investigated the phase behavior and the partitioning of BSA and lysozyme in the ASTP system formed by mixtures of dodecyltriethylammonium bromide and sodium dodecylsulfate (SDS). The pseudo ternary phase diagram of these mixtures at low total surfactant concentrations contains two narrow two-phase regions, which represent two kinds of different ASTP systems formed when cationic and anionic surfactants are in excess, respectively (called ASTP-C and ASTP-A). The phase separation is associative, one phase is surfactant-rich, and the other phase is surfactant-depleted. Mechanisms behind the phase behavior are discussed. The phase behavior, especially phase separation time and phase volume ratio, is strongly influenced by total concentration and molar ratio of mixed surfactants. The effect of molar ratio is strong, which enables one to get desired phase systems also at very low total concentration by tuning the molar ratio of the surfactants. It was shown that the marked differences of surfactant concentration between the phases makes proteins distribute with different partitioning coefficients. The charges on the micellar surface, which can be adjusted by tuning the molar ratio of cationic surfactants to anionic surfactants, enhance the selectivity of protein partitioning by electrostatic effects. At pH 7.1, in the ASTP-C systems, negatively charged BSA is concentrated in the surfactant-rich phase and positively charged lysozyme in the surfactant-depleted phase, while in ASTP-A systems, a totally opposite partitioning was observed. It was shown that lysozyme could retain activity in ASTP systems.