Jinling Chai

Phase behavior studies of quaternary systems containing N-lauroyl-N-methylglucamide/alcohol/alkane/water

The three-phase behavior of quaternary systems comprising N-lauroyl-N-methylglucamide (MEGA-12)/alcohol/alkane/water has been studied using epsilon-beta fishlike phase diagrams. From the epsilon-beta fishlike phase diagrams a series of phase inversions Winsor I (2) --> III (3) --> II (2) were observed, and the hydrophilic-lipophilic balanced (HLB) plane equation for the quaternary system was deduced. Some physicochemical parameters, such as the mass fraction of alcohol in the HLB interfacial layer, A S, the coordinates of the start (beta B, epsilon B) and end points (beta E, epsilon E) of the middle-phase microemulsion, the mass fractions of MEGA-12 and alcohol in the total system (C S and C A), and the solubilities of MEGA-12 and alcohol in oil phase (S O and A O), were calculated. The effects of different alcohols, alkanes, and NaCl concentrations in the aqueous phase on the phase behavior and solubilization capacity were investigated, which indicates that alcohol with longer and alkane with shorter hydrocarbon chains have a larger solubilization capacity. NaCl concentration has little influence on the phase behavior.

Self-Assembly and Rheological Properties of a Pseudogemini Surfactant Formed in a Salt-Free Catanionic Surfactant Mixture in Water

The surface and bulk properties of bola-type dicarboxylic acid (sebacic acid, SA) and zwitterionic surfactant tetradecyldimethylamine oxide (C14DMAO) mixtures in aqueous solutions were studied. Surface tension measurements indicate a pronounced synergistic effect between SA and C14DMAO. In bulk aqueous solutions, rich phase behavior was observed with a varied SA-to-C14DMAO ratio (ρ) and a total surfactant concentration. Typically at ρ = 0.5, a novel pseudogemini surfactant (C14-S-C14) forms, driven by electrostatic interaction and hydrogen bonding. The C14-S-C14/H2O system exhibits rich phase behavior induced by the transition of aggregates. With increasing concentration of C14-S-C14, one can observe a viscous L1 phase, an L1/Lα two-phase region where a birefringent Lα phase is on the top of an L1 phase, a single Lα phase, and finally a mixture of an Lα phase and a precipitate. Microstructures formed in the Lα phases were determined by freeze-fracture transmission electron microscopy (FF-TEM) and cryogenic-transmission electron microscopy (cryo-TEM) observations. Polymorphic aggregation behavior was observed with the formation of a variety of bilayer structures including unilamellar vesicles, onions, and open and hyperbranched bilayers. Rheological measurements showed that the Lα phases are viscoelastic and sensitive to temperature where a quick loss of viscoelasticity was observed at elevated temperature.

Effects of various additives on the cloud point of dodecyl polyoxyethylene polyoxypropylene ether

Effects of various additives, including electrolytes, alcohols and organic acids, polymers, and ionic and nonionic surfactants, on the cloud point of dodecyl polyoxyethylene (5) polyoxypropylene (4) ether nonionic surfactant aqueous solutions are investigated. The salting-out electrolytes decrease the cloud point while salting-in electrolytes increase it. Most alcohols and organic acids can lower the cloud point except for methanol and ethanol. The polymers form complexes with the surfactant and decrease the cloud point. The added surfactants can be inserted into the micelles of the nonionic surfactant and form mixed micelles, thus raising the cloud point.

Dynamic surface tension and adsorption mechanism of surfactant benzyltrimethylammonium bromide at the air/water interface

The air‐solution equilibrium tension, γc and dynamic surface tension, γt, of aqueous solutions of a novel ionic surfactant benzyltrimethylammonium bromide (BTAB) were measured by Wilhelmy method and Maximum bubble pressure method (MBPM), respectively. Adsorption equilibrium and mechanism of BTAB at the air‐solution interface were studied. The CMC was determined to be 0.11 mol/L. The results show that at the start, the adsorption process is controlled by a diffusion step. Toward the end, it changes to a mixed kinetic‐diffusion controlled mechanism with the adsorption activation energy of about 11.0 KJ/mol. Effects of temperature, inorganic salts, and alcohols on adsorption kinetics also are discussed.

Comparison Between Phase Behavior of Gemini Imidazoliums and Monomeric Ionic Liquid Surfactants in W/O Microemulsion Systems

The composition and structural parameters of W/O microemulsions containing gemini surfactant 1,4-bis(3-dodecylimidazolium-1-yl)butane bromide [C12(Bim)2-2Br] and W/O microemulsions containing ionic liquid type surfactant 1-dodecyl-3-methylimidazolium bromide (C12mimBr) were studied and compared at different molar ratios of water to surfactant (ωo). The mole fractions of the alcohol in the interfacial layer in C12(Bim)2-2Br-based systems are always larger than that in C12mimBr-based systems. However, the mole fractions of the alcohol in the oil phase are nearly the same for both the systems. The C12(Bim)2-2Br-based systems have greater absolute values of the Gibbs energy (−ΔG o o→i ) than that of C12mimBr-based systems. In the C12(Bim)2-2Br-based systems, a large number of cosurfactants at the interfacial layer is conducive for the formation of a smaller droplet. The effects of alcohols, alkanes, and salinity on the composition and structural parameters of the two systems were also investigated and discussed.

Phase behavior and solubilization of microemulsion systems containing Gemini imidazoliums and their monomeric analogues

The Gemini imidazolium surfactants with a four-methylene spacer group [Cn(Bim)2-2Br, n = 12, 14, 16] and their corresponding monomers [CnmimBr, n = 12, 14, 16] were synthesized and characterized. The phase behavior and solubilization of microemulsion systems containing Cn(Bim)2-2Br/butan-1-ol/octane/brine as well as microemulsion systems containing CnmimBr/butan-1-ol/octane/brine were studied and compared. The Cn(Bim)2-2Br-based microemulsion systems have greater solubilization ability than that of the corresponding mono surfactants CnmimBr-based systems. As the carbon chain lengths of the surfactants [Cn(Bim)2-2Br and CnmimBr] increase, the mass fraction of the alcohol in the interfacial layer AS would decrease, whereas the solubilization ability (SP*) would increase. The maximum solubilization ability (SP*) of the two microemulsion systems was attained when the oil/water mass ratio (α) approaches 0.5. The solubilization ability of both microemulsion systems would increase with increasing NaCl concentrations in aqueous phase. In Cn(Bim)2-2Br-based microemulsion systems, the alcohol is significantly more soluble in aqueous phase than in the oleic phase. And it was noted that the alcohol is more soluble in Cn(Bim)2-2Br-based systems than in CnmimBr-based systems in both aqueous and oleic phases.

Interfacial Composition and Structural Parameters of Aqueous NaCl(HCl/NaOH)/CnmimBr/1-Pentanol/n-Octane Microemulsions

Abstract The interfacial composition, thermodynamic properties and structure parameters of the W/O microemulsion systems containing alkyl-3-methyl imidazolium bromide (CnmimBr, n = 12, 14, 16)/1-pentanol/n-octane/aqueous NaCl (HCl or NaOH) have been studied by a dilution method. The molar solubility of 1-pentanol in oil phase (Xoa) and the molar fraction of 1-pentanol at the interfacial layer (Xia) were obtained from the dilution equation of the W/O microemulsions. Furthermore, the distribution constant K of 1-pentanol between the interfacial layer and the bulk oil phase was determined, along with the standard Gibbs’ free energy change of transferring alcohol from the continuous oil phase to the interfacial layer, –ΔGoo→i. Some structure parameters related to the microemulsion droplets were also calculated. The effects of NaCl, HCl and NaOH on the properties and structures of the W/O microemulsions were also explored. It was found that as the content of the aqueous NaCl (HCl and NaOH) increases, Xoa and Xia would decrease, the formation of the microemulsion would be more thermodynamically spontaneous, and the radius of the water pool significantly increases.

Properties and ionic self-assembled structures from mixture of a bola-type strong alkali dication and a branched phosphoric acid.

Ionic self-assembled structures have been prepared successfully between di-(2-ethylhexyl) phosphoric acid (DEHPA) and hexamethonium hydroxide (HMO(OH)2). The DEHPA/HMO(OH)2 complexes show good surface activity at a wide mixing molar ratio of DEHPA to HMO(OH)2 (ρ), within which the critical micellar concentration (cmc) is far below that of any single component. In bulk aqueous solutions, rich phase behavior was observed by varying cDEHPA and cHMO(OH)2. When the concentration of HMO(OH)2 is in the range of 10-100 mmol L(-1), isotropic L1 phases, birefringent Lα phases and a phase-separated region were successively observed with increasing cDEHPA. At high cHMO(OH)2 range (>78 mmol L(-1)), a narrow L1/Lα two-phase region with the Lα phase at the bottom was noticed between the single L1 and single Lα phase regions. The rheological properties of the samples in the single Lα phase region at 2.6 ⩽ ρ ⩽ 2.8 are quite similar. Cryo-TEM and freeze-fracture TEM (FF-TEM) observations revealed the presence of multilamellar vesicles with flexible and even branched bilayers. At 2.2 ⩽ ρ ⩽ 2.6, however, the rheological properties are highly sensitive to ρ due to the sophisticated self-assembly behavior as proved by imaging studies and (2)H NMR measurements. Closely-stacked flat structures which look like foams or cellular networks have been newly discovered. Interestingly, NaCl could arouse an L1 to Lα phase transition due to the suppression of the effective area of the hydrophilic headgroups of the ionic complexes, leading to an increase of the critical packing parameter p. The viscoelasticity properties of the salt-containing Lα phases decreased with increasing salinity. We hope our research can provide new ideas for the construction of supramolecular materials by surfactant ionic self-assembly (SISA) strategy.

Phase Behavior and Solubilization of Microemulsion Systems Containing Imidazolium Type Surfactant CnmimBr and Butyric Acid as Cosurfactant

Abstract The phase behavior and solubilization of two microemulsion systems 1-alkyl-3-methylimidazolium bromide (CnmimBr, n = 12,14,16)/butyric acid/hexane/brine (5% NaCl) and CnmimBr/1-butanol/hexane/brine (5% NaCl) were studied and compared. The physico-chemical parameters, such as the solubility (∊B) of the cosurfactant, the mass fraction of the cosurfactant in the interfacial layer (AS), and the solubilization ability (SP*) of the two microemulsion systems were calculated and discussed. As the carbon chain length of CnmimBr molecules increases, SP* increases, and the difference of SP* values between the two microemulsion systems is reduced. The effects of aqueous and oleic phases and temperatures on the phase behavior and solubilization of C14mimBr/butyric acid/alkane/aqueous phase microemulsion systems were also discussed.

Phase Behavior of Microemulsions Prepared from Surfactant-like Ionic Liquids

Abstract The phase behavior and the influencing factors of middle phase microemulsions prepared from surfactant-like ionic liquid 1-alkyl-3-methylimidazolium bromide (C12mimBr, C14mimBr and C16mimBr) were studied systematically with Winsor-type phase diagrams. The minimum alcohol content needed to form the middle phase microemulsion, the alcohol width (the range of the alcohol concentrations from forming to disappearing of the middle-phase microemulsion) and the percent volume of the optimal middle phase at the midpoint of the middle phase region were obtained from the phase diagrams. It was found that with the increase in the carbon chain length of CnmimBr molecules, the minimum alcohol content and the alcohol width decrease, and the solubilization ability (the percent volume of the middle phase microemulsion) increases. With the increase in CnmimBr content, the minimum alcohol content increases, and the alcohol width increases at first and then decreases, and the solubilization ability of the microemulsion systems increases. The minimum alcohol content, the alcohol width and the solubilization ability are also influenced by alcohols, oils and brine. The minimum alcohol content and the alcohol width decrease, and the solubilization ability increases, with the increase in the carbon chain length of the alcohols, the decrease in the carbon chain length of the oils, and the increase in NaCl contents.