Phase behaviour and microstructures of microemulsions(Ⅰ)

By the orthogonal design,the optimal formation conditions for the middle-phase microemulsions in the system dioctadeeyldimethylammornum chloride (DODMAC)/ sodium dodecyl sulfate (SDS)/n-butanol/n-hep-ane/brine were obtained as follows.Investigations have been made on the effects of the concentrations of NaCl and n-butanol(1.0%-14.0%),the rantos of W to Wshs and the kinds of alcohols (n-propanol,n-butanol,and n-pentanol) on the formation,the phase behavtour,the ultralow interfacial tensions,the optimal salinity (S*),and the length of salinity (S).Some rules and data were worked out about the formation and characteristics of the middle-phase microemulsions.The mi-crostruenres of the middle-phase microemulsions were also studied by using FT-IR,ESR,and freeze fracture electron microscopy techmques The results from the three methods show that the microstructures of the middle-phase mi-croemnlsions undergo the change from O/W to bicontinuous(B C.) and to W/O.The distribution rule of the orga-mzed molecule ass     

Tween80/BmimPF6/醇/甲苯体系的相行为

以环境友好型的Tween80为表面活性剂, 以醇(乙醇、正丁醇、正己醇、正辛醇、正癸醇和异戊醇)为助表面活性剂, 对离子液体1-丁基-3-甲基咪唑六氟磷酸盐(bmimPF6)和甲苯进行了微乳化实验, 绘制了不同条件下Tween80离子液体的微乳体系的拟三元相图, 考察了醇的种类、含量对单相微乳区的影响, 并用电导法研究了在乙醇为助表面活性剂情况下, 单相微乳区的结构转变. 结果表明, 当醇(异戊醇)固定时, 随着表面活性剂/醇的质量比增加, 单相微乳区的面积逐渐增大; 不同链长的直链醇对单相微乳区的面积影响与该醇在离子液体中的溶解情况有关, 单相微乳区的面积随着直链醇链长的增加而越小; 当乙醇作助表面活性剂时, 所得到的单相微乳区的面积最大, 且单相微乳区存在着O/IL(oil-in-ionic liquid)、双连续相和IL/O(ionic liquid-in-oil)三种微结构. 尤其对离子液体微乳体系的电导随油的含量的增加而最初增大的现象进行了解释, 这一现象是由于油主要起到减少离子液体中离子对或离子的积聚, 提高带电离子淌度的作用.     

Study of nano-emulsion formation by dilution of microemulsions

The influence of different dilution procedures on the properties of oil-in-water (O/W) nano-emulsions obtained by dilution of oil-in-water (O/W) and water-in-oil (W/O) microemulsions has been studied. The system water/SDS/cosurfactant/dodecane with either hexanol or pentanol as cosurfactant was chosen as model system. The dilution procedures consisted of adding water (or microemulsion) stepwise or at once over a microemulsion (or water). Starting emulsification from O/W microemulsions, nano-emulsions with droplet diameters of 20 nm are obtained, independently on the microemulsion composition and the dilution procedure used. In contrast, starting emulsification from W/O microemulsions, nano-emulsions are only obtained if the emulsification conditions allow reaching the equilibrium in an O/W microemulsion domain during the process. These conditions are achieved by stepwise addition of water over W/O microemulsions with O/S ratios at which a direct microemulsion domain is crossed during emulsification. The nature of the alcohol used as cosurfactant has been found to play a key role on the properties of the nano-emulsions obtained: nano-emulsions in the system using hexanol as cosurfactant are smaller in size, lower in polydispersity, and have a higher stability than those with pentanol.     

SDBS／正辛烷／正丁醇／盐水体系中相微乳液微观结构的研究

利用冷冻蚀刻电镜、ＦＴ－ＩＲ、ＥＳＲ和ＮＭＲ方法研究了ＳＤＢＳ／ｎ－Ｃ４Ｈ９ＯＨ／ｎ－Ｃ８Ｈ１８盐水体系中相微乳液微观结构。四种方法均表现随着体系含盐度的增加，中相微乳液微观结构经历了从Ｏ／Ｗ型到Ｂ．Ｃ型，再到Ｗ／Ｏ型的转变。     

Phase behaviour and microstructures of microemulsions (I)

By the orthogonal design, the optimal formation conditions for the middle-phase microemulsions in the system dioctadecyldimethylammonium chloride (DODMAC)/ sodium dodecyl sulfate (SDS)/n-butanol/n-hep-tane/brine were obtained as follows: W_DODMAC: W_SDS = 1:4-1:5,C _π-butanol (%) = 11.0-12.0, andC _NaCl (%) = 3.25 Investigations have been made on the effects of the concentrations of NaCl and n-butanol (l.0%-14.0%), the ratios ofWDODMAC: to W_SDS, and the kinds of alcohols (n-propanol, n-butanol, and n-pentanol) on the formation, the phase behaviour, the ultralow interfacial tensions, the optimal salinity (S^*), and the length of salinity (δS). Some rules and data were worked out about the formation and characteristics of the middle-phase microemulsions. The mi-crostructures of the middle-phase microemulsions were also studied by using FT-IR, ESR, and freeze fracture electron microscopy techniques. The results from the three methods show that the microstructures of the middlephase mi-croemulsions undergo the change from O/W to bicontinuous (B.C.) and to W/O. The distribution rule of the orga-nized molecule assemblies in the middle-phase microemulsions is conducible to constructing the model of microemulsion systems, to recognizing the microstructures of the middle-phase microemulsions, and to setting forth the relationship between the microstructures and macro-properties of rnicroemulsions. Project supported by the Niltional Natural Science Foundation of China and the Chinese Postdoctoral Science Foundation.     

STATISTICAL MECHANICAL MODEL THEORY OF THE STABILITY OF O/W AND W/O MICROEMULSIONS

A theoretical model to clarify the molecular origin of the mechanical and thermal stabilities of O/W or W/O microemulsion is proposed in which the low concentration of surfactants (emulsifiers) is limited. We assume only a short range interaction between surfactants and a bending stiffness energy which expresses the deformation energy from a preferable monolayer membrane curvature. We have found an interrelation among the interfacial pressure, Δp, of the monolayer due to the adsorption of surfactants in the microemulsion interface, interfacial tensions of oil-water interface and of the microemulsion, and the bending stiffness energy. We conclude that the interfacial tension and the stable form of the microemulsions (O/W type or W/O type) are infuenced largely by the effect of the bending stiffness energy. The interrelationship between the therraodynamical and mechanical stabilities of microemulsions is clarified by the use of our assumption.     

Effect of ionic surfactants on the phase behavior and structure of sucrose ester/water/oil systems

The phase behavior and structure of sucrose ester/water/oil systems in the presence of long-chain cosurfactant (monolaurin) and small amounts of ionic surfactants was investigated by phase study and small angle X-ray scattering. In a water/sucrose ester/monolaurin/decane system at 27 degrees C, instead of a three-phase microemulsion, lamellar liquid crystals are formed in the dilute region. Unlike other systems in the presence of alcohol as cosurfactant, the HLB composition does not change with dilution, since monolaurin adsorbs almost completely in the interface. The addition of small amounts of ionic surfactant, regardless of the counterion, increases the solubilization of water in W/O microemulsions. The solubilization on oil in O/W microemulsions is not much affected, but structuring is induced and a viscous isotropic phase is formed. At high ionic surfactant concentrations, the single-phase microemulsion disappears and liquid crystals are favored.     

微乳液结构的研究

测定了十二烷基磺酸钠／正丁醇／２０％苯乙烯／水体系的相平衡，用冷冻刻蚀、ＥＳＲ、ＦＴ－ＩＲ研究了上述体系微乳液的结构，研究表明，苯乙烯含量恒定时，随着体系中水含量增加，电导确定的双连续结构的微乳液经历着从油包水到以连续再到水包油变化，ＦＴ－ＩＲ测定表明，Ｗ／Ｏ微乳兴较Ｏ／Ｗ微乳液的ＯＨ伸缩振动和弯曲振动频率有显著减小，说明Ｗ／Ｏ微乳兴中氢键缔合要比Ｏ／Ｗ强得多。ＥＳＲ测定表明Ｏ／Ｗ微乳液的旋转相关     

O/W微乳中的2，4-二硝基氯苯水解反应

微乳状液，简称微乳，通常是由表面活性剂、助表面活性剂、水和油形成的澄清、透明、稳定的分散体系．分散相直径一般在20-100nm之间[1].表面活性剂和助表面活性剂通常占微乳的15－25％（质量分数）[2]、典型的助表面活性剂是中等碳键长度的醇．显然，微乳是一种高度分散的间隔     

Formation of 1-Butyl-3-methylimidazolium Bis(2-ethyl-1-hexyl)sulfosuccinate Stabilized Water-in-1-Butyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)imide Microemulsion and the Effects of Additives

A new strategy is proposed here to formulate a bis(2-ethyl-1-hexyl)sulfosuccinate (AOT^?) stabilized water-in-ionic liquid microemulsion without any additives. Replacing the inorganic counter ion Na⁺ by the organic 1-butyl-3-methylimidazolium ([Bmim]⁺) ion greatly improves the solubility of AOT^? in hydrophobic 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Bmim]Tf₂N) (IL) and favors the formation of water-in-IL (W/IL) microdroplets. The existence of the W/IL microdroplets has been confirmed by dynamic light scattering, Fourier transform infrared absorption spectroscopy and ultraviolet–visible absorption spectroscopy. Also, presented for the first time are the effects of salts and alcohols on the microstructure and water solubilization capacity of the ternary H₂O/[Bmim]AOT/[Bmim]Tf₂N system. For inorganic salts, larger concentrations of the salt and higher charge density of the cation result in smaller microdroplet size and weak water solubilization capacity. For 1-hexanol, a high concentration of this alcohol results in small microdroplet size but high water solubilization capacity. Analyses indicate that the salts compress the electric double layers of W/IL microemulsions, decrease the size of the microdroplets and consequently reduce the water solubilization capacity; the alcohol, however, facilitates the aggregation of AOT^?, increases the number of W/IL microdroplets, and therefore improves the water solubilization capacity of the system.     

Microemulsion polymerization of acrylamide and styrene: Effect of the structures of reaction media

Isothermal phase diagrams of the system cetyltrimethylammonium bromide (CTAB)/n‐butanol/n‐octane/water were constructed, and the effect of the oil (n‐octane) contents on the microemulsions was studied at 40 °C. We determined the microemulsion structures of two systems, CTAB/n‐butanol/10% n‐octane/water and sodium dodecyl sulfonate (As)/n‐butanol/20% styrene/water, by conductivity measurements to investigate the polymerization of acrylamide and styrene in the two microemulsion systems. The polymerization kinetics of the water‐soluble monomer acrylamide in CTAB micelles and the different CTAB/n‐butanol/10% n‐octane/water microemulsion media [water‐in‐oil (W/O), bicontinuous (BC), and oil‐in‐water (O/W)] were studied with water‐soluble sodium bisulfite as the initiator. The maximum polymerization rate in CTAB micelles was found at the second critical micelle concentration. A mechanism of polyacrylamide formation and growth was proposed. A connection between the structures of the microemulsions and the polymerization rates was observed; the maximum polymerization rate occurred at two transition points, from W/O to BC and from BC to O/W, and the polyacrylamide molecular weights, which depended on the structures of the microemulsions, were also found. A square‐root dependence of the polymerization rates on the initiator concentrations was obtained in CTAB micelles and O/W microemulsion media. The polymerization of the oil‐soluble monomer styrene in different As/n‐butanol/20% styrene/water microemulsion media (W/O, BC, and O/W) was also investigated with different initiators: water‐soluble potassium persulfate and oil‐soluble azobisisobutyronitrile. A similar connection between the structures of the microemulsions and the conversions of styrene in CTAB/n‐butanol/10% n‐octane/water for the polymerization of acrylamide was observed again. The structures of the microemulsions had an important role in the molecular weights and sizes of polystyrene. The polystyrene particles were 10–20 nm in diameter in BC microemulsion media and 30–60 nm in diameter in O/W microemulsion media according to transmission electron microscopy. We determined the solubilization site of styrene in O/W microemulsion drops by ¹H NMR spectra to analyze the results of the microemulsion polymerization of styrene. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3320–3334, 2001     

THE HYDROLYSIS OF PHOSPHATIDYLCHOLINE BY PHOSPHOLIPASE A2 IN MICROEMULSION AS MICROREACTOR

Phosphotipase A₂ (PLA₂) was used to hydrolyze phosphatidylcholine (PC) in microemulsions. Phase diagrams were constructed for mixtures of alcohols (C₂-C₆), medium chain triglycerides (tricaprylin, TC) or vegetable oils, PC and water, and areas corresponding to isotropic systems were identified. The PC hydrolysis was carried out with high yields at various PC/(TC+alcohol) compositions within the areas of isotropic systems at increasing amounts of solubilized water.

The initial reaction rates depended on the aggregation state of the PC (size and nature of microemulsion structures), as well as on temperature and mode of calcium addition.

At low enzyme concentrations, hydrolysis was preceded by a “lag phase” followed by an abrupt increase in rate. By contrast, no latency was observed at higher PLA₂ PC ratios and the rate was significantly higher.

The easy access of the enzyme to the substrate in the curved phospholipid-containing microemulsion particles facilitate activation of the enzyme and “pushes” the reaction to completion. Hence, these microemulsions can serve as microreactors for the enzymatic high yield hydrolysis.     

Fluorescence quenching of anthracene by N,N-diethylaniline in the O/W microemulsion

Photoinduced electron-transfer system of anthracene-N,N-di-ethylaniline (DEA) was studied in the oil in water (O/W) mi-croemulsions formed by SDS (sodium dodecyl sulfate),BA (benzyl alcohol) and H2O.The time-resolved fluorescence study showed that the fluorescence quenching of the excited anthracene by DEA occurs at the interface of the O/W mi-croemulsions.Besides as the quencher of the excited anthracene,N,N-diethylaniline could act as a cosurfactant to change the structures of the microemulsions,just as BA did.The quenching rate constants for the different structures of the system were determined.     

醇对高效氯氟氰菊酯微乳液相图的影响

通过电导率的测定研究了高效氯氟氰菊酯微乳液的结构结构及结构转变。在表面活性剂、高效氯氟氰菊酯环己酮溶液、醇相对含量一定的情况下,当醇为乙醇时,微乳液经历了由W/O到双连续最后到O/W型的变化;当醇为正辛醇时,微乳液经历了由W/O到液晶、双连续最后到O/W型的变化。绘制了不同条件下高效氯氟氰菊酯微乳体系的拟三元相图,讨论了醇种类、醇含量对各类型微乳区形成的影响。结果表明,随着醇碳链的增大,微乳区面积先增大后减小;醇(正辛醇)固定时,随着醇含量增加,微乳区面积先减小后增大。     

MICROEMULSION SYSTEMS WITH A NONIONIC COSURFACTANT

The conditions to obtain W/0 microemulsions using ionic surfactants and a nonionic cosurfactant, a polyoxyethylene alkyl ether, were investigated. The length of the polyoxyethylene chain was critical to obtain the typical water solubilization maximum

The variation of the W/0 microemulsion region with hydrocarbon content was different from that of the usual type of microemulsions having a medium chain length alcohol as cosurfactant. In the present systems the W/0 microemulsion region was not a direct continuation of the inverse micellar area at zero content of hydrocarbon. Addition of hydrocarbon was necessary for the formation of inverse micelles

The microemulsion regions were sensitive to the kind of hydrocarbon used; a sign of the importance of the nonionic surfactant for the stability of this kind of microemulsions.     

FORMATION AND DECAY KINETICS OF BACTERIORHODOPSIN'S N INTERMEDIATE: SOFTENING THE PROTEIN CONFORMATION WITH ALCOHOLS AFFECTS INTRA-PIROTEIN PROTON TRANSFER AND RETINAL ISIOMERIZATION

Abstract— The trans photocycle of bacteriorhodopsin was investigated in the presence of organic solvents with a hydrogen-bonding group; i.e . methanol, ethanol, 1-propanol and so on. These alcohols scarcely or only slightly affected the L→M and O₅₇₀ transitions, but they perturbed the M→N and N→O transitions greatly. The rate of the M→N transition increased linearly with increasing alcohol concentration and, at maximal alcohol concentrations under which the native protein conformation was retained, the M→N transition was accelerated by a factor of ∼5. This alcohol effect was reversible. It is suggested that a long-distance proton transfer involved in the M→N transition (Asp.96→retinal) becomes easier when the protein conformation is softened bv partially breaking hydrogen-bonding networks in the protein. Another significant effect of alochol is inhibition of the N→O transition at weakly acidic pH, which was slowed down maximally by a factor of ˜10. This alcohol effect was less significant at alkaline pH, where reprotonation of Asp-96 from the cytoplasmic membrane surface is a rate-limiting reaction. It is suggested that, at acidic pH, thi: cis-to-trans isomerization involved in the N→O transition is a rate-limiting reaction and that this step is inhibited in the presence of a high concentration of alcohols.     

Microemulsions as microreactors for food applications

Major recent advances. Structured self-assembled liquids have been considered as efficient microreactors for organic and enzymatic reactions. Only recently scientists learned to use food-grade cosolvents and coemulsifiers together with hydrophilic non-ionic surfactants and to construct U-type phase diagrams with large isotropic regions ranging continuously from the oil-rich corner to the water-rich corner without any phase separation. The U-type microemulsions facilitate triggering and control of certain reactions by changing water activities. Maillard thermal degradation between sugars and amino acids is the main, and almost the only, chemical reaction that has been studied in food-grade microemulsions. Some examples of recent studies include: Maillard processes in binary structured fluids composed of monoglycerides of fatty acids and water forming microemulsions and lyotropic liquid crystalline structures; pseudoternary and pseudoquaternary W/O microemulsions; U-type microemulsions (W/O, O/W and bicontinuous microemulsions); enzymatic reactions aimed to prepare other surfactants such as sugar esters, monoglycerides and lysolecithins or triglycerides. Reactions in microreactors lead to unique new products. The reaction products and rates are controlled by the hydrophilicity/lipophilicity of the reagents (guest molecules), their molar ratios, type of oil phase, nature of surfactants and oil/surfactant ratios, nature of curvature and its elasticity (adjusted by cosolvent and coemulsifier) and by the water activity. The field is in its infancy and will need work of many more model reactions before it will be used in industrial food applications. Enzymatic reactions in non-food microemulsions are common practice but only few examples of food microemulsions as enzymatic microreactors have been extensively studied.     

Tailoring of horseradish peroxidase activity in cationic water-in-oil microemulsions

Horseradish peroxidase (HRP) in cationic water-in-oil (W/O) microemulsions has always been ignored in reverse micellar enzymology, mainly because cationic surfactants are inhibitors of enzyme peroxidase. In the present study, for the first time, we have successfully introduced the cationic W/O microemulsion as an attractive host for efficient HRP activity. To this notion, much improved activity of HRP was observed in the W/O microemulsion of cetyltrimethylammonium bromide (CTAB) with an increase in n-hexanol concentration and W0 ([water]/[surfactant]), presumably due to the increased interfacial area of the microemulsions. In support of our above observation, six surfactants were synthesized with an increased headgroup size where the methyl groups of CTAB were subsequently replaced by the n-propyl and 2-hydroxyethyl groups, respectively, to prepare mono-, di-, and tripropylated/hydroxyethylated n-hexadecylammonium bromide. The peroxidase activity enhanced with headgroup size and also followed an overall trend similar to that found in the case of CTAB. Possibly, the reduced positive charge density at the augmented interfacial area by means of increase, either in headgroup size, cosurfactant concentration, and/or W0, is not capable of inactivating HRP. Also, the larger space at the interface may facilitate easier solubilization of the enzyme and increase the local concentration of enzyme and substrate, leading to the higher activity of HRP. The best activity was obtained with surfactant N-hexadecyl-N,N,N-tripropylammonium bromide, the highest ever found in any cationic W/O microemulsions, being almost 3 times higher than that found in water. Strikingly, this observed highest activity is comparable with that observed in an anionic bis(2-ethylhexyl)sulfosuccinate sodium salt (AOT)-based system, the best W/O microemulsions used for HRP.