小角X射线散射表征AOT/水层状溶致液晶的有序性

用小角X射线散射研究了AOT/水层状溶致液晶的有序性. 通过对散射曲线的解析, 讨论了表面活性剂浓度、温度和助表面活性剂等三个方面对溶致液晶层状相结构有序性的影响. 在一定的范围内, 提高温度, 改变表面活性剂浓度和加入少量助表面活性剂可使碳氢链排列由稀疏转变为密实, 层状相也相应地由“柔性双层”过渡到更加有序化的“平面双层”. 基于形状因子和体系内分子间作用力, 提出了层状相形成与有序化的机理, 同时采用分子模拟的方法展现了不同浓度下的液晶结构.     

Water/ionic surfactant/alkanol/hydrocarbon systems. Realms-of-existence and transport properties of microemulsion type media

From a thorough study of many systems incorporating water, the ionic surfactant sodium dodecylsulfate, straighter or branched alkanols and aliphatic or aromatic hydrocarbons, it clearly appears that the molecular structure of the alkanol used as the cosurfactant is the composition factor that primarily determines the configuration of the microemulsion domain and, correlatively, the type of the microemulsion electroconductive and viscous behavior.     

Characterization of structural transitions in the SLS/decanol/water system

The ternary system sodium-dodecylsulphate (SLS)/decanol/water has been investigated at three different water contents and varying ratios of cosurfactant to surfactant by means of polarized optical microscopy,²H-NMR quadrupole splittings and small angle x-ray scattering. Upon addition of decanol a hexagonal phase transforms into a lamellar phase. For the highest water content of 0.65 no intermediate two-phase regions are detected but nematic phases are formed between. The lamellar phase at low cosurfactant content is very sensitive to changes of temperature and seems to be a so-called defective one with curved interfaces. From the scaling behavior it is concluded that the building units seem to be ribbons of increasing width on addition of cosurfactant or amphiphilic substance. By reaching a decanol mole fraction of 0.4 a classical lamellar phase with well-known behavior is formed. During these transformations the position of the first diffraction maximum changes gradually irrespective of phase transitions. The maximum mole fraction of cosurfactant the lamellar phase of our system can incorporate is 0.77.     

卵磷脂/正丙醇/肉豆蔻酸异丙酯/水微乳体系的相结构研究

以卵磷脂为表面活性剂,正丙醇为助表面活性剂,肉豆蔻酸异丙酯(IPM)为油相,配制成W/O型微乳。并通过浊点法、电导法、动态光散射法(DLS)以及差示扫描量热法(DSC)研究了微乳相结构随含水量的变化。对于选定配比微乳,浊点法在含水量超过10.71%时变浑浊;电导率在含水量达到3.85%之前增长缓慢,之后快速增大,含水量超过10.71%时电导率下降;DLS显示微乳粒径随含水量先减小后增大,其转折点在5.66%,而含水量超过10.71%后粒径突增3个数量级;DSC曲线在含水量超过3.85%后出现水的结晶峰,且随含水量的增大峰位往高温方向平移,同时峰面积增大。当含水量达到11.5%时出现两水峰叠加。研究表明含水量在3.85%~5.66%范围内属于W/O向双连续相转变的过程,而含水量10.71%则是体系发生相分离的临界点。     

A Visible Spectroscopic Study of Microstructure of O/W Microemulsions of Anionic Surfactants: Effect of Cosurfactant

The microstructure of o/w microemulsions, stabilized by sodium dodecyl benzene sulfonate (SDBS) and sodium dodecyl sulfate (SDS) with different cosurfactants, has been studied by partitioning of a dye, phenol red, between the oil‐water interface and bulk water. The cosurfactants used are propan‐1‐ol, propan‐2‐ol, butan‐1‐ol, butan‐2‐ol, pentane‐1‐ol, pentane‐2‐ol, and pentan‐3‐ol. The effects of changing the oil volume fraction and surfactant‐cosurfactant w/w ratio on the oil‐water interface and droplet size have also been discussed. Larger droplet size was predicted for SDS than SDBS. The predicted droplet radius increased with increase in the oil fraction, decrease in the surfactant concentration, increase in the C‐number of the linear cosurfactant, and decrease in branching of the cosurfactant. Surfactant‐cosurfactant ratio and pH did not affect the droplet size significantly. The minimum concentrations of surfactants with which microemulsions were formed were found to be higher for larger oil fraction, smaller C‐number of the alcohol, more branching of the alcohol, and higher pH.     

W/O microemulsions of styrene monomer and dimer

The reason for the lower water solubility in W/O microemulsions of the styrene dimer, trans, trans-1,4-diphenyl-1,3-butadiene, in comparison with the monomer was investigated by determining the phase equilibria in the microemulsion system with pentanol as the cosurfactant and sodium dodecyl sulfate as the surfactant. The main factor for the low tolerance for water in the system was the incompatibility of the dimer with the cosurfactant and surfactant.     

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.     

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     

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.     

Surfactant-free oil/water and bicontinuous microemulsion composed of benzene, ethanol and water

<正>Generally,a microemulsion consists of oil,water,surfactant and sometimes cosurfactant.Herein,we report a novel suffactant-free microemulsion(denoted as SFME) composed of benzene,water and ethanol without the amphiphilic molecular structure of traditional surfactant.The phase behavior of the ternary system was investigated,finding that there were a single-phase region and a two-phase region in ternary phase diagram.The electrical conductivity measurement was employed to investigate the microregion of the single-phase region,and a bicontinuous microregion and a benzene-in-water(O/W) microemulsion microregion were identified,which was confirmed by freeze-fracture transmission electron microscopy(FF-TEM) observations.The sizes of the microemulsion droplets are in the range of 20-50 nm.     

Emulsion stability in sucrose monoalkanoate system with addition of cosurfactants

The hydrophile-lipophile property of the sucrose monododecanoate changes from hydrophilic to lipophilic by adding an alcohol as a cosurfactant. With the addition of a short-alkyl-chain alcohol (pentanol, hexanol), the surfactant forms the middle-phase microemulsion whereas a lamellar liquid crystal (L_!) appears with a medium- or long-chain alcohol (heptanol, octanol, decanol) at the balanced state in water/ SE/ cosurfactant/ decane system. The effect of changing oil was also studied in the presence of a middle-chain cosurfactant (heptanol). A short-chain aromatic oil (m-xylene) forms middle-phase microemulsion whereas a longer aliphatic one (hexadecane) forms lamellar liquid crystalline phase in a dilute region when the HLB of surfactant is balanced in a given system. O/W emulsions become stable on the hydrophilic-surfactant-rich side whereas W/O emulsions are stable on the cosurfactant-rich side. Emulsions are very unstable in the three-phase regions. However, when the lamellar phase is produced, emulsions become stable at the balanced state because water and oil are incorporated in L_! phase in the longer cosurfactant systems such as water/ SE/ octanol/ decane and water/ SE/ decanol/ decane.     

Water Transport by Nanodispersion Droplets in a Water-in-Oil Emulsion

The mechanisms of water transport through an organic dispersion medium are considered for an emulsion during Ostwald ripening and for a three-phase system upon a contact of a water-in-oil emulsion with an external aqueous phase. Electron microscopy shows a formation of nanodispersion droplets during the diffusion of water through the organic phase of water-in-oil emulsions. The experimental water diffusion coefficient during Ostwald ripening in emulsions is 40 times smaller than the calculated molecular diffusion coefficient. The experimental diffusion coefficients are determined for rhodamine C, which solubilizes in the surfactant micelles, and for ethyl alcohol, a cosurfactant, which reduces the interfacial tension in the emulsion and promotes the formation of nanodispersion droplets. The experimental diffusion coefficients of rhodamine C and ethanol are three orders of magnitude smaller than the calculated values. The ratio between the numbers of rhodamine C and water molecules diffusing through the organic phase is 1 : 10000. The nanodispersion droplets are shown to make the main contribution to the water transport in the organic dispersion medium of the emulsions. Water can also be transported by single surfactant molecules, but this mechanism is not the predominant one.     

Wormlike micelles and microemulsions in aqueous mixtures of sucrose esters and nonionic cosurfactants

A study of the phase and rheological behavior of sucrose hexadecanoate (C16SE)/cosurfactant/water systems in the presence of solubilized oil, using complementary techniques such as dynamic light scattering and small angle X-ray scattering, is presented. Viscoelastic wormlike micellar solutions are found when a nonionic lipophilic cosurfactant is added to C16SE aqueous systems. Contrary to previous reports, the effect of oil solubilization on these wormlike micelles is not unique and depends on several factors. Linear alkyl chain oils that tend to solubilize in the micellar core have a disrupting effect, decreasing the relaxation time and the viscosity of the systems. This effect is larger as the molecular volume of oil increases and as the solubility of the cosurfactant in oil increases. On the other hand, oils that penetrate in the palisade layer, such as p-xylene, induce micellar growth and have a thickening effect at a given micellar composition. Thermodynamic considerations are used to explain the experimental results.     

Structural and spectroscopic investigation of ZnS nanoparticles grown in quaternary reverse micelles

ZnS nanoparticles were synthesized in four component "water in oil" microemulsions formed by a cationic surfactant (cetyltrimethylammonium bromide, CTAB), a cosurfactant (pentanol or butanol), n-hexane and water. The effect of various parameters (nature of cosurfactant, water/surfactant W(0), and alcohol/surfactant P(0)) on the formation and stability of ZnS nanoparticles was investigated thoroughly. UV-Vis spectroscopy was employed to directly follow the formation of ZnS systems in the microemulsions. Thus, particle size was estimated from the position of the first excitonic transition by employing an approximate finite-depth equation and an empirical correlation, giving average diameters in the ranges 2.3-2.5 and 3.0-3.5nm, respectively. Stable ZnS nanoparticles were obtained by employing low water and high cosurfactant amounts. This suggests that at high concentration the cosurfactant molecules act as capping agents on the surface of the inverse micelles, while low water amounts are needful to obtain water droplets with a radius close to that of the interfacial film spontaneous curvature. HRTEM analysis showed that the samples are formed by a few crystalline ZnS nanoparticles of spherical shape, embedded in and amorphous organic matrix, with a coherent scattering domain between 2 and 4nm.     

The structure of O/W microemulsions formulated with alkylglucosides

By following a method proposed by Kahlweit, an equilibrium diagram was determined in O/W quaternary microemulsions. These systems were formed by octanol (cosurfactant)/water/octane (oil)/alkylglucoside (surfactant). The experiment study was performed at two different temperatures (25°C and 50°C). The objective of this study work was to determine the structure of these lower microemulsions and to study the influence of the cosurfactant. Hence, different experimental techniques were employed: light scattering (static and dynamic), Kerr effect (static and dynamic), viscosity and refractometric measurements. It was concluded that the surfactant volume fraction in equilibrium with micelles is 0.044 and the micelle shapes are revolution ellipsoids.     

Percolation in alkyl polyglycoside microemulsions

Mixtures of oil, water, alkyl polyglycosides and long-chain alcohols form almost-temperature-invariant microemulsions. The phase behaviour depends on the content of cosurfactant, usually long-chain alcohols. We show that the system C_8/10G_1.5/octane/water/octanol exhibits cosurfactant-induced percolation phenomena. The percolation transition from an electrically conducting oil-in-water microemulsion to an electrically non-conducting water-in-oil microemulsion with increasing cosurfactant content is observed by measurements of electrical conductivity and time-resolved electric birefringence. The field-off relaxation time yields information on the internal length scale. The scaling behaviour of field-off relaxation times and Kerr constants with respect to the percolation point leads to insight into the influence of cosurfactant on phase behaviour. Received: 27 July 1999/Accepted: 8 February 2000     

无表面活性剂微乳液体系：N,N－二甲基甲酰胺/呋喃甲醛/水

通常微乳液一般由四个组分构成：水相、油相、表面活性剂和助表面活性剂。本文报道了一种不含表面活性剂的微乳液体系(简称SFME),由呋喃甲醛(油相),水和N,N－二甲基甲酰胺(DMF)三组分构成,不含传统的表面活性剂。对其相行为进行了研究,发现存在一个单相微乳液区和一个两相平衡区。采用电导率法和冷冻蚀刻电镜(FF-TEM)考察了单相区域中微乳液的微结构,结果表明可分为油包水(O/W)、双连续(BC)和水包油(W/O)三个区域。液滴直径介于40-70nm。     

Physicochemical studies on cetylammonium bromide and its modified (mono-, di-, and trihydroxyethylated) head group analogues. Their micellization characteristics in water and thermodynamic and structural aspects of water-in-oil microemulsions formed with them along with n-hexanol and isooctane

The micellization behavior of cetylammonium bromide and its mono-, di-, and trihydroxyethylated head group analogues and water/oil (w/o) microemulsion formation with them have been studied with detailed thermodynamic and structural considerations. The critical micellar concentration, micellar aggregation number, and behavior of the surfactants at the air/solution interface have been studied in detail. The results have been analyzed and discussed. The formation of the w/o microemulsion stabilized by the aforesaid surfactants in conjunction with the cosurfactant n-hexanol in isooctane has been investigated by the dilution method. The energetics of the transfer of cosurfactant from oil to the interface has been estimated. The structural parameters, namely, droplet dimension, droplet number, and population of surfactant and cosurfactant on the droplet surface, have also been estimated. The efficacy of the surfactants in respect to water dispersion in oil and cosurfactant concentration level at the oil/water interface has been worked out. Such microemulsions are prospective compartmentalized systems to assist enzyme activities. In this respect, the trihydroxyethylated head group analogue in the above series has been found to be a better performer for the preparation and stabilization of microemulsions that has correlated well with its performance than the others in the hydrolysis of p-nitrophenyl-n-hexanoate by the enzyme Chromobacterium viscosum lipase.     

BUTYL LACTATE: A USEFUL COSURFACTANT TO PREPARE O/W MICROEMULSIONS WITH SDS

The possibility of substitution of the conventional pentanol as cosurfactant by butyl lactate, on the preparation of OAV microemulsions in a system with SDS as anionic surfactant, is investigated. Whereas a narrow region of OAV microemulsion is described for the system with pentanol for a critical ratio 85/15 between water and SDS, butyl lactate leads to wider regions of solubility for different water/surfactant proportions, making easy the preparation of these microemulsions. Besides this advantage, being butyl lactate obtained from renewable resources and considered as a safe and biodegradable product, the microemulsions prepared with this cosurfactant could be applied in technological fields as cosmetic and dermopharmaceutical, where the biological agressivity of pentanol could avoid any practical application. As a complementary study, the influence that 1,3-buryleneglycol as polar cosolvent exert on the microemulsion regions, was also considered. Although according to experimental data given in the paper 1,3-butyleneglycol affects only slightly the OAV region of microemulsions, it can be foreseen that its presence could provide emollient characteristics to the final compositions.     

Structural changes induced by addition of a hydrocarbon to water/amphiphile mixtures

The phase conditions in a system of water, hexadecane, sodium dodecyl sulphate, and di-ethylene glycol dodecyl ether showed theW/O microemulsions to be obtained first after destabilization of a liquid crystalline phase by addition of the hexadecane. The original lamellar liquid crystalline phase was moved towards higher surfactant/cosurfactant ratios and a new phase with inverse amphiphile cylinders in a hexagonal packing appeared.