An attempt to detect bicontinuity from SANS data

SANS is a powerful tool to characterise microemulsions, which can have a discontinuous droplet-like structure (oil in water (O/W), water in oil (W/O)) or a bicontinuous one. In the present study, we try to distinguish O/W, W/O and bicontinuous microemulsions by SANS measurements under practical conditions and by a certain evaluation technique. For this reason we chose the well characterised ternary system water-non-ionic surfactant (C(12)E(5))-oil (n-octane), at a fixed surfactant concentration and performed SANS measurements throughout its one-phase channel where droplet-like phases as well as bicontinuous phases are well established. We evaluated the scattering data via the 'Generalised Indirect Fourier Transformation' method (GIFT) which is based on a particulate picture. It should therefore give good results in the droplet domains while a poor fit could be expected for the bicontinuous regime. For comparison we also applied the model of Teubner and Strey (TS) which was developed especially for bicontinuous phases, here a bad fit can be expected for the particulate regime. The data evaluation via GIFT leads to relatively good fits throughout the one-phase channel. The results are physically meaningful and are comparable to those of the TS model. We show that the scattering pattern of a bicontinuous microemulsion can be represented by that of a polydisperse particulate system. This is in clear contradiction to the expectation that the particle picture used in the GIFT method must fail when the bicontinuous regime is reached.     

Decontamination of chemical warfare agents using perchloroethylene–Marlowet IHF–H2O-based microemulsions: wetting and extraction properties on realistic surfaces

At the present time, considerable efforts are being made to develop new media for the decontamination of a variety of toxic compounds. In the present contribution, new microemulsions with promising properties are presented. Moreover, the decontamination of surfaces, with an emphasis on varnished metal surfaces of exterior and interior equipment, is investigated using these microemulsions. Studies of the phase behavior of the system water–perchloroethylene–IHF–2-propanol are reported and the microemulsion phases are recognized. The wetting behavior on contaminated surfaces and the extraction capabilities with respect to contaminants are essential for an efficient decontamination. Hence, suitable microemulsions are identified on the basis of these properties. The decontamination efficiency of these microemulsions is first estimated on the basis of the ability to wet typical chemical nonresistant varnished steel sheets, which are authentic model systems for real surfaces. Afterwards, promising microemulsions and, as reference, different solvents are tested with respect to their capability to solubilize sulfur-mustard agent, again using realistic surfaces contaminated with this chemical warfare agent. Several microemulsions are found, which have the desired properties.     

Gelled polymerizable microemulsions. 2. Microstructure

Using bicontinuous microemulsions as templates opens a new field for the design of novel structures and thus novel materials, but has significant challenges due to the very small composition and temperature windows in which microemulsions are bicontinuous. In previous work we had shown that we can take a ternary base system (water-n-dodecane--C 13/15E 5), add monomer and cross-linker ( N-isopropylacrylamide and N, N'-methylenebisacrylamide) to the water phase, and add a gelator (12-hydroxyoctadecanoic acid) to the oil phase while remaining in the one-phase region of the phase diagram. It was also possible to allow the gelator to form an organogel by changing the temperature such that we crossed the sol--gel line, which fell within the one-phase region. In this work, we show conclusively that addition of the monomers and the gelator does not affect the microemulsion microstructure and that, even in the gelled state, the polymerizable microemulsion is indeed bicontinuous. 1H NMR self-diffusion, conductivity, and small-angle neutron scattering measurements all confirm the bicontinuous nature of the gelled polymerizable microemulsion.     

The effect of structure of oil phase, surfactant and co-surfactant on the physicochemical and electrochemical properties of bicontinuous microemulsion

Efforts were made to prepare bicontinuous microemulsions with ten different oil phases involving aliphatic, linear, and aromatic hydrocarbons as oil phases, two co-surfactants (n-butanol and n-pentanol) and two surfactants: cationic (CTAB) and anionic (SDS). Different weight percentages were employed for the preparation of cationic and anionic surfactant based microemulsions as reported in the literature. Out of the 40 compositions (10 oil phasesx2 co-surfactantsx2 surfactants) thus selected only 28 systems showed stable bicontinuous microemulsion phase. This behavior is explained on the basis of the structures of various constituents present in the microemulsions. Viscosity variations of stable bicontinuous microemulsions are found to depend mainly on the nature of co-surfactant. Conductivity behavior on the other hand depends mainly on the weight percentage and composition of aqueous phase. The solubility of pyrene in the oil phase determines the excimer formation and fluorescence behavior in microemulsions. The electron transfer property of both the water-soluble and the oil-soluble redox systems does not depend on the oil phase and the co-surfactant. The significance and importance of characterizing well defined bicontinuous microemulsions is thus highlighted.     

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.     

Design of highly porous melamine-based networks through a bicontinuous microemulsion templating strategy

Designing low density polymeric porous materials with defined pore sizes (diameters in the 100 nm range) still remains a real synthesis challenge. Here, for the first time, we present a strategy by which bicontinuous microemulsions are used as templating agents for the in-situ aqueous polycondensation of organic resins (melamine formaldehyde, MF). The behaviour of surfactants with different head-groups in systems including oil and MF-containing aqueous phase is studied. While many surfactants are not compatible with aqueous MF precondensates, here we report a non-ionic surfactant either used solely or along with anionic surfactants which prove to be successful at keeping bicontinuous microemulsion systems homogeneous even during early stages of polymerisation. However, upon acid-catalysis it becomes clear that the pore structure of the organic material is largely controlled by the kinetics of phase separation due to the sol–gel process rather than by the thermodynamic equilibrium of the template (microemulsion). Indeed, despite numerous attempts, stabilising the microemulsion interface with zero curvature (bicontinuous) has remained problematic. Instead, we show a new behaviour for the MF resin whereby non-spherical MF morphologies (i.e. thread-like structures) can be obtained by specific interactions between the aqueous amino resin and the acid counterions.     

Mesoscopic scale structures in self-organized surfactant solutions determined by small-angle neutron scattering

A novel procedure for SANS data analysis is described which enables one to use the fitted parameters to compute the average mean, Gaussian and square mean curvatures of the interface in systems which show a micro-phase-separated bicontinuous structure. This procedure also leads to a 3-D reconstruction of the connected internal interface which allows one to visualize the mesoscopic scale morphology of the material. The method has been successfully applied to various bicontinuous structures such as microemulsions made of surfactant, water and oil, porous silica glasses and phase-separated homopolymer blends. In this lecture, we show examples of analyses of SANS data taken from one-phase bicontinuous microemulsions at the hydrophile-lipophile-balance temperature and a light scattering intensity taken from a symmetric micro-phase-separated polymer blend at the late stage of spinodal decomposition.     

Hollow-fiber membranes coated with polymerizable bicontinuous microemulsions

A new method has been successfully employed to prepare hollow-fiber membranes by coating and polymerizing bicontinuous microemulsions onto the internal surfaces of hollow-fiber membranes. The bicontinuous microemulsion consisting of water, a polymerizable zwitterionic surfactant of acryloyloxyundecyl dimethylammonio acetate, methyl methacrylate, and 2-hydroxylethyl methacrylate (HEMA) can form a transparent polymer thin film after polymerization. The hollow-fiber membranes as the supports for microemulsion coatings were fabricated from the spinning solution of polyethersulfone/diethylene glycol/N-methyl-2-pyrrolidone. The microemulsion coated hollow-fiber membranes were evaluated by the separation efficiency and the permeation rate of polyethylene glycol (PEG) solutions. The performance of coated membrane on the PEG separation is strongly dependent on the concentration of HEMA and water in precursor bicontinuous microemulsions. The pore size of the hollow-fiber membranes can be regulated between about 2 to 40 nm by varying the composition of precursor bicontinuous microemulsions. The characteristics of the coated membranes is believed to be directly related to the bicontinuous structures of precursor bicontinuous microemulsions. The use of polymerizable bicontinuous microemulsions enable one to better control the microstructures of coated membranes via in situ polymerization.     

Probing the microstructure of nonionic microemulsions with ethyl oleate by viscosity, ROESY, DLS, SANS, and cyclic voltammetry

Microemulsions are important formulations in cosmetics and pharmaceutics and one peculiarity lies in the so-called "phase inversion" that takes place at a given water-to-oil concentration ratio and where the average curvature of the surfactant film is zero. In that context, we investigated the structural transitions occurring in Brij 96-based microemulsions with the cosmetic oil ethyl oleate and studied the influence of the short chain alcohol butanol on their structure and properties as a function of water addition. The characterization has been carried out by means of transport properties, spectroscopy, DLS, SANS, and electrochemical methods. The results confirm that the nonionic Brij 96 in combination with butanol as cosurfactant forms a U-type microemulsion that upon addition of water undergoes a continuous transition from swollen reverse micelles to oil-in-water (O/W) microemulsion via a bicontinuous region. After determining the structural transition through viscosity and surface tension, the 2D-ROESY studies give an insight into the microstructure, i.e., the oil component ethyl oleate mainly is located at the hydrophobic tails of surfactant while butanol molecules reside preferentially in the interface. SANS experiments show a continuous increase of the size of the structural units with increasing water content. The DLS results are more complex and show the presence of two relaxation modes in these microemulsions for low water content and a single diffusive mode only for the O/W microemulsion droplets. The fast relaxation reflects the size of the structural units while the slower one is attributed to the formation of a network of percolated microemulsion aggregates. Electrochemical studies using ferrocene have been carried out and successfully elucidated the structural transformations with the help of diffusion coefficients. An unusual behavior of ferrocene has been observed in the present microheterogeneous medium, giving a deeper insight into ferrocene electrochemistry. NMR-ROESY experiments give information regarding the internal organization of the microemulsion droplets. In general, one finds a continuous structural transition from a W/O over a bicontinuous to an O/W microemulsion, however with a peculiar network formation over an extended concentration range, which is attributed to the somewhat amphiphilic oil ethyl oleate. The detailed knowledge of the structural behavior of this type of system might be important for their future applications.     

Dynamic properties of microemulsions modified with homopolymers and diblock copolymers: the determination of bending moduli and renormalization effects

The properties of bicontinuous microemulsions, consisting of water, oil, and a surfactant, can be modified by the addition of diblock copolymers (boosting effect) and homopolymers (inverse boosting effect) or a combination of both. Here, the influence of the addition of homopolymers (PEP(X) and PEO(X), X=5k or 10k molecular weight) on the dynamics of the surfactant layer is studied with neutron spin echo spectroscopy (NSE). Combining the results with the previous findings for diblock copolymers allows for a better separation of viscosity and bending modulus effects. With the addition of homopolymers, a significant increase of the relaxation rate compared to the pure microemulsion has been observed. The influence on the bending rigidity kappa is measured with NSE experiments. Homopolymer addition reduces kappa by up to Deltakappa approximately -0.5k(B)T, whereas the diblock copolymer yields an increase of kappa by approximately 0.3k(B)T. Comparison of the bending moduli that are obtained by analysis of the dynamics to those obtained from small angle neutron scattering (SANS) sheds light on the different renormalization length scales for NSE and SANS. Variation of the surfactant concentration at otherwise constant conditions of homopolymer or diblock-copolymer concentration shows that NSE results are leading to the pure bending rigidity, while the renormalized one is measured with SANS.     

TX-100/water/1-butyl-3-methylimidazolium hexafluorophosphate microemulsions

Both ionic liquids and water are typical green solvents. In this work, the phase behavior of the ternary system consisting of ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6), TX-100, and water was determined at 25.0 degrees C. The water-in-bmimPF6, bicontinuous, and bmimPF6-in-water microregions of the microemulsions were identified by cyclic voltammetry method using potassium ferrocyanide K4Fe(CN)6 as the electroactive probe. Dynamic light scattering (DLS) and the UV-vis method were used to characterize the microemulsions. It was demonstrated that the hydrodynamic diameter (Dh) of the bmimPF6-in-water microemulsions is nearly independent of the water content but increases with increasing bmimPF6 content due to the swelling of the micelles by the ionic liquid. The UV-vis further confirmed the existence of water domains in the water-in-bmimPF6 microemulsions, and the salt potassium ferricyanide K3Fe(CN)6 could be dissolved in the water domains.     

Structural changes in poly(ethyleneimine) modified microemulsion

The influence of branched poly(ethyleneimine) on the phase behavior of the system sodium dodecylsulfate/toluene-pentanol (1:1)/water has been studied. The isotropic microemulsions still exist when water is replaced with aqueous solutions of PEI (up to 30% in weight), but their stability is significantly influenced. From a polymer concentration of 20 wt%, the polymer enhances the solubilization of water in oil, changes the sign of the spontaneous curvature of the surfactant film, and induces an inversion of the microemulsion type from water-in-oil (L(2)) to oil-in-water (L(1)), by the formation of a bicontinuous channel. Further investigations show that the addition of polymer in the L(2) phase changes the droplet-droplet interactions as the conductivity drops and the percolation disappears. In the bicontinuous channel, higher viscosities can be detected, as well as a weak percolation followed by a steep increase of the conductivity, which can be related to evident structural changes in the system. DSC measurements allow then to follow the changes of the water properties in the system, from interfacial-water in the L(2) phase to free-water in the sponge-like phase. Finally, all the measurements performed permit to characterize the structural transitions in the system and to understand the role of the added polymer.     

双连续相微乳液辐射聚合制备多孔材料的研究

利用6 0 Co γ射线在室温下辐照双连续相微乳液体系以制备多孔聚合物材料 ,试图在控制多孔材料的微孔结构形态和减少微乳液聚合过程中的相分离方面做一些探索 .通过电导率的测量分析微乳液的结构类型 ,并确定微乳液的双连续相区域范围 .微乳液聚合后所得的样品的孔结构和聚合前的微乳液结构类型有关 ,扫描电镜和热重分析的结果表明双连续相微乳液在聚合时容易发生相分离 ,未必能够得到开孔结构的聚合物 .但适当控制聚合前微乳液的组成 ,如选择合适的水油比例、交联剂的用量和加入一些功能性单体 (如甲基丙烯酸或丙烯酸钠 ) ,可以有效地抑制相分离 ,调节所得聚合物的结构形态 .     

Studies on the micropolarities of bmimBF4/TX-100/toluene ionic liquid microemulsions and their behaviors characterized by UV-visible spectroscopy

Ionic liquids (ILs), 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4), were substituted for polar water and formed nonaqueous microemulsions with toluene by the aid of nonionic surfactant TX-100. The phase behavior of the ternary system was investigated, and microregions of bmimBF4-in-toluene (IL/O), bicontinuous, and toluene-in-bmimBF4 (O/IL) were identified by traditional electrical conductivity measurements. Dynamic light scattering (DLS) revealed the formation of the IL microemulsions. The micropolarities of the IL/O microemulsions were investigated by the UV-vis spectroscopy using the methyl orange (MO) and methylene blue (MB) as absorption probes. The results indicated that the polarity of the IL/O microemulsion increased only before the IL pools were formed, whereas a relatively fixed polar microenvironment was obtained in the IL pools of the microemulsions. Moreover, UV-vis spectroscopy has also shown that ionic salt compounds such as Ni(NO3)2, CoCl2, CuCl2, and biochemical reagent riboflavin could be solubilized into the IL/O microemulsion droplets, indicating that the IL/O microemulsions have potential application in the production of metallic or semiconductor nanomaterials, and in biological extractions or as solvents for enzymatic reactions. The IL/O microemulsions may have some expected effects due to the unique features of ILs and microemulsions.     

Interfacial Modification and Structural Transitions Induced by Guest Molecules Solubilized in U‐Type Nonionic Microemulsions

Abstract

Alcohols and polyols are essential components (in addition to the surfactant, water, and oil) in the formation of U‐type self‐assembled nano‐structures, (sometimes called L‐phases or U‐type microemulsions). These microemulsions are characterized by large isotropic regions ranging from the oil side of the phase diagram up to the aqueous corner. The isotropic oily solutions of reverse micelles (“the concentrates”) can be diluted along some dilution lines with aqueous phase to the “direct micelles” corner via a bicontinuous mesophases (i.e., two structural transitions). This dilution takes place with no phase separations or occurrence of liquid crystalline phases. The structural transitions were determined by viscosity, conductivity, and pulsed gradient spin echo NMR (PGSE NMR), and are not visible to the eye. Two guest nutraceutical molecules (lutein and phytosterols) were solubilized, at their maximum solubilization capacity, in the reversed micellar solutions (L₂ phase) and were further diluted with the aqueous phase to the aqueous micellar corner (L₁ phase). Structural transitions (for the two types of molecule) from water‐in‐oil to bicontinuous microstructures were induced by the guest molecules. The transitions occurred at an earlier stage of dilution, at a lower water content (20 wt.% aqueous phase), than in the empty (blank) microemulsions (transitions at 30 wt.% aqueous phase). The transitions from the bicontinuous microstructure to the oil‐in‐water microemulsions were retarded by the solubilizates and occurred at later dilution stage at higher aqueous phase contents (50 wt.% aqueous region for empty microemulsion and >60 wt.% for solubilized microemulsion). As a result, the bicontinuous isotropic region, in the presence of the guest molecules, becomes much broader. It seems that the main reason for such “guest‐induced structural transitions” is related to a significant flattening and enhanced rigidity of the interface. The guest molecules of the high molecular volume are occupying high volume fraction of the interface (when the solubilization is maximal).     

Anaerobic toxicity and biodegradability of hydrolysis products of chemical warfare agents

The toxicity and biodegradability of the main hydrolysis products of chemical warfare agents were investigated under methanogenic conditions. Among the tested substances, only MPhA does not have any toxic effect with regard to the aceticlastic methanogenic activity. The toxicity of other compounds varied between moderate (TDG, mercaptoethanol) to strong (ethanolamine, diisobutyl ester of MPhA). Biodegradability tests showed that all the products of chemical detoxification of mustard gas (ethanolamine, ethylene glycol, TDG, mercaptoethanol) can be biomineralized under methanogenic conditions. On the contrary, phosphorus-containing compounds from the chemical detoxification of nerve warfare agents (Sarin, Soman, V_x-gases) are quite persistent under these conditions.     

From the plateau problem to periodic minimal surfaces in lipids,surfactants and diblock copolymers

A novel method is presented for generating periodic surfaces. Such periodic surfaces appear in all systems which are characterized by internal interfaces and which additionally exhibit ordering. One example are systems of AB diblock copolymers, where the internal interfaces are formed by the chemical bonds between the A and B blocks. In these systems at least two bicontinuous phases are formed: the ordered bicontinuous double diamond phase and the gyroid phase. In these phases the ordered domains of A monomers and B monomers are separated by a periodic interface of the same symmetry as the phases themselves. Here we present a novel method for the generation of such periodic surfaces based on the simple Landau-Ginzburg model of microemulsions. We test the method on four known minimal periodic surfaces, find two new surfaces of cubic symmetry, and show how to obtain periodic surfaces of high genus and n-tuply continuous phases (n > 2). So far only bicontinuous (n = 2) phases have been known. We point out that the Landau model used here should be generic for all systems characterized by internal interfaces, including the diblock copolymer systems.     

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     

微乳液聚合制备多孔高吸油甲基丙烯酸酯类树脂的研究

研究了双连续相微乳液聚合制备多孔高吸油树脂,以甲基丙烯酸甲酯(MMA)、丙烯酸丁酯(BA)为共聚单体(油相),水(H2O)/乙醇(EtOH)为混合水相,2,2′-偶氮二异丁腈(AIBN)为引发剂,采用十二烷基硫酸钠(SDS)和复配十二烷基硫酸钠/吐温80(SDS/T80)两种乳化体系,调节油相和水相比例,配制出双连续相微乳液.聚合在无搅拌下进行.研究了乳化体系、混合水相含量、单体配比、交联剂和引发剂用量等因素对树脂吸油性能的影响.结果表明,多孔高吸油树脂比同系无孔树脂的吸油速率大大提高,最快可以在2min内达到吸油饱和.树脂对苯,四氢呋喃,四氯化碳的吸油倍率分别达到15.5g/g,15.5g/g,31.7g/g.     

Sugar-based microemulsion glass templates

Complex fluids comprising of surfactants with water and/or oil form a rich variety of dynamic self-assembled structures, ranging from spherical swollen micelles, viscous rod-like micelles, and bicontinuous microemulsions to ordered liquid crystalline phases. The wide range of practical and specialized applications of complex fluids has made them the subject of intense research for many decades. Here, we demonstrate for the first time how bicontinuous microemulsions containing equal masses of oil and sugar can be driven to the glassy state without phase separation at ambient temperatures by controlled desiccation of sugar-rich microemulsions. The robust nanostructure of these microemulsion glasses allows polymerization of hydrophobic liquid monomers within the interstices of the glassy microemulsion template without macroscopic phase separation. Yet after polymerization, the sugar and surfactant template can be easily removed by dissolution in water.