烷基聚葡糖苷C9.6G1.3/n-C4H9OH/n-C6H14/H2O微乳液体系的介电弛豫谱研究

The pseudotertiary phase diagram of the microemulsion system alkyl polyglucoside/n-butanol/n-hexane/water was plotted at （30.0±0.1） ℃. The dielectric measurements, including permittivity, conductivity, relaxation strength, characteristic relaxation time, etc,, were applied to investigate the microstructure of the system. Unique dielectric relaxations were observed over the frequency range of 5-10^7 Hz, taking place possibly through an interracial polarization mechanism. According to the results obtained from dielectric spectroscopy, the structures of the microemulsion O/W, BC and W/O were determined, and some dielectric and phase parameters were calculated.     

Theory of dielectric relaxations due to the interfacial polarization for two-component suspensions of spheres

A theoretical formula of dielectric relaxation in a form of complex relative permittivity is derived for dilute suspensions of spherical particles of two kinds on the basis of the Maxwell-Wagner theory of interfacial polarization. Another theoretical formula is derived further for concentrated suspensions of spheres of two kinds on condition that the formula derived above holds for the infinitesimally increasing process in concentration of the dispersed spheres. Furthermore a theoretical formula is derived for concentrated suspensions of shelled spheres of two kinds as the extension of the formula for concentrated suspensions. By use of the theoretical formulas proposed, values of the permittivities and the conductivities of the two-component suspensions were calculated for some examples with different sets of phase parameters. Results of the numerical calculation demonstrates dielectric relaxation profiles full of variety and characteristic of the suspensions containing two kinds of spheres covered with or without shells.     

壳聚糖微球悬浊液的介电谱研究: 弛豫机制的解释和内部信息的获得

结合DLVO理论和壳聚糖微球的特点, 提出了适合实验数据的电动力学模型, 并分析了浓厚分散系的界面极化弛豫的微观机制. 进而测量了不同粒径壳聚糖微球悬浊液的介电谱, 发现在10～100 MHz频率范围内均出现明显的介电弛豫现象. 利用上述模型合理解释了该弛豫现象以及微球粒径对界面极化弛豫的影响, 结果也证明了我们提出的模型的适当性. 此外, 利用Hanai方法, 通过介电参数准确计算出了各悬浊液的内部信息, 并且分析了这些实时信息的合理性. 研究结果从实验和理论两方面展示了介电谱方法在即时获取壳聚糖内部信息上的独到优势.     

稀薄细胞悬浊系模型的介电解析法

对稀薄细胞粒子是浊液体系进行了介电模型化,在导出的描述该体系介电行为的理论公式的基础上,确立了从实验观察到的介电参数获得体系相参数的精确解析方法,对该体系可能产生介电弛豫的原因进行了现象论的分析,并以一个微胶囊作为细胞模型进行了介电测量和解析,获得了合理的结果.     

Dielectric model and theoretical analysis of cationic reverse micellar solutions in CTAB/isooctane/n-hexanol/water systems

Dielectric relaxation spectra of CTAB reverse micellar solutions, CTAB/isooctane/n-hexanol/water systems with different concentrations of CTAB and different water contents, were investigated in the frequency range from 40 Hz to 110 MHz. Two striking dielectric relaxations were observed at about 10(4) Hz and 10(5) Hz, respectively. Dielectric parameters were obtained by fitting the data using the Cole-Cole equation with two Cole-Cole dispersion terms and the electrode polarization term. These parameters show different variation with the increase of the concentration of CTAB or the water content. In order to explain the two relaxations systematically and obtain detailed information on the systems and the inner surface of the reverse micelles, an electrical model has been constituted. On the basis of this model, the low-frequency dielectric relaxation was interpreted by the radial diffusion of free counterions in the diffuse layer with Grosse model. For the high-frequency dielectric relaxation, Hanai theory and the corresponding analysis method were used to calculate the phase parameters of the constituent phases in these systems. The reasonable analysis results suggest that the high-frequency relaxation probably originated from the interfacial polarization. The structural and electrical information of the present systems were obtained from the phase parameters simultaneously.     

聚吡咯微粒掺入的聚苯乙烯膜在电解质溶液中的介电弛豫谱及其解析

在40 Hz～11 MHz频率范围测量了聚苯乙烯膜以及混入聚吡咯粒子的聚苯乙烯膜和电解质溶液构成的体系的介电谱, 发现了特异的弛豫现象: 纯的和掺入导电性聚吡咯后的聚苯乙烯膜分别显示出单一弛豫和双弛豫的不同模式的介电谱. 在Maxwell-Wagner界面极化概念基础上解释了该弛豫机制: 高、低频弛豫分别由膜-液界面极化和膜相本身的不均一性引起的. 将体系进行了模型化, 并利用Hanai理论方法对谱进行了解析, 获得了内部电性质的诸多参数. 对不同聚吡咯掺入量的膜/溶液体系的介电测量和解析结果表明, 电解质溶液的种类、浓度以及膜中混入聚吡咯的量都影响着膜相的介电响应. 这些结论为利用加入导电粒子改善绝缘高分子聚合物的电性质的研究以及制备既具有导电功能又使基体的力学性能得到提高的高分子复合物提供了重要的线索.     

Dielectric behavior of double emulsions with "core-shell droplet" morphology

The dielectric behavior of double emulsions with "core-shell droplet" morphology is investigated over a broad range of frequency. A new modified Pauly-Schwan model is proposed for the complex permittivity of double emulsions. The proposed model takes into consideration the morphology and packing limit of droplets. The dielectric behaviors of oil-in-water-in-oil (O/W/O) and water-in-oil-in-water (W/O/W) types of double emulsions, as predicted by the proposed model, are discussed.     

Stabilization and destabilization of water-in-crude oil emulsions from the norwegian continental shelf. Correlation with model systems

A summary of properties of water-in-crude oil emulsions from the Norwegian Continental Shelf or model water-in-oil emulsions is given. A separation method for the indigenous surface active crude oil components based on adsorption/extraction was developed. These components and their films were characterized by M_w determinations, FT-IR, Langmuir-Blodgett, surface/interfacial tension, dielectric spectroscopy and interactions with chemical destabilizers. The stability/instability properties of authentic water-in-crude oil emulsions can be reproduced by model W/O emulsions stabilized by the interfacially active crude oil fraction. Processes inside the water droplets and at the W/O interface taking place upon destabilization were followed by means of dielectric spectroscopy.     

Dielectric relaxation behavior of ternary systems of water/toluene/Triton X-100: the effects of water and oil contents on microemulsion structure

Dielectric relaxation studies were conducted on the ternary systems of the nonionic surfactant Triton X-100 (a nonionic surfactant with a polyoxyethylene chain)/toluene/water in the frequency range from 40 Hz to 110 MHz. The contents of water and toluene were varied separately while the ratios of the other two components were fixed. Remarkable dielectric relaxations were observed around 1 MHz and dielectric intensity shows different variation with the increase of the contents of water or toluene. Dielectric parameters were obtained by fitting the data using the Cole–Cole equation with one dispersion term. The reverse micelles, water-in-oil, and oil-in-water micro-regions of the microemulsions were identified by the dependence of conductivity of the dispersed phase and continuous phase on the contents of water or toluene. Hanai theory and the corresponding analysis method were used to calculate the phase parameters of the constituent phases. The analysis results suggest that the dielectric relaxation probably arises from the interfacial polarization.     

Interface composition of multiple emulsions: rheology as a probe

We have investigated the dynamic rheological properties of concentrated multiple emulsions to characterize their amphiphile composition at interfaces. Multiple emulsions (W1/O/W2) consist of water droplets (W1) dispersed into oil globules (O), which are redispersed in an external aqueous phase (W2). A small-molecule surfactant and an amphiphilic polymer were used to stabilize the inverse emulsion (W1 in oil globules) and the inverse emulsion (oil globules in W2), respectively. Rheological and interfacial tension measurements show that the polymeric surfactant adsorbed at the globule interface does not migrate to the droplet interfaces through the oil phase. This explains, at least partly, the stability improvement of multiple emulsions as polymeric surfactants are used instead of small-molecule surfactants.     

Dielectric properties of emulsions

Summary Dielectric constants of O/W emulsions were measured over a wide range of concentration and at frequencies ranging from 20 cps. to 3 mc. No dielectric dispersion due to the interfacial polarization was observed in the experimental range of frequency, while the electrode polarization was observed below 100 kc. Experimental results were compared with theoretical values for spherical dispersions. It was concluded that the dielectric constants of O/W emulsions were expressed best byBruggeman's equation over the whole range of concentration.

---

Zusammenfassung Die DK von ?l/Wasser-Emulsionen wurden über einen weiten Konzentrationsbereich und für Frequenzen zwischen 20 Hz und 3 MHz gemessen. Es war keine dielektrische Dispersion verursacht durch Oberfl?chenpolarisation innerhalb des experimentellen Frequenzbereiches zu beobachten. Dagegen wurde unterhalb 100 kHz Elektrodenpolarisation bemerkbar. Die experimentellen Ergebnisse wurden mit den theoretischen Darstellungen der Misch-DK für Dispersionen mit kugligen Teilchen verglichen. Der Verlauf der DK der ?l/Wasser-Emulsion wird am besten und über den ganzen Konzentrationsbereich durch die Gleichung vonBruggeman dargestellt.

     

聚吡咯/聚苯乙烯混合膜/电解质溶液体系的介电谱解析电解质种类和浓度对膜透过性的影响

测量了混入聚吡咯粒子的聚苯乙烯混合膜在不同浓度的氯化钠、氯化钾、氯化钙及氯化镁体系的介电谱, 在40 Hz~11 MHz, 发现了显著的双介电弛豫现象(Double-relaxation phenomena). 基于Maxwell-Wagner理论讨论了弛豫产生的机制, 将体系进行了模型化, 并利用Hanai理论方法对介电谱进行了解析, 从获得的内部参数对混合后的膜荷电性质以及混合膜对离子的透过性进行了详细的讨论, 进而利用Donnan平衡理论推导的膜电位的表达式拟合, 获得了混合膜的固定电荷等参数.     

中相微乳液的介电弛豫谱解析及弛豫机制研究

对由SDS、CTAB、正庚烷、正丁醇和盐水组成的中相微乳体系进行了介电测量,在不同盐度下低频段出现显著的介弛豫现象,它给出了弛豫时间随盐度的变化关系。通过解析介电谱获得了体系内部结构和电性质等信息,几个介电模型和理论公式被用来解释解析的结果。对弛豫时间的计算结果发现,该弛豫是由多种极化机制参与、界面极化为支配的动力学过程。介电解析和模型计算相互验证,结果暗示着体系盐度变化对中相微乳结构变化的影响和可能的转化机制。     

Dielectric study on membrane adsorption and release: Relaxation mechanism and diffusion dynamics

Dielectric monitoring of the adsorption or release process of salicylic acid (SA) by chitosan membrane shows that the dielectric spectra of the chitosan membrane/ SA solution systems change regularly in the adsorption or release process. By analyzing the regularity, a new mechanism for the relaxations is proposed. The concentration polarization layer (CPL) caused by SA adsorption or release is confirmed to be essential for the dielectric relaxations. The changes of the spectra with time are explained by account of the relationship between CPL properties and dielectric strength. Based on this relaxation mechanism, a theoretical method can be established to calculate dynamical parameters of inner structure of the adsorption or release systems from their dielectric spectra. Therefore, dielectric spec- troscopy is demonstrated to be a promising method for estimating interfacial distribution of ionic sub- stances and their binding to membrane in a non-invasive way.     

Simulation of dielectric relaxation in periodic binary systems of complex geometry

Dielectric relaxation in binary mixtures containing particles or lamellae with complex geometry has been simulated within the quasielectrostatic approximation by a three-dimensional finite-difference method. The method was tested using simple models corresponding to water-in-oil (W/O) and oil-in-water (O/W) emulsions with volume fraction P up to 0.5. The dielectric spectra calculated by the finite difference method agreed with those expected from Wagner's equation at P < or =0.3 and approached those from Hanai's equation at P>0.4. This method was applied to more complicated binary mixtures of oil and water: a bicontinuous cubic structure, a suspension of particles with projections, and a planar bilayer with a rippled or interdigitated interface. The bicontinuous phase that is supposed to appear near the transition between W/O and O/W emulsions showed dielectric properties similar to those of the O/W emulsion. The undulation of the particle surface and the interface of the planar bilayer affected all parameters of dielectric relaxation, especially the relaxation intensity.     

Dielectric analysis of chitosan gel beads suspensions: influence of low crosslinking agent concentration on the dielectric behavior

Dielectric measurements were carried out for the suspensions of chitosan gel beads (CGB) crosslinked with glutaraldehyde (GA), ranging in crosslinking time from 1 to 180 min at six fixed low GA concentrations over a frequency range from 40 to 110 MHz. The distinct dielectric relaxations observed in the frequency range of 10(4)-10(5) Hz were explained by the effects of the interfacial polarization. By fitting the experimental data with Cole-Cole equation the dielectric parameters of the suspensions were obtained, and the phase parameters were calculated using Hanai's method. The influence of crosslinking on the dielectric spectra of CGB was investigated by viewing the crosslinking time dependencies of conductivity increment (Deltakappa), relaxation frequency (f(0)), permittivity of CGB (epsilon(i)), conductivity of CGB (kappa(i)) and conductivity of continuous media (kappa(a)) at six fixed GA concentrations. Some information were gained, such as, thinner electric double layer, particle with rougher surface and more compact gel backbone with increasing crosslinking time. The basic information obtained can provide valuable references for the preparation of CGB and the application to more extensive fields such as controlled-release technology of medicament.     

The effect of an anionic surfactant on the rheology and stability of high volume fraction O/W emulsion stabilized by PVA

The effect of the addition of an anionic surfactant (sodium dodecyl benzene sulphonate) on the rheology and storage stability of concentrated O/W emulsions stabilized by poly (vinyl alcohol) is reported. It was found that the surfactant markedly reduced the magnitudes of the storage modulii of the emulsions. This could be attributed to a reduction in the interfacial tension resulting from the formation of polyelectrolyte type complexes between the PVA and NaDBS at the O/W interface. The results were compared to the equation (given by Princen) relating concentrated emulsion rheology to the interfacial tension and droplet size. Reasonable agreement was found, though there was a small difference in the constants in the equation given by Princen and those found here. The agreement suggested that the emulsions were deforming above a critical volume fraction and that the rheological properties were dominated by the dilation of the interface during shear. Microelectrophoresis measurements showed that the addition of the surfactant conferred a charge onto the PVA stabilized droplets as a result of the formation of the polyelectrolyte complex. The NaDBS was found to reduce the long-term stability of the emulsions compared to emulsions containing PVA alone.     

Preparation of highly monodisperse W/O emulsions with hydrophobically modified SPG membranes

Experimental investigations on the hydrophobic modification of SPG membranes and the preparation of monodisperse W/O (water-in-oil) emulsions using the modified membranes were carried out. Effects of the osmotic pressure of disperse phase, the average pore size of membranes, emulsifier concentrations in continuous phase and the transmembrane pressure on the average size, size distribution and size dispersion coefficient of emulsions were systematically studied. The stability of W/O emulsions was also investigated. The results showed that SPG membranes took on excellent hydrophobicity through the modification by silane coupler reagent (octyltriethoxysilane) or by silicone resin (polymethylsilsesquioxane). Monodisperse W/O emulsions with size dispersion coefficient of about 0.25, which meant high monodispersity, were successfully prepared by using the hydrophobically modified SPG membranes with average pore sizes of 1.8, 2.0, 2.5, 4.8 and 11.1 microm. When the osmotic pressure was lower than 0.855 MPa, the average size of emulsions was gradually increased while the size dispersion coefficient delta gradually decreased with the osmotic pressure; when the osmotic pressure was higher than 0.855 MPa, both the coefficients kept unvarying. When kerosene was saturated with disperse phase in advance, the average size of emulsions became larger and the monodispersity of emulsions was slightly better than that prepared using unsaturated kerosene. The smaller the pore size of SPG membranes was, the better the monodispersity of the W/O emulsions. The average size and size dispersion coefficient delta were nearly independent on the emulsifier concentrations when the PGPR concentration was in the range from 0.5 to 5.0 wt%, whereas both of them slightly increased as the PGPR concentration was below 0.5 wt%. The effect of the transmembrane pressure on size distributions was slight. Both the average size and size dispersion coefficient delta slightly increased to some extent with the increase of the transmembrane pressure in the experimental range. The stability of the W/O emulsions was dependent on the storage time. The mean size of W/O emulsions decreased gradually with the increase of storage time at the first 35 days, and then kept constant; while the size dispersion coefficient of W/O emulsions was nearly not changed.     

Phase transitions and microstructure of emulsion systems prepared with acylglycerols/zinc stearate emulsifier

The emulsification processes, during which acylglycerols/zinc stearate emulsifier, water, and oil phase formed ternary systems, such as water-in-oil (W/O) emulsions, oil-in-water (O/W) dispersions, and unstable oil-water mixtures, were investigated in order to characterize the progressive transformations of the dispersed systems. The type, structure, and phase transitions of the systems were found to be determined by temperature and water phase content. Crystallization of the emulsifier caused the destabilization and subsequent phase inversion of the emulsions studied, at a temperature of 60-61 degrees C. The observed destabilization was temporary and led, at lower temperature, to W/O emulsions, "O/W + O" systems, or O/W dispersions, depending on the water content. Simultaneous emulsification and cooling of 20-50 wt % water systems resulted in the formation of stable W/O emulsions that contained a number of large water droplets with dispersed oil globules inside them ("W/O + O/W/O"). In water-rich systems (60-80 wt % of water), crystallization of the emulsifier was found to influence the formation of crystalline vesicle structures that coexisted, in the external water phase, with globules of crystallized oil phase. Results of calorimetric, rheological, and light scattering experiments, for the O/W dispersions obtained, indicate the possible transition of a monostearoylglycerol-based alpha-crystalline gel phase to a coagel state, in these multicomponent systems.     

Effect of Nanoparticle Hydrophobicity on Stability of Highly Concentrated Emulsions

The effect of hydrophobicity index (HI) of fumed nanosilica specimens on stability of water-in-oil (W/O) highly concentrated emulsions (HCE with ? = 90 vol%) with an overcooled dispersed phase was studied. A series of five silica with HI in the 0.60–1.34 range and HI > 3 were used separately and in combination with a low molecular weight traditional surfactant, Sorbitan MonoOleate (SMO). First, it was shown that SMO alone can stabilize W/O HCE whereas only silica nanoparticles with intermediate HI in the range 0.97 ≤ HI ≤ 1.34 could form W/O emulsions only up to 77–79 vol%. Then, on the contrary to SMO-based emulsions, Pickering emulsions are unstable under shearing. When mixed (silica plus SMO) emulsifier systems were used, firstly a thermodynamic consideration revealed that only SMO is likely to adsorb at the W/O interface and controls the emulsifying process by the decrease in the interfacial tension. Then, interestingly, all different kinds of emulsion stability investigated in this study demonstrate a breaking point (BP) at HI = 0.97. Below the BP the emulsions were found to be very unstable on shelf as well as under shear. Above the BP, a clear synergy between colloidal silica and SMO surfactant has been found.