ISSN:0005-9021    

DOI:10.1002/bbpc.19961000302

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractIn this introductory article we approach microemulsions from the binary water‐surfactant side. Model systems of the water ‐ nonionic surfactant (CiEj) type are examined. Many features of microemulsions are observable in these binary systems. As such we discuss the dependence of the cloud points on i and j, the temperature dependence of the viscosity within the micellar phase, and the formation of dilute bilayer phases. The effect of additives is examined, as it permits to gain insight into the structures and interactions. Towards the end of the paper the most important additive for microemulsion formation, the oil, is considered. A special feature of long‐chain surfactants is highlighted, namely, non‐monotonic critical lines leading to very peculiar two‐phase lobes as precursors to the formation of the three‐p

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000303

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractWe review and summarize the features of nonionic microemulsion phase behavior. Particular emphasis is given to the behavior of mixtures of oil, water or other polar materials with nonionic surfactants from the family of n‐alkyl polyglycol ethers, usually denoted as CiEj. The patterns of phase behavior are reviewed and the roles of various additives such as electrolytes and alcohols are discusse

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000304

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractNon‐polar oils and water can form thermodynamically stable quasi‐homogeneous (colloidal) mixtures (called microemulsions) in the presence of relatively large amounts (several %) of ionic surfactants. If the surfactant contains a single hydrocarbon chain (e.g. Sodium Dodecyl Sulphate) the presence of a non‐ionic cosurfactant (e.g. hexanol) and electrolyte (concentration of the order 0.1 M) is essential. With a double chain surfactant (e.g. Aerosol OT) the cosurfactant can be missed. At increasing concentrations of electrolyte and/or cosurfactant the nature of the microemulsion changes from droplets of oil in water via a presumably bicontinuous pattern to droplets of water in oil. It should be obvious that thermodynamic stability requires the interfacial tension between water and oil to be low (order of 0.01‐0.1 mN m−1) so that the dispersion entropy can offset the interfacial free energy. At these low interfacial tensions the influence of curvature on the interfacial tensions becomes important. It turns out that a given amount of surfactant (and co‐surfactant) can only disperse a limited amount of oil in water or of water in oil or of water and oil into one another and therefore a microemulsion may be in equilibrium with non colloidal oil and/or water phases. In the bicontinuous microemulsion oil and water may have a geometrically irregular interface or they may form lamellae of more or less constant thickness or other structures, such as a “molten cubic phase”. These equilibria lead to very interesting, but rather complicated phase diagrams. It will be discussed by what mechanisms the various components of the mixture influence the interfacial tension and promote the stability of the microemulsion and how this depends on the chemical nature of

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000305

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractNeutron reflectivity has been used to study the effect of temperature on the adsorption of non‐ionic surfactants and non‐ionic surfactant mixtures at the air‐water interface. For a range of polyoxyethylene non‐ionic surfactants the adsorption is invariant with temperature in the range 25 to 50 c; however some subtle changes in the structure of the adsorbed layer are observed.For the non‐ionic mixture of monododecyltriethylene glycol, C12EO3, and monododecyloctaethylene glycol, C12EO18, measurements over a wide concentration range, from below to above the cmc (10−5to 10−2M), provide a direct qualitative confirmation of the abrupt change in surface composition at the cmc due to the onset on mixed micelle formation predicted recently by Nikas, Puvvada, and Blankschtein, Langmuir, 8 (1992) 2680.For the same non‐ionic mixtures and at concentrations below and above the cmc (at concentrations of 1.25 × 10−5and 5 × 10−4M) a change in surface composition with increasing temperature is observed. The surface becomes more rich in the least surface active component, the C12EO8. In the same temperature range the total adsorption from the mixture at the interfa

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000306

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractWe have measured the adsorption isotherms for dodecane adsorption at the solution‐vapour surface for surfactant monolayer covered aqueous surfactant solutions at concentrations in excess of their critical micelle concentration (cmc) values. The temperature dependence of the adsorption have been determined for both a nonionic surfactant (H(CH2)12(OCH2CH2)5OH, abbreviated to C12E5) and an ionic surfactant (n‐dodecyltrimethyl‐ammonium bromide, abbreviated to DoTAB). For the nonionic surfactant, dodecane adsorption decreases with increasing temperature at low surface concentration of the oil whereas it increases at high surface concentrations. With the ionic surfactant DoTAB, the temperature effect shows a similar crossover in behaviour but the changes in adsorption are opposite in direction to those seen for the nonionic surfactant. The adsorption data are correlated to the effects of temperature on the microemulsion phase behaviour of ionic and nonionic surfactants and discussed in relation to the microstructures of the mixed oil/surfactant films as determined by neutron reflect

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000307

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractThe phase behaviour and aggregation of the semifluorinated alkane F‐(CF2)8‐(CH2)16‐H (abbreviated to F8H16) in hydrocarbon and perfluorinated solvents has been investigated. The variation of solubility with temperature for F8H16in perfluorinated solvents shows highly non‐ideal behaviour and exhibits a sharp increase at a temperature a few degrees below the melting point of F8H16. The behaviour is similar to that in the region of the Krafft point of a conventional surfactant in water. Withiso‐octane as solvent, the solubility shows only slight deviations from ideal behaviour. Vapour pressure osmometry (VPO) results confirm the near ideal behaviour of F8H16iniso‐octane. For F8H16in perfluorodecalin at 38 °C, VPO results show that aggregates are formed at concentrations above approximately 0.02 mole fraction. The aggregation number is 6 and is virtually independent of the SFA concentration. The results are discussed in terms of the antipathy between hydrocarbons and fluorocarbons as reflected in the values of the upper critical solution temperatures (UCST) of binary mixtures of hydrocarbons with perfluorina

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000308

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractThe interfacial tensions between water‐ and oil‐rich phases in microemulsion systems have been measured for a series of ternary water‐alkane‐CiEjsystems. It is found that interfacial tensions vary over orders of magnitude with temperature displaying a pronounced minimum for each surfactant. The center of the three‐phase temperature interval,Tu‐T1, i.e. the phase inversion temperature (PIT), corresponds to the temperatureTmof the minimum in interfacial tension. Increasing the surfactant chain length the minimum value decreases by 3 orders of magnitude for a change of i from 6 to 12. Interestingly, all interfacial tension curves have a similar shape. Centering the curves aroundTmand reducing the temperature scale byTu‐T1permits determining the factors, by which the individual interfacial tension curves differ. The factors are found to be proportional, respectively, to square of the maximum length scale ζ or the inverse surfactant volume fraction Φc,iin the interface. Accordingly, plotting σab/Φc, j2vs. 2(T‐Tm)/(Tu‐T1) an almost perfect superposition of all interfacial tensi

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000309

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractThe major classes of models that have been applied and analyzed in the theoretical discussion of microemulsions are described. These include both continuum and lattice models, and models based on phenomenological free‐energy densities as well as those based on microscopic Hamiltonians. Some of the issues addressed by such models are the progression of microemulsion phase equilibria, the interfacial tensions, the wetting or non‐wetting of the interfaces, and the small‐angle X‐ray or neutron scattering from microemulsions. The ways in which the models address these issues are described and some characteristic results are quoted. Most of these matters are taken up later with more technical detail by other authors; the present paper is intended only to provide an o

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000310

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractWe review the theory of curvature elasticity of thin, fluid films starting with a phenomenological formalism motivated by microscopic, physical examples. The effects of finite compressibility of the layer, exchange of molecules between the film and the solution, and the intrinsic bending stiffness of the film are taken into account; these degrees of freedom account for all the important molecular modes of the system. The effects of fluctuations of the number of molecules in the film (which is in equilibrium with surfactant molecules or micelles in solution) and in the area per molecule about its equilibrium value is shown to soften the curvature elastic moduli. The relationship of the bending moduli to the pressure distribution in the film is discussed and it is demonstrated that isotropic liquid films have no bending modulus, in the continuum limit. The bending moduli for charged membranes and for block copolymers and estimated. Finally, some recent experimental measure of curvature elasticity are discussed and compared with the theory.

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000311

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY