Chemical Engineering Department, Chemistry Faculty, Barcelona University , Marti i Franquès 1-11, 08028, Barcelona, Catalonia, Spain.
Langmuir. 2011 Mar 15;27(6):2286-98. doi: 10.1021/la104539q. Epub 2011 Feb 2.
This article reports the phase behavior determi-nation of a system forming reverse liquid crystals and the formation of novel disperse systems in the two-phase region. The studied system is formed by water, cyclohexane, and Pluronic L-121, an amphiphilic block copolymer considered of special interest due to its aggregation and structural properties. This system forms reverse cubic (I2) and reverse hexagonal (H2) phases at high polymer concentrations. These reverse phases are of particular interest since in the two-phase region, stable high internal phase reverse emulsions can be formed. The characterization of the I2 and H2 phases and of the derived gel emulsions was performed with small-angle X-ray scattering (SAXS) and rheometry, and the influence of temperature and water content was studied. The H2 phase experimented a thermal transition to an I2 phase when temperature was increased, which presented an Fd3m structure. All samples showed a strong shear thinning behavior from low shear rates. The elastic modulus (G') in the I2 phase was around 1 order of magnitude higher than in the H2 phase. G' was predominantly higher than the viscous modulus (G''). In the gel emulsions, G' was nearly frequency-independent, indicating their gel type nature. Contrarily to water-in-oil (W/O) normal emulsions, in W/I2 and W/H2 gel emulsions, G', the complex viscosity (|η*|), and the yield stress (τ0) decreased with increasing water content, since the highly viscous microstructure of the continuous phase was responsible for the high viscosity and elastic behavior of the emulsions, instead of the volume fraction of dispersed phase and droplet size. A rheological analysis, in which the cooperative flow theory, the soft glass rheology model, and the slip plane model were analyzed and compared, was performed to obtain one single model that could describe the non-Maxwellian behavior of both reverse phases and highly concentrated emulsions and to characterize their microstructure with the rheological properties.
本文报道了形成反相液晶的体系的相行为确定以及在两相区形成新型分散体系的情况。所研究的体系由水、环己烷和 Pluronic L-121 组成，Pluronic L-121 是一种两亲嵌段共聚物，由于其聚集和结构特性而被认为具有特殊的兴趣。该体系在高聚合物浓度下形成反向立方（I2）和反向六方（H2）相。这些反向相特别有趣，因为在两相区可以形成稳定的高内相反向乳液。通过小角 X 射线散射（SAXS）和流变学对 I2 和 H2 相以及衍生的凝胶乳液进行了表征，并研究了温度和含水量的影响。当温度升高时，H2 相经历了向 I2 相的热转变，I2 相具有 Fd3m 结构。所有样品在低剪切速率下均表现出强烈的剪切稀化行为。I2 相中的弹性模量（G'）比 H2 相高约 1 个数量级。G' 比粘性模量（G''）高得多。在凝胶乳液中，G'几乎与频率无关，表明其具有凝胶性质。与油包水（W/O）正常乳液相反，在 W/I2 和 W/H2 凝胶乳液中，随着含水量的增加，G'、复黏度（|η*|）和屈服应力（τ0）降低，因为连续相的高粘性微结构是导致乳液高粘度和弹性行为的原因，而不是分散相的体积分数和液滴尺寸。进行了流变分析，分析和比较了协同流动理论、软玻璃流变学模型和滑移面模型，以获得一个能够描述反向相和高浓度乳液的非麦克斯韦行为并通过流变特性来表征其微观结构的单一模型。
