Montalvo Gemma, Valiente Mercedes, Khan Ali
Química Física, Universidad de Alcalá, E-28871 Alcalá de Henares (Madrid), Spain.
Langmuir. 2007 Oct 9;23(21):10518-24. doi: 10.1021/la701539f. Epub 2007 Sep 15.
The viscoelastic behavior of the two different liquid crystalline lamellar phases and the liquid crystalline cubic phase of the mixed soybean lecithin/DDAB system in water was studied through rheology, with mechanical parameters studied as a function of composition. The swollen or diluted lamellar region is formed by vesicles, and its characteristic flow curve presents two-power law regions separated by a region where viscosity passes through a maximum. Yield stress and shear-dependent flow behavior were also observed. The microstructure suffers transformation under shear stress, and rheological response shifts from thixotropic to antithixotropic loops. Similar rheological behavior has been observed for samples in the collapsed or concentrated lamellar region, at the water-rich corner of the phase diagram. Vesicle formation may therefore occur by shearing the initial stacked and open bilayers. However, concentrated lamellar samples in the water-poor part of the phase diagram are less sensitive to shear effects and show plastic behavior and thixotropy. All lamellar samples manifest high elasticity. The dynamic responses of both lamellar topologies, i.e., vesicles and open bilayers, are comparable and exhibit an infinite relation time. The bicontinuous cubic, liquid crystalline phase is highly viscous. Its dynamic response cannot be modeled by a Maxwell model.
通过流变学研究了混合大豆卵磷脂/二甲基二烯丙基氯化铵（DDAB）体系在水中的两种不同液晶层状相和液晶立方相的粘弹性行为，并研究了力学参数随组成的变化。膨胀或稀释的层状区域由囊泡形成，其特征流动曲线呈现出两个幂律区域，中间由一个粘度达到最大值的区域隔开。还观察到屈服应力和剪切依赖的流动行为。微观结构在剪切应力作用下发生转变，流变响应从触变环转变为反触变环。在相图的富水角，对于塌陷或浓缩层状区域的样品也观察到了类似的流变行为。因此，囊泡的形成可能是通过剪切初始堆叠的开放双层来实现的。然而，相图贫水部分的浓缩层状样品对剪切效应不太敏感，表现出塑性行为和触变性。所有层状样品都表现出高弹性。两种层状拓扑结构，即囊泡和开放双层的动态响应相当，并且表现出无限的关联时间。双连续立方液晶相具有高粘性。其动态响应不能用麦克斯韦模型来模拟。
