Centre de Recherche Paul Pascal, Université Bordeaux 1, CNRS, Avenue du Dr Albert Schweitzer, 33600 Pessac, France.
Langmuir. 2010 Nov 16;26(22):16782-90. doi: 10.1021/la1027288. Epub 2010 Sep 29.
We produced triglyceride-in-water emulsions comprising semicrystallized droplets, stabilized by a mixture of protein and low molecular weight surfactant. In these systems, partial (unrelaxed) coalescence could be produced by a thermal treatment referred to as tempering or by the application of a shear. Both primary emulsions and thermally induced gels were submitted to shear strains of variable amplitude, and the resulting transitions were identified. Partial or total destruction of the materials took place and was revealed by the formation of macroscopic clumps. We examined the impact of the initial average droplet size and of the interface composition (controlled by the bulk surfactant-to-protein molar ratio) on the sensitivity to partial coalescence. The evolution under shear occurred via two limiting mechanisms, depending on the susceptibility to partial coalescence. Materials that exhibited fast partial coalescence underwent gelling followed by phase inversion and partial expulsion of the aqueous phase. Alternatively, when the rate of partial coalescence was quite low, large clumps were randomly distributed over the volume and coexisted with a fluid emulsion. The same phenomenology was observed under both oscillatory and steady shear conditions. Interestingly, in oscillatory conditions, clumping was observed above a very well-defined and reproducible value of the strain amplitude independent of the initial state of the system (emulsion or gel).
我们制备了由半结晶液滴组成的甘油三酯水乳液，并用蛋白质和低分子量表面活性剂的混合物稳定。在这些体系中，通过称为回火的热处理或施加剪切，可以产生部分（未弛豫）聚结。将初级乳液和热诱导凝胶都经受了可变幅度的剪切应变，并确定了由此产生的转变。部分或完全破坏材料发生并通过形成宏观团块来揭示。我们研究了初始平均液滴尺寸和界面组成（通过控制体相表面活性剂与蛋白质的摩尔比来控制）对部分聚结敏感性的影响。在剪切下的演变通过两种极限机制发生，这取决于对部分聚结的敏感性。表现出快速部分聚结的材料经历胶凝，然后发生相反转和水相的部分排出。或者，当部分聚结的速率相当低时，大团块随机分布在整个体积中，并与流体乳液共存。在振荡和稳态剪切条件下都观察到相同的现象。有趣的是，在振荡条件下，在应变幅值非常明确且可重复的情况下观察到结块，而与体系的初始状态（乳液或凝胶）无关。
