稀薄的乳剂呈现颗粒状物质
Skinny emulsions take on granular matter
摘要：
在过去的20年里，我们对泡沫和乳液的结构特征的理解有了显著的进步。然而，随着对“超稳定”液体分散体的研究，泡沫和乳液科学采用越来越复杂的配方，这些配方在气泡/液滴表面产生固体状粘弹性层。这些导致气泡/液滴之间的弹性力、粘附力和摩擦力，强烈影响它们如何相互挤压和变形，要求对当前可用的结构描述进行调整。系统地改变界面性质的可能性使这些分散体成为探索具有复杂相互作用的软颗粒材料的理想体系。我们在这里提出了第一个系统的分析，这样一个系统的结构特征，使用模型硅乳液含有毫米大小的聚乙二醇滴（PEG）。通过在PEG-硅酮界面处的聚合物交联反应获得固体状液滴表面。使用一种新的液滴显微操作器，我们强调两滴之间的弹性，粘性和摩擦的相互作用的存在。然后，我们提供了第一次完整的断层分析这些乳液的结构特征。对不同皮肤配方的休止角、局部体积分数分布、配对关联函数和液滴变形的深入分析使我们能够证明具有流体状液滴表面的“普通”乳液的显著差异。虽然可以得出与摩擦硬球系统的强烈类比，但由于液滴的高变形性，这些系统显示出一系列独特的特征，有待系统的探索。
英文摘要：
Our understanding of the structural features of foams and emulsions has advanced significantly over the last 20 years. However, with a search for "super-stable" liquid dispersions, foam and emulsion science employs increasingly complex formulations which create solid-like visco-elastic layers at the bubble/drop surfaces. These lead to elastic, adhesive and frictional forces between bubbles/drops, impacting strongly how they pack and deform against each other, asking for an adaptation of the currently available structural description. The possibility to modify systematically the interfacial properties makes these dispersions ideal systems for the exploration of soft granular materials with complex interactions. We present here a first systematic analysis of the structural features of such a system using a model silicone emulsion containing millimetre-sized polyethylene glycol drops (PEG). Solid-like drop surfaces are obtained by polymeric cross-linking reactions at the PEG-silicone interface. Using a novel droplet-micromanipulator, we highlight the presence of elastic, adhesive and frictional interactions between two drops. We then provide for the first time a full tomographic analysis of the structural features of these emulsions. An in-depth analysis of the angle of repose, local volume fraction distributions, pair correlation functions and the drop deformations for different skin formulations allow us to put in evidence the striking difference with "ordinary" emulsions having fluid-like drop surfaces. While strong analogies with frictional hard-sphere systems can be drawn, these systems display a set of unique features due to the high deformability of the drops which await systematic exploration.
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