Hypothesis

Temperature-controlled self-faceting of liquid droplets has been recently discovered in surfactant-stabilized alkane-in-water emulsions. We hypothesize that similar self-faceting may occur in emulsion droplets of UV-polymerizable linear hydrocarbons. We further hypothesize that the faceted droplet shapes can be fixed by UV-initiated polymerization, thus providing a new route towards the production of solid polyhedra.

Experiments

Temperature-induced shape variations were studied by optical microscopy in micron-size emulsion droplets of UV-polymerizable alkyl acrylate. When polymerized, the resultant solid particles’ 3D shape and internal structure were determined by combined scanning electron microscopy (SEM) and focused ion beam (FIB) slicing. The SEM and FIB nanoscale resolution provided a far greater detail imaging than that achievable for the liquid droplets, which could only be studied by optical microscopy, severely limiting their 3D shape determination.

Findings

We demonstrate the formation of solid icosahedra, polyhedral platelets, and rods of hitherto-unreported sizes, well below the 3D-printing resolution ($\sim 20\mathrm{\mu }$m). The presence of icosahedral shapes and the absence of any resolvable internal structure at sub-$\mathrm{\mu }$m length scales, are in line with the surface-freezing-driven mechanism proposed for the faceting phenomenon. Further development of the method presented here may allow large-quantity production of shaped micron- to nano- sized colloidal building blocks for 3D metamaterials and other applications.

中文翻译：

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乳剂液滴的自成膜作用是固体二十面体和其他多面体的一种途径

假设

最近在表面活性剂稳定的水包烷烃乳液中发现了温度可控的液滴自成膜。我们假设在可紫外线聚合的线性烃的乳液液滴中可能发生类似的自成膜现象。我们进一步假设可以通过紫外线引发的聚合作用固定多面液滴形状，从而为生产固体多面体提供了一条新途径。

实验

通过光学显微镜在可紫外线聚合的丙烯酸烷基酯的微米大小的乳液液滴中研究了温度引起的形状变化。聚合后，通过组合扫描电子显微镜（SEM）和聚焦离子束（FIB）切片确定所得固体颗粒的3D形状和内部结构。SEM和FIB纳米级分辨率提供了比液滴可实现的更大的细节成像，而液滴只能通过光学显微镜进行研究，从而严重限制了其3D形状的确定。

发现

我们展示了固态二十面体，多面体血小板和迄今为止尚未报道的大小的棒的形成，该大小远低于3D打印分辨率（$〜20\mathrm{\mu }$m）。二十面体形状的存在以及在亚面处没有任何可分辨的内部结构$\mathrm{\mu }$m的长度刻度与针对小面现象提出的表面冻结驱动机制是一致的。此处提出的方法的进一步发展可能允许大批量生产用于3D超材料和其他应用的微米级到纳米级的胶体构建基块。