Jambon-Puillet Etienne
Institute of Physics, Van der Waals-Zeeman Institute , University of Amsterdam , Science Park 904 , 1098 XH Amsterdam , The Netherlands.
Langmuir. 2019 Apr 23;35(16):5541-5548. doi: 10.1021/acs.langmuir.9b00084. Epub 2019 Apr 12.
The evaporation of droplets of colloidal suspensions onto a surface is a common tool to achieve surface coatings and self-assembly. However, because of the spontaneous flow developing within an evaporating drop, the deposit is difficult to control, and an unwanted ring-like structure often forms, with particles aggregating along the drop edge. Here, by freezing the drops before sublimating them in dry air we propose a new approach that produces a different kind of stain where most particles are clustered in the center of the drops instead. We demonstrate that these deposits can be continuously tuned from wide but thin to concentrated and thick by varying the droplet's aspect ratio. Unlike evaporated liquid drops, stains from freeze-dried drops do not depend on the drying conditions or substrate roughness and possess a porous and branched microstructure somewhat reminiscent of freeze-casted ceramics. With these stains being governed by the freezing process rather than the drying, this opens alternative ways to control colloidal deposits.
将胶体悬浮液的液滴滴到表面上进行蒸发，是实现表面涂层和自组装的常用方法。然而，由于蒸发液滴内部会产生自发流动，沉积物难以控制，并且经常会形成 unwanted 环状结构，颗粒会沿液滴边缘聚集。在此，我们提出一种新方法，即在干燥空气中升华之前先将液滴冷冻，从而产生一种不同类型的污渍，其中大多数颗粒反而聚集在液滴中心。我们证明，通过改变液滴的纵横比，可以将这些沉积物从宽而薄连续调整为浓缩且厚。与蒸发的液滴不同，冷冻干燥液滴产生的污渍不依赖于干燥条件或基底粗糙度，并且具有一种多孔且分支的微观结构，有点类似于冷冻铸造陶瓷。由于这些污渍由冷冻过程而非干燥过程控制，这为控制胶体沉积物开辟了替代途径。
