Technische Universität Berlin (TU Berlin) , Institut für Chemie - Stranski Laboratorium für Physikalische und Theoretische Chemie, Straße des 17. Juni 124, D-10623 Berlin, Germany.
University of Ioannina , Department of Physics, P.O. Box 1186, GR-45110 Ioannina, Greece.
Langmuir. 2016 Jul 12;32(27):6902-8. doi: 10.1021/acs.langmuir.6b01236. Epub 2016 Jun 30.
Evaporating drops of nanoparticle suspensions on superhydrophobic surfaces can give anisotropic superaparticles. Previous studies implied the formation of a stiff shell that collapses, but the exact mechanism leading to anisotropy was unclear so far. Here we report on a new experiment using confocal laser scanning microscopy for a detailed characterization of particle formation from droplets of aqueous colloidal dispersions on superhydrophobic surfaces. In a customized setup, we investigated droplets of fumed silica suspensions using two different fluorescent dyes for independently marking silica and the water phase. Taking advantage of interfacial reflection, we locate the drop-air interface and extract normalized time-resolved intensity profiles for dyed silica throughout the drying process. Using comprehensive image analysis we observe and quantify shell-like interfacial particle accumulation arising from droplet evaporation. This leads to a buildup of a stiff fumed silica mantle of ∼20 μm thickness that causes deformation of the droplet throughout further shrinkage, consequently leading to the formation of solid anisometric fumed silica particles.
在超疏水表面上蒸发纳米颗粒悬浮液滴可以得到各向异性的超粒子。先前的研究表明，形成了一个刚性的外壳，然后外壳坍塌，但迄今为止，导致各向异性的确切机制尚不清楚。在这里，我们报告了一个新的实验，使用共焦激光扫描显微镜对超疏水表面上的水性胶体分散液滴中颗粒形成进行详细的特性描述。在定制的设置中，我们使用两种不同的荧光染料研究了气相二氧化硅悬浮液的液滴，以独立标记二氧化硅和水相。利用界面反射，我们定位液滴-空气界面，并提取整个干燥过程中染色二氧化硅的归一化时间分辨强度分布。通过综合的图像分析，我们观察和量化了由于液滴蒸发而产生的壳状界面颗粒堆积。这导致了约 20μm 厚的刚性气相二氧化硅覆盖层的形成，从而导致在进一步收缩过程中使液滴变形，从而导致形成固体各向异性的气相二氧化硅颗粒。
