Graduate School of Bio-Applications and Systems Engineering, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan.
Soft Matter. 2017 Dec 6;13(47):8990-8998. doi: 10.1039/c7sm01989k.
We have investigated drying of water droplets stabilized by solid particles or surfactant molecules in a thin oil layer. The surfactant-stabilized droplets isotropically shrink, whereas the droplets stabilized by spherical particles severely deform during drying because of buckling of the particulate shells. However, buckling of the shells hardly affects droplet drying. The drying times for complete evaporation are almost the same for water droplets with the same initial diameter and the drying time is independent of the type of surface stabilizer (particles or surfactant). The drying kinetics of the water droplets is well described by mathematical models, in which diffusion of water molecules in the oil phase to the oil-air interface is proposed as the rate-determining process. Droplets with a diameter comparable with the thickness of the oil layer shrink faster than small droplets because of the short diffusion length from the water droplets to the oil-air interface. We also investigated drying of water droplets stabilized by plate-like mica particles. The droplets also buckled but larger shells of mica particles remained compared with those of spherical particles. In addition, a longer drying time is necessary for some droplets stabilized by mica particles. These results indicate the possible effect of the particle morphology on the buckling and drying kinetics of particle-stabilized water droplets.
我们研究了在薄油层中由固体颗粒或表面活性剂分子稳定的液滴的干燥过程。各向同性收缩的是由表面活性剂稳定的液滴，而由球形颗粒稳定的液滴在干燥过程中由于颗粒壳的屈曲而严重变形。然而，壳的屈曲对液滴干燥几乎没有影响。具有相同初始直径的水液滴完全蒸发的干燥时间几乎相同，并且干燥时间与表面稳定剂（颗粒或表面活性剂）的类型无关。液滴的干燥动力学可以很好地用数学模型来描述，其中提出了油相中的水分子向油-气界面扩散作为控制步骤。由于水分子从液滴到油-气界面的扩散长度较短，直径与油层厚度相当的液滴比小液滴收缩得更快。我们还研究了由片状云母颗粒稳定的液滴的干燥。这些液滴也发生了屈曲，但与球形颗粒相比，云母颗粒的壳更大。此外，对于一些由云母颗粒稳定的液滴，需要更长的干燥时间。这些结果表明颗粒形态对颗粒稳定的液滴的屈曲和干燥动力学可能有影响。
