Li Xi, Maki Kara L, Schertzer Michael J
Department of Mechanical Engineering, Rochester Institute of Technology, 1 Lomb Memorial Drive, Rochester, New York 14623, United States.
School of Mathematics and Statistics, Rochester Institute of Technology, 85 Lomb Memorial Drive, Rochester, New York 14623, United States.
Langmuir. 2023 Nov 28;39(47):16843-16853. doi: 10.1021/acs.langmuir.3c02224. Epub 2023 Nov 14.
This work investigates the deposition patterns left by evaporating particle-laden droplets on heterogeneous surfaces with spatially varying wettability. Spatial differences in receding contact angles give rise to scalloped-shaped contact lines. During evaporation, the contact line recedes in one location and remains pinned in another. This nonuniform contact line recession results in particle self-assembly above areas where the contact line remains pinned but not where it recedes. This behavior is fairly robust across a variety of particle sizes, concentrations, and device geometries. We hypothesize that particle self-assembly in these cases is due to the competition between particle diffusion and evaporative-driven advective flow. Diffusion appears to be more pronounced in regions where the contact line recedes, while advection appears to be more pronounced near the pinned portion of the contact line. As such, particles appear to diffuse away from receding areas and toward pinned areas, where advection transports them to the contact line. The distribution of particle deposition above the pinned regions was influenced by the particle size and the concentration of particles in the droplet. Similar to homogeneous surfaces, deposition was more prevalent at the pinned portion of the contact line for smaller particles and lower concentrations and more uniformly distributed across the entire pinned region for larger particles and higher concentrations. A better understanding of this process may be beneficial in a wide variety of particle separation applications, such as printing, cell patterning, biosensing, and anti-icing.
这项工作研究了载有颗粒的液滴在具有空间变化润湿性的异质表面上蒸发后留下的沉积模式。后退接触角的空间差异导致了扇形的接触线。在蒸发过程中，接触线在一个位置后退，而在另一个位置保持固定。这种不均匀的接触线后退导致颗粒在接触线保持固定的区域上方自组装，而在接触线后退的区域则不会。这种行为在各种颗粒尺寸、浓度和器件几何形状中都相当稳定。我们假设在这些情况下颗粒的自组装是由于颗粒扩散和蒸发驱动的平流之间的竞争。扩散在接触线后退的区域似乎更明显，而平流在接触线固定部分附近似乎更明显。因此，颗粒似乎从后退区域扩散离开并朝着固定区域移动，在那里平流将它们输送到接触线。固定区域上方颗粒沉积的分布受颗粒大小和液滴中颗粒浓度的影响。与均匀表面类似，对于较小颗粒和较低浓度，沉积在接触线的固定部分更为普遍，而对于较大颗粒和较高浓度，沉积则更均匀地分布在整个固定区域。更好地理解这个过程可能在各种颗粒分离应用中有益，例如打印、细胞图案化、生物传感和防冰。
