通过毛细管桥蒸发形成的胶体沉积物及其颗粒分选

Colloidal Deposits via Capillary Bridge Evaporation and Particle Sorting Thereof.

作者信息

Upadhyay Gaurav, Bhardwaj Rajneesh

机构信息

Department of Mechanical Engineering, Indian Institute of Technology Bombay, Mumbai 400076, India.

出版信息

Langmuir. 2021 Oct 19;37(41):12071-12088. doi: 10.1021/acs.langmuir.1c01869. Epub 2021 Oct 5.

Abstract

Evaporating droplets of colloidal suspensions leave behind particle deposits which could be effectively controlled via manipulating the surrounding conditions and particles and liquid properties. While previous studies extensively focused on sessile and pendant droplets, the present work investigates the evaporation dynamics of capillary bridges of colloidal suspensions formed between two parallel plates. We vary the wettability of the plates and the particle size and composition of the colloidal suspensions, keeping the same spacing between the plates. We employ side visualization, optical microscopy, fluorescence microscopy, and scanning electron microscopy and develop computational and theoretical models to collect the data. A computational model based on diffusion-limited evaporation is used to characterize the timescale of the evaporation of the capillary bridge. The model predictions are in good agreement with the present and prior experimental measurements. We discuss about the deposits of monodispersed particle suspension formed by the interplay of pinning of the contact line and evaporation dynamics. Multiple rings on the plates are observed due to the stick-slip motion of the contact line. The larger particles tend to form asymmetric deposits, with most particles concentrated on the bottom plates due to a considerably stronger gravitational pull than the hydrodynamic drag. This deposition is explained by estimating the competing forces on the particles during the evaporation. A regime map is proposed for classifying deposits on the particle size wettability plane. Lastly, we demonstrate size-based particle sorting of bidispersed colloidal suspensions in this framework. We describe two mechanisms: gravity-assisted and geometry-assisted sorting, which can be designed to sort particles efficiently. A regime map depicting the regions of influence of each mechanism is presented.

摘要

胶体悬浮液的蒸发液滴会留下颗粒沉积物,通过控制周围条件以及颗粒和液体的性质,可以有效地控制这些沉积物。虽然先前的研究广泛关注于静止和悬垂液滴,但本工作研究了在两个平行板之间形成的胶体悬浮液毛细管桥的蒸发动力学。我们改变板的润湿性以及胶体悬浮液的颗粒大小和组成,同时保持板之间的间距不变。我们采用侧面可视化、光学显微镜、荧光显微镜和扫描电子显微镜,并开发计算和理论模型来收集数据。基于扩散限制蒸发的计算模型用于表征毛细管桥蒸发的时间尺度。模型预测与当前和先前的实验测量结果高度吻合。我们讨论了由接触线钉扎和蒸发动力学相互作用形成的单分散颗粒悬浮液的沉积物。由于接触线的粘滑运动,在板上观察到多个环。较大的颗粒倾向于形成不对称沉积物,由于重力拉力比流体动力阻力大得多,大多数颗粒集中在底板上。通过估计蒸发过程中颗粒上的竞争作用力来解释这种沉积现象。提出了一个状态图,用于在颗粒大小 - 润湿性平面上对沉积物进行分类。最后,我们在这个框架内展示了双分散胶体悬浮液基于尺寸的颗粒分选。我们描述了两种机制:重力辅助分选和几何辅助分选,它们可以被设计用于高效地分选颗粒。给出了一个描绘每种机制影响区域的状态图。

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