Abstract

Understanding the evaporation of a multi-component droplet has found immense importance in various technological applications. This study investigates the evaporation behaviour of a colloidal binary droplet system comprising of the ethanol-water mixture and polystyrene nanoparticles. The wetting and evaporation dynamics were studied with an emphasis on the collective influence of ethanol and nanoparticle concentrations. The temporal behaviour of the contact angles, shapes and volumes of the droplets was monitored in order to analyse the evaporative behaviour. With increase of ethanol concentrations, the binary droplet volumes were found to decrease nonlinearly with time. Ethanol being more volatile evaporated in the initial stage. Towards the end of the evaporation process, the evaporation characteristics mimics the behaviour of pure water. Our study shows that the initial contact angle decreases monotonically with increased concentration of ethanol in the mixture. The contact angle is maximum for a particular nanoparticle concentration. Droplets with higher ethanol concentration show higher wettability which in its turn is maximum for low nanoparticle concentrations. This trend shows the interconnected effect of ethanol and nanoparticle concentrations on evaporation. Rim width of the final deposition pattern increases with nanoparticle concentration although it is almost independent of ethanol concentration. Finally, it is noticed that fast evaporation of a relatively more volatile component in a binary mixture droplet leads to nanoparticle segregation for low nanoparticle concentrations. Thus for binary mixtures, the evaporation of the more volatile component, ethanol for our case, offers characteristic differences in the resulting evaporation dynamics from that of pure water which finds applicability for multi-component evaporation processes.

Graphic abstract

中文翻译：

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纳米颗粒负载水-乙醇二元液滴中的相互联系的干燥现象

摘要

在多种技术应用中，了解多组分液滴的蒸发非常重要。这项研究调查了由乙醇-水混合物和聚苯乙烯纳米颗粒组成的胶态二元液滴系统的蒸发行为。研究了润湿和蒸发动力学，重点研究了乙醇和纳米颗粒浓度的共同影响。监测液滴的接触角，形状和体积的时间行为，以分析蒸发行为。随着乙醇浓度的增加，发现二元液滴体积随时间非线性减小。在初始阶段，乙醇挥发得更多。在蒸发过程快要结束时，蒸发特性模仿了纯水的行为。我们的研究表明，初始接触角随混合物中乙醇浓度的增加而单调减小。对于特定的纳米颗粒浓度，接触角是最大的。具有较高乙醇浓度的液滴显示出较高的润湿性，而对于较低的纳米颗粒浓度，其又是最大的。这种趋势表明乙醇和纳米颗粒浓度对蒸发的相互影响。最终沉积图案的轮辋宽度随纳米颗粒浓度的增加而增加，尽管它几乎与乙醇浓度无关。最后，注意到在二元混合物液滴中较易挥发的组分的快速蒸发导致低纳米颗粒浓度的纳米颗粒分离。因此，对于二元混合物，挥发性较高的成分（在我们的情况下为乙醇）的蒸发

图形摘要