Overcoming the "Coffee-Stain" Effect by Compositional Marangoni-Flow-Assisted Drop-Drying
Overcoming the "Coffee-Stain" Effect by Compositional Marangoni-Flow-Assisted Drop-Drying
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DOI：
10.1021/jp3009628
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发表时间：
2012-06-07
影响因子：
3.3
通讯作者：
Pasquali, Matteo
中科院分区：
文献类型：
--
作者：
Majumder, Mainak;Rendall, Clint S.;Pasquali, Matteo
通过滴干法沉积均匀纳米颗粒薄膜的尝试由于宏观对流流进入接触线而产生的“咖啡渍”效应而受挫。在这里，我们证明了纳米颗粒在水悬浮液中的均匀沉积可以很容易地通过在乙醇蒸气气氛中干燥液滴来实现。这种技术允许携带颗粒的水滴在各种表面上扩散，如玻璃、硅、云母、PDMS，甚至特氟龙。液滴形状和内部流动的可视化显示了初始液滴的扩散和在扩散和收缩过程中的强再循环流动。最初的扩散是由于接触线处乙醇从蒸气中吸收而使接触角减小。在干燥阶段，蒸汽在乙醇中饱和，导致接触线上的水优先蒸发。这产生了一个表面张力梯度，驱动了一个强大的再循环流动，使纳米颗粒浓度均匀化。我们表明，这种方法可以用于沉积催化剂纳米颗粒，用于单壁碳纳米管的生长，也可以用于制造间距良好、未聚集的金纳米颗粒的等离子体膜。
Attempts at depositing uniform films of nanoparticles by drop-drying have been frustrated by the "coffee-stain" effect due to convective macroscopic flow into the contact line. Here, we show that uniform deposition of nanoparticles in aqueous suspensions can be attained easily by drying the droplet in an ethanol vapor atmosphere. This technique allows the particle-laden water droplets to spread on a variety of surfaces such as glass, silicon, mica, PDMS, and even Teflon. Visualization of droplet shape and internal flow shows initial droplet spreading and strong recirculating flow during spreading and shrinkage. The initial spreading is due to a diminishing contact angle from the absorption of ethanol from the vapor at the contact line. During the drying phase, the vapor is saturated in ethanol, leading to preferential evaporation of water at the contact line. This generates a surface tension gradient that drives a strong recirculating flow and homogenizes the nanoparticle concentration. We show that this method can be used for depositing catalyst nanoparticles for the growth of single-walled carbon nanotubes as well as to manufacture plasmonic films of well-spaced, unaggregated gold nanoparticles.