Miles Rachael E H, Glerum Michael W J, Boyer Hallie C, Walker Jim S, Dutcher Cari S, Bzdek Bryan R
School of Chemistry , University of Bristol , Cantock's Close , Bristol BS8 1TS , United Kingdom.
Department of Mechanical Engineering , University of Minnesota, Twin Cities , Minneapolis , Minnesota 55455 , United States.
J Phys Chem A. 2019 Apr 4;123(13):3021-3029. doi: 10.1021/acs.jpca.9b00903. Epub 2019 Mar 21.
Aerosols are key components of the atmosphere and play important roles in many industrial processes. Because aerosol particles have high surface-to-volume ratios, their surface properties are especially important. However, direct measurement of the surface properties of aerosol particles is challenging. In this work, we describe an approach to measure the surface tension of picoliter volume droplets with surface age <1 ms by resolving their dynamic oscillations in shape immediately after ejection from a microdroplet dispenser. Droplet shape oscillations are monitored by highly time-resolved (500 ns) stroboscopic imaging, and droplet surface tension is accurately retrieved across a wide range of droplet sizes (10-25 μm radius) and surface ages (down to ∼100 μs). The approach is validated for droplets containing sodium chloride, glutaric acid, and water, which all show no variation in surface tension with surface age. Experimental results from the microdroplet dispenser approach are compared to complementary surface tension measurements of 5-10 μm radius droplets with aged surfaces using a holographic optical tweezers approach and predictions of surface tension using a statistical thermodynamic model. These approaches combined will allow investigation of droplet surface tension across a wide range of droplet sizes, compositions, and surface ages.
气溶胶是大气的关键组成部分，在许多工业过程中发挥着重要作用。由于气溶胶颗粒具有高的表面积与体积比，其表面性质尤为重要。然而，直接测量气溶胶颗粒的表面性质具有挑战性。在这项工作中，我们描述了一种通过解析皮升体积液滴从微滴分配器喷出后立即产生的动态形状振荡来测量表面年龄小于1毫秒的皮升体积液滴表面张力的方法。通过高时间分辨率（500纳秒）的频闪成像监测液滴形状振荡，并在很宽的液滴尺寸范围（半径10 - 25微米）和表面年龄范围（低至约100微秒）内准确获取液滴表面张力。该方法已针对含有氯化钠、戊二酸和水的液滴进行了验证，这些液滴的表面张力均未随表面年龄发生变化。将微滴分配器方法的实验结果与使用全息光镊方法对具有老化表面的半径为5 - 10微米液滴的补充表面张力测量结果以及使用统计热力学模型对表面张力的预测结果进行了比较。这些方法相结合将能够在很宽的液滴尺寸、组成和表面年龄范围内研究液滴表面张力。
