Shahabadi Vahid, Vennes Benjamin, Schmedding Ryan, Zuend Andreas, Mauzeroll Janine, Schougaard Steen B, Preston Thomas C
Department of Atmospheric and Oceanic Sciences, McGill University, Montréal, QC, Canada.
Department of Chemistry, McGill University, Montréal, QC, Canada.
Nat Commun. 2024 Dec 2;15(1):10457. doi: 10.1038/s41467-024-54106-3.
Accurate surface tension measurements are key to understanding and predicting the behavior of atmospheric aerosols, particularly their formation, growth, and phase transitions. In Earth's atmosphere, aerosols often exist in metastable states, such as being supercooled or supersaturated. Standard tensiometry instruments face challenges in accessing these states due to the large sample volumes they require and rapid phase changes near surfaces. We present an instrument that uses a strong electric field, nearing the dielectric strength of air, to deform aerosol microdroplets and measure surface tension in a contact-free, humidity-controlled environment. A dual-beam optical trap holds single microdroplets between two electrodes and excites Raman scattering. When a high voltage is applied, droplet deformations reach tens of nanometers. These small shape changes are precisely measured through the splitting of morphology-dependent resonances, seen as sharp peaks in Raman spectra. Our measurements cover water activities where droplets are supersaturated, a region with limited previous data, and show good agreement with existing data where comparisons are possible. Unlike prior levitation-based methods, this approach measures surface tension in systems with viscosities over 10 Pa s without relying on dynamic processes.
精确测量表面张力是理解和预测大气气溶胶行为的关键，尤其是它们的形成、生长和相变。在地球大气中，气溶胶常常处于亚稳态，比如过冷或过饱和状态。标准张力测量仪器由于所需样本体积大且表面附近存在快速相变，在获取这些状态时面临挑战。我们展示了一种仪器，它利用接近空气介电强度的强电场使气溶胶微滴变形，并在无接触、湿度可控的环境中测量表面张力。双光束光阱将单个微滴捕获在两个电极之间并激发拉曼散射。施加高电压时，液滴变形可达数十纳米。通过形态依赖共振的分裂精确测量这些微小的形状变化，在拉曼光谱中表现为尖锐峰。我们的测量涵盖了液滴过饱和的水活度范围，这是一个此前数据有限的区域，并且在可比较的情况下与现有数据显示出良好的一致性。与先前基于悬浮的方法不同，这种方法在粘度超过10 Pa·s的系统中测量表面张力，而不依赖于动态过程。
