Dual-Balance Electrodynamic Trap as a Microanalytical Tool for Identifying Gel Transitions and Viscous Properties of Levitated Aerosol Particles
Dual-Balance Electrodynamic Trap as a Microanalytical Tool for Identifying Gel Transitions and Viscous Properties of Levitated Aerosol Particles
复制标题
双平衡电动阱作为微分析工具，用于识别悬浮气溶胶颗粒的凝胶转变和粘性特性
DOI：
10.1021/acs.analchem.9b04487
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发表时间：
2020
影响因子：
7.4
通讯作者：
Davis, Ryan D.
中科院分区：
文献类型：
--
作者：
Richards, David S.;Trobaugh, Kristin L.;Hajek-Herrera, Josefina;Davis, Ryan D.
气溶胶颗粒内凝胶状网络的形成显着改变了气溶胶材料的物理化学性质。研究凝胶转变的现有技术依赖于体积流变测量法，其受到与样品接触的限制，或者依赖于昂贵的设备和能够降解光吸收气溶胶的高功率激光器的微流变技术，例如全息光镊。在这里，我们提出了一种新技术来探测气溶胶颗粒的微流变特性，并探索大气条件下非接触环境下的凝胶形成，而不需要高功率光源。在双平衡四极电动平衡中，相反极性的悬浮液滴被捕获并在固定相对湿度 (RH) 下平衡，然后合并，并使用成像技术监测合并液滴的物理特性作为时间和 RH 的函数。通过在固定平衡时间尺度下比较 MgSO4（已知经历凝胶转变）与葡萄糖和蔗糖（已知保持粘性牛顿流体）的相对湿度依赖性特征，我们证明可以在气溶胶颗粒中识别凝胶相变，MgSO4 在 30% RH 下突然转变为刚性微凝胶。此外，我们证明该技术还可用于测量气溶胶粘度并识别由 NaCl、CaCl2 和山梨糖醇组成的模型海喷雾气溶胶中的非牛顿流体动力学。因此，使用该实验技术，可以区分形成粘性牛顿流体的气溶胶组合物和经历凝胶转变或形成非牛顿流体的气溶胶组合物。该技术提供了一种简单且经济高效的分析工具，用于探测体积溶解度极限之外的凝胶转变，相关应用范围从大气科学到软物质材料的微工程。
The formation of gelatinous networks within an aerosol particle significantly alters the physicochemical properties of the aerosol material. Existing techniques for studying gel transitions rely on bulk rheometry, which is limited by contact with the sample, or microrheological techniques such as holographic optical tweezers, which rely on expensive equipment and high-powered lasers that can degrade light-absorbing aerosol. Here, we present a new technique to probe the microrheological characteristics of aerosol particles and explore gel formation under atmospheric conditions in a contactless environment without the need for high-power light sources. In a dual-balance quadrupole electrodynamic balance, levitated droplets of opposite polarity are trapped and equilibrated at fixed relative humidity (RH) and then subsequently merged, and the physical characteristics of the merged droplets are monitored as a function of time and RH using imaging techniques. By comparing the RH-dependent characteristics of MgSO4(known to undergo a gel transition) to glucose and sucrose (known to remain as viscous Newtonian fluids) under fixed equilibration time scales, we demonstrate that gel phase transitions can be identified in aerosol particles, with MgSO4abruptly transitioning to a rigid microgel at 30% RH. Further, we demonstrate this technique can be used to also measure aerosol viscosity and identify non-Newtonian fluid dynamics in model sea spray aerosol composed of NaCl, CaCl2, and sorbitol. Thus, using this experimental technique, it is possible to distinguish between aerosol compositions that form viscous Newtonian fluids and those that undergo a gel transition or form non-Newtonian fluids. This technique offers a simple and cost-effective analytical tool for probing gel transitions outside of bulk solubility limits, with relevant applications ranging from atmospheric science to microengineering of soft matter materials.