Berlinger Sarah A, Chen Xunkai, Yutkin Maxim, Radke Clayton J
Department of Chemical and Biomolecular Engineering, University of California, Berkeley, Berkeley, California 94720 United States.
Energy Resources and Petroleum Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900 Saudi Arabia.
Langmuir. 2022 Aug 23;38(33):10114-10127. doi: 10.1021/acs.langmuir.2c00998. Epub 2022 Aug 11.
Quartz crystal microbalance with dissipation (QCM-D) conveniently monitors mass and mechanical property changes of thin films on solid substrates with exquisite resolution. QCM-D is frequently used to measure dissolved solute/sol adsorption isotherms and kinetics. Unfortunately, currently available methodologies to interpret QCM-D data treat the adlayer as a homogeneous medium, which does not adequately describe solution-adsorption physics. Tethering of the adsorbate to the solid surface is not explicitly recognized, and the liquid solvent is included in the adsorbate mass, which is especially in error for low coverages. Consequently, the areal mass of adsorbate (i.e., solute adsorption) is overestimated. Further, friction is not considered between the bound adsorbate and the free solvent flowing in the adlayer. To overcome these deficiencies, we develop a two-phase (2P) continuum model that self-consistently determines adsorbate and liquid-solvent contributions and includes friction between the attached adsorbate and flowing liquid solvent. We then compare the proposed 2P model to those of Sauerbrey for a rigid adlayer and Voinova et al. for a viscoelastic-liquid adlayer. Effects of 2P-adlayer properties are examined on QCM-D-measured frequency and dissipation shifts, including adsorbate volume fraction and elasticity, adlayer thickness, and overtone number, thereby guiding data interpretation. We demonstrate that distinguishing between adsorbate adsorption and homogeneous-film adsorption is critical; failing to do so leads to incorrect adlayer mass and physical properties.
带有耗散监测功能的石英晶体微天平（QCM-D）能够以极高的分辨率方便地监测固体基底上薄膜的质量和力学性能变化。QCM-D常用于测量溶解溶质/溶胶的吸附等温线和动力学。不幸的是，目前用于解释QCM-D数据的方法将吸附层视为均匀介质，这并不能充分描述溶液吸附物理过程。吸附质与固体表面的连接未得到明确认识，并且液体溶剂被包含在吸附质质量中，这对于低覆盖率情况尤其错误。因此，吸附质的面质量（即溶质吸附）被高估。此外，未考虑束缚吸附质与在吸附层中流动的自由溶剂之间的摩擦。为克服这些不足，我们开发了一种两相（2P）连续介质模型，该模型能自洽地确定吸附质和液体溶剂的贡献，并包括附着的吸附质与流动的液体溶剂之间的摩擦。然后，我们将提出的2P模型与用于刚性吸附层的绍尔布雷（Sauerbrey）模型以及用于粘弹性液体吸附层的沃伊诺娃（Voinova）等人的模型进行比较。研究了2P吸附层性质对QCM-D测量的频率和耗散位移的影响，包括吸附质体积分数和弹性、吸附层厚度以及谐波次数，从而指导数据解释。我们证明区分吸附质吸附和均匀膜吸附至关重要；不这样做会导致吸附层质量和物理性质错误。
