Three-Dimensional Sag Tracking in Falling Liquid Films
Three-Dimensional Sag Tracking in Falling Liquid Films
复制标题
下落液膜的三维流挂跟踪
DOI：
10.1021/acs.langmuir.2c01232
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发表时间：
2022
期刊：
影响因子：
3.9
通讯作者：
Wirth, Christopher L.
中科院分区：
文献类型：
--
作者：
Issa, Marola W.;Yu, Hairou;Roffin, Maria Chiara;Barancyk, Steven V.;Rock, Reza M.;Gilchrist, James F.;Wirth, Christopher L.
涂层缺陷通常出现在闪光阶段，即涂膜后溶剂蒸发后的10分钟间隔。了解涂层系统的瞬态流变学和运动学对于避免诸如凹陷等缺陷是必要的，这些缺陷会导致不良的外观。本文综述了一种用于测量这些现象的新技术——变角度检测显微术。这种新的非侵入性流变技术的本质是测量已知重力应力下的流场。用VAIM测量任意方向通过液体薄膜体积的流动剖面。从粒子跟踪测量中推断出薄膜下落的流动运动学。在没有干燥的情况下，最初的基准测量跟踪了已知粘度大于水的~ 140 μm厚薄膜中二氧化硅探针颗粒的速度，倾角为5°和10°。探针颗粒被跟踪到薄膜的整个厚度，速度高达~ 100 μm/s。凹陷流场在~ 10 μm厚的截面上被很好地分解，而且VAIM的测量结果通常具有很高的重复性。利用已知模型，利用互补剖面仪测量的薄膜减薄来预测沉降速度。模型预测结果与实测结果吻合较好，验证了该方法在关联材料性能和流动运动学方面的有效性。
Coating defects often arise during application in the flash stage, which constitutes the ∼10 min interval immediately following film application when the solvent evaporates. Understanding the transient rheology and kinematics of a coating system is necessary to avoid defects such as sag, which results in undesirable appearance. A new technique named variable angle inspection microscopy (VAIM) aimed at measuring these phenomena was developed and is summarized herein. The essence of this new, non-invasive, rheological technique is the measurement of a flow field in response to a known gravitational stress. VAIM was used to measure the flow profile through a volume of a liquid thin film at an arbitrary orientation. Flow kinematics of the falling thin film was inferred from particle tracking measurements. Initial benchmarking measurements in the absence of drying tracked the velocity of silica probe particles in ∼140 μm thick films of known viscosity, much greater than water, at incline angles of 5° and 10°. Probe particles were tracked through the entire thickness of the film and at speeds as high as ∼100 μm/s. The sag flow field was well resolved in ∼10 μm thick cross sections, and in general the VAIM measurements were highly reproducible. Complementary profilometer measurements of film thinning were utilized to predict sag velocities with a known model. The model predictions showed good agreement with measurements, which validated the effectiveness of this new method in relating material properties and flow kinematics.