Spatio-temporal thickness variation and transient Marangoni number in striations during spin coating
Spatio-temporal thickness variation and transient Marangoni number in striations during spin coating
复制标题
旋涂过程中条纹中的时空厚度变化和瞬态马兰戈尼数
DOI：
10.1016/j.ijheatmasstransfer.2020.119678
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发表时间：
2020
影响因子：
5.2
通讯作者：
Shimano Kenjiro
中科院分区：
文献类型：
--
作者：
Shiratori Suguru;Kato Daiki;Sugasawa Kyosuke;Nagano Hideaki;Shimano Kenjiro
实验研究了环氧树脂和二甲苯溶剂混合物在旋涂过程中产生的径向轮辐状厚度起伏条纹的形成过程。通过厚度变化的光学测量证实，条纹的产生在旋涂的非常早期的阶段开始。时空厚度变化表现出相当复杂的行为，涉及波长光谱的剧烈变化。值得注意的是，在早期阶段缓慢增长的短波长分量在中期突然消失。实验观察到的瞬态厚度变化示出对应于流态的变化，下的假设，条纹是由于溶质Marangoni-Bénard不稳定性的衍生形式产生的。瞬态Marangoni数预测的数值模拟的基础上一个简单的数学模型，其中的厚度减小，由于离心力和溶剂蒸发被认为是，连同在厚度方向上的浓度分布的时间演化。Marangoni数Mais预计将增加以及减少了一些数量级。在实验中观察到的短波长分量的突然消失可能与Madown下降到亚临界值的流态的某一分叉。当转动速率较小时，分岔的Marangoni数在1000 <Ma< 1800范围内。
A formation process of striation, radial spoke-like thickness undulations arising during a spin coating, was experimentally investigated for mixtures of epoxy resin and xylene solvent. It was confirmed by optical measurement of thickness variations that the generation of striation started at a very early stage of spin coating. The spatio-temporal thickness variation exhibited a rather complex behavior that involved drastic changes to the wavelength spectrum. It is noteworthy that the short-wavelength components, which slowly grow during the early stage, suddenly vanished in the middle stage. The experimentally observed transient thickness variations are shown to correspond to changes in the flow regimes, under the hypothesis that striation is generated due to a derivative form of the solutal Marangoni-Bénard instability. The transient Marangoni number is predicted by a numerical simulation based on a simple mathematical model in which the thickness decreases due to centrifugal force and solvent evaporation is considered, together with the time evolution of the concentration distribution in the thickness direction. The Marangoni numberMais predicted to increase as well as a decrease by some order of magnitude. The sudden disappearance of the short-wavelength component observed in the experiment might be associated with the falling ofMadown to the sub-critical value for a certain bifurcation of the flow regimes. The Marangoni number for the bifurcation is predicted to be in the range 1000 <Ma< 1800 when the rotation rate is small.