Junisu Belda Amelia, Sun Ya-Sen
Department of Chemical and Materials Engineering, National Central University, Taoyuan 32001, Taiwan.
Department of Chemical Engineering, National Cheng Kung University, Tainan 70101, Taiwan.
Langmuir. 2023 Oct 31;39(43):15249-15259. doi: 10.1021/acs.langmuir.3c01936. Epub 2023 Oct 20.
This study demonstrates hierarchical instabilities in thin films. The hierarchical instabilities display three morphological characteristics: (1) windmill-like patterns at the macroscale, (2) Bénard cells and striations at the microscale, and (3) holes at the mesoscale. Such hierarchical instabilities occurred when spin coating was performed on high-volatile solutions under a high relative humidity (RH) but were suppressed when spin coating was performed on low-volatile solutions regardless of the RH. The high-volatile solutions comprise poly(4-vinylpyridine) (P4VP) in methanol or ethanol. The low-volatility solutions comprise P4VP in propanol or butanol. P4VP molecular weights, P4VP concentrations, spin rates, and film thicknesses are not vital factors in forming hierarchical instability in spin-coated P4VP films. Instead, the formation of hierarchical instabilities depends on the RH and solvent types. Namely, the hierarchical instabilities are driven by Bénard-Marangoni convection, water vapor condensation, and disturbance of spin-up and spin-off stages during spin coating of highly volatile solutions under high RH. Mechanisms of hierarchical instabilities are interpreted in detail.
本研究展示了薄膜中的分层不稳定性。这些分层不稳定性呈现出三种形态特征：（1）宏观尺度上的风车状图案；（2）微观尺度上的贝纳德细胞和条纹；（3）中观尺度上的孔洞。当在高相对湿度（RH）下对高挥发性溶液进行旋涂时会出现这种分层不稳定性，但当对低挥发性溶液进行旋涂时，无论RH如何，这种不稳定性都会受到抑制。高挥发性溶液包括甲醇或乙醇中的聚（4-乙烯基吡啶）（P4VP）。低挥发性溶液包括丙醇或丁醇中的P4VP。P4VP分子量、P4VP浓度、旋转速率和薄膜厚度并非旋涂P4VP薄膜中形成分层不稳定性的关键因素。相反，分层不稳定性的形成取决于RH和溶剂类型。也就是说，分层不稳定性是由贝纳德-马兰戈尼对流、水蒸气凝结以及在高RH下对高挥发性溶液进行旋涂过程中加速和减速阶段的扰动所驱动的。详细解释了分层不稳定性的机制。
