Tomar Bhawana Singh, Shahin A, Tirumkudulu Mahesh S
Department of Chemical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai, 400076, India.
Soft Matter. 2020 Apr 14;16(14):3476-3484. doi: 10.1039/c9sm02294e. Epub 2020 Mar 25.
Thin films of polymer coatings have important industrial applications ranging from paints and coatings to pharmaceuticals. In many applications, the coatings are obtained by applying thin films of dilute polymer solutions, wherein the solvent evaporates to leave behind a thin polymer film. In some cases, the thin films may crack due to shrinkage stresses developed during drying. While a number of studies have focused on the stress development, the phenomenon of cracking in polymer films is not fully investigated. In the present work, thin films of a silicone polymer solution were cast on substrates of varying Young's moduli and investigated for cracking as a function of film thickness and substrate modulus. Micro-Raman spectroscopy measurements show that thin films dry uniformly while thick films form a skin at the top surface leading to slow drying rates. Transverse stresses were measured using the cantilever technique and related to the extent of cracking in the film. We investigated the influence of substrate rigidity on the cracking behavior and found that decreasing the stiffness of the substrate increases the extent of cracking.
聚合物涂层薄膜在从油漆和涂料到制药等众多工业领域都有重要应用。在许多应用中，涂层是通过施加稀聚合物溶液的薄膜来获得的，其中溶剂蒸发后留下一层薄聚合物膜。在某些情况下，薄膜可能会因干燥过程中产生的收缩应力而开裂。虽然已有多项研究聚焦于应力的产生，但聚合物薄膜的开裂现象尚未得到充分研究。在本研究中，将有机硅聚合物溶液的薄膜浇铸在具有不同杨氏模量的基材上，并研究其作为薄膜厚度和基材模量函数的开裂情况。显微拉曼光谱测量表明，薄膜均匀干燥，而厚膜在顶表面形成一层表皮，导致干燥速度缓慢。使用悬臂技术测量横向应力，并将其与薄膜中的开裂程度相关联。我们研究了基材刚度对开裂行为的影响，发现降低基材的刚度会增加开裂程度。
