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Cracking in drying films of polymer solutions.
Bhawana Singh Tomar1, A Shahin, Mahesh S Tirumkudulu
1Department of Chemical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai, 400076, India. mahesh@che.iitb.ac.in.
Soft Matter
|March 27, 2020
Summary
Polymer film cracking during drying is influenced by film thickness and substrate stiffness. Thicker films crack more, and less stiff substrates increase cracking extent, impacting industrial coating applications.
Area of Science:
- Materials Science
- Polymer Science
- Surface Chemistry
Background:
- Thin polymer films are crucial in industries like paints, coatings, and pharmaceuticals.
- Film formation involves solvent evaporation, which can induce shrinkage stresses.
- Cracking in polymer films due to drying stresses is a significant issue, yet not fully understood.
Purpose of the Study:
- To investigate the cracking behavior of silicone polymer thin films.
- To understand the influence of film thickness and substrate Young's modulus on cracking.
- To correlate stress development with observed cracking patterns.
Main Methods:
- Casting thin films of silicone polymer solutions onto substrates with varying Young's moduli.
- Utilizing Micro-Raman spectroscopy to analyze film drying uniformity and rates.
- Employing the cantilever technique to measure transverse stresses in the films.
Main Results:
- Thin films exhibited uniform drying, while thicker films developed a surface skin, slowing drying.
- Transverse stresses were measured and linked to the degree of film cracking.
- A decrease in substrate stiffness was found to significantly increase the extent of cracking.
Conclusions:
- Substrate rigidity plays a critical role in the cracking behavior of drying polymer films.
- Understanding these mechanics is essential for optimizing thin film coating processes and preventing defects.
- Further research can leverage these findings to design more robust polymer coatings.
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