Structural and optical characteristics modifications of surface polyimide films by ultrasonic chemical treatment

We report on a simple and low-cost method for the surface modification of polymers by ultrasonic chemical treatment at atmospheric pressure and room temperature. Polyimide films (Kapton) were immersed in different solvents for various durations. After being subjected to ultrasonic cleaning, the surface energies of the Kapton films were determined by the wettability method to improve the adhesion of the films to a suitable coating. The results show that the surface energy of the polyimide films has an optimum value of approximately 55.1 mJ/m² obtained for ethanol cleaning for 25 min. These values are comparable to those achieved with higher-cost and more complex techniques such as plasma treatment. The optical band gap (E_g) and the number of carbon atoms were measured by using UV-visible spectroscopy on Kapton samples to analyze their absorption. Notably, the optical band gap decreased from 2.30 to 2.24 eV after 25 min of ethanol treatment, indicating improved electronic properties. This reduction in E_g enhances light absorption and is crucial for optimizing the material’s performance in optoelectronic applications. The vibration peaks of the chemical bonds present in these films were identified using FTIR spectroscopy, which was used to characterize the films and track their progression over time. Following the use of the optimized ultrasonic cleaning method, the FTIR analysis showed an increase in the C=O symmetrical and asymmetrical stretching peaks at 1713 and 1774 cm⁻¹, respectively, as well as C–O–C bond stretching at 1240 cm⁻¹. Mechanical tensile tests (MTSs) were used to measure elastic parameters such as Young’s modulus, tensile strength, and strain to failure for untreated and treated samples.