Carbonization of polyimide using CO2 laser and femtosecond laser for sensor applications
Biswas, Ratul Kumar
Biswas, Ratul Kumar
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Publication Date
2023-10-05
Type
Thesis
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Abstract
Laser carbonization is the process of photothermal conversion of polymers rich in aromatic carbons such as Polyimide (PI) into graphene, via a process called Laser Induced Graphene (LIG) using a laser as the source of heat and pressure. This process allows the printing of conductive graphene-circuits on flexible polymeric substrates without chemicals in liquid or gaseous state and transfer printing process used in other graphene deposition methods. The Carbon-di-oxide (CO2) laser is most commonly for this process due to the strong absorption of PI at 10.6 µm. Femtosecond lasers reduce the interaction with the material and include multiphoton absorption process in dielectrics and polymers allowing both carbonization and ablation using a single IR laser source. In this project, the interaction of both CO2 laser and femtosecond laser radiation with PI is studied and techniques such as laser graphitization and plasma treatment of PI surface were applied to improve the electrical conductivity of LIG by ~2.6 times and ~51% respectively. Photothermal models were solved using Finite Element Method to estimate the irradiation temperatures (400-900 K) of PI and were experimentally validated from threshold conditions. The temperature estimated was used to study the thin film growth kinetics of LIG using the Arrhenius model and the activation temperature and energy of formation of LIG from PI were calculated as 2.35±0.30 x 103 K and 0.20±0.03 eV respectively. Finally, the carbonization of PI using femtosecond laser radiation was modelled using heat accumulation model and the multiphoton absorption of laser radiation by PI was used to create ablation which enables precise cutting without any thermal damage. This technique was used to print a Kirigami inspired strain sensor using a single laser source. Kirigami patterning of PI was used to improve the sensitivity of strain sensors. Kirigami cuts showed ~3 times better sensitivity to body motions when compared to planar sensors, and femtosecond laser processed LIG showed that the Gauge Factor was improved by ~4 times than that obtained using CO2 laser due to different morphology of LIG.
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NUI Galway