Effect of polydimethylsiloxane content on the electrothermal performance and tensile strength of laser induced graphene films: Experimental and theoretical

Background

Since its discovery in 2014, laser induced graphene (LIG) has gained a lot of interest from research institutions and the industry as a result of its single-step fabrication process and tailorable properties. Nonetheless, LIG's brittle nature makes it susceptible to any mechanical disturbances thus shearing off from the polyimide (PI) sheet surface. This limits its applicability in electrothermal heating and other applications requiring high flexibility. Therefore, there is a need to enhance LIG's robustness on the precursor surface.

Methods

To overcome this, LIG films were fabricated from PI using a 10.6 µm CO₂ laser machine and polydimethylsiloxane (PDMS) contents were infused into the LIG structure by spin coating to form LIG/PDMS films. Furthermore, the adhesion strength of LIG/PDMS films was further improved by making micro scratches on the substrate surface by pressing the PI sheets in between the jaws of a Universal Testing Machine (UTM). The joule heating of LIG and LIG/PDMS heaters was evaluated before, during, and after mechanical testing. Theoretical models (heat balance and Ansys Finite Element, FE) were also performed to validate experimental results.

Significant findings

At an input DC voltage of 8 V, the LIG/PDMS with 50 μL PDMS and LIG heaters generated saturation temperatures of 250 and 308.86 °C, respectively. Much as the saturation temperatures were lower for LIG/PDMS heaters, their mechanical strength was enhanced in comparison with the LIG heaters. LIG/PDMS films could undergo more bending cycles (4800) than LIG films (2400). Additionally, LIG/PDMS film accommodated more stress (⁓ 0.16 Mpa) than LIG film (⁓ 0.04 Mpa) after tensile tests. Interestingly, the LIG/PDMS heater's electrothermal performance was better than that of LIG heater after tension. The heat balance equation and simulation results showed a tight match with experimental generated temperatures, verifying the approach's trustworthiness. Hence, the demonstrated effectiveness and efficiency of LIG-based heaters with high flexibility under various mechanical stresses open new possibilities for diverse electronic applications.