Fabrication of optically-functionalized colorless polyimide patterns with high durability

Colorless polyimide (CPI) is a promising material for flexible substrates because of its excellent mechanical hardness, chemical durability, thermal stability, and high optical transmittance. In particular, its superior durability under heating and mechanical forces compared with other polymeric materials makes polyimide compatible for industrial applications. Thus, it has been actively investigated for use in preparing flexible and transparent substrates for optical devices. Nevertheless, there is little research on the direct pattering of CPI to form structures with various optical functions. In this research, a simple and cost-effective process involving the patterning of optically functional structures and imidization via thermal nanoimprint lithography (NIL) was developed. CPI films patterned with structures such as nanoscale and microscale cones were fabricated by thermal NIL, and their optical functions, including their anti-reflection and high scattering properties, were demonstrated by UV-vis analysis. Moreover, the patterned CPI film has an excellent thermal stability and a mechanical hardness up to 1.12 GPa; this value was nearly maintained even at 400 °C. Therefore, nano- to microscale optical patterns of CPI were successfully formed, and these structures are stable towards mechanical damage and high temperatures.