Photo-Programmable Semi-IPN Glycol Gels with Microscale Thermal-Mechanical Encoding

Abstract

Organogels, particularly glycol gels, have emerged as promising candidates for flexible electronic substrates due to their inherent stretchability and wide operating temperature range compared to conventional hydrogels. However, their application in next-generation deformable displays is often hindered by insufficient mechanical robustness, thermal dimensional instability, and vulnerability to chemical processing. To address these limitations, this study proposes a robust semi-Interpenetrating Polymer Network (semi-IPN) substrate, wherein a rigid polyimide (PI) network is physically entangled within a tunable glycol gel matrix. The fabrication process was streamlined by leveraging a spatially selective photo-thermal imidization technique, eliminating the need for high-temperature ovens. Optimization of the precursor concentration revealed that a 1 wt% poly(amic acid) loading provides the ideal balance between optical clarity and mechanical reinforcement. The introduction of the PI network significantly enhanced the material’s performance, achieving a 35% reduction in the Coefficient of Thermal Expansion (CTE), superior moisture resistance under accelerated aging conditions (85°C/85% RH), and robust stability against aggressive display process solvents such as D2 and NI555. Furthermore, the developed material demonstrated intrinsic thermo-responsive shape memory capabilities with high fixity (>96%) and recovery rates. Utilizing the photo-thermal patterning capability, a "Rigid Island" architecture was successfully realized. This structure induces a modulus mismatch between the rigid, imidized islands and the compliant matrix, effectively achieving strain isolation to protect integrated electronic components during deformation. Consequently, this study establishes the photo-thermally imidized semi-IPN glycol gel as a versatile and process-compatible platform for advanced form-factor-free electronics.

Keywords: Semi-IPN Polymer Gel; Glycol Gel; Polyimide composite; Flexible Substrate; Shape Deformable Substrate; Free-form Display