Generation and Combination of Ionogel Microstructures Using the Vacuum-Driven Lithography Technique

Ionogels have gained significant attention as versatile materials for various advanced applications, particularly in environmental monitoring and biomedical sensing. Their ability to serve as highly sensitive and adaptable materials stems from their unique combination of ionic conductivity, mechanical flexibility, and tunable chemical and physical properties. However, the fabrication of precise and intricate microstructures with these materials remains a challenge, limiting their optimization for specific high-performance applications, such as miniaturized sensors, actuators, or devices requiring enhanced surface area or structural complexity. Addressing this limitation, this study introduces vacuum-driven lithography as an efficient, high-resolution method for generating homogeneous photocurable ionogel microstructures. This technique leverages a controlled vacuum environment to ensure precise and reproducible material distribution within intricate mold architectures, achieving detailed structures in a single loading and polymerization step. By optimizing the process with 20 Ultraviolet (UV) exposure cycles, ionogel microstructures with heights below 25 μm were fabricated, achieving the resolution defined by the mold generated by photolithographic techniques. These microstructures were fabricated using three distinct ionogels based on cross-linked poly(isopropylacrylamide) using ionic liquids as solvents: 1-ethyl-3-methylimidazolium ethyl sulfate, trihexyl(tetradecyl)phosphonium dicyanamide, and choline acetate. Furthermore, the functional versatility of these microstructures was demonstrated by incorporating bromocresol purple into the ionogel based on choline acetate, resulting in a robust colorimetric pH sensor capable of detecting pH values from 3 to 12. This study underscores the adaptability and stability of vacuum-driven lithography for ionogel microstructure fabrication, introducing a novel ionogel processing method.