CO₂-triggered reversible transformation of soft elastomers into rigid and highly fluorescent plastics

Polymers that alter their properties and functions in response to carbon dioxide (CO₂) exposure offer significant potential for the development of smart technologies and innovative CO₂ utilization approaches. Nonetheless, effectively regulating the behavior of solid-state polymers using CO₂ remains a considerable challenge, highlighting the need for robust and reliable strategies to address this issue. This study presents elastomers that feature nanophase-separated morphologies composed of CO₂-vitrifiable polyethyleneimine and CO₂-permeable polydimethylsiloxane components. The elastomers (Young's modulus (E) of approximately 1 MPa) reversibly transform into hard plastics (E > 2 GPa) in the presence of CO₂. In addition to bulk stiffening, their surface adhesion and friction rapidly shift, and the material's fluorescence is significantly amplified. Here, we show that these multifunctional responses to CO₂ position the materials as innovative platforms for responsive mechanical systems and CO₂-activated optical devices, with potential applications in sensing, display, and data storage technologies.