Ionic Liquid Microemulsion-Templated Bacterial Cellulose−Poly(ionic liquid)/Carbon Black Membranes with Coupled Porous and Conductive Networks for Stable Humidity Sensing

Abstract Humidity sensing membranes combining high sensitivity, mechanical robustness, and long-term stability remain challenging to fabricate via simple, scalable routes. Using a surfactant-free ionic liquid microemulsion and nanofibrillar bacterial cellulose, we fabricated a short-range ordered bicontinuous porous composite membrane in one step. In situ polymerized poly(ionic liquid) forms strong hydrogen-bonded interfaces with cellulose, while microemulsion templating generates interconnected pores. Carbon black (CB) and isopropyl alcohol (i-PA) synergistically regulate the membrane structure and properties. Increasing the CB content enhances mechanical strength and lowers electrical resistance through conductive percolation, whereas i-PA controls fracture morphology and porosity. The optimized formulation (5 wt % CB, 37.5% excess i-PA) achieves a tensile strength of 2.66 MPa and a relative resistance response of 87% at 95% relative humidity, with negligible performance degradation after 1000 tensile cycles. These findings establish ionic liquid microemulsion templating as a scalable route to durable, porous iontronic membranes for high-performance humidity monitoring.