Application of partially zwitterionic poly(ionic liquid)s in humidity sensors

Polyelectrolytes have shown promise as sensitive material for high-performance humidity sensors in recent years. How to obtain fast recovery and high sensitivity polyelectrolyte humidity sensors is a great challenge. A kind of poly(ionic liquid)s (PILs) humidity sensors modified by zwitterionic polymers (partially zwitterionic PILs, named PZPILs) were prepared in this work. The PZPILs can transform between PILs and zwitterionic polymers in different humidity sensitive processes. In the adsorption process of water molecules, characteristics of PZPILs are similar to those of PILs. When desorbing water molecules, the characteristics of PZPILs trend to those of sulfobetaine (SB) type zwitterionic polymers. This design endowed the humidity sensors high response and fast response/recovery characteristics. The optimized PZPILs sensor shows high response (4862.8) in a wide relative humidity (RH) range of 11 %-95 %, with short response/recovery time (1.0 s/15.0 s) and small humidity hysteresis about 0.6 % RH. The PZPILs shortened the recovery time of the PILs humidity sensors (from 143.4 s to 15.0 s), and improved the response (from 1980.8 to 4862.8).