Preparation of stable crosslinked polyelectrolyte and the application for humidity sensing

In order to obtain stable humidity sensitive polyelectrolyte, crosslinked polyelectrolyte with cage-shaped polyhedral oligomeric silsesquioxane (POSS) and hydrophilic tetraphenylphosphonium bromide (TPPBr) units has been synthesized via Friedel-Crafts alkylation. The obtained polyelectrolyte POSS-TPPBr owns both porous structure and hydrophilic property. The structure of POSS-TPPBr has been characterized with fourier transform infrared spectroscopy (FT-IR), nitrogen (N-2) isotherms and scanning electron microscopy (SEM). Humidity sensor based on POSS-TPPBr was prepared, which demonstrated a good response towards humidity, with impedance changing three orders of magnitude over the whole relative humidity (RH) range and little humidity hysteresis. Further, the composited film of POSS-TPPBr blended with polystyrene (PS) was developed to enhance the film-forming capability of the crosslinked polymer. As we expected, the humidity hysteresis and recovery speed of POSS-TPPBr/PS sensor have been improved compared with POSS-TPPBr sensor.