Improving humidity sensing properties of copolymer-based polyelectrolytes by modifying the chemical structure and content of the comonomers

Three kinds of copolymer based polyelectrolytes, including hydrolyzed and sulfonated poly(styrene-alt-maleic anhydride) (HSPSMA), hydrolyzed poly(sodium p-styrenesulfonate-co-maleic anhydride) (HPSSMA), and poly (sodium p-styrenesulfonate-co-itaconic acid) (PSSIA), have been synthesized by the radical copolymerization and functionalized via sulfonation and hydrolyzation. The polyelectrolytes were characterized by FT-IR, H-1-NMR and C-13-NMR, scanning electron microscopy and static water contact angle measurements, and their humidity sensing properties have been investigated at room temperature. The chemical structure and content of the comonomers have great effect on the humidity sensing behaviors of corresponding polyelectrolytes, such as response time, hysteresis and response magnitude, which is ascribed to the distinct interactions of the sensing materials with water molecules. Under optimal conditions, the composite of crosslinked PSSIA (molar feed ratio of SS/IA = 1/4) with polyaniline displayed good response magnitude (impedance variation of two orders of magnitude between 10%RH and 90%RH), small hysteresis ((similar to)4.5%RH) and fast response (t(90%) of 9 s and 17 s for adsorption and desorption process). The work provides a new approach for the construction of high performance polyelectrolyte based humidity sensors.