Sulphonated polystyrene-b-poly(4-vinylpyridine) with nanostructures induced by phase separation as promising humidity sensitive material

Abstract

Nanostructured humidity sensors have been facilely prepared by solvent annealing of polystyrene-b-poly(4-vinylpyridine) deposited on interdigitated gold electrodes and subsequent sulphonation. The structure, composition, morphology and hydrophilicity of the block copolymer (BCP) have been characterized by gel-permeation chromatography, 1H NMR, FT-IR, elemental analysis, scanning electron microscopy and static water contact angle measurements. Phase separation of the BCP film induced by annealing in CHCl3 vapor and hot ethanol resulted in its fishnet-like porous nanostructure. Humidity sensing properties of the nanostructured BCP based sensor have been examined at room temperature, and the sensing mechanism was examined. Both concentration of polymer solution for film preparation, and the sulphonation duration seriously affected the sensing properties of the BCP based sensor. Under optimal conditions, the BCP based sensor demonstrated high response magnitude towards relative humidity (RH) (impedance change of three orders of magnitude in the range of 40–90%RH). Moreover, it was featured with quick response (t90% of 10s and 13s for humidification and desiccation, respectively), good sensing repeatability and relatively small hysteresis (∼5%RH), which is attributed to its special nanostructure. The desirable sensing performance suggests the potentials of the BCP with phase separation-induced nanostructures as high performance humidity sensing material.