Highly sensitive humidity sensors based on electro-spinning/netting a polyamide 6 nano-fiber/net modified by polyethyleneimine

Abstract

A simple and straightforward strategy of depositing a nanostructured complex, based on a polyethyleneimine (PEI) functionalized polyamide 6 (PA 6) (PEI-PA 6) nano-fiber/net (NFN), on a quartz crystal microbalance (QCM) sensor for humidity detection is demonstrated. The PA 6 NFN substrate, comprising common electrospun nanofibers and spider-web-like nano-nets fabricated by a versatile electro-spinning/netting (ESN) process, exhibits several fundamental characteristics, such as a remarkable specific surface area, high open porosity and good interconnectivity. Therefore, the sensors based on PEI-PA 6 NFN membranes show high sensitivity and fast response/recovery time to humidity, which outperform current porous structure-based sensors. The frequency changes by approximately three orders of magnitude with relative humidity (RH) varying from 2% to 95%. Moreover, the resultant sensors also presents relatively small hysteresis and long-term stability. For low RH levels, the response of the QCM sensor is dependent on water molecules adsorbed/desorbed masses on NFN membranes, whereas for increasing RH levels variations in interlayer expansion stress of NFN membranes derived from the swelling effect become prevalent. This study demonstrates that NFN structured materials are have potential applications for fabricating high performance humidity sensors.