Water-resistive humidity sensor prepared by printing process using polyelectrolyte ink derived from new monomer

A simple strategy was developed based on a new monomer containing both photocurable function and ammonium salt, N-(2-cinnamoyloxy)ethyl-N-(2-(methacryloyloxy) ethyl)-N, N-dimethyl ammonium bromide (CMDAB) to obtain photocurable polyelectrolyte ink and stable humidity-sensitive membranes by printing process. Humidity-sensitive membranes are photocrosslinked polyelectrolytes obtained from copolymers of [2-(methacryloyloxy) ethyl] dimethyl propyl ammonium bromide (MEPAB), CMDAB and MMA. A flexible gold electrode/polyimide was pretreated with 2-(mercaptoethyl) cinnamamide (MEC) containing a thiol-coupling agent for the purpose of anchoring the humidity-sensitive polyelectrolyte to the gold electrode. The sensors using screen printing methods reduced the deflection of sensor characteristics showing humidity precision +/- 1% RH. The photocured copolymer MEPAB/CMDAB/MMA = 63/7/30 show good sensitivity (0.0586 logU/%RH) changing resistance approximately four orders of magnitude with relative humidity varying from 20% to 95% and fast response and recovery time. The resultant sensors showed acceptable linearity (Y = 0.04X + 7.0, R-2 = -0.9900) and small hysteresis. The reliability including water resistance and a long-term stability were estimated for the application of the flexible humidity sensor prepared by screen printing process.