Poly(N-isopropylacrylamide) microgel-based thin film actuators for humidity sensing

Abstract

In this submission we fabricated a humidity-responsive polymer-based actuator by layering negatively charged poly(N-isopropylacrylamide)-co-acrylic acid microgels and positively charged poly(diallyldimethyl ammonium chloride) on top of a flexible plastic substrate. We show that the extent of the actuation (bending) was dependent on the atmospheric humidity. This property was used to detect atmospheric humidity by hanging weights from the actuator, which were rested on the pan of a top loading balance. This was done in such a way that the amount of the mass resting on the balance depended on the extent of actuator bending, which could then be related to humidity. We found the mass read by the balance to be linearly dependent on the atmospheric humidity in the range of 0–50% humidity, and the devices could be used to detect 0.02% humidity changes. These experiments show that the actuation of the devices can be used for sensing applications, in this case humidity, but will be used in the future to detect various atmospheric gases and other vapors.