Paper-based printed impedance sensors for water sorption and humidity analysis

Abstract

The hygroscopic nature of cellulose-based materials poses a challenge in utilising paper for printed electronics. Adsorbed moisture strongly modulates the conductive and dielectric properties of paper. While affecting the function of printed electronic elements, this behaviour is beneficial for low-cost humidity sensing. Here we describe a simple, sensitive paper-based sensor with a pair of inkjet-printed interdigitated electrodes for analysing water sorption of cellulose over a wide range of relative humidity from 10% to 90%. Impedance spectroscopy between 100 Hz and 1 MHz reveals the humidity-dependent electrical properties of paper. We show in particular that measurements at 1 MHz provide reliable information about the water adsorption and desorption of paper. In contrast, testing at frequencies below 200 kHz is dominated by ionic electrode polarisation, masking the water sorption kinetics of the sensor. Transient adsorption follows nearly an exponential function, while desorption is described by a stretched exponential law. At equilibrated conditions, the effective paper permittivity measured during adsorption and desorption is characterised by a Guggenheim-Anderson-de Boer sorption isotherm which allows for a quantitative evaluation of the sorption hysteresis. Our means of sensing provides a simple and practical method of recording and analysing simultaneously conductivity and permittivity as well as wetting and drying of moist paper.

A Potassium Metal-Organic Framework based on Perylene-3,4,9,10-tetracarboxylate as Sensing Layer for Humidity Actuators

“…Many of them are capacitive with a quite linear response in RH but there are also resistive sensors. The materials normally used are paper 32 , polyimide 33 (both materials serve as sensing layer and substrate at the same time), cellulose acetate butyrate (CAB) 34 or carbon nanotubes (CNTs) 35 . But they cannot be utilized as actuators because no abrupt change in their response occurs at any value of moisture content contrary to the here described device whose behavior varies from capacitive to resistive in less than 5%RH.…”

Rice Husk-Derived Cellulose Nanofibers: A Potential Sensor for Water-Soluble Gases

“…The findings indicate that the surface structure could also influence the sensors’ sensing performance because CNF was more porous and less crystalline than TOCNF/G, as confirmed by SEM and XRD analysis. Although there is no definitive answer to the gas sensing mechanism of nanocellulose, our proposed mechanism can be supported by a similar consensus on studying a thin film of water in the interconnected network of cellulose that reacts with the gas molecules modulates cellulose conductivity [ 2 , 4 , 5 ].…”

“…Cellulose can be modified into different structures by chemical methods, and these modified forms have fascinating applications in flexible and disposable sensors [ 2 ]. Cellulose is porous, and it has a hygroscopic network consisting of intertwined fibers in which hydroxyl groups exist on its molecular chains [ 4 ]. Dry cellulose paper contains around 5% moisture by weight at 50% relative humidity [ 5 ].…”

Gold Inks for Inkjet Printing on Photo Paper: Complementary Characterisation

“…In recent years, printed paper electronics have gained attention in various applications, like electrochemical sensors, energy storage devices, solar cells, and radiofrequency identification tags [1][2][3][4][5][6][7][8][9]. Paper-based inkjet-printed flexible electronic circuits with costeffective recyclability, and ecological features, are an alternative to the ongoing current electronic devices [10][11][12].…”