Design and development of flexible humidity sensor for baby diaper alarm: Experimental and theoretical study

Solvent-free synthesis of nanocomposite for flexible humidity sensor is gaining immense interest to fulfill the criteria for its practical application. Herein, present paper reports the development of cadmium sulfide/polyacrylamide nanocomposite as a flexible humidity sensor, which was fabricated by the facile spin-coating technique on PET (polyethylene terephthalate) substrate. Morphological, optical and crystalline nature of CdS/polyacrylamide nanocomposite were investigated using Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), differential scanning calorimetric (DSC), Fourier transmission infrared spectroscopy (FTIR), UV–Visible, and Particle size analysis. Characteristic surface area and pore volume were estimated using BET analysis whereas the hydrophilicity of the sample was investigated using contact angle measurement. As fabricated sensor showed an outstanding humidity sensing response with good linearity in the humidity ranging from 11% to 95%RH. The sensitivity of nanocomposite at high humidity range (50–95%RH) was calculated as 306.47 nF/%RH and is utilized for moisture detection of commonly used baby diapers with alarm. The simulated & optimized computer model of the synthesized composite (Cd-S & Polyacrylamide) using density functional theory and performed several analyses. HOMO-LUMO and correspondingly obtained other electronic parameters were evaluated, which revealed that band gap of the synthesized composite material tends to decrease upon increasing the level of water molecules owing to be better humidity sensing mechanism, and therefore, can be used as humidity sensor.