Feasibility verification for using flexible spiral MWCNTs/ZSM-5/TOCNFs composites to measure humidity and distance

This study develops a dual-functional flexible spiral element based on multi-walled carbon nanotubes/ ZSM-5/2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)- oxidized cellulose nanofibers (MWCNTs/ZSM-5/TOCNFs) composites for humidity-distance detection in critical equipment interlayers, fabricated via mask-assisted spray deposition. Through systematic optimization of component ratio (MWCNTs: 20 mg, ZSM-5: 200/400/800 mg, TOCNFs: 0.125/0.25/0.5/1 mg), the optimal element M₂₀Z₄₀₀T_0.25 (MWCNTs/ZSM-5/TOCNFs=20:400:0.25) demonstrates a great humidity resistance response of 2520.15%/90% RH with a short response/recovery time of 6.5/15 s (43-90% RH), owing to the exceptional tri-phase synergy: MWCNTs establish conductive pathways, TOCNFs enable humidity- selective surface interactions, and ZSM-5 sieves provide nanochannels for rapid diffusion of water molecules. The spiral architecture enables impedance to be sensitive to the distance between the element and the target (copper). As temperature increases from 15℃ to 35℃, the humidity resistance response rises from 1486.20%/90% RH to 3189.55%/90% RH, and the distance sensitivity (0-2.5 mm, 40~90% RH) of impedance amplitude reduces from 9.537%·mm^-1 to 3.059%·mm^-1. A measuring strategy is proposed based on humidity-exclusive resistance and humidity/distance-coupled impedance. This work offers a promising solution for health monitoring of key facilities.