TEMPO-oxidized cellulose nanofibre (TOCN) films and composites with PVOH as sensitive dielectrics for microwave humidity sensing

• Published in: Sensors and actuators. B, Chemical Chemical, 2019-07, Vol.291, p.385-393
• Main Authors: Ayissi Eyebe, Guy François Valery, Bideau, Benoît, Loranger, Éric, Domingue, Frédéric
• Format: Article
• Language: English
• Subjects: Cellulose; Coplanar waveguides; Dielectrics; Electromagnetic fields; Gels; Grounded coplanar waveguide technology (CPWG); Humidity; Microwave frequencies; Microwave humidity sensing; Nanofibers; Poly-vinyl alcohol (PVOH); Polyvinyl alcohol; Resonant frequencies; Resonators; Sensitivity; TEMPO oxidized cellulose nanofibers (TOCN); Thin films
• ISSN: 0925-4005; 1873-3077
• DOI: 10.1016/j.snb.2019.04.070

•Humidity sensing using environmentally-friendly TOCN films as sensitive materials is demonstrated.•Original sensing scheme in CPWG technology combined with slots is proposed and validated through electromagnetic resonance analysis.•Effect of PVOH integration on TOCN materials as host-matrix is studied.•Sensitivity reached with TOCN/PVOH films with CPWG-based resonator is by far better than previous results in literature.•Characterization of the humidity-dependent dielectric properties of TOCN films is achieved.•Quality of the microwave analysis along the humidity measurement range is analyzed. This paper investigates TEMPO oxidized cellulose nanofibers (so-called TOCN) films as sensitive dielectrics for humidity detection in microwave frequencies. TOCN is used either as a sensitive material or as a host-matrix enclosing polyvinyl alcohol (PVOH) to achieve highly sensitive humidity sensing. A resonator in coplanar waveguide grounded (CPWG) technology was designed and fabricated. TOCN and TOCN/PVOH gels were dropped in the area of the resonator where the analysis showed the electromagnetic field to be maximum at the resonance. Gels became thin films after drying. Experimental humidity tests were then conducted within the 21.9–89.3%RH range, using the resonant frequency and the transmission phase as measurement variables. The best sensitivity with TOCN was 2.67 MHz/%RH regarding the resonant frequency, and 0.523°/%RH regarding the transmission phase. The effects of PVOH were visible starting from 55%RH, where the sensitivity was raised to 6.000 MHz/%RH and 0.785°/%RH respectively.