Oxidized Carbon Nanohorn-Hydrophilic Polymer Nanocomposite as the Resistive Sensing Layer for Relative Humidity

Abstract

This study presents relative humidity (RH) sensing response of resistive sensors composed of nanocomposites with oxidized single-wall carbon nanohorns (SWCNHs) and hydrophilic polymers in different ratios at room temperature. The poly(ethylene glycol)-blockpoly(propylene glycol)-block-poly(ethylene glycol) (PEG-PPG-PEG) and polyvinylpyrrolidone (PVP) materials were selected to be the hydrophilic polymers. Two types of nanocomposites with PVP were synthesized, one using SWCNHs/VP at 1/2 (w/w) ratio and another with SWCNHs/PVP in a 1/1 (w/w) ratio. The sensing structure is composed of a Si substrate, a SiO₂ layer, and interdigitated (IDT) electrodes, on which the sensing layer is deposited via the drop-casting method. The sensor has a response comparable to that of a commercially available, state-of-the-art, capacitive relative humidity sensor, being characterized by a rapid response time and excellent stability with time. Two sensing mechanisms are considered and analyzed. The first involves the rapid swelling of the host hydrophilic polymer at higher relative humidity levels. The second involves a decrease in the number of holes due to interaction with water molecules, which act as electron donors.

Keywords:

• Humidity sensor
• oxidized single wall carbon nanohorns
• polyvinylpyrrolidone
• swelling

Additional information

Funding

This work has been funded by the Romanian Ministry for Research and Innovation (MCI), through the PN 1916/2019 - MICRO-NANO-SIS PLUS/08.02.2019 program.