Vapor sensing properties of a conductive polymer composite containing Nickel particles with nano-scale surface features

This paper presents an unusual conductive polymer composite, produced by Peratech Ltd under the trademark QTC™, which has many vapor sensing applications. Nickel particles are intimately coated by an elastomeric binder such that no percolative conduction can occur. However, the nickel particles are shown to possess spiky nanoscale surface features, which promote conduction by a field-assisted quantum tunneling mechanism. Granular QTC™ can be dispersed into a polymer matrix to produce a vapor sensor. Under exposure to vapor, the polymer swells and the resistance of the composite increases. In this work, granular sensors are subjected to acetone and tetrahydrofuran (THF) vapors. The response for THF shows an increase in resistance of a factor of 10⁸, over a time-scale of a few seconds. This response is larger and faster than many conventional vapor sensing composites. This is a significantly larger response than that obtained historically for the same sensor, suggesting that some degree of sensor aging is desirable. The response and subsequent recovery can be explained by a case II diffusion model, and linked to Hildebrand solubility parameters of the vapor and polymer components.