Chemochromic PAni/PVA nanocomposite towards pH measurement in soils

Measuring pH is important for characterising a range of different environmental conditions– including within agricultural soils when understanding the availability of nutrients for crops. Optical pH sensing is one method that holds promise for continuous in-ground measurements with spatial mapping capability. One key element in achieving this is the development of chemochromic materials that change their optical properties in response to changes in pH. Conducting polymers are one such class of material –more specifically polyaniline (PAni)– that interact with ions in their surrounding environment with resultant changes in their optical properties. In this study, a nanocomposite of PAni particles dispersed within a polyvinyl alcohol (PVA) matrix is fabricated and tested. The resultant composite shows promise within the pH range of 5 to 8.5, typical of most agricultural soils. The key finding is that a ratiometric approach that combines the visible and infrared response removes the need for prior characterisation of the sensing layer.