Direct Colorimetric Temperature Measurement Ahead of Flame Zone with Polydiacetylenes

Measurement of temperature and heat transfer ahead of spreading fire is essential to developing our understanding of the mechanisms involved in fire spread and explosions. Because the temperature gradients in spreading fires are often steep and occur on short spatial and time scales, these measurements are notoriously difficult. Current techniques such as thermocouples require painstakingly careful engineering to ensure accurate results. Other approaches such as thermal cameras and Schlieren imaging require expensive, complex optical setups that are expensive, not amenable to widespread deployment, and require specialized expertise to deploy. Polydiacetylenes (PDAs), a class of color-changing polymers, were developed into dynamic temperature sensors, enabling the direct measurement of temperature gradients ahead of a spreading fire. Diacetylene (DA) precursors (polymerized to form PDAs) were synthesized to undergo visible color changes in response to well-defined temperatures ranging from ≈50 to 200 °C. PDAs were coated on flammable substrates, and their responsiveness was demonstrated with the combustion of paper, cardboard, and nitrocellulose. PDAs were found to be able to directly track temperature gradients ahead of the combustion zone with sub-millimeter and microsecond resolution. The developed sensors were demonstrated to have broad applicability due to their ease of deployment, simple readout, and low cost. Dynamic PDA sensors are particularly applicable to situations demanding high spatial and temporal resolutions, such as deflagrations (fast) or backing fires (short-range temperature gradients).