Liquid metal nanoparticles enable ultrafast fire detection

By incorporating liquid metals into sensors, researchers have created a fire warning system that is ultrafast, flame-retardant and reusable. Based on MXene/cellulose films, the new design incorporates gallium-based liquid metal nanoparticles coated in polydopamine that reinforce conductive pathways to improve signal stability and, unexpectedly, fire resistance.

Conventional smoke detectors suffer from false positives and response times that can exceed one minute. One strategy for improved fire warning sensors uses thermoresistive materials to send a rapid and quantifiable electrical signal when exposed to elevated temperatures.

MXenes – 2D materials made of layers of transition metal carbides, nitrides or carbonitrides – are highly conductive, thermoresistive and flame-retardant, making them excellent candidates. Unmodified, however, they are not mechanically robust enough for practical use. Cellulose/MXene systems were developed to be more robust; however, cellulose decreases thermal stability. Attempts to modify and improve the flame resistance of cellulose/MXene have so far come at the cost of rapid and repeatable sensor response.

Now, an international team of researchers has combined cellulose/MXene with gallium–indium alloy nanoparticles in a low-cost, scalable process to create a durable film that enables ultrafast, reversible thermoresistive switching. The new material can activate alarms in roughly 4 seconds upon exposure to flame, and recover its resistance in about half that time.

In tests, it maintained stable resistance switching after over one hour of fire exposure. If the film did ignite, it self-extinguished within 1 second. Crucially, it showed repeatability after over 120 cycles. Incorporating the liquid metal also suppressed the release of volatiles.

The researchers attribute the remarkable thermal stability to the formation of a dense conductive–insulating network made of carbon and oxides derived from titanium and liquid metal. In tests, the flame-resistance of the films increased with liquid metal content.