Thermographic Analysis of the Cooling Dynamics of Liquid Metal Droplets.

This work presents an experimental study of the thermal dynamics of cooling galinstan liquid metal droplets using thermographic and optical imaging techniques. Galinstan droplets were subjected to controlled cooling on a Peltier-based system with their temperature and morphological evolution recorded simultaneously. Thermography enabled the detection of transient thermal phenomena and localized phase transitions, including supercooling and dendrite formation. The analysis revealed complex, nonequilibrium behaviors, such as metastable thermal and morphological behaviors with coupled variations in temperature and droplet volume that may be consistent with transient or heterogeneous intermediate states. A normalization procedure based on droplet volume enabled comparison across samples, revealing characteristic features in the cooling and heating cycles despite differences in the droplet morphology. Furthermore, directional contact angle measurements using image processing revealed significant variations in wetting behavior throughout the cooling process, showing a gradual reduction in contact angles during intermediate stages, followed by a partial recovery upon rapid phase transformation. Crucially, unlike previous studies that rely on ultrahigh-vacuum chambers and highly specialized equipment, this entire diagnostic methodology was developed under ambient conditions. This makes the approach significantly more practical and optimal for translating liquid metals to real-world applications. The methodology is simple and highly sensitive, providing a noninvasive approach to studying phase transitions in thermally dynamic systems.