Thermo-responsive droplet deposition and solidification

The spreading of a thermo-responsive droplet on a heated surface is studied. The spatio-temporal pattern~of gel formation within the droplet is visualized using a new experimental method based on spectral~domain optical coherence tomography. The method relies on a collective motion of sub-micron buoyant~particles inside the droplet. The mechanisms that lead to the arrest of the spreading droplet are~explored.~The importance of evaporation-induced gel formation and heat conduction~through surrounding air are highlighted.~The proposed experimental technique can potentially be used to analyze the~solidification of different fluids such as molten waxes. Thermo-responsivity is demonstrated to provide~an effective control over the final shape of the droplet.