Marangoni-driven spreading dynamics of ethanol-water mixture droplets on hydrogel surfaces

This study investigates the Marangoni-driven spreading of ethanol-water mixture droplets on hydrogel surfaces, aiming to develop potential technologies of controlling flow for drug delivery on bio surfaces, cleaning flexible displays and hydrogel coating. We conducted experiments to observe the spreading behavior of the binary mixture droplet on various hydrogel surfaces in two main setups: (1) modifying hydrogel properties through varying concentrations, drying, and surfactant addition, and (2) varying the concentrations of ethanol in water. We measured the time evolution of the spreading droplet radius R(t) using a high-speed camera. From the experimental results, we observed that the spreading rate exhibited various power-law trends depending on the initial and boundary conditions. In particular, we found that the ethanol droplet showed R~t^(1/3), which is different from the power-law with previous Marangoni spreading research. Furthermore, the change in spreading-rate due to ethanol concentration in the droplet was more significant (i.e.,R~t^(1/10) to R~t^(1/3)) than the change in spreading-rate due to variations in substrate properties (i.e.,R~t^(1/4) to R~t^(1/3)). At the talk, physical arguments to support the observations will be discussed.