Marangoni flows in polymer solution droplets drying on heating surfaces

The effect on substrate temperature on the fluid dynamics in a polymer solution droplet evaporating on a substrate is investigated experimentally and numerically. It is found from the experiments that fluid velocities in the droplets increase with increasing initial substrate temperature and with decreasing initial solute concentration. A mathematical model, which takes thermal and solutal Marangonl effects into account, are numerically solved using a finite element method. The calculated fluid velocities agree with the experiment. Both experiments and calculations show that, though thermal Marangonl forces dominate the fluid dynamics, solute Marangonl forces should never be neglected. The calculations predict that solute Marangonl effects are more emphasized with decreasing contact angle.