Polymer Transports Inside Evaporating Water Droplets at Various Substrate Temperatures

The flow dynamics inside evaporating water droplets containing a polymer solute were investigated at various substrate temperatures. A new experimental method (laser absorbance monitoring system) was established to estimate the flow dynamics by measuring the central concentration of the solute in the evaporating droplet. The system showed that the polymer transports inside the evaporating droplets near the end of evaporation changed direction depending on the substrate temperature. The resulting deposit patterns after the evaporation were also changed from center-concentrated to edge-concentrated deposit patterns by the flow dynamics. The experimental results are discussed with the calculation results obtained from a simple heat transfer model. This study clearly shows that controlling substrate temperature is an effective way to manipulate the flow dynamics inside evaporating water droplets.