Drop spreading and gelation of thermoresponsive polymers

TL;DR

This study investigates how heat transfer influences the spreading and solidification of thermoresponsive Pluronic F127 solutions, revealing the critical role of temperature differences and evaporation effects in droplet arrest during additive manufacturing.

Contribution

It provides a systematic analysis of the interplay between temperature, concentration, and evaporation in droplet spreading and gelation of thermoresponsive polymers, highlighting a local arrest mechanism.

Findings

Spreading stops primarily when substrate temperature exceeds the gelation temperature.

Spreading can also halt below gelation temperature due to local polymer concentration increase.

Evaporation near the contact line influences the arrest of droplet spreading.

Abstract

Spreading and solidification of liquid droplets are elementary processes of relevance for additive manufacturing. Here we investigate the effect of heat transfer on spreading of a thermoresponsive solution (Pluronic F127) that undergoes a sol-gel transition above a critical temperature $T_m$. By controlling the concentration of Pluronic F127 we systematically vary $T_m$, while also imposing a broad range of temperatures of the solid and the liquid. We subsequently monitor the spreading dynamics over several orders of magnitude in time and determine when solidification stops the spreading. It is found that the main parameter is the difference between the substrate temperature and $T_m$, pointing to a local mechanism for arrest near the contact line. Unexpectedly, the spreading is also found to stop below the gelation temparature, which we attribute to a local enhancement in polymer concentration due to evaporation near the contact line.