Continuous evolution of the re-entrant phase separation in evaporating droplets of polymer solutions

The re-entrant phase separation inside an evaporating droplet of poly (N-isopropyl acryl amide) (PNIPAM) solution with the binary solvent of ethanol and water is discovered and monitored continuously by optical microscopy. Because of the higher evaporation rate of ethanol than water, the solvent composition is changed by evaporation. As a result, the cononsolvency of PNIPAM makes the polymer precipitate into the solution and redissolve...