Continuous evolution of the re-entrant phase separation in evaporating droplets of polymer solutions. (10th December 2021)

• Record Type: Journal Article
• Authors: Cheng, Bin; Zhao, Haitong; Yang, Jingfa; Zhao, Jiang
• Is Part Of: Polymer. Volume 237(2021)
• Publication Date: 2021-12-10
• Subjects: Cononsolvency -- Droplet under evaporation -- Marangoni flow; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; 547.7
• DOI: 10.1016/j.polymer.2021.124327
• Languages: English
• ISSNs: 0032-3861

Abstract

Abstract: 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 afterwards along the proceeding of the evaporation. Such a simple strategy enables a continuous observation of the re-entrant phase separation due to cononsolvency. Direct optical microscopic observation is made with quantitative description of the process and the details of the flow patterns during the process. The phase separation is found to occur at the air-liquid interface and the precipitates are brought into the droplet by circulations induced by Marangoni flow, providing a new way of mass transportation during phase separation. Graphical abstract: Image 1 Highlights: Change in solvent composition by evaporation of a droplet made of binary solvents. Continuous evolution of re-entrant phase separation of PNIPAM by cononsolvency due to solvent composition change. Novel mass transportation during the phase separation by Marangoni flow.