Single droplet formation by controlling the viscoelasticity of polymer solutions during inkjet printing

Inkjet printing has emerged as a potential solution processing method for large-area patterned films. During inkjet printing, a single droplet without satellite droplet is required for high-quality film. Herein, we propose a strategy for obtaining a single droplet by adjusting the reduced concentration (c/c*, where c* is the critical overlap concentration) in the range of 1.0-1.5. Droplet formation can be categorized into three distinct regimes: (1) c/c* < 1.0, satellite droplet; (2) c/c* = 1.0-1.5, single droplet; (3) c/c* > 2.0, no droplet. Furthermore, an inertial-capillary balance led to the 2/3-power scaling of the minimum radius with time for the solutions of c/c* < 1.0. However, for the solutions of c/c* = 1.0-1.5, the ligament radius decreased exponentially with time. Moreover, the Weissenberg number was higher than the critical value of 0.5, indicating that the polymer chains underwent coil-stretch transition. The viscoelastic-capillary balance dominated instead of the inertial-capillary balance. The resulting viscoelastic resistance reduced the length of the ligament and increased the velocity difference between the satellite and main droplets. Consequently, a single droplet was formed. In addition, the law can be successfully generalized to various molecular weights, molecular structures and solvents. (c) 2024Published by Elsevier B.V. onbehalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.