Figure 2

FEM simulation and experimental SEM cross-sections of SIBS coatings from different solvents. FEM heatmaps (A) at the time the simulation stopping criterion is reached for scenarios with different solvent coefficient of surface tension values and additional solution stabilizing effect strengths. A high solvent concentration indicates a polymer solution, and a low solvent concentration indicates a solid polymer film. The additional effect strength in FEM simulations is defined as the solvent concentration dependent coefficient of surface tension. In case of the highest additional effect, the coefficient of surface tension is set to approach zero when the solvent concentration approaches zero during drying. In case of no additional effect, the coefficient of surface tension is kept constant during drying. Linear decreases to 0.75, 0.5 and 0.25 of the initial value during drying correspond to the intermediate scenarios of lower, medium, and higher additional effect strength, respectively. Further details on the simulation can be found in the Methods section. SEM cross-sections in B, C, D are obtained by dip-coating pH indicator strips 5 times under the respective solvent atmosphere at different dipping speeds, then cryo-fracturing them in liquid nitrogen and subsequently sputtering with 24 k gold (5 nm) before imaging. Experimental situations showing no coating (B) or exposed sides (C) of the pH strip could correspond to simulations, where the stopping criterion is reached when the coating formulation still contains a high amount of the solvent. Simulations with the stopping criterion reached later when the coating has almost or fully dried could correspond to an experimental situation where a solvent with extremely low coefficient of surface tension would be used (e.g., 5 mN/m or below) or indicate additional solution stabilizing effects (e.g., when midblock-selective solvents like 2,2,4-trimethylpentane were used (D)).