(255bf) Morphogenesis of Microstructured Polymer Foams Formed By Thermally Induced Phase Separation: Theoretical and Experimental Study

Polymer foam applications depend both on the polymer and the foam morphology. Generally, the tailored preparation of foams with various morphologies using a single method would open new application possibilities. A method enabling this tailoring is the thermally induced phase separation (TIPS). However, a deeper understanding of the TIPS preparation route is still missing. In this work, we present a validated model for the morphogenesis of micro-structured polystyrene (PS) foams formed by TIPS, in particular by spinodal decomposition [1]. The foam morphologies were predicted by the Cahn-Hilliard approach with the only input being the Flory-Huggins lattice model. To validate the model, we prepared PS foams via TIPS at various conditions using solvents with and without polar interactions (cyclohexane, cyclohexanol), characterized the morphologies and compared them with the predicted ones. Furthermore, using a thermo-optical method we determined the boundaries of the phase separation conditions, i.e., binodal curves. The morphology prediction is in a very good agreement with the experimental results. The model predicts correct length scales of close-cell morphologies for a variety of system compositions and temperatures in 2D and 3D. Moreover, it enables to predict different morphologies: (i) aggregated particles, (ii) open-cell structure, (iii) combination of open- and closed-cell structure, and (iv) closed-cell structure. Furthermore, we present our first experimental results of the dynamics of foam morphogenesis by TIPS. The addition of the real time scale into the model is the last step for the full description of the process dynamics and, thus, the preparation of foams of desired structures.

References

1. Vonka M., Nistor A., Rygl A., Toulec M., Kosek J.: Morphology model for polymer foams formed by thermally induced phase separation. Chem. Eng. Journal 2016. 284: 357-371.