(494c) Polymer Architecture Plays a Crucial Role in Structure Formation during in-Situ growth of Microgels in Mixed-Matrix Polymer-Polymer Membranes

Polymer membranes are increasingly important in energy generation, water purification, and resource recovery. Control over chemistry, morphology, and mechanical properties gives organic polymers unparalleled advantages for membrane technology—but only if these complementary functions can be married into a cohesive material. To integrate diverse polymers into a membrane, we grow functional microgels in situ in a casting solution containing a preformed scaffold polymer, a method pioneered by co-PI Diallo. The hierarchical structure of the resulting mixed-matrix polymer-polymer (M2P2) membrane is governed by a kinetic competition between polymerization and phase separation of the microgel from the scaffold polymer. With membrane properties intimately tied to the metastable structure that builds from these competing processes, understanding the interplay of different components is paramount to realizing the full potential of M2P2 membranes.

Herein, we probed the relationship between microgel precursor and membrane structure using a newly developed ultra-small angle neutron scattering (uSANS) technique, in which we measured structure formation as the in situ synthesis proceeded. Specifically, we compared casting solutions with two microgel precursors: (i) randomly hyperbranched polyethyleneimine (PEI), and (ii) low-generation polyamidoamine (PAMAM) dendrimer. Transient uSANS patterns reveal that microgel architecture profoundly affects structure formation. For membranes with PEI-based microgels, the in situ synthesis quickly plunges the system into spinodal decomposition, whereas membranes containing PAMAM dendrimers develop structure much more slowly by nucleation and growth. These divergent kinetics in turn effect appreciable differences in domain size of membranes. Ultimately, our results indicate that polymer architecture provides a utile handle to systematically tune M2P2 membrane structure, enabling facile tailoring to various applications.