(342a) Design and Synthesis of Polymer Membranes Based on Theoretical Principles

To optimize the filtration performance of synthetic polymer membranes, their internal microstructure needs to be designed and synthesized based on theoretical principles and not empirically, as is done at present, using phase inversion and interfacial polymerization. Here, we present a rational approach in which we develop an in-silico tool to (a) simulate separation of particles with different properties (i.e., chemistry, size, shape, flexibility, etc.), and (b) propose, test, and optimize novel microstructures. To validate these predictions, experiments are required. The in-silico tool comprises 2D computational fluid and particle drag mechanics combined with particle and membrane force measurements in ionic solutions, modeled by the DLVO and the extended DLVO (xDLVO) theories, to study particle intrusion and capture in and escape through microporous polymer membranes. We have previously demonstrated¹ that (a) the in-silico tool predictions for a commercial membrane show substantial flow channeling and qualitatively agree with experimental filtration measurements using scanning electron microscopy with particle tracking via energy dispersive X-ray spectroscopy, and (b) tear-drop microstructures of different orientation weakly separate particles that differ in size by a factor of 2.

In this work, we have conducted extensive intermolecular force measurements between streptavidin, a stable protein coated on a polystyrene sphere, and two commercial microfiltration poly(ether sulfone) and poly(vinylidene difluoride) membranes and obtained requisite parameters such as the Hamaker constants, surface potentials, hydrogen-bonding free energies of cohesion between the water molecules and characteristic decay lengths of water (l=1.0 nm at 20ºC) from theoretical fits of DLVO and xDLVO theories² for 100s of experimental runs at various solution conditions (pH and ionic strength). We have also used the in-silico tool to obtain filtration performance predictions with membranes comprising a series of spherical microstructures of one size and in mixtures of different sizes to separate suspensions of particles that differ in size by a factor of 10 (i.e., the holy grail of membrane filtration). These microstructures allow adjustment of the tortuosity of the flow path and variation of the reactivity of the surface. Experiments are also underway testing these spherical particle microstructures. To our knowledge, this is the first attempt combining particle drag mechanics with intermolecular force measurements to design and synthesize microfiltration membranes based on theoretical principles. The in-silico tool can be used to characterize membranes for separation performance and guide improved design, synthesis, and testing of new microporous membranes.

References

1. Sorci, M.; Wookcock, C. C.; Andersen, D. J.; Behzad, A. R.; Nunes, S.; Plawsky, J.; Belfort, G., Linking microstructure of membranes and performance. J. Membr. Sci. 2020, 594, 1-9.
2. van Oss, C., Long-range and short-range mechanisms of hydrophobic attraction and hydrophilic repulsion in specific and aspecific interactions. Journal of Molecular Recognition 2003, 16, 177-190.