(379a) How Does Membrane Microstructure Affect Performance?

The microstructure of membranes plays a significant role in controlling their overall efficiency, capacity and selectivity during filtration. Most commercial polymer membranes are fabricated using a phase inversion (PI) process that does not allow controlling the formation of the membrane microstructure. Hence, empirical pre- and post-fabrication methods are used to improve performance. The overall goal of this work is to replace PI with fabrication methods that rationally control the formation of the membrane microstructure and hence improve particle filtration performance. Our approach is to propose a microstructure design and then test that design computationally by passing a swarm of particles of different properties (size, surface forces) through the membrane microstructure to determine its selectivity and capacity. Here we release micron-size particles in a KCl solution flowing through the 3D crystal-like membrane structure. Using AFM in force measurement mode, zeta-potential, and surface tension measurements, the particles' physical and chemical properties were determined experimentally. The extended DLVO (xDLVO) theory, which includes van der Waals, electrostatic and Lewis acid-base interactions, was invoked to describe the interactions between the particles and the membrane pore walls. Combining these forces with fluid and particle drag, a comprehensive model was used to track particles through the microstructure. Discrete element method (DEM) was used with open-source software (Multiphase Flow with Interphase eXchanges, MFix) to describe the motion of the particles in the 3D microstructure. By modulating the details of the 3D structure (i.e with different pore size distribution), selectivity and capacity were obtained and further used for selecting an optimal microstructure with desired filtration performance. The novelty of this work lies in the combination of computational modeling incorporating measurement of molecular interactions to design and fabricate membranes with improved performance.