Resistance and Permselectivity of 3D-Printed Micropatterned Anion Exchange Membranes

It has been demonstrated that a micropatterned surface can decrease the resistance of anion-exchange membranes (AEMs) and can induce desirable flow properties in devices, such as mixing. Previously, a model that related the resistance of flat and patterned membranes with the same equivalent thickness was proposed, which used the patterned area and thickness ratio of the features to describe the membrane resistance. Here, we explored the validity of the parallel resistance model for a variety of membrane surface designs and area ratios. We demonstrated that the model can predict the resistance of a wide range of patterned AEMs. We showed that the resistance is independent of the spatial ordering of the design by examining random patterns, which is relevant for applications that require, for example, increased mixing in multilayered devices. Some experimental values of resistance obtained for patterned membranes presented deviations from the model. Scanning electron microscopy (SEM) images of the patterned membranes revealed resolution variations and pattern replication errors due to the stereolithographic process. A geometric correction of the target ratios improved the fit of the modeled data to the experimental values, showing that light bleeding during curing was a source of error. Two additional experimental factors were not accounted for in the model: a distinct interface between the bottom and top layer and overcuring of the bottom layer during successive steps. These sources of error were investigated by examining the resistance of single- and double-layered membranes, as well as single-layer membranes with different curing times. The differences obtained in the resistances for control samples demonstrated that both the interface and the overcuring influenced the resistance of the membrane. The results obtained in this study enlighten the discussion relating membrane-surface morphology and transport properties, as well as the optimization of 3D-printed membranes using a stereolithography process.