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 turbulent liquid flow 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 modelled 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, and single layer membranes with different curing times. The differences obtained in the resistances for control samples demonstrated that both the interface and overcuring influence 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.

Redox-responsive anion exchange membranes were developed using photoinitiated free-radical polymerization and reversible oxidation and reduction of viologen. The membranes were formulated using poly­(ethylene glycol diacrylate) and diurethane dimethacrylate oligomers, dipentaerythritol penta-/hexa-acrylate cross-linker, photoinitiators, and 4-vinylbenzyl chloride as precursors for functionalization. In the membrane, 4,4′-bipyridine reacted with the 4-vinylbenzyl chloride residues, and subsequently, unreacted amines were methylated with iodomethane to obtain viologen as both the ion carrier and redox-responsive group. Upon oxidation, viologen supports two cations, where the reduced form only contains one cation. Thus, the redox responsiveness changed the membrane ionicity by a factor of 2. The area-specific resistance of the membranes in the oxidized, +2, state was lower than in the reduced, +1, state. The resistance increased between 40.6 ± 0.1 and 111.6 ± 0.1%, depending on membrane thickness, with the most significant increment being a resistance change from 4.88 × 10–4 Ω m2 in the oxidized state to 1.03 × 10–3 Ω m2 in the reduced state. Membrane permselectivity in the reduced, +1, state was between 15.9 ± 0.1 and 26.5 ± 0.01% lower than in the oxidized, +2, state, with no change in water uptake, spanning an average of 0.87 ± 0.02 in the oxidized state to an average of 0.7 ± 0.01 in the reduced state. Upon reduction, membrane ion-exchange capacity decreases, increasing ionic resistance and decreasing membrane permselectivity due to a reduction in fixed charge concentration without a measurable change in water uptake. This trend is not generally observed for ion-exchange membranes and explains that the changes in transport properties result from changes in ionicity, not water uptake or domain size. The reversibility and stability of the stimuli responsiveness were confirmed by the absence of transport property changes after redox cycling.

Excessive N and P in surface waters can promote eutrophication (algae-dominated, low-O 2 waters), which decreases water quality and aquatic life. Duckweed (Lemnaceae), a floating aquatic plant, rapidly absorbs N and P from water and its composition shows strong potential as a soil amendment. Therefore, it may be used to transfer N and P from eutrophic water bodies to agricultural fields. In this work, dried duckweed was incorporated into agricultural soil in microcosm, column, and field tests to evaluate biological N cycling, nutrient retention, and crop yield compared with compost, diammonium phosphate (DAP), and an amendmentfree control. In microcosm tests, 25 ± 13% of duckweed N was mineralized, providing on average less mineral N than DAP (107 ± 21%), but more than compost (11 ± 12%). In columns, duckweed treatments leached only 2% of the N added, significantly less than DAP, which leached 60% of its N. Compared with the control, DAP leached significantly more phosphate (78%), whereas duckweed and compost treatments leached less (56 and 27%, respectively). Crop yield, as well as runoff N and P, were measured in field tests growing forage sorghum [Sorghum bicolor (L.) Moench.]. Although less total N was applied to duckweed plots than to DAP plots (75 vs. 130 kg ha −1 , respectively), duckweed was found to retain 30% more total mineral N in a tilled agricultural field than DAP, while supporting a comparable yield. These tests indicate that duckweed may provide a sustainable source of N and P for agriculture.• In microcosm tests, 25% of organic N in duckweed was mineralized within 5 d.• In 22-d column tests, duckweed leached only 2% of the N applied from its biomass.• In 22-d column tests, duckweed leached 56% less phosphate than the control.• In field tests, duckweed reduced inorganic N runoff by 30% compared with mineral fertilizer.• In field tests, sorghum yield was comparable for duckweed and mineral fertilizer treatments.

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