CO₂-Responsive Superabsorbent Hydrogels Capable of >90% Dewatering When Immersed in Water

Abstract

Superabsorbent polymer (SAP) hydrogels function by absorbing and retaining water. Facile removal of the absorbed water would make it easier to recycle used SAP hydrogels. However, the hydrophilic interior of traditional SAP hydrogels inhibits the desorption of the absorbed fluid. Herein, we report the synthesis and properties of CO2-responsive SAP hydrogels capable of switching from being relatively hydrophobic to hydrophilic in the presence of CO2, and vice versa when the CO2 is removed, accompanied by the simultaneous absorption and expulsion of large volumes of water respectively, mimicking a CO2-directed sponge. The hydrogels studied are synthesized by the free-radical copolymerization of either N-[3-(dimethylamino)­propyl]­methacrylamide (DMAPMAm) or 2-N-morpholinoethyl methacrylate (MEMA) with N,N′-dimethylacrylamide (DMAAm), which acts as both a monomer and a self-cross-linker. In the presence of CO2, both p­(DMAAm-co-DMAPMAm) and p­(DMAAm-co-MEMA) gels were able to achieve a maximum swelling ratio (SR) of ∼800, demonstrating that they are superabsorbent. These gels release more than 70% of the absorbed water if they are immersed in noncarbonated water. Repeated swelling/deswelling of the hydrogels (with recovery of the original swelling ratio) in this manner over four cycles demonstrates the reusability of these materials and their potential use in a variety of applications.

Electrical Response of Poly(N-[3-(dimethylamino)Propyl] Methacrylamide) to CO2 at a Long Exposure Period

“… 36 But the system midpoint of solid or incompletely dissolved pDMAPMAm is unknown and most likely depends on the water content. 44 …”

“…36 But the system midpoint of solid or incompletely dissolved pDMAP-MAm is unknown and most likely depends on the water content. 44 The conversion of neutral side groups to charged states is representative of the "range of operation" through which the tertiary amine groups in the side chains of the polymers interact with CO 2 via the protonation process. Therefore, to have a wide range of operation, the starting pH of the system should be considerably higher than the system midpoint before CO 2 exposure, with the pH going well below the system midpoint after the exposure to CO 2 .…”

CO2-Responsive Branched Polymers for Forward Osmosis Applications: The Effect of Branching on Draw Solute Properties

“…As part of an ongoing project on CO 2 -switchable draw agents for FO, − we recently reported on design and evaluation of nitrogen-rich CO 2 -responsive polymeric draw solutes that reversibly change their osmotic pressure upon addition or removal of CO 2 . In the presence of CO 2 , polymers with tertiary amine groups (linear poly­( N -methylethylenimine) (l-PMEI), branched poly­( N -methylethylenimine) (b-PMEI), and poly­( N , N -dimethylallylamine) (PDMAAm)) form tertiary ammonium bicarbonate salts and exhibit high osmotic pressure (e.g., π CO2 ≈ 60 bar for 35 wt % PDMAAm solution).…”

Analyzing the Water Confined in Hydrogel Using Near-Infrared Spectroscopy

“…Shape memory is an important property of hydrogels, that is, a hydrogel deforms with an external stimulus such as temperature and recovers its original shape when the stimulus disappears. 3,54 Swelling and deswelling is generally used to describe the phase transition. With the analysis above, the swelling process may start with the formation of S 1NH water, then the hydrated water around CH and finally the bulk-like water, and the deswelling may be controlled by the synergistic effect of S 1NH and the hydration water of CH.…”