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

Abstract

Amine-functionalized polymers (AFPs) are able to react with carbon dioxide (CO 2 ) and are therefore useful in CO 2 capture and sensing. To develop AFP-based CO 2 sensors, it is critical to examine their electrical responses to CO 2 over long periods of time, so that the device can be used consistently for measuring CO 2 concentration. To this end, we synthesized poly( N -[3-(dimethylamino)propyl] methacrylamide) (pDMAPMAm) by free radical polymerization and tested its ability to behave as a CO 2 -responsive polymer in a transducer. The electrical response of this polymer to CO 2 upon long exposure times was measured in both the aqueous and solid phases. Direct current resistance measurement tests on pDMAPMAm films printed along with the silver electrodes in the presence of CO 2 at various concentrations reveal a two-region electrical response. Upon continuous exposure to different CO 2 flow rates (at a constant pressure of 0.2 MPa), the resistance first decreased over time, reaching a minimum, followed by a gradual increase with further exposure to CO 2 . A similar trend is observed when CO 2 is introduced to an aqueous solution of pDMAPMAm. The in situ monitoring of pH suggests that the change in resistance of pDMAPMAm can be attributed to the protonation of tertiary amine groups in the presence of CO 2 . This two-region response of pDMAPMAm is based on a proton-hopping mechanism and a change in the number of free amines when pDMAPMAm is exposed to various levels of CO 2 .

CO2-responsive gels

“…The increase in diameter corresponds to a relatively small volume increase (0.5%), due to the IPN, which acts to constrain the microgels. A simple HCl/NH 3 ·H 2 O titration demonstrated that the initial change in the particle size appeared at a pH (surrounding solution) similar to the p K aH of pDMAPMAm (8.8), 295 corresponding to protonation of 41% of the pDMAPMAm-component (calculation based on prior work 296 ).…”

Insect-Inspired Strategy for Conferring Reversible, High Responsivity on Microgels to Dilute-Source CO2

“…126 ppm, and the peaks of bicarbonate and carbonate ions (ca. 161–169 ppm) were not observed. , These results suggest that the responsivity of the microgels to dilute CO 2 should obey a distinct mechanism, unlike the responsivity of amine-containing polymers to concentrated CO 2 reported previously that essentially is the pH-responsive behavior. − In Figure d the observation of the lower SW in the PC/water mixture for a high CO 2 of ≥25.0 vol %, compared to results of no PC, should also reflect the existence of CO 2 (aq) (even if not all), thus, indirectly support the possibility of obeying a different CO 2 -response mechanism. Considering the CO 2 -unresponsivity of a control sample without feeding DEAEMA (Figure S11), , we therefore tentatively ascribed the vital role of amines of DEAEMA unit to promotion on the CO 2 capture ability of microgels (Figure S9) without significant CO 2 hydrolysis.…”

“…Stimuli-responsive polymers have received increased attention and seem to continue to be one critical topic in several disciplines, owing to their adaptive ability similar to living organisms . In particular, CO 2 -responsive polymers recently went through a rapid development because of the appeal of greenhouse gas CO 2 as a trigger, rather than liquid acid or base as in conventional pH-responsive systems. − A variety of functional moieties, such as base groups, including guanidines, imidazoles, amidines and tertiary, secondary, or primary amines, carboxylic acid groups, and more recently, frustrated Lewis pairs, have been incorporated into polymer chains through direct polymerization or postmodification to impart CO 2 -responsiveness. − Those functional moieties can react with CO 2 in water following an acid–base principle to introduce a significant change in their hydrophilicities and polarities, which can recover to their original state upon CO 2 removal by purging with an inert gas (e.g., argon, nitrogen) or heating, thus, free of any contamination by accumulated chemical agents. However, the reversible nature of CO 2 -responsiveness also makes the application of the developed responsive materials heavily limited by the input side, since CO 2 with a relatively high purity or concentration (≥5 vol % usually) is required. − The uptake of CO 2 from a gas mixture with an even lower CO 2 concentration poses a much greater challenge thermodynamically, which needs favorable and selective CO 2 binding energetics on functional moieties. − Unfortunately, with a high binding affinity, the release of the captured CO 2 becomes difficult, which inevitably leads to a poor reversibility under mild conditions.…”

A Flexible and Polymer‐Based Chemiresistive CO2 Gas Sensor at Room Temperature

“…Our Previous study explored the performance of a CO 2 sensor based on poly( N ‐[3‐(dimethylamino)propyl] methacrylamide) (pDMAPMAm) through the proton hopping mechanism. [ 39 ] Despite its capability for CO 2 detection at room temperature, the sensor suffered from the non‐linear and irreversible response to CO 2 at different concentrations, due to the saturation of amine sites, which hindered its potential as a reversible sensor for accurate CO 2 measurements. [ 39 ] The drawback of saturation of amine sites can be resolved by adjusting the basicity of pDMAPMAm.…”

“…[39] Despite its capability for CO 2 detection at room temperature, the sensor suffered from the non-linear and irreversible response to CO 2 at different concentrations, due to the saturation of amine sites, which hindered its potential as a reversible sensor for accurate CO 2 measurements. [39] The drawback of saturation of amine sites can be resolved by adjusting the basicity of pDMAPMAm. Therefore, adding a less basic monomer such as 2-N-morpholinoethyl methacrylate (MEMA) (pK aH of homopolymer = 4.9) [31,40] would provide more free amine sites (especially at lower pH).…”