The real realm and recent advances of piezoelectricity after thinning down to two-dimensional materials have been introduced.

CO2 sensing is important in many applications ranging from air‐quality monitoring to food packaging. In this study, an amine‐functionalized copolymer, poly(N‐[3‐(dimethylamino)propyl]‐methacrylamide‐co‐2‐N‐morpholinoethyl methacrylate) (p(D‐co‐M)) is synthesized, offering moderate basicity suitable for a wide CO2 detection range. Taking advantage of this characteristic of p(D‐co‐M), this polymer is used for designing a chemiresistive, low‐cost, flexible, and reversible CO2 sensor. The p(D‐co‐M)‐based sensors show a noticeable decrease in their direct current resistance and alternating current impedance upon exposure to a wide range of CO2 concentration (1–100%) at room temperature with a response and a recovery time of 6 and 14 min, respectively. Additionally, the p(D‐co‐M)‐based sensors demonstrate a favorable selectivity to CO2 in the presence of interfering gases including methanol, ethanol, toluene, and acetone. Surface potential measurements show an increase of +6.34 V upon exposure to humidity and CO2, indicating the protonation of the polymer's amine sites, facilitating the detection of CO2 in the wet environment. This sensor is efficient for detecting CO2 concentration released during fermentation of kimchi as a food model.

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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 .

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