Real-time in-situ thermal monitoring of gelation process of polyacrylamide hydrogel using PDMS sensitized in-fiber MZI

Real-time and in-situ monitoring the gelation temperature information of the polyacrylamide hydrogel is of great significance for revealing its reaction kinetics information and regulating the performance and quality. In this paper, based on PDMS sensitized in-fiber Mach-Zehnder interferometer (MZI), a sensitive temperature sensor with a temperature sensitivity of 10.22 nm/℃ is proposed, which is used for in-situ thermal monitoring of the gelation process of polyacrylamide hydrogel. By establishing the gelation thermal curve, it is demonstrated that the gelation process mainly includes four stages: initial lag, rapid gelation, cooling stage and stabilization stage. Among them, the rapid gelation stage is the most critical, which shows the heat released in the gelation process and the gelation time. In addition, experimental results confirmed that with the increase of monomer and crosslinker concentration, the heat released during the gelation process gradually increases, but the gelation time is almost unaffected. Since the proposed PDMS sensitized MZI sensor has the advantages of miniaturization, high sensitivity, intrinsically safe, etc., it can be further extended to other dynamic reaction processes for real-time monitoring of temperature information.