Deswelling Dynamics of Thermoresponsive Microgel Capsules and Their Ultrasensitive Sensing Applications: A Mesoscopic Simulation Study

Thermoresponsive microgels with a hollow capsule architecture have been widely used in drug delivery and molecular encapsulation, and their efficacy is contingent on the internal structure in the deswelling dynamics process. Despite a large number of experimental studies on microgels, proper theoretical methods based on an individual microgel capsule are still a few because of the complexity of the microgels. Herein, we first propose a novel methodology to investigate the structural properties and deswelling dynamics of microgel capsules by integrating a temperature-dependent Morse potential with Langevin dynamics simulation. Different properties, including volume phase transition temperature, temperature-dependent diameter, and structural morphologies of individual microgels, are assessed to rationalize our simulation method, and a good agreement between simulation predictions and experimental observations has been obtained. Depending on the system temperature, the morphological transition of three regimes in the shell structure is identified: scattered nanogels, progressively porous sponge gels, and dense ribbonlike gels. The temperature-switchable sensors composed of microgel capsules on the substrates are devised, which exhibit tunable reflectivity or thickness by simply varying the system temperature. Our mesoscale results provide helpful insights into the transient structure within the networked microgels and the design of smart polymeric nanomaterials, such as biosensors, drug delivery systems, and actuators.