As stimulus-responsive polymeric materials undergo dramatic changes in their structure/shape and physical/chemical properties in response to changes in the environment, they are also called “smart materials”. The key factors and requirements for stimulus-responsive materials to undergo changes are to be fast, reversible, complex, and robust in response to the external stimuli. One type of stimulus-responsive materials with the potential to fulfill the aforementioned requirements is hydrogel microspheres (microgels). Microgels are colloidal particles that can respond rapidly to external stimuli because of their microscopic dimensions. Owing to their rapid stimulus-responsiveness, microgels have been used for numerous applications in, for example, molecular separation, drug-delivery vehicles, sensors, and actuators. So far, the stimulus-responsive properties of microgels have been mainly evaluated by scattering techniques, calorimetry, sensors, and so forth. However, these techniques provide ensemble-averaged signals for the entire system. Therefore, undesired artifacts such as unexpected morphology changes in microgels induced by external stimuli might be included in the obtained data, which would hamper the correct interpretation of the data. More reliable data and a deeper insight into the stimulus-responsive behavior of individual microgels should be obtained from real-time direct observations of microgels, which should provide accurate and relevant information on the morphological changes experienced by microgels. In this context, we have achieved a direct visualization of thermoresponsive morphological changes in individual microgels in real time in aqueous solution using high-speed atomic force microscopy (HS-AFM). In this study, we have investigated how highly water-swollen microgels respond to temperature changes using light scattering, electrophoresis and temperature-controlled HS-AFM.

Evaluation of thermoresponsive behavior of charged hydrogel microspheres with different charge distributions

ACS Spring Meeting 2021

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