Optimization of Microgel Imaging Using SEM

Microgels are polymer-based nanoparticles suspended in water that exhibit. The standard, noninvasive method for characterizing microgels is dynamic light scattering (DLS), which measures collective diffusion of microgels. While DLS provides reliable estimates for particle structure/dynamics, more direct methods of imaging are useful for studying polydisperse samples. Traditionally, scanning electron microscopy (SEM) uses an electron beam under high vacuum to characterize individual dried particles of dried. The dry microgel imaging suffers from two drawbacks: dehydrated particles collapse under vacuum and their dynamics is not observable. This project explored wet particle imaging in an ionic liquid stable under high vacuum. Particles were suspended in an ionic liquid film on a copper grid. Still images/movies were recorded to analyze microgel size distribution and dynamics. The average SEM size generally agreed with DLS both in ionic liquid and in water at room temperature. Variation was observed in individual particle sizes, but the average SEM size for both samples were close to the DLS size. Initial attempts at diffusion analysis using SEM particle tracking yielded mixed results as it requires tracing of many particles and further optimization.