Microgel Dynamics Characterization Using SEM

Abstract

A methodology for imaging the dynamics of individual microgel particles using high resolution scanning electron microscopy (SEM) is presented. To enable this, the microgels are dispersed in an ionic liquid, which due to its low vapor pressure allows them to remain in suspension even under the high vacuum conditions present in a typical electron gun. Thus, compared with conventional electron microscopy studies of microgels, no sample drying or freezing is necessary which preserves their morphology while also allowing to probe microgel dynamics in solution. The results based on the individually tracked particles are compared with results from dynamic light scattering (DLS) which measures the mean size and diffusion properties of large collectives of particles. For the size measurements, the SEM and DLS data are in general agreement. For the particle dynamics, monitoring individual microgel motion reveals complex dynamics in which, aside from the expected thermal motion, one observes effects such as clustering, rotation and drift. This is in contrast with a control sample of hard sphere-like silica particles where the motion is primarily diffusional in good agreement with DLS studies.