Optimizing the Direct Visualization of Microgels via Scanning Electron Microscopy

To better understand the dynamics of microgels in solution, their volume phase transition, and to correlate images of individual particles with Dynamic Light Scattering (DLS) data on their diffusion, new imaging techniques were developed using scanning electron microscopy (SEM). Accurate imaging of such systems is challenging as microgel samples lose water content under high vacuum. To address these issues, a controlled environment chamber was developed, allowing the microgels to dry over a longer period of time at higher humidity levels than standard room conditions. Using the controlled humidity environment allowed microgels to better maintain original structure for imaging and produced microgel size distributions more consistent with DLS both below and above the volume phase transition. Another method for microgel imaging was developed by suspending particles in ionic liquids. Low vapor pressures and high ionic concentrations of these suspensions allowed the capture real time dynamics of swollen microgels. Microgels in ionic liquid were observed to be smaller than expected, whilst maintaining size distribution uniformity. Such observations could be due to charge screening or the increased salt concentration due to presence of ionic liquid.