A temperature-controlled cell (HC321Gi, INSTEC) mounted above a microscope (Axio Observer, Zeiss) was used for imaging the SOA material during heating. The temperature of the cell was controlled by offsetting hot (electrical) and cold (liquid nitrogen) inputs around the inner walls of the cell. We performed some heating experiments while viewing the particles from the top, and others while viewing the particles from the side (Fig. ). These two orientations required different sample preparation. For the top view experiments, particles on the glass slide were scraped into a pile using a razor blade, and the glass slide was then directly inserted into the temperature-controlled cell. For a side view, the particles on the glass slides were scraped into a pile and then attached to the flat end of an ultra-fine needle (Roboz Surgical Instruments Co.) by bringing the needle surface into contact with the scraped particles. The needle was then inserted into the temperature-controlled cell as detailed previously. The results and conclusions presented herein were not sensitive to the viewing method (top view vs. side view).