Presenter puts Mentos candy into soda to create a soda fountain. This is a dramatic demonstration of the effects of surface area.
This demonstration isn’t heavily focused on nanotechnology,but can be a spectacular finale that you add on to other nano demos like Intro to Nano or Surface Area. (It’s probably best as a substitution for Alka-Seltzer, rather than being performed with it.) It’s also just a crowd pleasing demo that briefly mentions nano.