Viscosity. The viscosities of the BBOA were probed using the poke-flow technique. If the particles cracked upon being poked and then did not show any signs of recovery after 2 hours, they were classified as being amorphous solids (also known as glassy) or highly viscous semi-solids with viscosities of at least 2.5×10 8 Pa s. Amorphous solids have a viscosity of >10 Pa s and semi-solids have a viscosity between 10 2 and 10 12 Pa s. For details, see the Methods and Materials section.