Solgels are colloids, or liquids with uniformly dispersed solid particles (like milk) that are converted to gel form.

FORBES: The Science of Small

Colloidal suspensions contain particles of one material (a solid or a liquid) dispersed in another (which can be solid, liquid or gaseous).

ECONOMIST: A new way to build complicated materials, micron by micron

Which is why scientists have decided to look no farther than the Earth itself for elusive particles which are thought to be as old as the Universe and endowed with the ability to traverse solid matter: neutrinos.

UNESCO: Open Access to Scientific Information