A material’s properties depend not only on its constituents but also on how the constituents are arranged in space. Diamond, for example, shares the same atomic constituents as graphite and the same tetrahedral structure as silicon, yet it resembles neither black flaky graphite nor gray brittle silicon.
So if you want to make a new material with preternatural properties—a transparent magnet, say, or a chemical-sensing resistor—you may need to choose your construction plan as well as your building blocks. And to avoid having to put each block in its individual place, you’d rather the material assembled itself, like a virus’s protein coat or a cell’s lipid membrane.
Colloids may provide a path toward that ideal. Their nanometer-to-micrometer particles can be tailored by size and chemistry. And even the simplest colloids—identical hard spheres that neither attract nor repel each other—will spontaneously crystallize (see Alice Gast and William Russel’s Physics Today article,...
