All physical properties of matter, such as weight, hardness, and color, are determined by the kind of atoms present in a substance, the way they interact with each other, and the type of arrangements they form. The size of atoms and the complex ways groups of atoms organize themselves to form various states of matter make them very difficult to study. One way to overcome these problems is by studying systems of simple, larger particles that behave in similar ways. The second Colloidal Disorder-Order Transition experiment will test fundamental theories that describe atomic behavior.
Colloids are systems of fine particles suspended in fluid.
Milk, orange juice, and paint are some common examples. The experiment uses colloidal suspensions of uniformly sized microscopic solid plastic spheres as a model of atomic interactions. On Earth, gravity causes the denser particles in a colloidal suspension to settle to the bottom, which is why some colloids, like orange juice and paint, must be stirred before use. Microgravity enables scientists to study colloids because the effects of density differences between particles and their surrounding fluids are decreased, thus eliminating settling and maintaining an even distribution of particles in the fluid. During the STS-95 mission, researchers will use colloids to learn more about how the organization of atoms changes as they form into orderly solid structures.