Colloidal interactions are measured in a hermetically sealed glass sample container, shown in cross-section.
Spheres appear brighter when trapped because of light backscattered from the optical tweezers.
Curves are labelled by the spheres' radii. Solid lines are nonlinear least squares fits to Eq. Dashed lines are fits to the Sogami-Ise theory, Eq. Since its development, the DLVO theory has profoundly influenced the study of macroionic systems. Testing its predictions directly through measurements on pairs of spheres has become possible with the recent development of experimental techniques capable of resolving colloids' delicate interactions without disturbing them.