Measurement of the hard-sphere equation of state using screened charged polystyrene colloids

Using a high-resolution digital x-ray camera we have accurately measured the density profiles of several sediments of highly screened polystyrene colloidal spheres suspended in water. From the integral of the profile with height we directly measured the osmotic pressure as a function of volume fraction. The results are in excellent agreement with calculations of the hard-sphere equation of state for both the crystalline and disordered states. These results demonstrate experimentally that particles with a hard-sphere force law indeed exhibit the liquid-solid phase transition at the predicted volume fractions. © 1996 The American Physical Society.