Equilibrium sedimentation profiles of screened charged colloids: A test of the hard-sphere equation of state

Equilibrium sedimentation profiles of concentrated suspensions of charged colloids are accurately determined by measuring the intensity of the depolarized light scattered by optically anisotropic particles. From the data we derive the osmotic pressure Π versus the particle volume fraction Φ. The Π(Φ) values obtained with strongly screened colloids are in excellent agreement with the predicted hard-sphere equation of state. The data show that, besides gravitation, there is an additional force acting on the particles, probably due to the buildup of an electrostatic sedimentation potential.