  We show, using a model coupling mass transport and liquid theory calculations
for a charge-stabilized colloidal dispersion, that diffusion significantly
limits measurement times of its Equation Of State (EOS), osmotic pressure vs
composition, using the osmotic compression technique. Following this result, we
present a microfluidic chip allowing one to measure the entire EOS of a charged
dispersion at the nanoliter scale in a few hours. We also show that
time-resolved analyses of relaxation to equilibrium in this microfluidic
experiment lead to direct estimates of the collective diffusion coefficient of
the dispersion in Donnan equilibrium with a salt reservoir.
