Dipole moment of a microdroplet containing a macroion

A study was conducted on the density fluctuation of counterions within aqueou droplets containing no macroions by Monte Carlo simulations. In terms of mean-square dipole moment, the fluctuation grows and becomes saturated as the counterin concentration was increased. As such, the mean-square dipole was found to be proportional to the volume of the microdroplet and was much greater than that induced by particle fluctuations alone, which was estimated from the mean-field theory.