Macroion virial contribution to the osmotic pressure in charge-stabilized colloidal suspensions.

Instituto de F´isica, Universidad de Guanajuato, 37150 Leon, Mexico(Dated: February 6, 2008)Our interest goes to the different virial contributions to the equation of state of charged colloidalsuspensions. Neglect of surface effects in the computation of the colloidal virial term leads tospurious and paradoxical results. This pitfall is one of the several facets of the danger of a naiveimplementation of the so called One Component Model, where the micro-ionic degrees of freedomare integrated out to only keep in the description the mesoscopic (colloidal) degrees of freedom.On the other hand, due incorporation of wall induced forces dissolves the paradox brought forth inthe naive approach, provides a consistent description, and confirms that for salt-free systems, thecolloidal contribution to the pressure is dominated by the micro-ionic one. Much emphasis is puton the no salt case but the situation with added electrolyte is also discussed.I. INTRODUCTION