8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P7.128Thu 811:10-14:00Effect of ions on critical phenomena in confined binarymixtureAlina Ciach, 1 Faezeh Pousaneh, 1 Anna Maciolek, 1 and Siegfied Dietrich 21 Institute of Physical Chemistry of the Polish Academy of Sciences, ul. Kasprzaka 44/52,01-224, Warszawa, Poland2 Max-Planck-Institute for Metals Research, Stuttgart, GermanyNear-critical binary mixture containing dissolved ions and confined between charged and selectivewalls is considered. Landau-type theory is developed from microscopic description and Euler-Lagrange equations are obtained. Mutual effect between the concentration and charge profiles isdetermined analytically for the correlation and Debye screening lengths both much larger frommolecular size. For ions soluble only in one component of the mixture (water) we find strongeffect of the charge profile on the concentration profiles. The concentration profile near the hydrophobicwall is non-monotonic For strongly charged surfaces the hydrophobic wall may becomehydrophilic. For weakly charged hydrophobic wall excess water is found at some distance from itwhen the correlation length is smaller than the Debye screening length, and for sufficiently largeratio between the correlation and Debye lengths standard monotonic decay of excess concentrationof organic component is obtained. Properties of the concentration profiles lead to effectivepotential between hydrophilic and hydrophobic surface that is repulsive far from critical point, becomesattractive and again repulsive when the critical temperature is approached. Thus, by tuningtemperature or salt concentration one can reversibly change attraction to repulsion.128