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

Thu 811:10-14:00P7.99Complex ions in a slit - Monte Carlo and Debye HückelapproachJurij Rescic 1 and Klemen Bohinc 21 Faculty of Chemistry and Chemical Technology, University of Ljubljana, Askerceva 5,Si-1000, Ljubljana, Slovenia2 Faculty of Health Sciences, University of Ljubljana, Ljubljana, SloveniaAqueous solutions relevant to biological systems often contain multivalent complex ions with spatiallyseparated charges. Such ions are short polyamines, peptides and even short and stiff polymersegments, and they do play important roles in processes such as DNA condenstaion and proteinprecipitation. In addition, these solutions are regularly found between charged surfaces such ascharged lipid membranes and charged surfaces of colloidal particles. Several theoretical studieshave addressed such systems. Until recently, Debye - Hückel theory has only been able to studymodels containing simple ions, and was also found unable to predict attraction between equallycharged surfaces [1]. With extension which accounts for intra-ionic correlations, it is possible touse the Debye - Hückel theory also for systems containing multivalent ions with spatially separatedcharges, yielding results which are in good agreement with Monte Carlo simulations [2]. In presentwork, a model solution composed of a mixture of divalent charged rodlike ions with spatially separatedcharges and a simple salt was placed in a slit between two equally charged plates. It wasstudied utilizing both the canonical Monte Carlo simulations and the extended Debye - Hückeltheory. Dependence of thermodynamic and structural properties on parameters such as separationbetween the two plates, length of rodlike ions, and the plates’ charge density was investigated.Results show that the attraction between plates arises from both depletion and charge-charge correlationmechanisms, the latter being weakened with added simple salt. Good agreement betweenthe extended Debye - Hückel and the canonical Monte Carlo simulations is observed, allowing forthe theory to be extended beyond divalent rodlike ions.[1] Safran S. A. Statistical thermodynamics of surfaces, interfaces, and membranes (Colorado:Westview Press), (2003).[2] Bohinc K. , Iglič A. , and May S. Europhys. Lett. 68, 494 (2004).99