Effects of Hofmeister anions in the formation of inorganic solids: Insights through model systems

Specific ion effects are ubiquitous in colloid science. In recent years, with the great increase of activity in the area of colloidal (wet chemical) production of new inorganic materials, “spectator” ions have been found to play significant – and some times unexpected – roles in materials syntheses. The situation respecting the production of mesoporous solids was recently reviewed [1], but similar phenomena have been found in the production of metal or semiconductor particles. Specific ion effects are particularly important in procedures that make use of surfactants or polymers as templates, stabilizers, or habit-modifiers. Such ionic effects are closely related to the Hofmeister series of ions, which was created on the basis of salt effects on protein solubility in water [2]. The Hofmeister series appears in a wide range of chemical and biological phenomena, but its exact origin is not quite understood to date, since it stems from the interplay of ion-surface and ion-water interactions. In this presentation, I will try to make the connection between the two worlds: that of inorganic colloid production and that of specific ion effects at surfactant interfaces. To understand the basis of specific ion effects in the complex systems of inorganic colloid synthesis it is useful to consider much simpler model systems. I will discuss two model systems that are currently being exploited both experimentally and theoretically. One is the free surface of electrolyte solutions, with emphasis on the effect of electrolytes on the surface tension of water [3,4]. The other is a sequence of precisely controlled phospholipid structures (micelles, monolayers, and bilayers). The emerging picture is quite complex and supports the notion that specific ion effects do not act through a – more or less obscure – modification of the structure of water, as was believed until recently in the biological community. Recent results from Langmuir monolayer work imply that the subtle balance in the total free energy of an electrolyte system may allow ions to appear into regions of space that would be considered unfavorable at a first glance.

References.
[1] E. Leontidis, Curr. Opin. Colloid Int. Sci. 7 (2002) 81
[2] K.D. Collins, M.W. Washabaugh, Quart. Rev. Biophys. 18 (1984) 323
[3] M. Boström, D.R.M. Williams, B.W. Ninham, Langmuir 17 (2001) 4475
[4] P. Jungwirth, D.J. Tobias, J. Phys. Chem. B 105 (2001) 10468

Corresponding Author: Epameinondas Leontidis
Associate Professor of Chemistry
Department of Chemistry, University of Cyprus, PO Box 20537, Nicosia 1678, Cyprus
Phone: +357 22 892767 – FAX: +357 22 892801 – E-mail: