Theory of the Structure of Charged Liquids and Some Applications

This thesis aims to be a detailed introduction to and a critical discussion of the work that we have done to develop suitable techniques for such liquids. We have caPried out quantitative calculations o~ thermodynamic and structural properties of widely different charged liquids (molten salts, liquid alkali metals and their alloys, a two dimensional layer o.P electrons on the sur·Pace of liquid helium and some related model systems like classical Jellia and charged--haT'd .. ·~sphere!; liquids). We regard as the main result of! our· work the development of theoretical techniques of remarkable accuracy, this being a CT'UCial prerequisite for a meaningful quantitative discussion o~ physical properties and for contact with experiment. Each chapter in this thesis begins with a general intr-oduction to set up the scen<-~rio :in uJhic:h the discussion of: the knot.tin r·esults and of our· original contributions aT"e embedded. Our results are usually discussed in a self-contained way but a copy of the related papers has been put in a physically separate appendix. Ch. 1 is mainly a =~uHHTiart.J of the theoretical tools, as developed in the literature, from which we have started. In chapter 2 we discuss some important model systems: the classical Jellia and the liquid of charged-hard-spheres. In the case of the 3-dimensional one-component plasma (classical Jellium) we summarize the known exact results and we compare the p e T' for man c e s of the best a v a i 1 a b 1 e approximate theories for the stT·ucture. Beside its intrin:5 ic this discussion is useful for the following chapter on liquid alkali metals and to intl'·oduce the methods used to deal with the two-dimensional one-component plasma [lJ which models an elec·tron layer on thE~ surface o·r- lictuid helium. For this system we present a very accurate determination of the static structure which allouJs us to descr:i.be the freezing transition within the density wave theory of freezing. Again in the context of very idealized model systems we present the liquid of charged har·d spheres and our own contribui;ion [2J to the investigations of effects of size non-additivity, in relation to structural studies of some electrolyte solut;ians. to Gh. 3 main 1 y liquid alkali concerns the electron-ion plasma approach metals. Our contr·ibuticm to this problem is twofold: we have checked the accuracy of the lowest order approximation to the coupled system of electrons and ions through resistivity calculations [3J and successfully implemented an extension of this RPA theory [4] to obtain very good agreement with computer simulation and to describe the observed structure in terms of the basic constituents of the liquid metal (ions and electrons). The last chapter is about molten salts. The technological interest for such systems is very high and extensive experimental characterizations have been presented in the ph1J<::~ic;,3l and physico·-chemical literature. Due to the complex chemical-bonding behavior of these systems, a truly microscopic description is confined to the simplest sa.lts i. e. ·those for which the ionic characte·r of the interaction is dominant: alkali halides and, to some extent.. t:h~? alkalin~~-earth halide·:;. A.Pter i;he usual introduction to the subject, we shall describe our treatment o~ the theory of structure [5,6,?J for these liquids. This is a suitable extension to multicomponent charged -1- 1 u i d s of the modified hypernetted chain integral equation CMHNC) as fluids by Lado, successfully developed for Rosenfeld and Ashcroft. monocomponent The comparison between our MHNC results \' er y s a t; i s .P 'J i n g . Hen c e insight in the observed and computer simulation and the computer simulation is we can use the theory to get some discrepancies between [8] and therefore experiments to attempt a microscopic picture far more complex salts [9].