ABSTRACT
An overview of classic theories is presented that describes the
structural and thermodynamic properties of fluids of charged
particles, such as (poly-)electrolyte solutions, ionic liquids, plasmas,
and charged colloids, and their relevance is discussed for current
challenges, both in materials design and in fundamental research on
soft and biological matter. The chapter is illustrated with examples
of novel applications, and complemented with recent improvements
on theoretical and numerical methods. Initially, the structural
properties of homogeneous fluids of charged hard spheres are
studied by means of Debye-Hu¨ckel (DH) and Ornstein-Zernike (OZ)
theory. A recently derived closure for the OZ equation is highlighted
that approximates the accuracy of the hyper-netted chain (HNC),
but with a superior numerical efficiency and stability. The results
shed light on charge ordering and clustering behavior in charged
fluids. Classical density functional theory (DFT) is then addressed
as a powerful framework to study fluids that are inhomogeneous,
whether due to awall, amembrane, or an ensemble of nanoparticles,
using the information obtained for bulk fluids to estimate the
position-dependent excess chemical potential, which accounts for
the correlations between the particles. In the special case of
planar symmetry, the rigorous method proposed by Kjellander and
Marcˇelja can be applied, known as the anisotropic hyper-netted
chain (AHNC), in which the excess chemical potential is actually
calculated instead of heuristically estimated, using a mathematical
mapping of the inhomogeneous system to a more polydisperse, yet
homogeneous system of lower dimension. The AHNC reveals how
walls and dielectric interfaces deform the screening cloud around
charged particles, and how the average force between the particles
is modified. The chapter is concluded by a perspective on different
origins for like-charge attractions.
