From Hard-Sphere Functionals to Square-Well Droplets

Abstract

This thesis investigates thermodynamic and structural properties of simple fluids using classical density functional theory. A major focus is the construction and optimization of Helmholtz excess free energy functionals for hard-sphere fluids. Guided by dimensional crossover principles, a new class of excess functional is considered — the so-called Lutsko functional — and systematically optimized by taking into account thermodynamic sum rules and being compared to other well-established hard-sphere functionals. Furthermore, classical density functional theory is applied to droplets containing larger solute particles, motivated by questions of airborne lifetime of water droplets laden with nanoparticles. Using a square-well mixture and capillary modelling complemented by full density functional calculations, equilibrium droplet properties and density profiles are discussed under varying environmental conditions.