Structure, thermodynamic properties, and phase diagrams of few colloids confined in a spherical pore

TL;DR

This paper investigates the structural and thermodynamic behavior of a few colloids confined in a spherical cavity, using simulations and theoretical analysis to understand phase-like behaviors and map interactions to colloid-polymer models.

Contribution

It provides a detailed analysis of few colloids in confinement, linking their properties to macroscopic phase diagrams and extending the law of corresponding states to confined systems.

Findings

Characterized structures of 2-6 colloids as functions of density and temperature.

Mapped square-well interactions to the Asakura-Oosawa model for colloid-polymer mixtures.

Identified qualitative behaviors across the thermodynamic plane for confined few-particle systems.

Abstract

We study a system of few colloids confined in a small spherical cavity by event driven molecular dynamics simulations in the canonical ensemble. The colloidal particles interact through a short range square-well potential, which takes into account the basic elements of attraction and excluded-volume repulsion of the interaction among colloids. We analyze the structural and thermodynamic properties of this few-body confined system in the framework of the theory of inhomogeneous fluids. Pair correlation functions and density profiles across the cavity are used to determine the structure of the system and the spatial characteristics of its inhomogeneities. Pressure on the walls, internal energy and surface quantities such as surface tension and adsorption are also analyzed for the whole range of densities, temperatures and number of particles considered. We have characterized the structure of systems from 2 to 6 confined particles as function of density and temperature, identifying the distinctive qualitative behaviors all over the thermodynamic plane $T-\rho$ in a few-particle equivalence to phase diagrams of macroscopic systems. Applying the extended law of corresponding states the square well interaction is mapped to the Asakura-Oosawa model for colloid-polymer mixtures. We link explicitly the temperature in the confined square-well fluid to the equivalent packing fraction of polymers in the Asakura-Oosawa model. Using this approach we study the confined system of few colloids in a colloid-polymer mixture.