Phase behavior of dipolar fluids and ion-dipole mixtures, and surface diffusion of adsorbed polymers

摘要

Dipole moments are ubiquitous in nature. Studying dipole moments is the first step toward understanding phase behavior of various colloids with strong dipole moments. Since the Dipolar Hard Sphere fluid (DHS) is the simplest model described by dipolar interactions, studying this model is fundamentally important for understanding the structures and thermodynamics of polar fluids. A variety of unsolved scientific questions arises when the dimensionality of this model is changed and when other species are introduced in this model. Finally, the last part of this dissertation discusses the diffusion behavior of adsorbed polymers over the full concentration range. In Chapter 2, I study the phase behavior of dipolar fluids by means of Monte Carlo simulations. My goal in this chapter is to examine the possibility of phase separation in a dipolar fluid system and to use quantitative structural information to shed light on this controversy. How dimensionality affects the phase behavior of dipolar fluids is an interesting question. Thus, in Chapter 3, I examine the possibility of phase separation in quasi-2D dipolar fluids. In Chapter 4, I proceed to binary systems. Since I have excluded the possibility of phase separation in the DHS system and it is well known that the RPM system exhibits phase separation, these result naturally lead to the question whether phase separation takes place in mixtures that contain ions as well as dipolar particles. I map out the phase diagrams by varying the strength ratio of the dipolar to the ionic interaction and I also locate the critical points. In Chapter 5, I turn to a rather different research topic, namely the dynamics of adsorbed polymers. I employ molecular dynamics to investigate the relation between surface diffusion and conformation of adsorbed polymers over the full coverage range.