Catálogo de publicaciones - libros

Some theoretical concepts on polymer + solvent systems and Monte Carlo simulations of corresponding coarse-grained models are briefly reviewed. While the phase diagram of polymers in bad solvents invoking the incompressibility approximation for the polymer solution has been a standard problem of polymer science for a long time, a more complete understanding of compressible polymer solutions, where liquid-liquid phase separation and liquid-vapor transitions compete, has emerged only recently. After giving a phenomenological introduction, we outline and compare three complementary approaches: self-consistent field theory, thermodynamic perturbation theory and grandcanonical Monte Carlo simulation. In order to give a specific example, we focus on the mixture of hexadecane with carbon dioxide. Attention is paid to correlate the description of the phase diagram with the properties of interfaces and the nucleation barrier that needs to be overcome to form a droplet (or bubble, respectively) of critical size, necessary for the decay of the corresponding super-saturated metastable state. Particular emphasis is given to new techniques used for the computer simulation of such phase diagrams where several order parameters compete, and to systematic difficulties that still hamper the prediction of accurate nucleation barriers from the observation of droplets (or bubbles, respectively) in finite volumes. The extent to which real materials can be modeled will also be examined.

Molecular dynamics simulations rely on integrating the classical (Newtonian) equations of motion for a molecular system and thus, sample a microcanonical (constant-energy) ensemble by default. However, for compatibility with experiment, it is often desirable to sample configurations from a canonical (constant-temperature) ensemble instead. A modification of the basic molecular dynamics scheme with the purpose of maintaining the temperature constant (on average) is called a thermostat algorithm. The present article reviews the various thermostat algorithms proposed to date, their physical basis, their advantages and their shortcomings.

Computer simulation, Molecular dynamics, Canonical ensemble, Thermostat algorithm

This article reviews the recent progress that has been made in the application of computer simulations to study crystal nucleation in colloidal systems. We discuss the concept and the numerical methods that allow for a quantitative prediction of crystal nucleation rates. The computed nucleation rates are predicted from first principles and can be directly compared to experiments. These techniques have been applied to study crystal nucleation in hard-sphere colloids, polydisperse hard-sphere colloids, weakly charged or slightly soft colloids and hard-sphere colloids that are confined between two plane hard walls.

This review covers the most recent developments using the Polymer Reference Interaction Site Model (PRISM) integral equation theory to study polymer melts and blends. Comparisons to computer simulations are presented that have isolated the deficiencies in the theory and led to improvements including the self-consistent approach where the theory is coupled with single chain Monte Carlo simulations. Using recent simulation results, we outline the strengths and weaknesses of the theory at different levels of detail, from coarse grained bead-spring models to explicit atom models. We conclude with an overview of future directions that are beginning to be undertaken.