Análise da anomalia da densidade na água contendo impurezas

Abstract

This work is the result of the research carried out in the realization of the project titled \Thermodynamic, Dynamic and Structural Anomalies in Continuous Potentials". We know that water is a fundamental substance for life, it is found in intra and extracellular media, acting as a universal solvent. Understanding their properties is an essential step in understanding the biological processes involved in maintaining life. When analyzing a glass with water and ice, we can realize that the ice solid state of the water, oats in the water, liquid state. This example shows the anomalous behavior of water, which we classify as anomaly in density. The density anomaly happens due to the competition between two scales that water can possess, one of low density and one of high density. The objective of this work was to apply two techniques to determine the existence of density anomaly in a heterogeneous mixture of water and silicon. Both the water and the silicon present anomaly in the density, when they are analyzed individually. When we make a heterogeneous mixture between these two substances, what will be the behavior of the anomaly in the density? To answer this problem, we used computer simulation using the Molecular Dynamics method in the NVT ensemble and controlled the temperature through the Nos e-Hoover thermostat. Molecular Dynamics is a simulation method that calculates the motion of the individual molecules the positions and moments of the particles are described by Newton's equation. We built a system using two types of particles, water and silicon. When the mixture is made, the silicon has the function of solute and the water has the function of solvent. The interaction potential between water particles and silicon particles is an e ective continuous potential of two scales, providing anomaly in density. Already the interaction potential between water and silicon particles is the effective continuous potential of a scale, thus providing the absence of density anomaly. To verify the existence of the anomalies in this mixture, we use radial distribution function techniques and the pressure-temperature phase diagram. After analyzing, we can conclude that both techniques of data analysis are e cient in demonstrating the existence or not of the density anomaly. Thus, both techniques demonstrated consistency in the results obtained.