Density anomaly in a minimum model of water-alcohol mixtures

TL;DR

This study investigates how small amounts of solute affect the temperature of maximum density in water-like mixtures, revealing that strong solute-solvent attraction determines whether the TMD increases or decreases.

Contribution

It demonstrates that strong solute-solvent attraction is key to modeling structure makers and breakers in water-alcohol mixtures using both one-dimensional and three-dimensional simulations.

Findings

Strong solute-solvent attraction increases TMD when solute is a structure maker.

Weak or attractive interactions lead to TMD decrease when solute is a structure breaker.

Both models confirm the importance of solute-solvent attraction in density anomalies.

Abstract

We study the change in the temperature of maximum density (TMD) of a water-like solvent when small amounts of solute are added to the mixture. The water is modeled as a two length scales potential, which is known to exhibit water-like characteristic anomalies, while the solute is chosen to have an attractive interaction with the solvent. If the solute is a structure maker the TMD increases with the addition of solute, while if it is a structure breaker the TMD decreases. Both in an exact one dimensional model and using molecular dynamics in three dimensions we show that the necessary ingredient to represent structure makers is a strong solute-solvent attraction.