Influence of temperature, pressure and internal degrees of freedom on hydrogen bonding and diffusion in liquid ethanol

Abstract

Influence of temperature and pressure on the static and dynamic properties of the hydrogen bond network and on diffusion is investigated for 10 state points of liquid ethanol. By gradually freezing the internal degrees of freedom, we also study the influence of the model for the internal motions on H-bonding and diffusion. Whereas an increase in temperature decreases the average length and lifetime of H-bonded chains, we found that compression at constant temperature has little effect upon structure and stability of chains. Flexibility of the molecule is identified as an important mechanism for H-bond breaking in ethanol at all state points. Comparison with a fictitious aprotic molecule-which has the same mechanical and electrostatic properties as ethanol - allows us to show that H-bonding tends to decrease thermal expansion and compressibility. In H-bonded fluid, diffusion is found to be more sensitive to changes in temperature and less sensitive to changes in pressure.