Investigating hydrogen bonds in liquid ethylene glycol structure by means of molecular dynamics

Abstract

Models of liquid ethylene glycol are built by means of molecular dynamics at temperatures ranging between 268 and 443 K, with 1000 molecules in rectangular parallelepiped basic cells. The dependences of structures of O-H…O hydrogen bonds on modeling time and temperature are analyzed. It is found that the hydrogen bonds emerge at different sites of a model, thus forming a hydrogen bonds network that is continuously rebuilt under the action of thermal fluctuations. The number of hydrogen bonds in the models is observed to decrease when the temperature is raised. The energy of hydrogen bond formation is found to be −20.0 ± 2.6 kJ mol−1, the average bond lifetime is 370 ps at 268 K and 147 ps at 323 K, and the activation energy of hydrogen bond rupture at these temperatures is ∼12.1 kJ mol−1. It is concluded that the data on the breaking of H-bonds at temperatures of 323 to 443 K can be explained by the molecules moving away from each other as a result of diffusive motion, accompanied by rearrangement of the hydrogen bonds network. The concentration of dimers in the models is shown to be rather low, while the average energy of forming a dimer from two ethylene glycol molecules is −35.4 kJ mol−1.