Mixing Thermodynamics and Flory–Huggins Interaction Parameter of Polyethylene Oxide/Polyethylene Oligomeric Blends from Kirkwood–Buff Theory and Molecular Simulations
Fotis Venetsanos, Stefanos D. Anogiannakis, Doros N. Theodorou
Abstract
In this study, we conduct a full thermodynamic analysis of polyethylene oxide/polyethylene oligomeric blends, building on the methodology introduced by Petris et al. [J. Phys. Chem. B, 2019, 123, 247–57], using which we contribute to the interpretation of large-scale molecular dynamics (MD) oligomeric blend simulations in the light of Kirkwood–Buff (KB) theory, featuring a composition-dependent estimation of the Flory–Huggins interaction parameter. The KB integrals are calculated from NpT MD trajectories using the particle fluctuation method. The component activity coefficients, the excess Gibbs energy of mixing, the volume, enthalpy, and entropy of mixing are extracted as functions of the mole fraction. The Flory–Huggins interaction parameter χ is estimated by interpreting the Gibbs energy of mixing in the framework of Flory–Huggins theory, and its dependence on composition is explored. A structural analysis of the studied oligomeric blends is performed to obtain the mean squared radius of gyration, the molecular pair distribution functions, and the dihedral angle distributions of the two components and is used to interpret the predicted thermodynamic properties. All the results are compared against experimental measurements and previous simulations, where available, and the agreement is found to be very good, validating our proposed methodology.