Abstract: Claiming that activity coefficients are the easiest properties
to calculate was a utopia until few years ago. Conventional techniques
sample configurational space by particle insertion/deletion methods or by
thermodynamic integration ones. They are particularly time-consuming and almost
intractable for large solutes in entangled polymer matrices. Conversely, we
developed new tailored methods to estimate chemical potentials or activity
coefficients in situations met in food packaging applications: aqueous dominant
mixtures, homopolymers and copolymers. They rely on a compressible
Flory-Huggins formulation at atomistic scale with additional entropy and
enthalpy corrections inferred by molecular dynamics simulation. Corrections are
particularly important to reproduce radial distributions, cooperative hydrogen
bonding and the residual elastic energy in glassy polymers. The whole approach
has been validated to estimate partition coefficients of various substances (e.g.,
aroma, plastic additives, homologous series of alkanes and alcohols) between a
broad range of polymers and food simulants.
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