Efficient sampling of solvent free energies in polymers

Solvent excess chemical potentials in amorphous polymers were calculated by means of molecular dynamics simulations using two different methods, the thermodynamic integration method and an extended ensemble method, during which the coupling of a test particle with the rest of the system is continuously changing. The latter method was found to probe the simulation box very efficiently whereas, in the thermodynamic integration, only limited regions of the box were sampled. Excess free energies of chloroform in swollen polydimethylsiloxane were found to decrease with increasing solvent swelling in qualitative agreement with experiment.