Complete free energy landscape and statistical thermodynamics of single poly(ethylene glycol) molecules

In this paper, we revisit the statistical mechanics of poly( ethylene glycol) with the intention to check ad hoc approximations made in previous works, namely to keep all C - O bonds along the chain in the trans configuration. The theory developed here includes all the bonds on an equal footing. Starting with density functional theory calculations for the ethylene glycol monomer, dimer and trimer one can determine all the energetic and geometric parameters needed for a rotationally isomeric state model with interactions between nearest neighbour monomers included. The properties of short molecules are presented in detail, including the force-extension curves, end-to-end distributions, and also a discussion of the local helix properties. Finally, we use the transfer matrix method for long chains of 200 ethylene glycol monomers, i.e. 600 bonds. The agreement with the experimental force-extension curve is excellent.