Statistical description of co-nonsolvency suppression at high pressures

Abstract: We present an application of Flory-type self-consistent field theory of the flexible polymer chain dissolved in the binary mixture of solvents to theoretical description of co-nonsolvency. We show that our theoretical predictions are in good quantitative agreement with the recently published MD simulation results for the conformational behavior of a Lennard-Jones flexible chain in a binary mixture of the Lennard-Jones fluids. We show that our theory is able to describe co-nonsolvency suppression through pressure enhancement to extremely high values recently discovered in experiment and reproduced by full atomistic MD simulations. Analysing a co-solvent concentration in internal polymer volume at different pressure values, we speculate that this phenomenon is caused by the suppression of the co-solvent preferential solvation of the polymer backbone at rather high pressure imposed. We show that when the co-solvent-induced coil-globule transition takes place, the entropy and the enthalpy contributions to the solvation free energy abruptly decrease, while the solvation free energy remains continuous.