Co-nonsolvency Transition in Polymer Solutions: A Simulation Study

Z Mohammadyarloo and JU Sommer, MACROMOLECULES, 55, 8975-8986 (2022).

DOI: 10.1021/acs.macromol.2c01280

We study the phase segregation in polymer solutions in the presence of a co-nonsolvent (CNS) using molecular dynamics simulations, where CNS particles are a preferential solvent for the polymers. To investigate the condensation transition, we use a movable wall that exerts an osmotic pressure on the polymers but is permeable with respect to the CNS. We focus on the semidilute state of the polymer solution in the absence of CNS. Increasing the amount of CNS results in a condensation of the polymer-CNS phase, which is related to a sharp drop of the polymer volume, followed by a re-entry behavior at higher concentrations of CNS. Simulation results for different interaction energies between monomers and CNS particles are compared with the prediction of the adsorption-attraction mean-field theory under constant osmotic pressure. By calculating the radius of gyration and the structure factor of the individual chains, we found that the conformation statistics of the chains is consistent with the behavior in semidilute solution at the given concentration, resulting from the co-nonsolvency response. Concerning the diffusion dynamics of the polymer chains, we found a monotonous slowing down with increasing CNS concentration and no indication for network-like dynamics or exceptional slow dynamics at the condensation point. Our results are consistent with the collective nature of the co-nonsolvency transition due to weak and transient monomer-CNS-monomer bridging which can be rationalized using mean-field- like concepts.

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