Speaker
Description
The coil-globule transition of a polymer in a bath of solvent molecules is a paradigmatic
example of phase transition. Theoretical approaches to the problem usually adopt an
implicit solvent description, where the solvent degrees of freedom are traced out to obtain
an effective polymer – polymer interaction. This approach fails when a detailed description
of the solvent is required. Recent computational studies [1] have shown that even a simple
bead-spring chain in explicit solvent displays a reentrant collapse that is not explainable
within an implicit solvent framework. Another example is co-nonsolvency, a phenomenon
in which a polymer in a solution of two solvents, each being a good solvent for the polymer,
collapses [2]. A recently discovered phenomenon is polymer-assisted condensation [3],
where phase separation of two liquids is induced by preferential attachment of a polymer
chain to one of them.
With the aim of providing a unifying theoretical, analytical framework for all these
phenomenologies, we present a lattice model for polymer solutions [4] which exploits
the well-known analogy between polymer systems and the O(n → 0)-vector spin model.
We derive an exact field-theoretic expression for the partition function: a saddle-point
approximation then leads to the mean-field free energy. We study the stability with respect
to phase separation through a numerical approach based on convex hull evaluation, and
show how our theory recapitulates all the phenomena listed above; also, we predict new
low-temperature regions of the phase diagram that have not been studied numerically
before.
[1] Y. Huang, S. Cheng, Journal of Polymer Science 59 (2021) 2819–2831.
[2] D. Mukherji, C.M. Marques, K. Kremer, Nature communications 5 (2014)
4882.
[3] J. U. Sommer, H. Merlitz, H. Schiessel, Macromolecules 55 (2022) 4841-4851.
[4] D. Marcato, A. Giacometti, A. Maritan, A. Rosa, Physical Review Materials 8 (2024)
1256011
| Role | Master/PhD student |
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