A novel microscopic origin of co-nonsolvency

Area of Science:

• Polymer Physics
• Soft Matter Physics
• Physical Chemistry

Background:

• Co-nonsolvency describes polymer collapse or precipitation in mixed good solvents, a counterintuitive phenomenon.
• Understanding the driving forces behind co-nonsolvency is crucial for controlling polymer behavior in solution.

Purpose of the Study:

• To elucidate the fundamental mechanism behind co-nonsolvency and associated liquid-liquid phase separation (LLPS).
• To investigate the distinct effects of co-nonsolvency on single-chain versus multi-chain polymer systems.

Main Methods:

• Simulations of polymer systems (homopolymers, block copolymers, single-chain, multi-chain) in binary good solvents.
• Theoretical validation using ternary Flory-Huggins theory.

Main Results:

• Co-nonsolvency arises from the competition between system enthalpy and solvent mixing entropy, leading to LLPS of the preferred solvent (S-solvent).
• In single-chain systems, S-solvent localization within the polymer domain induces local folding and reduced chain size.
• In multi-chain systems, inter-chain sharing of S-solvent molecules leads to chain condensation and increased average chain size.

Conclusions:

• A novel mechanism for co-nonsolvency is proposed, involving LLPS of the S-solvent to optimize enthalpy and entropy.
• The observed effects on polymer size differ significantly between single-chain and multi-chain systems.
• Findings offer insights into LLPS phenomena in broader soft matter systems.