Polymer collapse in miscible good solvents is a generic phenomenon driven by preferential adsorption

Area of Science:

• Polymer science
• Physical chemistry
• Solution thermodynamics

Background:

• Poly(N-isopropylacrylamide) (PNIPAm) precipitates in water-alcohol mixtures, despite dissolving in pure water and alcohols.
• Cononsolvency is a phenomenon where polymers or proteins are insoluble in mixed solvents but soluble in individual cosolvents.
• Existing explanations for cononsolvency are chemically specific and lack a universal framework.

Purpose of the Study:

• To develop a simple and universal theoretical treatment for cononsolvency.
• To explain the precipitation of polymers in mixed solvents based on fundamental interactions.
• To provide a new perspective on understanding macromolecular solubility.

Main Methods:

• Combination of theoretical modeling and computational simulations.
• Analysis of preferential interaction between cosolvents and the polymer.
• Comparison of theoretical predictions with experimental data and chemically specific simulations.

Main Results:

• A universal theory for cononsolvency is presented, requiring only preferential solvent-polymer interaction.
• The model demonstrates striking quantitative agreement with experimental results.
• The theory successfully explains the precipitation of PNIPAm in water-alcohol mixtures.

Conclusions:

• A simple, universal explanation for cononsolvency is established.
• Preferential interaction of a cosolvent with a polymer is the key factor driving cononsolvency.
• This work offers an operational understanding of macromolecular solubility in mixed solvents.