Asymmetry in Polymer-Solvent Interactions Yields Complex Thermoresponsive Behavior.

Area of Science:

• Polymer Science
• Statistical Mechanics
• Physical Chemistry

Background:

• Standard Flory-Huggins theory models polymer solutions but often fails to predict complex phase behaviors like lower critical solution temperatures.
• Existing models frequently require empirical, temperature-dependent parameters, limiting their predictive power and fundamental insight.

Purpose of the Study:

• To develop a novel theoretical framework combining Flory-Huggins theory and the q-state Potts model to study polymer solution phase behavior.
• To investigate the role of orientation-dependent interactions in driving complex phase transitions without empirical parameters.
• To analyze single-chain conformational changes associated with emergent phase behavior.

Main Methods:

• Development of a lattice-based Flory-Huggins-Potts framework.
• Incorporation of orientation-dependent monomer-solvent interactions.
• Single-chain Monte Carlo simulations to observe conformational transitions.
• Validation against experimental polymer solution data.

Main Results:

• The Flory-Huggins-Potts framework successfully predicts lower critical solution temperatures, miscibility loops, and hourglass spinodal curves.
• Orientation-dependent interactions were identified as sufficient drivers for complex phase behavior.
• Monte Carlo simulations revealed heating/cooling-induced coil-globule transitions linked to energy fluctuations.
• The model accurately describes diverse experimental polymer systems.

Conclusions:

• The Flory-Huggins-Potts framework offers a powerful, parameter-free approach to understanding thermoresponsive polymer behavior.
• Orientation-dependent interactions are crucial for complex phase transitions in polymer solutions.
• This work provides fundamental insights into the microscopic origins of polymer phase complexity.