A local annealing strategy for equilibrium-like solute insertion into glassy polymer matrices

Area of Science:

• Polymer Science
• Materials Science
• Computational Chemistry

Background:

• Solute diffusion in glassy polymers is crucial for applications like drug delivery and material design.
• The non-equilibrium dynamics of glassy polymers significantly impact solute transport properties.
• Understanding the free-energy landscape of solute insertion is key to predicting diffusion behavior.

Purpose of the Study:

• To investigate the influence of polymer dynamics on small molecule insertion into glassy poly(vinyl acetate) (PVAc).
• To analyze the potential of mean force (PMF) for sorbitol insertion into dry and hydrated PVAc.
• To develop and validate a computational strategy for modeling solute insertion in non-ergodic glassy systems.

Main Methods:

• Atomistic molecular dynamics simulations were employed to model sorbitol insertion into PVAc slabs.
• Potential of Mean Force (PMF) calculations were used to determine free-energy barriers.
• A novel local annealing strategy was introduced to overcome kinetic trapping in dry PVAc.

Main Results:

• Dry PVAc exhibits a large, non-equilibrium insertion barrier due to kinetic trapping and steric effects.
• Hydration plasticizes PVAc, enhancing local mobility and reducing the insertion barrier.
• The local annealing strategy reduced the insertion barrier by over 70%, yielding an equilibrium-like free-energy profile.

Conclusions:

• The dynamical state of glassy polymers critically affects solute insertion.
• Water-induced plasticization facilitates solute transport by increasing polymer mobility.
• Local annealing is an effective computational method for studying solute insertion in glassy polymers, even when full equilibration is not feasible.