Extreme Nanoconfinement Dramatically Enhances Small Molecule Solubility in Nonpolar Polymers

Area of Science:

• Polymer Physics
• Materials Science
• Nanotechnology

Background:

• Understanding gas solubility in confined polymers is crucial for advancing gas barrier materials, separation technologies, and polymer upcycling.
• Existing knowledge gaps hinder the optimization of polymer-based systems for gas interactions in confined environments.

Purpose of the Study:

• To investigate the solubility of gases (methanol and n-hexane) in polymers (polystyrene and low-density polyethylene) confined within silica nanoparticle packings.
• To determine the primary factors influencing gas solubility enhancement under nanoconfinement.

Main Methods:

• Polymers were infiltrated into silica nanoparticle packings using capillary rise infiltration.
• Gas solubility in confined polymers was quantified using a quartz crystal microbalance.
• Atomistic simulations were employed to elucidate the underlying mechanisms of solubility enhancement.

Main Results:

• Confinement within nanoparticle pores resulted in a 10- to ~100-fold increase in gas solubility compared to bulk polymers.
• Pore size was identified as the dominant factor influencing solubility enhancement; polymer molecular weight and nanoparticle surface chemistry had minimal impact.
• Atomistic simulations indicated that both confinement and surface-polymer interactions contribute to enhanced solubility, modulated by polymer packing.

Conclusions:

• Geometric nanoconfinement is the principal driver of gas solubility enhancement in polymers within nanoporous materials.
• Changes in polymer segment arrangement due to confinement are responsible for the observed solubility trends.
• Confined polymers offer significant potential for engineering advanced separation membranes and improving polymer upcycling processes.