Surfactant in a Polyol-CO₂ Mixture: Insights from a Classical Density Functional Theory Study

Area of Science:

• Materials Science
• Chemical Engineering
• Physical Chemistry

Background:

• Silicone-polyether (SPE) surfactants, composed of polydimethyl-siloxane (PDMS) and polyether, enhance polymeric foam properties.
• Gas bubble nucleation is critical in foam production, but the role of SPE surfactants remains unclear.

Purpose of the Study:

• Investigate the effect of SPE surfactants on CO2 bubble nucleation in polyol formulations.
• Elucidate the mechanism of surfactant-mediated nucleation using computational methods.

Main Methods:

• Classical density functional theory (DFT) was employed.
• Simulations focused on CO2 bubble nucleation in a polyol-CO2 system with and without SPE surfactant.

Main Results:

• SPE surfactant addition decreased polyol-CO2 interfacial tension by approximately threefold at the critical micelle concentration.
• The surfactant reduced the free energy barrier for CO2 bubble nucleation.
• Nucleation shifted from a single-barrier pathway to a two-step process involving a liquid-like CO2 core aggregate, followed by a vapor-like CO2 core bubble.

Conclusions:

• SPE surfactants facilitate CO2 bubble nucleation through a stabilized, liquid-like CO2 aggregate intermediate.
• The PDMS backbone's affinity for CO2 likely drives this stabilization.
• This mechanism may lead to foams with finer microstructures and enhanced insulating capabilities.