Raman Line Imaging of Poly(ε-caprolactone)/Carbon Dioxide Solutions at High Pressures: A Combined Experimental and...

Area of Science:

• Polymer Science
• Spectroscopy
• Thermodynamics

Background:

• Understanding gas solubility in polymers is crucial for material design and applications.
• Polycaprolactone (PCL) is a biodegradable polyester with potential uses in gas separation membranes.
• High-pressure gas-polymer interactions require advanced characterization techniques.

Purpose of the Study:

• To investigate the in situ carbon dioxide (CO2) sorption mechanism in molten polycaprolactone (PCL) at elevated pressures.
• To quantitatively measure CO2 concentration and characterize molecular interactions using Raman spectroscopy.
• To develop and validate a thermodynamic model for the PCL-CO2 system.

Main Methods:

• Raman line-imaging spectroscopy for in situ monitoring of CO2 sorption.
• Quantitative time-resolved and space-resolved concentration measurements.
• Development of a compressible lattice fluid thermodynamic model incorporating specific interactions.

Main Results:

• CO2 occupies a volume similar to its van der Waals volume in molten PCL.
• Partial molar volume of CO2 remained constant with increasing pressure.
• Lewis acid-Lewis base interactions between CO2 and PCL carbonyls were confirmed as the primary mechanism.
• Steric effects, rather than electronic effects, govern the complex geometry and interaction site.

Conclusions:

• Raman spectroscopy provides molecular-level insights into high-pressure CO2-PCL interactions.
• The developed thermodynamic model accurately predicts solution molar volumes and CO2 partial molar volumes.
• Steric factors play a dominant role in the CO2-PCL supramolecular complex formation.