Revisiting the driving force inducing phase separation in PEG-phosphate aqueous biphasic systems.

Area of Science:

• Chemical Engineering
• Physical Chemistry
• Biotechnology

Background:

• Aqueous biphasic systems (ABS) are crucial for industrial macromolecule separation.
• Polymers, ionic liquids, and salts are used to induce phase separation in water.
• Previous theories proposed solvation differences or enthalpy changes as driving forces for polymer-salt ABS.

Purpose of the Study:

• To investigate the driving forces behind phase separation in polyethylene glycol (PEG)/dipotassium phosphate (K2HPO4)/water systems.
• To re-evaluate the role of water solvation and enthalpy changes in ABS.

Main Methods:

• Liquid-phase Nuclear Magnetic Resonance (NMR) spectroscopy.
• High-resolution Raman spectroscopy.
• Injection microcalorimetry.

Main Results:

• NMR and Raman showed similar water solvation properties in both PEG-rich and salt-rich phases.
• PEG interacts with salt ions in the PEG-rich phase, indicated by NMR shifts.
• Microcalorimetry revealed minimal enthalpy changes during mixing of PEG- and salt-rich phases.

Conclusions:

• Large differences in water solvation are not the driving force for PEG/K2HPO4 phase separation.
• Significant enthalpy changes do not explain the phase separation mechanism in these systems.
• The study challenges existing theories on polymer-salt ABS driving forces.