Smooth transition from metastability to instability in phase separating protein solutions

Area of Science:

• Physical Chemistry
• Biophysics
• Materials Science

Background:

• Understanding phase transitions is crucial in various scientific fields.
• The metastability/instability boundary in solutions is not fully understood.
• Protein solutions offer a complex system to study phase behavior.

Purpose of the Study:

• To investigate the structure and dynamics of emergent phases after crossing the metastability/instability boundary.
• To monitor real-time, real-space phase generation in protein solutions.
• To compare experimental observations with theoretical predictions.

Main Methods:

• Optical microscopy was used to observe phase generation in real time and space.
• High-concentration lysozyme solutions were subjected to temperature quenches.
• Thermodynamically defined metastable and unstable regions were targeted.

Main Results:

• The evolution of the structure factor during nucleation mirrors spinodal decomposition.
• No singularity was observed upon crossing the metastability boundary, contrary to some predictions.
• Kinetic definitions of the boundary were introduced, showing it as an area rather than a sharp line.
• Significant delay times for new phase appearance indicate kinetic barriers to growth.

Conclusions:

• Experimental results align with non-mean-field theories of phase transformations.
• Observed protein phase behavior is more complex than current theories predict.
• The study provides new insights into nucleation and spinodal decomposition dynamics.