Extensional Flow-Induced Concentration Gradient in Entangled Polymer Solutions with Chemically Identical Species

Area of Science:

• Polymer Physics
• Rheology
• Materials Science

Background:

• Entangled polymer solutions exhibit distinct rheological behaviors compared to polymer melts under fast extensional flow.
• This discrepancy challenges the predictions of the classic tube model, highlighting an unresolved issue in polymer physics.
• The classic tube model assumes homogeneous polymer concentration, which may not hold true in dynamic flow conditions.

Purpose of the Study:

• To investigate the occurrence of extensional flow-induced concentration gradients in polymer solutions.
• To reconcile the observed rheological differences between polymer solutions and melts in fast extensional flow.
• To challenge the homogeneity assumption of the classic tube model under specific flow conditions.

Main Methods:

• Utilizing aggregation-induced emission (AIE) probes labeled on oligomeric solvents to visualize concentration changes.
• Combining rheological measurements with *ex situ* fluorescence microscopy to observe flow-induced phenomena.
• Analyzing the formation and characteristics of solvent microdomains under extensional flow.

Main Results:

• Extensional flow induces concentration gradients in polymer solutions, even with chemically identical components.
• Visualization revealed microdomains of oligomeric solvents with characteristic length scales of tens of micrometers.
• These observed microdomains significantly influence the overall rheological behavior of the polymer solutions.

Conclusions:

• The classic tube model needs refinement to account for flow-induced concentration heterogeneity in polymer solutions.
• Solvent microdomain formation under extensional flow is a critical factor affecting polymer solution rheology.
• This research provides a new perspective on understanding polymer dynamics in non-equilibrium flow conditions.