Polymer conformation during flow in porous media

Area of Science:

• Polymer physics
• Fluid dynamics
• Microfluidics

Background:

• Understanding polymer behavior in porous media is crucial for applications like enhanced oil recovery and drug delivery.
• Flow-induced polymer dynamics can lead to complex phenomena such as elastic instabilities.
• Single-molecule imaging provides high-resolution insights into these dynamics.

Purpose of the Study:

• To directly observe and characterize the molecular conformations of individual polymers during flow through porous media.
• To investigate the nature of elastic instabilities and their impact on polymer behavior in microfluidic systems.
• To analyze the stretching and coiling dynamics of polymer chains within dead-zones.

Main Methods:

• Utilized single-DNA imaging techniques in microfluidic devices to visualize individual polymer chains.
• Controlled polymer flow through porous media by varying the Weissenberg number (Wi).
• Analyzed polymer conformations and movements, particularly within stagnant regions (dead-zones).

Main Results:

• Observed two distinct types of elastic instabilities: stationary and time-dependent dead-zone washing.
• Demonstrated that stretched polymer chains first recoil upon entering a dead-zone.
• Found that polymers subsequently rotate and re-stretch within the dead-zone, exhibiting heterogeneous and broad probability distributions of stretched conformations.

Conclusions:

• The study provides direct visualization of polymer conformational changes and elastic instabilities in porous media flow.
• The observed phenomena of coiling, rotation, and re-stretching within dead-zones are critical for understanding polymer dynamics.
• The heterogeneous distribution of stretched DNA chains highlights the complex nature of polymer behavior under these flow conditions.