Modeling steady-state dynamics of macromolecules in exponential-stretching flow using multiscale...

Area of Science:

• Fluid dynamics
• Soft matter physics
• Computational physics

Background:

• Studying macromolecule response to extensional flow is crucial in soft matter physics.
• Experimental realization of ideal extensional flow is challenging, often limited to specific geometries.

Purpose of the Study:

• Introduce a novel computational method for simulating steady-state uniaxial exponential-stretching flow.
• Enable detailed computer simulations of suspended macromolecule behavior under extensional flow conditions.
• Provide a potential experimental scheme for realizing this type of flow.

Main Methods:

• Developed a simulation technique for incompressible exponential-stretching flow (v(x) = εx).
• Utilized periodic boundary conditions in a uniform square cross-section channel to avoid boundary effects.
• Maintained fluid density and mass conservation by adding fluid particles that exit the channel.
• Embedded spherical colloids and star polymers (bead-spring model) to study their responses.

Main Results:

• The simulation method successfully reproduces flow conditions similar to experimental extensional flow.
• Responses of suspended colloids and star polymers in the simulated flow closely match those in ideal extensional flow.
• Observed that the critical flow gradient for the coil-to-stretch transition in star polymers is independent of the number of arms (f=2, 5, 10, 20).

Conclusions:

• The proposed simulation method is a valuable tool for studying soft matter systems in extensional flow.
• The independence of the critical stretch transition on arm number provides key insights into polymer dynamics.
• The study validates the simulation approach by comparing macromolecule responses to known behaviors.