Trajectories of probe spheres in generalized linear viscoelastic complex fluids

Area of Science:

• Physics
• Materials Science
• Physical Chemistry

Background:

• Understanding complex fluid dynamics is crucial for materials science.
• Probe sphere dynamics reveal insights into viscoelastic material properties.
• Existing models often struggle with the broad dynamic range of complex fluids.

Purpose of the Study:

• To develop a fast and accurate simulation for probe sphere random walks in viscoelastic complex fluids.
• To introduce and validate the coupled harmonically bound Brownian particle (c-HBBP) model.
• To analyze particle trajectories across a wide dynamic range in various complex fluids.

Main Methods:

• Developed a coupled harmonically bound Brownian particle (c-HBBP) model.
• Treated viscoelastic relaxation modes as harmonic wells coupled to a probe sphere.
• Implemented variable temporal step sizes with a uniform logarithmic time distribution.
• Simulated trajectories for polymer systems, emulsions, polymer blends, and anisotropic soft systems.

Main Results:

• Generated random walk trajectories for isolated probe spheres in diverse viscoelastic fluids.
• Demonstrated that trajectories are generally not self-similar or self-affine, except for specific cases like polymer gel points.
• Mean square displacements align with the generalized Stokes-Einstein relation for linear passive microrheology.

Conclusions:

• The c-HBBP model provides a computationally efficient and accurate method for simulating probe dynamics in complex viscoelastic fluids.
• The simulation captures the essential physics governing particle motion across an extended dynamic range.
• Results support the applicability of linear passive microrheology principles to these complex systems.