Structure-rheology relationship in a sheared lamellar fluid

Area of Science:

• Soft Matter Physics
• Rheology
• Mesoscale Modeling

Background:

• Understanding the structure-rheology relationship is crucial for lamellar fluids.
• Shear flow significantly influences the alignment and properties of these complex fluids.
• Mesoscale models offer a way to study these phenomena computationally.

Purpose of the Study:

• To investigate the structure-rheology relationship in shear-aligned lamellar fluids.
• To analyze how dimensionless groups like Reynolds, Schmidt, and Ericksen numbers affect fluid behavior.
• To examine the evolution of lamellar configurations and rheology under shear.

Main Methods:

• Utilized a mesoscale model to simulate lamellar fluid dynamics.
• Employed the lattice Boltzmann method to solve concentration and momentum equations.
• Systematically varied dimensionless parameters (Reynolds, Schmidt, Ericksen numbers, viscosity contrast, system size to layer spacing ratio) in a 2D system.

Main Results:

• At low Schmidt numbers, random domains form and align with flow, increasing resistance.
• At high Schmidt numbers, shear disrupts and reforms layers, creating defects (edge dislocations).
• High Ericksen numbers lead to homogenization and significant viscosity reduction, even disrupting layering at very high values.
• Low Ericksen numbers result in well-aligned layers with defects that anneal slowly, increasing viscosity.
• Increased viscosity contrast between hydrophilic and hydrophobic parts raises viscosity due to layer pinning.

Conclusions:

• The study reveals distinct regimes of lamellar fluid alignment and rheology based on key dimensionless parameters.
• Shear flow dynamics, influenced by diffusion and elastic forces, dictate the final structure and flow resistance.
• Defect formation and annealing dynamics are critical factors controlling viscosity in shear-aligned lamellar systems.