Dynamic behaviour of multilamellar vesicles under Poiseuille flow

Area of Science:

• Colloid and Surface Science
• Rheology
• Fluid Dynamics

Background:

• Multilamellar surfactant vesicles (MLVs) are common in industrial applications and influence fluid properties.
• While collective MLV dynamics are studied, individual MLV flow behavior remains under-investigated.

Purpose of the Study:

• To investigate the flow behavior of single MLVs in a concentrated linear alkylbenzene sulfonic acid (HLAS) solution.
• To understand MLV deformation and velocity under shear flow conditions.

Main Methods:

• Utilized high-speed video microscopy and image analysis to observe HLAS solutions in glass capillaries under pressure-driven shear flow.
• Performed rheological tests to characterize the shear-thinning behavior and power-law index of the HLAS solution.

Main Results:

• Observed MLVs deform into shapes analogous to unilamellar vesicles (e.g., parachute, bullet-like).
• Demonstrated that individual MLV velocity aligns with Hetsroni's droplet theory when considering the shear-dependent viscosity.
• Identified a flow-focusing effect of the lamellar phase in the capillary core.

Conclusions:

• Individual MLV flow behavior can be accurately modeled using droplet dynamics theories with appropriate viscosity considerations.
• Findings are crucial for optimizing industrial processes involving surfactant-based systems, such as cosmetics and food products, where flow-induced morphology is key.