Multilamellar vesicle formation from a planar lamellar phase under shear flow

Area of Science:

• Soft Matter Physics
• Materials Science
• Physical Chemistry

Background:

• Nonionic surfactant systems like C12E5/D2O can form complex structures.
• Understanding the formation of multilamellar vesicles (MLVs) under external forces is crucial for materials science.
• Previous studies often showed isotropic orientation of lamellae in flow, lacking detailed in-plane dynamics.

Purpose of the Study:

• To investigate the formation of multilamellar vesicles (MLVs) from the lamellar phase of C12E5/D2O under shear flow.
• To track the alignment of lamellae in the velocity-velocity gradient plane during MLV formation.
• To identify the underlying mechanism of MLV formation in simple shear flow.

Main Methods:

• Time-resolved small-angle neutron scattering (SANS) with a novel shear flow sample environment.
• Flow small-angle light scattering (SALS) synchronized with rheology.
• Analysis of Bragg peak tilting and pattern anisotropy.

Main Results:

• Lamellar ordering tilts during the lamellar-to-MLV transition, forming an anisotropic pattern with a primary axis ~25° to flow.
• This anisotropic pattern persists after MLV formation under flow.
• Critical strain and capillary number for MLV formation were determined and shown to be system-robust.

Conclusions:

• Novel SANS and SALS measurements reveal in-plane lamellar orientation dynamics during MLV formation.
• Observations support buckling-induced MLV formation models, suggesting a three-dimensional instability.
• The study identifies the mechanism of MLV formation in simple shear flow.