Shaping suspensions: Stabilizing anisotropy in viscoelastic media using oscillations

Area of Science:

• Materials Science
• Rheology
• Polymer Science

Background:

• Generating anisotropic structures is crucial for applications like meat analogues and conductive composites.
• Traditional methods for particle alignment in viscoelastic liquids require high shear rates or highly elastic fluids, limiting practical implementation.
• Existing processes often involve cumbersome additional steps due to processing parameter constraints.

Purpose of the Study:

• To develop an easier process for generating highly anisotropic structures and properties.
• To investigate the use of oscillatory flows for particle alignment in viscoelastic liquids.
• To compare the effectiveness of oscillatory flow with traditional steady shear methods.

Main Methods:

• Utilizing oscillatory flows to induce particle alignment in viscoelastic liquids.
• Comparing alignment efficiency and string formation at significantly lower shear rates than steady shear.
• Investigating cumulative alignment through flow reversal in oscillatory flows.
• Demonstrating extrusion of aligned structures using superposed oscillatory and steady shear.

Main Results:

• Oscillatory flows achieve particle alignment at shear rates two orders of magnitude lower than steady shear.
• Alignment in oscillatory flow is cumulative due to prevented string breakup by flow reversal, enabling unlimited anisotropic assembly.
• Steady shear alignment is non-cumulative due to Weissenberg number-dependent string stability and breakup.
• The mechanism is applicable to non-ideal particles and enables extruded aligned structures.

Conclusions:

• Oscillatory flow presents a more efficient and accessible method for creating anisotropic structures in viscoelastic materials.
• This technique overcomes the limitations of traditional steady shear methods, offering broader applicability.
• The cumulative nature of alignment under oscillatory flow allows for potentially unlimited anisotropic assembly, beneficial for advanced material design.