Shear-induced ordering in liquid microjets seen by x-ray cross correlation analysis.

Area of Science:

• Materials Science
• Fluid Dynamics
• Nanotechnology

Background:

• Understanding nanoparticle behavior under flow is crucial for applications like drug delivery and materials manufacturing.
• Microfluidic devices offer precise control over fluid environments for studying particle dynamics.
• Shear forces can induce complex self-assembly and ordering in colloidal dispersions.

Purpose of the Study:

• To investigate the shear-induced structural ordering of silica nanoparticles in a microfluidic jet.
• To analyze the direction-dependent nature of this ordering along and across the flow.
• To determine the decay dynamics of shear-induced order after flow cessation.

Main Methods:

• Utilizing a microfluidic jet device to apply controlled shear to silica nanoparticle dispersions.
• Employing X-ray cross-correlation analysis to quantify diffraction pattern asymmetries.
• Measuring the decay of shear-induced ordering for varying Rayleigh nozzle sizes and shear rates.
• Modeling particle distributions and comparing diffraction patterns with simulations.

Main Results:

• Observed direction-dependent nanoparticle structure formation along and across the flow.
• Quantified the decay of shear-induced ordering, finding longer characteristic times at larger tube sizes and lower shear rates.
• Péclet-weighted times did not exhibit linear scaling with Péclet numbers.
• Determined the azimuthal variation of volume fraction in the maximum ordered state via simulations.

Conclusions:

• Shear flow in microfluidic jets leads to anisotropic structuring of silica nanoparticles.
• The dynamics of order decay are complex and depend on flow geometry and shear conditions.
• The study provides insights into nanoparticle self-assembly under controlled flow, aiding in the design of advanced materials.