Binary Colloidal Nanoparticle Concentration Gradients in a Centrifugal Field at High Concentration

Area of Science:

• Colloid and Surface Chemistry
• Materials Science
• Nanotechnology

Background:

• Binary colloidal nanoparticles form diverse crystalline phases influenced by concentration gradients in centrifugal fields.
• Current methods for controlling these gradients are empirical and limited.
• Understanding and controlling these gradients is crucial for tailoring nanoparticle behavior.

Purpose of the Study:

• To develop a method for measuring, fitting, and simulating binary hard-sphere colloidal nanoparticle concentration gradients.
• To enable the creation of tailor-made gradients in a centrifugal field for nanoparticle research.
• To obtain an extended phase diagram for binary nanoparticles by accessing continuous concentration ratios in a single experiment.

Main Methods:

• Utilized multi-wavelength analytical ultracentrifugation (MWL-AUC) to measure individual concentration gradients of differently sized silica nanoparticles.
• Employed a refractive index matching solvent and fluorescence dyes for precise measurements.
• Corrected for turbidity effects using MWL spectra and fitted experimental data with a noninteracting nonideal sedimentation model.

Main Results:

• Successfully measured and simulated binary nanoparticle concentration gradients up to 30 vol %.
• Demonstrated agreement between simulated and experimental gradients at 10 vol %.
• Validated the simulation of binary concentration gradients in preparative ultracentrifuges (PUCs).

Conclusions:

• This study provides the first method to accurately measure, fit, and simulate binary nanoparticle concentration gradients.
• The developed technique allows for the generation of continuous concentration ratios, enabling the creation of extended binary nanoparticle phase diagrams.
• Simulating concentration gradients in PUCs offers a streamlined approach to studying nanoparticle phase behavior, reducing the need for numerous discrete experiments.