Diffusiophoretic Migration of Colloidal Particles in Sucrose Gradients

Area of Science:

• Colloid and Interface Science
• Physical Chemistry
• Microfluidics

Background:

• Diffusiophoresis (DP) is particle migration driven by solute gradients.
• Experimental data for neutral solutes, especially at high concentrations, are limited.
• Distinguishing DP from other phenomena in concentrated solutions is challenging.

Purpose of the Study:

• To experimentally investigate diffusiophoresis of dispersed colloids in concentrated sucrose solutions.
• To measure particle migration velocities and sucrose concentration profiles.
• To model DP using steric exclusion and compare with experimental data.

Main Methods:

• Utilized a microfluidic chip to create time-dependent sucrose gradients.
• Employed particle tracking to analyze individual particle trajectories.
• Used Raman confocal spectroscopy to measure unsteady sucrose concentration profiles.

Main Results:

• Observed significant particle migration towards low sucrose concentration regions (velocities up to a few μm s⁻¹).
• Measured sucrose concentration profiles align with diffusion equations, with concentration-dependent interdiffusion coefficients.
• A steric exclusion model accurately predicted observed particle trajectories with an exclusion length of 5 ± 0.9 Å.

Conclusions:

• Demonstrated and quantified diffusiophoresis in concentrated sucrose solutions.
• Validated a steric exclusion model for diffusiophoresis.
• Identified Brownian motion, diffusioosmosis, and buoyancy as potential sources of experimental data scattering.