Shape- and orientation-dependent diffusiophoresis of colloidal ellipsoids

Area of Science:

• Colloid and Interface Science
• Soft Matter Physics
• Transport Phenomena

Background:

• Diffusiophoresis, the movement of particles in solute gradients, is typically assumed to be shape-independent.
• Existing theories often rely on the thin Debye layer approximation, limiting their applicability to complex particle geometries.

Purpose of the Study:

• To investigate the influence of particle shape and orientation on diffusiophoresis.
• To challenge the conventional understanding of shape independence in diffusiophoretic transport.
• To develop a theoretical framework that accounts for particle geometry in diffusiophoresis.

Main Methods:

• Experimental tracking of the translation and rotation of various ellipsoidal particles.
• Analysis of particle movement under imposed ionic solute gradients.
• Modification of existing theoretical models for spherical particles to incorporate ellipsoidal geometry.

Main Results:

• Demonstrated that diffusiophoresis is not shape-independent, particularly when the thin Debye layer approximation is relaxed.
• Showcased the sensitivity of phoretic mobility to particle eccentricity and orientation relative to the solute gradient.
• Observed nonmonotonic diffusiophoretic behavior under conditions of strong confinement.
• Validated a modified theoretical approach capable of capturing shape- and orientation-dependent diffusiophoresis.

Conclusions:

• The shape and orientation of colloidal ellipsoids significantly impact their diffusiophoretic mobility.
• Relaxing the thin Debye layer approximation is crucial for understanding shape-dependent diffusiophoresis.
• Modified theories can effectively predict the diffusiophoretic behavior of ellipsoidal particles, extending beyond spherical models.