Artificial chemotaxis under electrodiffusiophoresis.

Area of Science:

• Colloid and Interface Science
• Soft Matter Physics
• Chemical Engineering

Background:

• Electric fields typically control colloidal interactions through dipole-dipole and hydrodynamic forces.
• Existing methods lack control over complex 3D colloidal structures driven by electric fields.

Purpose of the Study:

• To investigate electric field-induced colloidal interactions mediated by local chemical fields and diffusiophoretic flows.
• To demonstrate the generation and measurement of 3D chemical gradients under electric fields for colloidal manipulation.

Main Methods:

• Utilizing faradaic reactions to create global pH gradients and electrodiffusiophoresis for particle transport.
• Inducing local pH gradients by perturbing particle double layers with electric fields.
• Employing Brownian dynamics simulations alongside experimental measurements.

Main Results:

• Global pH gradients caused 2D focusing, while local gradients induced 3D aggregation.
• Observed diffusiophoresis-driven interactions dependent on particle surface chemistry, zeta potential, and size.
• Demonstrated tunable pH gradients via electric field voltage and frequency adjustments.
• Reported a collective, reactionless chemotactic-like collapse of particles at high Péclet numbers.
• Showcased emergence of non-reciprocal interactions between particles of different sizes.

Conclusions:

• Electric fields can induce novel colloidal interactions through diffusiophoresis and local chemical gradients.
• This provides a new mechanism for controlling 3D colloidal assembly and emergent behaviors.
• The findings open avenues for designing complex colloidal structures and responsive materials.