Tuning chemotactic and diffusiophoretic spreading via hydrodynamic flows.

Area of Science:

• Colloid and Interface Science
• Biophysical Transport Phenomena
• Microorganism Dynamics

Background:

• Chemotaxis and diffusiophoresis share a
• log-sensing
• response, despite distinct mechanisms.

Purpose of the Study:

• Analyze advective-diffusive transport of chemotactic/diffusiophoretic colloids in a circular tube under hydrodynamic flow and solute gradients.
• Investigate the impact of hydrodynamic flow on colloid spreading, including decaying colloids and finite-range log-sensing.
• Demonstrate the generality of macrotransport theory for arbitrary chemotactic models and explore anomalous spreading regimes.

Main Methods:

• Derivation of an exact solution for the log-sensing chemotactic/diffusiophoretic macrotransport equation.
• Generalization of the exact solution to include decaying colloids.
• Numerical solutions for a more general chemotaxis model with finite-range log-sensing.

Main Results:

• Strong hydrodynamic flow reduces spreading for solute-repelled colloids by suppressing super-diffusion.
• Hydrodynamic flows consistently enhance spreading for solute-attracted colloids.
• Tunable spreading phenomena persist for decaying colloids.
• New anomalous spreading regimes, qualitatively matching experiments, are revealed and tunable by hydrodynamic flows.

Conclusions:

• Macrotransport theory is broadly applicable to chemotactic and diffusiophoretic colloid transport.
• Hydrodynamic flows offer a method to tailor colloid transport for specific applications.
• Findings are relevant for optimizing processes such as oil recovery and bioremediation.