Feedback control of photoresponsive fluid interfaces

Area of Science:

• Fluid dynamics
• Materials science
• Physical chemistry

Background:

• Photoresponsive surfactants change molecular shape under light, altering fluid interface properties.
• This light-induced change in surface tension drives Marangoni flow, a key microfluidic mechanism.

Purpose of the Study:

• To model the dynamics of photoresponsive surfactant mixtures at planar interfaces.
• To investigate pattern formation and complex behaviors driven by light-induced Marangoni flow.

Main Methods:

• Formulation of diffusion-advection-reaction equations for surfactant densities, including adsorption, desorption, and photoisomerization.
• Analysis of interface response to single and multiple light spots with feedback coupling rules.

Main Results:

• A single light spot induces an exponentially decaying surfactant density profile and a radially reversing Marangoni flow.
• Feedback coupling between light spots leads to alternating on/off switching and complex periodic or irregular oscillation patterns on polygonal arrangements.

Conclusions:

• Simple feedback rules can generate intricate dynamic patterns in photoresponsive fluid interfaces.
• This work provides insights into controlling microfluidic systems using light-activated surfactants.