Thermo- and soluto-capillarity: Passive and active drops

Area of Science:

• Fluid dynamics
• Physical chemistry
• Surface science

Background:

• Drops can exhibit directed motion due to external or internal forces.
• Active drops possess the capability for autonomous, self-propelled movement.
• The underlying mechanisms of drop motion are complex, involving various physical and chemical interactions.

Purpose of the Study:

• To survey diverse problems involving directed drop motion.
• To present a minimal mathematical framework for understanding these phenomena.
• To incorporate factors like temperature/solute gradients, illumination, and chemical reactions.

Main Methods:

• Survey of existing problems in directed drop motion.
• Development of a minimal mathematical framework.
• Incorporation of thermo- and soluto-capillarity principles.
• Integration of external and internal driving forces into physico-chemical-hydrodynamics.

Main Results:

• Directed drop motion is fundamentally governed by interfacial tension gradients.
• Thermo- and soluto-capillarity are key drivers of drop movement.
• A unified mathematical framework can describe various scenarios of active and passive drop motion.
• The framework accommodates diverse stimuli including thermal, solute, and chemical gradients.

Conclusions:

• Interfacial tension gradients are the universal basis for directed drop motion.
• The presented mathematical framework provides a unified approach to understanding complex drop dynamics.
• This work offers insights into phenomena driven by thermocapillarity and solutocapillarity.
• The study integrates multiple physical and chemical factors influencing self-propelled drop behavior.