Marangoni Convection in Drops

Droplets are present in many microfluidic systems. This section presents the convective motion inside the droplet due to the variation in local properties of the liquid. Surface tension depends on temperature, concentration of chemical species at surface, and electric potential, that is. 

The classical relation between surface tension and temperature can be written as 

The strength of Marangoni convection is linked to the Marangoni number defined as 

Similar to the temperature-driven Marangoni convection, concentration-driven Marangoni convection is also present in microfluidics. When surfactants are added to the fluid, they migrate to the interface, and a gradient of interface concentration may occur, leading to a convective motion at the interface. In the case of concentration-driven convection, the nondi-mensional Marangoni number is defined as 

Solutal Marangoni number, Ma, is the ratio between the surface tension force due to concentration difference and the viscous force of fluid. 

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