Classification of Surface Tension Gradient-Driven Flow

12 Classification of Surface Tension Gradient-Driven Flow 

The Marangoni force can be used as a micropropulsion system, as some bacteria actually do in nature. The principle is simple. The bacteria emit some surfactant that lowers the surface tension behind the little body. The body is pushed forward as the interface tries to minimize the region of high surface tension (without surfactant) while maximizing the region of low surface tension (with surfactant). One can build a little boat illustrating this principle by attaching a piece of soap at the end of a stick. As the soap dissolves, the stick moves forward. 

Spatial variations in temperature at the interface. The resulting flow is termed as thermocapillary flow. 

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