Marangoni effect

In this video, we discuss the Marangoni effect which occurs when there is a gradient in the surface tension causing a mass transfer between be two immiscible fluids.

Following the brief description of the phenomena, there is a demonstration using black pepper sprinkled on the surface of the water (done by Victoria Barr; hereafter referred to as Victoria) Victoria goes on the add a small drop of dish soap the water and pepper causing the pepper to move away for the centre of the dish. This is due to the dish soap having a lower surface tension than the surrounding water. After the dish soap is added the centre has a lower surface tension causing the gradient in surface tension.

The video then transitions to a hand drawn diagram of water showing the positive and negative charges in the covalent in blue and red respectively. The diagram also shows the attraction between each of the different molecules in green in a dotted line. The voice over goes on to explain the mutual attraction between the molecules creates surface tension.

The video moves on to show a paper clip floating in a dish of water before the water is disturbed and the paper clip sinks. This demonstrates that although the there is an attraction between the water molecules it can be easily broken.

The video then goes on the talk about how this can be related to chemical industry by describing the process where silicon wafers in an integrated circuit are dried after a wet processing step. In this process alcohol vapour is sprayed over the wet surface causing a gradient in the surface tension. This is essential as if the water were left in the surface of the silicon wafers it would cause the silicon to oxidise in to silicon dioxide. On screen a diagram of the silicon wafers and how they are dried and be seen.

The voiceover then goes on the discuss an example of the phenomena in nature, the example used is the legs or tears on a glass of wine. The voiceover then explains that the effect can be observed as a ring of clear liquid that forms above the surface of the wine. The ring of liquid continuously forms and drops back into the wine and is a result of the alcohol content in the wine evaporating again causing a gradient in the surface tension. During this section a picture of the legs on a wine glass can be seen.

The voiceover goes on to thank the viewer for watching the video on the Marangoni, list the sources of research and show the copyright.

Sources used in this video:

NASA - The Marangoni Effect: A Fluid Phenom

Marangoni Effect - an overview | ScienceDirect Topics