What is Surface Tension?

Answer

High surface tension exists in liquids with high cohesion. Molecules below the surface of the liquid get pulled by inter-molecular attractions from all sides, while those at the surface only get pulled downwards and to the sides, resulting in a more stable conformation of the surface molecules. This is why pond skaters don't sink into the water.

 

Liquids with high surface tension don't need a big air gap, but the default is set at 1 μl as a precaution. The dispense immersion depth should also be lower, so the liquid adheres to the well bottom and the surface tension between dispensed liquid and liquid already in the tip helps to pull the volume out.

If there is low surface tension (e.g. ethanol), the air gap should be greater to prevent drips and the dwell time also reduced so the liquid has less time to drip.

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