A DuNouy ring is slowly raised through the sample to quantify the liquid-liquid or liquid-air interface tension due to the attraction force (Newtons) exerted from asymmetric intermolecular interactions at the interface that can appreciably differ from the more uniform interactions within the sample. 

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Water walker insects are among many that use surface tension to be supported by water.

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More information can be found in the references listed in Helpful Links page.