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Surface Tension

By Little Pro on 2016-01-13 Views:  Update:2017-01-18

Surface tension is the force that causes the molecules on the surface of a liquid to be pushed together and form a layer. Surface tension has the dimension of force per unit length (uN/cm or N/M) or of energy per unit area. You can often find it in the section 9 of a safety data sheet (SDS).

Because of the relatively high attraction of water molecules for each other, water has a high surface tension (72.8 millinewtons per meter at 20 °C) compared to that of most other liquids. Surface active substances (surfactants) can reduce water surface tension.

Regulatory Implications of Surface Tension

Surfactants are used in a great number of formulation applications such as detergent, personal care products and pesticides. Most surfactants have a hydrophobic (water repellent) part and a hydrophilic (‘water loving’) part. They reduce the surface tension of the water so it can wet the fibres and surfaces. They loosen and encapsulate the dirt and in that way ensure that the soiling will not re-deposit on the surfaces.

Most surfactants are more or less toxic to aquatic organisms due to their surface activity which will react with the biological membranes of the organisms. The biological degradability varies according to the nature of the carbohydrate chain. Generally the linear chains are more readily degradable than branched chains. [Reference]

 

Measuring the surface tension of a substance can help us understand its surface activity . For example, a chemical (i.e, oil spills) with low surface tention tend to spread quicker on water surface and cause bigger threats.

Under REACH, the study need only be conducted if:

  • based on structure, surface activity is expected or can be predicted, or
  • surface activity is a desired property of the material.

If the water solubility of a substance is below 1 mg/l at 20 °C the test does not need to be conducted.

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 Tags: Topics - CRAPhysiochemical Property

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