Wetting Liquids

A good wetting liquid for capillary flow porometry  should have the following properties:

  • Zero contact angle
  • Low surface tension
  • Low vapor pressure

Also, it has to be chemically inert and should not cause swelling of the sample.

In many cases, the best results are obtained by using fluorinated hydrocarbons. These liquids have low surface tension (around 16 dyn/cm) and low vapour pressures, which minimises any potential evaporation during the measuement.

Sometimes silicone oils are used. They have a high viscosity, a low surface tension and a low vapor pressure. The disadvantage of silicone oils is that it is hard to clean them out of inserts. the sample holder and supports. The residual silicone oil can contaminate subsequent tests, which can prevent the porometer from getting good dry curves.

The use of water is not recommended because it tends to evaporate during measurements, which may lead of an overestimation of the pore sizes (the pores are detected as open too early). Moreover, the surface tension of water is rather high (72 dyn/cm), which means that for a given pore size a  much higher pressure than when measuring with Porefil or Galpore is required. Furthermore, water, like some alcohols, often cause swelling of samples.

We recommend using as much as possible the same liquid, because, in theory, as long as you apply the correct vapor pressure, different liquids should give the same results, but in practice it is not always the case.

POROMETER offers different types of wetting fluids in different quantities. All of our wetting fluids come with a certificate showing the measured surface tension.

Porefil 
Chemical natureperfluoroether
Surface tension16 mN/m
Vapor pressure399 Pa
Viscosity2.2 mPa.s
Available volumes250, 1000 ml
Galpore 
Chemical natureperfluoroether
Surface tension15.6 mN/m
Vapor pressure3.33 Pa
Viscosity4.4 mPa.s
Available volumes250, 1000 ml