Understanding Hydrophobicity and Oleophobicity

Understanding Hydrophobicity and Oleophobicity - Medical Device - Parker Performance MaterialsMedical device manufacturers rely on membrane microfiltration media to filter, vent and protect a wide range of sensitive equipment and instrumentation. The combination of consistent airflow, excellent retention and chemical resistance make polytetrafluoroethylene (PTFE) membranes ideal for life science applications.

But what makes PTFE membranes impermeable to the ingress of water and oily fluids? The answer is hydrophobicity and oleophobicity. Let’s explore these terms in more detail.


Understanding Hydrophobicity and Oleophobicity - Hydrophobicity repels water - Parker Performance MaterialsHydro means water and phobia means fear or aversion to something. That said, if a material is hydrophobic, it repels water.

PTFE is naturally hydrophobic due to its low surface energy. When water is applied to the surface of the membrane, it beads up instantly and repels directly off.

There are two important characteristics of a material relating to how it reacts to water:


  • Water entry pressure (WEP). This is the amount of pressure required for water to penetrate through the pores of the membrane.
  • Pore size. This refers to the size of the pores on the surface of the membrane. A small pore size would lead to a high WEP rate — as high as 70 PSI in some instances. 



When a substance is oleophobic, it repels oil. 

Parker aspire® PTFE membranes, for example, are treated with a proprietary oleophobic coating on both the membrane and substrate sides to provide critical, added protection against liquids and oils.  


Membrane repellency

The repellency of a membrane can be measured by using a standard AATCC 118 test kit. The oils are rated from grade 1 to 8. The images below illustrate how the Parker aspire® membrane compares with a standard membrane to repel the highest rated oil in the test kit (number 8) as well as a commonly encountered oily liquid, diesel fuel, which is rated at a 6.

Understanding Hydrophobicity and Oleophobicity - Oleophobicity - oily fluid comparison - Parker Performance Materials


Understanding Hydrophobicity and Oleophobicity - Oleophobicity - isopropyl alcohol comparison - Parker Performance MaterialsA non-oily liquid worth noting is isopropyl alcohol which quickly wets into the pores of a standard, untreated membrane, but does not wet out when applied to the treated Parker aspire® membrane.








Now, watch the demonstration:


Versatile, naturally inert, and particularly effective against the ingress of water and oily fluids, Parker aspire® PTFE membranes consistently prove to be a valuable component when designing safe and dependable medical filtration devices. Proprietary oleophobic treatment extends the membrane’s adaptability across an even wider assortment of fluids and applications.

aspire® product portfolio includes a broad range of specialized microfiltration and venting solutions that are available in a variety of formats, including membranes, laminates and custom die cuts. Learn more by visiting our website.


Understanding Hydrophobicity and Oleophobicity - Sarah Propp Parker HannifinArticle contributed by Sarah Propp, engineering manager, Parker Performance Materials.






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