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Aug 28th, 2012
 
Joining the Un-Joinable. How to join Silicone and Teflon?
 
Ever tried to paint on top of silicone? After a few hours, the paint will peel off.
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  • New polymer linking technology based on zinc oxide nano crystals

Annoying. Silicone is a so-called low surface energy polymer, well known from flexible baking forms: A synthetic material that has an extremely low adhesion or “stickiness”. Teflon is similarly non-sticky and well known from frying pans. Researchers of Kiel University (Germany) have now developed the first technology which is capable of joining these two “unjoinable” materials. The technology applies passive nano-scaled crystal linkers as internal staples. The nano staples open up solutions to a large number of technical challenges, for example in medical engineering.

The linkers are micro and nano scaled crystals made of zinc oxide. They are shaped like tetrapods, where four legs protrude from the point of origin. Large-scale tetrapods are known for their ability to interlock and form strong bonds, for example in coastal protection.

During the joining process, the zinc oxide crystals are sprinkled evenly onto a heated layer of Teflon. Then, a layer of silicone is poured on top. In order to join the materials firmly, they are then heated to 100°Celsius for less than an hour. “It’s like stapling two non-sticky materials from the inside with the crystals: When they are heated up, the nano tetrapods in between the polymer layers pierce the materials, sink into them, and get anchored”, explains Xin Jin, the first author of the publication, who is currently working on her PhD thesis. Her colleague and supervisor, Dr. Yogendra Kumar Mishra, explains the adhesive principle: “If you try to pull out a tetrapod on one arm from a polymer layer, the shape of the tetrapod will simply cause three arms to dig in deeper and to hold on even firmer.”

In high technology businesses such as medical engineering, there is a strong demand for innovative ways to make polymers, particularly silicone, stick to other materials, for example to further develop breathing masks, implants or sensors. Medical applications require materials that are absolutely non-harmful, i.e. biocompatible. Many joining methods involve chemical reactions, which may change the polymers’ properties and can cause injurious or even toxic effects on organisms. The tetrapod stapling, on the contrary, is a purely mechanical process. Therefore the Kiel team assumes it to be biocompatible.

 

 
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