Some materials, such as silicone and Teflon, are designed to be non-sticky. But some products would be improved if other materials could “stick” to them.
For example, try painting silicone. After a few hours, the paint peels off because the silicone is a low surface energy polymer that has extremely low adhesive qualities. Basically, the silicon’s molecular structure makes it hard for any other molecular structure to join to it.
But now, researchers in Germany have developed a technology that joins silicone and Teflon. They are using non-scaled crystal linkers as internal staples, reports R&D.
“If the nano staples make even extreme polymers like Teflon and silicone stick to each other, they can join all kinds of other plastic materials,” says Professor Rainer Adelung, who is the leader of the nano materials group at the Institute of Materials Science at Kiel University. A summary of the group’s work was summarized in the scientific journal, Advanced Materials.
What binds the materials together are micro- and nano-scaled crystals made of zinc oxide, shaped like tetrapods, with four legs protruding from their point of origin. Those zinc oxide crystals are sprinkled evenly onto a heated layer of Teflon. Then, a layer of silicone is poured on top. The mixture is then headed to 100 C for less than an hour so that they can more easily join together.
“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.
“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,” says Dr. Yogendra Kumar Mishra, a supervisor in the project.
In businesses that require high-functioning technology, such as medical engineering, there is a strong demand for new ways to make polymers, 
particularly silicone, stick to other materials. Breathing masks, implants, and sensors are some of these items that come to mind.
Also, these devices need to be non-harmful. The chemical reactions used to bind some polymer materials together can cause toxic effects. Because the Kiel method using tetrapod stapling is a mechanical process, the resulting materials are bio-compatible, the researchers say.
The stapling has achieved a “stickiness” that is similar to having sticky tape on glass. It takes 200 Newtons per meter of force to peel it apart. “The stickiness we have achieved with the nano tetrapods is remarkable, because as far as we could verify, no one has ever made silicone and Teflon stick to each other at all,” says co-author Lars Heepe, a doctoral student from the Zoological Institute of Kiel University, who precisely measured the adhesion and described what the stapled material looks like on the microscopic scale.
Source: “Polymer linking technology joins the unjoinable,” R&D, 8/24/12
Image by U.S. Navy.
Dale McGeehon has been a journalist and editor for more than 25 years, covering chemical regulation and testing for Pesticides and Toxic Chemical News and innovations in material sciences for the National Technology Transfer Center. His writing credits include Omni and College Park magazines and The New York Times.
