Super slick molecules

Chemical engineers from North Carolina State University have found a way to group molecules so tightly that they form a slick surface useful for a multitude of medical, technical and industrial applications.

Researchers Jan Genzer and Kirill Efimenko have forced molecules to create an almost impenetrable layer by bonding them chemically to a polymer material that has been stretched then released again to regain its original shape.

The molecules are jammed into a tight-knit, non-stick layer that, they claim, could one day coat everything from frying pans, disk drives, medical implants and aeroplanes. Such surfaces would be highly water-repellent and nearly frictionless, and might reduce the need for many lubricants.

‘This was a very clever way to pack molecules more closely than nature intended,’ said Andrew Lovinger, the US National Science Foundation program manager for polymers. ‘While much research has gone into synthesising new non-stick materials, Genzer’s technique is the only one that can improve the surface of any of these materials by squeezing their molecules tightly together.’

Lovinger said potential applications from this finding include improving the biocompatibility of medical implants or prostheses by reducing friction and inhibiting the interaction with surrounding cells; and coating aeroplanes with a water repellent that could eliminate the need for de-icing.

‘By increasing a material’s surface area before you chemically attach the layer of molecules that forms its final coating, you can tailor the material’s physical and chemical surface properties, such as water resistance and durability,’ said Genzer. Genzer and Efimenko stretched a substrate material before applying the non-stick coating, thereby depositing more of the desired molecules than on a non-stretched substrate.

When the tension was released, the chemically grafted molecules were squeezed together into a ‘locked’ configuration that excluded all previous irregularities on its surface. With just the right amount of stretching all the extra room between molecules that previously made even non-stick surfaces irregular at the molecular level was squeezed out.

The resulting surface not only had much greater density and ‘smoothness,’ but also proved to be more chemically inert than natural substances. Without any of the ordinary irregularities in its surface, even down to the atomic level, nothing could attach itself to the material.

So far, the researchers have worked with a nano-sized layer of fluorinated molecules (common in the polymer surface of products such as non-stick cookware, water-repellent fabrics, and self-lubricating engine parts.), bonded to an elastic polymer similar to silicone rubber.

Genzer’s next step will be to test the coating’s long-term stability and resistance to industrial acids and extreme environmental conditions. He predicts that it will be five years or more before commercial formulas for the process can be put into mass production.

‘By manipulating materials at the nanoscale, we can vastly improve on what Mother Nature offers, for the benefit of both manufacturers and consumers,’ concluded Genzer.

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