A different class

Researchers at the

have discovered a new class of ultra-thin polymer films with potential applications ranging from coating tiny microelectronic devices to plastic solar cells.

The research, which involved polymer chemist Chris Snively, Jochen Lauterbach, professor of chemical engineering at UD and doctoral student Seth Washburn, focused on formerly non-polymerisable ethylenes. Among them are several compounds that are derived from natural sources, such as cinnamon, and are US Food and Drug Administration (FDA) approved for use in fragrances and foods.

Polymerisation is a chemical reaction in which monomers, which are small molecules with repeating structural units, join together to form a long chain-like molecule. Each polymer typically consists of 1,000 or more of these monomer “building blocks.” Since the late 1990s, Lauterbach and Snively have been developing a method to make extremely thin polymer layers on surfaces. These nanofilms are becoming increasingly important as coatings for optics, solar cells, electrical insulators, advanced sensors and numerous other applications.

Formerly, to make a pound of polymer, scientists would take a monomer and a solvent and subject them to heat or light. Recently, Lauterbach and Snively developed a new polymer-making technique that eliminates the need for a solvent.

Their deposition-polymerisation (DP) process takes place in a vacuum chamber, where the air is pumped out and the pressure is similar to outer space. The material to be coated, such as a piece of metal, is placed in the chamber, and the metal is cooled below the monomer's freezing point, which causes the monomer vapour to condense on the metal. Then the resulting film is exposed to ultraviolet light to initiate polymerisation.

The two-step process allows for the formation of uniform, defect-free films with thicknesses that can be controlled to within billionths of a metre.

The process is fairly “green,” in that not only are no solvents used, but there also is very low energy consumption using this method, according to Lauterbach.

‘You also can do photolithography with it,’ he said, meaning that the polymer will appear only where the light hits the monomer film.

While their polymerisation technique was reported a few years ago, the class of materials the UD scientists have applied it to lately is new and unique.

‘We can make nanometre-thick films, but we can't make a gram of the material yet,’ Snively noted. ‘We're working on ways to scale up the process.’