Penn researchers to study molecule packing in ultra-thin glass films

Thin glass films like coatings that cover the surface of smart phone screens are made up of many different kinds of molecules, with numerous properties.

“These are stacked on top of each other to give you the properties that you like,” says Zahra Fakhraai, an assistant professor in the Department of Chemistry in the School of Arts & Sciences, who studies these films. “For example, there are coatings that are anti-fog, there are coatings that are anti-fingerprint, and coatings that prevent back reflection.”

Fakhraai, along with Patrick Walsh, a professor of chemistry, and Robert Riggleman, an assistant professor of chemical and biomolecular engineering in the School of Engineering and Applied Science, received a three-year, $1.2 million grant from the National Science Foundation to investigate how to better produce glass films.

The Penn researchers’ goal is to learn how different kinds of molecules pack together so glass films can be made thinner and stronger. Understanding these structures will also help engineers design and implement new films with interesting properties, like a coating with high conductivity or the ability to effectively block ultraviolet rays.

The team is interested in films that are applied using a process called vapor deposition, which is used in manufacturing a spectrum of products, including touch screens, sunglasses, and high-resolution screen displays. The goal of research into vapor disposition is typically to make even thinner coatings for consumer goods electronics. However, scientists have recently discovered that if you make the size of a film below a few tens of nanometers, the solid glass becomes more like a liquid, resulting in holes in the film crystal formation, which can reduce transparency of the coating.

The Penn team is researching how to pack these molecules in very thin layers, while maintaining their solid glassy properties.

Fakhraai says that molecule packing can be thought of as pouring a bag of candy into a jar.

“If you throw the whole bag into it, the packing is what it is,” she says. “But if you very slowly throw them in, maybe shake it a little bit, help them find better states, then you can pack them better and better.”

Instead of shaking the jar and hoping for the best, the team will look for the ideal temperatures and conditions for molecules to form a thin, solid layer, preventing the liquid-like properties as size is decreased.

With the new grant, Fakhraai says that they will be able to test many new molecules and learn the rules for how different kinds of molecules behave in a film. She hopes their team will develop a way to predict the properties of a film before it is tested.

“We are trying to find a predictive way to [design films] from molecular level interactions,” says Fakhraai. “Then I could start from molecular level design of the molecule and think about, ‘What do I need to add to make this kind of coating?’”

Glass Films