"Aminopropyltrethoxysilane (APS) is the most common silane coupling agent used to coat common silicate glasses, so that is the coupling agent we looked at," says Amy Barnes, Ph.D. candidate in materials science and engineering. "Very little is known about coupling agents for phosphate glasses or the surface of these glasses."
Barnes; Dr. Carlo G. Pantano, director of Penn State's Materials Research Institute and distinguished professor of materials science and engineering; and Dr. Samuel D. Conzone of Schott Glass Technologies looked at sodium aluminophosphate glass. These glasses, doped with rare earth elements such as erbium and ytterbium, are used in optical and photonic systems, as laser sources and as wave guide amplifiers.
"Very little is currently known about the surface of phosphate glasses because, traditionally, the glass quickly reacts with the atmosphere," says Barnes. " It is only in recent years that there have been advances in making this glass more durable."
The researchers studied the phosphate glass without the rare earth elements, to see how the silane adhered to the surface of the phosphate glass. The glass was dipped in APS and rinsed. "We have shown that we can get silane to adhere to phosphate glass surfaces," Barnes told attendees today (July 2) at the 19th International Congress on Glass, sponsored by the Society for Glass Technology in Edinburgh, Scotland.
"The coating can protect the surface, minimizing corrosion or can be a mediator between the glass and a polymer." The silane forms a single or multiple molecular layers on the glass surface. The acidity of the silane solution affects the coverage of the surface differently than on traditional silicate glasses. Also, the stability of the bond that forms may be different if the surface corrodes during coating.
"Applications to join two phosphate glasses, phosphate glass and polymers, or phosphate glass and other organic chemicals are just beginning," says Barnes. "With a silane coating, these glasses can be used as hybrids rather than stand alone materials. We can connect and combine them with dissimilar materials."