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The Liquids Reflectometer enables scientists to look within and between layers of film and determine how they are structured. Svetlana Sukhishvili is a professor of chemistry and co-director of the Nanotechnology Graduate Program at Stevens Institute of Technology in Hoboken, New Jersey. As part of the Spallation Neutron Source's (SNS) user program, she and her students are using the facility's Liquids Reflectometer to study layered polymer films. These thin films are composed of polymer layers of varying composition, built up one layer at a time. "These layered films currently have many potential applications in controlled delivery, as well as in optics as antifog coatings and antireflective coatings," she says. "However, very little is known about the internal structure of such films." The Liquids Reflectometer provides a way for scientists to look within and between the layers of film and determine how they are structured and how those structural features are related to the film's properties. "We asked several questions," Sukhishvili says. "When we are depositing polymer layers on surfaces to make films, will these films remain layered when used in wet environments? Also, if the internal structure changes, under what conditions does it change and how does this affect the internal structure of the film?"
One of the technology's applications is controlled delivery, or "time-release" delivery of functional small molecules. This behavior could be utilized in a drug delivery system or as a coating on the surface of a biomedical device that would release different compounds at predetermined times. The polymer layers can trap small molecules and then release them on demand or in response to changes in environmental conditions, such as temperature or acidity. "For these films to function properly, it is important that the layers remain well structured," Sukhishvili explains. "This depends on the dynamics of the polymer molecules at the layer boundaries, which are not not well understood." Sukhishvili's group created their films by depositing layers of material containing deuterium, an element that is easily "seen" by neutrons, with hydrogen-containing layers in between. The purpose of having alternating layers containing deuterium and hydrogen is to provide contrast between the layers at their interfaces. "We wanted to look at how the structure would spread when we changed the environmental conditions. We found interesting trends between the strength of intermolecular interactions and intertwining of polymer layers and the structure of the films." Sukhishvili points out that using alternating layers of deuterated and hydrogenated materials to enhance contrast is a unique technique and is well suited to the capabilities of the SNS. "We are one of the few groups in the country that decided to take advantage of the SNS to look at this fundamentally important, yet practically relevant, question to shed some light on the structure-property relationships of such films," she says. Sukhishvili views the SNS as a new kind of user facility that offers broad opportunities for networking and collaboration. "The SNS is a growing and forward-thinking user facility," she says. "I also think the potential for collaboration with ORNL's Center for Nanophase Materials Sciences and the combination of these capabilities with the ability to do new and exciting neutron reflectivity experiments provide much broader options. The result, she believes, will be an attraction to users for years to come.
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