About the topic
Polymer nanocomposites represent an important class of materials both from a scientific and an industrial standpoint. From nanocomposites consisting of blends of small concentrations of nanoparticles with a broad range of polymers to so-called “bricks-and-mortar” systems containing much higher nanoparticle concentrations, many compositions have been studied and impressive properties have been described. At the same time, in spite of decades of work in this area, critical questions concerning the behavior of these materials remain to this day. The behavior of the confined polymer phase remains poorly understood and the properties of intercalated stacks of layers continue to be debated, in spite of the ubiquity of these features in polymer / clay nanocomposites. Various analytical models have been used over the years to describe mechanical and barrier performance in these systems – but how well do they work, and how general are these results?
Here we present a summary of an in-depth investigation of two families of spray-deposited polymer / clay nanolaminates – nanocomposites consisting of highly aligned clay layers embedded in a polymer matrix, spanning the entire composition range from pure polymer to pure (modified) clay. The polymer phase is entirely amorphous and the chemistry of these systems is effectively identical except for a subtle change that enables us to turn intercalation off in one system while leaving it on in the other. Scanning electron microscopy and 2D wide-angle x-ray diffraction provide the needed structural details, while dynamic mechanical analysis and oxygen permeation measurements are used to assess changes in elastic and barrier performance, respectively. The observed trends highlight the insufficiencies in the effective aspect ratio model commonly invoked in the field. Micromechanical models commonly used to describe nanocomposite performance are unable to account for the modulus variations in what is otherwise an ideal model system, with well-aligned layers and a fully amorphous polymer phase. These same materials produce oxygen permeation results dominated by the single layer aspect ratio regardless of intercalation state and highlight the importance of the organic phase in determining the barrier properties of high clay content bricks-and-mortar structures in particular. In sum, these results provide insights into the behavior of these complex and interesting materials, as well as useful guidance concerning materials design and modeling.
About the speaker
Dr. Schmidt holds a B.S. in Materials Science & Engineering and a B.S. in Chemistry from Carnegie Mellon University and a Ph.D. in Materials Science & Engineering from Cornell University, earned under the direction
of Prof. Emmanuel P. Giannelis on the subject of silicone nanocomposites. He was a post-doc in Strasbourg, France for BASF, where he developed nanoporous materials for thermal insulation (commercialized under the SLENTITE® tradename). He joined the Plastics Engineering faculty at the University of Massachusetts Lowell in 2005, where he has pursued work on polymer composites and nanocomposites, polymer networks, materials chemistry & characterization, pre-ceramic polymers and sustainable materials. His work has been cited over 2,000 times in the literature, and he is listed as an inventor in 9 families of patents and patent applications. Since September 1, 2017 he has been on professional leave at the Luxembourg Institute of Science and Technology (LIST), where he serves as a Lead Research and Technology Associate focused on composite materials.