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Summary Sentence: Join Materials Science and Engineering as they present Dr. Alexei Sokolov from the University of Tennessee & Oak Ridge National Laboratory.
Full Summary: No summary paragraph submitted.
Alexei SokolovDesigning Polymer Nanocomposites: Critical Role of the Interfacial Layer
Alexei Sokolov, Professor and ORNL Governors Chair
University of Tennessee & Oak Ridge National Laboratory
Abstract:
Polymer nanocomposites (PNC) play important role in many current technologies due to their light weight, high tunability of properties, and relatively low costs. It is now well recognized that interfacial layer controls macroscopic properties in PNCs. In this talk we overview recent studies on structure and dynamics of the interfacial layer in various polymeric nanocomposite materials. We employ broad array of experimental techniques and MD-simulations that provide detailed characterization of the interfacial layer at the nanometer scale. Dielectric relaxation studies and MD-simulations revealed a gradient in the interfacial layer dynamics, but no “glassy” or “dead“ layer. Small angle X-ray scattering, dielectric spectroscopy and differential scanning calorimetry provide consistent estimates of the interfacial layer thickness in various PNCs. The thickness of the layer increases upon cooling to Tg, and depends strongly on polymer rigidity, increasing from ~2nm in flexible polymers to ~5 nm in more rigid ones. At the same time, the increase in stregth of the polymer-nanoparticle interactions does not affect the thickness of the interfacial layer, but increases the slowing down of its dynamics. Detailed studies revealed unexpected molecular weight dependence of PNCs properties ascribed to frustration in packing of long polymer chains in the interfacial region. Analysis of mechanical properties using Brilloin light scattering and advanced scanning probe microscopy revealed more than 2 times increase in polymer mechanical modulus in the interfacial layer. This huge increase was ascribed to stretching of the chain in the interfacial region. All these results clearly demonstrate the existence of the interfacial layer with much slower dynamics that propagates a few nm (~2-5 nm) into the polymer matrix, but no signs of any long range (larger than ~10nm) effects. Recent studies also revealed unexpectedly large effects in nanocomposite properties caused by very small (~2nm) nanoparticles. In particular, these small nanoparticles lead to a very sharp temperature variations of viscosity. This effect has been ascribed to mobility of nanoparticles and relatively short chain-nanoparticle association time. At the end, we present a general picture how microscopic parameters control the interfacial layer, and how by tuning the interfacial layer we can tune macroscopic properties of polymer nanocomposites.
Biography:
Alexei Sokolov received an MS in Physics in 1981 from the Novosibirsk State University (Russia), and a PhD in Physics in 1986 from the Russian Academy of Sciences. He worked several years in Germany before joining faculty In College of Polymer Science and Engineering at the University of Akron, USA, in 1998. In 2009 he accepted Governor’s Chair position at the University of Tennessee and Oak Ridge National Laboratory, where he leads the Soft Matter group. He is a Fellow of the American Physical Society and a Fellow of the American Association for the Advancement in Science. His current research interest focuses primarily on Dynamics of Soft Materials, including topics of the glass transition, polymer dynamics and dynamics of biological macromolecules, composite materials and materials for energy applications. He is an author of more than 300 papers.
Reception at 3:30 p.m. in the Georgia Tech Manufacturing Institute Atrium
The Sokolov Group profile page
