- Materials Characterization
Contradicting theoretical expectations, researchers discovered that increased molecular weight of a polymer significantly reduces the influence of nanoparticles on macroscopic properties of polymer nanocomposite. These results are ascribed to an increased frustration in chain packing (increased free volume) with increase of chain length. The demonstrated universality of the phenomena not only calls for a significant revision of our understanding of structure and dynamics in polymer nanocomposites, but also provides solid guidance for rational design of materials with desired macroscopic properties.
Small angle X-ray scattering, dielectric spectroscopy, differential scanning calorimetry and density measurements were employed to characterize the structure and dynamics of interfacial layer in polymer nanocomposites. All results converge to the same conclusion: Despite attractive polymer-nanoparticle interactions the mass density of the interfacial layer decreases as molecular weight of the polymer increases. This reduces the effect the nanoparticles impose on the polymer matrix, and increases free volume. The results deepen our fundamental understanding of structure and dynamics of polymer nanocomposites, and provide novel insights that can be used for the design of polymer membranes for many applications, including gas separation and batteries.
S. Cheng, A. P. Holt, H. Wang, F. Fan, V. Bocharova, H. Martin, T. Etampawala, B. T. White, T. Saito, N.-G. Kang, M. D. Dadmun, J. W. Mays, and A. P. Sokolov, “Unexpected molecular weight effect in polymer nanocomposites,” Phys. Rev. Lett. 116, 038302 (2016). DOI: 10.1103/PhysRevLett.116.038302
For more information, contact Alexei Sokolov, sokolov@utk.edu
