Dr. Diddo Diddens "Segmental Mobilities in Polymer Melts, Polymer Blends and Polymer Electrolytes"

This talk focuses on two different parts, each dealing with the specific role of the local segmental mobility in complex polymeric materials.

The first part introduces a novel statistical method [1], which allows one to characterize the mobilities of distinct polymer segments from simulation data. To this purpose, a Langevin-like, stroboscopic picture of the local chain motion is employed, comprising a systematic, a random and a frictional compound. As an example, a dynamically heterogeneous polymer blend consisting of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) will be discussed [2]. Both components have largely different glass transition temperatures, and the fast PEO compound moves in a nearly-frozen, disordered PMMA matrix. Phenomenologically, experimental data on these systems can be reproduced when assuming a largely heterogeneous mobility distribution for the PEO segments. Contrarily, the MD simulations reveal that the mobility distribution is rather narrow, and that instead enhanced forward-backward correlations due to the stiff PMMA surroundings account for the experimental observations.

The second part is dedicated to ternary mixtures of conventional PEO/lithium-salt polymer electrolytes and an ionic liquid [3]. Again, the mobility of the PEO segments plays a decisive role, as it strongly affects the precise value of the macroscopic lithium diffusion coefficient, which is an important characteristic for battery applications. This is due to the fact that the ionic liquid serves as a plasticizer, as it significantly enhances the dynamics of the polymer chains, and, consequently, also the dynamics of the lithium ion coordinating to the PEO chains. Additionally, the overall lithium motion is captured by an analytical ion transport model, which allows one to extrapolate the simulation data to the experimentally relevant long-chain limit.

[1] D. Diddens, M. Brodeck, A. Heuer, Europhys. Lett., 2010, 91, 66005
[2] D. Diddens, M. Brodeck, A. Heuer, Europhys. Lett., 2011, 95, 56003
[3] D. Diddens, A. Heuer, ACS Macro Lett., 2013, 2, 322-326