No abstract

We recently showed that two systems have the same nonlinear flow dynamics if they have (1) the same number of entanglements, Z, (2) the same number of Kuhn segments between entanglements, N e, and (3) a single monomeric friction reduction between all species. Because differences in polymer chemistry result in different values of (1)–(3), these results show that the likelihood of two melts having the same nonlinear behavior is improbable. This work determines the dependence of the nonlinear extensional flow behavior on N e for three polymer melts: polystyrene, poly­(methyl methacrylate), and poly­(tert-butylstyrene). We show that polymer melts with the same Z have almost identical scaled linear viscoelasticity. Extensional rheology at constant strain rate shows strain hardening depends strongly on the value of N e. More specifically, our data suggest a power-law dependence of steady state stress on the Weissenberg number which increases with increasing N e.

Understanding electrical percolation and charging mechanisms in electrochemically active biphasic flowable electrodes is critical for enabling scalable deionization (desalination) and energy storage. Flowable electrodes are dynamic material systems which store charge (remove ions) and have the ability to flow. This flow process can induce structural changes in the underlying material arrangement and result in transient and non-uniform material properties. Carbon-based suspensions are opaque, multi-phase, and three dimensional, and thus prior characterization of the structural properties has been limited to indirect methods (electrochemical and rheology). Herein, a range of mixed electronic and ionically conducting suspensions are evaluated to determine their static structure, function, and properties, utilizing synchrotron radiation X-ray tomographic microscopy (SRXTM). The high brilliance of the synchrotron light enables deconvolution of the liquid and solid phases. Reconstruction of the solid phase reveals agglomeration cluster volumes between 10 μm and 10μm (1 pL) for low loaded samples (5 wt% carbon). The largest agglomeration cluster in the low loaded sample (5 wt%) occupied only 3% of the reconstructed volume whereas samples loaded with 10 wt% activated carbon demonstrated electrically connected clusters that occupied 22% of the imaged region. The highly loaded samples (20 wt%) demonstrated clusters of the order of a microliter, which accounted for 63-85% of the imaged region. These results demonstrate a capability for discerning the structural properties of biphasic systems utilizing SRXTM techniques, and show that discontinuity in the carbon particle networks induces decreased material utilization in low-loaded flowable electrodes.