Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userControl of Ionic Mobility via Charge Size Asymmetry in Random Ionomers
331
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Solid polymer electrolytes are considered a promising alternative to traditional liquid electrolytes in energy storage applications because of their good mechanical properties, and excellent thermal and chemical stability. A gap, however, still exists in understanding ion transport mechanisms and improving ion transport in solid polymer electrolytes. Therefore, it is crucial to bridge composition--structure and structure--property relationships. Here we demonstrate that size asymmetry, $lambda$, represented by the ratio of counterion to charged monomer size, plays a key role in both the nanostructure and in the ionic dynamics. More specifically, when the nanostructure is modified by the external electric field such that the mobility cannot be described by linear response theory, two situations arise. The ionic mobility increases as $lambda$ decreases (small counterions) in the weak electrostatics (high dielectric constant) regime. Whereas in systems with strong electrostatic interactions, ionomers with higher size symmetry ($lambda approx 1$) display higher ionic mobility. Moreover, ion transport is found to be dominated by the hopping of the ions and not by moving ionic clusters (also known as vehicular charge transport). These results serve as a guide for designing ion-containing polymers for ion transport related applications.
rate research
Read More
We have performed simulations to study how increasing humidity affects the structure of Nafion-like ionomers under conditions of low sulfonate concentration and low humidity. At the onset of membrane hydration, the clusters split into smaller parts. These subsequently swell, but then maintain constant the number of sulfonates per cluster. We find that the distribution of water in low-sulfonate membranes depends strongly on the sulfonate concentration. For a relatively low sulfonate concentration, nearly all the side-chain terminal groups are within cluster formations, and the average water loading per cluster matches the water content of membrane. However, for a relatively higher sulfonate concentration the water-to-sulfonate ratio becomes non-uniform. The clusters become wetter, while the inter-cluster bridges become drier. We note the formation of unusual shells of water-rich material that surround the sulfonate clusters.
In metal/oxide heterostructures, rich chemical, electronic, magnetic and mechanical properties can emerge from interfacial chemistry and structure. The possibility to dynamically control interface characteristics with an electric field paves the way towards voltage control of these properties in solid-state devices. Here we show that electrical switching of the interfacial oxidation state allows for voltage control of magnetic properties to an extent never before achieved through conventional magnetoelectric coupling mechanisms. We directly observe, for the first time, in situ voltage driven O$^{2-}$ migration in a Co/metal-oxide bilayer, which we use to toggle the interfacial magnetic anisotropy energy by >0.6 erg/cm$^2$. We exploit the thermally-activated nature of ion migration to dramatically increase the switching efficiency and to demonstrate reversible patterning of magnetic properties through local activation of ionic migration. These results suggest a path towards voltage-programmable materials based on solid-state switching of interface oxygen chemistry.
Computer simulations of (i) a [C12mim][Tf2N] film of nanometric thickness squeezed at kbar pressure by a piecewise parabolic confining potential reveal a mesoscopic in-plane density and composition modulation reminiscent of mesophases seen in 3D samples of the same room-temperature ionic liquid (RTIL). Near 2D confinement, enforced by a high normal load, relatively long aliphatic chains are strictly required for the mesophase formation, as confirmed by computations for two related systems made of (ii) the same [C12mim][Tf2N] adsorbed at a neutral solid surface and (iii) a shorter-chain RTIL ([C4mim][Tf2N]) trapped in the potential well of part i. No in-plane modulation is seen for ii and iii. In case ii, the optimal arrangement of charge and neutral tails is achieved by layering parallel to the surface, while, in case iii, weaker dispersion and packing interactions are unable to bring aliphatic tails together into mesoscopic islands, against overwhelming entropy and Coulomb forces. The onset of in-plane mesophases could greatly affect the properties of long-chain RTILs used as lubricants.
A simple theory of electromechanical transduction for single-charge-carrier double-layer electroactuators is developed, in which the ion distribution and curvature are mutually coupled. The obtained expressions for the dependence of curvature and charge accumulation on the applied voltage, as well as the electroactuation dynamics, are compared with literature data. The mechanical- or sensor- performance of such electroactuators appears to be determined by just three cumulative parameters, with all of their constituents measurable, permitting a scaling approach to their design.
Ionic liquids constrained at interfaces or restricted in subnanometric pores are increasingly employed in modern technologies, including energy applications. Understanding the details of their behavior in these conditions is therefore critical. By using molecular dynamics simulation, we clarify theoretically and numerically the effect of confinement at the nanoscale on the static and dynamic properties of an ionic liquid. In particular, we focus on the interplay among the size of the ions, the slit pore width, and the length scale associated to the long-range organization of polar and apolar domains present in the bulk material. By modulating both the temperature and the extent of the confinement, we demonstrate the existence of a complex reentrant phase behavior, including isotropic liquid and liquid-crystal-like phases with different symmetries. We show how these changes impact the relative organization of the ions, with substantial modifications of the Coulombic ordering, and their dynamical state. In this respect, we reveal a remarkable decoupling of the dynamics of the counterions, pointing to very different roles played by these in charge transport under confinement. We finally discuss our findings in connection with very recent experimental and theoretical work.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
