It is well-known that the nature and size of the counterions affect the ionic conductivity and glass transition temperature of ionic polymers in a significant manner. However, the microscopic origin of the underlying changes in the dynamics of chains and counterions is far from completely understood. Using coarse-grained molecular dynamics simulations of flexible and semi-flexible ionic polymers, we demonstrate that the glass transition temperature of ionic polymeric melts depends on the size of monovalent counterions in a non-monotonic manner. The glass transition temperature is found to be the highest for the smallest counterions and decreases with an increase in the counterion radii up to a point, after which the glass transition temperature increases with a further increase in the radii. This behavior is because the counterions have significant effects on the coupled dynamics of the charges on the chains and counterions. In particular, increase in the radii of the counterions leads to strongly coupled dynamics between the charges on the chains and the counterions. The static dielectric constant of the polymer melts also has a significant effect on the coupling and the glass transition temperature. The glass transition temperature is predicted to decrease with an increase in the dielectric constant. This, in turn, leads to an increase in the diffusion constant of the counterions at a given temperature. Backbone rigidity is shown to increase the glass transition temperature and decrease the coupling. Furthermore, faster counterion dynamics is predicted for the melts of semi-flexible chains in comparison with flexible chains at the same segmental relaxation time. As the semi-flexible chains tend to have a longer segmental relaxation time, semi-flexible polymers with high dielectric constants are predicted to have diffusion constants of counterions comparable with flexible polymers.

Polymerized ionic copolymers have recently evolved as a new class of materials to overcome the limited range of mechanical properties of ionic homopolymers. In this paper, we investigate the structural and mechanical properties of charged ionic homopolymers and di-block copolymers, while using coarse-grained molecular dynamics simulation. Tensile and compressive deformation are applied to the homopolymers and copolymers in the glassy state. The effect of charge ratio and loading direction on the stress-strain behavior are studied. It is found that the electrostatic interactions among charged pairs play major roles, as evidenced by increased Young’s modulus and yield strength with charge ratio. Increased charge ratio lead to enhanced stress contribution from both bonding and pairwise (Van der Waals + coulombic) interaction. The increase in the gyration of the radius is observed with increasing charge ratio in homopolymers, yet a reversed tendency is observed in copolymers. Introduced charge pairs leads to an increased randomness in the segmental orientation in copolymers.

growing interest in developing single-ion conducting polymer electrolytes for the purpose of improving the ion conductivity and/or the Li + transference number. [9] A single-ion conducting polymer comprising lithium poly(4styrenesulfonyl(trifuoro-methylsulfonyl) imide) (LiPSTFSI) and polyethylene oxide (PEO) polymer was shown to reach to close to unity Li + transference number and a high ionic conductivity (about 10-5 S cm-1). A PEO/lithium poly(perfuoroalkylsulfonyl)imide (LiPFSI) blended single-ion polymer electrolyte also exhibited superior electrochemical properties including ionic conductivity, electrochemical stability, and Li + transport number. [10] In addition, the structure of the functional groups in polyanionic lithium salts plays an important role in the electrochemical and thermal properties of polymer electrolytes. [11] Both the ionic conductivity and the Li + transference number have been observed to increase with the addition of a Lewis acid in the PEO/polylactic acid (PLA) and PEO/poly(lithium vinylsulfonate (PLVS) blended polymer electrolytes. [11] Compared with single-ion homopolymers, copolymers provide the flexibility to fine-tune both the ion conductivity and mechanical properties. [12,13] Bouchet et al. [14] synthesized a new BAB type of polymer electrolytes through self-assembling the polyanionic triblock copolymers (P(STFSILi)-b-PEO-b-P(STFSILi). This multifunctional ionic copolymer exhibited up to 5 V electrochemical stability window versus Li + /Li, an ionic conductivity on the order of 10-5 S cm-1 at 60 °C, a close-tounity Li + transference number, and excellent mechanical properties. A Li[PSTFSI-co-MPEGA] copolymer has been designed by the copolymerization of LiSTFSI and methoxypolyethylene glycol acrylate (MPEGA). [15] It has been found that its ionic conductivity was increased by 10-1000 times than its blended electrolyte counterpart. A maximum conductivity of 7.6 ×10-6 S cm-1 at 25 °C can be obtained by maximizing the ratio of ethylene oxide (EO)/Li +. The mechanical integrity of ionic copolymers is one of the most important factors that need to be considered in the application of solid electrolyte. [16] However, there is very limited understanding in the mechanical properties of ionic copolymers. In this study, we will investigate the effect of important polymeric parameters on the viscoelastic-plastic and configurational properties of ionic charged block copolymers (BCPs). By varying the volume fraction of A block f A , tunable morphologies Polymer electrolytes have attracted ever-increasing attention in the field of energy storage and conversion due to their significantly improved safety features and processability compared with liquid electrolytes and inorganic solid electrolytes. The mechanical integrity of ionic copolymers is one of the most important properties that need to be considered in the development of polymer electrolytes. In this study, the uniaxial tension-recovery studies are conducted in single-ion diblock copolymers via coarse-grained molecular dynamics simulat...

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