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Download or read book Investigation of Charge Transport and Mechanical Properties in Ion Associating Polymeric Materials written by Joshua Everett Bostwick and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Gel polymer electrolytes (GPEs) are ion-conducting polymers where the polymer matrix is swollen with a certain amount of solvent. While GPEs are able to take advantage of both the mechanical properties of the polymer matrix and the conductive properties of the solvent, they are limited due to the inverse relationship between the ionic conductivity ([sigma]o) and the modulus, diminishing their potential as next generation lithium-ion battery electrolytes. In this dissertation, we studied the fundamental properties of three different GPEs, molecular ionic composites (MICs) where the solvent is an ionic liquid (IL), single-ion-based MICs where the 'solvent' is poly(ethylene glycol), and cellulose-ionic liquid solutions, for their potential use as battery electrolytes. MICs utilize the mechanical and thermal stability of a rigid-rod sulfonated polyelectrolyte, poly(2,2')-disulfonyl-4,4'benzidine terephthalamide (PBDT), and the high conductivity, electrochemical stability, and low volatility of ILs. This allows the MICs to produce a simultaneous high modulus (from the PBDT) and a high conductivity (from the IL). The first half of this dissertation explores how the change in either the PBDT concentration with a constant IL or the IL molecular volume (Vm) and chemistry with a constant PBDT concentration affects both the mechanical and charge transport properties of the MICs. The varying PBDT concentration MICs were produced via an ion exchange method to form 3 mm diameter cylinders (ingots) while the varying IL Vm MICs were produced via solvent casting to form six free-standing films. The single-ion PBDT membranes were also formed via the solvent casting method. The mechanical properties were measured using a combination of oscillatory shear rheology and uniaxial tensile tests (only for the films), while the dielectric properties and morphology of the films were determined through dielectric relaxation spectroscopy (DRS) and atomic force microscopy (AFM) respectively. Increasing the MIC PBDT concentration with a constant IL, 1-butyl- 3-methylimidazolium tetrafluoroborate (BMIm-BF4), showed a minimal change in dynamic glass transition temperature (Tg) of roughly 2 °C through rheology with its respective IL. This allowed for the MIC ionic conductivity ([sigma]o) at elevated PBDT concentrations to be within a factor of two of the neat IL at room temperature while also producing a shear modulus (G') in the MPa range up to 200 °C. This is due to the MICs producing a two-phase environment corresponding to an IL-rich "puddle" phase and a PBDT-rich "bundle" phase, shown through the phase contrast in atomic force microscopy (AFM), where IL ions form alternating sheaths of cations and anions around each PBDT rod. As the PBDT concentration increases, these puddles shrink and produce a near single bundle phase. This potentially increases the polarizability of the MIC, shown by an increasing static dielectric constant, as well as allowing for more IL ions to contribute to [sigma]o shown by a decrease in the Haven ratio (HR), the ratio between the total number of charge carriers observed through NMR and the number conductive charge carriers that can be analyzed through the ionic conductivity. Incorporating ILs with different molecular volumes (Vm) and chemistries in the MICs with a constant PBDT concentration showed that all MICs maintain low Tgs, ranging between 0 -- 8 °C above their respective neat IL. This was confirmed through analyzing the derivative spectra from DRS to determine the dynamic Tg as well as measuring the thermal Tg through differential scanning calorimetry (DSC). The agreement in Tg between these two methods suggests that the glassy dynamics of MICs is dictated by the rearrangement of IL ions during charge transport. All MICs are able to produce high [sigma]o, ranging from 1 -- 6 mS cm-1 at 30 °C with smaller imidazolium-based cations producing higher [sigma]o than MICs with larger imidazolium cations and similar anions due to their larger molar conductivity. Tensile measurements showed that all MICs produce IL-dependent Young's modulus (E), ranging from 50 -- 500 MPa at 30 °C, up to 60 x higher when compared to the G' of the same MICs. We propose this is due the difference in the distribution of PBDT chains between the shear and tensile planes as well as the competing interactions between the IL ions and the PBDT rods. This hypothesis is supported by the AFM phase contrast images, where the 1-ethyl- 3-methylimidazolium (EMIm+) based MICs show the largest formation of the bundle phase (with very small puddles) while the BMIm+ based MICs produce a larger puddle phases as the anion Vm decreases, thus lowering E. Relating the [sigma]o to their corresponding diffusive coefficients through the Nernst-Einstein shows that all MIC have an ionicity (inverse Haven ratio, HR--1) range between 0.54 -- 0.63, suggesting that a fraction of the diffusive ions do not contribute to charge transport. Along with the IL-based MICs, we analyzed the dielectric and mechanical dynamics of single-ion conducting PBDT-based membranes by incorporating poly(ethylene glycol) with a molecular weight of 400 g mol-1 (PEG400) and either Na+ or Li+ counterions are studied in detail. Varying the PBDT and PEG400 wt% allowed for the preparation of varying PBDT concentrated membranes. All membranes have low DSC Tgs, regardless of counterion attached to the PBDT and the Tg increases with elevated PBDT concentration. The ionic conductivity of the membranes systematically decreases with increasing PBDT concentration, ranging from 0.1 -- 7 [mu]S cm-1` at 30 °C and reaching 100 [mu]S cm-1 at 120 °C in the lowest NaPBDT concentration film. Normalizing the temperature-dependent ionic conductivities divided by their respective Coulombic dielectric constant by the dynamic DRS Tg show that all data roughly collapse onto a single curve, suggesting that the glassy dynamics are dictated the speed of the diffusive motion and the dissociation of ion-pairs produced from strong ionic interactions in the membrane. Tensile stress-strain analysis on the membranes reveal that the E is dominated by the counterion used with the Na+-based membranes producing an E ranging from approximately 100 -- 400 MPa while the Li+-based membranes produced an E ranging from approximately 300 -- 2100 MPa. We suggest that Li+ counterions forms a stronger network with the PBDT sulfonate groups off of the PBDT than the Na+ counterions. The smaller Li+ binds to the sulfonates on the PBDT chain more strongly, confirming that the modulus of this class of materials has ionic origins. We investigated the dielectric dynamics of cellulose in ILs through DRS to understand the fundamental properties of cellulose-IL solutions with varying cellulose concentration and IL. Like the MICs, the cellulose-IL solutions showed relatively high ionic conductivity compared to their respective neat IL, all within a factor of 4 at 30 °C at the highest cellulose concentration, as well as minimal increase in the dynamic DRS Tg (up to 10 °C). The ionic conductivity normalized by the DRS Tg show all data collapsing on a single curve with each IL suggesting that the glassy dynamics in these solutions is dictated by the ion arrangement produced on charge transport. Additionally, increasing the cellulose concentration increases the static dielectric constant relative to the neat ILs suggesting the association between the cellulose and IL ions enhances the polarizability of the solution over the neat IL.