No abstract

Natural Fiber Welding (NFW) is process that leverages the unique solvating power of ionic liquids (IL) to mobilize a natural fiber’s outermost polymer strands and enable these mobile polymers to reconfigure and interact with mobilized polymers of adjacent fibers. Upon removal of the ionic liquid via a solvent exchange and drying process, the biopolymer material is welded into a new matrix while still maintaining the vast majority of its native structural hierarchy. Recent work in our laboratory has shown relatively simple modifications to the NFW process can drastically impact the modified matrix morphology, particularly regarding surface structure. Changes in polarity during the solvent exchange process, for instance, can be used to very the surface area over a 1000-fold and produce high surface are materials with tunable mesoporosity. In the present work we investigate the impact of variable ionic liquid treatment time on the development of mesoporosity in fiber welded cotton substrates. Nitrogen gas adsorption/desorption measurements were employed to evaluate changes in surface area and pore size with ionic liquid treatment time. Raman spectroscopy was carried out on epoxy potted material cross sections to assess the impact of treatment time on cellulose decrystallization, and epoxy penetration measured by Raman spectroscopy was used to evaluate the continuity of the mesoporous regions and further asses material porosity.

The designer nature of ionic liquids makes them a promising material for applications spanning disciplines from material processing to energy generation. While a great deal of interest has been directed towards dialkylimidazolium-based ionic liquids, there are many understudied classes of cations with favorable properties for energy related applications, such as disubstituted boroniums. To date only a handful of boronium cation-based ionic liquids have been thoroughly characterized despite exhibiting electrochemical stabilities (> 5.0 V) far surpassing what is seen with their alkylimidazolium and alkylpyrrolidinium counterparts. This work investigates a series of novel boronium-bistriflimide [TFSI-] ionic liquids using electrochemical and physical characterization techniques such as cyclic voltammetry, broadband dielectric spectroscopy, oscillatory shear rheology, and thermogravimetric analysis. Systematic variations in boronium cation structure were employed to help identify the structural motifs that lead to optimal electrochemical and physical properties. The best performing boronium-based ionic liquids were then tested for initial lithium stability to further probe their potential for use in battery applications.

While imidazolium based chloroaluminate ionic liquids have been studied for decades, with interest increasing over the last several years, phosphonium analogues have received less attention. Recent work has shown phosphonium-based chloroaluminate ionic liquids have significant potential as battery electrolytes due to their high thermal stability and wide electrochemical windows. In order to realize their full potential, fundamental studies on the ion dynamics and transport properties of these systems are required. This work focuses on studying the anion speciation and ion dynamics of a series of acidic chloroaluminates containing phosphonium cations with incrementally varied structures. Their properties are probed through broadband dielectric spectroscopy and oscillatory shear rheology to reveal the frequency and temperature dependence of properties such as conductivity, permittivity, and modulus. We will present preliminary work on the impact of changes in cation structure and ionic liquid composition on anion speciation, transport properties, and dynamics. The results expand our understanding of these important electrolyte systems that hold significant promise for applications such as energy storage, electrodeposition, and chemical synthesis.

Mesoscale aggregates arising from the separation of ionic and alkyl groups into polar and nonpolar regions have been observed for a variety of ionic liquids (ILs). The existence of these distinct regions provides ILs with the ability to solvate both polar and nonpolar molecules and has important implications for applications such as energy storage, nanoparticle growth, biomass processing, and organic synthesis. It has been found by computational studies and x-ray scattering that the morphology of the mesoscopic structure is highly sensitive to the alkyl chain length, however, the influence of aggregate formation and morphology on physicochemical properties, such as ionic conductivity and dynamics, is not yet well understood. In this study, a homologous series of imidazolium, quaternary ammonium and phosphonium-based ionic liquids are investigated by broadband dielectric and shear-mechanical spectroscopy as well as molecular dynamics simulations to elucidate the impact of alkyl chain length and hydrophobic aggregation on charge transport and dynamics. It is observed that systematic ordering of ionic liquids into complex polar and nonpolar domains results in the emergence of slow, sub-α dynamics in both the dielectric and shear-mechanical spectra. These findings confirm the existence of long-lived nanoscale aggregates in neat ionic liquids and provide a new avenue to elucidate the interplay of morphology, ion transport and dynamics in these nanostructured fluids.