Search for: All records

Ionic liquids (ILs) are highly tailorable materials with unique physical and chemical properties that set them apart from conventional organic solvents. As the library of readily accessible ILs continues to grow, so too does their relevance in applications ranging from material processing to electrochemical energy storage as solvents capable of accessing new chemistries disallowed by traditional chemicals. While a great deal of interest has been directed towards imidazolium and quaternary ammonium based ionic liquids, there are other understudied classes of cations which have potentially favorable properties for energy related applications. One such class is that with boronium cations. These cations have a unique structure with a formally negative boron flanked by positive nitrogens. This inherently zwitterionic structure presents interesting possibilities for electrochemical applications. To date only a handful of boronium cation-based ionic liquids have been thoroughly characterized despite exhibiting impressive electrochemical stabilities (> 5.0 V). In the present study we synthesized a series of ILs with novel boronium cations coupled with the bis(trifluoro-methanesulfonyl)imide anion. We then characterized the electrochemical and physical properties of these boronium ionic liquids by techniques such as cyclic voltammetry, broadband dielectric spectroscopy, oscillatory shear rheology, and thermogravimetric analysis. We will discuss how systematic variations in boronium cation structure impacted electrochemical and physical properties. 

Broadband dielectric spectroscopy is employed to probe dynamics in low molecular weight poly(cis-1,4-isoprene) (PI) confined in unidirectional silica nanopores with mean pore diameter, D, of 6.5nm. Three molecular weights of PI (3, 7 and 10kg/mol) were chosen such that the ratio of D to the polymer radius of gyration, Rg, is varied from 3.4, 2.3 to 1.9, respectively. It is found that the mean segmental relaxation rate remains bulk-like but an additional process arises at lower frequencies with increasing molecular weight (decreasing D/Rg). In contrast, the mean relaxation rates of the end-to-end dipole vector corresponding to chain dynamics are found to be slightly slower than that in the bulk for the systems approaching D/Rg ∼ 2, but faster than the bulk for the polymer with the largest molecular weight. The analysis of the spectral shapes of the chain relaxation suggests that the resulting dynamics of the 10 kg/mol PI confined at length-scales close to that of the Rg are due to non-ideal chain conformations under confinement decreasing the chain relaxation times. The understanding of these faster chain dynamics of polymers under extreme geometrical confinement is necessary in designing nanodevices that contain polymeric materials within substrates approaching the molecular scale.