Structure of ionic liquids with cationic silicon-substitutions

Abstract

Significantly lower viscosities result when a single alkyl carbon is replaced by a silicon atom on the side chain of an ionic liquid cation. To further explore this effect, we compare liquid structure factors measured using high-energy X-ray scattering and calculated using molecular dynamics simulations. Four ionic liquids are studied that each has a common anion, bis(trifluoromethylsulfonyl)amide (NTf2−). The four cations for this series of NTf2−-anion ionic liquids are 1-methyl-3-trimethylsilylmethylimidazolium (Si-mim+), 1-methyl-3-neopentylimidazolium (C-mim+), 1-methyl-3-pentamethyldisiloxymethylimidazolium (SiOSi-mim+), and 1-methyl-1-trimethylsilylmethylpyrrolidinium (Si-pyrr+). To achieve quantitative agreement between the structure factors measured using high-energy X-ray scattering and molecular dynamics simulations, new transferable parameters for silicon were calibrated and added to the existing force fields.

Connecting Structural and Transport Properties of Ionic Liquids with Cationic Oligoether Chains

“…While the ether chains are more polar than alkyl analogues, they still induce a degree of local nanophase segregation, an effect that has also been observed for more strongly polar alkylsilyl and alkylsiloxy tails on the same cations. 57,58 In the case of the ethers, however, this segregation is incomplete and disordered, as shown by the partitioned structure factors discussed above. Instead of a distinct peak in the polarity alternation region, as observed (Figure 8), the inter-ionic correlations in Figure 7 drop off in that region, reflecting the incomplete segregation.…”

“…As we have shown previously, 2,49,53,[56][57][58] understanding the intermediate-range order contributions to the IL structure can best be understood by partitioning the S(q) obtained from molecular simulations. Figure 7 shows the ionic partitioning, where the total S(q) is considered as the sum of structural correlations between ions as follows: 53,56 …”

“…2,49,57,58 The IL samples were contained in flame-sealed 3 mm glass NMR tubes under argon atmosphere. The X-ray beam wavelength was 0.21140 Å.…”

“…The CL&P transferable force field for ILs, in itself a generalization of Jorgensen's OPLS-AA force field, has provided very good predictive capability for IL structures. 2,49,53,[56][57][58] The radial pair distribution functions g(r) between all atom pairs are obtained from the trajectory of the production run. The structure functions are calculated using Equation 1:…”

The Effect of Phenyl Substitutions on Microstructures and Dynamics of Tetraalkylphosphonium Bis(trifluoro‐ methylsulfonyl)imide Ionic Liquids

“…Compared with extensively studied nitrogen based ILs, such as imidazolium, piperidinium, pyrrolidinium, pyridinium, and guanidinium ILs, tetraalkylphosphonium ILs present additional and practical advantages in large‐scale industrial operations . The tetraalkylphosphonium orthoborate ILs exhibit outstanding friction reducing and anti‐wear performance in tribological contacts with a wide variety of solid materials, and thus are attractive as alternative high‐performance lubricants and lubricant additives in tribology .…”