Department of Electronic and Nanostructured Materials, Sandia National Laboratories, Albuquerque, New Mexico 87185-0886, USA.
J Phys Chem B. 2013 Feb 14;117(6):1967-77. doi: 10.1021/jp3111953. Epub 2013 Feb 4.
The translational self-diffusion coefficients (D(T)) for a series of tetra-alkyl acyclic ammonium and cyclic pyrrolidinium ionic liquids (ILs) were measured using (1)H pulse field gradient (PFG) NMR spectroscopy over various temperatures. These NMR diffusion results were combined with previously measured rotational diffusion coefficients (D(R)) obtained from (14)N NMR relaxation measurements for the same ILs (Alam, T. M.; et al. J. Phys. Chem. A 2011, 115, 4307- 4316). The D(T)/D(R) ratio was then used to estimate the effective hydrodynamic radius and corresponding volumes without the need to directly measure the viscosities of the ILs. The generality, validity, and performance of using this D(T)/D(R) ratio is discussed and compared to the effective hydrodynamic volumes obtained using classic D(T)/viscosity and D(R)/viscosity relationships. The temperature variation observed for the molecular volumes obtained using the D(T)/D(R) ratio is argued to be a signature for the breakdown or decoupling of the Stokes-Einstein and Stoke-Einstein-Debye relationships in these neat IL systems, consistent with recent molecular dynamic simulations.
采用（1）H 脉冲梯度场（PFG）NMR 光谱法在不同温度下测量了一系列四烷基无环季铵和环状吡咯烷鎓离子液体（ILs）的自扩散系数（D（T））。这些 NMR 扩散结果与先前通过（14）N NMR 弛豫测量获得的相同 ILs 的旋转扩散系数（D（R））相结合（Alam，TM；等人。J. Phys. Chem. A 2011，115，4307-4316）。然后，使用 D（T）/D（R）比来估算有效流体力学半径和相应的体积，而无需直接测量 ILs 的粘度。讨论并比较了使用此 D（T）/D（R）比的通用性、有效性和性能，以及使用经典 D（T）/粘度和 D（R）/粘度关系获得的有效流体力学体积。使用 D（T）/D（R）比获得的分子体积的温度变化被认为是这些纯 IL 体系中 Stokes-Einstein 和 Stokes-Einstein-Debye 关系破裂或解耦的特征，与最近的分子动力学模拟一致。
