Flämig Max, Gabrielyan Liana, Minikejew Rafael, Markarian Shiraz, Rössler Ernst A
Nordbayerisches NMR-Zentrum, Universität Bayreuth, 95440 Bayreuth, Germany.
Chair of Physical Chemistry, Yerevan State University, 0025 Yerevan, Armenia.
Phys Chem Chem Phys. 2020 Apr 29;22(16):9014-9028. doi: 10.1039/d0cp00501k.
Mixtures of glycerol and dimethyl sulfoxide (DMSO) are studied by dielectric spectroscopy (DS) and by 1H field-cycling (FC) NMR relaxometry in the entire concentration range and down to glass-forming temperatures (170-323 K). Molecular dynamics is accessed for 0 < xDMSO ≤ 0.64, at higher concentration phase separation occurs. The FC technique provides the frequency dependence of the spin-lattice relaxation rate which is transformed to the susceptibility representation and thus allows comparing NMR and DS results. The DS spectra virtually do not change with xDMSO and T, only the relaxation times become shorter. This is in contrast to the non-associated mixture toluene/quinaldine for which strong spectral changes occur. The FC relaxation spectra of glycerol in solution with DMSO or (deuterated) DMSO-d6 display a bimodal structure with a high-frequency part reflecting rotational and a low-frequency part reflecting translational dynamics. Regarding the rotational contribution in the glycerol/DMSO-d6 mixtures, no spectral change with xDMSO and T is observed. Yet, the non-deuterated mixture reveals a broader relaxation spectrum. Time constants τrot(T) probed by the two techniques complement each, a range 10-11 s < τ < 10 s is covered. The glass transition temperature Tg(xDMSO) is determined, yielding Tg = 149.5 ± 1 K of pure DMSO by extrapolation. Analysing the low-frequency FC NMR spectra allows to determine the diffusion coefficient Dtrans. Its logarithm shows a linear xDMSO-dependence as does lg τrot. The ratio Dtrans/Drot is independent of xDMSO and its low value indicates large separation of translation and rotation. The corresponding unphysically small hydrodynamic radius indicates strong failure of Stokes-Einstein-Debye relation. Such anomaly is taken as characteristics of a 3d hydrogen-bonded network. We conclude, although DMSO is an aprotic liquid the molecule is continuously incorporated in the hydrogen network of glycerol. Both molecules display common dynamics, i.e., no decoupling of the component dynamics is found in contrast to quinaldine/toluene with a similar Tg difference of its components.
通过介电谱（DS）和¹H场循环（FC）核磁共振弛豫测量法，在整个浓度范围以及直至玻璃化形成温度（170 - 323 K）的条件下，对甘油和二甲基亚砜（DMSO）的混合物进行了研究。在0 < xDMSO ≤ 0.64范围内研究了分子动力学，在更高浓度下会发生相分离。FC技术提供了自旋晶格弛豫率的频率依赖性，将其转换为磁化率表示形式，从而可以比较核磁共振和DS的结果。DS光谱实际上不随xDMSO和温度T变化，只是弛豫时间变短。这与非缔合混合物甲苯/喹哪啶形成对比，后者会发生强烈的光谱变化。甘油与DMSO或（氘代）DMSO - d6的溶液的FC弛豫光谱呈现双峰结构，高频部分反映旋转动力学，低频部分反映平动动力学。关于甘油/DMSO - d6混合物中的旋转贡献，未观察到随xDMSO和温度T的光谱变化。然而，非氘代混合物显示出更宽的弛豫光谱。两种技术探测到的时间常数τrot(T)相互补充，覆盖了10⁻¹¹ s < τ < 10 s的范围。确定了玻璃化转变温度Tg(xDMSO)，通过外推得到纯DMSO的Tg = 149.5 ± 1 K。分析低频FC核磁共振光谱可以确定扩散系数Dtrans。其对数显示出与lg τrot一样的线性xDMSO依赖性。Dtrans/Drot的比值与xDMSO无关，其低值表明平动和旋转有很大分离。相应的异常小的流体动力学半径表明斯托克斯 - 爱因斯坦 - 德拜关系严重失效。这种异常被视为三维氢键网络的特征。我们得出结论，尽管DMSO是一种非质子液体，但该分子不断地融入甘油的氢键网络中。两种分子表现出共同的动力学，即与喹哪啶/甲苯不同，其组分具有相似的Tg差异，但未发现组分动力学解耦。
