We develop and apply advanced solution and solid state as well as computational NMR methods for materials research.
The experimental methods comprise, along with standard multinuclear NMR spectroscopy, relaxation and diffusion measurements (Laplace NMR), NMR cryoporometry, remote detection NMR, microscopic magnetic resonance imaging (MRI), and xenon NMR.
Computational modeling involves electronic structure calculations of NMR parameters in cluster and periodic solid-state models as well as statistical averaging of them over thermal motions with MC and MD simulations. Due to heavy elements (see below) in the materials, relativistic methods are often utilized.
The materials include, for example, ionic liquids, liquid crystals, porous media, wood, lignins, nanocellulose, cement, shale, geopolymers, soil organic matter, phosphates and other molecular complexes and solids containing dia- and paramagnetic rare earth elements (REEs), supramolecular cages, clathrates, cryptophanes, fullerenes, graphenes, carbon nanotubes, SnWO2, as well as Pt-, Hg-, Bi-containing molecules and their solids.
We have developed and applied various NMR methods for determination of pore sizes of porous materials from nanometer to centimeter range. For example, microscopic MRI allows direct visualization of pores from tens of micrometers to centimeter scale, while xenon NMR, NMR cryoporometry, as well as relaxation and diffusion experiments provide indirect information about the pore sizes from nanometer to millimeter range. We have also introduced an efficient remote detection based NMR method for quantifying multicomponent gas adsorption in porous media. We have exploited combined experimental and computational xenon NMR approach for the investigation of host-guest dynamics of Xe in supramolecular cages as well as adsorption dynamics of xenon in porous organic cages.
We have demonstrated that multidimensional Laplace NMR, accompanied with relaxation modelling, reveal detailed information about ionic liquids. For example, it enabled us to estimate the size of aggregates formed in a novel, halogen-free orthoborate based ionic liquid.
Liquid crystals form a class of materials with importance in particularly in modern display technology. We have applied NMR experiments both on LC molecules themselves as well as on dissolved xenon spy atoms to obtain information about the physical properties of the different LC phases. Both the overall phase behavior of uni- and biaxial nematic LCs as well as Xe NMR in the former are modelled by coarse-grained Gay-Berne MC simulations. Over the years LC materials have also been heavily utilized in the group for determinations of anisotropic NMR parameters for small molecules.
In principle, all the NMR observables, spin-spin coupling, nuclear shielding and quadrupole coupling, are magnetic field-dependent. The field dependence may be classified into two categories: direct and indirect (apparent) dependence. The former arises from the magnetic field-induced deformation of the molecular electronic cloud, while the latter stems from a slightly anisotropic orientation distribution of molecules, due to the interaction between the anisotropy of the molecular susceptibility tensor and the external magnetic field. There is a tendency to further increase the magnetic field of NMR spectrometers, which leads to more pronounced indirect contributions and eventually significant direct effects as well. We have studied the field-induced effects (e.g. nuclear shielding of cobalt, quadrupole coupling of deuterated benzenes as well as of xenon gas) on NMR parameters both experimentally and computationally.