After forever changing the drug discovery process in the pharmaceutical industry, combinatorial chemistry methodologies are increasingly being applied to the discovery and optimization of more efficient catalysts and materials (see picture). With the advent of new combinatorial synthesis and screening technologies, coupled with integrated data management systems, the application of these technologies to materials science and catalyst research holds tremendous potential and brings high expectations to this new and exciting field.

Macroscopically oriented silicate−surfactant liquid crystals are produced by slow cooling of lamellar and hexagonal mesophases through their isotropic−anisotropic phase transition in an 11.7 T magnetic field. Comparisons of in situ experimental and simulated 2H NMR spectra quantify the degrees of orientational order in the silicate−surfactant liquid crystals. The overall orientations of the mesophases with respect to the applied magnetic field depend upon the combined diamagnetic susceptibilities of the individual molecular species in the multicomponent surfactant−silicate mixtures. As a result, macroscopic alignment of these liquid crystalline systems can be controlled by adjusting their composition:  lamellar or hexagonal domains are shown to adopt different orientations, according to the diamagnetic susceptibilities of different organic additives present in otherwise identical mixtures. These results demonstrate the utility of liquid crystal processing strategies for organizing inorganic−organic hybrid materials over mesoscopic and macroscopic length scales.

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The main chain dynamics of amorphous poly(ethyl methacrylate) (PEMA) and poly(methyl methacrylate) (PMMA) below and above their respective glass transition temperatures T g are analyzed by two-dimensional solid-state exchange 2H NMR spectroscopy. In both polymers, a restricted mobility of the polymer backbone is already present in the glassy state, as is directly demonstrated and quantified using samples deuterated at the methyl and methylene moieties of the polymer main chain. The unusual main chain mobility below T g is coupled to the β-relaxation process, which involves 180° flips of the carboxyl side groups. At their respective glass transition temperatures, the coupling of the β-process to the main chain motions manifests itself differently in both polymers; the smaller ester side group reorients comparatively fast in PMMA, whereas in PEMA, the reorientation of the bulkier side group remains anisotropic and the correlation times are slower by about 1 order of magnitude. Therefore, in PMMA, the β-relaxation predominantly influences the time scale of the α-relaxation, leading to a particularly high mobility of the main chain itself. In contrast, in PEMA, a slow uniaxial diffusion of the main chain around its local axis sets in at T g, the β-process thus affecting mainly the geometry of backbone motions, as is further corroborated by comparing one-dimensional 13C NMR spectra with two-dimensional exchange 2H NMR spectra at higher temperatures. In summary, the coupling of the α- and β-processes leads to longer mean correlation times for the α-relaxation in PEMA than in PMMA.

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2H NMR results from 2D exchange, solid echo, and wide-line absorption spectra as well as spin-lattice relaxation times are analyzed in terms of different reorientation models applied to the C-2H bond directions of chain-deuterated polystyrene. The dominant mechanism is rotational diffusion by small angular steps where the mean rotational correlation time agrees with relaxation times from dynamic mechanical experiments over a dynamic range of 10 decades. However, the width of the correlation time distribution extracted from the NMR results varies from about 5 decades at Tg to not more than 1 decade at T £ Tt + 40 K, whereas other relaxation techniques yield constant correlation time distributions. The results of the different methods employed for the study of chain motion are compared. It is shown that the motions of well-defined C-H bond directions which are probed by NMR are tightly coupled to the cooperative motion of the o-process. Moreover, they also monitor the separation of the fast 3-process from the slow a-process when approaching Tg by cooling down from the melt.

Twodimensional exchange nuclear magnetic resonance of powder samples. IV. Distribution of correlation times and line shapes in the intermediate dynamic range J. Chem. Phys. 97, 7944 (1992); 10.1063/1.463469The determination of the reorientational angle distribution in twodimensional exchange nuclear magnetic resonance spectroscopy on powder samples Twodimensional exchange nuclear magnetic resonance of powder samples. III. Transition to motional averaging and application to the glass transition

The two-dimensional (2D) exchange nuclear magnetic resonance (NMR) experiment is applied to study ultraslow as well as faster motions in powdered solids. The theoretical framework required for the simulation of 2D exchange of the faster motions, and for the evaluation of the experimental data, is developed. Calculations are presented for two standard models: two-site jump and isotropic rotational diffusion. For discrete jump motion, anisotropic spin-lattice relaxation during the mixing time is also considered. The resulting, simulated 2D line shapes show new characteristics in the intermediate dynamic range. Experimental data are presented for two-site exchange in the model compound polycrystalline dimethylsulphone. The technique is then applied to study the chain dynamics of linear polystyrene in the glass transition range. Close to Tg the correlation times extracted from 2D exchange NMR exhibit strong non-Arrhenius behavior. This data together with correlation times obtained at higher temperatures from conventional T1 data follows the WLF equation over 11 orders of magnitude, from 10−6 to 1000 s. It is shown that 2D exchange NMR and spin-lattice relaxation probe the α and the β process, respectively, of the chain dynamics in the glass transition region.