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Hadamard-encoded heteronuclear-resolved NMR diffusion and relaxation measurements allow overlapping signal decays to be resolved with substantially shorter measuring times than are generally associated with 2D heteronuclear cross-correlation experiments. Overall measuring time requirements can be reduced by approximately an order of magnitude, compared to typical 2D heteronuclear single-quantum correlation-resolved diffusion or relaxation measurements. Specifically, in cases where chemical shift correlation information provides enhanced spectral resolution, the use of Hadamard encoding can be used to overcome uniqueness challenges that are associated with the analysis of concurrent dynamic processes and the extraction of time constants from overlapping exponential signal decays. This leads to substantially improved resolution of similar time constants than can be achieved solely through the use of postacquisition processing techniques. In the ideal case of complete spectral separation of the signal decays, the usual constraint that time constants must be sufficiently different to resolve by exponential analysis can be circumvented entirely. Hadamard-based pulse sequences have been used to determine ¹H{13C}-resolved diffusion coefficients and spin-relaxation time constants for the chemically similar components of an aqueous solution of ethanol, glycerol, and poly(ethylene glycol), and a dye-containing block-copolymer solution, which exhibit significant spectral overlap in their ¹NMR spectra. [ABSTRACT FROM AUTHOR]

Characterizing the density of states (DOS) width accurately is critical in understanding the charge‐transport properties of organic semiconducting materials as broader DOS distributions lead to an inferior transport. From a morphological standpoint, the relative densities of ordered and disordered regions are known to affect charge‐transport properties in films; however, a comparison between molecular structures showing quantifiable ordered and disordered regions at an atomic level and its impact on DOS widths and charge‐transport properties has yet to be made. In this work, for the first time, the DOS distribution widths of two model conjugated polymer systems are characterized using three different techniques. A quantitative correlation between energetic disorder from band‐bending measurements and charge transport is established, providing direct experimental evidence that charge‐carrier mobility in disordered materials is compromised due to the relaxation of carriers into the tail states of the DOS. Distinction and quantification of ordered and disordered regions of thin films at an atomic level is achieved using solid‐state NMR spectroscopy. An ability to compare solid‐state film morphologies of organic semiconducting polymers to energetic disorder, and in turn charge transport, can provide useful guidelines for applications of organic conjugated polymers in pertinent devices. [ABSTRACT FROM AUTHOR]

From the assignment of the solid-state 13 C NMR signals in the C4 region, distinct types of crystalline cellulose, cellulose at crystalline surfaces, and disordered cellulose can be identified and quantified. For regenerated cellulose, complete 13 C assignments of the other carbon regions have not previously been attainable, due to signal overlap. In this study, two-dimensional (2D) NMR correlation methods were used to resolve and assign 13 C signals for all carbon atoms in regenerated cellulose. 13 C-enriched bacterial nanocellulose was biosynthesized, dissolved, and coagulated as highly crystalline cellulose II. Specifically, four distinct 13 C signals were observed corresponding to conformationally different anhydroglucose units: two signals assigned to crystalline moieties and two signals assigned to non-crystalline species. The C1, C4 and C6 regions for cellulose II were fully examined by global spectral deconvolution, which yielded qualitative trends of the relative populations of the different cellulose moieties, as a function of wetting and drying treatments. [ABSTRACT FROM AUTHOR]

Bulk thermodynamic and kinetic properties of mixtures are generally composition dependent, often in complicated ways, especially for partially miscible and multicomponent systems. Combined ¹H chemical shift, ¹H diffusion NMR, and surface forces analyses establish the compositional dependences of water solubility and self-diffusion in ternary polymeric polydimethylsiloxane-water-tetrahydrofuran (THF) mixtures. The addition of THF significantly increases the solubility of water, while decreasing its diffusivity, in hydrophobic polydimethylsiloxane. Minimum values for the self-diffusivities of both water and THF coincide with a minimum in the hydrophobic adhesion energy between silicone polymer thin films near the same binary composition of 0.20 mole fraction THF. Such interrelated diffusivities, solubilities, and hydrophobic interactions are analyzed with respect to hydrogen bonding among the constituent species to account for the bulk physical properties of technologically important mixtures of silicone polymers with water and/or cosolvents. [ABSTRACT FROM AUTHOR]

A general protocol is demonstrated for determining the structures of molecularly ordered but noncrystalline solids, which combines constraints provided by X-ray diffraction (XRD), one- and two-dimensional solid-state nuclear magnetic resonance (NMR) spectroscopy, and first-principles quantum chemical calculations. The approach is used to determine the structure(s) of a surfactant-directed layered silicate with short-range order in two dimensions but without long-range periodicity in three-dimensions (3D). The absence of long-range 3D molecular order and corresponding indexable XRD reflections precludes determination of a space group for this layered silicate. Nevertheless, by combining structural constraints obtained from solid-state 29Si NMR analyses, including the types and relative populations of distinct 29Si sites, their respective 29Si–O–29Si connectivities and separation distances, with unit cell parameters (though not space group symmetry) provided by XRD, a comprehensive search of candidate framework structures leads to the identification of a small number of candidate structures that are each compatible with all of the experimental data. Subsequent refinement of the candidate structures using density functional theory calculations allows their evaluation and identification of "best" framework representations, based on their respective lattice energies and quantitative comparisons between experimental and calculated 29Si isotropic chemical shifts and ²J(29Si–O–29Si) scalar couplings. The comprehensive analysis identifies three closely related and topologically equivalent framework configurations that are in close agreement with all experimental and theoretical structural constraints. The subtle differences among such similar structural models embody the complexity of the actual framework(s), which likely contain coexisting or subtle distributions of structural order that are intrinsic to the material. [ABSTRACT FROM AUTHOR]

Glucose, maltodextrin, and sucrose exhibit significantdifferencesin their alkaline reaction properties and interactions in aluminate/silicatecement slurries that result in diverse hydration behaviors of cements.Using 1D solution- and solid-state 13C nuclear magneticresonance (NMR), the structures of these closely related saccharidesare identified in aqueous cement slurry solutions and as adsorbedon inorganic oxide cement surfaces during the early stages of hydration.Solid-state 1D 29Si and 2D 27Al{1H} and 13C{1H} NMR techniques, including theuse of very high magnetic fields (18.8 T), allow the characterizationof the hydrating silicate and aluminate surfaces, where interactionswith adsorbed organic species influence hydration. These measurementsestablish the molecular features of the different saccharides thataccount for their different adsorption behaviors in hydrating cements.Specifically, sucrose is stable in alkaline cement slurries and exhibitsselective adsorption at hydrating silicate surfaces but not at aluminatesurfaces in cements. In contrast, glucose degrades into linear saccharinicor other carboxylic acids that adsorb relatively weakly and nonselectivelyon nonhydrated and hydrated cement particle surfaces. Maltodextrinexhibits intermediate reaction and sorption properties because ofits oligomeric glucosidic structure that yields linear carboxylicacids and stable ring-containing degradation products that are similarto those of the glucose degradation products and sucrose, respectively.Such different reaction and adsorption behaviors provide insight intothe factors responsible for the large differences in the rates atwhich aluminate and silicate cement species hydrate in the presenceof otherwise closely related saccharides. [ABSTRACT FROM AUTHOR]

The compositions and molecular structures of anhydrous and hydrated cements are established by using advanced solid-state nuclear magnetic resonance (NMR) spectroscopy methods to distinguish among different molecular species and changes that occur as a result of cement hydration and setting. Oneand two-dimensional (2D) solid-state 29Si and 27Al magic-angle spinning NMR methodologies, including T1-relaxation-timeand chemical-shift-anisotropy-filtered measurements and the use of very high magnetic fields (19 T), allow resonances from different silicate and aluminate moieties to be resolved and assigned in complicated spectra. Single-pulse 29Si and 27Al NMR spectra are correlated with X-ray fluorescence results to quantify the different crystalline and disordered silicate and aluminate species in anhydrous and hydrated cements. 2D 29Si(1H) and 27Al(1H) heteronuclear correlation NMR spectra of hydrated cements establish interactions between water and hydroxyl moieties with distinct 27Al and 29Si species. The use of a 29Si T1-filter allows anhydrous and hydrated silicate species associated with iron-containing components in the cements to be distinguished, showing that they segregate from calcium silicate and aluminate components during hydration. The different compositions of white Portland and gray oilwell cements are shown to have distinct molecular characteristics that are correlated with their hydration behaviors. [ABSTRACT FROM AUTHOR]

The structure of a novel molecularly ordered two-dimensional (2D) silicate framework in a surfactant-templated mesophase has been established by using a combination of solid-state nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction, and quantum chemical and empirical force- field modeling. These materials are unusual in their combination of headgroup-directed 2D crystalline framework ordering, zeolite-like ring structures within the layers, and long-range mesoscopic organization without three-dimensional (3D) atomic periodicity. The absence of registry between the silicate sheets, resulting from the liquidlike disorder of the alkyl surtactant chains, has presented significant challenges to the determination of framework structures in these and similar materials lacking 3D crystalline order. Double- quantum 29Si NMFI correlation experiments establish the interactions and connectivities between distinct intra-sheet silicon sites from which the structure of the molecularly ordered inorganic framework is determined. [ABSTRACT FROM AUTHOR]