Spin Diffusion Studies Research Articles

Basic principles of static proton low-resolution spin diffusion NMR in nanophase-separated materials with mobility contrast

We review basic principles of low-resolution proton NMR spin diffusion experiments, relying on mobility differences in nm-sized phases of inhomogeneous organic materials such as block-co- or semicrystalline polymers. They are of use for estimates of domain sizes and insights into nanometric dynamic inhomogeneities. Experimental procedures and limitations of mobility-based signal decomposition/filtering prior to spin diffusion are addressed on the example of as yet unpublished data on semicrystalline poly(ϵ-caprolactone), PCL. Specifically, we discuss technical aspects of the quantitative, dead-time free detection of rigid-domain signals by aid of the magic-sandwich echo (MSE), and magic-and-polarization-echo (MAPE) and double-quantum (DQ) magnetization filters to select rigid and mobile components, respectively. Such filters are of general use in reliable fitting approaches for phase composition determinations. Spin diffusion studies at low field using benchtop instruments are challenged by rather short 1H T1 relaxation times, which calls for simulation-based analyses. Applying these, in combination with domain sizes as determined by small-angle X-ray scattering, we have determined spin diffusion coefficients D for PCL (0.34, 0.19 and 0.032nm2/ms for crystalline, interphase and amorphous parts, respectively). We further address thermal-history effects related to secondary crystallization. Finally, the state of knowledge concerning the connection between D values determined locally at the atomic level, using 13C detection and CP- or REDOR-based “1H hole burning” procedures, and those obtained by calibration experiments, is summarized. Specifically, the non-trivial dependence of D on the magic-angle spinning (MAS) frequency, with a minimum under static and a local maximum under moderate-MAS conditions, is highlighted.

Simulation of radiation damping in rings, using stepwise ray-tracing methods

The ray-tracing code Zgoubi computes particle trajectories in arbitrary magnetic and/or electric field maps or analytical field models. It includes a built-in fitting procedure, spin tracking, many Monte Carlo processes. The accuracy of the integration method makes it an efficient tool for multi-turn tracking in periodic machines. Energy loss by synchrotron radiation, based on Monte Carlo techniques, had been introduced in Zgoubi in the early 2000s for studies regarding the linear collider beam delivery system. However, only recently has this Monte Carlo tool been used for systematic beam dynamics and spin diffusion studies in rings, including the eRHIC electron-ion collider project at the Brookhaven National Laboratory. Some beam dynamics aspects of this recent use of Zgoubi capabilities, including considerations of accuracy as well as further benchmarking in the presence of synchrotron radiation in rings, are reported here.

Proton NMR spin-diffusion studies of PS-PB block copolymers at low field: two- vs three-phase model and recalibration of spin-diffusion coefficients

Low-field proton nuclear magnetic resonance (NMR) methods were used to assess the phase fractions, domain thicknesses, T1 relaxation properties and spin diffusion (SD) coefficients D of different phases in nanophase-separated polystyrene-polybutadiene block copolymers. At low field, SD experiments are challenged by rather short longitudinal relaxation times (T1), requiring careful consideration of the interplay of T1 relaxation and SD effects. Building on earlier work, we used a numerical fitting procedure for a separate as well as combined analysis of phase-resolved rigid- and mobile-phase filtered SD, as well as saturation recovery curves taken on a well-defined lamellar sample. We demonstrate the advantages in using three-component model, distinguishing a rigid and a mobile, as well as an interphase that can be resolved by fits to the refocused free-induction decay. We further use domain sizes from small-angle X-ray scattering as a gauge and find that SD coefficients from literature calibrations are overestimated. Under static low-field conditions, D for the rigid polystyrene phase is found to be 0.38±0.06 nm2 ms−1, and we propose a rescaling of a literature calibration correlating D for the mobile phase with its T2 relaxation time.

Spatial relationships between polymers in Sitka spruce: Proton spin-diffusion studies

Abstract The spatial arrangement of polymers in Sitka spruce (Picea sitchensis) was investigated by NMR proton spin-diffusion studies, supplemented by deuterium-exchange experiments monitored by FTIR spectroscopy. The FTIR spectra of earlywood sections after vapour-phase exchange with deuterium oxide showed that 43% of the hydroxyl groups were accessible to deuteration. This value is lower than predicted in the absence of aggregation of cellulose microfibrils into larger units, but greater than the predicted level of deuteration if 3.5-nm microfibrils surrounded by hemicellulose sheaths were aggregated into 4×4 arrays without space for deuterium oxide to penetrate between the microfibrils. The rate of proton spin diffusion between lignin and cellulose was consistent with the presence of microfibril arrays with approximately these dimensions and with lignin located outside them, in both earlywood and latewood. Proton spin-diffusion data for hemicelluloses were complicated by difficulties in assigning signals to glucomannans and xylans, but there was evidence for the spatial association of one group of hemicelluloses, including acetylated glucomannans, with cellulose surfaces, while another group of hemicelluloses was in spatial proximity to lignin. These data are consistent with a number of nanoscale models for the Sitka spruce cell wall, including a model in which glucomannans are associated with microfibril surfaces within the aggregate and water can penetrate partially between these surfaces, and one in which all non-cellulosic polymers and water are excluded from the interior of each microfibril aggregate.

Clay Intercalation of Poly(styrene−ethylene oxide) Block Copolymers Studied by Two-Dimensional Solid-State NMR

The intercalation of poly(styrene−ethylene oxide) block copolymers (PS-b-PEO) into a smectite clay, hectorite, has been studied by multinuclear solid-state nuclear magnetic resonance (NMR). The behaviors of two copolymers with similar PEO block lengths (7 and 8.4 kDa) but different PS block lengths (3.6 vs 30 kDa) were compared. Polymer intercalation is assessed by two-dimensional 1H−29Si heteronuclear correlation (HETCOR) NMR with spin diffusion and refocused 29Si detection for enhanced sensitivity. Hydroxyl protons in the smectite layers serve as crucial spin diffusion references and 1H magnetization relay points from the polymer to the 29Si in the silicate. Experiments with CRAMPS evolution, with 1H spin diffusion, and with detection of the sharp OH proton signal after a 1H T2 filter provide excellent sensitivity for spin diffusion studies with mixing-time series. Because of the mobility of PEO, in this homonuclear experiment we can observe PEO−PS and clay−polymer spin diffusion simultaneously. While t...

Fast magic-angle spinning proton NMR studies of polymers at surfaces and interfaces

Solid-state proton NMR with fast magic-angle sample spinning has been used to study the structure and dynamics of polymers and the water interface in porous glass composites. The composites were prepared by photopolymerization of poly(ethyl acrylate) and other acrylate formulations in a high surface-area rigid glass matrix with 40-Å interconnected pores. High resolution solid-state proton spectra were obtained for polymer films and composites with 15 kHz magic-angle sample spinning at temperatures above the polymer glass transition temperature. The solid-state proton spectra can be detected with high sensitivity and used to determine the composition of polymer and water filling the pores. These results and spin diffusion studies using 1H– 29Si 2D heteronuclear correlation and wideline separation NMR show that the polymer fills the central 30 Å of the pore, and that the remaining volume is filled with surface hydroxyl groups and water.

Fast Magic-Angle Proton NMR Studies of Polymer Interfaces in Poly(ethyl acrylate)/Vycor Composites

Fast magic-angle spinning solid-state proton NMR has been used to study the structure and dynamics of poly(ethyl acrylate) in bulk and polymerized in a Vycor glass with 40 A pores. Bulk poly(ethyl acrylate) is a low-T g material, and high-resolution solid-state proton NMR spectra are observed at ambient temperature because the dipolar interactions are averaged by the combination of chain motion and fast magic-angle sample spinning. The spectrum of the poly(ethyl acrylate)/Vycor composite shows signals in addition to those of the polymer that are assigned to water and surface hydroxyl groups in the porous glass. Integration of the composite and bulk poly(ethyl acrylate) signals reveals that the volume fraction of polymer in the pores is 0.56 and that the polymer occupies the central 30 A in a 40 A pore. Spin diffusion studies demonstrate that filling of the poly(ethyl acrylate)/Vycor is incomplete, and a fraction of the water in the pores is isolated from the polymer. Multiple-quantum NMR studies reveal a large difference in chain dynamics between the bulk poly(ethyl acrylate) and the porous glass composite, and 2D wide line separation NMR shows that the polymer is restricted at the surface of the pores but has bulklike mobility in the center of the pore.

Experiments and strategies for the assignment of fully 13C/15N-labelled polypeptides by solid state NMR.

High-resolution heteronuclear NMR correlation experiments and strategies are proposed for the assignment of fully 13C/15N-labelled polypeptides in the solid state. By the combination of intra-residue and inter-residue 13C-15N correlation experiments with 13C-13C spin-diffusion studies, it becomes feasible to partially assign backbone and side-chain resonance in solid proteins. The performance of sequences using 15N instead of 13C detection is evaluated regarding sensitivity and resolution for a labelled dipeptide (L-Val-L-Phe). The techniques are used for a partial assignment of the 15N and 13C resonances in human ubiquitin.

Structural changes of cellulose, wood, and paper under shear deformation and high pressure

AbstractStructural changes of wood and its components have been studied after shear deformation under high pressure (SDHP) at up to 6 GPa. Cellulose amorphization and chain depolymerization was observed. Approximately 30% of microcrystalline cellulose was soluble in water after a 360‐degree twist of the Bridgman anvils. The water‐insoluble part was re‐crystallized into cellulose II lattice. Repeated treatment applied to the nondissolved part of the sample, the so‐called cascade experiment, permits the dissolving of about 30% of the residual nondissolved material once again. Extraction with water, followed by 10% sodium hydroxide, allows almost complete dissolving of microcrystalline cellulose (98%). Water‐soluble saccharides were studied by HPLC and 13C NMR. It was found that destruction of the wood lignin network needs more severe treatment conditions than cellulose destruction does. Lignin domains in wood act as “grinding stones” during cellulose destruction. Long‐living lignin free radicals have been detected with EPR after SDHP. 13C NMR CP/MAS spin diffusion studies showed that SDHP leads to separation of wood components into different biopolymer domains, which turns the system toward thermo‐dynamic equilibrium. SDHP does not permit achievement of initial compulsary compatibility of components in native wood. SDHP technique appears as a promising method for wood delignification and carbohydrate saccharification in the solid state without using harmful chemical reagents of solvents, which is important for technological safety and ecology. © 1994 John Wiley & Sons, Inc.

Proton Spin Diffusion Studies of Polymer Blends Having Modest Monomer Size. 2. Blends of Cellulose with either Poly(acrylonitrile) or Poly(4-vinylpyridine)

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTProton Spin Diffusion Studies of Polymer Blends Having Modest Monomer Size. 2. Blends of Cellulose with either Poly(acrylonitrile) or Poly(4-vinylpyridine)D. L. Vanderhart, R. St. John Manley, and J. D. BarnesCite this: Macromolecules 1994, 27, 10, 2826–2836Publication Date (Print):May 1, 1994Publication History Published online1 May 2002Published inissue 1 May 1994https://doi.org/10.1021/ma00088a025RIGHTS & PERMISSIONSArticle Views94Altmetric-Citations27LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

Solid‐state NMR of Heterogeneous Materials

AbstractMost solid matrials are hetorogeneous on a microscopic or a microscopic scale, or both. Examoles of hetrogeneties are the phase structure of incompatible polymers, pores in ceramics, distributions in mechanical stress, variations in molecular order and mobility of extruded polymers, and chemical composition in composite materials. Nuclear magnetic resonance (NMR) spectroscopy has unique capabilities for detailed characterization of such hetrogeneities: Microscopic structures between 1 nm and 200 nm can be investigated in spin‐diffusion studies, whereas macroscopic structures above 10 μm can be analyzed in imaging experiments.

Proton spin diffusion as a tool for characterizing polymer blends

AbstractProton spin diffusion studies for characterizing minimum domain dimensions have been carried out on three blends: a 40/60 blend of nylon 6,6 with the aromatic rigid rod polymer poly(benzo[a,d]dithiazol‐2,6‐diyl‐1,4‐phenylene), PBZT, a 47/53 blend of an amorphous nylon with PBZT, and a 50/50 blend of a polyetherimide (PEI) and a polybenzimidazole (PBI). Polarization gradients necessary for these experiments were generated using both chemical shift differences (via multiple pulse techniques) and linewidth differences. Polarization readout techniques included proton lineshape deconvolution, multiple pulse proton lineshapes and 13C CPMAS spectra utilizing short CP times. The two nylon/PBZT blends are expected to phase separate from thermodynamic arguments; however, kinetic considerations, more than thermodynamics, determine domain size. In the 40/60 blend, the minimum domain dimensions of each of the nylon and the PBZT phases were about 4 nm with some scattered larger crystals of nylon. In the 47/53 blend, mixing in some regions indicated domain dimensions similar to the 40/60 blend. In contrast to the 40/60 blend, however, the 47/53 blend was still far from internal spin polarization equilibrium after spin diffusion times of 140 ms. The implication is that the sample‐average composition is not found over dimensions like 40 nm; the problem is that the possible morphological explanations are manifold. By investigating the proton rotating frame relaxation, T1p, the possibility that some of the PBZT domains are isolated from the nylon, in a spin diffusion sense, was eliminated. It is more likely that about half of the nylon protons are isolated by spin diffusion from the PBZT protons on a 140 ms timescale. The PEI/PBI blend is a compatible blend of two aromatic polymers where mixing on a molecular scale is expected. We were interested in a measurement of the lower limit of domain size using proton spin diffusion. This lower limit turned out to be about 2.5 nm based on low temperature T1p measurements as opposed to room temperature multiple pulse methods. The latter measurements monitored the disappearance of a polarization gradient between the PEI methyl protons and all the remaining protons. The superiority of the T1p measurements over the multiple pulse method for establishing the smaller minimum domain dimension is not a general result and reasons are discussed. Finally, some general remarks about characterizing polymer blends by solid state NMR, particularly blends which have undergone spinodal phase separation, are included.

Solid-State Nmr Studies of Molecular Composites and Thermally Cured Copolymers

ABSTRACTProton spin diffusion experiments are conducted on two blends of nylon and poly(phenylenebenzobisthiazole) (PBZT). The blends are prepared different ways and utilize either a semicrystalline or fully amorphous nylon. The spin diffusion experiment, which was conducted using three different schemes, yields information about the shortest distances typifying the individual domains. Results suggest that in a 40/60 nylon 6,6/PBZT blend, the nylon and PBZT molecules do not mix on the molecular level, however, each domain is only about 4 nm in its minimum dimension. At the same time, some crystalline nylon regions also exist having somewhat larger dimensions. In contrast, a 50/50 amorphous nylon/PBZT sample, made via a different processing route, showed evidence for similar mixing in only a portion of the material; there was also strong evidence for compositional heterogeneity on a scale larger than 10 nm. The exact stoichiometries describing this compositional heterogeneity could not be uniquely identified on the basis of the spin diffusion studies alone; however the possibilities range from 55% of pure nylon to 35% of pure PBZT being sequestered from the more intimately mixed phase.In a second set of experiments, the 250°C thermal polymerization chemistry of a benzocyclobutene (BCB), a bismaleimide (BMI) and an equimolar mixture of BCB and BMI was studied. These materials are candidates for thermally polymerizable matrix materials in blends with rigid-rod polymers like PBZT. Polymerization of the BCB homopolymer is found to involve multiple pathways and there is reasonably strong evidence that the reactive carbons generated by thermal ring opening of the cyclobutene moiety not only attack one another; they also attack aromatic carbons adjacent to carbonyl carbons at sites far from the ring opening reaction. Spectra of the BCB homopolymer aged at 300°C in vacuum indicate that significant chemical changes occur. This result casts a shadow on the interpretation of the good apparent thermogravimetric stability of the BCB homopolymer in air at this temperature. The equimolar mixture of BCB and BMI ideally can polymerize via the Diels-Alder mechanism to produce a linear chain of alternating BCB and BMI repeat units. The spectrum of this thermally polymerized mixture suggests a maximum of 50% of the reaction following the Diels-Alder addition; the other 50% follows homopolymerization pathways.

63Cu spin lattice relaxation in Cu-Mn and Cu-Cr. Electron spin dynamics

The 63Cu nuclear spin lattice relaxation rate (T1)-1 in Cu-Mn and Cu-Cr dilute alloys, measured between 0.32 and 20K, are interpreted in the light of recent spin diffusion studies done by the authors (1972) in Cu-Mn alloys. It is shown that, the most important impurity contribution to (T1)-1 is through the RKY coupling with the transverse fluctuations of the impurity moment. The impurity spin relaxation rate involved in the NMR data is different from the ESR linewidth and is associated with simple impurity fluctuations.