The Determination of Surface Development in Cement Pastes by Nuclear Magnetic Resonance

Pulsed proton NMR was used to determine the specific surface of hydrating cement pastes. The method is based on the fact that the measured proton spin-lattice relaxation rate (l/ T₁ ) of water in cement pastes is (in view of the fast exchange between water molecules in the adsorbed and bulk phase) proportional to the fraction of water molecules covering the solid surface and thus proportional to the NMR surface of the newly grown hydration products. In general, the method can be used for powders, fibrous and porous materials in contact with liquid water, or other fluids containing protons.     

Mobility study of amorphous polymers by high-resolution NMR at solid-state

Summary Mobility of amorphous polymers such as poly(vinyl chloride) (PVC), atactic polypropylene (PPA) and ethylene-propylene-diene terpolymer (EPDM) were studied by proton spin-lattice relaxation time (T₁ H), proton spin-lattice relaxation time in the rotating frame (T₁ ^H ), and dipolar dephasing pulse sequence. The data are discussed in terms of mobility and by the distribution of configurational sequences.     

Miscibility and intermolecular specific interactions in blends of poly(hydroxyether of bisphenol A) and poly(4-vinyl pyridine)

The blends of poly(hydroxyether of bisphenol A) (phenoxy) with poly(4-vinyl pyridine) (P4VPy) were investigated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and high-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy. The single, composition-dependent glass transition temperature (T_g) was observed for each blend, indicating that the system is completely miscible. The sigmoid T_g-composition relationship is characteristic of the presence of the strong intermolecular specific interactions in the blend system. FTIR studies revealed that there was intermolecular hydrogen bonding in the blends and the intermolecular hydrogen bonding between the pendant hydroxyl groups of phenoxy and nitrogen atoms of pyridine ring is much stronger than that of self-association in phenoxy. To examine the miscibility of the system at the molecular level, the high resolution ¹³C cross-polarization (CP)/magic angle spinning (MAS) together with the high-power dipolar decoupling (DD) NMR technique was employed. Upon adding P4VPy to the system, the chemical shift of the hydroxyl-substituted methylene carbon resonance of phenoxy was observed to shift downfield in the ¹³C CP/MAS spectra. The proton spin-lattice relaxation time T₁(H) and the proton spin-lattice relaxation time in the rotating frame T_1ρ(H) were measured as a function of the blend composition. In light of the proton spin-lattice relaxation parameters, it is concluded that the phenoxy and P4VPy chains are intimately mixed on the scale of 20-30 Å.     

Mobility study of amorphous polymers by high-resolution NMR at solid-state

Summary Mobility of amorphous polymers such as poly(vinyl chloride) (PVC), atactic polypropylene (PPA) and ethylene-propylene-diene terpolymer (EPDM) were studied by proton spin-lattice relaxation time (T₁ H), proton spin-lattice relaxation time in the rotating frame (T₁H), and dipolar dephasing pulse sequence. The data are discussed in terms of mobility and by the distribution of configurational sequences.     

NMR study of starch based polymer gel electrolytes: Humidity effects

In this work, nuclear magnetic resonance spectroscopy (NMR) was used to study the effect of water absorption in polymer gel electrolytes formed by amylopectin rich starch, plasticized with glycerol and containing lithium perchlorate. The position of the ⁷Li spin-lattice relaxation rate maximum is shifted progressively towards lower temperatures with increasing hydration, reflecting an increase of the lithium mobility. The mechanism responsible for the spin-lattice relaxation of the ⁷Li nuclei in the gel electrolytes are the fluctuations of the quadrupolar interaction due to the lithium motions. The ⁷Li relaxation results of the gel electrolyte hydrated with 2.2 water per complex unit suggest that the lithium ions are almost decoupled from the polymer chain and coordinate, hence preferring the water molecules.     

NMR Line Shape-Spin-Lattice Relaxation Correlation Study of Portland Cement Hydration

The proton free induction decay of a portland cement paste in an advanced stage of hydration can be roughly divided into three main components: (1) a component with a very short spin-spin relaxation time, T², representing the protons of the solid OH groups and the water of crystallization, (2) a component with an intermediate T, representing the bonded water in the gel phase, and (3) a third component with a relatively long T² representing the water in the micropores and layers. The dependences of the intensities, T²'s, and spin-lattice relaxation times (T¹'s) of these three components on the cement hardening time have been determined. The proton spin-lattice relaxation time of the "solid" component increases with hardening time whereas T¹ decreases for the other two components. The observed time dependence of the diffusion coefficient, D, of water in a tricalcium silicate paste supports the findings of the above correlation study.     

Characterization of aged nitrile rubber elastomers by NMR spectroscopy and microimaging

¹H spin-lattice and spin-spin NMR relaxation times change markedly during the aging of nitrile rubber elastomers. NMR microimaging reveals heterogeneous changes in the aged samples. Aging proceeds mainly via additional chain cross-linking, and scission of the polymer chains does not appear to contribute. T₁ imaging shows that there is no spatial distribution of spin-lattice relaxation times.     

Solid state NMR study of segmented polymer networks: fine-tuning of phase morphology via their molecular design

Segmented polymer networks (SPNs) based on thermo-sensitive poly(N-isopropyl acryl amide) (PNIPAA) and poly(tetrahydrofuran) (PTHF) have been synthesized by free radical copolymerization of PTHF bis-macromonomers with N-isopropyl acrylamide. The nature of the polymerizable end group on the bis-macromonomer has been varied, respectively from acrylate to acrylamide end groups. The multiphase behaviour of the corresponding SPNs has been examined as a function of the nature of the end group by making use of solid-state ¹³C CP/MAS NMR relaxometry, ¹H wideline NMR relaxometry and dynamic mechanical analysis (DMA). When PTHF with acrylate end groups was used during the SPN formation, analysis of proton spin-lattice relaxation times (T_1H) and proton spin-lattice relaxation times in the rotating frame (T_1ρH) revealed phase separation with domain sizes larger than 5 nm when the PTHF fraction exceeds 10 wt%. Only for lower PTHF-amounts, the SPNs were homogeneous on the nanometer scale. On the other hand, when PTHF with acrylamide end groups was used as macromolecular cross-linker, the NMR results showed the absence of any domain formation for SPNs with PTHF fractions up to 50 wt%. The major impact of the molecular design on the ultimate phase morphology of bicomponent polymer networks has been confirmed in all cases by DMA-analysis.     

Microstructure and texture of hydrated cement-based materials: A proton field cycling relaxometry approach

We show how the measurement of proton nuclear magnetic spin-lattice relaxation as a function of magnetic field strength (and hence nuclear Larmor frequency) can provide reliable information on the microstructure (specific surface area and pore size distribution) throughout the progressive hydration of cement-based materials. We present in details the experimental and theoretical characteristic features of the relaxation dispersion to support an interpretation in terms of coupled solid-liquid relaxation at pore interfaces, surface diffusion, and nuclear paramagnetic relaxation. The measurement does not require any drying temperature modification and is sufficiently fast to be applied continuously during the progressive hydration of the material. Coupling this method with the standard proton nuclear spin relaxation and high resolution NMR allows us to follow the development of micro-scale texture within the material.     

Determination of the solid contents of fats by wide-line nuclear magnetic resonance: The signal of liquid oils

In order to ascertain the sources of error in the determination of the solid fat content by wide-line nuclear magnetic resonance (NMR) an investigation has been made of the factors governing the amplitude of NMR signals of liquid oils measured with a Newport Quantity Analyzer. The varying saturation properties of the oils concerned were found to be of major importance. The spin-lattice relaxation times (T₁) of 16 oils were measured on a pulse spectrometer at 20, 40 and 60 C, and quantitatively related to the saturation phenomenon. The observed deviation from the theoretical linearity of the NMR signal with the inverse of temperature is explained by the strong dependence of T₁ on temperature and viscosity, and new relationships are derived for these parameters. Since the improvement of the signal to noise ratio of the NMR signal, obtained by increasing the RF level (H₁), increases the saturation as (H₁)², a compromise must be chosen between these two factors to obtain optimal measurement. The results are used to establish criteria for selecting two reference oils to be used in solid fat content determinations.     

NMR diffusion and relaxation studies during cement hydration—A non-destructive approach for clarification of the mechanism of internal post curing of cementitious materials

Internal post-curing of hardening cement pastes by addition of alginate spheres, which contain 98% of water, is studied by non-destructive ¹H NMR measurements of transverse relaxation time and self-diffusion. The onset and amount of water transition from the alginate gel used as additive with temporary delayed release of water to cement pastes was observed continuously during the dormant and accelerated period of cement hydration. During hydration, the water transition from the alginate into the cement matrix as well as the development of pore size is monitored quantitatively by studying the time dependence of characteristic peaks in the transverse relaxation time distribution. Comparison between samples without and with internal post curing shows that the addition of alginate gel does not influence the pore size in the micropore region. NMR diffusion studies demonstrate that the physically bound pore water has sufficient mobility to ensure homogeneous distribution of water from the alginate source into the surrounding cement matrix during the dormant and accelerated period.     

Two-dimensional correlation relaxometry studies of cement pastes performed using a new one-sided NMR magnet

We present preliminary results of the first NMR T₁-T₂ two-dimensional relaxation correlation experiments performed using a one-sided NMR system in cement based materials. Two-dimensional correlation relaxometry has itself only recently been demonstrated in cement paste where it proved to be a particularly sensitive probe of pore-water dynamics providing direct information on exchange of water between the gel and capillary pore networks. Further to this we have observed differences in the structural development of a selection of cement pastes throughout the early stages of hydration and verified the theoretical frequency dependence of the ratio T₁ / T₂. When coupled with instrumentation developments in one-sided NMR magnets the way is opened to detailed, spatially resolved studies of the development of hydration and porosity in the surface layers (top 50 mm) of cementitious materials. A new magnet, suitable for such applications, is discussed.     

Influence of silica fume on the microstructure of cement pastes: New insights from 1H NMR relaxometry

¹H NMR has been used to characterise white Portland cement paste incorporating 10 wt.% of silica fume. Samples were measured sealed throughout the hydration without sample drying. Paste compositions and C–S–H characteristics are calculated based on ¹H NMR signal intensities and relaxation analysis. The results are compared with a similar study of plain white cement paste. While the presence of silica fume has little influence on C–S–H densities, the chemical composition is impacted. After 28 days of sealed hydration, the Ca/(Si + Al) ratio of the C–S–H is 1.33 and the H₂O/(Si + Al) ratio is 1.10 when 10% of silica fume is added to the white cement. A densification of the C–S–H with time is observed. There are no major changes in capillary, C–S–H gel and interlayer pore sizes for the paste containing silica fume compared to the plain white cement paste. However, the gel/interlayer water ratio increases in the silica fume blend.     

Study of the thermal elimination process of sulphinyl-based PPV precursors by solid state NMR

A sensitive protocol to judge the completeness of the elimination reaction for soluble and insoluble conjugated polymers prepared via precursor routes is presented based on UV/vis and ¹H wideline NMR relaxometry in the solid state. Especially the proton spin-lattice decay time in the rotating frame, T_1ρH, has proven to be suitable for an accurate determination of the completeness of the elimination reaction. Especially for long side-chain substituted PPV derivatives, UV/vis seems to be limited due to thermochromic effects. Furthermore, it is shown by solid state ²H wideline NMR spectroscopy that incomplete elimination results in an enhanced polymer backbone chain mobility. Both the completeness of elimination and insight into the molecular dynamics can be of significant importance toward the performance of photovoltaic devices.     

1H N.m.r. relaxation and molecular motion of polyethylene in solution as studied by the isotopic dilution technique

The molecular motion of polyethylene has been studied in decalin-d₁₈ solution by ¹H n.m.r. relaxation with the isotopic dilution technique which can separate the proton spin-lattice relaxation times into the intra- and intermolecular contributions, intra T₁ and inter T₁. The temperature dependences of intra and inter T₁s show that the intra- and intermolecular motions are in the extreme narrow region. These results, also, were compared with the results of molten polyethylene reported in our previous work.     

NMR determination of crystallinity for poly(?-l-lysine)

Crystallinity of poly(?-l-lysine) (?-PL) was discussed by analyzing the differences in the ¹H spin-spin relaxation times (T₂^H), the ¹³C spin-lattice relaxation times (T₁^C), and the ¹³C NMR signal shapes between the crystalline and the non-crystalline phases. The observed ¹H relaxation curve (free induction decay followed by solid-echo method) showed the sum of Gaussian and exponential decays. Similarly, the observed ¹³C relaxation curves obtained from the Torchia method were double-exponential. The ¹³C NMR spectrum of ?-PL was divided into the narrow and the broad lines by utilizing the intrinsic differences in the ¹H spin-lattice relaxation times in the rotating-frame between them, which are attributed to the crystalline and the non-crystalline phases, respectively. Even though the crystallinity is obtained from the identical NMR measurements, the estimated values are different with each other. The crystallinity estimated from the T₂^H differences was 75.8 ± 0.1% at 333 K and 60.7 ± 0.4% at 353 K. From the T₁^C differences, the value was estimated to be 62 ± 11%. Furthermore, the value estimated from the NMR signal separation was 54 ± 5%. In this study we have explained these discrepancies by the difference in susceptibility among the experiments for the inter-phase, which exists in-between the crystalline and the amorphous phases. Furthermore, the estimated crystallinity was ascertained by the X-ray diffraction experiment.     

Characterization by solid-state NMR and selective dissolution techniques of anhydrous and hydrated CEM V cement pastes

The long term behaviour of cement based materials is strongly dependent on the paste microstructure and also on the internal chemistry. A CEM V blended cement containing pulverised fly ash (PFA) and blastfurnace slag (BFS) has been studied in order to understand hydration processes which influence the paste microstructure. Solid-state NMR spectroscopy with complementary X-ray diffraction analysis and selective dissolution techniques have been used for the characterization of the various phases (C₃S, C₂S, C₃A and C₄AF) of the clinker and additives and then for estimation of the degree of hydration of these same phases. Their quantification after simulation of experimental ²⁹Si and ²⁷Al MAS NMR spectra has allowed us to follow the hydration of recent (28 days) and old (10 years) samples that constitutes a basis of experimental data for the prediction of hydration model.     

Miscibility and hydrogen bonding in blends of poly(vinyl acetate) with phenolic resin

The miscibility of phenolic resin and poly(vinyl acetate) (PVAc) blends was investigated by differential scanning calorimeter (DSC), Fourier transform infrared spectroscopy (FT-IR) and solid state ¹³C nuclear magnetic resonance (NMR). This blend displays single glass transition temperature (T_g) over entire compositions indicating that this blend system is miscible in the amorphous phase due to the formation of hydrogen bonding between hydroxyl groups of phenolic resin and carbonyl groups of PVAc. Quantitative measurements on fraction of hydrogen-bonded carbonyl group using both ¹³C solid-state NMR and FT-IR analyses result in good agreement between these two spectroscopic techniques. According to the proton spin-lattice relaxation time in the rotating frame (T_1ρ^H), the phenolic/PVAc blend is intimately mixed on a scale less than 2-3 nm. Furthermore, the inter-association equilibrium constant and its related enthalpy of phenolic/PVAc blends were determined as a function of temperatures by infrared spectra based on the Painter-Coleman association model.     

C NMR study of C-enriched single-wall carbon nanotubes synthesized by catalytic decomposition of methane

¹³C NMR spectra and spin-lattice relaxation times were measured for single-wall carbon nanotubes with 99.9 and 50.0% ¹³C enrichments and natural abundance (1.1% ¹³C) prepared by catalytic decomposition of CH₄. The ¹³C isotropic shift is about 116 ppm from tetramethylsilane, being estimated from magic-angle-spinning (MAS) spectra. The value does not depend on the degree of the ¹³C enrichment. The ¹³C MAS NMR spectra show two additional small peaks at 171 and 152 ppm, which are ascribed to carbon species at defects or edges. The line widths of the main isotropic peak in MAS spectra are about 30 ppm, the origin of which is mostly chemical shift dispersion, reflecting a distribution of diameter and helicity. The line width in the ¹³C static spectra originates from chemical shift dispersion, chemical shift anisotropy and dipole–dipole interactions between ¹³C spins as well as between ¹³C and ¹H spins at defects or edges. ¹H NMR spectra confirm the presence of H-containing species. The ¹³C spin-lattice relaxation is dominated presumably by interaction with magnetic impurities.     

An X-Ray Diffraction,Fourier-Transform Infrared Spectroscopy,and Scanning Electron Microscopy/Energy-Dispersive Spectroscopic Investigation of the Effect of Sodium Lignosulfonate Superplasticizer on the Hydration of Portland Cement Type V

This study investigated the effects of a common superplasticizer, ligno-sulfonate, on the hydration of Portland cement Type V. Samples of plain cement and superplasticizer-treated cement have been examined by x-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy/energy-dispersive spectroscopy. Lignosulfonate has been observed to retard the hydration of cement through specific surface chemical reactions which involve Ca²⁺ ions in pore solution. The admixture has been found to retard the formation of Ca(OH)₂ and stabilize ettringite [Ca₆(Al₂2O₆)(SO₄)₃.32H₂O]. The inhibition of the rate of conversion of ettringite to monosulfate [Ca₄Al₂(OH)₁₂.SO₄.6H₂O] is attributed to charge-controlled reactions caused by large quantities of Ca²⁺ ions from initial hydration reactions. Leaching of the admixture doped cement by water-removed lignosulfonate and caused complete hydration of cement. A charge-controlled-reaction model involving the Ca²⁺ ions is proposed to explain the role of the admixtures during hydration of cement.