Istvan Furó - Academia.edu (original) (raw)

Papers by Istvan Furó

Research paper thumbnail of Women in Science: Cultural Comparisons

Science, 1994

Der 1~o c h e l'sche Standor~ (wahrscheinli(.h der ,,locus classicus "~) des Asplenium lepid,um w... more Der 1~o c h e l'sche Standor~ (wahrscheinli(.h der ,,locus classicus "~) des Asplenium lepid,um war den jetzt lebenden ungarischen Bo

Research paper thumbnail of Comparison of NMR Cryoporometry, Mercury Intrusion Porosimetry, and DSC Thermoporosimetry in Characterizing Pore Size Distributions of Compressed Finely Ground Calcium Carbonate Structures

Industrial & Engineering Chemistry Research, 2004

Research paper thumbnail of On experimental aspects of electrophoretic NMR

Concepts in Magnetic Resonance, 2004

Artefacts in electrophoretic NMR experiments are investigated in detail. We identify electroosmos... more Artefacts in electrophoretic NMR experiments are investigated in detail. We identify electroosmosis, sample heating, and gas development on the electrodes as main error sources and suggest experimental strategies and setups to suppress their influence on the monitored electrophoretic mobilities. We hereby demonstrate essentially artefact-free experiments up to currents and electric fields 3 mA and 70 V/cm, respectively.

Research paper thumbnail of High resolution solid state nuclear magnetic resonance study of the electronic structure of rapidly quenched alloys

Research paper thumbnail of Pores in Nanostructured TiO2 Films. Size Distribution and Pore Permeability

Journal of Physical Chemistry C, 2007

ABSTRACT Nanoporous films of crystalline anatase with intended application in dye-sensitized phot... more ABSTRACT Nanoporous films of crystalline anatase with intended application in dye-sensitized photovoltaic cells were investigated by NMR cryoporometry, NMR diffusiometry, electron microscopy, and X-ray diffraction. The nanoparticles from which the films were subsequently sintered were prepared in two ways, one with an acidic and one with a basic aqueous process environment and along different temperature regimes. The average morphology was similar in all films as indicated by the roughly identical 2κV/S values where κ is the mean curvature of the pore surface and S/V denotes the surface-to-volume ratio. Self-diffusion of water in the pores is strongly reduced with respect to that of bulk and is influenced both by micrometer-scale obstructions to molecular displacement and by pore-size effect in pore interconnectivity. The investigated samples exhibit different transport regimes as concerning those phenomena. In this initial study performed on a limited set of samples, we found no linear correlation between particle and pore sizes. Instead, total porosity is controlled by particle−particle jamming which, together with particle size polydispersity, may also dominate the effects that lead to the observed pore size distributions for the different samples. The rich variation of structural effects and transport properties among the few prepared films call for further studies in order to find an optimal film structure.

Research paper thumbnail of Dynamic properties of water in silicalite-1 powder

Magnetic Resonance Imaging, 2012

Self-diffusion of D 2 O in partially filled silicalite-1 crystals was studied at 25°C by 2 H nucl... more Self-diffusion of D 2 O in partially filled silicalite-1 crystals was studied at 25°C by 2 H nuclear magnetic resonance (NMR) with bipolar field gradient pulses and longitudinal Eddy-current-delay. For the first time, reliable experimental diffusion data for this system were obtained. Analysis of NMR diffusion decays revealed the presence of a continuous distribution of apparent self-diffusion coefficients (SDCs) of water, ranging from 10 −7 to ∼10 −10 m 2 /s, which include values much higher and lower than that of bulk water (∼10 −9 m 2 /s) in liquid phase. The observed distribution of SDC changes with variation of the diffusion time in the range of 10-200 ms. A two-site Kärger exchange model was successfully fitted to the data. Finally, the water distribution and exchange in silicalite-1 pores were described by taking into account (a) a gas-like phase in the zeolite pores, a gas-like phase in mesopores and an intercrystalline gas-like phase and (b) intercrystalline liquid droplets with intermediate exchange rate with the other phases. The other phases experience fast exchange on the NMR diffusion time scale. Diffusion coefficients and mean residence times of water in some of these states were estimated.

Research paper thumbnail of Lack of Association between a Cationic Protein and a Cationic Fluorosurfactant

Langmuir, 2007

Surface tension, 19F and 1H NMR spectroscopy, and cryotransmission electron microscopy are used t... more Surface tension, 19F and 1H NMR spectroscopy, and cryotransmission electron microscopy are used to characterize the state of association in aqueous solutions of a fluorosurfactant CF3(CF2)nSO2NH(CH2)3-4N(CH3)3+ I- (n = 8, 6) with and without lysozyme added. In the absence of lysozyme, we find monomers, small aggregates, and large vesicles to coexist, with the individual fluorosurfactant molecules exchanging slowly (>1 ms) among those states. When both lysozyme and fluorosurfactant are present in the solution, they have no measurable influence on the physical state of the other. In contrast, a hydrogenated cationic surfactant with the same headgroup, hexadecyltrimethylammonium bromide, is shown to associate to lysozyme.

Research paper thumbnail of Bulk properties of dendronized polymers with tailored end-groups emanating from the same backbone

Journal of Polymer Science Part A: Polymer Chemistry, 2005

Dendronized polymers with a methacrylate backbone bearing pendant aliphatic polyester dendrons ba... more Dendronized polymers with a methacrylate backbone bearing pendant aliphatic polyester dendrons based on 2,2-bis(methylol)propionic acid have been investigated by rheological measurements, differential scanning calorimetry (DSC), size exclusion chromatography (SEC), and 1 H NMR self-diffusion techniques. The change in material properties due to the attachment of larger dendrons and/or different endgroups to a backbone of the same length is investigated. Dendronized polymers of the second to fourth generation with hydroxyl, acetonide, or hexadecyl end-group functionalities have been studied. DSC revealed that the glass transition temperature of the amorphous polymers increases with increasing size of the dendrons, and that the ability for the hexadecyl functional polymers to crystallize decreases with increasing size of dendrons. 1 H NMR self-diffusion and longitudinal relaxation data are consistent with an elongated rod-like model of the polymers in solution. Larger dendrons lead to a larger rod diameter that approximately double when increasing the generation of dendronized polymer from two to four. Rheological measurements demonstrated that the complex viscosity at low frequency increased with dendron size. Independently of the functionality, the second and third generation samples initially showed a Newtonian plateau, followed by a shear thinning region at higher frequencies. The fourth generation samples only showed shear thinning over the whole frequency region.

Research paper thumbnail of 31 P nuclear magnetic resonance Knight shift and linewidth in Ni 3 P and Cu 3 P: a magic-angle spinning study

Journal of Physics: Condensed Matter, 1990

ABSTRACT Accurate measurements of small 31P Knight shift effects in crystalline Ni3P and Cu3P all... more ABSTRACT Accurate measurements of small 31P Knight shift effects in crystalline Ni3P and Cu3P alloys have been performed by using a magic-angle spinning (MAS) nuclear magnetic resonance (NMR) technique. Both the average Knight shift and the width of its distribution have been found to be different when comparing a normal (equilibrium) and a melt-quenched Ni3P alloy and this is attributed to possible differences in defect concentration and grain size. The 31P NMR line shift of Cu3P is much smaller (K=0.012%) than that of Ni3P (K=0.179%) but spin-lattice relaxation time measurements indicated a Korringa-type relaxation mechanism for both alloys, i.e. Cu3P has also a metallic character.

Research paper thumbnail of Evidence of Antiferromagnetic Ordering in La 2 CuO 4 : Reinterpretation of 139 La Nuclear Quadrupole Resonance (NQR) Data

Japanese Journal of Applied Physics, 1987

A reinterpretation of the results of recent 139La nuclear quadrupole resonance (NQR) measurements... more A reinterpretation of the results of recent 139La nuclear quadrupole resonance (NQR) measurements on La2CuO4 by Kitaoka et al. (Jpn. J. Appl. Phys. 26 (1987) L397) reveals an antiferromagnetic order in this material at low temperature. The magnitude and the direction of the local field at the La sites are calculated. Supposing localized moments on copper atoms as the source of the magnetic field, it is shown that the ordering of magnetic moments on copper sites is not the simplest ``chessboard'' antiferromagnetic type.

Research paper thumbnail of The Effect of Partial Acylglycerols on the Exchange Between Liquid and Solid Tripalmitoylglycerol

Journal of the American Oil Chemists' Society, 2007

Exchange of molecules between liquid and solid components of a triacylglycerol (TAG) system is an... more Exchange of molecules between liquid and solid components of a triacylglycerol (TAG) system is an important process in the degradation of many food components as well as for many industrial processes such as fractionation. NMR is a technique that can be used to measure the exchange between solid and liquid phases. In this work we show that monoacylglycerols (MAG) and diacylglycerols (DAG) have a retarding effect on the rate of exchange between solid and liquid TAG. In particular dipalmitoylglycerol significantly retards the rate of exchange. It is postulated that this result suggests that exchange occurs primarily through certain hotspots, probably kinks and defects on the crystal surface. MAG and, in particular, DAG can block these hotspots. It is suggested that because of their molecular structure they can partially co-crystallize with the TAG crystal during the exchange process and then block further exchange.

Research paper thumbnail of Molecular exchange in thermal equilibrium between dissolved and crystalline tripalmitin by NMR

Journal of the American Oil Chemists' Society, 2003

An NMR technique to measure exchange kinetics at thermal equilibrium in dispersions of moderately... more An NMR technique to measure exchange kinetics at thermal equilibrium in dispersions of moderately soluble crystalline material is presented. By monitoring the exchange of molecules between pools in solid and dissolved form, one can characterize the surface specific exchange rate. Illustrative experiments were performed in a model system with β-type crystals of tripalmitin as the solid phase and tripalmitin, a fraction of it deuterated, dissolved in a medium-chain TG oil as the liquid phase. The concentration of deuterated tripalmitin in the solvent was followed by 2 H NMR after the crystals, which initially lack deuterated tripalmitin, were immersed in the liquid. The variation of the 2 H concentration in the solvent provided the surface specific exchange rate. No systematic errors, due to the slight difference in properties of the deuterated tripalmitin compared to hydrogenated tripalmitin, were observed. The methodology worked well between crystal concentrations of 2 and 4 wt%.

Research paper thumbnail of Comparison of NMR Cryoporometry, Mercury Intrusion Porosimetry, and DSC Thermoporosimetry in Characterizing Pore Size Distributions of Compressed Finely Ground Calcium Carbonate Structures

Industrial & Engineering Chemistry Research, 2004

ABSTRACT This work investigates for the first time how mercury intrusion porosimetry (MIP), NMR-b... more ABSTRACT This work investigates for the first time how mercury intrusion porosimetry (MIP), NMR-based cryoporometry, and DSC-based thermoporosimetry compare in revealing the porous characteristics of ground calcium carbonate structures compacted over a range of pressures. The comparison is made using the same source samples throughout. MIP, a much-used method in the characterization of porous structures, has the drawback that the high pressure needed to intrude the mercury may either distort the skeletal porous structure of the sample, especially when compressible materials such as cellulose or binders/latex are present, or lead to a reduction in the measured number of large pores due to the shielding by smaller pores. These effects have previously been addressed using bulk modulus corrections and by modeling the structure permeability to account for the potential shielding. Cryoporometry gives detailed information about the pore size distribution of an imbibition saturated structure. Thermoporosimetry is a relatively new candidate in this field, and it yields both pore size distribution and pore volume. Currently it is somewhat limited in the pore size range detectable, but it is relevant to pigmented coatings. Its potential is identified for capturing the pores involved in the progress of imbibition before saturation is reached.

Research paper thumbnail of Fe-induced magnetic transition in YBa2(Cu1−x 57Fe x )3O6 by NQR and Mössbauer spectroscopy

Hyperfine Interactions, 1990

ABSTRACT Nuclear quadrupole resonance spectroscopy (around 30 MHz) on the chain site Cu(1) nuclei... more ABSTRACT Nuclear quadrupole resonance spectroscopy (around 30 MHz) on the chain site Cu(1) nuclei in oxygen deficient YBa2(Cu1−x Fe x )3O6 doped with different amounts of57Fe (x≤0.01) reveal an onset of magnetic order at low temperatures represented by a symmetrical doublet contribution to the nuclear quadrupole resonance (NQR) spectrum. The onset temperatureT N2 depends on the concentration of Fe reaching 130 K forx=0.01. The splitting forx=0.01 at 100 K corresponds to a net internal field of 0.09 T with a distribution of ≈0.08 T representing about 70 percent of the Cu(1) nuclei.57Fe and57Co Mssbauer spectroscopy at 4.2 K with and without an external magnetic field of 5 T revealed that belowx=0.00015 Fe spins are decoupled from the Cu(2) moments in the antiferromagnetic state. Results are interpreted in terms of the magnetic model structure suggested by Kadowaki et al. [1].

Research paper thumbnail of Counterion surface diffusion in a lyotropic mesophase: a sodium-23 two-dimensional quadrupolar echo NMR relaxation study

The Journal of Physical Chemistry, 1990

In the first systematic application of the two-dimensional quadrupolar echo (2DQE) method, we stu... more In the first systematic application of the two-dimensional quadrupolar echo (2DQE) method, we study the 23Na NMR relaxation behavior of counterions in the reversed hexagonal mesophase of the AOT/D20/isooctane system, consisting of long cylindrical aggregates with the water and ions on the inside. Using a combination of relaxation experiments, performed on magnetically aligned samples, we determine the three spectral densities at two sample orientations. The orientational dependence of the spectral densities allows us to separate contributions from different types of molecular motion. In particular, we find a dominant contribution from surface diffusion of counterions along the periphery of the cylindrical aqueous regions (diameter ca. 50 A). From the frequency dependence of this contribution, we determine the diffusion coefficient of sodium ions in the interfacial region, a quantity which is important for a variety of phenomena in colloid and polymer science, electrochemistry, and biophysics. We thus obtain D(Na+) = (2.8 f 0.3) X 1O-Io m2 s-l, which is a factor of 3.6 lower than in an infinitely dilute aqueous (DzO) electrolyte solution at the same temperature (20.6 "C). In addition, our analysis of the 23Na relaxation rates and spectral line shapes provides information about the fast local ion and water dynamics in the interfacial region, as well as about the equilibrium structure of the liquid crystalline phase.

Research paper thumbnail of Core Freezing and Size Segregation in Surfactant Core-Shell Micelles

The journal of physical chemistry. B, Jan 6, 2015

Nonionic surfactants containing poly(ethylene oxide) are chemically simple and biocompatible and ... more Nonionic surfactants containing poly(ethylene oxide) are chemically simple and biocompatible and form core-shell micelles at a wide range of conditions. For those reasons, they and their aggregates have been widely investigated. Recently, irregularities that were observed in the low-temperature behavior of surfactants of the kind [CH3(CH2)nO(CH2CH2O)mH], (abbreviated CnEm) were assigned to a freezing-melting phase transition in the micellar core. In this work we expand the focus from the case of single component systems to binary surfactant systems at temperatures between 1 and 15 °C. By applying small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), and density measurements in pure C18E20 and C18E100 solutions and their mixtures, we show that core freezing/melting is also present in mixtures. Additionally, comparing SAXS data obtained from the mixture with those from the single components, it was possible to demonstrate that ...

Research paper thumbnail of 13 C SPE MAS measurement of ligand concentration in compressible chromatographic beads

Magnetic Resonance in Chemistry, 2015

A method for measuring the ligand concentration in heterogeneous materials like chromatography me... more A method for measuring the ligand concentration in heterogeneous materials like chromatography media is described. In this method, (13) C single pulse excitation magic angle spinning NMR experiment with broadband (1) H decoupling is used to determine the peak integrals for a butyl ligand in the spectrum of a dried chromatography medium. Within a carefully controlled protocol, those integrals compared with that of the internal reference compound dimethyl sulfone provide the required volume concentration with an accuracy of ca 2%. The effects of temperature, degree of hydration, and other experimental parameters are discussed. Copyright © 2015 The Authors. Magnetic Resonance in Chemistry published by John Wiley & Sons Ltd.

Research paper thumbnail of 7Li and 133Cs spin relaxation in macroscopically oriented Li- and Cs-DNA fibers

Journal of Magnetic Resonance (1969), 1991

A 'Li and "'Cs NMR relaxation study of macroscopically oriented hydrated Li-and Cs-DNA fibers at ... more A 'Li and "'Cs NMR relaxation study of macroscopically oriented hydrated Li-and Cs-DNA fibers at three different magnetic fields is presented. Two-dimensional quadrupolarecho and spin-echo techniques were used to determine the homogeneous linewidths free from the broadening due to magnetic field inhomogeneity and to a small distribution of the orientation of DNA helix axes. The reIaxation rates obtained show the presence of quadrupolar, dipolar. and paramagnetic relaxation processes in Li-DNA. The separation of these relaxation contributions was made by studying HZO/D20 exchanged samples and (for Li-DNA) 6Li relaxation. For G-DNA, the dipolar and paramagnetic contributions are negligible, but relaxation caused by site-exchange modulation of the Cs chemical shift can be observed. The observed relaxation behavior of the two ions is interpreted in terms of two moiecutar motions on different time SCakS. 0 1991 Academic Press. Inc.

Research paper thumbnail of Nanostructural effects on polymer and water dynamics in cellulose biocomposites - 2H and 13C NMR relaxometry

Biomacromolecules, Jan 8, 2015

Improved moisture stability is desired in cellulose biocomposites. In order to clarify nanostruct... more Improved moisture stability is desired in cellulose biocomposites. In order to clarify nanostructural effects, a new approach is presented where water and polymer matrix mobilities are characterized separately. Nanocomposites from cellulose nanofibers (CNF) in xyloglucan (XG) biopolymer matrix are investigated at different hydration states. Films of XG, CNF and CNF/XG composites are subjected to detailed 2H and 13C NMR relaxation studies. Since the 2H NMR signal arises from heavy water and the 13C signal from the polysaccharides, molecular water and polymer dynamics is for the first time investigated separately. In the neat components, 2H transverse relaxation (T2) data are consistent with water clustering at the CNF fibril surfaces, but bulk spread of moisture in XG. The new method results in a description of water interaction with the nanoscale phases. At low hydration, water molecules at the CNF/XG interface exhibit higher water mobility than in neat CNF or XG, due to locally hig...

Research paper thumbnail of Molecular self-diffusion in a columnar liquid crystalline phase determined by deuterium NMR

Physical review. E, Statistical, nonlinear, and soft matter physics, 2002

We report translational diffusion coefficients in a columnar phase of a discotic liquid crystal f... more We report translational diffusion coefficients in a columnar phase of a discotic liquid crystal formed by a triphenylene-based compound. The experiments were performed using 2H stimulated-echo-type pulsed-field-gradient spin-echo NMR applied to a chain-deuterated sample. The diffusion coefficients were found in the range of 1x10(-14)-4x10(-14) m2/s, three orders of magnitude lower than in the isotopic phase of the same compound. This, together with the high activation energy obtained in columnar phase, indicates that the diffusion is dominated by solidlike jump processes.

Research paper thumbnail of Women in Science: Cultural Comparisons

Science, 1994

Der 1~o c h e l'sche Standor~ (wahrscheinli(.h der ,,locus classicus "~) des Asplenium lepid,um w... more Der 1~o c h e l'sche Standor~ (wahrscheinli(.h der ,,locus classicus "~) des Asplenium lepid,um war den jetzt lebenden ungarischen Bo

Research paper thumbnail of Comparison of NMR Cryoporometry, Mercury Intrusion Porosimetry, and DSC Thermoporosimetry in Characterizing Pore Size Distributions of Compressed Finely Ground Calcium Carbonate Structures

Industrial & Engineering Chemistry Research, 2004

Research paper thumbnail of On experimental aspects of electrophoretic NMR

Concepts in Magnetic Resonance, 2004

Artefacts in electrophoretic NMR experiments are investigated in detail. We identify electroosmos... more Artefacts in electrophoretic NMR experiments are investigated in detail. We identify electroosmosis, sample heating, and gas development on the electrodes as main error sources and suggest experimental strategies and setups to suppress their influence on the monitored electrophoretic mobilities. We hereby demonstrate essentially artefact-free experiments up to currents and electric fields 3 mA and 70 V/cm, respectively.

Research paper thumbnail of High resolution solid state nuclear magnetic resonance study of the electronic structure of rapidly quenched alloys

Research paper thumbnail of Pores in Nanostructured TiO2 Films. Size Distribution and Pore Permeability

Journal of Physical Chemistry C, 2007

ABSTRACT Nanoporous films of crystalline anatase with intended application in dye-sensitized phot... more ABSTRACT Nanoporous films of crystalline anatase with intended application in dye-sensitized photovoltaic cells were investigated by NMR cryoporometry, NMR diffusiometry, electron microscopy, and X-ray diffraction. The nanoparticles from which the films were subsequently sintered were prepared in two ways, one with an acidic and one with a basic aqueous process environment and along different temperature regimes. The average morphology was similar in all films as indicated by the roughly identical 2κV/S values where κ is the mean curvature of the pore surface and S/V denotes the surface-to-volume ratio. Self-diffusion of water in the pores is strongly reduced with respect to that of bulk and is influenced both by micrometer-scale obstructions to molecular displacement and by pore-size effect in pore interconnectivity. The investigated samples exhibit different transport regimes as concerning those phenomena. In this initial study performed on a limited set of samples, we found no linear correlation between particle and pore sizes. Instead, total porosity is controlled by particle−particle jamming which, together with particle size polydispersity, may also dominate the effects that lead to the observed pore size distributions for the different samples. The rich variation of structural effects and transport properties among the few prepared films call for further studies in order to find an optimal film structure.

Research paper thumbnail of Dynamic properties of water in silicalite-1 powder

Magnetic Resonance Imaging, 2012

Self-diffusion of D 2 O in partially filled silicalite-1 crystals was studied at 25°C by 2 H nucl... more Self-diffusion of D 2 O in partially filled silicalite-1 crystals was studied at 25°C by 2 H nuclear magnetic resonance (NMR) with bipolar field gradient pulses and longitudinal Eddy-current-delay. For the first time, reliable experimental diffusion data for this system were obtained. Analysis of NMR diffusion decays revealed the presence of a continuous distribution of apparent self-diffusion coefficients (SDCs) of water, ranging from 10 −7 to ∼10 −10 m 2 /s, which include values much higher and lower than that of bulk water (∼10 −9 m 2 /s) in liquid phase. The observed distribution of SDC changes with variation of the diffusion time in the range of 10-200 ms. A two-site Kärger exchange model was successfully fitted to the data. Finally, the water distribution and exchange in silicalite-1 pores were described by taking into account (a) a gas-like phase in the zeolite pores, a gas-like phase in mesopores and an intercrystalline gas-like phase and (b) intercrystalline liquid droplets with intermediate exchange rate with the other phases. The other phases experience fast exchange on the NMR diffusion time scale. Diffusion coefficients and mean residence times of water in some of these states were estimated.

Research paper thumbnail of Lack of Association between a Cationic Protein and a Cationic Fluorosurfactant

Langmuir, 2007

Surface tension, 19F and 1H NMR spectroscopy, and cryotransmission electron microscopy are used t... more Surface tension, 19F and 1H NMR spectroscopy, and cryotransmission electron microscopy are used to characterize the state of association in aqueous solutions of a fluorosurfactant CF3(CF2)nSO2NH(CH2)3-4N(CH3)3+ I- (n = 8, 6) with and without lysozyme added. In the absence of lysozyme, we find monomers, small aggregates, and large vesicles to coexist, with the individual fluorosurfactant molecules exchanging slowly (>1 ms) among those states. When both lysozyme and fluorosurfactant are present in the solution, they have no measurable influence on the physical state of the other. In contrast, a hydrogenated cationic surfactant with the same headgroup, hexadecyltrimethylammonium bromide, is shown to associate to lysozyme.

Research paper thumbnail of Bulk properties of dendronized polymers with tailored end-groups emanating from the same backbone

Journal of Polymer Science Part A: Polymer Chemistry, 2005

Dendronized polymers with a methacrylate backbone bearing pendant aliphatic polyester dendrons ba... more Dendronized polymers with a methacrylate backbone bearing pendant aliphatic polyester dendrons based on 2,2-bis(methylol)propionic acid have been investigated by rheological measurements, differential scanning calorimetry (DSC), size exclusion chromatography (SEC), and 1 H NMR self-diffusion techniques. The change in material properties due to the attachment of larger dendrons and/or different endgroups to a backbone of the same length is investigated. Dendronized polymers of the second to fourth generation with hydroxyl, acetonide, or hexadecyl end-group functionalities have been studied. DSC revealed that the glass transition temperature of the amorphous polymers increases with increasing size of the dendrons, and that the ability for the hexadecyl functional polymers to crystallize decreases with increasing size of dendrons. 1 H NMR self-diffusion and longitudinal relaxation data are consistent with an elongated rod-like model of the polymers in solution. Larger dendrons lead to a larger rod diameter that approximately double when increasing the generation of dendronized polymer from two to four. Rheological measurements demonstrated that the complex viscosity at low frequency increased with dendron size. Independently of the functionality, the second and third generation samples initially showed a Newtonian plateau, followed by a shear thinning region at higher frequencies. The fourth generation samples only showed shear thinning over the whole frequency region.

Research paper thumbnail of 31 P nuclear magnetic resonance Knight shift and linewidth in Ni 3 P and Cu 3 P: a magic-angle spinning study

Journal of Physics: Condensed Matter, 1990

ABSTRACT Accurate measurements of small 31P Knight shift effects in crystalline Ni3P and Cu3P all... more ABSTRACT Accurate measurements of small 31P Knight shift effects in crystalline Ni3P and Cu3P alloys have been performed by using a magic-angle spinning (MAS) nuclear magnetic resonance (NMR) technique. Both the average Knight shift and the width of its distribution have been found to be different when comparing a normal (equilibrium) and a melt-quenched Ni3P alloy and this is attributed to possible differences in defect concentration and grain size. The 31P NMR line shift of Cu3P is much smaller (K=0.012%) than that of Ni3P (K=0.179%) but spin-lattice relaxation time measurements indicated a Korringa-type relaxation mechanism for both alloys, i.e. Cu3P has also a metallic character.

Research paper thumbnail of Evidence of Antiferromagnetic Ordering in La 2 CuO 4 : Reinterpretation of 139 La Nuclear Quadrupole Resonance (NQR) Data

Japanese Journal of Applied Physics, 1987

A reinterpretation of the results of recent 139La nuclear quadrupole resonance (NQR) measurements... more A reinterpretation of the results of recent 139La nuclear quadrupole resonance (NQR) measurements on La2CuO4 by Kitaoka et al. (Jpn. J. Appl. Phys. 26 (1987) L397) reveals an antiferromagnetic order in this material at low temperature. The magnitude and the direction of the local field at the La sites are calculated. Supposing localized moments on copper atoms as the source of the magnetic field, it is shown that the ordering of magnetic moments on copper sites is not the simplest ``chessboard'' antiferromagnetic type.

Research paper thumbnail of The Effect of Partial Acylglycerols on the Exchange Between Liquid and Solid Tripalmitoylglycerol

Journal of the American Oil Chemists' Society, 2007

Exchange of molecules between liquid and solid components of a triacylglycerol (TAG) system is an... more Exchange of molecules between liquid and solid components of a triacylglycerol (TAG) system is an important process in the degradation of many food components as well as for many industrial processes such as fractionation. NMR is a technique that can be used to measure the exchange between solid and liquid phases. In this work we show that monoacylglycerols (MAG) and diacylglycerols (DAG) have a retarding effect on the rate of exchange between solid and liquid TAG. In particular dipalmitoylglycerol significantly retards the rate of exchange. It is postulated that this result suggests that exchange occurs primarily through certain hotspots, probably kinks and defects on the crystal surface. MAG and, in particular, DAG can block these hotspots. It is suggested that because of their molecular structure they can partially co-crystallize with the TAG crystal during the exchange process and then block further exchange.

Research paper thumbnail of Molecular exchange in thermal equilibrium between dissolved and crystalline tripalmitin by NMR

Journal of the American Oil Chemists' Society, 2003

An NMR technique to measure exchange kinetics at thermal equilibrium in dispersions of moderately... more An NMR technique to measure exchange kinetics at thermal equilibrium in dispersions of moderately soluble crystalline material is presented. By monitoring the exchange of molecules between pools in solid and dissolved form, one can characterize the surface specific exchange rate. Illustrative experiments were performed in a model system with β-type crystals of tripalmitin as the solid phase and tripalmitin, a fraction of it deuterated, dissolved in a medium-chain TG oil as the liquid phase. The concentration of deuterated tripalmitin in the solvent was followed by 2 H NMR after the crystals, which initially lack deuterated tripalmitin, were immersed in the liquid. The variation of the 2 H concentration in the solvent provided the surface specific exchange rate. No systematic errors, due to the slight difference in properties of the deuterated tripalmitin compared to hydrogenated tripalmitin, were observed. The methodology worked well between crystal concentrations of 2 and 4 wt%.

Research paper thumbnail of Comparison of NMR Cryoporometry, Mercury Intrusion Porosimetry, and DSC Thermoporosimetry in Characterizing Pore Size Distributions of Compressed Finely Ground Calcium Carbonate Structures

Industrial & Engineering Chemistry Research, 2004

ABSTRACT This work investigates for the first time how mercury intrusion porosimetry (MIP), NMR-b... more ABSTRACT This work investigates for the first time how mercury intrusion porosimetry (MIP), NMR-based cryoporometry, and DSC-based thermoporosimetry compare in revealing the porous characteristics of ground calcium carbonate structures compacted over a range of pressures. The comparison is made using the same source samples throughout. MIP, a much-used method in the characterization of porous structures, has the drawback that the high pressure needed to intrude the mercury may either distort the skeletal porous structure of the sample, especially when compressible materials such as cellulose or binders/latex are present, or lead to a reduction in the measured number of large pores due to the shielding by smaller pores. These effects have previously been addressed using bulk modulus corrections and by modeling the structure permeability to account for the potential shielding. Cryoporometry gives detailed information about the pore size distribution of an imbibition saturated structure. Thermoporosimetry is a relatively new candidate in this field, and it yields both pore size distribution and pore volume. Currently it is somewhat limited in the pore size range detectable, but it is relevant to pigmented coatings. Its potential is identified for capturing the pores involved in the progress of imbibition before saturation is reached.

Research paper thumbnail of Fe-induced magnetic transition in YBa2(Cu1−x 57Fe x )3O6 by NQR and Mössbauer spectroscopy

Hyperfine Interactions, 1990

ABSTRACT Nuclear quadrupole resonance spectroscopy (around 30 MHz) on the chain site Cu(1) nuclei... more ABSTRACT Nuclear quadrupole resonance spectroscopy (around 30 MHz) on the chain site Cu(1) nuclei in oxygen deficient YBa2(Cu1−x Fe x )3O6 doped with different amounts of57Fe (x≤0.01) reveal an onset of magnetic order at low temperatures represented by a symmetrical doublet contribution to the nuclear quadrupole resonance (NQR) spectrum. The onset temperatureT N2 depends on the concentration of Fe reaching 130 K forx=0.01. The splitting forx=0.01 at 100 K corresponds to a net internal field of 0.09 T with a distribution of ≈0.08 T representing about 70 percent of the Cu(1) nuclei.57Fe and57Co Mssbauer spectroscopy at 4.2 K with and without an external magnetic field of 5 T revealed that belowx=0.00015 Fe spins are decoupled from the Cu(2) moments in the antiferromagnetic state. Results are interpreted in terms of the magnetic model structure suggested by Kadowaki et al. [1].

Research paper thumbnail of Counterion surface diffusion in a lyotropic mesophase: a sodium-23 two-dimensional quadrupolar echo NMR relaxation study

The Journal of Physical Chemistry, 1990

In the first systematic application of the two-dimensional quadrupolar echo (2DQE) method, we stu... more In the first systematic application of the two-dimensional quadrupolar echo (2DQE) method, we study the 23Na NMR relaxation behavior of counterions in the reversed hexagonal mesophase of the AOT/D20/isooctane system, consisting of long cylindrical aggregates with the water and ions on the inside. Using a combination of relaxation experiments, performed on magnetically aligned samples, we determine the three spectral densities at two sample orientations. The orientational dependence of the spectral densities allows us to separate contributions from different types of molecular motion. In particular, we find a dominant contribution from surface diffusion of counterions along the periphery of the cylindrical aqueous regions (diameter ca. 50 A). From the frequency dependence of this contribution, we determine the diffusion coefficient of sodium ions in the interfacial region, a quantity which is important for a variety of phenomena in colloid and polymer science, electrochemistry, and biophysics. We thus obtain D(Na+) = (2.8 f 0.3) X 1O-Io m2 s-l, which is a factor of 3.6 lower than in an infinitely dilute aqueous (DzO) electrolyte solution at the same temperature (20.6 "C). In addition, our analysis of the 23Na relaxation rates and spectral line shapes provides information about the fast local ion and water dynamics in the interfacial region, as well as about the equilibrium structure of the liquid crystalline phase.

Research paper thumbnail of Core Freezing and Size Segregation in Surfactant Core-Shell Micelles

The journal of physical chemistry. B, Jan 6, 2015

Nonionic surfactants containing poly(ethylene oxide) are chemically simple and biocompatible and ... more Nonionic surfactants containing poly(ethylene oxide) are chemically simple and biocompatible and form core-shell micelles at a wide range of conditions. For those reasons, they and their aggregates have been widely investigated. Recently, irregularities that were observed in the low-temperature behavior of surfactants of the kind [CH3(CH2)nO(CH2CH2O)mH], (abbreviated CnEm) were assigned to a freezing-melting phase transition in the micellar core. In this work we expand the focus from the case of single component systems to binary surfactant systems at temperatures between 1 and 15 °C. By applying small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), and density measurements in pure C18E20 and C18E100 solutions and their mixtures, we show that core freezing/melting is also present in mixtures. Additionally, comparing SAXS data obtained from the mixture with those from the single components, it was possible to demonstrate that ...

Research paper thumbnail of 13 C SPE MAS measurement of ligand concentration in compressible chromatographic beads

Magnetic Resonance in Chemistry, 2015

A method for measuring the ligand concentration in heterogeneous materials like chromatography me... more A method for measuring the ligand concentration in heterogeneous materials like chromatography media is described. In this method, (13) C single pulse excitation magic angle spinning NMR experiment with broadband (1) H decoupling is used to determine the peak integrals for a butyl ligand in the spectrum of a dried chromatography medium. Within a carefully controlled protocol, those integrals compared with that of the internal reference compound dimethyl sulfone provide the required volume concentration with an accuracy of ca 2%. The effects of temperature, degree of hydration, and other experimental parameters are discussed. Copyright © 2015 The Authors. Magnetic Resonance in Chemistry published by John Wiley & Sons Ltd.

Research paper thumbnail of 7Li and 133Cs spin relaxation in macroscopically oriented Li- and Cs-DNA fibers

Journal of Magnetic Resonance (1969), 1991

A 'Li and "'Cs NMR relaxation study of macroscopically oriented hydrated Li-and Cs-DNA fibers at ... more A 'Li and "'Cs NMR relaxation study of macroscopically oriented hydrated Li-and Cs-DNA fibers at three different magnetic fields is presented. Two-dimensional quadrupolarecho and spin-echo techniques were used to determine the homogeneous linewidths free from the broadening due to magnetic field inhomogeneity and to a small distribution of the orientation of DNA helix axes. The reIaxation rates obtained show the presence of quadrupolar, dipolar. and paramagnetic relaxation processes in Li-DNA. The separation of these relaxation contributions was made by studying HZO/D20 exchanged samples and (for Li-DNA) 6Li relaxation. For G-DNA, the dipolar and paramagnetic contributions are negligible, but relaxation caused by site-exchange modulation of the Cs chemical shift can be observed. The observed relaxation behavior of the two ions is interpreted in terms of two moiecutar motions on different time SCakS. 0 1991 Academic Press. Inc.

Research paper thumbnail of Nanostructural effects on polymer and water dynamics in cellulose biocomposites - 2H and 13C NMR relaxometry

Biomacromolecules, Jan 8, 2015

Improved moisture stability is desired in cellulose biocomposites. In order to clarify nanostruct... more Improved moisture stability is desired in cellulose biocomposites. In order to clarify nanostructural effects, a new approach is presented where water and polymer matrix mobilities are characterized separately. Nanocomposites from cellulose nanofibers (CNF) in xyloglucan (XG) biopolymer matrix are investigated at different hydration states. Films of XG, CNF and CNF/XG composites are subjected to detailed 2H and 13C NMR relaxation studies. Since the 2H NMR signal arises from heavy water and the 13C signal from the polysaccharides, molecular water and polymer dynamics is for the first time investigated separately. In the neat components, 2H transverse relaxation (T2) data are consistent with water clustering at the CNF fibril surfaces, but bulk spread of moisture in XG. The new method results in a description of water interaction with the nanoscale phases. At low hydration, water molecules at the CNF/XG interface exhibit higher water mobility than in neat CNF or XG, due to locally hig...

Research paper thumbnail of Molecular self-diffusion in a columnar liquid crystalline phase determined by deuterium NMR

Physical review. E, Statistical, nonlinear, and soft matter physics, 2002

We report translational diffusion coefficients in a columnar phase of a discotic liquid crystal f... more We report translational diffusion coefficients in a columnar phase of a discotic liquid crystal formed by a triphenylene-based compound. The experiments were performed using 2H stimulated-echo-type pulsed-field-gradient spin-echo NMR applied to a chain-deuterated sample. The diffusion coefficients were found in the range of 1x10(-14)-4x10(-14) m2/s, three orders of magnitude lower than in the isotopic phase of the same compound. This, together with the high activation energy obtained in columnar phase, indicates that the diffusion is dominated by solidlike jump processes.