Ioan Ardelean - Academia.edu (original) (raw)
Papers by Ioan Ardelean
Coatings
Calcium phosphate cements are widely used biomaterials for bone regeneration due to their biologi... more Calcium phosphate cements are widely used biomaterials for bone regeneration due to their biological properties, such as biocompatibility, biodegradability, and bioactivity. The presence of chitosan in cement composition influences the resorption rate of the material and its mechanical properties. In the present work, the water absorption and solubility of a tricalcium phosphate bone cement, prepared with and without chitosan addition, was comparatively evaluated. The absorption and solubility properties were monitored for 21 days by immersing the samples in water at room temperature and then weighing them. A morphological analysis of the samples was carried out via scanning electron microscopy (SEM). The absorption dynamics and pore evolution were investigated with low-field nuclear magnetic resonance (NMR) relaxometry. It was demonstrated that the presence of chitosan accelerates the hardening dynamics, reduces water absorption, and influences the solubility and degradation behavi...
Coatings
This work aims to show the advantages of using GGBS (Ground Granulated Blast Furnace Slag) and AC... more This work aims to show the advantages of using GGBS (Ground Granulated Blast Furnace Slag) and ACBFS aggregate (Air-Cooled Blast Furnace Slag) on the tensile strength and durability properties of infrastructure concrete at the reference age of 28 days. Three concrete mixes were prepared: the first one was a control sample; the second one had 15% GGBS (instead of Portland cement) and 25% ACBFS (instead of natural sand); and the third had 15% GGBS (instead of Portland cement) and 50% ACBFS (instead of natural sand). The studies on mortars focused on the ratio of compressive strength (CS) in correlation with the specific surface area (obtained by the Blain method). The microstructure of the prepared mortars was examined at the age of 28 days by X-ray diffraction, SEM electron microscopy with an energy-dispersive EDX spectrometer, and NMR nuclear magnetic resonance relaxometry. The results of the tests carried out afterwards on the concretes containing slag (15% GGBS and 25% or 50% ACBF...
Molecules
The hydration process of Portland cement is still not completely understood. For instance, it is ... more The hydration process of Portland cement is still not completely understood. For instance, it is not clear what produces the induction period, which follows the initial period of fast reaction, and is characterized by a reduced reactivity. To contribute to such understanding, we compare here the hydration process of two cement samples, the simple cement paste and the cement paste containing calcium nitrate as an accelerator. The hydration of these samples is monitored during the induction period using two different low-field nuclear magnetic resonance (NMR) relaxometry techniques. The transverse relaxation measurements of the 1H nuclei at 20 MHz resonance frequency show that the capillary pore water is not consumed during the induction period and that this stage is shortened in the presence of calcium nitrate. The longitudinal relaxation measurements, performed at variable Larmor frequency of the 1H nuclei, reveal a continuous increase in the surface-to-volume ratio of the capillary...
Materials
Incorporating blast furnace slag into the composition of paving concrete can be one of the cost-e... more Incorporating blast furnace slag into the composition of paving concrete can be one of the cost-effective ways to completely eliminate by-products from the pig iron production process (approximately 70% granulated slag and 30% air-cooled slag). The possibility to reintroduce blast furnace slag back into the life cycle will provide significant support to current environmental concerns and the clearance of tailings landfills. Especially in recent years, granulated and ground blast furnace slag (GGBS) as a substitute for cement and air-cooled blast furnace slag (ACBFS) aggregates as a substitute for natural aggregates in the composition of concretes have been studied by many researchers. But concrete compositions with large amounts of incorporated blast furnace slag affect the mechanical and durability properties through the interaction between the slag, cement and water depending on the curing times. This study focuses on identifying the optimal proportions of GGBS as a supplementary ...
New Developments in NMR
Standard PGSE techniques have proven to be powerful and popular tools for diffusion studies in ma... more Standard PGSE techniques have proven to be powerful and popular tools for diffusion studies in materials. However, there are a number of challenges that might arise if the investigation is to refer to media of a more complex nature. Examples are heterogeneous, micro-textured, porous, granular, composite or high-viscosity materials. In these cases, there will be tendencies to anomalous diffusion, superimposed components, extremely small displacement rates, and displacement restrictions. Artifacts in the experiments or in interpretations can moreover be due to eddy currents, magneto-acoustic ringing, short-T2-limitations, and internal field gradients. In this chapter, alternative NMR techniques based on (a) strong, stationary field gradients in the fringe field of magnets, (b) rotating-frame imaging with the aid of gradients of the RF field amplitude, and (c) multiple stimulated echoes arising in modulated demagnetizing fields will be described. The common principle of all these variants is to generate a so-called grating of the z magnetization, which then tends to be leveled by translational displacements of the spin-bearing nuclei. It will be shown how such techniques can help to solve or avoid the before mentioned problems. Finally, it will be proposed to combine the diverse diffusometry techniques to cover an unsurpassed time scale ranging from microseconds to seconds with options to extend the scale even down to nanoseconds and up to hours or days by additionally referring to NMR relaxometry and microimaging methods, respectively.
The present study investigates the chemical composition governing the physical properties of mono... more The present study investigates the chemical composition governing the physical properties of mono- and diglycerides (MDGs) at the microstructural level, as a function of aging and lot-to-lot variability. The physical structure of the MDG plays a vital role in ameliorating the emulsion stability and is widely explored in diverse research horizons related to the pharmaceutical, cosmetic, and food industries. In an effort to understand the mechanism of emulsion stabilization, physical properties were extensively evaluated in selective commercial lots to determine if there is a correlation between the chemical composition of MDG and physical properties. The solid state of the MDG samples with different aging profiles was characterized using X-ray scattering, differential scanning calorimetry, attenuated total reflection-Fourier transform infrared spectroscopy, and NMR relaxometry. Moreover, the kinetic aspect of solid-state transformation was also evaluated via treating MDG samples with a heat-cool cycle. The chemical composition of MDGs was quantified using a quantitative NMR (qNMR) method. Interestingly, the X-ray scattering results demonstrated a change in the MDG polymorphic form and an increase in the %β content as a function of aging. The increase in the %β content led to the formation of rigid crystal structures of MDG, as evident from the NMR relaxometry. Chemical quantification of isomeric composition revealed chemical composition change as a potentially critical factor responsible for the altered physical structures of MDG with respect to aging and lot-to-lot variability. The findings correlated the solid-state transformation with the change in the chemical composition of the MDG as a combined effect of aging and lot-to-lot variability. This work serves as a basis to better understand the interdependency of the physicochemical properties of MDG. Furthermore, the present work can also be used as guidance for setting up the specifications of MDG, as per the required polymorphic form for a multitude of applications.
Journal of the Science of Food and Agriculture, 2021
BACKGROUND Adulteration is defined as the intentional addition of a material that is not a part o... more BACKGROUND Adulteration is defined as the intentional addition of a material that is not a part of the nature. In this study, a non-conventional time domain NMR (TD-NMR) pulse sequence: Magic Sandwich Echo (MSE) was used to detect the adulteration of honey by glucose (GS) and high fructose corn syrups (HFCS) accompanied with T1 and T2 relaxation times. Also, fast field cycling NMR (FFC NMR) relaxometry and multivariate analysis were performed to investigate the adulteration. RESULTS Higher maltose in GS and changing glucose to water ratio of HFCS gave high correlation with the crystal content values. In HFCS adulteration, two separate populations of protons having different T2 values were detected and T1 times were also used to determine GS adulteration. Addition of GS increased T1 while addition of HFCS increased T2 , significantly. CONCLUSION The results showed that it is possible to differentiate the unadulterated and adulterated honey samples by using TD-NMR relaxation times and crystal content values (CC) obtained by the MSE sequence. By FFC NMR relaxometry, not only GS addition but also the amount of GS was examined. The multivariate analysis technique of principal component analysis (PCA) was able to distinguish the types of adulterants. This article is protected by copyright. All rights reserved.
Fast Field Cycling (FFC) nuclear magnetic resonance (NMR) relaxometry is used to monitor the infl... more Fast Field Cycling (FFC) nuclear magnetic resonance (NMR) relaxometry is used to monitor the influence introduced on the hydration process by the addition of silica fume in a cement paste mixture, prepared with white Portland cement. The FFC relaxometry technique was implemented due to its sensitivity to a wider range of molecular motions, which gives more information than other relaxometry techniques performed at a fixed frequency. This unique feature of FFC relaxometry allows better separation of the surface and bulk contributions from the global measured relaxation rate. The relaxation process is dominated by the interaction of water protons with the paramagnetic centers located on the surface of cement grains. In the frame of a two-phase exchange model, this allows the monitoring of the influence of an addition of silica fume on the evolution of surface-to-volume ratio during the early hydration stages.
Molecular Physics, 2018
The hydration process of four different cement-based materials at different depths inside the sam... more The hydration process of four different cement-based materials at different depths inside the sample was investigated using localised nuclear magnetic resonance relaxation measurements. All the samples are based on white Portland cement (CEM I 42.5 R), with a water-to-cement ratio of 0.5. One sample is a simple cement paste and the other three additionally contain 5% (by mass of cement) silica nanoparticles (50-200 nm size), silanised silica nanoparticles (with silane A 174) or silica fume (80% silica; 0.15 µm average size). The localised transverse relaxation measurements were performed using a single-sided NMR instrument. The relaxation rates were monitored for 48 h during the hydration process at different depths inside the sample. The results showed that the presence of nanoparticles influences not only the speed of hydration overall, but also the homogeneity of the materials.
Analytical Letters, 2020
The need to develop specific magnetic nanostructures for resonance imaging becomes more evident b... more The need to develop specific magnetic nanostructures for resonance imaging becomes more evident by the day. In this study, iron oxide magnetic nanoparticles stabilized with ethylenediaminetetraacetic acid (EDTA), followed by a gadolinium (Gd) ion chelation reaction Gd-EDTA-MNPs were synthesized and evaluated as a potential magnetic resonance imaging contrast agent. The contrast agent has been developed by a facile and universal coordination chemistry method. The compositions, structures, as well as the physicochemical characterization techniques, are reported. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy demonstrate the success of gadolinium complexation by the carboxyl group of EDTA coated iron oxide nanoparticles. Cytotoxicity measurements have been performed using a cell culture of normal human keratinocytes (HaCaT cell line) and human malignant melanoma (A375). Our results show a significant increase in the transverse relaxivity induced by the complexation with gadolinium, 540 mM À1 s À1 for Gd-EDTA-MNPs. The longitudinal relaxation dispersion curves show one order of magnitude enhancement of the longitudinal relaxivity from 2.2 mM À1 s À1 (EDTA-MNPs) to 29.6 mM À1 s À1 (Gd-EDTA-MNPs) at a 20 MHz resonance frequency. The results suggest that Gd complexation may represent a viable approach in obtaining contrast agents able to reduce both T 1 and T 2 nuclear relaxation times.
The Journal of Physical Chemistry C, 2019
AIP Conference Proceedings, 2017
In the present work the liquid morphology, under partially saturated conditions inside two carbon... more In the present work the liquid morphology, under partially saturated conditions inside two carbon aerogel and xerogel samples, was investigated using the low-field nuclear magnetic resonance (NMR) relaxometry. Information about the tortuosity of the two samples was also extracted using pulse field gradient NMR diffusometry. The molecules under investigation were water and cyclohexane. They were chosen due to their different interaction with the carbonaceous matrix. It was found a non-uniform coverage of molecules on the pore surface except for the case of cyclohexane filled carbon xerogel when the distribution was uniform. It was also observed an influence of the cyclohexane- surface interaction on the tortuosity factor characterizing the xerogel sample.
Molecular Physics, 2018
The influence of silanised silica fume addition on the pore size distribution and wettability of ... more The influence of silanised silica fume addition on the pore size distribution and wettability of white cement paste was investigated using T 1-T 2 correlation nuclear magnetic resonance (NMR) relaxometry. Surface silanisation of silica fume particles was achieved by the hydrolysis reaction of APTES (3-Aminopropyltriethoxysilane) and condensation of the silanol functional groups on the surface. The methods used for characterisation of the silanised silica fume particles were scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). By adding silanised silica fume to the cement paste, the accessibility of water molecules to the porous system becomes restricted, leading to a lower permeability in comparison with the unmodified cement paste. Differential scanning calorimetry (DSC) measurements on the cement pastes saturated with Octamethylcyclotetrasiloxane confirm also that the size of inter-C-S-H and capillary pores is not influenced by the addition of silica fume in a detectable manner.
Magnetic Resonance in Chemistry, 2019
Low-field nuclear magnetic resonance techniques are employed to extract information about the eff... more Low-field nuclear magnetic resonance techniques are employed to extract information about the effects introduced by the interaction with the surface on the rotational and translational dynamics of molecules confined inside a mesoporous carbon xerogel. The molecules under study were water, cyclohexane, and hexane. They were chosen due to their different interaction strength with the carbonaceous matrix. Frequency dependent longitudinal relaxation measurements, using the fast field cycling technique, allowed extraction of the fractal dimension of the carbon xerogel surface. It was observed that the measured value is influenced by the molecule affinity to the surface. Diffusion measurements, using the pulse field gradient technique, have revealed that the stronger interaction with the surface of cyclohexane and hexane molecules leads to an increased diffusive tortuosity, as compared with water.
Applied Magnetic Resonance, 2015
AbstractNuclear magnetic resonance (NMR) relaxometry is used here as a noninvasive tool to monito... more AbstractNuclear magnetic resonance (NMR) relaxometry is used here as a noninvasive tool to monitor the influence introduced by the addition of 3-Aminopropyltriethoxysilane (APTES) on the hydration of pure cement paste and a cement paste containing quartz powder. It is observed extension of the dormancy stage up to 12 h in the presence of the aminosilane and a slight reduction in the size of capillary pores. The extension of the dormancy stage can be also associated with a slower hydration process which leads to enhancement of the final flexural strength in the case of sample containing quartz.
AIP Conference Proceedings, 2013
ABSTRACT In the present work we study the internal gradient effects on diffusion attenuation of t... more ABSTRACT In the present work we study the internal gradient effects on diffusion attenuation of the echo train appearing in the well-known Carr-Purcell-Meiboom-Gill (CPMG) technique, extensively used for transverse relaxation measurements. Our investigations are carried out on two porous ceramics, prepared with the same amount of magnetic impurities (Fe2O3) but different pore sizes. It is shown that diffusion effects on the CPMG echo train attenuation are strongly influenced by the pore size for the same magnetic susceptibility of the two samples. The experimental results were compared with a theoretical model taking into account the limit of free or restricted diffusion on echo train attenuation. The NMR experiments were performed on water filled samples using a low-field NMR instrument. The porous ceramics were prepared using both the replica technique and the powder compression technique. Magnetic susceptibility measurements indicated close values of the susceptibility constant for the two samples whereas the SEM images indicated different pore sizes. The results reported here may have impact in the interpretation of NMR relaxation measurements of water in soils or concrete samples.
ABSTRACT The residual monomer present in post-polymerized dental materials encourages premature d... more ABSTRACT The residual monomer present in post-polymerized dental materials encourages premature degradation of the reconstructed tooth. That is why the residual monomer should be quantified in a simple, fast, accurate and reproducible manner. In our work we propose such an approach for accurate determination of the residual monomer in dental materials which is based on low-field nuclear magnetic resonance (NMR) relaxometry. The results of the NMR approach are compared with those of the high performance liquid chromatography (HPLC) technique. The samples under study contain the main monomers (2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane and triethylene glycol dimethacrylate) constituting the liquid phase of most dental materials and an initiator. Two samples were analyzed with different ratios of chemical initiation systems: N,N-dimethyl-p-toluide: benzoyl peroxide (1:2 and 0.7:1.2). The results obtained by both techniques highlight that by reducing the initiator the polymerization process slows down and the amount of residual monomer reduces. This prevents the premature degradation of the dental fillings and consequently the reduction of the biomaterial resistance.
ABSTRACT In the present work, we study the transverse relaxation time evolution of water molecule... more ABSTRACT In the present work, we study the transverse relaxation time evolution of water molecules confined inside cement paste during the hydration process. The cement paste under study was manufactured with different water-to-cement ratios and using two types of cement: gray cement (CEM I 52.5 R) having a high content of magnetic impurities and white cement (CEM I 52.5 N) with lower amount of magnetic impurities. The two cement types were chosen in order to better distinguish the surface contribution to the relaxation process. On this basis a relationship between porosity evolution, ettringite formation and the transverse relaxation time evolution was established. It was also observed that the increase in the water-to-cement ratio better reveals the ettringite formation.
ChemInform, 2004
ABSTRACT Starting from basic differential equations for the description of ordinary and anomalous... more ABSTRACT Starting from basic differential equations for the description of ordinary and anomalous diffusion the theory of the standard field gradient pulse sequences for diffusion studies with the aid of NMR is developed. Anomalous diffusion can be due to an “obstruction effect” or to a “trapping effect” depending on the geometry and nature of the system matrix confining the diffusing particles. The NMR methods under consideration refer both to pulsed and steady field gradients, and both to laboratory and rotating-frame variants. The advantages and disadvantages are weighed up. More recent results refer to the attenuation of so-called multiple (or nonlinear) echoes by diffusion, and the use of internal field gradients for diffusion studies in fluid filled porous media. The diffusion of ordinary or laser-polarized gases is discussed for applications to porous media again. On a much longer time scale, isotope interdiffusion can be used as a technique for the elucidation of anomalous diffusion on percolation networks. A further and very distinct example of anomalous displacement characteristics was predicted for entangled polymers. Corresponding studies are reviewed and discussed with respect to the experimental limits. Finally, spin diffusion by flip-flop processes of dipolar coupled spins is shown to be a competitive mechanism if Brownian diffusion is strongly hindered by obstacles.
Applied Magnetic Resonance, 2014
In the present work, we use fast field cycling (FFC) nuclear magnetic resonance relaxometry to ev... more In the present work, we use fast field cycling (FFC) nuclear magnetic resonance relaxometry to evaluate the influence introduced by the curing temperature on the hydration process of gray cement. The main advantage of FFC relaxometry as compared with other relaxation studies performed at a specific frequency is that it is sensitive to a wider range of molecular motions and better separates the surface and bulk contributions from the global measured relaxation rate. In the case of cement hydration, the relaxation process is dominated by the interaction of water protons with the paramagnetic centers located on the surface of cement grains. This allows us in the frame of a two-phase exchange model to monitor the temperature dependence of the transverse diffusional correlation time at the surface of cement grains. An increase of the surface diffusion coefficient of water molecules with the temperature was revealed. Another outcome is that the surface-to-volume ratio of capillary pores continuously increases during the early hydration and this process is strongly enhanced by rising the temperature.
Coatings
Calcium phosphate cements are widely used biomaterials for bone regeneration due to their biologi... more Calcium phosphate cements are widely used biomaterials for bone regeneration due to their biological properties, such as biocompatibility, biodegradability, and bioactivity. The presence of chitosan in cement composition influences the resorption rate of the material and its mechanical properties. In the present work, the water absorption and solubility of a tricalcium phosphate bone cement, prepared with and without chitosan addition, was comparatively evaluated. The absorption and solubility properties were monitored for 21 days by immersing the samples in water at room temperature and then weighing them. A morphological analysis of the samples was carried out via scanning electron microscopy (SEM). The absorption dynamics and pore evolution were investigated with low-field nuclear magnetic resonance (NMR) relaxometry. It was demonstrated that the presence of chitosan accelerates the hardening dynamics, reduces water absorption, and influences the solubility and degradation behavi...
Coatings
This work aims to show the advantages of using GGBS (Ground Granulated Blast Furnace Slag) and AC... more This work aims to show the advantages of using GGBS (Ground Granulated Blast Furnace Slag) and ACBFS aggregate (Air-Cooled Blast Furnace Slag) on the tensile strength and durability properties of infrastructure concrete at the reference age of 28 days. Three concrete mixes were prepared: the first one was a control sample; the second one had 15% GGBS (instead of Portland cement) and 25% ACBFS (instead of natural sand); and the third had 15% GGBS (instead of Portland cement) and 50% ACBFS (instead of natural sand). The studies on mortars focused on the ratio of compressive strength (CS) in correlation with the specific surface area (obtained by the Blain method). The microstructure of the prepared mortars was examined at the age of 28 days by X-ray diffraction, SEM electron microscopy with an energy-dispersive EDX spectrometer, and NMR nuclear magnetic resonance relaxometry. The results of the tests carried out afterwards on the concretes containing slag (15% GGBS and 25% or 50% ACBF...
Molecules
The hydration process of Portland cement is still not completely understood. For instance, it is ... more The hydration process of Portland cement is still not completely understood. For instance, it is not clear what produces the induction period, which follows the initial period of fast reaction, and is characterized by a reduced reactivity. To contribute to such understanding, we compare here the hydration process of two cement samples, the simple cement paste and the cement paste containing calcium nitrate as an accelerator. The hydration of these samples is monitored during the induction period using two different low-field nuclear magnetic resonance (NMR) relaxometry techniques. The transverse relaxation measurements of the 1H nuclei at 20 MHz resonance frequency show that the capillary pore water is not consumed during the induction period and that this stage is shortened in the presence of calcium nitrate. The longitudinal relaxation measurements, performed at variable Larmor frequency of the 1H nuclei, reveal a continuous increase in the surface-to-volume ratio of the capillary...
Materials
Incorporating blast furnace slag into the composition of paving concrete can be one of the cost-e... more Incorporating blast furnace slag into the composition of paving concrete can be one of the cost-effective ways to completely eliminate by-products from the pig iron production process (approximately 70% granulated slag and 30% air-cooled slag). The possibility to reintroduce blast furnace slag back into the life cycle will provide significant support to current environmental concerns and the clearance of tailings landfills. Especially in recent years, granulated and ground blast furnace slag (GGBS) as a substitute for cement and air-cooled blast furnace slag (ACBFS) aggregates as a substitute for natural aggregates in the composition of concretes have been studied by many researchers. But concrete compositions with large amounts of incorporated blast furnace slag affect the mechanical and durability properties through the interaction between the slag, cement and water depending on the curing times. This study focuses on identifying the optimal proportions of GGBS as a supplementary ...
New Developments in NMR
Standard PGSE techniques have proven to be powerful and popular tools for diffusion studies in ma... more Standard PGSE techniques have proven to be powerful and popular tools for diffusion studies in materials. However, there are a number of challenges that might arise if the investigation is to refer to media of a more complex nature. Examples are heterogeneous, micro-textured, porous, granular, composite or high-viscosity materials. In these cases, there will be tendencies to anomalous diffusion, superimposed components, extremely small displacement rates, and displacement restrictions. Artifacts in the experiments or in interpretations can moreover be due to eddy currents, magneto-acoustic ringing, short-T2-limitations, and internal field gradients. In this chapter, alternative NMR techniques based on (a) strong, stationary field gradients in the fringe field of magnets, (b) rotating-frame imaging with the aid of gradients of the RF field amplitude, and (c) multiple stimulated echoes arising in modulated demagnetizing fields will be described. The common principle of all these variants is to generate a so-called grating of the z magnetization, which then tends to be leveled by translational displacements of the spin-bearing nuclei. It will be shown how such techniques can help to solve or avoid the before mentioned problems. Finally, it will be proposed to combine the diverse diffusometry techniques to cover an unsurpassed time scale ranging from microseconds to seconds with options to extend the scale even down to nanoseconds and up to hours or days by additionally referring to NMR relaxometry and microimaging methods, respectively.
The present study investigates the chemical composition governing the physical properties of mono... more The present study investigates the chemical composition governing the physical properties of mono- and diglycerides (MDGs) at the microstructural level, as a function of aging and lot-to-lot variability. The physical structure of the MDG plays a vital role in ameliorating the emulsion stability and is widely explored in diverse research horizons related to the pharmaceutical, cosmetic, and food industries. In an effort to understand the mechanism of emulsion stabilization, physical properties were extensively evaluated in selective commercial lots to determine if there is a correlation between the chemical composition of MDG and physical properties. The solid state of the MDG samples with different aging profiles was characterized using X-ray scattering, differential scanning calorimetry, attenuated total reflection-Fourier transform infrared spectroscopy, and NMR relaxometry. Moreover, the kinetic aspect of solid-state transformation was also evaluated via treating MDG samples with a heat-cool cycle. The chemical composition of MDGs was quantified using a quantitative NMR (qNMR) method. Interestingly, the X-ray scattering results demonstrated a change in the MDG polymorphic form and an increase in the %β content as a function of aging. The increase in the %β content led to the formation of rigid crystal structures of MDG, as evident from the NMR relaxometry. Chemical quantification of isomeric composition revealed chemical composition change as a potentially critical factor responsible for the altered physical structures of MDG with respect to aging and lot-to-lot variability. The findings correlated the solid-state transformation with the change in the chemical composition of the MDG as a combined effect of aging and lot-to-lot variability. This work serves as a basis to better understand the interdependency of the physicochemical properties of MDG. Furthermore, the present work can also be used as guidance for setting up the specifications of MDG, as per the required polymorphic form for a multitude of applications.
Journal of the Science of Food and Agriculture, 2021
BACKGROUND Adulteration is defined as the intentional addition of a material that is not a part o... more BACKGROUND Adulteration is defined as the intentional addition of a material that is not a part of the nature. In this study, a non-conventional time domain NMR (TD-NMR) pulse sequence: Magic Sandwich Echo (MSE) was used to detect the adulteration of honey by glucose (GS) and high fructose corn syrups (HFCS) accompanied with T1 and T2 relaxation times. Also, fast field cycling NMR (FFC NMR) relaxometry and multivariate analysis were performed to investigate the adulteration. RESULTS Higher maltose in GS and changing glucose to water ratio of HFCS gave high correlation with the crystal content values. In HFCS adulteration, two separate populations of protons having different T2 values were detected and T1 times were also used to determine GS adulteration. Addition of GS increased T1 while addition of HFCS increased T2 , significantly. CONCLUSION The results showed that it is possible to differentiate the unadulterated and adulterated honey samples by using TD-NMR relaxation times and crystal content values (CC) obtained by the MSE sequence. By FFC NMR relaxometry, not only GS addition but also the amount of GS was examined. The multivariate analysis technique of principal component analysis (PCA) was able to distinguish the types of adulterants. This article is protected by copyright. All rights reserved.
Fast Field Cycling (FFC) nuclear magnetic resonance (NMR) relaxometry is used to monitor the infl... more Fast Field Cycling (FFC) nuclear magnetic resonance (NMR) relaxometry is used to monitor the influence introduced on the hydration process by the addition of silica fume in a cement paste mixture, prepared with white Portland cement. The FFC relaxometry technique was implemented due to its sensitivity to a wider range of molecular motions, which gives more information than other relaxometry techniques performed at a fixed frequency. This unique feature of FFC relaxometry allows better separation of the surface and bulk contributions from the global measured relaxation rate. The relaxation process is dominated by the interaction of water protons with the paramagnetic centers located on the surface of cement grains. In the frame of a two-phase exchange model, this allows the monitoring of the influence of an addition of silica fume on the evolution of surface-to-volume ratio during the early hydration stages.
Molecular Physics, 2018
The hydration process of four different cement-based materials at different depths inside the sam... more The hydration process of four different cement-based materials at different depths inside the sample was investigated using localised nuclear magnetic resonance relaxation measurements. All the samples are based on white Portland cement (CEM I 42.5 R), with a water-to-cement ratio of 0.5. One sample is a simple cement paste and the other three additionally contain 5% (by mass of cement) silica nanoparticles (50-200 nm size), silanised silica nanoparticles (with silane A 174) or silica fume (80% silica; 0.15 µm average size). The localised transverse relaxation measurements were performed using a single-sided NMR instrument. The relaxation rates were monitored for 48 h during the hydration process at different depths inside the sample. The results showed that the presence of nanoparticles influences not only the speed of hydration overall, but also the homogeneity of the materials.
Analytical Letters, 2020
The need to develop specific magnetic nanostructures for resonance imaging becomes more evident b... more The need to develop specific magnetic nanostructures for resonance imaging becomes more evident by the day. In this study, iron oxide magnetic nanoparticles stabilized with ethylenediaminetetraacetic acid (EDTA), followed by a gadolinium (Gd) ion chelation reaction Gd-EDTA-MNPs were synthesized and evaluated as a potential magnetic resonance imaging contrast agent. The contrast agent has been developed by a facile and universal coordination chemistry method. The compositions, structures, as well as the physicochemical characterization techniques, are reported. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy demonstrate the success of gadolinium complexation by the carboxyl group of EDTA coated iron oxide nanoparticles. Cytotoxicity measurements have been performed using a cell culture of normal human keratinocytes (HaCaT cell line) and human malignant melanoma (A375). Our results show a significant increase in the transverse relaxivity induced by the complexation with gadolinium, 540 mM À1 s À1 for Gd-EDTA-MNPs. The longitudinal relaxation dispersion curves show one order of magnitude enhancement of the longitudinal relaxivity from 2.2 mM À1 s À1 (EDTA-MNPs) to 29.6 mM À1 s À1 (Gd-EDTA-MNPs) at a 20 MHz resonance frequency. The results suggest that Gd complexation may represent a viable approach in obtaining contrast agents able to reduce both T 1 and T 2 nuclear relaxation times.
The Journal of Physical Chemistry C, 2019
AIP Conference Proceedings, 2017
In the present work the liquid morphology, under partially saturated conditions inside two carbon... more In the present work the liquid morphology, under partially saturated conditions inside two carbon aerogel and xerogel samples, was investigated using the low-field nuclear magnetic resonance (NMR) relaxometry. Information about the tortuosity of the two samples was also extracted using pulse field gradient NMR diffusometry. The molecules under investigation were water and cyclohexane. They were chosen due to their different interaction with the carbonaceous matrix. It was found a non-uniform coverage of molecules on the pore surface except for the case of cyclohexane filled carbon xerogel when the distribution was uniform. It was also observed an influence of the cyclohexane- surface interaction on the tortuosity factor characterizing the xerogel sample.
Molecular Physics, 2018
The influence of silanised silica fume addition on the pore size distribution and wettability of ... more The influence of silanised silica fume addition on the pore size distribution and wettability of white cement paste was investigated using T 1-T 2 correlation nuclear magnetic resonance (NMR) relaxometry. Surface silanisation of silica fume particles was achieved by the hydrolysis reaction of APTES (3-Aminopropyltriethoxysilane) and condensation of the silanol functional groups on the surface. The methods used for characterisation of the silanised silica fume particles were scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). By adding silanised silica fume to the cement paste, the accessibility of water molecules to the porous system becomes restricted, leading to a lower permeability in comparison with the unmodified cement paste. Differential scanning calorimetry (DSC) measurements on the cement pastes saturated with Octamethylcyclotetrasiloxane confirm also that the size of inter-C-S-H and capillary pores is not influenced by the addition of silica fume in a detectable manner.
Magnetic Resonance in Chemistry, 2019
Low-field nuclear magnetic resonance techniques are employed to extract information about the eff... more Low-field nuclear magnetic resonance techniques are employed to extract information about the effects introduced by the interaction with the surface on the rotational and translational dynamics of molecules confined inside a mesoporous carbon xerogel. The molecules under study were water, cyclohexane, and hexane. They were chosen due to their different interaction strength with the carbonaceous matrix. Frequency dependent longitudinal relaxation measurements, using the fast field cycling technique, allowed extraction of the fractal dimension of the carbon xerogel surface. It was observed that the measured value is influenced by the molecule affinity to the surface. Diffusion measurements, using the pulse field gradient technique, have revealed that the stronger interaction with the surface of cyclohexane and hexane molecules leads to an increased diffusive tortuosity, as compared with water.
Applied Magnetic Resonance, 2015
AbstractNuclear magnetic resonance (NMR) relaxometry is used here as a noninvasive tool to monito... more AbstractNuclear magnetic resonance (NMR) relaxometry is used here as a noninvasive tool to monitor the influence introduced by the addition of 3-Aminopropyltriethoxysilane (APTES) on the hydration of pure cement paste and a cement paste containing quartz powder. It is observed extension of the dormancy stage up to 12 h in the presence of the aminosilane and a slight reduction in the size of capillary pores. The extension of the dormancy stage can be also associated with a slower hydration process which leads to enhancement of the final flexural strength in the case of sample containing quartz.
AIP Conference Proceedings, 2013
ABSTRACT In the present work we study the internal gradient effects on diffusion attenuation of t... more ABSTRACT In the present work we study the internal gradient effects on diffusion attenuation of the echo train appearing in the well-known Carr-Purcell-Meiboom-Gill (CPMG) technique, extensively used for transverse relaxation measurements. Our investigations are carried out on two porous ceramics, prepared with the same amount of magnetic impurities (Fe2O3) but different pore sizes. It is shown that diffusion effects on the CPMG echo train attenuation are strongly influenced by the pore size for the same magnetic susceptibility of the two samples. The experimental results were compared with a theoretical model taking into account the limit of free or restricted diffusion on echo train attenuation. The NMR experiments were performed on water filled samples using a low-field NMR instrument. The porous ceramics were prepared using both the replica technique and the powder compression technique. Magnetic susceptibility measurements indicated close values of the susceptibility constant for the two samples whereas the SEM images indicated different pore sizes. The results reported here may have impact in the interpretation of NMR relaxation measurements of water in soils or concrete samples.
ABSTRACT The residual monomer present in post-polymerized dental materials encourages premature d... more ABSTRACT The residual monomer present in post-polymerized dental materials encourages premature degradation of the reconstructed tooth. That is why the residual monomer should be quantified in a simple, fast, accurate and reproducible manner. In our work we propose such an approach for accurate determination of the residual monomer in dental materials which is based on low-field nuclear magnetic resonance (NMR) relaxometry. The results of the NMR approach are compared with those of the high performance liquid chromatography (HPLC) technique. The samples under study contain the main monomers (2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane and triethylene glycol dimethacrylate) constituting the liquid phase of most dental materials and an initiator. Two samples were analyzed with different ratios of chemical initiation systems: N,N-dimethyl-p-toluide: benzoyl peroxide (1:2 and 0.7:1.2). The results obtained by both techniques highlight that by reducing the initiator the polymerization process slows down and the amount of residual monomer reduces. This prevents the premature degradation of the dental fillings and consequently the reduction of the biomaterial resistance.
ABSTRACT In the present work, we study the transverse relaxation time evolution of water molecule... more ABSTRACT In the present work, we study the transverse relaxation time evolution of water molecules confined inside cement paste during the hydration process. The cement paste under study was manufactured with different water-to-cement ratios and using two types of cement: gray cement (CEM I 52.5 R) having a high content of magnetic impurities and white cement (CEM I 52.5 N) with lower amount of magnetic impurities. The two cement types were chosen in order to better distinguish the surface contribution to the relaxation process. On this basis a relationship between porosity evolution, ettringite formation and the transverse relaxation time evolution was established. It was also observed that the increase in the water-to-cement ratio better reveals the ettringite formation.
ChemInform, 2004
ABSTRACT Starting from basic differential equations for the description of ordinary and anomalous... more ABSTRACT Starting from basic differential equations for the description of ordinary and anomalous diffusion the theory of the standard field gradient pulse sequences for diffusion studies with the aid of NMR is developed. Anomalous diffusion can be due to an “obstruction effect” or to a “trapping effect” depending on the geometry and nature of the system matrix confining the diffusing particles. The NMR methods under consideration refer both to pulsed and steady field gradients, and both to laboratory and rotating-frame variants. The advantages and disadvantages are weighed up. More recent results refer to the attenuation of so-called multiple (or nonlinear) echoes by diffusion, and the use of internal field gradients for diffusion studies in fluid filled porous media. The diffusion of ordinary or laser-polarized gases is discussed for applications to porous media again. On a much longer time scale, isotope interdiffusion can be used as a technique for the elucidation of anomalous diffusion on percolation networks. A further and very distinct example of anomalous displacement characteristics was predicted for entangled polymers. Corresponding studies are reviewed and discussed with respect to the experimental limits. Finally, spin diffusion by flip-flop processes of dipolar coupled spins is shown to be a competitive mechanism if Brownian diffusion is strongly hindered by obstacles.
Applied Magnetic Resonance, 2014
In the present work, we use fast field cycling (FFC) nuclear magnetic resonance relaxometry to ev... more In the present work, we use fast field cycling (FFC) nuclear magnetic resonance relaxometry to evaluate the influence introduced by the curing temperature on the hydration process of gray cement. The main advantage of FFC relaxometry as compared with other relaxation studies performed at a specific frequency is that it is sensitive to a wider range of molecular motions and better separates the surface and bulk contributions from the global measured relaxation rate. In the case of cement hydration, the relaxation process is dominated by the interaction of water protons with the paramagnetic centers located on the surface of cement grains. This allows us in the frame of a two-phase exchange model to monitor the temperature dependence of the transverse diffusional correlation time at the surface of cement grains. An increase of the surface diffusion coefficient of water molecules with the temperature was revealed. Another outcome is that the surface-to-volume ratio of capillary pores continuously increases during the early hydration and this process is strongly enhanced by rising the temperature.