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•Diffusion-relaxation correlation maps in single-sided NMR.•Reduced experimental time with increased sensitivity.•Saturation recovery-diffusion is faster than diffusion-transverse ...relaxation.
Diffusion-relaxation correlation experiments in nuclear magnetic resonance are a powerful technique for the characterization of fluid dynamics in confined geometries or soft matter, in which relaxation may be either spin-spin (T2) or spin-lattice (T1). The general approach is to acquire a set of bidimensional data in which diffusion is codified by the evolution of the magnetization with either Hahn or stimulated echoes (STE) in the presence of a constant magnetic field gradient. While T2 is codified by a Carr-Purcell-Meiboom-Gil (CPMG) sequence, T1 is either encoded by saturation or inversion-recovery methods. In this work, we analyse the measurement time of diffusion-relaxation times in single-sided NMR and show that T1-D acquisition is always shorter than D-T2. Depending on the hardware characteristics, this time reduction can be up to an order of magnitude. We present analytical calculations and examples in model porous media saturated with water and in a dairy product.
Multiphase aqueous-organic systems where a bicontinuous phase is in equilibrium with an excess organic and aqueous phase find various applications in industry. These systemsalso known as Winsor ...IIIare complex not only for the different phases that develop therein but also because they are multicomponent systems. In this work, we explore for the first time the use of a benchtop low-field single-sided NMR to determine the species distribution in Winsor III systems. The proposed methodology provides information at macroscopic and microscopic levels. In particular, we show the use of single-sided NMR to determine the phases’ dimensions and the species distribution in a polymer-based bicontinuous system. The phases’ dimensions and limits can be resolved with micrometric precision and are indicative of the bicontinuous phase stability. The species distribution is determined by means of spatially resolved NMR relaxation and diffusion experiments. It was observed that the salinity of the aqueous phase also impacts the species distribution in the bicontinuous system. Experiments show that the additive and the polymer are mainly located in the bicontinuous phase. As the salinity of the aqueous phase increases, the amount of organic components in the bicontinuous phase decreases as a consequence of the species distribution in the system. This influences the total amount of recovered organic liquid from the organic phase. The information is obtained in a relatively fast experiment and is relevant to the system’s possible applications, such as enhanced oil recovery (EOR). This methodology is not only circumscribed to its application in EOR but can also be applied to the study of any emulsion or microemulsion systems without sample size or geometry constraints.
•Two-dimensional relaxation maps at low field NMR.•Kerogen and bitumen detection at low field NMR.•Simultaneous determination of liquid and solid components in unconventional reservoirs.•Acquisition ...of fast decaying signals enables the detection of solid components of rocks.
Quantification of organic matter and fluids contained in oil source rocks from shale plays is a fundamental goal for the petrophysical and geochemical assessment of the production potential of a well. Laboratory 1H nuclear magnetic resonance (NMR) is a fast, reliable, and non-destructive method widely used in the oil industry. Measurement of T1-T2 correlation maps have been found to be critical for identifying the presence of solid organic matter, liquid hydrocarbons, and brine in these formations. However, the inherent long echo times associated with standard laboratory equipment for large sample volume challenge the detection of contribution from kerogen and viscous bitumen. In this work, we use a commercial low field NMR rock-core analyzer where a novel T1- T2*&T2 pulse sequence is implemented to enable the detection of solid organic matter by acquiring the free induction decay after the first excitation pulse. This acquisition is followed by a train of refocusing pulses that generate multiple echoes from which liquid components are detected. A set of outcrop and well samples from the Vaca Muerta Formation in Argentina, with a varying amount of total organic content, were measured. The signal intensity assigned to solid matter was correlated with RockEval 6 pyrolisis. The novel pulse sequence presented here can be implemented in any commercial apparatus without the need for hardware modifications.
The ability to create extended porous networks, such as those composed of metal–organic frameworks (MOFs), with tailored hydrophilic/hydrophobic character is crucial for adapting such widely used ...supports to different applications. To achieve this goal, direct polymer inclusion has proven to be a suitable strategy, and functional composite materials with multiple additional properties have been obtained in such a way. We have explored, by means of nuclear magnetic resonance diffusion experiments, the effect of polymer capping using a conducting polymer (polyaminobencylaminePABA), which results in the positioning of −NH2 moieties on the otherwise eminently hydrophobic surface of Zn-based ZIF-8 MOF nanocrystals. Our results demonstrate that increasingly higher amounts of PABA can confer, aside from conductivity, an increased hydrophilic character to the porous network, while also allowing for the identification of different environments available for water molecule diffusion.
Relaxation in nuclear magnetic resonance (NMR), both transverse and longitudinal, provides information on microscopic features of a wide variety of systems and may be used to monitor dynamic ...processes such as cementation, chemical reactions, gelatinization, and evaporation. Dynamic relaxometry, in combination with spatial resolution, is a useful technique that provides deep insight into complex systems evolution. In this work, we explore the range of applicability of single-sided NMR to determine the evaporation kinetics of fluid from porous media. We show that, due to technical experimental restrictions, the determination of the time-dependent amount of fluid in different voids as a function of the position is in general not feasible with transverse relaxation experiments. However, as opposed to common intuition, longitudinal relaxation experiments provide reliable and fast acquisition, compatible with the requirements needed to monitor a water evaporation process from a model oil-reservoir rock sample.
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•Multi-imaging single-shot velocimetry.•Simultaneous determination of kinematic viscosity and transverse relaxation.•Rewinding of velocity encoding gradients in each EPI enables long ...echo train acquisition.
The ability of single-shot NMR imaging methods to follow the time evolution of a velocity distribution within an object is strongly limited by the phase errors accumulated as velocity maps are acquired. In the particular case of Carr-Purcell based sequences combined with Echo Planar Imaging acquisition, phase accumulates through subsequent images, hampering the possibility to acquire several velocity maps, which would be useful to determine transient behavior. In this work, we propose the use of a rewinding velocity encoding module applied after the acquisition of each image during the CPMG echo train. In this way, the first velocity module imparts a velocity dependent phase prior to the image acquisition and the second pair cancels this phase out before the next refocusing radiofrequency pulse is applied. The performance and limits of this method are studied by acquiring 100 images of a co-rotating Couette cell over a period of 1.6 s as a function of the rotation speed. The method is applied to determine the kinematic viscosity of a water/alcohol mixture, which is a relevant topic in many physical, chemical and biological processes.
NMR is a fast, nondestructive, and noninvasive technique that can provide information about the pore structure of macroporous polymer beads and the dynamics of liquids confined in them. In this work, ...we describe the study of the pore structure of the macroporous polymer of ethylene glycol dimethacrylate and 2-hydroxyethyl methacrylate poly(EGDMA-co-HEMA) in the dry but also in the swollen state by measuring relaxation times of liquids contained in the polymer network. The results show that the pore architecture differs from the dry to the soaked state. The behavior of polar liquids during evaporation and deswelling dynamics is monitored and described. An internal migration of water from the swollen polymer mesh into expanding pores takes place. With this procedure it is possible to obtain information about the microscopic morphology behavior of the matrix during evaporation and deswelling. This information is of great interest with the aspect of possible and future applications for these types of materials.
Hierarchical porous polymer systems are increasingly applied to catalysis, bioengineering, or separation technology because of the versatility provided by the connection of mesopores with percolating ...macroporous structures. Nuclear magnetic resonance (NMR) is a suitable technique for the study of such systems as it can detect signals stemming from the confined liquid and translate this information into pore size, molecular mobility, and liquid–surface interactions. We focus on the properties of water confined in macroporous polymers of ethylene glycol dimethacrylate and 2-hydroxyethyl methacrylate poly(EGDMA-co-HEMA) with different amounts of cross-linkers, in which a substantial variation of hydroxyl groups is achieved. As soft polymer scaffolds may swell upon saturation with determined liquids, the use of NMR is particularly important as it measures the system in its operational state. This study combines different NMR techniques to obtain information on surface interactions of water with hydrophilic polymer chains. A transition from a surface-induced relaxation in which relaxivity depends on the pore size to a regime where the organic pore surface strongly restricts water diffusion is observed. Surface affinities are defined through the molecular residence times near the network surface.
The characterization of non-crystalline complexes is particularly difficult when techniques like X-ray diffraction or NMR cannot be used. We propose a simple procedure to characterize the ...physicochemical properties of amorphous new coordination compounds between cyclodextrins (CD) and Cu(2+) salts, by means of the integration of the information provided by several techniques including elemental analysis, flame atomic absorption, TGA, UV-Vis diffuse reflectance, colorimetry, FT-IR and EPR. On the basis of these procedures, we suggest geometrical and structural approximations resulting in an octahedral or distorted octahedral geometry with diverse positions for the metallic centre. According to the EPR spectrum, only one of the complexes may have rhombic symmetry. We also analyzed enthalpy-entropy compensation and the isokinetic effect. In addition, general trends in thermal stability, spectroscopic properties and inclusion in the cavity were analysed. This complete characterization methodology becomes essential for their future application as catalysts.
In order to gain understanding about how “HA-like substances” from organic amendments may change some properties in the soil solution, the knowledge of chemical and physicochemical characteristics ...(charge development, acid–base behavior and heterogeneity) should be known.
The aim of this research were (i) to study the elemental and functional composition, (ii) to determine charge behavior, acid–base properties (apparent dissociation constant and buffer capacity) and (iii) to evaluate heterogeneity of humic acids (HA) isolated from municipal solid waste compost (MWC) and from the corresponding MWC-amended soil, in comparison to those of the unamended soil HA using potentiometric titration and differential scanning potentiometry (DSP).
Potentiometric titration and the first derivative of −
Q versus pH (negative charge development versus pH) curves could be used to determine proton-affinity distribution and the chemical heterogeneity of the HA as well as the average p
K
app and buffer capacity in a wide range of pH.
Differential scanning potentiometry allows determination of the p
K
app values in a narrower range of pH than potentiometric titrations and is another simple methodology to study acid–base behavior of HA.
DSP allows us to determine seven different p
K
app values for HA-S and HA-E and four different p
K
app for HA-C. Each one of these values corresponds to known acidic groups that can be present in the macromolecule of HA.
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