Surface Relaxation Rate Research Articles

Detecting pore size distribution of activated carbon by low-field nuclear magnetic resonance.

In this study, the transverse relaxation time (T2 ) of activated carbon (AC) in different relative environment humidity was detected firstly by low-field nuclear magnetic resonance (LFNMR). The pore size (diameter) of AC distributions was calculated by the relationship between T2 and surface relaxation rate (ρ), where ρ was obtained by the detection of nine porous materials with known pore size. The results showed that the pore size distributions of AC calculated by ρ < 0.19 nm/ms were in good agreement with that obtained by nitrogen adsorption method and proved that LFNMR as a new detection method was feasible for characterizing AC pore size distribution.

Fuzzy Random Characterization of Pore Structure in Frozen Sandstone: Applying Improved Niche Genetic Algorithm

Nuclear magnetic resonance (NMR) technology provides an innovative method employed in detecting the porous structures in frozen rock and soil masses. On the basis of NMR relaxation theory, fuzzy random characteristics of the NMR T2 spectrum and pore structure are deeply analyzed in accordance with the complex and uncertain distribution characteristics of the underground rock and soil structure. By studying the fuzzy random characteristics of the NMR T2 spectrum, the fuzzy random conversion coefficient and conversion method of the T2 spectrum and pore size distribution are generated. Based on the niche principle, the traditional genetic algorithm is updated by the fuzzy random method, and the improved niche genetic algorithm is proposed. Then, the fuzzy random inversion of the conversion coefficient is undertaken by using the improved algorithm. It in turn makes the conversion curve of the T2 spectrum and pore size distribution align with the mercury injection test curve in diverse pore apertures. Compared with the previous least square fitting method, it provides a more accurate approach in characterizing complicated pore structures in frozen rock and soil masses. In addition, the improved niche genetic algorithm effectively overcomes the shortcomings of the traditional genetic algorithm, such as low effectiveness, slow convergence, and weak controllability, which provides an effective way for parameter inversion in the section of frozen geotechnical engineering. Finally, based on the T2 spectrum test of frozen sandstone, the fuzzy random characterization of frozen sandstone pore distribution is carried out by using this transformation method. The results illustrate that the conversion coefficient obtained through the improved algorithm indirectly considers the different surface relaxation rates of different pore sizes and effectively reduces the diffusion coupling effects, and the pore characteristics achieved are more applicable in engineering practices than previous methods.

Simulations of Ion-Guiding Through Insulating Nanocapillaries of Varying Diameter: Interpretation of Experimental Results

The guiding of highly charged ions through a single nanocapillary is simulated in comparison with previous experiments performed with highly insulating polyethylene terephthalate (PET). The simulations are carried out using 3-keV Ne7+ ions injected into capillaries with diameters ranging from 100 nm to 400 nm. In the calculations, non-linear effects are applied to model the charge transport along the capillary surface and into the bulk depleting the deposited charges from the capillary walls. In addition to the surface carrier mobility, the non-linear effects are also implemented into the bulk conductivity. A method is presented to determine the parameters of the surface charge transport and the bulk conductivity by reproducing the oscillatory structure of the mean emission angle. A common set of charge depletion rates are determined with relatively high accuracy providing confidence in the present theoretical analysis. Significant differences in the oscillatory structures, experimentally observed, are explained by the calculations. Experimental and theoretical results of the guiding power for capillaries of different diameters are compared. Finally, dynamic non-linear effects on the surface and bulk relaxation rates are determined from the simulations.

Measurement of pore sized microporous-mesoporous materials by time-domain nuclear magnetic resonance

Time-domain nuclear magnetic resonance (TD NMR) technology has been used for pore detection in porous materials for a long time, but there are few pore detection methods for microporous-mesoporous materials. The surface of different materials is obtained by pore detection of known pore materials. Relaxation rate, which obtains aperture information, has an important practical significance for the application of time-domain NMR technology in the characterization of porous materials. In this study, the T2 peaks of pores of known pore size materials, namely zeolite molecular sieves (0.3 nm and 1 nm) and anodized aluminum porous membranes (30 nm and 90 nm), were used to calculate the pore surface relaxation of zeolite molecular sieve with 0.3 nm pore size and 1 nm pore size. The ratio of the rate of the surface is 3.379; the ratio of the pore surface relaxation ratio of the 30 nm and 90 nm apertures of the anodized aluminum porous film is 3.031. This result is very close to the pore size ratio, indicating that the surface relaxation rate of the same material is directly related to the pore size, while the T2 peak can qualitatively measure the pore size.

Method of determining the relaxation force of fish

There have been repeated cases of fish sales during the spawning period in the Ukrainian market, which consumer value is much lower, and fish re-freezing products. The aforementioned methods of abuse can be identified by commodity experts, while ordinary consumers, unfortunately, often cannot independently determine the quality of the fish. The basis of the vast majority of sensory checks of the elastic properties of fish is the process of compressing the product. The advantage of determining the surface relaxation rate is that it is non-destructive testing and the product appearance of the product after the examination does not change. However, this method requires some practical experience and depends essentially on the qualifications of an expert. The method and equipment for instrumental assessment of relaxation compression deformation force to define structural and mechanical properties of fish is given; it makes possible to minimize the experimenter influence on the results and obtain a quantitative value of relaxation speed at anytime in the experiment. The method of investigation of relaxation force and the rate of fish carcasses relaxation was theoretically grounded. A 3D-diagram of force that act on the indenter while pressing the surface of white cupid carcass is given. The type of dynamometer and measuring device for fixation of relaxation force dynamics is grounded. There was developed the sensor for determining the dynamics of the relaxation force with a constant depth of lowering of the indenter; scheme and photo of it is given. The mathematical models of relaxation velocity at axial deformation of compression and tension were constructed. The proposed method for quantifying the relaxation rate involves the construction of a compression deformation curve in the second of pressing a fish carcass and determining their angle of inclination. Based on the mathematical analysis of the deformation curves, it was found that for chilled meat of white cupid for 8 hours of storage, the relaxation rate at strain by 33% is greater than for the compression deformation; the primary force upon pressing on the product is 23% greater than when the specimen is subjected to a similar cross-sectional area. The developed methodology and system allows to determine the relaxation force when squeezing a fish sample just like a commodity science expert does and make quantitative assessment of its structural and mechanical properties.

Numerical simulation of multi-dimensional NMR response in tight sandstone

Conventional logging methods have limitations in the evaluation of tight sandstone reservoirs. The multi-dimensional nuclear magnetic resonance (NMR) logging method has the advantage that it can simultaneously measure transverse relaxation time (T 2), longitudinal relaxation time (T 1) and diffusion coefficient (D). In this paper, we simulate NMR measurements of tight sandstone with different wettability and saturations by the random walk method and obtain the magnetization decays of Carr–Purcell–Meiboom–Gill pulse sequences with different wait times (TW) and echo spacings (TE) under a magnetic field gradient, resulting in D-T 2-T 1 maps by the multiple echo trains joint inversion method. We also study the effects of wettability, saturation, signal-to-noise ratio (SNR) of data and restricted diffusion on the D-T 2-T 1 maps in tight sandstone. The results show that with decreasing wetting fluid saturation, the surface relaxation rate of the wetting fluid gradually increases and the restricted diffusion phenomenon becomes more and more obvious, which leads to the wetting fluid signal moving along the direction of short relaxation and the direction of the diffusion coefficient decreasing in D-T 2-T 1 maps. Meanwhile, the non-wetting fluid position in D-T 2-T 1 maps does not change with saturation variation. With decreasing SNR, the ability to identify water and oil signals based on NMR maps gradually decreases. The wetting fluid D-T 1 and D-T 2 correlations in NMR diffusion-relaxation maps of tight sandstone are obtained through expanding the wetting fluid restricted diffusion models, and are further applied to recognize the wetting fluid in simulated D-T 2 maps and D-T 1 maps.

A laboratory study to determine the effect of surface area and bead diameter on NMR relaxation rates of glass bead packs

ABSTRACTA laboratory study was conducted to explore the relationship between pore size, pore surface‐area‐to‐volume ratio and NMR relaxation rates and to determine which geometric parameter best predicts the average NMR relaxation rate. NMR relaxation measurements were collected on water‐saturated glass beads with controlled sets of bead diameters and surface areas. Four sets of beads were used with average diameters ranging from 55‐1125 m. The surface areas of the glass beads were altered by chemically treating the beads with a weak acid, a strong base and a cream commonly used to etch glass surfaces. Following the chemical treatments, the surface areas of the beads were quantified with krypton BET gas adsorption measurements. It was found that, for the range of bead diameters used in this study, relaxation did not strictly occur in the fast diffusion regime and, as such, the relaxation time associated with the peak of the largest mode in the distribution was found to more accurately represent the pore‐scale geometry than the mean log relaxation time. Using the relaxation time associated with this peak, the results from this study show that the pore surface‐area‐to‐volume ratio is a significantly better predictor of the surface relaxation rate than the mean grain radius ( = 0.014).

Dynamics of Surface Fluctuations on Macrocyclic Melts

A hydrodynamic continuum theory (HCT) of thermally stimulated capillary waves describing surface fluctuations of linear polystyrene melts is found to describe surface fluctuations of sufficiently thick films of unentangled cyclic polystyrene. However, for cyclic polystyrene (CPS) films thinner than 10Rg, the surface fluctuations are slower than expected from the HCT universal scaling, revealing a confinement effect active over length scales much larger than Rg. Surface fluctuations of CPS films can be slower than those of films of linear polystyrene analogues, due to differences between the glass transition temperatures, Tg, of the linear and cyclic chains. The temperature dependences of the surface fluctuations match those of bulk viscosities, suggesting that whole chain dynamics dictate the surface height fluctuation dynamics at temperatures 25–60 °C above Tg. When normalized surface relaxation rates of thicker films are plotted as a function of T/Tg, a universal temperature behavior is observed for lin...

Characteristics of the nuclear magnetic resonance logging response in fracture oil and gas reservoirs

Fracture oil and gas reservoirs exist in large numbers. The accurate logging evaluation of fracture reservoirs has puzzled petroleum geologists for a long time. Nuclear magnetic resonance (NMR) logging is an effective new technology for borehole measurement and formation evaluation. It has been widely applied in non-fracture reservoirs, and good results have been obtained. But its application in fracture reservoirs has rarely been reported in the literature. This paper studies systematically the impact of fracture parameters (width, number, angle, etc), the instrument parameter (antenna length) and the borehole condition (type of drilling fluid) on NMR logging by establishing the equation of the NMR logging response in fracture reservoirs. First, the relationship between the transverse relaxation time of fluid-saturated fracture and fracture aperture in the condition of different transverse surface relaxation rates was analyzed; then, the impact of the fracture aperture, dip angle, length of two kinds of antennas and mud type was calculated through forward modeling and inversion. The results show that the existence of fractures affects the NMR logging; the characteristics of the NMR logging response become more obvious with increasing fracture aperture and number of fractures. It is also found that T2 distribution from the fracture reservoir will be affected by echo spacing, type of drilling fluids and length of antennas. A long echo spacing is more sensitive to the type of drilling fluid. A short antenna is more effective for identifying fractures. In addition, the impact of fracture dip angle on NMR logging is affected by the antenna length.

A laboratory study of the effect of Fe(II)-bearing minerals on nuclear magnetic resonance (NMR) relaxation measurements

A laboratory study was conducted to measure the effect of the mineralogic form and concentration of iron(II) [Fe(II)] minerals on nuclear magnetic resonance (NMR) relaxation rates of water-saturated sand mixtures. We measured mixtures of quartz sand and three common Fe(II)-bearing minerals in granular form: siderite [Formula: see text], pyrite [Formula: see text], and pyrrhotite ([Formula: see text]; [Formula: see text]) at two concentrations of iron by weight. The NMR response of these samples was used to calculate four transverse relaxation rates for each Fe(II) mineral mixture: total mean log, bulk fluid, diffusion, and surface relaxation rates. The surface area of the samples was used to calculate the surface relaxivity of the sample and the magnetically active surface. For each iron mineral, the mean log and surface relaxation rates were greater for samples with higher Fe(II) concentration. For the siderite,pyrrhotite, and high-concentration pyrite mixtures, surface relaxation was the dominant relaxation mechanism. Bulk fluid relaxation contributed significantly to the total relaxation for the siderite and pyrite mixtures; for the low-concentration pyrite mixtures, bulk fluid relaxation was the dominant relaxation mechanism. For the pyrrhotite mixtures, the diffusion relaxation rate was nonzero and slower than the surface relaxation rate; for the siderite and pyrite mixtures, the diffusion relaxation rate was zero. Surface relaxivity calculations revealed that, for the pyrite mixtures, relaxation occurred in the fast diffusion regime; for the siderite and pyrrhotite mixtures, relaxation did not occur in the fast diffusion regime. The range of surface relaxivity values calculated depends on mineralogic form. We conclude that Fe(II) concentration and mineralogic form are important factors in determining relaxation rate.

Effects of organic film morphology on the formation of Rb clusters on surface coatings in alkali metal vapor cells

Surface relaxation rates differ for spin-polarized alkali atoms interacting with monolayer or bilayer octadecyltrichlorosilane (OTS) coatings. The morphology and composition of Rb vapor-exposed films of OTS have been studied with atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS). On OTS monolayers, numerous small (&amp;lt;500 nm wide) Rb containing islands nucleate at the boundaries of the ∼1–2 μm wide organic domains. On OTS bilayers, singular large (∼3 μm wide) Rb containing islands were found. Alkali island formation mediated by surface structure could affect the antirelaxation behavior of organic coatings used in atomic magnetometer cells.

High‐resolution NMR imaging of paramagnetic liposomes targeted to a functionalized surface

A major application of molecular MR imaging is receptor mapping of cells lining blood vessels with targeted contrast agents. Since these agents accumulate at interfaces, knowledge of their influence on the relaxation process in this specific configuration is a prerequisite for understanding their working principle. A methodology is presented to study the influence of targeted contrast agents on surface relaxation in vitro. Paramagnetic liposomes attached to a functionalized surface were studied with high-resolution NMR imaging. The surface was prepared by covering a solid substrate with a layer of collagen. Paramagnetic liposomes were targeted to this surface by functionalizing the liposomes with collagen adhesion protein CNA-35. With a saturation-recovery sequence, 1D magnetization profiles with a resolution of 5 microm were measured in water in contact with the surface. Analytical predictions, obtained with the Bloch-Torrey equation, perfectly agreed with the experimental data. Therefore, the magnitude of the surface relaxation rate could be determined from the measurements without any assumption. By using the relaxivity of liposome solutions the surface coverage by liposomes could be estimated. With the presented methodology the behavior of Gd-based targeted contrast agents at biological interfaces can be studied in vitro. Their influence on relaxation processes can be characterized and quantified.

A laboratory study of the effect of magnetite on NMR relaxation rates

We conducted a laboratory study to measure the effect of magnetite concentration and grain size on proton nuclear magnetic resonance (NMR) relaxation rates of sand mixtures and to determine the dominant mechanism by which relaxation occurs. We measured mixtures of quartz and three different forms of magnetite: a powdered synthetic magnetite; a small-grained, natural magnetite; and a large-grained, natural magnetite. The powdered synthetic magnetite was mixed with quartz in five concentrations ranging from 0.14 to 1.4% magnetite by weight; both sizes of natural magnetite were mixed with quartz in concentrations of 1 and 2% magnetite by weight. The NMR response of the water-saturated samples was measured and used to calculate four averaged relaxation rates for each magnetite concentration: the total mean log, bulk fluid, surface, and diffusion relaxation rates. The results of this study show that: 1) surface relaxation was the dominant relaxation mechanism for all samples except the powdered synthetic magnetite sample containing 1.4% magnetite; 2) the surface relaxivity is a function of the fraction of the surface area in the sample composed of magnetite; 3) there is no clear dependence of the diffusion relaxation rate on the concentration of magnetite.

A laboratory study to determine the effect of iron oxides on proton NMR measurements

Using laboratory methods, we investigate the effect of the presence and mineralogic form of iron on measured proton nuclear magnetic resonance (NMR) relaxation rates. Five samples of quartz sand were coated with ferrihydrite, goethite, hematite, lepidocrocite, and magnetite. The relaxation rates for these iron-oxide-coated sands saturated with water were measured and compared to the relaxation rate of quartz sand saturated with water. We found that the presence of the iron oxides led to increases in the relaxation rates by increasing the surface relaxation rate. The magnitude of the surface relaxation rate was different for the various iron-oxide minerals because of changes in both the surface-area-to-volume ratio of the pore space, and the surface relaxivity. The relaxation rate of the magnetite-coated sand was further increased because of internal magnetic field gradients caused by the presence of magnetite. We conclude that both the concentration and mineralogical form of iron can have a significant impact on NMR relaxation behavior.

Two-dimensional spectral-spatial image of highly oriented pyrolytic graphite

Experimentally observed electron paramagnetic resonance (EPR) spectra of highly oriented pyrolytic graphite samples can be considered as a sum of three signals coming from two adjacent faces and crystal edges. Contributions from faces can be analyzed analytically by Dyson’s theory based on an infinite flat conductive plate, while the contribution from edges is not described by this theory. Overlapping of these signals makes it difficult to get useful information about the sample from spectra observed. Implementation of two-dimensional spectral-spatial imaging technique proved to be helpful to solve this problem. It permits the characterization of the EPR spectrum from a selected flat spatial region located far from crystal edges where the model of the infinite flat conductive plate can be applied. By analyzing the EPR signal from spatial slices by Dyson’s equation we have obtained the values of the diffusion coefficient and the surface relaxation rate.

Wettability, Saturation, and Viscosity From NMR Measurements

Summary This paper discusses a new nuclear magnetic resonance (NMR) method that can provide wettability, saturation, and oil viscosity values in rocks partially saturated with oil and brine. The method takes advantage of two new technological advances in NMR well logging—the MRF* Magnetic Resonance Fluid Characterization Method and NMR "diffusion-editing" (DE) pulse sequences. We discuss the principles underlying the fluid characterization method and the pulse sequences. The fluid characterization method is used to provide robust inversions of DE data suites acquired on fully brine-saturated and partially saturated rock samples. The outputs of the inversion are separate diffusion-free brine and oil T2 distributions for the fluids measured in the rocks. NMR measurements on partially saturated rocks are sensitive to wettability because of surface relaxation of the wetting-phase fluid. The surface relaxation rate, however, must be significant compared to the bulk relaxation rate in order for wettability to noticeably affect the NMR response. We present results showing that the surface relaxation rate at lower wetting-phase saturations is enhanced compared to that measured at higher saturations. The consequence of wetting-phase saturation on NMR-based wettability determination is discussed. Wettability affects the relaxation rates of both the wetting and nonwetting phases in partially saturated rocks. Surface relaxation of the wetting phase in a rock results in shorter relaxation times than would otherwise be observed for the bulk fluid. The nonwetting-phase fluid molecules do not come into contact with the pore surfaces, and therefore their relaxation rate in the rock is the same as in the bulk fluid. We present accurate and robust computations of diffusion-free T2 relaxation time distributions for both the wetting and nonwetting phases in four rocks that include two sandstones and two dolomites. A DE data suite was acquired on each rock, measured in two different partial saturation states and also fully brine-saturated. Wettability is determined by comparing the oil and brine T2 relaxation-time distributions measured in the partially saturated rocks with the bulk oil T2 distribution and with the T2 distribution of the fully brine-saturated sample. The brine and oil T2 distributions are used to compute saturation and oil viscosity values. A general discussion elucidating the sensitivity range and T2 limits of diffusion-based NMR methods is given in the appendix. The appendix also derives and displays the gain in signal-to-noise ratio that is achieved by using DE data sequences for fluid characterization in place of Carr-Purcell-Meiboom-Gill (CPMG) data suites.

Hydrogen transport in nickel (111)

The intricate dynamics of hydrogen on a nickel (111) surface is investigated. The purpose is to understand the unique recombination reaction of subsurface with surface hydrogen on the nickel host. The analysis is based on the embedded diatomics in molecules many-body potential surface. This potential enables a consistent evaluation of different hydrogen pathways in the nickel host. It is found that the pathway to subsurface-surface hydrogen recombination involves crossing a potential-energy barrier. Due to the light mass of the hydrogen the primary reaction route at low temperature occurs via tunneling. A critical evaluation of tunneling dynamics in a many-body environment has been carried out, based on a fully quantum description. The activated transport of subsurface hydrogen to a surface site, the resurfacing event, has been studied in detail. It is shown that the tunneling dynamics is dominated by correlated motion of the hydrogen and the nickel hosts. A fully correlated quantum-dynamical description in a multimode environment was constructed and employed. The ``surrogate Hamiltonian method'' represents the nickel host effect on the hydrogen dynamics as that of a set of two-level systems. The spectral density, which is the input of the theory is obtained via classical molecular-dynamics simulations. The analysis then shows that the environment can both promote and hinder the tunneling rate by orders of magnitude. Specifically for hydrogen in the nickel host, the net effect is suppression of tunneling compared to a frozen lattice approximation. The added effect of nonadiabatic interactions with the electron-hole pairs on the hydrogen tunneling rate was studied by an appropriate ``surrogate Hamiltonian'' with the result of a small suppression depending on the electron density of nickel. The resurfacing rates together with surface recombination rates and relaxation rates were incorporated in a kinetic model describing thermal-desorption spectra. Conditions for a thermal-programmed-desorption peak which manifest the subsurface-surface hydrogen recombination were found.

NUCLEAR RELAXATION IN IRREGULAR OR FRACTAL PORES

We apply a fractal description of pore surface irregularity to study the nuclear relaxation of a liquid confined in an irregular pore. Our calculation on a pre-fractal volume with infinite surface relaxation rate shows that the long time relaxation behavior is dominated by an exponential mode characterizing a free diffusive volume. At short time, the calculated magnetization follows closely the power-law behavior previously proposed by de Gennes. For finite surface relaxation rate, we extend our studies of the efficiency of exchange on fractal membranes to nuclear relaxation in the same geometry. We predict a decay involving two characteristic times. For very slow surface relaxation, there will exist exponential relaxation governed by the surface relaxation. These laws show that the pore surface irregularities may play an important role in nuclear relaxation.

NUCLEAR RELAXATION IN IRREGULAR OR FRACTAL PORES

We apply a fractal description of pore surface irregularity to study the nuclear relaxation of a liquid confined in an irregular pore. Our calculation on a pre-fractal volume with infinite surface relaxation rate shows that the long time relaxation behavior is dominated by an exponential mode characterizing a free diffusive volume. At short time, the calculated magnetization follows closely the power-law behavior previously proposed by de Gennes. For finite surface relaxation rate, we extend our studies of the efficiency of exchange on fractal membranes to nuclear relaxation in the same geometry. We predict a decay involving two characteristic times. For very slow surface relaxation, there will exist exponential relaxation governed by the surface relaxation. These laws show that the pore surface irregularities may play an important role in nuclear relaxation.

Dynamic Penetration of Surfactant into an Insoluble Monolayer

We studied the dynamics of adsorption/desorption of soluble surfactant (C 12 E 6 ) into an insoluble n-dodecyl p-toluenesulfonate (DTS) monolayer at an air/wafer interface through stress relaxation experiments. The resulting surface tension changes due to a small imposed surface area disturbance, as a function of time, are measured using a capillary wave probe. We derived two theoretical models for this insoluble/soluble mixed surfactant system. The first assumes that adsorption/desorption of surfactant molecules in the presence of an insoluble monolayer is controlled by diffusive matter interchange between bulk and surface, while the second assumes that adsorption/desorption of the soluble component is controlled by an energy barrier mechanism due to the insoluble monolayer. It is found that measured stress relaxation experimental data are in good agreement with the diffusion-controlled model. Both the diffusion characteristic frequency, ω 0 , and high-frequency limit surface modulus, e 0 , were found to increase with increasing surface concentration of the insoluble monolayer. The increase in ω 0 , or the surface relaxation rate, is shown to be related to the static property (∂C 2 /∂Γ 2 )Γ 1 , where Γ 1 , Γ 2 , and Ca represent the surface concentrations of DTS and C 12 E 6 and the bulk concentration of C 12 E 6 , respectively