Low-field Nuclear Magnetic Resonance Technique Research Articles

New insights into the influencing mechanisms of hemicellulose removal on dynamic wood-water interactions characterized with low-field NMR

Hemicellulose, one of the most hygroscopic components, highly affected wood properties and wood-water interactions. To get more knowledge about the effects of hemicellulose on wood, this study changed hemicellulose content of wood through hydro-thermal removal of about 8 %, 20 % and 70 %. The dynamic cell water state and distribution during 384 h water absorption and air drying were characterized with low-field nuclear magnetic resonance technique (LFNMR). During water absorption, wood with less hemicellulose initially had higher and faster moisture increase, consisting of more free water in cell lumina and some large voids in cell walls than bound water in cell walls. The highest ratio of free water to bound water reached over 4.5, which was higher than that of untreated wood by over 15 %. This was because hemicellulose removal changed wood-water interaction environments suggested by SEM, FTIR and N2 absorption analysis. Specifically, hemicellulose removal enriched porous structures, especially the mesopore in cell walls. Although sorption sites decreased after hemicellulose removal, increased water paths and water accommodations played a more important role during initial water absorption. Besides, hemicellulose removal facilitated wood air drying, and the decreased moisture included more free water than bound water. This was because the enriched water paths accelerated water exchange, and sorption site decrease after hemicellulose loss reduced wood attraction to water molecules. Therein, the bound water leaving was generally slower than free water for hydrogen bond interaction with wood. The T2 s of bound water and free water were both shortened after hemicellulose removal, possibly because mesopore diameter reduction tightened wood-water bonding. This study provided new insights into understanding role of hemicellulose removal in dynamic wood-water interactions and facilitating development of wood processing technology.

Study on multi-performance optimization of basalt stone powder supplementary cementitious materials

In order to better apply basalt powder to supplementary cementitious materials (SCMs), this paper chooses the content of basalt stone powder, fly ash and slag as the influencing factors, and the 7d drying shrinkage rate, 28d drying shrinkage rate, fluidity, 7d and 28d compressive strength of mortar as the evaluation indexes of SCMs. Based on the response surface and multi-objective optimization method, the Box-Benken experimental design method was used to study the influence of the physical and chemical superposition of various factors on the properties of supplementary cementitious materials and optimize the ratio. The low-field nuclear magnetic resonance technique was used to detect the water change and porosity difference between the reference group and the optimization group at each age. The results show that the linear interaction and interaction of basalt powder, fly ash and slag have an effect on the strength, fluidity and drying shrinkage of cementitious materials. The optimal mixing ratio of basalt stone powder supplementary cementitious material is stone powder (10.8 %), fly ash (5 %) and slag (22.69 %). Under this mix ratio, the properties of basalt powder-assisted cementitious materials have been improved and close to the reference group. In the early hydration process, the physical filling effect of supplementary cementitious materials such as stone powder can better optimize the pore structure inside the slurry and the water loss is small, the strength is improved slowly, the dry shrinkage pure cement sample is similar, and the fluidity is improved. With the extension of hydration time, the water loss of the optimized group increased, and the strength and drying shrinkage increased.

Experimental Study on the Grouting Diffusion Process in Fractured Sandstone with Flowing Water Based on the Low-Field Nuclear Magnetic Resonance Technique

Experimental Study on the Grouting Diffusion Process in Fractured Sandstone with Flowing Water Based on the Low-Field Nuclear Magnetic Resonance Technique

Evaluation of visible spectroscopy and low-field nuclear magnetic resonance techniques for screening the presence of defects in broiler breast fillets

The potential of using simple visible spectroscopy (VIS) and low-field nuclear magnetic resonance (LF-NMR) was evaluated for differentiating three muscle conditions, normal (NORM), pale, soft and exudative (PSE), and woody breast (WB), in broiler pectoralis major. A total of 162 of pectoralis major, 54 for each condition, were collected from a commercial plant. Meat VIS spectra and transverse relaxation curve were collected using a spectrophotometer and LF-NMR, respectively. Principal component analyses (PCA) showed the better separation of PSE from NORM by VIS spectra. LF-NMR distinguished WB from NORM and PSE meat. However, the combination of VIS spectra and NMR relaxation curve differentiated the three conditions. PCA linear discriminant analysis and support vector machine discriminant analysis models further demonstrated that PCA analyses of combined VIS and LF-NMR data can correctly identify the presence of the defects in broiler breast meat.

A statistical learning perspective on the inversion of NMR relaxation data

T 2 distribution is a powerful tool in the low-field nuclear magnetic resonance technique. The T2 distribution obtained from time-domain data involves an ill-posed inverse Laplace transformation. Tikhonov regularization with an L2 penalty term is most commonly used in this kind of problem, and the discrepancy principle, generalized cross-validation, L-curve, and S-curve methods are widely used in the selection of the regularization parameter. However, these selection approaches require prior knowledge, such as an accurate estimation of the threshold level of noise or setting a default value. In this paper, we propose a new method—the stability-enhanced k-fold cross-validation (SECV) approach—to perform a robust automatic search for the regularization parameter from a statistical learning perspective. In addition to considering test set residuals, additional terms—the Pearson’s correlation coefficients of the solutions of the disjoint subsets—are put forward to enhance the stability of the solution and make a trade-off between its imitative effect and interpretability. A bimodal T2 distribution model was constructed, and abundant echo trains with different noise levels were generated for the validation of the proposed method. The relative error of the estimates is used as a measure to evaluate the performance. The inversion results from the SECV method were compared with the solutions from the conventional methods, and the results showed that the proposed method is robust without manual intervention and suitable for both low- and high-signal-to-noise ratio data. Finally, mercury injection and nuclear magnetic resonance experiments were carried out on rock core samples to verify the correctness of our method.

THE CORRELATION BETWEEN FLUID FLOW AND HEAT TRANSFER OF UNSATURATED SHALE RESERVOIR BASED ON FRACTAL GEOMETRY

The dissimilar multi-scale structures of shale to conventional reservoirs make it a challenge to understand the fluid flow and heat transfer through unsaturated shale formations. In this paper, the pore structure and moisture content of shale samples are measured by low-field nuclear magnetic resonance technique and thermogravimetric differential scanning calorimetry test, respectively. A pore-scale model is accordingly developed for the immiscible two-phase fluid flow and heat conduction through unsaturated shale based on the statistically self-similar fractal scaling law of pore size distribution. The analytical expressions of effective and relative permeability, as well as effective thermal conductivity (ETC), are proposed, which indicate good agreement with experimental results. It has been shown that the capillary pressure and gas slippage play important role in multiphase flow through unsaturated shale. Both pore and tortuosity fractal dimensions show significant influence on the relative permeability for nonwetting phase (RPNW), while they indicate the marginal effect on the relative permeability for the wetting phase (RPW). The ETC decreases with the increase of pore and tortuosity fractal dimensions, and it is positively and negatively correlated with RPW and RPNW, respectively. The correlation between ETC and relative permeability is found to follow a logistic function. The present fractal model can characterize the multiscale structures of shale reservoirs and may help understand transport mechanisms of immiscible multiphase flow and heat transfer through unsaturated shale.

Real-time characterization of the grouting diffusion process in fractured sandstone based on the low-field nuclear magnetic resonance technique

Investigations of the flow and diffusion mechanism of grout slurry in underground fractured rock mass are of critical significance to guarantee the grouting reinforcement of deep soft rock tunnel and to ensure the construction safety. This paper reports a series of permeation grouting tests in fractured sandstone samples based on the low-field nuclear magnetic resonance (LF-NMR) technique. During the grouting process, the NMR signal characteristics of the grout were monitored in real-time, and the parameters such as the slurry injection volume, effective grouting time and grout filling speed were comprehensively analyzed under various temperatures, confining pressures, flow velocities and numbers of fractures. The results show that the final injection amount of the grout decreases with increasing temperature and confining pressure. The effective grouting time is inversely proportional to the flow velocity, while it is positively related to the temperature. The filling speed decreases with increasing the temperature and confining pressure, while it increases with increasing the grout flow velocity. Compared to the single fractured sample, the sample with more fractures is injected with more grout slurry in a shorter effective grouting time and a higher filling speed. Under the conditions of high confining pressure (e.g., 15 MPa) or high flow velocity (e.g., ≥5 ml/min), the grout slurry preferentially transports into the micropores, and then the mesopores and macropores. However, the temperature and number of fractures have equal effects on the grout flow and diffusion in the three types of pores. The grouting filling performance becomes worse when the temperature and confining pressure are higher. The findings in this study provide meaningful guidance for the grouting reinforcement of deep soft rock tunnel.

Experimental investigation on the dynamic volume changes of varied-size pores during shale hydration

In order to improve the seepage channels in shale, soaking operation is often conducted after fracturing to carry out full shale hydration by the fracturing fluid. Previous research has mainly focused on the changes in the overall pore volume of shale due to hydration, but there is a lack of understanding on the volume changes of varied-size pores during the hydration process. In this study, a nuclear magnetic resonance (NMR) measurement method was carried out to obtain the size distribution of the pores in the shale in its unaltered state using ethanol as the saturation medium. Subsequently, through experiments, the shale core was saturated with fracturing fluid, and the dynamic changes in the pore size distribution under hydration were monitored using the low-field NMR technique. In addition, the relationships between the type of clay, the salinity of the fracturing fluid and the volume changes of varied-size pore were analyzed. The results of this study indicate that when the shale and fracturing fluid underwent hydration, the increase in the volumes of varied-size pores was concentrated in a certain pore-size area. This pore -size area was related to the type of clay that the shale contained. There was a strong correlation between the mixed-layer illite-smectite content and the increase in the small meso-pore volume. And the same between the illite content and the increase in the micro-pore volume. The saline fracturing fluid had an inhibitory effect on the shale hydration, mainly in the micro-pore domain. The results of this study is significant to optimize the selection of shale gas reservoirs and fracturing fluids for use in soaking measures.

Tailor-made microstructures lead to high-performance robust PEO membrane for CO2 capture via green fabrication technique

Emerging excessive greenhouse gas emissions pose great threats to the ecosystem, which thus requires efficient CO2 capture to mitigate the disastrous issue. In this report, large molecular size bisphenol A ethoxylate diacrylate (BPA) was employed to crosslink poly (ethylene glycol) methyl ether acrylate (PEGMEA) via the green and rapid UV polymerization strategy. The microstructure of such-prepared membrane could be conveniently tailored by tuning the ratio of the two prepolymers, aiming at obtaining the optimized microstructures with suitable mesh size and PEO sol content, which was approved by a novel low-field nuclear magnetic resonance technique. The optimum membrane overcomes the trade-off challenge: dense microstructures lower the gas permeability while loose microstructures lower high-pressure-resistance capacity, realizing a high CO2 permeability of 1711 Barrer and 100-h long-term running stability under 15 atm. The proposed membrane fabrication approach, hence, opens a novel gate for developing high-performance robust membranes for CO2 capture.

An experimental investigation in the formation damage mechanism of deposited coke in in-situ combustion process using nuclear magnetic resonance

The success of an in situ combustion process is dependent on the stability and movement of the combustion front. During an in situ combustion process, coke is an important product for maintaining the stability of the combustion front. However, before being consumed by the combustion reaction, coke is deposited in the porous media; thus, it may cause the blockage of the pore throat and affect the subsequent air injection. In this study, the low-field nuclear magnetic resonance technique was applied to examine the influence of oxidized coke and pyrolyzed coke on the porous media. The results revealed that the coke deposition phenomenon was considerable in porous media and affected porosity. The formation damage was considerably severe in oxidized coke because of the drastic low-temperature oxidation. In case of the pyrolyzed core, the influence of coke on porosity is limited because of the low amount of coke generation. The average reduction in porosity was 21.90%, while that of the pyrolyzed coke is only 9.09%. Montmorillonite had the greatest catalytic effect on coke deposition for both oxidation and pyrolysis processes. Illite, kaolinite, and chlorite have an impact on coke deposition; however, because the change in porosity is attribute to a combination of multiple factors, the result is a lack of regularity. Heat causes the pore to reform and the fracture to form. The change in porous media can reduce the impact of coke deposition phenomenon on total porosity. Because of the high-temperature environment, this influence is more pronounced in the pyrolyzed core.

Experimental research on methane hydrate formation in porous media based on the low-field NMR technique

In the experiment, three kinds of sandy soil tests with various particle sizes and starting water substances were chosen for analysis of methane hydrate formation in porous media. In this article, low-field nuclear magnetic resonance (NMR) innovation was utilized to consider methane hydrate the kinetics and to analyse the relationship among the adjustments in water signal force, the temperature and pressure, the various qualities of the T2 relaxation time, and the substance of unhydrated water. In view of the varieties in the NMR signal intensity, the methane-hydrate formation can be separated into four phases: induction, nucleation, growth, and steadiness. In addition, for the samples with particle size of 0.25–0.5 mm, the content of unhydrated water was higher. At a similar particle size, the content of unhydrated water increments with an increasing initial water content; thusly, low unhydrated water content for the most part exists in little and moderately enormous pores.

Behaviors of CO2 Hydrate Formation in the Presence of Acid-Dissolvable Organic Matters.

Carbon storage in the form of solid hydrate under seafloor has been considered to be promising for greenhouse gas control. Yet, open issues still remain on the role of the organic matters abundant in marine environments in the kinetics of hydrate formation; of particular interest is the involvement of the acid-dissolvable organic matters accompanying the acidification upon CO2 injection. In this work, the CO2 hydrate formation in the presence of the organic matters was in-situ monitored through the low-field nuclear magnetic resonance technique. It was found that the organic matters could kinetically promote the formation of CO2 hydrate; this effect was further enhanced by the sulfur-containing acid-dissolvable organic matters. Water in the large pores was preferentially consumed; the following water conversion facilitated by the organic matters would result in a fragmentation of the large pores into separated small pores isolated by the hydrate clusters. Consequently, a further enhancement of the gas-water contact is suggested as the existence of substantial hydrate patches could act as a mass transfer barrier. Our findings expand our understandings on the kinetics of CO2 hydrate formation in the presence of the organic matters and indicate the stability zone of gas hydrate a kinetically favorable geological setting for CO2 sequestration.

Effects of protein macromolecules and metabolic small molecules on kinetics of methane hydrate formation in marine clay

Numerous efforts have been made to mimic the natural marine environments to understand the behavior of hydrate formation and accumulation in the sediments under seafloor. Yet it is found that the role of organic matters in the kinetics of hydrate formation is largely veiled, which should be much enriched as a result of the activities of the marine ecosystem. Therefore in this study, the kinetic effects of protein macromolecules and metabolic small molecules on CH4 hydrate formation were examined; the organic compounds were extracted from the samples gathered from the hydrate reservoir located in the South China Sea. A total of 2058 species classified into 10 types of protein macromolecules and metabolic molecules were identified. Low-field nuclear magnetic resonance technique was used to in-situ monitor the hydrate formation process. The results showed that the metabolic molecules could remarkably promote hydrate formation, with more water converted into hydrate within a shorter time. Proteins have been widely studied to inhibit hydrate formation; here it is for the first time confirmed that the proteins extracted from the natural samples drilled in the hydrate reservoir could act as kinetic inhibitor, lowering the possibility of hydrate nucleation. It was further indicated that hydrate formation majorly consumed the water in the macro pores; this was followed by a diffusion-limitation process with the hydrate shell acting as mass transfer barrier slowing down the water conversion. The water in the micropores was yet found to be very difficult to participate in the reaction, potentially resulting from the unavailable gas-water contact. The findings could provide insights into the kinetics of hydrate formation in the presence of organic matters abundant in natural sediments and expand the current understandings on the occurrence of natural gas hydrate under marine environments.

Influence of water re-curing on microstructure of heat-damaged cement mortar characterized by low-field NMR and MIP

Water re-curing has been recognized as a potential method to recover the mechanical strength and durability of heat-damaged cement-based materials, which benefits from the improvement of its microstructure due to the rehydration and carbonation of dehydration products. In this contribution, the influence of water re-curing on the microstructure of heat-damaged cement mortar was evaluated by combining Mercury Intrusion Porosimetry (MIP) with low-field Nuclear Magnetic Resonance (LF-NMR). The heat-damaged cement mortar specimens were prepared through exposing to a series of ascending temperatures (105 °C, 200 °C, 400 °C, 600 °C, 800 °C). First, the influence of water re-curing on the porosity and pore size of the heat-damaged cement mortar was analysed with the results of MIP tests. Then, the microstructural evolution of the heat-damaged cement mortar was monitored by means of LF-NMR in the process of water re-curing. At last, a conversion of T2 spectra into pore size distribution (PSD) curves was performed. Causes for the difference in the PSD curves determined by LF-NMR and MIP were discussed. Results demonstrated that LF-NMR was a powerful tool to follow the microstructural evolution of heat-damaged mortar specimens during water re-curing. When combined with MIP tests, the LF-NMR technique can provide quantitative information with respect to the evolution of PSD in a nondestructive way. Capillary pores can be segmented into smaller pores due to the filling of products generated by the rehydration of dehydrated products. The microdamage was partially healed after 10.5 days of water re-curing. The original exposure temperature has a noteworthy impact on the recovery rate and level of the heat-damaged mortar during water re-curing.

Assessment of Water Mobility in Surf Clam and Soy Protein System during Gelation Using LF-NMR Technique.

Water mobility and distribution of a dual-protein system of surf clam myofibrillar protein (MP) and soy protein (SP) was investigated by the nondestructive low field nuclear magnetic resonance (LF-NMR) technique. Four proton populations were found in the contour plots of T2 relaxation times for the SP-MP system. The first component, (T21), was assigned to the highly integrated water located in protein macromolecules with a relaxation time of approximately 1.15 ms. The second signal, T22, with a relaxation time of 2.20 to 38.00 ms was regarded as the inter-myofibrillar water trapped in organized protein structures. The third component, T23, with a relaxation time of around 100 ms was ascribed to the extra-myofibrillar water. With an increase in temperature, T24 appeared which was assigned to the free water within the extra-myofibrillar space. The gelation behavior occurred at 70, 62, and 52 °C as the proportion of SP/MP was 4:6, 2:8, and 0:10, respectively. The principal component analysis (PCA) and heatmap of LF-NMR data analysis showed potential for distinguishing the different dual-protein systems formed at various temperatures. The analysis of storage modulus G′, loss modulus G″, and tanδ confirmed the change trend of the LF-NMR results. The measurements of cooking loss, water holding capability, and gel strength further revealed that the SP and MP were likely to form a gel network with an increase of additional clam protein. The hydrophobicity analysis showed, for the systems with the SP/MP proportions of 4:6, 2:8, and 0:10, more hydrophobic groups were exposed when the temperature was over 50 °C. Scanning electron microscopy showed that the number of the micropores increased with an addition of MP in the dual-protein system of SP/MP. All the results demonstrated that LF-NMR has great potential for characterizing the gelation process of a dual-protein system.

Effect of moisture transfer on texture uniformity of cooked rice after heat preservation with electric rice cooker

The texture uniformity of rice cooked by electric rice cooker (ERC) will deteriorate during the heat preservation process. In this study, the uniformity of rice texture and water dynamic were investigated by means of physical property analyzer and low-field nuclear magnetic resonance technique. The water content, distribution and migration in rice were compared to illustrate the effect of heat preservation mode with different temperature at pot cover. The middle-upper layer of rice was drier and harder after 24 h of heat preservation in conventional mode, while the outer-upper layer of rice absorbed water, swelled or even broken. The difference of water content between the two parts was 6.55%, and the difference of hardness was 333.31 g. The relaxation signal indicated that the binding force between immobile water of the two parts and the rice matrix became weaker after heat preservation. By adjusting the heat preservation mode with higher temperature of the cover, the moisture content difference between the internal-upper layer and the peripheral upper layer was decreased to 0.39% after 24 h of heat preservation, and the hardness difference was reduced to 2.99 g. These mean that the texture uniformity of the whole pot rice after heat preservation was maintained.

Determination of drying kinetics and quality changes of Panax quinquefolium L. dried in hot-blast air

The drying kinetics and quality changes of American ginseng dried in hot-blast air were studied at three temperatures (30, 40 and 50 °C). Low-field nuclear magnetic resonance (LF-NMR) and MRI techniques were used to study the water conditions and its distribution during the drying process. The experimental results show that the Henderson and Pabis model provided the best prediction of the drying process. The times at which the second phase began in the drying kinetic curve corresponded exactly with the turning point at which T2 free water decreased to its equilibrium with times of 168, 48 and 24 h at drying temperatures of 30, 40 and 50 °C, respectively. MRI image analysis showed that the internal moisture distribution of American ginseng was uneven, and that the water diffused inwards and outwards during the drying process. Based on the analysis of T2, color parameters and the HPLC data, the free water in American ginseng dissipated slowly at 30 °C, its color was brighter, and the content of ginsenosides was higher than at 40 and 50 °C. The LF-NMR technique can monitor the changes of the water state and predict the turning point of the sample drying curve during the drying process.

A novel pulse sequence and inversion algorithm of three-dimensional low field NMR technique in unconventional resources.

Compared with two-dimensional (2D) nuclear magnetic resonance (NMR) technique like correlations among the transversal relaxation time (T2), the longitudinal relaxation time (T1), and the diffusion coefficient correlation (D), three-dimensional (3D) NMR technique is superior with the complete measurement of T2, T1, and D simultaneously. It can solve the problem of overlaps in 2D correlation map and is helpful to characterize relaxation components in unconventional resources such as tight gas and oil shale. However, the existed 3D NMR technique is restricted due to the loss of short relaxation information and the inversion inaccuracy that caused by the incomplete measurement of the diffusion editing window. We developed a tri-window pulse sequence to collect the full decaying information of porous media. In the first window, the inversion-recovery pulse sequence is applied for T1 encoding. In the second window, D and T2 are encoded by an adjustable continuous pulse field gradient and echo spacing (TE). In the last window, CPMG with the shortest TE is used to acquire diffusion-free relaxation information. We then proposed a joint inversion algorithm named "composite-data-processing" to obtain the 3D correlation map. The algorithm adopts the dimension reduction technique and the truncated singular value decomposition (TSVD) to speed up the inversion process and enhance the inversion stability. Numerical simulations show that good estimations of the inversion results are obtained at different signal to noise ratios (SNRs). Our results suggest that the novel pulse sequence and inversion algorithm of 3D NMR can be effectively applied to the exploration of unconventional resources.

A Study of Gel-Based Conformance Control Within Fractured Carbonate Cores Using Low-Field Nuclear-Magnetic-Resonance Techniques

SummaryThe extreme heterogeneity of carbonate in the form of fracture corridors and superpermeability zones challenges the efficient sweep of oil in both secondary- and tertiary-recovery operations. In such reservoirs, conformance control is crucial to ensure injected water and any enhanced-oil-recovery (EOR) chemicals optimally contact the remaining oil with minimal throughput. Gel-based conformance control has been successfully applied on both sandstone and carbonate reservoirs. Achieving effective deep conformance control in high-temperature reservoirs, however, remains a challenge because of severe gel syneresis and significant reduction in gelation time. The first step to improve the performance of gel in these challenging environments is the accurate understanding of the gel-conformance-control mechanism inside reservoir rocks.In this work, a laboratory study was conducted to evaluate a polyacrylamide/chromium gel system for application in a high-temperature/high-salinity carbonate reservoir. Oil-displacement experiments on carbonate-core samples, combined with nuclear-magnetic-resonance (NMR) measurements, were performed to demonstrate oil-recovery improvement using gel treatment and to illustrate the mechanisms of the improvement. In these tests, the gel solution was injected into specially prepared heterogeneous carbonate-composite-core samples, in which different configurations of high-permeability channels were created. Gel treatment was conducted after waterflooding and was followed by chase waterflooding.Oil-recovery improvement by gel treatment was 18% of original oil in core (OOIC) in the composite core with high-permeability channels extending midway through the composite, whereas the improvement was 38% of OOIC in the composite core with channels extending all the way through the composite. Detailed spatial fluid variations inside the core samples before and after gel treatment were closely monitored using low-field NMR techniques. Heavy water (D2O) was used in place of water to enhance the contrast between oil and brine for NMR by eliminating the protons in the aqueous phase. NMR measurements indicated that the bypassed oil during waterflooding was effectively recovered after gel treatment.Results in this study demonstrate the potential of the studied gel system and its favorable effect on the sweep-efficiency-improvement application in high-temperature/high-salinity carbonate reservoirs. The NMR study enhances our understanding of how gel helps improve the sweep efficiency of subsequent floods through blocking/reducing the permeability of highly conductive zones.

Surface influence on the rotational and translational dynamics of molecules confined inside a mesoporous carbon xerogel.

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.