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Bhat A, Harris MT, Jaeger VW. Structural Insights into Self-Assembled Aerosol-OT Aggregates in Aqueous Media Using Atomistic Molecular Dynamics. J Phys Chem B 2021; 125:13789-13803. [PMID: 34898216 DOI: 10.1021/acs.jpcb.1c07136] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In water, the surfactant dioctyl sulfosuccinate (Aerosol-OT or AOT) exhibits diverse aggregate structures, ranging from micelles to lamella. An atomic-level understanding, however, of the formation and structure of these aggregates is lacking. Herein, using atomistic molecular dynamics (MD) with microsecond-long simulations, self-assembly of AOT in water is studied for concentrations of 1, 7.2, and 20 wt % at 293 K and for 7.2 wt % at 353 K. Assembly proceeds through stepwise association and dissociation of single AOT molecules, and the fusion and fission of AOT clusters. At 293 K, AOT self-assembles into either (i) spherical micelles (1 wt %), (ii) biphasic systems consisting of rod-like and prolate spheroidal micelles (7.2 wt %), or (iii) bilayers (20 wt %). We hypothesize that the observed rod-like structure is a precursor to lamellar microdomains found experimentally in biphasic dispersions. Increasing temperature to 353 K at 7.2 wt % results in a system consisting of prolate micelles but no rod-like micelles. Simulated phase behavior agrees with previously published experimental observations. Individual aggregates formed during self-assembly are identified using graph theory. Structural metrics of these aggregates like the radius of gyration, shape anisotropy, and prolateness are presented. Trends in structural metrics quantitatively reflect how shapes and sizes of AOT aggregates vary with surfactant concentration and temperature. These simulations provide deeper insight into open questions in the scientific community and demonstrate a method to generate physics-based micelle structures that can be used to rationalize experimental observations.
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Affiliation(s)
- Anuradha Bhat
- Division of Environmental and Ecological Engineering, Purdue University, Potter Engineering Center, 500 Central Drive, West Lafayette, Indiana 47907, United States
| | - Michael T Harris
- Davidson School of Chemical Engineering, Purdue University, Forney Hall of Chemical Engineering 1060, 480 Stadium Mall Drive, West Lafayette, Indiana 47907, United States
| | - Vance W Jaeger
- Department of Chemical Engineering, University of Louisville, Ernst Hall, Room 312, 216 Eastern Parkway, Louisville, Kentucky 40292, United States
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Nilsson M, Larsson J, Lundberg D, Szczepankiewicz F, Witzel T, Westin C, Bryskhe K, Topgaard D. Liquid crystal phantom for validation of microscopic diffusion anisotropy measurements on clinical MRI systems. Magn Reson Med 2018; 79:1817-1828. [PMID: 28686785 PMCID: PMC5756689 DOI: 10.1002/mrm.26814] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Revised: 05/21/2017] [Accepted: 06/08/2017] [Indexed: 01/05/2023]
Abstract
PURPOSE To develop a phantom for validating MRI pulse sequences and data processing methods to quantify microscopic diffusion anisotropy in the human brain. METHODS Using a liquid crystal consisting of water, detergent, and hydrocarbon, we designed a 0.5-L spherical phantom showing the theoretically highest possible degree of microscopic anisotropy. Data were acquired on the Connectome scanner using echo-planar imaging signal readout and diffusion encoding with axisymmetric b-tensors of varying magnitude, anisotropy, and orientation. The mean diffusivity, fractional anisotropy (FA), and microscopic FA (µFA) parameters were estimated. RESULTS The phantom was observed to have values of mean diffusivity similar to brain tissue, and relaxation times compatible with echo-planar imaging echo times on the order of 100 ms. The estimated values of µFA were at the theoretical maximum of 1.0, whereas the values of FA spanned the interval from 0.0 to 0.8 as a result of varying orientational order of the anisotropic domains within each voxel. CONCLUSIONS The proposed phantom can be manufactured by mixing three widely available chemicals in volumes comparable to a human head. The acquired data are in excellent agreement with theoretical predictions, showing that the phantom is ideal for validating methods for measuring microscopic diffusion anisotropy on clinical MRI systems. Magn Reson Med 79:1817-1828, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
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Affiliation(s)
- Markus Nilsson
- Diagnostic Radiology, Department of Clinical SciencesLund UniversityLundSweden
| | - Johan Larsson
- Physical Chemistry, Department of ChemistryLund UniversityLundSweden
| | | | | | - Thomas Witzel
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General HospitalHarvard Medical SchoolBostonMassachusettsUSA
| | | | | | - Daniel Topgaard
- Physical Chemistry, Department of ChemistryLund UniversityLundSweden
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Borsacchi S, Geppi M, Macchi S, Ninham BW, Fratini E, Ambrosi M, Baglioni P, Lo Nostro P. Phase transitions in hydrophobe/phospholipid mixtures: hints at connections between pheromones and anaesthetic activity. Phys Chem Chem Phys 2018; 18:15375-83. [PMID: 27210443 DOI: 10.1039/c6cp00659k] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The phase behavior of a mixture of a typical insect pheromone (olean) and a phospholipid (DOPC)/water dispersion is extensively explored through SAXS, NMR and DSC experiments. The results mimic those obtained with anaesthetics in phospholipid/water systems. They also mimic the behavior and microstructure of ternary mixtures of a membrane mimetic, bilayer-forming double chained surfactants, oils and water. Taken together with recent models for conduction of the nervous impulse, all hint at lipid involvement and the underlying unity in mechanisms of pheromone, anaesthetic and hydrophobic drugs, where a local phase change in the lipid membrane architecture may be at least partly involved in the transmission of the signal.
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Affiliation(s)
- Silvia Borsacchi
- Istituto di Chimica dei Composti OrganoMetallici (ICCOM) del CNR, 56124 Pisa, Italy
| | - Marco Geppi
- Department of Chemistry and Industrial Chemistry, University of Pisa, 56124 Pisa, Italy
| | - Sara Macchi
- Department of Chemistry and Industrial Chemistry, University of Pisa, 56124 Pisa, Italy
| | - Barry W Ninham
- Department of Chemistry & CSGI, University of Florence, 50019 Sesto Fiorentino (Firenze), Italy. and Department of Applied Mathematics, Research School of Physical Sciences and Engineering, Australian National University, Canberra, ACT 0200, Australia
| | - Emiliano Fratini
- Department of Chemistry & CSGI, University of Florence, 50019 Sesto Fiorentino (Firenze), Italy.
| | - Moira Ambrosi
- Department of Chemistry & CSGI, University of Florence, 50019 Sesto Fiorentino (Firenze), Italy.
| | - Piero Baglioni
- Department of Chemistry & CSGI, University of Florence, 50019 Sesto Fiorentino (Firenze), Italy. and Enzo Ferroni Foundation, 50019 Sesto Fiorentino (Firenze), Italy
| | - Pierandrea Lo Nostro
- Department of Chemistry & CSGI, University of Florence, 50019 Sesto Fiorentino (Firenze), Italy. and Enzo Ferroni Foundation, 50019 Sesto Fiorentino (Firenze), Italy
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Benjamini D, Komlosh ME, Basser PJ. Imaging Local Diffusive Dynamics Using Diffusion Exchange Spectroscopy MRI. PHYSICAL REVIEW LETTERS 2017; 118:158003. [PMID: 28452522 PMCID: PMC11079612 DOI: 10.1103/physrevlett.118.158003] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2016] [Indexed: 06/07/2023]
Abstract
The movement of water between microenvironments presents a central challenge in the physics of soft matter and porous media. Diffusion exchange spectroscopy (DEXSY) is a powerful 2D nuclear magnetic resonance method for measuring such exchange, yet it is rarely used because of its long scan time requirements. Moreover, it has never been combined with magnetic resonance imaging (MRI). Using probability theory, we vastly reduce the required data, making DEXSY MRI feasible for the first time. Experiments are performed on a composite nerve tissue phantom with restricted and free water-exchanging compartments.
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Affiliation(s)
- Dan Benjamini
- Section on Quantitative Imaging and Tissue Sciences, NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Michal E. Komlosh
- Section on Quantitative Imaging and Tissue Sciences, NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA
- Center for Neuroscience and Regenerative Medicine, Henry M. Jackson Foundation for the Advancement of Military Medicine, Bethesda, Maryland 20892, USA
| | - Peter J. Basser
- Section on Quantitative Imaging and Tissue Sciences, NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA
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Topgaard D. Director orientations in lyotropic liquid crystals: diffusion MRI mapping of the Saupe order tensor. Phys Chem Chem Phys 2016; 18:8545-53. [PMID: 26948308 DOI: 10.1039/c5cp07251d] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The macroscopic physical properties of a liquid crystalline material depend on both the properties of the individual crystallites and the details of their spatial arrangement. We propose a diffusion MRI method to estimate the director orientations of a lyotropic liquid crystal as a spatially resolved field of Saupe order tensors. The method relies on varying the shape of the diffusion-encoding tensor to disentangle the effects of voxel-scale director orientational order and the local diffusion anisotropy of the solvent. Proof-of-concept experiments are performed on water in lamellar and reverse hexagonal liquid crystalline systems with intricate patterns of director orientations.
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Affiliation(s)
- Daniel Topgaard
- Division of Physical Chemistry, Department of Chemistry, Lund University, Lund, Sweden.
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Bernin D, Koch V, Nydén M, Topgaard D. Multi-scale characterization of lyotropic liquid crystals using 2H and diffusion MRI with spatial resolution in three dimensions. PLoS One 2014; 9:e98752. [PMID: 24905818 PMCID: PMC4048170 DOI: 10.1371/journal.pone.0098752] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2014] [Accepted: 05/07/2014] [Indexed: 11/19/2022] Open
Abstract
The ability of lyotropic liquid crystals to form intricate structures on a range of length scales can be utilized for the synthesis of structurally complex inorganic materials, as well as in devices for controlled drug delivery. Here we employ magnetic resonance imaging (MRI) for non-invasive characterization of nano-, micro-, and millimeter scale structures in liquid crystals. The structure is mirrored in the translational and rotational motion of the water, which we assess by measuring spatially resolved self-diffusion tensors and spectra. Our approach differs from previous works in that the MRI parameters are mapped with spatial resolution in all three dimensions, thus allowing for detailed studies of liquid crystals with complex millimeter-scale morphologies that are stable on the measurement time-scale of 10 hours. The data conveys information on the nanometer-scale structure of the liquid crystalline phase, while the combination of diffusion and data permits an estimate of the orientational distribution of micrometer-scale anisotropic domains. We study lamellar phases consisting of the nonionic surfactant C10E3 in O, and follow their structural equilibration after a temperature jump and the cessation of shear. Our experimental approach may be useful for detailed characterization of liquid crystalline materials with structures on multiple length scales, as well as for studying the mechanisms of phase transitions.
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Affiliation(s)
- Diana Bernin
- Applied Surface Chemistry, Chalmers University of Technology, Gothenburg, Sweden
- Swedish NMR Centre, University of Gothenburg, Gothenburg, Sweden
| | - Vanessa Koch
- Division of Physical Chemistry, Department of Chemistry, Lund University, Lund, Sweden
| | - Magnus Nydén
- Ian Wark Research Institute, University of South Australia, Adelaide, South Australia, Australia
| | - Daniel Topgaard
- Division of Physical Chemistry, Department of Chemistry, Lund University, Lund, Sweden
- * E-mail:
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Bernin D, Topgaard D. NMR diffusion and relaxation correlation methods: New insights in heterogeneous materials. Curr Opin Colloid Interface Sci 2013. [DOI: 10.1016/j.cocis.2013.03.007] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Kumar SKK, Tamimi A, Fayer MD. Dynamics in the interior of AOT lamellae investigated with two-dimensional infrared spectroscopy. J Am Chem Soc 2013; 135:5118-26. [PMID: 23465101 DOI: 10.1021/ja312676e] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The dynamics inside the organic regions of aerosol-OT (AOT)/water mixtures in the lamellar mesophase, bicontinuous cubic (BC) phase, and in an analogous molecule without the charged sulfonate headgroup are investigated by observing spectral diffusion, orientational relaxation and population relaxation using ultrafast two-dimensional infrared (2D IR) vibrational echo spectroscopy and IR pump-probe experiments on the asymmetric CO stretch of a vibrational probe, tungsten hexacarbonyl (W(CO)6). The water layer thickness between the bilayer planes in the lamellar phase was varied. For comparison, the dynamics of W(CO)6 in the normal liquid bis(2-ethylhexyl) succinate (EHS), which is analogous to AOT but has no charged sulfonate headgroup, were also studied. The 2D IR experiments measure spectral diffusion, which results from the structural evolution of the system. Spectral diffusion is quantified by the frequency-frequency correlation function (FFCF). In addition to a homogeneous component, the FFCFs are biexponential decays with fast and slow time components of ∼12.5 and ∼150 ps in the lamellar phase. Both components of the FFCF are independent of the number of water molecules per headgroup for the lamellae, but they slow somewhat in the BC phase. The dynamics in the ordered phases are in sharp contrast to the dynamics in EHS, which displays fast and slow components of the FFCF of 5 and 80 ps, respectively. As the hydration level of AOT increases, vibrational lifetime decreases, suggesting some change in the local environment of W(CO)6 with water content.
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Affiliation(s)
- S K Karthick Kumar
- Department of Chemistry, Stanford University , Stanford, California 94305, United States
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Eriksson S, Lasic S, Topgaard D. Isotropic diffusion weighting in PGSE NMR by magic-angle spinning of the q-vector. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2013. [PMID: 23178533 DOI: 10.1016/j.jmr.2012.10.015] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
When PGSE NMR is applied to water in microheterogeneous materials such as liquid crystals, foodstuffs, porous rocks, and biological tissues, the signal attenuation is often multi-exponential, indicating the presence of pores having a range of sizes or anisotropic domains having a spread of orientations. Here we modify the standard PGSE experiment by introducing low-amplitude harmonically modulated gradients, which effectively make the q-vector perform magic-angle spinning (MAS) about an axis fixed in the laboratory frame. With this new technique, denoted q-MAS PGSE, the signal attenuation depends on the isotropic average of the local diffusion tensor. The capability of q-MAS PGSE to distinguish between pore size and domain orientation dispersion is demonstrated by experiments on a yeast cell suspension and a polydomain anisotropic liquid crystal. In the latter case, the broad distribution of apparent diffusivities observed with PGSE is narrowed to its isotropic average with q-MAS PGSE in a manner that is analogous to the narrowing of chemical shift anisotropy powder patterns using magic-angle sample spinning in solid-state NMR. The new q-MAS PGSE technique could be useful for resolving size/orientation ambiguities in the interpretation of PGSE data from, e.g., water confined within the axons of human brain tissue.
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Moilanen DE, Fenn EE, Wong D, Fayer MD. Geometry and nanolength scales versus interface interactions: water dynamics in AOT lamellar structures and reverse micelles. J Am Chem Soc 2009; 131:8318-28. [PMID: 19449867 DOI: 10.1021/ja901950b] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
To determine the relative importance of the confining geometry and nanoscopic length scale versus water/interface interactions, the dynamic interactions between water and interfaces are studied with ultrafast infrared spectroscopy. Aerosol OT (AOT) is a surfactant that can form two-dimensional lamellar structures with known water layer thickness as well as well-defined monodispersed spherical reverse micelles of known water nanopool diameter. Lamellar structures and reverse micelles are compared based on two criteria: surface-to-surface dimensions to study the effect of confining length scales, and water-to-surfactant ratio to study water/interface interactions. We show that the water-to-surfactant ratio is the dominant factor governing the nature of water interacting with an interface, not the characteristic nanoscopic distance. The detailed structure of the interface and the specific interactions between water and the interface also play a critical role in the fraction of water molecules influenced by the surface. A two-component model in which water is separated into bulk-like water in the center of the lamellar structure or reverse micelle and interfacial water is used to quantitatively extract the interfacial dynamics. A greater number of perturbed water molecules are present in the lamellar structures as compared to the reverse micelles due to the larger surface area per AOT molecule and the greater penetration of water molecules past the sulfonate head groups in the lamellar structures.
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Affiliation(s)
- David E Moilanen
- Department of Chemistry, Stanford University, Stanford, California 94305, USA
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Ozarslan E. Compartment shape anisotropy (CSA) revealed by double pulsed field gradient MR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2009; 199:56-67. [PMID: 19398210 PMCID: PMC2696938 DOI: 10.1016/j.jmr.2009.04.002] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2009] [Revised: 03/25/2009] [Accepted: 04/03/2009] [Indexed: 05/08/2023]
Abstract
The multiple scattering extensions of the pulsed field gradient (PFG) experiments can be used to characterize restriction-induced anisotropy at different length scales. In double-PFG acquisitions that involve two pairs of diffusion gradient pulses, the dependence of the MR signal attenuation on the angle between the two gradients is a signature of restriction that can be observed even at low gradient strengths. In this article, a comprehensive theoretical treatment of the double-PFG observation of restricted diffusion is presented. In the first part of the article, the problem is treated for arbitrarily shaped pores under idealized experimental conditions, comprising infinitesimally narrow gradient pulses with long separation times and long or vanishing mixing times. New insights are obtained when the treatment is applied to simple pore shapes of spheres, ellipsoids, and capped cylinders. The capped cylinder geometry is considered in the second part of the article where the solution for a double-PFG experiment with arbitrary experimental parameters is introduced. Although compartment shape anisotropy (CSA) is emphasized here, the findings of this article can be used in gleaning the volume, eccentricity, and orientation distribution function associated with ensembles of anisotropic compartments using double-PFG acquisitions with arbitrary experimental parameters.
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Affiliation(s)
- Evren Ozarslan
- Section on Tissue Biophysics and Biomimetics, NICHD, National Institutes of Health, Bethesda, MD 20892, USA.
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Eastoe J, Zou A, Espidel Y, Glatter O, Grillo I. Photo-labile lamellar phases. SOFT MATTER 2008; 4:1215-1218. [PMID: 32907264 DOI: 10.1039/b802357c] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
UV light can be used to change ordering in lyotropic lamellar (Lα) phases containing a photolyzable anionic surfactant 4-hexylphenylazosulfonate (C6PAS).
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Affiliation(s)
- Julian Eastoe
- School of Chemistry, University of Bristol, Bristol, UKBS8 1TS.
| | - Aihua Zou
- School of Chemistry, University of Bristol, Bristol, UKBS8 1TS.
| | - Youssef Espidel
- School of Chemistry, University of Bristol, Bristol, UKBS8 1TS.
| | - Otto Glatter
- Institut für Chemie, Karl-Franzens Universität Graz, 8010 Graz, Austria
| | - Isabelle Grillo
- Institut Max-Von-Laue-Paul-Langevin, BP 156-X, F-38042 Grenoble, Cedex, France
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Ozarslan E, Basser PJ. Microscopic anisotropy revealed by NMR double pulsed field gradient experiments with arbitrary timing parameters. J Chem Phys 2008; 128:154511. [PMID: 18433239 PMCID: PMC2809669 DOI: 10.1063/1.2905765] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2008] [Accepted: 03/14/2008] [Indexed: 11/14/2022] Open
Abstract
We consider a general double pulsed field gradient experiment with arbitrary experimental parameters and calculate an exact expression for the NMR signal attenuation from restricted geometries, which is valid at long wavelengths, i.e., when the product of the gyromagnetic ratio of the spins, the pulsed gradients' duration, and their magnitude is small compared to the reciprocal of the pore size. It is possible to observe microscopic anisotropy within the pore space induced by the boundaries of the pore, which can be used to differentiate restricted from free or multicompartmental diffusion and to estimate a characteristic pore dimension in the former case. Explicit solutions for diffusion taking place between parallel plates as well as in cylindrical and spherical pores are provided. In coherently packed cylindrical pores, it is possible to measure simultaneously the cylinders' orientation and diameter using small gradient strengths. The presence of orientational heterogeneity of cylinders is addressed, and a scheme for differentiating microscopic from ensemble anisotropy is proposed.
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Affiliation(s)
- Evren Ozarslan
- Section on Tissue Biophysics and Biomimetics, NICHD, NIH, Bethesda, MD 20892, USA.
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