Characteristic length scales of the secondary relaxations in glass-forming glycerol

We investigate the secondary relaxations and their link to the main structural relaxation in glass-forming liquids using glycerol as a model system. We analyze the incoherent neutron scattering signal dependence on the scattering momentum transfer, Q , in order to obtain the characteristic length scale for different secondary relaxations. Such a capability of neutron scattering makes it somewhat unique and highly complementary to the traditional techniques of glass physics, such as light scattering and broadband dielectric spectroscopy, which provide information on the time scale, but not the length scales, of relaxation processes. The choice of suitable neutron scattering techniques depends on the time scale of the relaxation of interest. We use neutron backscattering to identify the characteristic length scale of 0.7 Å for the faster secondary relaxation described in the framework of the mode-coupling theory (MCT). Neutron spin-echo is employed to probe the slower secondary relaxation of the excess wing type at a low temperature ( ∼ 1.13Tg . The characteristic length scale for this excess wing dynamics is approximately 4.7 Å. Besides the Q -dependence, the direct coupling of neutron scattering signal to density fluctuation makes this technique indispensable for measuring the length scale of the microscopic relaxation dynamics

Characterization of natural porous media by NMR and MRI techniques: High and low magnetic field studies for hydraulic properties estimation

Soil is the natural material that covers most of the dry surface of the earth. It is the product of mechanical, chemical and biological interactions of different types of elements. Soils have a very complex composition and high variability in their occurrence and properties. The non-homogeneous mixture and interaction of their components and the changes induced upon usage ensures the complexity of their structure and a comfortable variable spatial distribution over the surface of the planet. The soils components can be found in nature in all the three aggregation states of matter: the solid state, the liquid state and the gas state. In spite of their complex structure and composition, soils can be easily handled and studied by a variety of methods. [Koorevaar, 1983] Prediction of water movement in soils is a controlling factor in various processes of interest in water resources management such as: the runoff generation, the water and nutrients supply to vegetation, the groundwater recharge and contamination. From the physics point of view water distribution and transport in unsaturated soil represents a rather complex problem of porous media hydraulics. Among various techniques developed for investigating hydraulic phenomena in soils, Nuclear Magnetic Resonance (NMR) can be used successfully for the characterization of natural porous media

Characterization of natural porous media by NMR and MRI techniques : high and low magnetic field studies for estimation of hydraulic properties

Soil is the natural material that covers most of the dry surface of the earth. It is the product of mechanical, chemical and biological interactions of different types of elements. Soils have a very complex composition and high variability in their occurrence and properties. The non-homogeneous mixture and interaction of their components and the changes induced upon usage ensures the complexity of their structure and a comfortable variable spatial distribution over the surface of the planet. The soils components can be found in nature in all the three aggregation states of matter: the solid state, the liquid state and the gas state. In spite of their complex structure and composition, soils can be easily handled and studied by a variety of methods. Prediction of water movement in soils is a controlling factor in various processes of interest in water resources management such as: the runoff generation, the water and nutrients supply to vegetation, the groundwater recharge and contamination. From the physics point of view water distribution and transport in unsaturated soil represents a rather complex problem of porous media hydraulics. Among various techniques developed for investigating hydraulic phenomena in soils, Nuclear Magnetic Resonance (NMR) can be used successfully for the characterization of natural porous media. The aim of this thesis is to apply different NMR techniques for: i) understanding the relaxometric properties of unsaturated natural porous media and ii) for a reliable quantification of water content and its spatial and temporal change in model porous media and soil cores. For that purpose, porous media with increasing complexity and heterogeneity were used (coarse and fine sand and different mixture of sand/clay) to determine the relaxation parameters in order to adapt optimal sequence and parameters for water imaging. Conventional imaging is mostly performed with superconducting high field scanners but low field scanners promise longer relaxation times and therefore smaller loss of signal from water in small and partially filled pores. By this reason high and low field NMR experiments were conducted on these porous media to characterize the dependence on the magnetic field strength. Correlations of the NMR experiments with classical soil physics method like mercury intrusion porosimetry; water retention curves (pF) and multi-step-outflow (MSO) were performed for the characterization of the hydraulic properties of the materials. Due to the extensive research the experiments have been structured in three major parts as follows. In the first part a comparison study between relaxation experiments in high and low magnetic field was performed in order to observe the influence of the magnetic field on the relaxation properties. Due to these results, in the second part of the study only low field relaxation experiments were used in the attempt of correlations with classical soil physics methods (mercury intrusion porosimetry and water retention curves) for characterizing the hydraulic behavior of the samples. Further, the aim was to combine also MRI experiments (2D and 3D NMR) with classical soil physics methods (multi-step-outflow, MSO) for the same purpose of investigating the hydraulic properties. Because low field MRI systems are still under developing for the moment, the MRI experiments were performed in high magnetic field and combined with MSO experiments in order to asses the changes in water content over the depth of the samples during pressure application, changes that are governed by the hydraulic properties of the material. The thesis is structured into 7 chapters. First chapter is an introduction to actual state of NMR research in soil science. The second and the third chapters are theoretical consideration over the NMR and soil physics methods that have been used for investigations. Nevertheless, only the basic theoretical aspects are covered here since due to extensive research we find it more appropriate to introduce each method used, separately, further on, into the content of the thesis. The materials and methods used for investigation differ from one part of the research to another; therefore they will be discussed in detail for each chapter separately. Chapter 4 is the comparison study between high and low field NMR; in chapter 5 is described the combination of low field NMR relaxometry with soil physics methods; chapter 6 presents the MRI studies on a coaxial sample and the parameterization of the water retention functions using a combination of MRI and MSO experiments. In chapter 7 a summary of the entire research is performed and the main conclusions are presented together with an outlook for further researches based on the obtained results

Characterization of natural porous media by NMR and MRI techniques : high and low magnetic field studies for estimation of hydraulic properties

Soil is the natural material that covers most of the dry surface of the earth. It is the product of mechanical, chemical and biological interactions of different types of elements. Soils have a very complex composition and high variability in their occurrence and properties. The non-homogeneous mixture and interaction of their components and the changes induced upon usage ensures the complexity of their structure and a comfortable variable spatial distribution over the surface of the planet. The soils components can be found in nature in all the three aggregation states of matter: the solid state, the liquid state and the gas state. In spite of their complex structure and composition, soils can be easily handled and studied by a variety of methods. Prediction of water movement in soils is a controlling factor in various processes of interest in water resources management such as: the runoff generation, the water and nutrients supply to vegetation, the groundwater recharge and contamination. From the physics point of view water distribution and transport in unsaturated soil represents a rather complex problem of porous media hydraulics. Among various techniques developed for investigating hydraulic phenomena in soils, Nuclear Magnetic Resonance (NMR) can be used successfully for the characterization of natural porous media. The aim of this thesis is to apply different NMR techniques for: i) understanding the relaxometric properties of unsaturated natural porous media and ii) for a reliable quantification of water content and its spatial and temporal change in model porous media and soil cores. For that purpose, porous media with increasing complexity and heterogeneity were used (coarse and fine sand and different mixture of sand/clay) to determine the relaxation parameters in order to adapt optimal sequence and parameters for water imaging. Conventional imaging is mostly performed with superconducting high field scanners but low field scanners promise longer relaxation times and therefore smaller loss of signal from water in small and partially filled pores. By this reason high and low field NMR experiments were conducted on these porous media to characterize the dependence on the magnetic field strength. Correlations of the NMR experiments with classical soil physics method like mercury intrusion porosimetry; water retention curves (pF) and multi-step-outflow (MSO) were performed for the characterization of the hydraulic properties of the materials. Due to the extensive research the experiments have been structured in three major parts as follows. In the first part a comparison study between relaxation experiments in high and low magnetic field was performed in order to observe the influence of the magnetic field on the relaxation properties. Due to these results, in the second part of the study only low field relaxation experiments were used in the attempt of correlations with classical soil physics methods (mercury intrusion porosimetry and water retention curves) for characterizing the hydraulic behavior of the samples. Further, the aim was to combine also MRI experiments (2D and 3D NMR) with classical soil physics methods (multi-step-outflow, MSO) for the same purpose of investigating the hydraulic properties. Because low field MRI systems are still under developing for the moment, the MRI experiments were performed in high magnetic field and combined with MSO experiments in order to asses the changes in water content over the depth of the samples during pressure application, changes that are governed by the hydraulic properties of the material. The thesis is structured into 7 chapters. First chapter is an introduction to actual state of NMR research in soil science. The second and the third chapters are theoretical consideration over the NMR and soil physics methods that have been used for investigations. Nevertheless, only the basic theoretical aspects are covered here since due to extensive research we find it more appropriate to introduce each method used, separately, further on, into the content of the thesis. The materials and methods used for investigation differ from one part of the research to another; therefore they will be discussed in detail for each chapter separately. Chapter 4 is the comparison study between high and low field NMR; in chapter 5 is described the combination of low field NMR relaxometry with soil physics methods; chapter 6 presents the MRI studies on a coaxial sample and the parameterization of the water retention functions using a combination of MRI and MSO experiments. In chapter 7 a summary of the entire research is performed and the main conclusions are presented together with an outlook for further researches based on the obtained results