Two-dimensional NMR relaxation study of the pore structure in silicone hydrogel contact lenses

A combination of two-dimensional nuclear magnetic resonance (NMR) proton relaxometry and differential interference contrast optical microscopy is used to compare the pore structures of hydroxyethyl methacrylate-based hydrogels used in conventional contact lenses with three silicone hydrogels primarily developed for continuous-wear contact lenses. It is shown that both types of hydrogel have a connected network of nanopores but that, in addition, the silicone hydrogels contain pores on the micrometer scale that enhances their permeability. The potential of other two-dimensional NMR relaxation and diffusion methods for detailed characterization of hydrogels is discussed.     

Investigation of the pore space structure by a scanning electron microscope using the computer program collector

The features and capabilities of the computer program developed for the estimation of petrophysical parameters of oil and gas field rocks are briefly presented. The program is based on the analysis of SEM images of the microstructure of samples.     

Specific features of proton NMR relaxation of hydrocarbons and water in the pore space of silicates

The relaxation of the proton magnetization of water and hydrocarbons in a model medium of glass beads and quartz sand is studied by the NMR method. The spectrum of relaxation times of fluids is one-component in the model environment and three-component in quartz sand. The surface relaxivities measured in the model medium are used to determine the pore size distribution in quartz sand. Estimates of the specific surface area of sand based on the relaxation data are consistent with the values measured by the sorption method. The EPR method is used to determine the chemical nature of the active paramagnetic centers responsible for the surface relaxation of the proton magnetization. Differences in the relaxation behavior of aqueous and hydrocarbon fluids are interpreted within the framework of a simple model of surface relaxation.     

NMR characterization of the pore structure and anisotropic self-diffusion in salt water Ice

NMR imaging and one- and two-dimensional self-diffusion propagator measurements of the liquid phase in salt water ice are presented. The properties of the network of brine-filled pores are found to depend on the growth conditions of the ice. Two types of samples are compared: (a) shock-frozen ice produced in the probe in situ and (b) ice grown over several hours under controlled conditions. By shock-freezing, an ice structure could be produced which featured streak-like porous channels of diameters of up to 300 μm allowing almost unrestricted self-diffusion along one preferential axis but reduced diffusivities in the remaining directions. In ice grown under controlled conditions, the pore sizes are near the resolution limit of the imaging experiment of typically 50 μm. For this type of samples, strongly non-Gaussian self-diffusion propagators are obtained, indicating restricted self-diffusion on rms scales of 30 μm. Common to all samples was the observation of highly anisotropic self-diffusion. One- and two-dimensional propagators are compared in order to estimate the degree of anisotropy and the size of the restrictions.     

Quantitative analysis of pore space of moraine clay soils by SEM images

Problems of studying the pore space of moraine clay soils are considered by analyzing SEM images of the surface of samples prepared using a special technique. A new algorithm for estimating the pore shape is described. The study of the microstructure of moraine clay soils showed that they are characterized by five pore types. Of particular interest is the existence of large micropores with specific anisometric crescent shape in such soils. These micropores are formed at the interface between the surface of large sand-dust quartz or feldspar grains and the finely divided unoriented clay matrix. Such pores can be ways of localized groundwater filtration through soils, significantly affecting the soil properties.     

EMCD real space maps of Magnetospirillum magnetotacticum

In this study we combine energy loss magnetic circular dichroism (EMCD) and energy filtered transmission electron microscopy (EFTEM) to map magnetic properties of nanoparticles. We show that it is a functional tool for investigating the magnetic behaviour of bio-mineralized magnetite crystals of Magnetospirillum magnetotacticum. We find that the spatial resolution of our experimental set-up is in the range of less than 2 nm. The results are compared with EMCD studies of abiogenic magnetite.     

Improved free space optical communications performance by using time diversity

A laser beam propagating through turbulence experiences random amplitude and phase fluctuations, which can severely degrade the performance of free space optical communication systems. It this letter, time diversity is demonstrated as a technique which can decrease turbulence influence. Statistically, laser propagation along an atmospheric path is uncorrelated with an earlier-time path for a time interval greater than the atmospheric turbulence correlation time. To estimate time diversity system performance, a 2.2-km optical link is set up for comparing the fade probability of a system using time diversity with a system not using time diversity. The experimental results obtained under different turbulence conditions are shown which are in good agreement with the theory.     

Interaction of loosely packed bubbly flow passing through a pore space

Journal of Visualization - The interactions of the bubbles in a loosely packed bubbly flow in a high viscous fluid approaching a pore space are studied using a shadowgraph imaging technique. The...