Advances in neutron imaging

During spontaneous imbibition, a wetting liquid is drawn into a porous medium by capillary forces. In systems with comparable pore length and diameter, such as paper and sand, the front of the propagating liquid forms a continuous interface. Sections of this interface advance in a highly correlated manner due to an effective surface tension, which restricts front broadening. Here we investigate water imbibition in a nanoporous glass (Vycor) in which the pores are much longer than they are wide. In this case, no continuous liquid–vapor interface with coalesced menisci can form. Anomalously fast imbibition front roughening is experimentally observed by neutron imaging. We propose a theoretical pore-network model, whose structural details are adapted to the microscopic pore structure of Vycor glass and show that it displays the same large-scale roughening characteristics as observed in the experiment. The model predicts that menisci movements are uncorrelated, indicating that despite the connectivity of the network the smoothening effect of surface tension on the imbibition front roughening is negligible. These results suggest a new universality class of imbibition behavior, which is expected to occur in any matrix with elongated, interconnected pores of random radii.

https://www.pnas.org/content/pnas/109/26/10245.full.pdf

Anomalous front broadening during spontaneous imbibition in a matrix with elongated pores

Water and protein dynamics on a nanometer scale were measured by quasi-elastic neutron scattering in the piezophile archaeon Thermococcus barophilus and the closely related pressure-sensitive Thermococcus kodakarensis, at 0.1 and 40 MPa. We show that cells of the pressure sensitive organism exhibit higher intrinsic stability. Both the hydration water dynamics and the fast protein and lipid dynamics are reduced under pressure. In contrast, the proteome of T. barophilus is more pressure sensitive than that of T. kodakarensis. The diffusion coefficient of hydration water is reduced, while the fast protein and lipid dynamics are slightly enhanced with increasing pressure. These findings show that the coupling between hydration water and cellular constituents might not be simply a master-slave relationship. We propose that the high flexibility of the T. barophilus proteome associated with reduced hydration water may be the keys to the molecular adaptation of the cells to high hydrostatic pressure.

/pdf/high-protein-flexibility-and-reduced-hydration-water-3yd6lwvtgw.pdf

High protein flexibility and reduced hydration water dynamics are key pressure adaptive strategies in prokaryotes.

The influence of high hydrostatic pressure on the internal sub-nanosecond dynamics of highly concentrated lysozyme in aqueous solutions was studied by elastic incoherent neutron scattering (EINS) up to pressures of 4 kbar. We have found, with increasing pressure, a reduction in the dynamics of H atoms of folded lysozyme, suggesting a loss in protein mobility that follows a change in the local energy landscape upon the increase in packing density. Moreover, the amplitude of the protein fluctuations depends drastically on the protein concentration, and protein structural and interaction parameters as well as the dynamical properties are affected by pressure in a nonlinear way. A significant reduction of the mean squared displacement of H atoms occurs already at rather low pressures of a few hundred bars for lysozyme in bulk water solution. This trend is lifted at ∼2 kbar, which is probably due to a solvent-mediated effect. Conversely, for high protein concentrations (e.g., 160 mg mL–1), that is, under stron...

Influence of pressure and crowding on the sub-nanosecond dynamics of globular proteins.

The challenge of understanding how localized deformation modifies fluid flow in porous rock is addressed. New approaches are presented, based on neutron radiography and digital image analyses, to track fluid flow in rock specimens and to calculate flow velocity fields providing local flow measurements. The results show that neutron radiography, backed up by appropriate image analysis, is a very powerful tool in this context, being far more sensitive to the fluids in the rock than X-ray radiography. Analysis of neutron radiography images of water imbibition into a laboratory-deformed sandstone specimen has provided new measurements of local fluid flow velocities within a shear band, indicating that flow is faster and water storage is higher in the band (attributed to higher capillary forces associated with damage). (Less)

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/grl.50528

Characterization of fluid flow in a shear band in porous rock using neutron radiography

The design of new high pressure equipment for structural and dynamical studies on samples in solution is described. We present two sample cells for applying pressures up to 150 and 700 MPa (i.e. 1.5 and 7 kbar), respectively. These cells are mounted on special sticks and inserted into the calorimeter of a cryostat to regulate the temperature. Different parts of the equipment – the pressure controller, the sticks and the cells – are described. In addition, radiography tests which were performed with neutrons in situ at the Institut Laue Langevin to verify the tightness of the cells and the hydrostatic transmission of the pressure to the sample are presented. First results on model lipids are in agreement with former results by R. Winter et al. [Towards an understanding of the temperature/pressure configurational and free-energy landscape of biomolecules, J. Non-Equilib. Thermodyn. 32 (2007), pp. 41–97].

High hydrostatic pressure equipment for neutron scattering studies of samples in solutions

Understanding fluid flow through rocks is of key interest in hydrocarbon production and CO(2) sequestration, amongst other applications. Such fluid injection or extraction from subsurface reservoirs can be significantly modified (increased or decreased) by deformation and in particular by localised deformation features (fractures, shear bands and compaction bands). How such deformation alters fluid flow is however not well characterised experimentally. Measurement of fluid-flow distributions throughout a specimen requires techniques that can, first, see inside a test specimen and, second, see the fluid distinctly from the solid part. Therefore, neutron absorption imaging is well adapted to fluid flow monitoring in rocks as water is largely opaque to neutrons (i.e., it is highly absorbing) and rocks are generally less absorbing. In this paper we present initial results of neutron radiography monitoring of fluid-flow through samples of a sandstone containing localised deformation features (shear-bands). A comparison of flow through an intact specimen and flow through samples containing localised deformation features is presented that provides insight into the effect of localised deformation on the flow properties. (Less)

/pdf/local-characterisation-of-fluid-flow-in-sandstone-with-yx8o39v6fm.pdf

Local characterisation of fluid flow in sandstone with localised deformation features through fast neutron imaging

The present study investigates the feasibility of utilizing polylactic acid (PLA) and PLA-based natural fiber-reinforced composites (NFRCs) in mechanical recycling. A conical twin screw extrusion (CTSE) process was utilized to recycle PLA and PLA-based NFRCs consisting of 90 wt.% PLA and a 10 wt.% proportion of either basalt fibers (BFs) or halloysite nanotubes (HNTs) for up to six recycling steps. The recycled material was then injection molded to produce standard test specimens for impact strength and tensile property analysis. The mechanical recycling of virgin PLA led to significant discoloration of the polymer, indicating degradation during the thermal processing of the polymer due to the formation of chromatophores in the structure. Differential scanning calorimetry (DSC) analysis revealed an increase in glass transition temperature (Tg) with respect to increased recycling steps, indicating an increased content of crystallinity in the PLA. Impact strength testing showed no significant detrimental effects on the NFRCs’ impact strength up to six recycling steps. Tensile testing of PLA/HNT NFRCs likewise did not show major decreases in values when tested. However, PLA/BF NFRCs exhibited a significant decrease in tensile properties after three recycling steps, likely due to a reduction in fiber length beyond the critical fiber length. Scanning electron microscopy (SEM) of the fracture surface of impact specimens revealed a decrease in fiber length with respect to increased recycling steps, as well as poor interfacial adhesion between BF and PLA. This study presents a promising initial view into the mechanical recyclability of PLA-based composites.

/pdf/effect-of-mechanical-recycling-on-the-mechanical-properties-2acfipt7.pdf

Steven Rowe

Papers

High hydrostatic pressure equipment for neutron scattering studies of samples in solutions

Local characterisation of fluid flow in sandstone with localised deformation features through fast neutron imaging

Effect of Mechanical Recycling on the Mechanical Properties of PLA-Based Natural Fiber-Reinforced Composites