Rheological Conditions Research Articles

Rheology Pathway to Macroscale Ordered Nanostructures of Polymeric Nanotemplates: Nanopores, Nanosheets and Nanofibers

The creation of nanotemplates under dynamic shear flow conditions is described. The structures used are based on the self-organization of comb-coil-like diblock copolymer systems with two intrinsic length scales, resulting from combining diblock copolymers with hydrogen-bonding amphiphiles. Rheological data of polymeric supramolecular order formation are studied under oscillating shear flow conditions and it was observed that the order of the polymeric nanodomains can be extended to macroscopic distances. It is proposed that the key success factor to obtain highly ordered samples is to perform the orientation process using appropriate rheological conditions (temperature, frequency and strain) selected such that the ratio of the elastic component G' to the viscous component G is larger than 1. This observation was used to select the rheological parameters for the three different samples investigated, where three different types of nanotemplates are observed after extracting the hydrogen-bonding amphiphile; nanosheets, hollow cylinders and nanofibres. SAXS is primarily used to inspect the resulting structures. Additionally, AFM and TEM were utilized to image the morphologies and to further act as visual proof for the efficiency of the rheological orientation process.

Flight path of electrospun polystyrene solutions: Effects of molecular weight and concentration

The behavior of the solution jet during electrospinning is a consequence of the balance between electrical, surface tension, and viscoelastic forces. Solution rheology, which is known to have a significant effect on the structure of the electrospun polymer, may also affect jet evolution and breakdown. In this study, the effect of polymer molecular weight and concentration on the behavior of polystyrene solution jet was investigated using high speed camera (2000 frames/s). The results indicate that the degree of elongational flow, bending instability, and jet branching depends on polymer molecular weight and concentration. It was observed that jet thinning and solidification may occur at different distances from the capillary when the rheological conditions are varied.

Rheological Behavior and Slip Casting of Al2O3–Ni Aqueous Suspensions

A strong effort has been devoted recently toward processing of metal–ceramic composites with tailored microstructure by colloidal methods. The aim of this work is to optimize the rheological behavior of concentrated Al2O3–nickel (Ni) aqueous suspensions and further slip casting in order to obtain dense green composites. Compositions with Ni relative contents ranging from 5 to 75 vol% were prepared from suspensions with high solids loadings (50 vol%) by adjusting the colloidal stability of each component in terms of pH, mobility, dissolution conditions, and influence of polyelectrolytes. The rheological properties were measured under controlled rate and controlled stress conditions at different basic pH conditions and contents of polyelectrolyte. Better rheological conditions of the mixtures were found for pH 10 and 1.0 wt% polyelectrolyte. Minimum viscosity was obtained for suspensions containing 15 vol% of Ni. The analysis of flow curves demonstrates that the suspensions form a structure at very low shear, hindering sedimentation. Homogeneous slip cast bodies with green densities up to 70% of theoretical and up to 75 vol% Ni were sintered in Ar to achieve dense biphasic composites.

Jurassic septarian concretions from NW Scotland record interdependent bacterial, physical and chemical processes of marine mudrock diagenesis

AbstractSeptarian concretions in the Staffin Shales Formation (Kimmeridgian, Isle of Skye) allow controls on concretion rheology and septarian cracking to be investigated. Stratabound concretions consist of anhedral ferroan calcite microspar enclosing clay and minor pyrite. Intergranular volumes range from 77% to 88%, and calcite δ13C and δ18O values in most concretion bodies range from −10·0‰ to −17·3‰ and +0·3‰ to −0·6‰ respectively, consistent with rapid and pervasive cementation in marine pore fluids. Septarian rupture occurred during incipient cementation, with a sediment volume reduction of up to 43%. Crack‐lining brown fibrous calcite records pore fluid re‐oxygenation during a depositional hiatus, followed by increasing Fe content and δ13C related to bacterial methanogenesis. Brown colouration results from an included gel‐like polar organic fraction that probably represents bacterially degraded biomass. A new hypothesis for concretion growth and septarian cracking argues that quasi‐rigid ‘proto‐concretions’ formed via binding of flocculated clays by bacterial extracellular polysaccharide substances (EPS). This provided rheological and chemical conditions for tensional failure, subcritical crack growth, volume contraction, calcite nucleation, and incorporation of degraded products into crack‐lining cements. Bacterial decay of EPS and syneresis of host muds provided internal stresses to initiate rupture at shallow burial. Development of septarian (shrinkage) cracks in muds is envisaged to require pervasive in situ bacterial colonization, and to depend on rates of carbonate precipitation versus EPS degradation and syneresis. Subsequent modification of septarian concretions included envelopment by siderite and calcite microspar, hydraulic fracturing associated with Cretaceous shallow burial or Palaeogene uplift; and cementation by strongly ferroan, yellow sparry calcite that records meteoric water invasion of the host mudrocks. An abundance of fatty acids in these spars indicates aqueous transport of organic breakdown products, and δ13C data suggest a predominantly methanogenic bicarbonate source. However, the wide δ18O range for petrographically identical cement (−1·3‰ to −15·6‰) is difficult to explain.

Effects of iota-carrageenan on the rheological properties of starches

The phycocolloid iota-carrageenan (ι-CAR) was extracted from the Brazilian seaweed Meristiella gelidium. At a concentration of 5 mg ml −1 it was mixed with solutions of common corn starch (CS), high amylose starch (MS), waxy corn starch (WS) and YS starch (YS), to give systems at a final concentration of 25 g l −1, which were subjected to rheological measurements. Each mixture gave rise to a different behaviour under dynamic rheological conditions showing a distinct degree of interaction between ι-CAR and the starch. The presence of ι-CAR in ι-CAR-WS, ι-CAR-MS and ι-CAR-CS systems resulted in synergy manifested as enhancements in thermal stability (absence of hysteresis), resulting in thermoreversible gels softer and more stable between 45 and 85 °C. In the ι-CAR-YS system, the synergistic effect occurred as an improvement in solid character, increasing the elastic nature of the gel, suggesting that the structural characteristic of YS, more regular structure with amylopectin having a low molar mass, can contribute to enhanced intermolecular binding.

Effect of Slurry Rheology on the Performance of Cross-Flow Filtration

Effects of slurry rheology and other operating conditions on the performance of cross-flow filtration are investigated. Aluminum oxide powders with a mean diameter of 34 μm are suspended in polyacrylamide (PAA) aqueous solution to prepare the viscoelastic slurry used in experiments. The filtration rate and the cake properties under various operating conditions, such as PAA concentration, filtration pressure and cross-flow velocity, are measured and discussed. The elastic behavior of permeating fluid plays an important role on the filtration performance as the Reynolds number exceeds a critical value that depends on the fluid rheology. The elastic effect is dominant at the beginning period of a filtration, which results in an extra filtration resistance and an excess cake compression. When the elastic effect vanishes, the permeating flow through the filter cake behaves as a pure viscous fluid, which can be modeled by the power law model. The pseudo-steady filtration rate increases with the increase of filtration pressure and cross-flow velocity, but with the decrease of PAA concentrations. These tendencies can be explained reasonably by the cake properties, e.g., the particle size distribution in the cake, the porosity and the specific filtration resistance of the cake under various conditions. The dynamic analysis method proposed by the authors is employed to estimate the cake properties. The calculated results agree fairly well with the experimental data.

Anti-thrombotic effect of bivalirudin compared with eptifibatide and unfractionated heparin in diabetic patients

Patients with diabetes who undergo percutaneous coronary intervention (PCI) are at high risk for thrombotic complications following the procedure. We sought to compare the anti-thrombotic effect of bivalirudin to that of eptifibatide plus unfractionated heparin in diabetic patients undergoing elective PCI. Thirty diabetic patients were randomized to receive during PCI either bivalirudin (bivalirudin group, n=15) or eptifibatide plus heparin (eptifibatide group, n=15) at standard dosing regimens. The drugs were continued for 20 minutes (bivalirudin) or 18 hours (eptifibatide) after PCI. Blood thrombogenicity was assessed using the Badimon ex vivo perfusion chamber. Each patient underwent two perfusion studies - at baseline (on aspirin and clopidogrel) and 15-20 minutes following PCI. Perfusion studies were performed at rheologic conditions of low and high shear rates (LSR, HSR). Porcine aortic tunica media served as the thrombogenic substrate. Aortic specimens were stained for total platelet-thrombus and fibrin deposition. Thrombus area was measured using computerized planimetry. There were no differences in clinical characteristics or baseline thrombus area between the two groups. Total platelet-thrombus area was reduced significantly in both groups, but the degree of reduction was lower in the bivalirudin group compared with the eptifibatide group (HSR: 69.5% vs. 89.3% reduction, respectively, P=0.04; LSR: 50.6% vs. 73.2%, P=0.03). Fibrin deposition was reduced in both groups by 47-49%. In conclusion, both bivalirudin and the combination of eptifibatide plus heparin, given to diabetic patients during PCI, achieved marked reductions in total thrombus formation and fibrin deposition. However, glycoprotein IIb/IIIa inhibition by eptifibatide caused a more pronounced reduction in thrombus formation.

The role of the East Asian active margin in widespread extensional and strike-slip deformation in East Asia

East Asia is a region of widespread deformation, dominated by normal and strike-slip faults. Deformation has been interpreted to result from extrusion tectonics related to the India–Eurasia collision, which started in the Early Eocene. In East and SE China, however, deformation started earlier than the collision (latest Cretaceous to Palaeocene), suggesting that extrusion tectonics is not the (only) driving mechanism for East Asia deformation. It is suggested that the East Asian active margin has influenced deformation in East Asia significantly. Along the margin, Cenozoic back-arc extension took place behind several adjoining arcs, implying eastward rollback of the subducting slab and collapse of the overriding plate towards the retreating hinge-line. We show that extension took place along a c . 7400 km long stretch of the East Asian margin during most of the Cenozoic. Physical models are presented simulating overriding plate collapse and back-arc extension. The models reproduce important aspects of the strain field in East Asia. For geometrical and rheological conditions scaled to represent East Asia, modelling shows that the active margin can be held responsible for deformation in East Asia as far west as the Baikal rift zone, located c . 3300 km from the margin.

Geological and mathematical framework for failure modes in granular rock

We synthesize all the available data on failure processes in granular rock and provide a geological framework for the corresponding structures. We describe two categories: (1) sharp discontinuities made up of two surfaces similar to elastic crack models, and (2) tabular structures resulting from strain localization into narrow bands. Each of these categories includes types predominated by shear and/or volumetric deformation. While shear failure can be in two different modes as sliding and tearing, the volumetric failure has two diametrically opposite types: compaction (contraction) and dilation (extension). Thus, we distinguish among bands predominantly by shearing, shortening, and extension. Slip surfaces, pressure solution surfaces, and joints represent corresponding sharp discontinuities. A survey of observations and measurements from naturally occurring structures indicates that although isochoric shear and pure volumetric deformation types represent end members, a complete spectrum of combined shear and volumetric deformation occurs in nature. Field observations also show that sharp structures overlap older narrow tabular structures in the same rock. This switch in failure modes is attributed to changing rock rheology and/or loading conditions. In the mathematical modeling, we focus on the strain localization into narrow tabular bands using classical bifurcation theory combined with nonlinear continuum mechanics and plasticity. We formulate a family of three invariant plasticity models with a compression cap and capture the entire spectrum of failure of geomaterials. In addition, we draw an analogy between the concepts of ‘strong’ and ‘sharp’ discontinuity and classic elastic crack representations to complement the mathematical treatment of the failure modes.

Deformation of oceanic lithosphere near slow-spreading ridge discontinuities

Transform and non-transform discontinuities that offset slow spreading mid-ocean ridges involve complex thermal and mechanical interactions. The truncation of the ridge axis influences the dynamics of spreading and accretion over a certain distance from the segment-end. Likewise, the spreading system is expected to influence the lithospheric plate adjacent to the ridge-end opposite of the discontinuity. Tectonic effects of the truncated ridge are noticeable in for example the contrast between seafloor topography at inside corners and outside corners, along-axis variations in rift valley depth, style of crustal accretion, and ridge segment retreat and lengthening. Along such slow-spreading discontinuities and their fossil traces, oceanic core complexes or mega-mullion structures are rather common extensional tectonic features. In an attempt to understand deformation of oceanic lithosphere near ridge offsets, the evolution of discontinuities, and conditions that may favor oceanic core complex formation, a three-dimensional thermo-mechanical model has been developed. The numerical approach allows for a more complete assessment of lithosphere deformation and associated stress fields in inside corners than was possible in previous 3-D models. The initial suite of results reported here focuses on deformation when axial properties do not vary along-strike or with time, showing the extent to which plate boundary geometry alone can influence deformation. We find that non-transform discontinuities are represented by a wide, oblique deformation zone that tends to change orientation with time to become more parallel to the ridge segments. This contrasts with predicted deformation near transform discontinuities, where initial orientation is maintained in time. The boundary between the plates is found to be vertical in the center of the offset and curved at depth in the inside corners near the ridge–transform intersection. Ridge–normal tensile stresses concentrate in line with the ridge tip, extending onto the older plate across the discontinuity, and high stress amplitudes are absent in the inside corners during the magmatic accretionary phase simulated by our models. With the tested rheology and boundary conditions, inside corner formation of oceanic core complexes is predicted to be unlikely during magmatic spreading phases. Additional modeling studies are needed for a full understanding of extensional stress release in relatively young oceanic lithosphere.

The squeezing test: a tool to identify firm cement-based material's rheological behaviour and evaluate their extrusion ability

The squeezing test is used in this paper as a rheological behaviour identification tool of cement-based materials in order to evaluate the extrusion ability. Experimental flow curves are obtained for firm cement pastes and fine sand firm mortars using two different compression speeds. These tested products may be considered as frictional plastic materials. Using the proposed testing method, two important aspects are discussed. On one hand, it is shown in this paper that the mortars bulk and apparent friction factors increase with sand addition proportion. On the other hand, cement paste's apparent yield shear stress increases at low compression speed because of fluid drainage through the granular skeleton and sample hardening. Some pictures obtained after squeezing test are used to illustrate this drainage phenomenon. Finally, some mortar mix design indications are proposed according to extrusion criteria based on rheological conditions.

Non-isothermal flow of a power law fluid past a rectangular obstacle (of aspect ratio 1 × 2) in a channel: Drag and heat transfer

A two-dimensional numerical study has been carried out to investigate the drag and Nusselt number characteristics under forced convection conditions between a streaming power law liquid and a rectangle (with its longer side aligned with the direction of flow) placed symmetrically between two solid walls. In particular, the values of the individual and total drag coefficients, and of the Nusselt number are obtained as functions of the flow behaviour index (1.4 ⩾ n ⩾ 0.5), of Reynolds number (5 ⩽ Re ⩽ 40) and of the Peclet number (5 ⩽ Pe ⩽ 400) for a fixed value of the blockage ratio (1/8). Within these ranges of kinematic and rheological conditions, the drag and Nusselt number show only fair to moderate deviation from the corresponding Newtonian values at the same values of the Reynolds and Peclet numbers. Qualitatively speaking, the shear-thinning behaviour ( n < 1) augments the drag and heat transfer while the shear-thickening behaviour ( n > 1) causes both the drag and heat transfer to drop below the corresponding Newtonian values. The power-law fluid behaviour does not seem to alter the streamline, isovorticity and isotherm plots in a significant manner, except for the fact that the shear-thinning behaviour not only delays the formation of a visible wake but the resulting wake is also somewhat shorter than that in a Newtonian fluid. The shear thickening, on the other hand, has exactly the opposite influence on wake formation.

A transient model for explosive and phreatomagmatic eruptions

Abstract We develop a model for explosive eruptions in cylindrical conduits generated by plug disruption at the top of the conduit. The eruption is calculated for a standard set of parameters for rhyolite. The model takes into account temperature variations and non-Newtonian magma rheology. We analyzed the influence of principal parameters such as fragmentation criteria, magma rheology, and initial conditions. We conclude that the variation of magma temperature is less than 70 K during eruption, and the model with bubble concentration-dependent viscosity leads to the increase of the steady discharge rate by about 40%. The eruption model is extended to include interaction between magma in the conduit and water in a surrounding aquifer. The phreatomagmatic eruption is also initiated by plug disruption. Two cases of initial aquifer pressure are considered: magmastatic and hydrostatic. These cases are valid for confined and unconfined aquifers. For the first case (confined aquifer), water influx influences the conduit flow soon after plug disruption and leads to the additional peaks of discharge rate; for the second case (unconfined aquifer), a purely magmatic, explosive eruption of longer duration is followed by a phreatomagmatic phase. In both cases, magma discharge rate increases by 10–100% in comparison with purely magmatic eruption.

Cross-Species Chemoattraction and Xenograft Failure: Do Neutrophils Play a Role?

Polymorphonuclear granulocytes (PMN, neutrophils) are well known to contribute to the pathogenesis of many congenital disorders (e.g., CR3 deficiency, chronic granulomatous disease, myeloperoxidase deficiency) and acquired disease states (e.g., inflammatory bowel disease, glomerulonephritis, immune vasculitis, rheumatoid arthritis, neutrophil dermatoses, sepsis). They play a key role in mediating ischemia-reperfusion injury following solid organ allotransplantation,andmorerecentevidencesuggeststhat,following early migration into the allograft, neutrophils are capable of amplifying T-cell mediated allograft rejection (1). In xenotransplantation, the major hurdle of hyperacute rejection (HAR) has led research efforts to focus on the role of natural xenoantibodies and complement activation, while the neutrophilwasconsideredtoplayasecondaryroleandwastherefore given little attention. Meanwhile, it seems that experimental prevention of HAR becomes feasible thanks to the genetic modification of donor animals (DAF/CD55 transgenicpigs,-Galknockoutpigsandmice)and,consequently, the mechanism of acute vascular rejection (AVR) and the cellular aspects of xenograft rejection now receive full attention. AVR is characterized by a dense cellular infiltrate, which is dominated not only by natural killer (NK) cells and macrophages, but also by PMN. It is therefore plausible to assume that neutrophils take an active part in the rejection process and this hypothesis is gaining increasing interest. Vercellotti et al. (2) showed that the adhesion of human neutrophils to porcine endothelial cells (PECs) was promoted by humannaturalxenoantibodiesandcomplement,and,particularly, that endothelial deposition of iC3b was critically involvedintheadhesionprocess.Ehrnfeltetal.(3)showedthat humanPMNsadheretoPECs,providedtheseareactivatedby human natural xenoantibodies. These studies indicate that the interaction between neutrophils and xenoendothelium requires preactivation of endothelial cells by complement and/or natural xenoantibodies and, consequently, that the PMN plays a secondary role in HAR. In contrast, others have providedevidencethathumanPMNhavetheinherentcapac

Development of asymmetric BTDA-TDI/MDI (P84) co-polyimide hollow fiber membranes for ultrafiltration: the influence of shear rate and approaching ratio on membrane morphology and performance

In this paper, the effects of dope composition (especially approaching ratio α), rheology and spinning conditions on the morphology and performance of asymmetric BTDA-TDI/MDI co-polyimide (P84, CAS#: 58698-66-1) hollow fiber membranes spun from P84/N-methyl-2-pyrrolidone (NMP, CAS#: 872-50-4)/H 2O dope solutions were studied. The velocity distribution and rheology of the dope solution within the spinneret were analyzed. The experimental results indicated that the defects on the outer surface of hollow fiber membranes were suppressed by increasing the shear rate of the dope solution within the spinneret. Therefore, membranes with a low flux and a high rejection could be obtained. By changing in shear rate, the hollow fiber membranes ranging from ∼20,000 to >200,000 MWCO can be obtained within a single formulation (such as 21 wt.% P84; H 2O/NMP: 3.6/96.4 (w/w). An increase of shear rate also increased the outer diameter and thickness of the hollow fiber membranes. The approaching ratio α of the dope solution played an important role in determining the membrane structure. The hollow fiber membranes spun at α = 0.45 (21 wt.% P84; H 2O/NMP: 3.6/96.4 (w/w) had a finger-like structure, but sponge-like structure was obtained for α = 0.82 (21 wt.% P84; H 2O/NMP: 6.4/93.6 (w/w). An increase of approaching ratio α resulted in a poor rejection and a high flux. With a decrease in the volume ratio of dope solution to bore fluid, the membrane became thinner and the flux increased. Compared to the dry–jet wet spinning process, the hollow fiber membranes from a wet spinning process had a high flux, a large outer diameter and a poor rejection. For a dry–jet wet spinning process, the increase in the air gap decreased the rejection of the hollow fiber membranes.

Geological, geochronological and geochemical features of granulites in the Eastern Tianshan, NW China

This paper reports new results on the petrology, geochronology and geochemistry of two km-scale high-pressure granulite exposures, namely the Weiya and the Yushugou granulites, that occur in the central and southern Tianshan Paleozoic sub-belts, respectively. Petrological and geochemical results suggest that the Weiya and the Yushugou granulites are different in both the rock types and geological structures. The protolith of the Weiya granulite is basic to intermediate rocks, and that of the Yushugou granulite is basic rocks; the former is distributed as fault-bounded blocks within the Precambrian schist-gneiss, and the latter occurs as thrust slabs in the allochthonous ophiolitic mélange. Observation of deformation structures provides some evidence for two-phase ductile deformation of the Tianshan granulites, characterized by deformed garnet-pyroxene and deformed feldspar-quartz microstructures, corresponding to rheological conditions of the lower crustal level and of the middle crustal level, respectively. The deformation structures also indicate that the Weiya granulite was involved in the late stage retrograde metamorphism forming new amphibole, following a thrusting movement toward the north and ductile deformation of feldspar-quartz grains. The Yushugou granulite underwent strong ductile shearing during the Silurian–Devonian interval. Three stages of metamorphism are recorded by mineral assemblages of the Weiya granulite: M1=Pl+Qtz+Bt, M2=Cpx+Grt+Pl+Qtz+Atp±Opx, and M3=Amp+Ep+Pl+Bt+Qtz, in contrast to a two-stage metamorphic history of the Yushugou granulite: M1=Cpx+Grt+Pl±Hyp, M2=Amp+Pl+Qtz±Bt. The P–T condition estimates suggest that the Weiya granulite was formed between 910–1025 °C and 1.08–1.12 GPa, and underwent retrograde metamorphism at 650–670 °C, while the peak metamorphism of the Yushugou granulite took place between 800–870 °C and 0.88–1.13 GPa. Geochemical characteristics (major, REE and incompatible elements) of the Weiya and Yushugou granulites indicate that their protoliths were formed in a volcanic arc setting, implying that a late Precambrian active continental margin may have existed in the study area. The Sm–Nd isochron dating for the Weiya granulite suggests that the peak metamorphism occurred at 538±24 Ma, which was likely related to the ancient plate subduction. The 40Ar/39Ar dating on amphibole grains separated from the Weiya granulite yielded a plateau age of 432±1 Ma for the retrograde metamorphism, which represents an exhumation age, suggesting a significant early Paleozoic tectonothermal event.

Aggregate formation of erythrocytes in postcapillary venules.

The purpose of the present study was to obtain information on erythrocyte aggregate formation in vivo. The movements of erythrocytes in postcapillary venules of the rat spinotrapezius muscle at various flow rates were recorded with a high-speed video camera before and after infusion of dextran 500. To distinguish aggregates, the following criteria were used: 1) a fixed distance (4 microm) between the center points of two adjacent cells, 2) lack of visible separation between the adjacent cells, and 3) movement of the adjacent cells in the same direction. Without dextran 500 infusion, 11 and 5% of erythrocytes formed aggregates in low (33.2 +/- 28.3 s) and high pseudoshear (144.2 +/- 58.3 s) conditions, respectively, based on the above criteria. After dextran 500 infusion, 53% of erythrocytes satisfied the criteria in the low pseudoshear condition (26.5 +/- 17.0 s) and 13% of erythrocytes met the criteria in the high pseudoshear condition (240.0 +/- 85.9 s), indicating erythrocyte aggregation is strongly associated with shear rate. Approximately 90% of aggregate formation occurred in a short time period (0.15-0.30 s after entering the venule) in a region 15 to 30 microm from the entrance. The time delay may reflect rheological entrance conditions in the venule.

Structure and Properties of Nanocomposites Based on Nylon-11 and -12 Compared with Those Based on Nylon-6

An in-depth analysis was made on the effect of polyamide repeat structure on the morphology and mechanical properties of nanocomposites based on nylon-6, nylon-11, and nylon-12. Special care was taken to make comparisons under fixed thermal and rheological conditions. Increasing the aliphatic content relative to nylon-6 results in a decrease in the extent of organoclay exfoliation as revealed by transmission electron photomicrographs. The extent of platelet separation as judged by low-angle X-ray scattering is more complicated for nylon-11 and -12 nanocomposites than those based on nylon-6 due the presence of crystalline peaks associated with the polyamide matrix. An “exfoliation index” is used to compare stiffness effects observed in the different nanocomposites due to the large difference in the modulus of nylon-6 as compared to nylon-11 and -12. Interestingly, the exfoliation efficiency parallels morphological trends in that nylon-6 exhibits higher efficiencies than the more aliphatic nylon-11 and -12 ...

A counterclockwise PTt path of high-pressure/low-temperature rocks from the Coastal Cordillera accretionary complex of south-central Chile: constraints for the earliest stage of subduction mass flow

Within the metamorphic basement of the Coastal Cordillera of central Chile, the Western Series constitutes the high-pressure (HP)/low-temperature (LT) part (accretionary prism) of a fossil-paired metamorphic belt dominated by metagreywackes. In its eastern part, blocks derived from small lenses of garnet amphibolite with a blueschist facies overprint are locally intercalated and associated with serpentinite and garnet mica-schist. Continuously developed local equilibria were evaluated applying various independent geothermobarometric approaches. An overall anticlockwise PT path results. The prograde path evolved along a geothermal gradient of ∼15 °C/km, passing the high-pressure end of greenschist facies until a transient assemblage developed within albite-epidote amphibolite facies transitional to eclogite facies at peak metamorphic conditions (600–760 °C, 11–16.5 kbar; stage I). This peak assemblage was overprinted during an external fluid infiltration by an epidote blueschist facies assemblage at 350–500 °C, 10–14 kbar (stage II) indicating nearly isobaric cooling. The retrograde equilibration stage was dated with a Rb–Sr mineral isochron at 305.3±3.2 Ma, somewhat younger (296.6±4.7 Ma) in an adjacent garnet mica-schist. Localized retrograde equilibration continued during decompression down to ∼300 °C, 5 kbar. The retrograde evolution is identical in the garnet amphibolite and the garnet mica-schist. The counterclockwise PT path contrasts the usual clockwise PT paths derived from rocks of the Western Series. In addition, their ages related to stage II are the oldest recorded within the fossil wedge at the given latitude. Its “exotic” occurrence is interpreted by the path of the earliest and deepest subducted material that was heated in contact with a still hot mantle. Later accreted and dehydrated material caused hydration and cooling of the earliest accreted material and the neighbouring mantle. After this change also related to rheological conditions, effective exhumation of the early subducted material followed at the base of the hydrated mantle wedge within a cooler environment (geothermal gradient around 10–15 °C/km) than during its burial. The exotic blocks thus provide important time markers for the onset of subduction mass circulation in the Coastal Cordillera accretionary prism during the Late Carboniferous. Continuous subduction mass flow lasted for nearly 100 Ma until the Late Triassic.

The influence of dispersant concentration on the pore morphology of hydroxyapatite ceramics for bone tissue engineering

There is a clinical need for synthetic scaffolds that will promote bone regeneration. Important factors include obtaining an optimal porosity and size of interconnecting windows whilst maintaining scaffold mechanical strength, enabling complete penetration of cells and nutrients throughout the scaffold, preventing the formation of necrotic tissue in the centre of the scaffold. To address this we investigated varying slip deflocculation in order to control the resulting porosity, pore size and interconnecting window size whilst maintaining mechanical strength. Hydroxyapatite (HA) porous ceramics were prepared using a modified slip casting process. Rheological measurements of the HA slips were used to identify deflocculation conditions which resulted in changes in the cell and window sizes of the resulting ceramics. Sintered ceramics were characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Pore and window size distribution was determined by SEM. XRD analysis confirmed that the crystal structure remained HA after the sintering process. SEM showed that HA porous ceramics presented a highly interconnected porous network with average pore sizes ranging from 391±39 to 495±25 μm. The average window size varied from 73±5 to 135±7 μm. Pore diameters obtained were controllable in the range 200–500 μm. Window sizes were in the range 30–250 μm. The use of dispersant concentration allows pore and window size to be modified whilst maintaining control over porosity demonstrated by a porosity of 85% for seven different dispersant concentrations. The advantage of this approach allows the correlation between the rheological conditions of the slip and the resultant sintered ceramic properties. In particular, optimising the ceramic strength by controlling the agglomeration during the casting process.