Science.gov

Sample records for sand-blended-cement pastes rheology

  1. Rheological Influence of Synthetic Zeolite on Cement Pastes

    NASA Astrophysics Data System (ADS)

    Baldino, N.; Gabriele, D.; Frontera, P.; Crea, F.; de Cindio, B.

    2008-07-01

    Self Compacting Concrete (SCC) is characterized by specific and particular mechanical properties, often due to the addition of components, able to modify the paste rheology. Concrete properties are strongly affected by characteristics of the fresh cement paste that is the continuous phase dispersing larger aggregates. Therefore, aiming to characterize mechanical properties of final concrete is relevant to know rheological properties of the base cement paste. In this work cement pastes for SCC were prepared by using, as additive, synthetic zeolite 5A in different amounts and they were analyzed by small amplitude oscillations. Experimental results have shown a relationship between dynamic moduli and zeolite content, identifying a proper level of zeolite addition. Moreover samples containing traditional fine additives, such as silica fume and limestone, were prepared and experimental data were compared to those obtained by using zeolite. It was found that zeolite seems to give better properties to cement paste than other additives can do.

  2. Pasting and rheological properties of quinoa-oat composites

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Quinoa (Chenopodium, quinoa) flour, known for its essential amino acids, was composited with oat products containing ß-glucan known for lowering blood cholesterol and preventing heart disease. Quinoa-oat composites were developed and evaluated for their pasting and rheological properties by a Rapid ...

  3. Extrusion and rheology of fine particulate ceramic pastes

    NASA Astrophysics Data System (ADS)

    Mazzeo, Fred Anthony

    A rheological study was conducted on an extruded blend of two alumina powders, Alcoa A-3500-SG and Reynolds ERC. These extruded blends were mixed in four compositions, varying in distribution modulus. This work focuses on the interaction of the composition components, mainly particle size distribution and amount of water at a constant binder amount. The rheological parameters of extruded pastes, Sigma, Tau, alpha and beta, were determined by using capillary rheometry modeling by the methodology set forth by Benbow and Bridgwater. This methodology makes use of capillary rheometer to determine extrusion parameters, which describe the flow behavior of a paste. The parameter values are indirectly determined by extrapolating high shear rate information obtained by the extrusion process. A goal of this research was to determine fundamental rheological properties directly from fundamental rheological equations of state. This was accomplished by assessing the material properties by using a dynamic stress rheometer. The rheological parameters used in this study to characterize the paste are elastic modulus, viscosity, tan delta, and relaxation time. This technique approaches a step closer in understanding the microstructural influence on flow behavior of a paste. This method directly determines rheological properties by using linear viscoelastic theory, giving a quantitative analysis of material properties. A strong correlation between the elastic modulus and sigma, and viscosity and alpha is shown to exist, indicating a relationship between these two techniques. Predictive process control methodology, based on particle packing modeling, quantitatively determined structural parameters useful in evaluating a composition. The determined parameters are: distribution modulus, interparticle separation distance, porosity, and particle crowding index, which are important to understand the extrudates packed state. A connection between the physical structure of the extrudate and its

  4. Correlating cement characteristics with rheology of paste

    SciTech Connect

    Vikan, H. Justnes, H.; Winnefeld, F.; Figi, R.

    2007-11-15

    The influence of cement characteristics such as cement fineness and clinker composition on the 'flow resistance' measured as the area under the shear stress-shear rate flow curve has been investigated. Three different types of plasticizers namely naphthalene sulphonate-formaldehyde condensate, polyether grafted polyacrylate, and lignosulphonate have been tested in this context on 6 different cements. The flow resistance correlated well with the cement characteristic (Blaine.{l_brace}d.cC{sub 3}A + [1 - d].C{sub 3}S{r_brace}) where the factor d represents relative reactivity of cubic C{sub 3}A and C{sub 3}S while cC{sub 3}A and C{sub 3}S represent the content of these minerals. It was found to be either a linear or exponential function of the combined cement characteristic depending on plasticizer type and dosage. The correlation was valid for a mix of pure cement and cement with fly ash, limestone filler (4%), as well as pastes with constant silica fume dosage, when the mineral contents were determined by Rietveld analysis of X-ray diffractograms.

  5. Cement paste prior to setting: A rheological approach

    SciTech Connect

    Bellotto, Maurizio

    2013-10-15

    The evolution of cement paste during the dormant period is analyzed via small amplitude oscillation rheological measurements. Cement paste, from the very first moments after mixing cement and water, shows the formation of an elastic gel whose strength is rapidly increasing over time. Up to the onset of Portlandite precipitation G′(t) increases by more than 2 orders of magnitude and in the acceleratory period G′(t) continues steadily to increase. A microstructural modification is likely to occur between the dormant and the acceleratory period. At low deformations in the linearity domain the storage modulus G′(ω) exhibits a negligible frequency dependence. At higher deformations cement paste shows a yield stress which increases on increasing paste concentration. The presence of superplasticizers decreases the yield stress and increases the gelation threshold of the paste. Above the gelation threshold the evolution of cement paste with superplasticizers follows similar trends to the neat paste. -- Highlights: •The gelation of cement paste during the dormant period is analyzed via rheometry. •The observed evolution is proposed to be related to the pore structure refinement. •Similarities are observed with colloidal gels and colloidal glasses.

  6. Rheological and pasting properties of buckwheat (Fagopyrum esculentum Moench) flours with and without jet-cooking

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Pasting, rheological and water-holding properties of buckwheat (Fagopyrum esculentum) flour obtained from whole achenes separated into three particle sizes, and three commercial flours (Fancy, Supreme and Farinetta) were measured with or without jet-cooking. Fancy had instantaneous paste viscosity ...

  7. Rheological evaluation of dense suspensions; Simulation of a fresh cement paste

    SciTech Connect

    Clark, P.E. ); Shaughnessy, R.J. III )

    1990-05-01

    The rheology of fresh cement pasts is a function of not only particle size, shape, and concentration, but also the cement setting reactions. This greatly complicates the analysis of data obtained in any rheological experiment. To separate the slurry contribution to the system rheology from the chemical reaction component, a slurry of marble-dust particles is used to represent a cement slurry. In this study, both tube-flow and concentric-cylinder rheometers are used to evaluate the rheological behavior of the dense suspensions. The apparent slip of the suspension makes correlation of the flow curves generated from the two viscometers difficult. The degree of slip in both viscometers becomes increasingly significant as the marble-dust concentration increases. The use of a grooved bob in the concentric-cylinder viscometer considerably reduces the amount of slip. Large annular gaps also contribute to inconsistent results. An analysis of the data from both types of viscometers is presented.

  8. Pasting and rheological properties of ß-glucan-enriched hydrocolloids from oat bran concentrate

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Pasting and rheological properties of four oat hydrocolloids with different contents of ß-glucan (Nutrim10, C-Trim20, C-Trim30, and C-Trim50) were characterized and compared with oat bran concentrate (OBC) and ß-Glucan 95%. C-Trim30 and C-Trim50 had significantly higher water holding capacities comp...

  9. Influence of superplasticizers on the rheology and stability of limestone and cement pastes

    SciTech Connect

    Mikanovic, Nikola Jolicoeur, Carmel

    2008-07-15

    The influence of superplasticizers on the rheological properties and dynamic stability of cement and reference limestone pastes were examined at room temperature. The pastes were initially formulated to exhibit nearly identical rheological parameters and bleeding-segregation characteristics, with w/c = 0.50 for the limestone and 0.55 for the cement. The former was examined at equilibrium pH {approx} 10 and at pH 12.5 following addition of Ca(OH){sub 2} to allow distinction of effects related to high pH and Ca{sup +2} from those related to cement hydration reactions. Both polynaphthalene- (PNS) and polyacrylate-type (PC) superplasticizers were investigated, adjusting the dosages to cover the same range of paste fluidity. Superplasticizer-particle interactions were monitored through binding isotherms and zeta potential measurements. The rheology of the pastes was evaluated through the mini-slump test and dynamic viscosity measurements which yielded key rheological parameters: yield stress, elastic and loss moduli (G' and G'') and zero-shear viscosity ({eta}{sub 0}). The paste stability was monitored as function of time, i.e. migration of solids and liquid phase measured in-situ and in 'real time', through surface bleeding measurements and from a multipoint conductivity method. The results provide new insight on the relative modes of action of PNS- and PC-type superplasticizers as dispersants. Also, the combined rheology and stability data allow an improved description of the processes responsible for bleeding and segregation in cementitious and reference systems.

  10. Fitting mathematical models to describe the rheological behaviour of chocolate pastes

    NASA Astrophysics Data System (ADS)

    Barbosa, Carla; Diogo, Filipa; Alves, M. Rui

    2016-06-01

    The flow behavior is of utmost importance for the chocolate industry. The objective of this work was to study two mathematical models, Casson and Windhab models that can be used to fit chocolate rheological data and evaluate which better infers or previews the rheological behaviour of different chocolate pastes. Rheological properties (viscosity, shear stress and shear rates) were obtained with a rotational viscometer equipped with a concentric cylinder. The chocolate samples were white chocolate and chocolate with varying percentages in cacao (55%, 70% and 83%). The results showed that the Windhab model was the best to describe the flow behaviour of all the studied samples with higher determination coefficients (r2 > 0.9).

  11. Effect of Maltodextrins on the Rheological Properties of Potato Starch Pastes and Gels

    PubMed Central

    Juszczak, Lesław; Gałkowska, Dorota; Fortuna, Teresa

    2013-01-01

    The study examines the effects of maltodextrins saccharified to various degrees on some rheological properties of potato starch dispersions. Pasting characteristics, flow curves, and mechanical spectra were determined for native potato starch and for its blends with potato maltodextrins having dextrose equivalents (DE) of 10.5, 18.4, and 26.5. The results showed that medium-saccharified maltodextrin (DE = 18.4) gave the strongest effect, manifesting itself as a considerable reduction in the viscosity at pasting, a decrease in apparent viscosity during flow, and a decrease in the storage and loss moduli. Addition of high-(DE = 26.5) or low-(DE = 10.5) saccharified maltodextrins had a markedly smaller effect on the rheological properties of starch. The differences in the effects produced by the maltodextrins are closely connected to the degree of polymerisation of the maltooligosaccharides in the systems. PMID:26904612

  12. Effect of various superplasticizers on rheological properties of cement paste and mortars

    SciTech Connect

    Masood, I.; Agarwal, S.K. )

    1994-01-01

    The effect of eight commercial superplasticizers including one developed from Cashew Nut Shell Liquid (CNSL) at CBRI on the rheological properties viz. viscosity and flow of cement paste and mortars have been investigated. The viscosity measurements have been made at various shear rates (5--100 rpm). It is found that at higher rates (100 rpm) even with the low concentration of superplasticizers (0.1), the viscosity of the cement paste is more or less the same as that obtained with 0.6 % dosages of SPs at lesser shear rates. The effect of split addition (delayed addition) of superplasticizers on viscosity of cement paste and 1:3 cement sand mortar have also been studied. A decrease in viscosity due to split addition has been observed in the cement paste and there is an increase of 15--20 % in flow of mortars.

  13. Influence of viscosity modifying admixtures on the rheological behavior of cement and mortar pastes

    NASA Astrophysics Data System (ADS)

    Bouras, R.; Kaci, A.; Chaouche, M.

    2012-03-01

    The influence of Viscosity-modifying admixtures (VMA) dosage rate on the steady state rheological properties, including the yield stress, fluid consistency index and flow behaviour index, of cementitious materials is considered experimentally. The investigation is undertaken both at cement paste and mortar scales. It is found that the rheological behaviour of the material is in general dependent upon shear-rate interval considered. At sufficiently low shear-rates the materials exhibit shear-thinning. This behaviour is attributed to flow-induced defloculation of the solid particles and VMA polymer disentanglement and alignment. At relatively high shear-rates the pastes becomes shear-thickening, due to repulsive interactions among the solid particles. There is a qualitative difference between the influence of VMA dosage at cement and mortar scales: at cement scale we obtain a monotonic increase of the yield stress, while at mortar scale there exists an optimum VMA dosage for which the yield stress is a minimum. The flow behaviour index exhibit a maximum in the case of cement pastes and monotonically decreases in the case of mortars. On the other hand, the fluid consistency index presents a minimum for both cement pastes and mortars.

  14. Studies on the Pasting and Rheology of Rice Starch with Different Protein Residual

    NASA Astrophysics Data System (ADS)

    Lin, Qinlu; Liu, Zhonghua; Xiao, Huaxi; Li, Lihui; Yu, Fengxiang; Tian, Wei

    Indica rice starch and japonica rice starch were used in the study. The protein contents of the two rice variety were respectively 0.43%, 0.62%, 0.84%, 1.08%, 1.25%. The pasting and rheological properties of samples were determined with Rapid Visco Analyzer and dynamic rheometer. The results indicated that, with the increase of protein content, the peak viscosity, breakdown viscosity and final viscosity of rice starch paste decreased, the setback viscosity increased and the pasting temperature did not change significantly. With the increase of protein content, the consistency coefficient of starch decreased, the corresponding yield stress also decreased, however, the flow behavior index increased with the decrease of consistency coefficient. At same temperature, the storage modulus G' was greater when the protein content was higher.

  15. Characterization and modeling of the rheology of cement paste: With applications toward self-flowing materials

    NASA Astrophysics Data System (ADS)

    Saak, Aaron Wilbur

    The objective of this research is to better understand the important mechanisms that control the rheology of cement paste. In order to understand these mechanisms, new experimental techniques are developed. The insights gained through these studies are then applied toward designing self-flowing materials, particularly self-compacting concrete (SCC). A new testing program is developed where both the peak and equilibrium stress flow curves of cement paste are obtained by testing only one sample. Additionally, the influence of wall slip on yield stress and viscoelastic measurements is determined using a vane. The results indicate that a slip layer develops when the shear stress approaches the yield point. A three-dimensional model relating slump to yield stress is derived as a function of cone geometry. The results indicate that the model fits experimental data for cylindrical slumps over a wide range of yield stress values for a variety of materials. When compared to other published models, the results suggest that a fundamental relationship exists between yield stress and slump that is material independent and largely independent of cone geometry. The affect of various mixing techniques on the rheology of cement paste is investigated using a rheometer as a highly controlled mixer. The results suggest that there is a characteristic shear rate where the viscosity of cement paste is minimized. The influence of particle packing density, morphology and surface area on the viscosity of cement paste is quantified. The data suggest that even though packing density increases with the addition of fine particles, the benefits are largely overshadowed by a dramatic increase in surface area. Finally, a new methodology is introduced for designing self-compacting concrete. This approach incorporates a "self-flow zone" where the rheology of the paste matrix provides high workability, yet segregation resistance. The flow properties of fresh concrete are measured using a U

  16. Plasticizer Effect on Rheological Behaviour of Screen Printing Pastes Based on Barium Titanate Nanopowder

    NASA Astrophysics Data System (ADS)

    Dulina, I.; Umerova, S.; Ragulya, A.

    2015-04-01

    The dependence of rheological behaviour of pastes based on BaTiO3 nanopowder vs. plasticizer content has been investigated. All pastes prepared for research can be divided into groups by structure types and viscosity. Such a grouping has been explained by different interaction between nanoparticles and binder in the pastes. Particles with molecules of binder form clusters - the representative units in the volume of paste where particles are uniformly distributed. Plasticizer adding effects on binder molecule conformation and change clusters size. Bond strength between clusters can be specified with rheopexy in the area of low shear stress and low strain rates. Rheopexy degree increasing authenticates interaction intensification between clusters. Rheopexy structure destruction leads to separate clusters formation and initiation of the pseudoplastic flow stage. The end of pseudoplastic flow corresponds to structure with clusters assembled into separated layers. Further shear stress increasing leads to inter-clusters bonds appear which can be deformed elastically and the temporary local linkage is possible. Such a phenomenon fully discloses the features of thixotropic structure destruction in plasticized pastes.

  17. Enabling Surgical Placement of Hydrogels Through Achieving Paste-Like Rheological Behavior in Hydrogel Precursor Solutions.

    PubMed

    Beck, Emily C; Lohman, Brooke L; Tabakh, Daniel B; Kieweg, Sarah L; Gehrke, Stevin H; Berkland, Cory J; Detamore, Michael S

    2015-10-01

    Hydrogels are a promising class of materials for tissue regeneration, but they lack the ability to be molded into a defect site by a surgeon because hydrogel precursors are liquid solutions that are prone to leaking during placement. Therefore, although the main focus of hydrogel technology and developments are on hydrogels in their crosslinked form, our primary focus is on improving the fluid behavior of hydrogel precursor solutions. In this work, we introduce a method to achieve paste-like hydrogel precursor solutions by combining hyaluronic acid nanoparticles with traditional crosslinked hyaluronic acid hydrogels. Prior to crosslinking, the samples underwent rheological testing to assess yield stress and recovery using linear hyaluronic acid as a control. The experimental groups containing nanoparticles were the only solutions that exhibited a yield stress, demonstrating that the nanoparticulate rather than the linear form of hyaluronic acid was necessary to achieve paste-like behavior. The gels were also photocrosslinked and further characterized as solids, where it was demonstrated that the inclusion of nanoparticles did not adversely affect the compressive modulus and that encapsulated bone marrow-derived mesenchymal stem cells remained viable. Overall, this nanoparticle-based approach provides a platform hydrogel system that exhibits a yield stress prior to crosslinking, and can then be crosslinked into a hydrogel that is capable of encapsulating cells that remain viable. This behavior may hold significant impact for hydrogel applications where a paste-like behavior is desired in the hydrogel precursor solution. PMID:25691398

  18. Impact of high pressure treatment on functional, rheological, pasting, and structural properties of lentil starch dispersions.

    PubMed

    Ahmed, Jasim; Thomas, Linu; Taher, Ayoub; Joseph, Antony

    2016-11-01

    Lentil starch (LS) dispersions (flour to water 1:4w/w) were subjected to high pressure (HP) treatment at 0.1, 400, 500 and 600MPa for 10min, followed by evaluation on the functional, particle size, rheological, pasting, and structural properties of post-process samples. Water holding capacity of pressurized starch increased with the pressure intensity due to increase in damaged starch. The amount of resistant starch increased from 5 to 6.8% after pressure treatment at 600MPa. An increase in starch granule particle size (196-207μm) was obvious after HP treatment. The lentil starch was completely gelatinized after pressure treatment at 600MPa for 10min as evidenced from differential scanning calorimetry, rheometry, X-ray diffraction (XRD) and scanning electron microscopy observation. The elastic modulus, G' of lentil starch gel was less frequency dependent, and higher in magnitude at high pressure (>500MPa) than at lower pressure range (≤400MPa). XRD analysis revealed the disappearance of two diffraction peak intensities at 14.86° and 22.82° at 600MPa for 10min, which confirms the transformation of crystalline to amorphous region of lentil starch. Pasting properties were significantly influenced by the pressure treatment especially at 600MPa, resulting in a considerable decrease in peak viscosity, breakdown and final viscosity, and an increase in peak time. It can be inferred that the functional properties of pressure-treated LS are mainly based on the structural destruction of granules. PMID:27516314

  19. Influence of rheology on deposition behavior of ceramic pastes in direct fabrication systems

    SciTech Connect

    King, B.H.; Morissette, S.L.; Denham, H.; Cesarano, J. III; Dimos, D.

    1998-12-01

    Rheology and deposition behavior of four commercially available thick-film inks and an aqueous alumina slurry were investigated using two different slurry-based deposition systems. The first of these deposition systems, a Micropen, is a commercially available system designed for the deposition of electronic thick film circuits. The second system, referred to as a Robocaster, is a developmental system designed to build thick or structural parts. Slurry rheology was seen to have a minor effect on deposition behavior and the bead shape when deposited using the Micropen. The deposition behavior was instead dominated by drying rate; too rapid of a drying rate led to excessive clogging of the tip. Slurry rheology had a greater impact on the shape of beads deposited using the Robocaster. Highly viscous slurries yielded initially well-defined beads, whereas beads deposited using fluid slurries spread quickly. In both cases, significant spreading occurred with time. These observations only held for slurries with slow drying rates. It was observed that very fluid slurries produced well-defined beads when the drying rate was suitably high.

  20. Fly and bottom ashes from biomass combustion as cement replacing components in mortars production: rheological behaviour of the pastes and materials compression strength.

    PubMed

    Maschio, Stefano; Tonello, Gabriele; Piani, Luciano; Furlani, Erika

    2011-10-01

    In the present research mortar pastes obtained by replacing a commercial cement with the equivalent mass of 5, 10, 20 and 30 wt.% of fly ash or bottom ash from fir chips combustion, were prepared and rheologically characterized. It was observed that the presence of ash modifies their rheological behaviour with respect to the reference blend due to the presence, in the ashes, of KCl and K2SO4 which cause precipitation of gypsum and portlandite during the first hydration stages of the pastes. Hydrated materials containing 5 wt.% of ash display compression strength and absorption at 28 d of same magnitude as the reference composition; conversely, progressive increase of ash cause a continuous decline of materials performances. Conversely, samples tested after 180 d display a marked decline of compression strength, as a consequence of potassium elution and consequent alkali-silica reaction against materials under curing. PMID:21762950

  1. On the rheology of pendular gels and morphological developments in paste-like ternary systems based on capillary attraction.

    PubMed

    Domenech, Trystan; Velankar, Sachin S

    2015-02-28

    We investigate capillary bridging-induced gelation phenomena in silica particle suspensions and pastes, where a particle-wetting fluid is added as the third component. Increasing the wetting fluid loading in the ternary system induces a morphological transition from a pendular network to compact capillary aggregates network, with an intermediate funicular state. To our knowledge, the formation of percolated structures from compact capillary aggregates when the volume fraction of a wetting fluid approaches that of the particles is unprecedented. Such structures appear to result from the arrested coalescence of compact capillary aggregates due to the balance between the Laplace pressure and solid-like properties (yield stress, elasticity) of the aggregates. Shear-induced yielding of the ternary systems, linked to their percolating nature, is strongly influenced by the amount of wetting fluid phase. A non-monotonic dependence of the yield stress on the amount of wetting fluid is found, with the maximum yield stress obtained for a wetting fluid-to-particle volume fraction ratio of 0.2-0.3. For pendular systems, linear viscoelastic properties display a soft glassy rheological behavior above the percolation threshold (around 4 vol% particles), and complex viscosity data can be scaled using the high frequency plateau value, as well as a single characteristic relaxation time, which decreases when the particle concentration is increased. In addition, the particle concentration dependence of the yielding transition in the pendular regime appears to be efficiently described by two parameters extracted from the steady state flow curves: the yield stress and the limiting viscosity at a high shear rate. Although these non-colloidal networks result from flow-driven assembly, the scaling laws for our pendular gels are reminiscent of colloidal gels with a fractal geometry. Our studies pinpoint new pathways to create physical gels where the interparticle attraction strength is

  2. Emptying Time of a Tank Filled up with Explosive Paste. Comparison between Experimental Measurements and Predictions Based on Rheological Characterization of the Paste

    NASA Astrophysics Data System (ADS)

    Guillemin, J. P.; Bonnefoy, O.; Thomas, G.; Brunet, L.; Forichon-Chaumet, N.

    2008-07-01

    One industrial process used by Nexter Munitions to manufacture pyrotechnical materials consists in preparing an emulsion of wax in TNT (2,4,6-trinitrotoluene) and adding Aluminium and ONTA (3-nitro-1,2,4-triazole-5-one) particles. When the suspension is homogeneous, it is allowed to flow by gravity through a pipe located at the bottom of the tank and to fill up a shell body. The suspension is characterized by a solid volume fraction of 53.4%, which leads to high viscosities. In some circumstances, the emptying time is prohibitively long and the economic profitability is reduced. This study has been performed to make the emptying time lower with the constraint of unchanged volume fractions and grains mean diameter. So, we investigated the influence of the grain size distribution on the suspension viscosity. Different samples of Aluminium and ONTA have been used, with rather small differences in grain size distributions. The suspensions have been prepared in the industrial tank and the flow cast times measured. It has been observed that they differ by one order of magnitude. To avoid situations with too high emptying times, a procedure has been implemented to make prior characterization of the suspension rheology. Because of particles sedimentation and emulsion destabilisation, the classical Couette rheometer is not adapted. So, we designed and built a small size tank (113 cm3), where the suspension is continuously stirred and kept homogeneous. The measurement of the torque and rotational speed together with the use of the Couette analogy allowed us to observe an Ostwald fluid behaviour (flow consistency index k, flow behaviour index n). For a better prediction, we established a correlation between the measured (k, n) values and the grain size distributions. We characterized each suspension by the ratio of φ to φm, where φ is the solid volume fraction (imposed by the commercial specifications) and φm is the maximum packing fraction. Because of the strong analogy

  3. Effect of an organic additive on the rheology of an aluminous cement paste and consequences on the densification of the hardened material

    NASA Astrophysics Data System (ADS)

    El Hafiane, Y.; Smith, A.; Bonnet, J. P.; Tanouti, B.

    2005-03-01

    The material used in the present work is Secar 71 (Lafarge) mixed with water containing an organic additive (acetic acid noted HOAc). The rheological behavior of these pastes is studied. The best dispersion is obtained when the mass content of the additive with respect to the cement is equal to 0.5%. The microstructural characterizations of samples aged 4 days at 20° C and 95 % relative humidity reveal a significant increase in the density and a reduction in porosity for very small percentages of additive. The remarkable effect of the acetic acid on the microstructure of hardened material is correlated with its good dispersing action.

  4. Effect of S. macrosiphon and L. perfoliatum seed gums on rheological characterization of bitter orange (Citrus aurantium L.) and pomegranate (Punica granatum L.) paste blends.

    PubMed

    Asnaashari, Maryam; Motamedzadegan, Ali; Farahmandfar, Reza; Rad, Tandis Khosravi

    2016-02-01

    The steady shear flow properties of bitter orange and pomegranate pastes and blend of two pastes including 0.5% Salvia macrosiphon (SMG) and L. perfoliatum (LPG) seed gums, two traditional Iranian hydrocolloids, were determined. All treatments exhibited shear-thinning behaviour. LPG added sample showed stronger shear thinning behaviour than the other due to its high molecular weight and intermolecular through hydrogen bonds and polymer entanglement. Ostwald model was found the best model to describe steady shear flow behaviour among different time-independent rheological model applied. Treatments including 0.5% these two seed gums indicated a flow behaviour index less than 0.6 and consistency coefficient raised by increasing concentration from 60 °Bx to 76 °Bx in bitter orange paste (from 0.55 Pa s(n) to 32.58 Pa s(n)), pomegranate paste (from 0.55 Pa s(n) to 84.87 Pa s(n)) and mix of these two pastes (from 0.64 Pa s(n) to 56.9 Pa s(n)). Oscillatory shear data showed weak gel-like behaviour of bitter orange and pomegranate pastes treatments including seed gums with the elastic modulus predominating over the viscous one at lower frequency. However, after weak gel formation, G″ was higher than G' in the frequency range of 0.01 to 10 Hz. An Ostwald model was used to describe the changes of viscose modulus with frequency. The results indicate that the elastic properties of bitter orange/ pomegranate paste and bitter orange paste may be increased by the presence of LPG and SMG due to associations of ordered chain segments of these gums, resulting in a weak three-dimensional network. PMID:27162409

  5. Empirical rheology and pasting properties of soft-textured durum wheat (Triticum turgidum ssp. durum) and hard-textured common wheat (T. aestivum)

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Puroindoline (PIN) proteins are the molecular basis for wheat kernel texture classification and affect flour milling performance. This study aimed at investigating the effect of PINs on kernel physical characteristics and dough rheological properties of common wheat (Alpowa cv, soft wheat) and durum...

  6. New apparatus for simultaneous determination of phase equilibria and rheological properties of fluids at high pressures: Its application to coal pastes studies up to 773 K and 30 MPa

    NASA Astrophysics Data System (ADS)

    Cohen, Albert; Richon, Dominique

    1986-06-01

    In this article, we present a new apparatus based on a static method to simultaneously measure rheological properties of a dense (liquid or liquid+solid) medium and sample phases (dense and gaseous) for analysis purposes. It was especially designed to study coal pastes in the working conditions of hydroliquefaction processes. It can also be used to study other mediums such as asphalts and polymers. The rheometer part of the apparatus was already tested and results published in a previous paper. The ability of the new apparatus to get reliable vapor-liquid equilibrium data in the range of thermal stability of chemical materials is shown as a result of measurements on the nitrogen-n-heptane system at 497.1 K and the methane-n-hexadecane system at 623.1 K and comparison to literature's data. Reproducibility tests have displayed very small data dispersion.

  7. Effect of enzymatic hydrolysis of starch on pasting, rheological and viscoelastic properties of milk-barnyard millet (Echinochloa frumentacea) blends meant for spray drying.

    PubMed

    Kumar, P Arun; Pushpadass, Heartwin A; Franklin, Magdaline Eljeeva Emerald; Simha, H V Vikram; Nath, B Surendra

    2016-10-01

    The influence of enzymatic hydrolysis of starch on the pasting properties of barnyard millet was studied using a rheometer. The effects of blending hydrolyzed barnyard millet wort with milk at different ratios (0:1, 1:1, 1:1.5 and 1:2) on flow and viscoelastic behavior were investigated. From the pasting curves, it was evident that enzymatically-hydrolyzed starch did not exhibit typical pasting characteristics expected of normal starch. The Herschel-Bulkley model fitted well to the flow behaviour data, with coefficient of determination (R(2)) ranging from 0.942 to 0.988. All milk-wort blends demonstrated varying degree of shear thinning with flow behavior index (n) ranging from 0.252 to 0.647. Stress-strain data revealed that 1:1 blend of milk to wort had the highest storage modulus (7.09-20.06Pa) and an elastically-dominant behavior (phase angle <45°) over the tested frequency range. The crossover point of G' and G" shifted to higher frequencies with increasing wort content. From the flow and viscoelastic behavior, it was concluded that the 1:1 blend of milk to wort would have least phase separation and better flowability during spray drying. PMID:27296446

  8. Rheology of hyaluronate.

    PubMed

    Bothner, H; Wik, O

    1987-01-01

    Solutions containing high molecular weight hyaluronate at concentrations around 10 mg/ml exhibit interesting rheological properties due to formation of a highly entangled network of flexible polysaccharide molecules. We have performed an extensive study of the rheological properties of hyaluronate solutions as a function of concentration and molecular weight. In this paper we review some basic rheological concepts, and discuss the rheological properties of hyaluronate solutions at high concentrations and medium to high molecular weights (1-5 million). The bulk viscosity (zero shear viscosity) of hyaluronate solutions is strongly dependent both on concentration and molecular weight. A 2-fold increase in concentration or molecular weight results in a 10-fold increase in bulk viscosity. For application in body compartments, the concentration of hyaluronate cannot be increased much above 10 mg/ml due to the highly non-ideal colloid osmotic behaviour of hyaluronate. High viscosity hyaluronate solutions must therefore be based on high molecular weight material. PMID:3481162

  9. Rheology of Active Gels

    NASA Astrophysics Data System (ADS)

    Chen, Daniel

    2015-03-01

    Active networks drive a diverse range of critical processes ranging from motility to division in living cells, yet a full picture of their rheological capabilities in non-cellular contexts is still emerging, e.g., How does the rheological response of a network capable of remodeling under internally-generated stresses differ from that of a passive biopolymer network? In order to address this and other basic questions, we have engineered an active gel composed of microtubules, bidirectional kinesin motors, and molecular depletant that self-organizes into a highly dynamic network of active bundles. The network continually remodels itself under ATP-tunable cycles of extension, buckling, fracturing, and self-healing. Using confocal rheometry we have simultaneously characterized the network's linear and non-linear rheological responses to shear deformation along with its dynamic morphology. We find several surprising and unique material properties for these active gels; most notably, rheological cloaking, the ability of the active gel to drive large-scale fluid mixing over several orders of flow magnitude while maintaining an invariant, solid-like rheological profile and spontaneous flow under confinement, the ability to exert micro-Newton forces to drive persistent directed motion of the rheometer tool. Taken together, these results and others to be discussed highlight the rich stress-structure-dynamics relationships in this class of biologically-derived active gels.

  10. Rheological Principles for Food Analysis

    NASA Astrophysics Data System (ADS)

    Daubert, Christopher R.; Foegeding, E. Allen

    Food scientists are routinely confronted with the need to measure physical properties related to sensory texture and processing needs. These properties are determined by rheological methods, where rheology is a science devoted to the deformation and flow of all materials. Rheological properties should be considered a subset of the textural properties of foods, because the sensory detection of texture encompasses factors beyond rheological properties. Specifically, rheological methods accurately measure "force," "deformation," and "flow," and food scientists and engineers must determine how best to apply this information. For example, the flow of salad dressing from a bottle, the snapping of a candy bar, or the pumping of cream through a homogenizer are each related to the rheological properties of these materials. In this chapter, we describe fundamental concepts pertinent to the understanding of the subject and discuss typical examples of rheological tests for common foods. A glossary is included as Sect. 30.6 to clarify and summarize rheological definitions throughout the chapter.

  11. Rheology of planetary ices

    SciTech Connect

    Durham, W.B.; Kirby, S.H.; Stern, L.A.

    1996-04-24

    The brittle and ductile rheology of ices of water, ammonia, methane, and other volatiles, in combination with rock particles and each other, have a primary influence of the evolution and ongoing tectonics of icy moons of the outer solar system. Laboratory experiments help constrain the rheology of solar system ices. Standard experimental techniques can be used because the physical conditions under which most solar system ices exist are within reach of conventional rock mechanics testing machines, adapted to the low subsolidus temperatures of the materials in question. The purpose of this review is to summarize the results of a decade-long experimental deformation program and to provide some background in deformation physics in order to lend some appreciation to the application of these measurements to the planetary setting.

  12. Rheology of aqueous foams

    NASA Astrophysics Data System (ADS)

    Dollet, Benjamin; Raufaste, Christophe

    2014-10-01

    Aqueous foams are suspensions of bubbles inside aqueous phases. Their multiphasic composition leads to a complex rheological behavior that is useful in numerous applications, from oil recovery to food/cosmetic processing. Their structure is very similar to the one of emulsions, so that both materials share common mechanical properties. In particular, the presence of surfactants at the gas-liquid interfaces leads to peculiar interfacial and dissipative properties. Foam rheology has been an active research topics and is already reported in several reviews, most of them covering rheometry measurements at the scale of the foam, coupled with interpretations at the local scale of bubbles or interfaces. In this review, we start following this approach, then we try to cover the multiscale features of aqueous foam flows, emphasizing regimes where intermediate length scales need to be taken into account or regimes fast enough regarding internal time scales so that the flow goes beyond the quasi-static limit. xml:lang="fr"

  13. Rheology of emulsions.

    PubMed

    Derkach, Svetlana R

    2009-10-30

    The review is devoted to the historical and modern understanding of rheological properties of emulsions in a broad range of concentration. In the limiting case of dilute emulsions, the discussion is based on the analogy and differences in properties of suspensions and emulsions. For concentrated emulsions, the main peculiarities of their rheological behaviour are considered. Different approaches to understand the concentration dependencies of viscosity are presented and compared. The effects of non-Newtonian flow curves and the apparent transition to yielding with increasing concentration of the dispersed phase are discussed. The problem of droplet deformation in shear fields is touched. The highly concentrated emulsions (beyond the limit of closest packing of spherical particles) are treated as visco-plastic media, and the principle features of their rheology (elasticity, yielding, concentration and droplet size dependencies) are considered. A special attention is paid to the problem of shear stability of drops of an internal phase starting from the theory of the single drop behaviour, including approaches for the estimation of drops' stability in concentrated emulsions. Polymer blends are also treated as emulsions, though taking into account their peculiarities due to the coexistence of two interpenetrated phases. Different theoretical models of deformation of polymer drops were discussed bearing in mind the central goal of predictions of the visco-elastic properties of emulsions as functions of the properties of individual components and the interfacial layer. The role of surfactants is discussed from the point of view of stability of emulsions in time and their special influence on the rheology of emulsions. PMID:19683219

  14. Rheology of giant micelles

    NASA Astrophysics Data System (ADS)

    Cates, M. E.; Fielding, S. M.

    2006-12-01

    Giant micelles are elongated, polymer-like objects created by the self-assembly of amphiphilic molecules (such as detergents) in solution. Giant micelles are typically flexible, and can become highly entangled even at modest concentrations. The resulting viscoelastic solutions show fascinating flow behaviour (rheology) which we address theoretically in this article at two levels. First, we summarize advances in understanding linear viscoelastic spectra and steady-state nonlinear flows, based on microscopic constitutive models that combine the physics of polymer entanglement with the reversible kinetics of self-assembly. Such models were first introduced two decades ago, and since then have been shown to explain robustly several distinctive features of the rheology in the strongly entangled regime, including extreme shear thinning. We then turn to more complex rheological phenomena, particularly involving spatial heterogeneity, spontaneous oscillation, instability and chaos. Recent understanding of these complex flows is based largely on grossly simplified models which capture in outline just a few pertinent microscopic features, such as coupling between stresses and other order parameters such as concentration. The role of ‘structural memory’ (the dependence of structural parameters such as the micellar length distribution on the flow history) in explaining these highly nonlinear phenomena is addressed. Structural memory also plays an intriguing role in the little-understood shear thickening regime, which occurs in a concentration regime close to but below the onset of strong entanglement, and which is marked by a shear-induced transformation from an inviscid to a gelatinous state.

  15. Complex Suspension Rheology Using High Performance Computing

    NASA Astrophysics Data System (ADS)

    Heine, David

    In processing advanced ceramic materials, the properties of the final product depend on the process conditions and the interactions between the materials at the scale of the individual particles. Along with general bulk properties, more subtle properties including particle orientation, segregation, and pore structure must be established during processing to achieve the desired functionality. Accomplishing this requires a thorough understanding of the mesoscale interactions and how they influence the macroscale behavior. We conduct a series of large scale simulations of highly filled polymer-nanoparticle composites as analogs of ceramic pastes and reveal how the ceramic particle and binder properties determine the structure and rheology of the bulk material. As with real ceramic pastes, particle shape and size distribution along with composition determine the shear modulus, extent of segregation, and degree of particle alignment. These factors are influenced by the binder through the rheology of the binder phase and the interaction between binder and particles. This talk presents the results of this study of polymer-nanoparticle composites along with a brief overview of research and development at Corning showing the similarities and differences between research in industry and academia.

  16. Fluctuation theorems and work relations for single polymer rheology

    NASA Astrophysics Data System (ADS)

    Latinwo, Folarin Babajide

    Synthetic and biological polymeric materials are ubiquitous in nature and modern technology. The emergent properties afforded by these materials allows for wide a array of applications as found in adhesives, coatings, and synthetic polymers for plastics. Importantly, the molecular properties of polymeric systems ultimately determine their bulk macroscopic response and behavior in equilibrium and highly nonequilibrium conditions. As a result, the field of single polymer rheology can play a key role in establishing a molecular level understanding of polymeric systems by investigating the dynamics of single chains. Single polymer rheology is now a well-established approach to study polymer dynamics from experimental and computational perspectives. In general, this approach allows for the determination of molecular subpopulations, relaxation, and polymer chain dynamics in a wide variety of flows. Despite recent progress, current methods in single polymer rheology do not allow for the determination of equilibrium and nonequilibrium thermodynamic properties of polymeric systems. Moreover, it is challenging to connect backbone dynamics to key macroscopic rheological phenomena. In this context, the impact of single polymer rheology has remained limited for the past two decades. In this thesis, we address these challenges by developing and applying fluctuation theorems and nonequilibrium work relations to the field of single polymer rheology. The discovery of thermodynamic identities known as nonequilibrium work relations (NWRs) and fluctuation theorems (FTs) has catalyzed recent advances in statistical mechanics. In general, work relations provide an unprecedented route to extract fundamental materials properties of equilibrium and nonequilibrium systems. Furthermore, these identities have uncovered a broad range of unexpected and remarkable thermodynamic phenomena, including molecular level violations to the second law of thermodynamics. In the context of rheology and

  17. The influence of graphene screen printing paste's composition on its viscosity

    NASA Astrophysics Data System (ADS)

    Dybowska-Sarapuk, Ł.; Janczak, D.; Wróblewski, G.; Słoma, M.; Jakubowska, M.

    2015-09-01

    In the thick film technology it is very important that paste can be printed easily on the substrate and that printed pattern is correct and precise. Paste printing behavior is characterized by its rheology. The main aim of this work was to examine the influence of paste composition on the rheology of pastes containing graphene nanoplatelts. The secondary aim was to find the optimal composition of the pastes. The resulting measurements graphs of viscosity curves shows the influence of: binder type, functional phase content, dispersant type and content on the rheological properties of polymer pastes. The thicknesses of printed layers, obtained from pastes which characterized by various viscosity, were measured. At the end composition of the pastes with graphene nanoplatelets that exhibit the best rheological properties was described.

  18. Rheological structure in Mars and its time evolution

    NASA Astrophysics Data System (ADS)

    Azuma, S.; Katayama, I.

    2014-12-01

    Mars is one of the terrestrial planets which are composed of rock and metal such as the Earth. There is no water, no life, and no plate tectonics on Mars, suggesting that Mars and Earth followed different evolutionary paths. Rheological structure, which indicates the deformation behavior and the strength of planetary interior, plays an important role in the evolution of planets. The rheological behavior of planetary interiors is strongly sensitive to temperature, which may produce strong rheological layering. Rheological structure of Mars in past must be different from the current rheological structure. First, the evolutions of temperature profiles in Mars are inferred from the surface heat flow and the heat conduction equation. The surface heat flow of Mars every 1 billion years was calculated from present abundances of the radioactive isotopes (235U, 235U, 232Th, and 40K) and their half-lives (Hahn et al 2011). Based on the temperature profile, we calculate the rheological structure of Mars every 1 billion years using flow-law of plagioclase and olivine. Calculated rheological structure shows that the brittle-ductile transition of present Mars, which is transition of deformation behavior from brittle failure to viscous flow, is deeper as compared with that of past Mars, suggesting that current elastic thickness also becomes thicker than that of past Mars. Under water-saturated conditions, the rheological structure which simulates the northern lowlands shows the strength contrast between the crust and mantle, indicating that the decoupling might occur at the Moho from 4 Ga to present day. Under dry conditions, lithosphere of northern lowlands has no strength contrast at the Moho, implying that crust and mantle might be coupled from 3 Ga to present day. Viscosity contrast between the surface and planetary interior is key for the mantle convection style (Moresi and Solomatov 1995), and the calculated viscosity contrast at present Mars is ~10-5 (Pa), suggesting that

  19. Review Of Rheology Modifiers For Hanford Waste

    SciTech Connect

    Pareizs, J. M.

    2013-09-30

    As part of Savannah River National Laboratory (SRNL)'s strategic development scope for the Department of Energy - Office of River Protection (DOE-ORP) Hanford Tank Waste Treatment and Immobilization Plant (WTP) waste feed acceptance and product qualification scope, the SRNL has been requested to recommend candidate rheology modifiers to be evaluated to adjust slurry properties in the Hanford Tank Farm. SRNL has performed extensive testing of rheology modifiers for use with Defense Waste Processing Facility (DWPF) simulated melter feed - a high undissolved solids (UDS) mixture of simulated Savannah River Site (SRS) Tank Farm sludge, nitric and formic acids, and glass frit. A much smaller set of evaluations with Hanford simulated waste have also been completed. This report summarizes past work and recommends modifiers for further evaluation with Hanford simulated wastes followed by verification with actual waste samples. Based on the review of available data, a few compounds/systems appear to hold the most promise. For all types of evaluated simulated wastes (caustic Handford tank waste and DWPF processing samples with pH ranging from slightly acidic to slightly caustic), polyacrylic acid had positive impacts on rheology. Citric acid also showed improvement in yield stress on a wide variety of samples. It is recommended that both polyacrylic acid and citric acid be further evaluated as rheology modifiers for Hanford waste. These materials are weak organic acids with the following potential issues: The acidic nature of the modifiers may impact waste pH, if added in very large doses. If pH is significantly reduced by the modifier addition, dissolution of UDS and increased corrosion of tanks, piping, pumps, and other process equipment could occur. Smaller shifts in pH could reduce aluminum solubility, which would be expected to increase the yield stress of the sludge. Therefore, it is expected that use of an acidic modifier would be limited to concentrations that do not

  20. Rheology of concentrated biomass

    NASA Astrophysics Data System (ADS)

    Samaniuk, J. R.; Wang, J.; Root, T. W.; Scott, C. T.; Klingenberg, D. J.

    2011-12-01

    Economic processing of lignocellulosic biomass requires handling the biomass at high solids concentration. This creates challenges because concentrated biomass behaves as a Bingham-like material with large yield stresses. Here we employ torque rheometry to measure the rheological properties of concentrated lignocellulosic biomass (corn stover). Yield stresses obtained using torque rheometry agree with those obtained using other rheometric methods, but torque rheometry can be used at much larger solids concentration (weight fractions of insoluble solids greater than 0.2). Yield stresses decrease with severity of hydrolysis, decrease when water-soluble polymers are added (for nonhydrolyzed biomass), and increase with particle length. Experimental results are qualitatively consistent with those obtained from particle-level simulations.

  1. Modelling the rheological behavior of high solids CWM systems using a new rheological equation

    SciTech Connect

    Hafaiedh, A.; Dinger, D.R.; Funk, J.E.

    1986-05-01

    The understanding of the rheology of concentrated suspensions is an important part of the control and preparation of ceramic slips and pastes and coal water slurries. Many studies have been conducted on concentrated suspensions; many attempts have been made to formulate equations which describe their behavior; and many attempts have been made to use these equations to predict the behavior of slurries and slips. This paper describes a modification to one of the more commonly used rheological equations, the Bingham equation (E.C. Bingham, ''An Investigation of the Laws of Plastic Flow'', Bulletin of the Bureau of Standards'', Volume 13, pp. 309-353 (1916-1917)), and the initial attempts to use it to understand and model the rheological behavior of high solids CWM. The paper will include the description of the new equation, its derivation, and examples of the various forms of the resulting rheograms. Then in the second part of the paper, the equation will be used to analyze the behavior of some typical CWM systems made from Cedar Grove and Moss seam coals. 8 refs., 18 figs.

  2. Pasting and rheological properties of chia composites containing barley flour

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The chia containing omega-3 polyunsaturated fatty acids (omega-3 PUFAs) was composited with barley flour having high ß-glucan content. Both omega-3 PUFAs and ß-glucan are well known for lowering blood cholesterol and preventing coronary heart disease. Barley flour was dry blended with ground chia ...

  3. Rheology of biological macromolecules

    NASA Astrophysics Data System (ADS)

    Ariyaratne, Amila Dinesh

    Proteins have interesting mechanical properties in addition to the remarkable functionality. For example, Guanylate kinase is an enzyme that catalyzes Guano- sine monophosphate (GMP) to Guanosine diphosphate (GDP) conversion and this enzyme is approximately 5 nm in size. A gold nano particle of similar size shows linear elasticity for strains up to ˜ 0.1% and shows plastic deformation beyond that, whereas the enzyme Guanylate kinase can have strains up to 1 % with reversible deformation. Our experiments show many different regimes of the mechanical response before the plastic deformation of these proteins. In this dissertation, I study the materials properties of two classes of proteins, an ion channel protein and a transferase, which is a globular protein. The experimental techniques to study the materials properties of these proteins were uniquely developed at the Zocchi lab. Therefore, we were able to observe previously unknown characteristics of these folded proteins. The mechanical properties of the voltage gated potassium channel KvAP was studied by applying AC depolarizing voltages. This technique gave new information about the system that was not seen in the previous studies. These previous experiments were based on applying DC depolarizing voltage steps across the membrane to study the ionic current. By monitoring the ionic current at different depolarizing voltage steps, the DC gating process of the channel could be under- stood. We probed the channel using AC depolarizing signals instead of DC pulses and the ionic current revealed new behaviors, which cannot be predicted with the DC response. We found that the conformational motion of the voltage sensing domain of the ion channel shows internal dissipation. Further, a new non linearity in the dissipation parameter was found in which the dissipation parameter increased with the shear rate of the applied force. Previous studies at the Zocchi lab used a nano rheology experiment on the protein Guanylate

  4. Rheology of magnesite

    NASA Astrophysics Data System (ADS)

    Holyoke, C. W.; Kronenberg, A. K.; Newman, J.; Ulrich, C. A.

    2012-12-01

    Magnesite (MgCO3) may be incorporated in the mantle either by the subduction of weathered oceanic crust or by reaction of lithospheric mantle with CO2, and it is commonly found within serpentinized peridotite bodies. Once magnesite is formed in subducting slabs, it is likely to remain as an important carbon-bearing phase, given that its stability extends to conditions of the mantle transition zone and possibly the lower mantle. Magnesite is a common mineral in kimberlites and it has been found as inclusions in diamonds, trapped at transition zone pressures. Our experimental results suggest that occurrences of magnesite in the mantle will lead to low strength and anomalous mantle rheology. In order to quantify the rheology of polycrystalline magnesite, we performed a series of triaxial compression experiments on cylinders of natural fine- (d~1 μm) and coarse-grained (d~100 μm) magnesite aggregates at temperatures of 400-1000°C and strain rates of 10-4/s - 10-7/s, at effective pressures of 300 and 900 MPa. Flow strengths of the fine-grained magnesite are only weakly dependent on temperature from 400 to 600°C at 1*10-5/s and decrease significantly at greater temperature, from 500 MPa (at T = 600°C) to 5 MPa (at T = 775°C). Strain rate stepping experiments performed at 650 to 750°C indicate that creep of the fine-grained magnesite in the strongly temperature dependent regime is nearly linear-viscous. Flow strengths of the coarse-grained magnesite are weakly dependent on temperature from 400 to 600°C at 1*10-5/s, gradually increase in temperature dependence from 600°C to 800°C, and become strongly temperature dependent from 800 to 1000°C (strengths decrease from 230 MPa to 30 MPa over this range). Strain rate stepping experiments performed at 500°C and 950°C indicate that the strain rate sensitivity of the strength of coarse-grained magnesite increases as the temperature sensitivity increases. The mechanical data of experiments on fine- and coarse

  5. Quantitative Rheological Model Selection

    NASA Astrophysics Data System (ADS)

    Freund, Jonathan; Ewoldt, Randy

    2014-11-01

    The more parameters in a rheological the better it will reproduce available data, though this does not mean that it is necessarily a better justified model. Good fits are only part of model selection. We employ a Bayesian inference approach that quantifies model suitability by balancing closeness to data against both the number of model parameters and their a priori uncertainty. The penalty depends upon prior-to-calibration expectation of the viable range of values that model parameters might take, which we discuss as an essential aspect of the selection criterion. Models that are physically grounded are usually accompanied by tighter physical constraints on their respective parameters. The analysis reflects a basic principle: models grounded in physics can be expected to enjoy greater generality and perform better away from where they are calibrated. In contrast, purely empirical models can provide comparable fits, but the model selection framework penalizes their a priori uncertainty. We demonstrate the approach by selecting the best-justified number of modes in a Multi-mode Maxwell description of PVA-Borax. We also quantify relative merits of the Maxwell model relative to powerlaw fits and purely empirical fits for PVA-Borax, a viscoelastic liquid, and gluten.

  6. Surface rheology and interface stability.

    SciTech Connect

    Yaklin, Melissa A.; Cote, Raymond O.; Moffat, Harry K.; Grillet, Anne Mary; Walker, Lynn; Koehler, Timothy P.; Reichert, Matthew D.; Castaneda, Jaime N.; Mondy, Lisa Ann; Brooks, Carlton, F.

    2010-11-01

    We have developed a mature laboratory at Sandia to measure interfacial rheology, using a combination of home-built, commercially available, and customized commercial tools. An Interfacial Shear Rheometer (KSV ISR-400) was modified and the software improved to increase sensitivity and reliability. Another shear rheometer, a TA Instruments AR-G2, was equipped with a du Nouey ring, bicone geometry, and a double wall ring. These interfacial attachments were compared to each other and to the ISR. The best results with the AR-G2 were obtained with the du Nouey ring. A Micro-Interfacial Rheometer (MIR) was developed in house to obtain the much higher sensitivity given by a smaller probe. However, it was found to be difficult to apply this technique for highly elastic surfaces. Interfaces also exhibit dilatational rheology when the interface changes area, such as occurs when bubbles grow or shrink. To measure this rheological response we developed a Surface Dilatational Rheometer (SDR), in which changes in surface tension with surface area are measured during the oscillation of the volume of a pendant drop or bubble. All instruments were tested with various surfactant solutions to determine the limitations of each. In addition, foaming capability and foam stability were tested and compared with the rheology data. It was found that there was no clear correlation of surface rheology with foaming/defoaming with different types of surfactants, but, within a family of surfactants, rheology could predict the foam stability. Diffusion of surfactants to the interface and the behavior of polyelectrolytes were two subjects studied with the new equipment. Finally, surface rheological terms were added to a finite element Navier-Stokes solver and preliminary testing of the code completed. Recommendations for improved implementation were given. When completed we plan to use the computations to better interpret the experimental data and account for the effects of the underlying bulk

  7. Rheological behavior of oxide nanopowder suspensions

    NASA Astrophysics Data System (ADS)

    Cinar, Simge

    Ceramic nanopowders offer great potential in advanced ceramic materials and many other technologically important applications. Because a material's rheological properties are crucial for most processing routes, control of the rheological behavior has drawn significant attention in the recent past. The control of rheological behavior relies on an understanding of how different parameters affect the suspension viscosities. Even though the suspension stabilization mechanisms are relatively well understood for sub-micron and micron size particle systems, this knowledge cannot be directly transferred to nanopowder suspensions. Nanopowder suspensions exhibit unexpectedly high viscosities that cannot be explained with conventional mechanisms and are still a topic of investigation. This dissertation aims to establish the critical parameters governing the rheological behavior of concentrated oxide nanopowder suspensions, and to elucidate the mechanisms by which these parameters control the rheology of these suspensions. Aqueous alumina nanopowders were chosen as a model system, and the findings were extrapolated to other oxide nanopowder systems such as zirconia, yttria stabilized zirconia, and titania. Processing additives such as fructose, NaCl, HCl, NaOH, and ascorbic acid were used in this study. The effect of solids content and addition of fructose on the viscosity of alumina nanopowder suspensions was investigated by low temperature differential scanning calorimetry (LT-DSC), rheological, and zeta potential measurements. The analysis of bound water events observed in LT-DSC revealed useful information regarding the rheological behavior of nanopowder suspensions. Because of the significance of interparticle interactions in nanopowder suspensions, the electrostatic stabilization was investigated using indifferent and potential determining ions. Different mechanisms, e.g., the effect of the change in effective volume fraction caused by fructose addition and electrostatic

  8. Rheology of Model Dough Formulation

    NASA Astrophysics Data System (ADS)

    Desai, Kiran; Lele, Smita; Lele, Ashish

    2008-07-01

    Dough is generally considered a viscoelastic material, and its elasticity is attributed to the hydrated gluten matrix. Since starch is a major constituent of flour (˜70 wt% on dry basis) we may expect it to contribute to dough rheology in a non-trivial manner. Considering dough to belong to the generic class of soft solid materials, we use the Strain-Rate Frequency Superposition (SRFS) technique to study rheology of various model dough compositions in which the starch/gluten ratio is systematically varied from 100/0 to 0/100. We find that for compositions containing 0-25% gluten the SRFS superposition principle works well, while for compositions containing greater than 25% gluten the quality of SRFS mastercurves deteriorates gradually. Thus we propose that starch particles contribute substantially to the rheology of dough containing up to 25% gluten.

  9. Local Oscillatory Rheology from Echography

    NASA Astrophysics Data System (ADS)

    Saint-Michel, Brice; Gibaud, Thomas; Leocmach, Mathieu; Manneville, Sébastien

    2016-03-01

    Local oscillatory rheology from echography consists of a traditional rheology experiment synchronized with high-frequency ultrasonic imaging which gives access to the local material response to oscillatory shear. Besides classical global rheological quantities, this method provides quantitative time-resolved information on the local displacement across the entire gap of the rheometer. From the local displacement response, we compute and decompose the local strain in its Fourier components and measure the spatially resolved viscoelastic moduli. After benchmarking our method on homogeneous Newtonian fluids and soft solids, we demonstrate that this technique is well suited to characterize spatially heterogeneous samples, wall slip, and the emergence of nonlinearity under large-amplitude oscillatory stress in soft materials.

  10. Course 3: Structural Relaxation and Rheology of Soft Condensed Matter

    NASA Astrophysics Data System (ADS)

    Cates, M. E.

    These lectures address the relation between structural dynamics and macroscopic flow behaviour (rheology) in soft condensed matter. After a brief introductions to soft condensed matter, various types of observed rheological behaviour are introduced and classified. I then move on to discuss the flow of entangled polymers. These exhibit slow dynamics, but nevertheless remain close to equilibrium locally at all times. I outline a simple version of the tube model as developed for nonlinear flows by Doi and Edwards in the late 1970s, and also outline an even simpler dumbell model. The success of these polymer models is hard to emulate, especially in systems which are nonergodic at rest. Those include many kinds of pastes, dense emulsions, liquid crystal textures etc., and recent attempts are described to develop rheological constitutive equations for these soft glasses. This is followed by a discussion of rheological aging, in which the flow properties of a sample depend on the time since its preparation. I then discuss some simple models of shear thickening, which attempt to connect jamming phenomena, seen in colloids and some other materials, with a stress-induced glass transition. Finally, I point to ongoing work on two further topics: chaotic dynamics in the flow of soft materials (rheochaos) and fundamental approaches to glasses under flow (based on mode-coupling theory).

  11. Microgravity foam structure and rheology

    NASA Technical Reports Server (NTRS)

    Durian, Douglas J.; Gopal, Anthony D.

    1994-01-01

    Our long-range objective is to establish the fundamental interrelationship between the microscopic structure and dynamics of foams and their macroscopic stability and rheology. Foam structure and dynamics are to be measured directly and noninvasively through the use and development of novel multiple light scattering techniques such as diffusing-wave spectroscopy (DWS). Foam rheology is to be measured in a custom rheometer which allows simultaneous optical access for multiple light drainage of liquid from in between gas bubbles as the liquid:gas volume fraction in increased towards the rigidity-loss transition.

  12. SUMMARY OF 2009 RHEOLOGY MODIFIER PROGRAM

    SciTech Connect

    Hansen, E.

    2009-12-08

    The overall objective of the EM-31 Rheological Modifiers and Wetting Agents program is to utilize commercially available rheology modifiers to increase the solids fraction of radioactive sludge based waste streams, resulting in an increase in throughput and decreasing the overall processing time. The program first investigates the impact of rheology modifiers on slurry simulants and then utilizes the most effective rheology modifiers on radioactive slurries. The work presented in this document covers the initial investigation of rheology modifier testing with simulants. This task is supported by both the Savannah River National Laboratory (SRNL) and Pacific Northwest National Laboratory (PNNL). The SRNL EM-31 task, for this year, was to investigate the use of rheology modifiers on simulant Defense Waste Processing Facility (DWPF) melter feeds. The task is to determine, based on the impact of the rheology modifier, if there are rheology modifiers that could reduce the water content of the slurry going to the DWPF melter, hence increasing the melt rate by decreasing the water loading. The rheology modifier in essence would allow a higher solids content slurry to have the same type of rheology or pumpability of a lower solids slurry. The modifiers selected in this report were determined based on previous modifiers used in high level waste melter feed simulants, on-going testing performed by counterparts at PNNL, and experiences gain through use of modifiers in other Department of Energy (DOE) processes such as grout processing. There were 12 rheology modifiers selected for testing, covering both organic and inorganic types and they were tested at four different concentrations for a given melter feed. Five different DWPF melter feeds were available and there was adequate material in one of the melter feeds to increase the solids concentration, resulting in a total of six simulants for testing. The mass of melter feed available in each simulant was not adequate for

  13. Modification of rheological, thermal and functional properties of tapioca starch using gum arabic

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The addition of gum arabic (GA) to native tapioca starch (TS) to modify the functionality of TS was investigated. GA is well known for its stabilizing, emulsifying, and thickening properties. The effects of adding GA (0.1-1.0%) on pasting, rheological and solubility properties of TS (5%) were analy...

  14. Anesthetics and red blood cell rheology

    NASA Astrophysics Data System (ADS)

    Aydogan, Burcu; Aydogan, Sami

    2014-05-01

    There are many conditions where it is useful for anesthetists to have a knowledge of blood rheology. Blood rheology plays an important role in numerous clinical situations. Hemorheologic changes may significantly affect the induction and recovery times with anesthetic agents. But also, hemorheologic factors are directly or indirectly affected by many anesthetic agents or their metabolites. In this review, the blood rheology with special emphasis on its application in anesthesiology, the importance hemorheological parameters in anesthesiology and also the effect of some anesthetic substances on red blood cell rheology were presented.

  15. Nonequilibrium thermodynamics of the soft glassy rheology model.

    PubMed

    Fuereder, Ingo; Ilg, Patrick

    2013-10-01

    The soft glassy rheology (SGR) model is a mesoscopic framework which proved to be very successful in describing flow and deformation of various amorphous materials phenomenologically (e.g., pastes, slurries, foams, etc.). In this paper, we cast SGR in a general, model-independent framework for nonequilibrium thermodynamics called general equation for the nonequilibrium reversible-irreversible coupling. This leads to a formulation of SGR which clarifies how it can properly be coupled to hydrodynamic fields, resulting in a thermodynamically consistent, local, continuum version of SGR. Additionally, we find that compliance with thermodynamics imposes the existence of a modification to the stress tensor as predicted by SGR. PMID:24229142

  16. Microgravity Foam Structure and Rheology

    NASA Technical Reports Server (NTRS)

    Durian, Douglas J.

    1997-01-01

    To exploit rheological and multiple-light scattering techniques, and ultimately microgravity conditions, in order to quantify and elucidate the unusual elastic character of foams in terms of their underlying microscopic structure and dynamics. Special interest is in determining how this elastic character vanishes, i.e. how the foam melts into a simple viscous liquid, as a function of both increasing liquid content and shear strain rate. The unusual elastic character of foams will be quantified macroscopically by measurement of the shear stress as a function of static shear strain, shear strain rate, and time following a step strain; such data will be analyzed in terms of a yield stress, a static shear modulus, and dynamical time scales. Microscopic information about bubble packing and rearrangement dynamics, from which these macroscopic non-Newtonian properties presumably arise, will be obtained non-invasively by novel multiple-light scattering diagnostics such as Diffusing-Wave Spectroscopy (DWS). Quantitative trends with materials parameters, such as average bubble size, and liquid content, will be sought in order to elucidate the fundamental connection between the microscopic structure and dynamics and the macroscopic rheology.

  17. Blood Rheology in Marine Mammals

    PubMed Central

    Castellini, Michael A.; Baskurt, Oguz; Castellini, Judith M.; Meiselman, Herbert J.

    2010-01-01

    The field of blood oxygen transport and delivery to tissues has been studied by comparative physiologists for many decades. Within this general area, the particular differences in oxygen delivery between marine and terrestrial mammals has focused mainly on oxygen supply differences and delivery to the tissues under low blood flow diving conditions. Yet, the study of the inherent flow properties of the blood itself (hemorheology) is rarely discussed when addressing diving. However, hemorheology is important to the study of marine mammals because of the critical nature of the oxygen stores that are carried in the blood during diving periods. This review focuses on the essential elements of hemorheology, how they are defined and on fundamental rheological applications to marine mammals. While the comparative rationale used throughout the review is much broader than the particular problems associated with diving, the basic concepts focus on how changes in the flow properties of whole blood would be critical to oxygen delivery during diving. This review introduces the reader to most of the major rheological concepts that are relevant to the unique and unusual aspects of the diving physiology of marine mammals. PMID:21423386

  18. Nonlinear rheology of colloidal dispersions.

    PubMed

    Brader, J M

    2010-09-15

    Colloidal dispersions are commonly encountered in everyday life and represent an important class of complex fluid. Of particular significance for many commercial products and industrial processes is the ability to control and manipulate the macroscopic flow response of a dispersion by tuning the microscopic interactions between the constituents. An important step towards attaining this goal is the development of robust theoretical methods for predicting from first-principles the rheology and nonequilibrium microstructure of well defined model systems subject to external flow. In this review we give an overview of some promising theoretical approaches and the phenomena they seek to describe, focusing, for simplicity, on systems for which the colloidal particles interact via strongly repulsive, spherically symmetric interactions. In presenting the various theories, we will consider first low volume fraction systems, for which a number of exact results may be derived, before moving on to consider the intermediate and high volume fraction states which present both the most interesting physics and the most demanding technical challenges. In the high volume fraction regime particular emphasis will be given to the rheology of dynamically arrested states. PMID:21386516

  19. Buckwheat and Millet Affect Thermal, Rheological, and Gelling Properties of Wheat Flour.

    PubMed

    Wu, Kao; Gan, Renyou; Dai, Shuhong; Cai, Yi-Zhong; Corke, Harold; Zhu, Fan

    2016-03-01

    Buckwheat (BF) and millet (MF) are recommended as healthy foods due to their unique chemical composition and health benefits. This study investigated the thermal and rheological properties of BF-WF (wheat flour) and MF-WF flour blends at various ratios (0:100 to 100:0). Increasing BF or MF concentration led to higher cold paste viscosity and setback viscosity of pasting properties gel adhesiveness, storage modulus (G') and loss modulus (G″) of dynamic oscillatory rheology, and yield stress (σ0 ) of flow curve of WF. BF and MF addition decreased peak viscosity and breakdown of pasting, gel hardness, swelling volume, and consistency coefficient (K) of flow curve of WF. Thermal properties of the blends appeared additive of that of individual flour. Nonadditive effects were observed for some property changes in the mixtures, and indicated interactions between flour components. This may provide a physicochemical basis for using BF and MF in formulating novel healthy products. PMID:26890337

  20. Rheologically interesting polysaccharides from yeasts

    NASA Technical Reports Server (NTRS)

    Petersen, G. R.; Nelson, G. A.; Cathey, C. A.; Fuller, G. G.

    1989-01-01

    We have examined the relationships between primary, secondary, and tertiary structures of polysaccharides exhibiting the rheological property of friction (drag) reduction in turbulent flows. We found an example of an exopolysaccharide from the yeast Cryptococcus laurentii that possessed high molecular weight but exhibited lower than expected drag reducing activity. Earlier correlations by Hoyt showing that beta 1 --> 3, beta 2 --> 4, and alpha 1 --> 3 linkages in polysaccharides favored drag reduction were expanded to include correlations to secondary structure. The effect of sidechains in a series of gellan gums was shown to be related to sidechain length and position. Disruption of secondary structure in drag reducing polysaccharides reduced drag reducing activity for some but not all exopolysaccharides. The polymer from C. laurentii was shown to be more stable than xanthan gum and other exopolysaccharides under the most vigorous of denaturing conditions. We also showed a direct relationship between extensional viscosity measurements and the drag reducing coefficient for four exopolysaccharides.

  1. The Rheology of Concentrated Suspensions

    SciTech Connect

    Andreas Acrivos

    2004-09-07

    Research program on the rheological properties of flowing suspensions. The primary purpose of the research supported by this grant was to study the flow characteristics of concentrated suspensions of non-colloidal solid particles and thereby construct a comprehensive and robust theoretical framework for modeling such systems quantitatively. At first glance, this seemed like a modest goal, not difficult to achieve, given that such suspensions were viewed simply as Newtonian fluids with an effective viscosity equal to the product of the viscosity of the suspending fluid times a function of the particle volume fraction. But thanks to the research findings of the Principal Investigator and of his Associates, made possible by the steady and continuous support which the PI received from the DOE Office of Basic Energy Sciences, the subject is now seen to be more complicated and therefore much more interesting in that concentrated suspensions have been shown to exhibit fascinating and unique rheological properties of their own that have no counterpart in flowing Newtonian or even non-Newtonian (polymeric) fluids. In fact, it is generally acknowledged that, as the result of these investigations for which the PI received the 2001 National Medal of Science, our understanding of how suspensions behave under flow is far more detailed and comprehensive than was the case even as recently as a decade ago. Thus, given that the flow of suspensions plays a crucial role in many diverse physical processes, our work has had a major and lasting impact in a subject having both fundamental as well as practical importance.

  2. Thixotropic properties of waxy potato starch depending on the degree of the granules pasting.

    PubMed

    Krystyjan, Magdalena; Sikora, Marek; Adamczyk, Greta; Dobosz, Anna; Tomasik, Piotr; Berski, Wiktor; Łukasiewicz, Marcin; Izak, Piotr

    2016-05-01

    This paper presents the rheological instability (thixotropy/antithixotropy) of waxy potato starch (WPS) pastes depending on their concentration (1-5% w/w) and pasting temperature (80, 95 and autoclaved: 121°C, at 0.1MPa). The hysteresis loop, apparent viscosity at constant shear rate as well as the in-shear structural recovery tests with and without pre-shearing were applied. The pastes were also characterized by the granularity profile, molecular weight, polydispersity and optical transmittance. Differences in rheological properties of the pastes prepared at 80 and 95°C as well as autoclaved resulted from degree of granules pasting. At 121 °C dissolution of the granules occurred, while at the lower temperatures only the partial pasting of the granules took place. Pasting temperature of WPS significantly influenced rheological parameters of the resulted pastes which had thixotropic, antithixotropic or mixed thixotropic/antithixotropic behavior. Autoclaved pastes, regardless their concentration were antithixotropic as demonstrated by the areas of hysteresis loops derived from the flow curves signalized by the degree of structure recovery (DSR) which exceeded unity. The apparent viscosity of WPS pasted at 121°C strongly decreased as compared to the samples pasted at lower temperatures. Samples pasted at 80 and 95°C showed both thixotropic and antithixotropic behavior, with a predominance of the latter. The starch concentration played an important role in the formation of the rheological properties of the resulted pastes. Its influence was strongly connected with the degree of the granules pasting, therefore with the temperature of pastes preparation. For the pastes prepared at 80 and 95°C the values of thixotropy and apparent viscosity increased, while the values of DSR decreased with an increase of concentration. In the autoclaved pastes the antithixotropy, DSR and apparent viscosity increased with increasing starch concentration. It was also found that apart

  3. Rheology of weakly vibrated granular media

    NASA Astrophysics Data System (ADS)

    Wortel, Geert H.; Dijksman, Joshua A.; van Hecke, Martin

    2014-01-01

    We probe the rheology of weakly vibrated granular flows as function of flow rate, vibration strength, and pressure by performing experiments in a vertically vibrated split-bottom shear cell. For slow flows, we establish the existence of a vibration-dominated granular flow regime, where the driving stresses smoothly vanish as the driving rate is diminished. We distinguish three qualitatively different vibration-dominated rheologies, most strikingly a regime where the shear stresses no longer are proportional to the pressure.

  4. On the cytoskeleton and soft glassy rheology.

    PubMed

    Mandadapu, Kranthi K; Govindjee, Sanjay; Mofrad, Mohammad R K

    2008-01-01

    The cytoskeleton is a complex structure within the cellular corpus that is responsible for the main structural properties and motilities of cells. A wide range of models have been utilized to understand cytoskeletal rheology and mechanics (see e.g. [Mofrad, M., Kamm, R., 2006. Cytoskeletal Mechanics: Models and Measurements. Cambridge University Press, Cambridge]). From this large collection of proposed models, the soft glassy rheological model (originally developed for inert soft glassy materials) has gained a certain traction in the literature due to the close resemblance of its predictions to certain mechanical data measured on cell cultures [Fabry, B., Maksym, G., Butler, J., Glogauer, M., Navajas, D., Fredberg, J., 2001. Scaling the microrheology of living cells. Physical Review Letters 87, 14102]. We first review classical linear rheological theory in a concise fashion followed by an examination of the soft glassy rheological theory. With this background we discuss the observed behavior of the cytoskeleton and the inherent limitations of classical rheological models for the cytoskeleton. This then leads into a discussion of the advantages and disadvantages presented to us by the soft glassy rheological model. We close with some comments of caution and recommendations on future avenues of exploration. PMID:18402964

  5. Rheology of Diabase: Implications for Tectonics on Venus and Mars

    NASA Technical Reports Server (NTRS)

    Kohlstedt, David L.

    2001-01-01

    Two important goals of our experimental investigation of the rheological behavior of diabase rocks were: (1) to determine flow laws describing their creep behavior over wide ranges of temperature, stress and strain rate and (2) to develop an understanding of the physical mechanisms by which these rocks flow under laboratory conditions. With this basis, a primary objective then was to construct constitutive equations that can be used to extrapolate from laboratory to planetary conditions. We specifically studied the rheological properties of both natural rock samples and synthetic aggregates. The former provided constraints for geologic systems, while the latter defined the relative contributions of the constituent mineral phases and avoided the influence of glass/melt found in natural samples. In addition, partially molten samples of crustal rock composition were deformed in shear to large strains (greater than 200%) important in crustal environments. The results of this research yielded essential rheological properties essential for models of crustal deformation on terrestrial planets, specifically Venus and Mars, as well as on the geodynamical evolution of these planets. Over the past three years, we also completed our investigation of the creep behavior of water ice with applications to the glaciers, ice sheets and icy satellites. Constitutive equations were determined that describe flow over a wide ranged of stress, strain rate, grain size and temperature. In the case of ice, three creep regimes were delineate. Extrapolation demonstrates that dislocation glide and grain boundary sliding processes dominate flow in ice I under planetary conditions and that diffusion creep is not an important deformation mechanism either in the laboratory or on icy satellites. These results have already been incorporated by other investigators into models describing, for example, the thickness and stability of the ice shell on Europa and to unravel long-standing discrepancies

  6. The rheology of structured materials

    NASA Astrophysics Data System (ADS)

    Sun, Ning

    2000-10-01

    In this work, the rheological properties of structured materials are studied via both theoretical (continuum mechanics and molecular theory) and experimental approaches. Through continuum mechanics, a structural model, involving shear-induced structural breakdown and buildup, is extended to model biofluids. In particular, we study the cases of steady shear flow, hysteresis, yield stress, small amplitude oscillatory flow as well as non-linear viscoelasticity. Model predictions are successfully compared with experimental data on complex materials such as blood and a penicillin suspension. Next, modifications are introduced into the network model. A new formulation involving non-affine motion is proposed and its applications are presented. The major improvement is that a finite elongational viscosity is predicted for finite elongational rate, contrary to infinite elongational viscosities existing at some elongational rates predicted by most previous network models. Comparisons with experimental data on shear viscosity, primary normal stress coefficient and elongational viscosity are given, in terms of the same set of model parameters. Model predictions for the stress growth are also shown. The model is successfully tested with data on a polyisobutylene solution (S1), on a polystyrene solution and on a poly-alpha-methylstyrene solution. A further extension of the network model is related to the prediction of the stress jump phenomenon which is defined as the instantaneous gain or loss of stress on startup or cessation of a deformation. It is not predicted by most existing models. In this work, the internal viscosity idea used in the dumbbell model is incorporated into the transient network model. Via appropriate approximations, a closed form constitutive equation, which predicts a stress jump, is obtained. Successful comparisons with the available stress jump measurements are given. In addition, the model yields good quantitative predictions of the standard steady

  7. Magma rheology variation in sheet intrusions (Invited)

    NASA Astrophysics Data System (ADS)

    Magee, C.; O'Driscoll, B.; Petronis, M. S.; Stevenson, C.

    2013-12-01

    The rheology of magma fundamentally controls igneous intrusion style as well as the explosivity and type of volcanic eruptions. Importantly, the dynamic interplay between the viscosity of magma and other processes active during intrusion (e.g., crystallisation, magma mixing, assimilation of crystal mushes and/or xenolith entrainment) will likely bear an influence on the temporal variation of magma rheology. Constraining the timing of rheological changes during magma transit therefore plays an important role in understanding the nuances of volcanic systems. However, the rheological evolution of actively emplacing igneous intrusions cannot be directly studied. While significant advances have been made via experimental modelling and analysis of lava flows, how these findings relate to intruding magma remains unclear. This has led to an increasing number of studies that analyse various characteristics of fully crystallised intrusions in an attempt to ';back-out' the rheological conditions governing emplacement. For example, it has long been known that crystallinity affects the rheology and, consequently, the velocity of intruding magma. This means that quantitative textural analysis of crystal populations (e.g., crystal size distribution; CSD) used to elucidate crystallinity at different stages of emplacement can provide insights into magma rheology. Similarly, methods that measure flow-related fabrics (e.g., anisotropy of magnetic susceptibility; AMS) can be used to discern velocity profiles, a potential proxy for the magma rheology. To illustrate these ideas, we present an integrated AMS and petrological study of several sheet intrusions located within the Ardnamurchan Central Complex, NW Scotland. We focus on the entrainment and transport dynamics of gabbroic inclusions that were infiltrated by the host magma upon entrainment. Importantly, groundmass magnetic fabrics within and external to these inclusions are coaxial. This implies that a deviatoric stress was

  8. The rheology of icy satellites

    NASA Technical Reports Server (NTRS)

    Sammis, C. G.

    1984-01-01

    High-temperature creep in orthoenstatite under conditions of controlled oxygen fugacity was studied. It was found that creep was conttrolled by the extremely thin layer of SiO2 which wetted the grain boundaries. Slight reduction of the (Mg, Fe)SiO3 enstatite during hot pressing produced microscopic particles of Fe and the thin film of intergranular SiO2. This result highlights another complication in determining the flow properties of iron bearing silicates which constitute the bulk of terrestrial planets and moons. The Phenomenon may be important in the ductile formation of any extraterrestrial body which is formed in a reducing environment. The rheology of dirty ice was studied. This involves micromechanical modeling of hardening phenomena due to contamination by a cosmic distribution of silicate particles. The larger particles are modeled by suspension theory. In order to handle the distribution of particles sizes, the hardening is readed as a critical phenomenon, and real space renormalization group techniques are used. Smaller particles interact directly with the dislocations. The particulate hardening effect was studied in metals. The magnitude of such hardening in ice and the defect chemistry of ice are studied to assess the effects of chemical contamination by methane, ammonia, or other likely contaminants.

  9. Lubricant Rheology in Concentrated Contacts

    NASA Technical Reports Server (NTRS)

    Jacobson, B. O.

    1984-01-01

    Lubricant behavior in highly stressed situtations shows that a Newtonian model for lubricant rheology is insufficient for explanation of traction behavior. The oil film build up is predicted by using a Newtonian lubricant model except at high slide to roll ratios and at very high loads, where the nonNewtonian behavior starts to be important already outside the Hertzian contact area. Static and dynamic experiments are reported. In static experiments the pressure is applied to the lubricant more than a million times longer than in an EHD contact. Depending on the pressure-temperature history of the experiment the lubricant will become a crystallized or amorphous solid at high pressures. In dynamic experiments, the oil is in an amorphous solid state. Depending on the viscosity, time scale, elasticity of the oil and the bearing surfaces, the oil film pressure, shear strain rate and the type of lubricant, different properties of the oil are important for prediction of shear stresses in the oil. The different proposed models for the lubricant, which describe it to a Newtonian liquid, an elastic liquid, a plastic liquid and an elastic-plastic solid.

  10. The effect of water to mantle rheology and convection

    NASA Astrophysics Data System (ADS)

    Brändli, Stefan

    2016-04-01

    Water has a significant influence to mantle rheology and therefore also to the convection of the mantle and the plate tectonics. The viscosity of the mantle can be decreased by up to two orders of magnitude when water is present. Another effect of the water is the change in the solidus of the mantle and therefore the melting regime. These two effects of water in the mantle have a significant influence on mantle convection and plate tectonics. The influx of water to the mantle is driven by plate tectonics as wet oceanic lithosphere is subducted into the mantle, then water is brought back to the lithosphere and the surface by MOR-, arc- and hotspot volcanism. Studies show that the amount of water in the mantle is about three times bigger than the water in the oceans. To model this water cycle multiple additions to our simulation code StagYY are necessary. A water diffusion to complement the water transport due to advection, and water dependent viscosity law are implemented. This additions to StagYY will be followed by implementations of a pressure-temperature law for maximum water content, additional transport mechanisms for water, water dependent solidus functions and the implementation of recent values for plate velocities and water capacities in subducting slabs. This will allow us to research the influence of water to the mantle convection and rheology over the past 200Ma.

  11. Fault rheology beyond frictional melting.

    PubMed

    Lavallée, Yan; Hirose, Takehiro; Kendrick, Jackie E; Hess, Kai-Uwe; Dingwell, Donald B

    2015-07-28

    During earthquakes, comminution and frictional heating both contribute to the dissipation of stored energy. With sufficient dissipative heating, melting processes can ensue, yielding the production of frictional melts or "pseudotachylytes." It is commonly assumed that the Newtonian viscosities of such melts control subsequent fault slip resistance. Rock melts, however, are viscoelastic bodies, and, at high strain rates, they exhibit evidence of a glass transition. Here, we present the results of high-velocity friction experiments on a well-characterized melt that demonstrate how slip in melt-bearing faults can be governed by brittle fragmentation phenomena encountered at the glass transition. Slip analysis using models that incorporate viscoelastic responses indicates that even in the presence of melt, slip persists in the solid state until sufficient heat is generated to reduce the viscosity and allow remobilization in the liquid state. Where a rock is present next to the melt, we note that wear of the crystalline wall rock by liquid fragmentation and agglutination also contributes to the brittle component of these experimentally generated pseudotachylytes. We conclude that in the case of pseudotachylyte generation during an earthquake, slip even beyond the onset of frictional melting is not controlled merely by viscosity but rather by an interplay of viscoelastic forces around the glass transition, which involves a response in the brittle/solid regime of these rock melts. We warn of the inadequacy of simple Newtonian viscous analyses and call for the application of more realistic rheological interpretation of pseudotachylyte-bearing fault systems in the evaluation and prediction of their slip dynamics. PMID:26124123

  12. Fault rheology beyond frictional melting

    PubMed Central

    Lavallée, Yan; Hirose, Takehiro; Kendrick, Jackie E.; Hess, Kai-Uwe; Dingwell, Donald B.

    2015-01-01

    During earthquakes, comminution and frictional heating both contribute to the dissipation of stored energy. With sufficient dissipative heating, melting processes can ensue, yielding the production of frictional melts or “pseudotachylytes.” It is commonly assumed that the Newtonian viscosities of such melts control subsequent fault slip resistance. Rock melts, however, are viscoelastic bodies, and, at high strain rates, they exhibit evidence of a glass transition. Here, we present the results of high-velocity friction experiments on a well-characterized melt that demonstrate how slip in melt-bearing faults can be governed by brittle fragmentation phenomena encountered at the glass transition. Slip analysis using models that incorporate viscoelastic responses indicates that even in the presence of melt, slip persists in the solid state until sufficient heat is generated to reduce the viscosity and allow remobilization in the liquid state. Where a rock is present next to the melt, we note that wear of the crystalline wall rock by liquid fragmentation and agglutination also contributes to the brittle component of these experimentally generated pseudotachylytes. We conclude that in the case of pseudotachylyte generation during an earthquake, slip even beyond the onset of frictional melting is not controlled merely by viscosity but rather by an interplay of viscoelastic forces around the glass transition, which involves a response in the brittle/solid regime of these rock melts. We warn of the inadequacy of simple Newtonian viscous analyses and call for the application of more realistic rheological interpretation of pseudotachylyte-bearing fault systems in the evaluation and prediction of their slip dynamics. PMID:26124123

  13. Rheology of dense bubble suspensions

    NASA Astrophysics Data System (ADS)

    Kang, Sang-Yoon; Sangani, Ashok S.; Tsao, Heng-Kwong; Koch, Donald L.

    1997-06-01

    The rheological behavior of rapidly sheared bubble suspensions is examined through numerical simulations and kinetic theory. The limiting case of spherical bubbles at large Reynolds number Re and small Weber number We is examined in detail. Here, Re=ργa2/μ and We=ργ2a3/s, a being the bubble radius, γ the imposed shear, s the interfacial tension, and μ and ρ, respectively, the viscosity and density of the liquid. The bubbles are assumed to undergo elastic bounces when they come into contact; coalescence can be prevented in practice by addition of salt or surface-active impurities. The numerical simulations account for the interactions among bubbles which are assumed to be dominated by the potential flow of the liquid caused by the motion of the bubbles and the shear-induced collision of the bubbles. A kinetic theory based on Grad's moment method is used to predict the distribution function for the bubble velocities and the stress in the suspension. The hydrodynamic interactions are incorporated in this theory only through their influence on the virtual mass and viscous dissipation in the suspension. It is shown that this theory provides reasonable predictions for the bubble-phase pressure and viscosity determined from simulations including the detailed potential flow interactions. A striking result of this study is that the variance of the bubble velocity can become large compared with (γa)2 in the limit of large Reynolds number. This implies that the disperse-phase pressure and viscosity associated with the fluctuating motion of the bubbles is quite significant. To determine whether this prediction is reasonable even in the presence of nonlinear drag forces induced by bubble deformation, we perform simulations in which the bubbles are subject to an empirical drag law and show that the bubble velocity variance can be as large as 15γ2a2.

  14. Synthesis, rheology and forming of Y-Ba-Cu-O ceramics

    SciTech Connect

    Green, T.M.

    1993-07-01

    A chemical synthesis route is discussed which results in a low- temperature precursor to Y-Ba-Cu-O ceramics; it is based on use of molten Ba(OH){sub 2}{center_dot}8H{sub 2}O flux. Two different chemical systems have been examined; the first one, based on nitrate salts, has been demonstrated to be a viable precursor material for tape casting and extrusion; the second, made from acetate salts, has been used for powder synthesis and extrusion. Rheology of pastes shows that their flow may be fit to either Bingham Plastic or Hershel- Bulkley models. Yield stress is controlled in both pastes by volume fraction solids. Viscosity also follows solids loading in the paste. Shear thinning is controlled by colloidal nature of precursor. The paste has colloidal microstructure. Comparison of concentric cylinder rheometry and piston extrusion rheometry shows order of magnitude differences in yield stress, resulting from the test method and paste dilation.

  15. Rheological Characterization Of Nano-Composite Hydrogels

    NASA Astrophysics Data System (ADS)

    Lombardi, Jack

    Engineered Polymer hydrogels and hydrogels from Bio macromolecules have visco-elastic properties that can be measured using Oscillatory Shear Rheology. Manipulation and measurement of physical properties in gels including F-127 Pluronic Block Co-Polymer and Poly(N-isopropylacrylamide)-Clay are shown through OSR by addition of salts, clays and glucose at physiological levels. Rheological analysis of f-127 illustrates changes in G' reduction with phase transition temperature. Measurements also indicate physical changes due to the aforementioned additives vary as a function of the gel physical and chemical structure. In particular, non-enzymatic glycation is shown to change the modulus of elasticity in both of the gels tested. Rheological analysis is also interpreted to produce a reduction In gel mesh size in the PNIPA -clay gels due to a possible co-solvency between phases of varying degrees of hydration.

  16. Rheological characterization of an artificial synovial fluid.

    PubMed

    Casentini, G; Di Paola, L; Marrelli, L; Palma, F

    2005-07-01

    Rheological measurements on two classes of artificial synovial fluids have been carried out in the attempt to get a suitable but cheap lubricant for wear tests of prosthetic materials. Fluids of both classes are solutions of hyaluronic acid (HA) that, for one class, is dissolved into a simple Ringer solution whereas, for the other class, into a mixture of human serum and Ringer solution. Similar rheological properties have been observed for both classes of fluids. Experimental results have been interpreted by two classical models that are commonly used in the literature to describe the rheological behavior of colloidal systems and of polymer solutions with high entanglement density, respectively. The quality of correlations shows that, at high HA concentrations, entangled structures are largely present and cannot be neglected. PMID:16049905

  17. The debris-flow rheology myth

    USGS Publications Warehouse

    Iverson, R.M.

    2003-01-01

    Models that employ a fixed rheology cannot yield accurate interpretations or predictions of debris-flow motion, because the evolving behavior of debris flows is too complex to be represented by any rheological equation that uniquely relates stress and strain rate. Field observations and experimental data indicate that debris behavior can vary from nearly rigid to highly fluid as a consequence of temporal and spatial variations in pore-fluid pressure and mixture agitation. Moreover, behavior can vary if debris composition changes as a result of grain-size segregation and gain or loss of solid and fluid constituents in transit. An alternative to fixed-rheology models is provided by a Coulomb mixture theory model, which can represent variable interactions of solid and fluid constituents in heterogeneous debris-flow surges with high-friction, coarse-grained heads and low-friction, liquefied tails. ?? 2003 Millpress.

  18. [In vivo rheologic studies of plasma substitutes].

    PubMed

    Dewachter, P; Laxenaire, M C; Donner, M; Kurtz, M; Stoltz, J F

    1992-01-01

    The aim of this study was to compare in 60 ASA1 patients, the rheological effects of a 500 ml plasma substitute infusion at induction of general anaesthesia. The 60 patients were allocated into 6 groups of 10. Each group received either albumin 4%, or dextran 40 3.5%, or dextran 60 6%, or hydroxyethylstarch (HES) 200 6%, or modified fluid gelatin or Ringer lactate. The infusion extended over 30 minutes. In blood samples obtained before infusion, immediately after the end, three and 24 hours after the end of infusion, osmotic pressure, oncotic pressure, proteins and fibrinogen concentration were measured. Following rheological parameters were also assessed: plasma viscosity, blood viscosity at two shear rates (0.5 and 128 s-1), erythrocyte aggregation by primary and final aggregation times as well as total and partial dissociation thresholds. The determinations were carried out at haematocrit corrected to 40%. At intergroup analysis of the different substitutes compared to albumin 4%, with the exception of Ringer lactate, there was no significant modification of osmotic and oncotic pressures or fibrinogen concentrations. Only gelatin and dextran 60 modified the rheological parameters. The intragroup comparison did not demonstrate significant variations of osmotic and oncotic pressures. Fibrinogen concentrations remained unchanged up to the 24th hours, where they increased as a reaction to surgery. Similar changes of rheological parameters occurred for Ringer lactate, albumin 4% and dextran 40: decrease of plasma viscosity (< 10%) and blood viscosity (< 20% at shear rate of 0.5 s-1), increase of primary aggregation time (30-50%) with decrease of total dissociation threshold (10-20%). These changes ended 24 hours after infusion. Dextran 60 and gelatin elicited a modification of blood rheology until the 24th hour after the end of infusion. Such modifications did not occur with HES. It is concluded that when a rheological effect is required albumin 4% or dextran 40 3

  19. Rheology of the lithosphere: selected topics.

    USGS Publications Warehouse

    Kirby, S.H.; Kronenberg, A.K.

    1987-01-01

    Reviews recent results concerning the rheology of the lithosphere with special attention to the following topics: 1) the flexure of the oceanic lithosphere, 2) deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins, 3) the rheological stratification of the continents, 4) strain localization and shear zone development, and 5) strain-induced crystallographic preferred orientations and anisotropies in body-wave velocities. We conclude with a section citing the 1983-1986 rock mechanics literature by category.-Authors

  20. Rheology of interfacial protein-polysaccharide composites

    NASA Astrophysics Data System (ADS)

    Fischer, P.

    2013-05-01

    The morphology and mechanical properties of protein adsorption layers can significantly be altered by the presence of surfactants, lipids, particles, other proteins, and polysaccharides. In food emulsions, polysaccharides are primarily considered as bulk thickener but can under appropriate environmental conditions stabilize or destabilize the protein adsorption layer and, thus, the entire emulsion system. Despite their ubiquitous usage as stabilization agent, relatively few investigations focus on the interfacial rheology of composite protein/polysaccharide adsorption layers. The manuscript provides a brief review on both main stabilization mechanisms, thermodynamic phase separation and electrostatic interaction and discusses the rheological response in light of the environmental conditions such as ionic strength and pH.

  1. Characterizing the rheology of fluidized granular matter.

    PubMed

    Desmond, Kenneth W; Villa, Umberto; Newey, Mike; Losert, Wolfgang

    2013-09-01

    In this study we characterize the rheology of fluidized granular matter subject to secondary forcing. Our approach consists of first fluidizing granular matter in a drum half filled with grains via simple rotation and then superimposing oscillatory shear perpendicular to the downhill flow direction. The response of the system is mostly linear, with a phase lag between the grain motion and the oscillatory forcing. The rheology of the system can be well characterized by the GDR MiDi model if the system is forced with slow oscillations. The model breaks down when the forcing time scale becomes comparable to the characteristic time for energy dissipation in the flow. PMID:24125256

  2. Rheology and timescales of welding

    NASA Astrophysics Data System (ADS)

    Quane, S.; Russell, J. K.

    2004-12-01

    We describe results from 15 high-temperature, constant strain rate and constant load deformation experiments on natural pyroclastic materials that simulate welding. Experiments were run on unconfined samples at temperatures between 835° and 900° C. Samples comprised 4.3 cm diameter, ˜6 cm length cores of sintered Rattlesnake Tuff rhyolite ash. Porosity of starting materials is ˜78%. The experiments used uniaxial load stresses of 0.2 to 5 MPa which corresponds to overburden depths of < 200 m in ignimbrite deposits. The experimental results track strain (porosity loss) and strain rate as a function of time at fixed conditions (load and temperature). Our results show that deformation of pyroclastic material has a strain dependent rheology. The effective viscosity (η e) of the samples increases during the experiment as strain acccumulates and porosity (φ ) is reduced. We describe this behaviour using the relationship: (1) log η e = log η o - α [φ /(1-φ )]. where effective viscosity is related to the viscosity of the framework material (melt), the sample porosity, and a fit-parameter for the material (α ). Our experimental work suggests a value of 0.63 for compaction of natural pyroclastic materials. Equation 1 is the basis for an empirical equation that describes the total strain during viscous compaction as a function of original porosity (φ o), the viscosity of framework melt (η o),load (σ ) and time: (2) \\epsilon = \\phi_{o} + (1-\\phi_{o})/\\alpha \\times ln [(\\alpha \\sigma \\Deltat)/(\\eta_{o} (1-\\phi_{o} ) + exp[-(\\alpha \\phi_{o})/(1 - \\phi_{o} ) ] ]. In this relationship, the values of φ o and η o are physical properties of the specific deposit and load relates to the thickness of the deposit and the position (depth) of the sample. Eq. 2 can be used to predict ɛ vs. time paths to compare against the original experimental data and to model natural deposits. By rearranging the above equation to isolate time (Δ t) we predict the times

  3. Rheological Limitations on Deep Earthquakes

    NASA Astrophysics Data System (ADS)

    Weidner, D. J.; Raterron, P.; Chen, J.; Li, L.

    2002-05-01

    The occurrence of earthquakes deeper than 50 km requires processes that differ from the friction-mitigated phenomena that control fault slip of shallow events. These earthquakes that extend to depths of about 700 km have been useful in delineating plate tectonic processes and stresses, but remain elusive as to why the stress is released as earthquakes and not dissipated by slow plastic flow. Indeed, our understanding of plate tectonic and fracture processes would not be challenged if these events did not occur at all. While the source of deviatoric stress for these earthquakes results from the dynamics of plate tectonics, the ability to store the stress and catastrophically release the stress in an earthquake is controlled by the properties of the minerals that constitute the subducting slab. Guided by our recent experimental results, we propose that the deep earthquake process is largely controlled by the rheology of the subducted material. The core of the slab for depths shallower than 400 km, at temperatures less than 500,aC, is capable of supporting high levels of shear stress with a mildly temperature dependent strength. This region is not seismogenic as it does not have access to stress instabilities. Above 600,aC, olivine becomes too weak to be seismogenic. Between 500 and 600,aC, olivine strength is highly temperature dependent and the region is ripe for runaway plastic instabilities which give rise to earthquakes. This can account for double seismic zones owing to the distorted temperature profile. If the tectonic stress is insufficient in one of these zones, then there will be only a single seismic plane. Deeper than 400 km even though temperature continues to increase, the properties of the high pressure phases of olivine, wadsleyite and ringwoodite, control the seismicity. Higher temperatures are required of these phases to access the plastic instability process, thus allowing seismicity to increase in this region. Our data for perovskite indicate that

  4. Rheological Modifier Testing with DWPF Process Slurries

    SciTech Connect

    MICHAEL, STONE

    2004-02-01

    Rheological modification agents were tested on simulated SRAT and SME products to determine if a suitable agent could be found for the DWPF process slurries. The agents tested were dispersants that lower the rheological properties of slurries by preventing agglomerization. Dolapix CE64, an ethylene glycol, and Disperse-Ayd W28, a polyacrylate, were the most effective dispersants tested. Further evaluation and testing should be performed on Dolapix CE64 and Disperse-Ayd W28 to determine if implementation is possible in DWPF. The initial phase of future work will include optimization of the rheology modifier by the Illinois Institute of Technology (IIT) and development of a maximum concentration limit for the rheology modifiers. IIT has been commissioned to evaluate the properties of these chemicals to determine if the chemical makeup can be optimized to enhance the properties of these modifiers. An initial concentration limit based upon the DWPF flammability limit and other constraints should be calculated to determine the potential downstream impacts.

  5. Aggregate of nanoparticles: rheological and mechanical properties

    NASA Astrophysics Data System (ADS)

    Wang, Yu; Wu, Xiaojun; Yang, Wei; Zhai, Yuanming; Xie, Banghu; Yang, Mingbo

    2011-12-01

    The understanding of the rheological and mechanical properties of nanoparticle aggregates is important for the application of nanofillers in nanocompoistes. In this work, we report a rheological study on the rheological and mechanical properties of nano-silica agglomerates in the form of gel network mainly constructed by hydrogen bonds. The elastic model for rubber is modified to analyze the elastic behavior of the agglomerates. By this modified elastic model, the size of the network mesh can be estimated by the elastic modulus of the network which can be easily obtained by rheology. The stress to destroy the aggregates, i.e., the yield stress ( σ y ), and the elastic modulus ( G') of the network are found to be depended on the concentration of nano-silica ( ϕ, wt.%) with the power of 4.02 and 3.83, respectively. Via this concentration dependent behavior, we can extrapolate two important mechanical parameters for the agglomerates in a dense packing state ( ϕ = 1): the shear modulus and the yield stress. Under large deformation (continuous shear flow), the network structure of the aggregates will experience destruction and reconstruction, which gives rise to fluctuations in the viscosity and a shear-thinning behavior.

  6. Rheological properties of defense waste slurries

    SciTech Connect

    Ebadian, M.A.

    1998-01-01

    The major objective of this two-year project has been to obtain refined and reliable experimental data about the rheological properties of melter feeds. The research has involved both experimental studies and model development. Two experimental facilities have been set up to measure viscosity and pressure drop. Mathematical models have been developed as a result of experimental observation and fundamental rheological theory. The model has the capability to predict the viscosity of melter slurries in a range of experimental conditions. The final results of the investigation could be used to enhance the current design base for slurry transportation systems and improve the performance of the slurry mixing process. If successful, the cost of this waste treatment will be reduced, and disposal safety will be increased. The specific objectives for this project included: (1) the design, implementation, and validation of the experimental facility in both batch and continuous operating modes; (2) the identification and preparation of melter feed samples of both the SRS and Hanford waste slurries at multiple solids concentration levels; (3) the measurement and analysis of the melter feeds to determine the effects of the solids concentration, pH value, and other factors on the rheological properties of the slurries; (4) the correlation of the rheological properties as a function of the measured physical and chemical parameters; and (5) transmission of the experimental data and resulting correlation to the DOE site user to guide melter feed preparation and transport equipment design.

  7. Rheology of latex-modified grouts

    SciTech Connect

    Allan, M.L.

    1997-12-01

    The pumpability and ability of cementitious grouts to penetrate voids and cracks is strongly dependent on the rheological behavior of the grout. This is important in diverse grouting applications including ground treatment, repair of concrete, reduction of rock or soil permeability, environmental remediation, prestressing concrete, rock anchors, sealing radioactive waste repositories, and well completion. The rheology of grouts containing latex was investigated. The two latex additives used were carboxylated styrene-butadiene and acrylic. The influences of superplasticizer, fly ash, and blast furnace slag on the rheology of latex-modified grouts were addressed. Shear stress-shear rate curves were determined for a variety of mix proportions. The time-dependent behavior of selected grouts was also studied. It was determined that the yield stress and apparent viscosity are influenced by latex content and that the grouts are shear thinning at low water/cement ratios. Latex imparts stability and thixotropy in grouts. Partial replacement of cement with either fly ash or slag diminishes the effect of latex on rheology.

  8. RHEOLOGY OF CONCENTRATED SOLUTIONS OF HYPERBRANCHED POLYESTERS

    EPA Science Inventory

    The solution rheology of different generations of hyperbranched polyesters in N-methyl-2- pyrrolidinone (NMP) solvent was examined in this study. The solutions exhibited Newtonian behavior over a wide range of polyester concentrations. Also, the relative viscosities of poly(amido...

  9. MORPHOLOGICAL AND RHEOLOGICAL CHARACTERIZATION OF BIOBLENDS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Bioblends are polymer blends in which at least one of the components is a biodegradable polymer. Melt extruded model bioblends, comprising a biodegradable polyester and polystyrene (PS), were investigated using rheological and morphological (TEM) methods. Blend compositions were varied from neat P...

  10. Basic program analyzes fluid rheology to determine pump rates

    SciTech Connect

    Moftah, K.R. )

    1994-05-09

    The use of statistical methods can improve the selection of a rheological model and the subsequent calculations for critical pump rate and pressure drop for cementing operations. The accompanying interactive Basic computer program allows the user to analyze fluid rheology to help determine the best data for use in predicting cementing pump rates. An accurate critical pump rate and pressure drop can then be calculated based on the correctly calculated rheological parameters. For cementing operations, the important methods of calculating the critical pump rate are the Hedstrom analysis, based on the Bingham plastic rheological model, and the Metzner and Reed analysis, based on the power law rheological model.

  11. Measurements and models of cytoskeletal rheology

    NASA Astrophysics Data System (ADS)

    Kamm, Roger

    2006-11-01

    Much attention has recently focused on understanding the rheology of living cells and reconstituted actin gels using a variety of experimental methods (e.g., single- and multi-particle tracking, magnetic twisting cytometry, AFM indentation) and several different models or descriptors (e.g., biopolymer models, tensegrity, cellular solids, power-law rheology), but the debate continues regarding the fundamental basis for the experimental observations. Our recent studies examine the time-dependent behavior of neutrophils as they deform to enter a narrow channel with capillary-scale dimensions. A sudden drop in the shear modulus is observed, followed by recovery to pre-deformation values in < 1 minute. These rheological changes coincide with a reduction in f-actin content and a transient increase in calcium ion concentration [Ca^++], and the change in storage modulus can be prevented by calcium chelation, suggesting that these observations are causally linked. Cells lacking the ability to increase [Ca^++] also become activated more rapidly following deformation, and the time to activation is independent of intracellular strain rates, contrary to experiments lacking the chelating agent. To better understand these processes and the nature of cytoskeletal rheology in general, we have developed a Brownian dynamics model for cytoskeletal self-assembly and subsequent rheological measurement by single particle tracking. Cross-linking proteins are included possessing a range of properties that lead to a variety of cytoskeletal structures from a fine, homogeneous mesh to a structure containing large stress fibers of varying thickness. These results are described in a multi-dimensional phase space that takes into account the geometry, dimensions and stiffness of the cross-linkers.

  12. Surface shear rheology of saponin adsorption layers.

    PubMed

    Golemanov, Konstantin; Tcholakova, Slavka; Denkov, Nikolai; Pelan, Edward; Stoyanov, Simeon D

    2012-08-21

    Saponins are a wide class of natural surfactants, with molecules containing a rigid hydrophobic group (triterpenoid or steroid), connected via glycoside bonds to hydrophilic oligosaccharide chains. These surfactants are very good foam stabiliziers and emulsifiers, and show a range of nontrivial biological activities. The molecular mechanisms behind these unusual properties are unknown, and, therefore, the saponins have attracted significant research interest in recent years. In our previous study (Stanimirova et al. Langmuir 2011, 27, 12486-12498), we showed that the triterpenoid saponins extracted from Quillaja saponaria plant (Quillaja saponins) formed adsorption layers with unusually high surface dilatational elasticity, 280 ± 30 mN/m. In this Article, we study the shear rheological properties of the adsorption layers of Quillaja saponins. In addition, we study the surface shear rheological properties of Yucca saponins, which are of steroid type. The experimental results show that the adsorption layers of Yucca saponins exhibit purely viscous rheological response, even at the lowest shear stress applied, whereas the adsorption layers of Quillaja saponins behave like a viscoelastic two-dimensional body. For Quillaja saponins, a single master curve describes the data for the viscoelastic creep compliance versus deformation time, up to a certain critical value of the applied shear stress. Above this value, the layer compliance increases, and the adsorption layers eventually transform into viscous ones. The experimental creep-recovery curves for the viscoelastic layers are fitted very well by compound Voigt rheological model. The obtained results are discussed from the viewpoint of the layer structure and the possible molecular mechanisms, governing the rheological response of the saponin adsorption layers. PMID:22830458

  13. Role of Yield Stress in Magma Rheology

    NASA Astrophysics Data System (ADS)

    Kurokawa, A.; Di Giuseppe, E.; Davaille, A.; Kurita, K.

    2012-04-01

    Magmas are essentially multiphase material composed of solid crystals, gaseous bubbles and silicate liquids. They exhibit various types of drastic change in rheology with variation of mutual volumetric fractions of the components. The nature of this variable rheology is a key factor in controlling dynamics of flowing magma through a conduit. Particularly the existence of yield stress in flowing magma is expected to control the wall friction and formation of density waves. As the volumetric fraction of solid phase increases yield stress emerges above the critical fraction. Several previous studies have been conducted to clarify this critical value of magmatic fluid both in numerical simulations and laboratory experiments ([Lejeune and Pascal, 1995], [Saar and Manga 2001], [Ishibashi and Sato 2010]). The obtained values range from 13.3 to 40 vol%, which display wide variation and associated change in rheology has not been clarified well. In this presentation we report physical mechanism of emergence of yield stress in suspension as well as the associated change in the rheology based on laboratory experiments using analog material. We utilized thermogel aqueous suspension as an analog material of multiphase magma. Thermogel, which is a commercial name for poly(N-isopropyl acrylamide) (PNIPAM) undergoes volumetric phase change at the temperature around 35C:below this temperature the gel phase absorbs water and swells while below this it expels water and its volume shrinks. Because of this the volumetric fraction of gel phase systematically changes with temperature and the concentration of gel powder. The viscosity measured at lower stress drastically decreases across this phase change with increasing temperature while the viscosity at higher stress does not exhibit large change across the transition. We have performed a series of rheological measurements focusing on the emergence of yield stress on this aqueous suspension. Since the definition of yield stress is not

  14. Colony Rheology: Active Arthropods Generate Flows

    NASA Astrophysics Data System (ADS)

    Daniels, Karen; Mann, Michael; Charbonneau, Patrick

    2015-03-01

    Hydrodynamic-like flows are observed in biological systems as varied as bacteria, insects, birds, fish, and mammals. Both the phenomenology (e.g. front instabilities, milling motions) and the interaction types (hydrodynamic, direct contact, psychological, excluded-volume) strongly vary between systems, but a question common to all of them is to understand the role of particle-scale fluctuations in controlling large-scale rheological behaviors. We will address these questions through experiments on a new system, Tyrolichus casei (cheese mites), which live in dense, self-mixing colonies composed of a mixture of living mites and inert flour/detritus. In experiments performed in a Hele-Shaw geometry, we observe that the rheology of a colony is strongly dependent on the relative concentration of active and inactive particles. In addition to spreading flows, we also observe that the system can generate convective circulation and auto-compaction.

  15. High Strain Rate Rheology of Polymer Melts

    NASA Astrophysics Data System (ADS)

    Kelly, Adrian; Gough, Tim; Whiteside, Ben; Coates, Phil D.

    2009-07-01

    A modified servo electric injection moulding machine has been used in air-shot mode with capillary dies fitted at the nozzle to examine the rheology of a number of commercial polymers at wall shear strain rates of up to 107 s-1. Shear and extensional flow properties were obtained through the use of long and orifice (close to zero land length) dies of the same diameter. A range of polyethylene, polypropylene and polystyrene melts have been characterized; good agreement was found between the three techniques used in the ranges where strain rates overlapped. Shear viscosity of the polymers studied was found to exhibit a plateau above approximately 1×106 s-1. A relationship between the measured high strain rate rheological behaviour and molecular structure was noted, with polymers containing larger side groups reaching the rate independent plateau at lower strain rates than those with simpler structures.

  16. Rheological behaviour of heated potato starch dispersions

    NASA Astrophysics Data System (ADS)

    Juszczak, L.; Witczak, M.; Ziêba, T.; Fortuna, T.

    2012-10-01

    The study was designed to investigate the rheological properties of heated potato starch dispersions. Water suspensions of starch were heated at 65, 80 or 95°C for 5, 15, 30 or 60 min. The dispersions obtained were examined for granule size distribution and rheology. It was found that the starch dispersions significantly differed in both respects. The mean diameters of starch granules were largest for the dispersion heated at 65°C and smallest for that heated at 95°C. As the heating temperature was raised, the yield stresses and consistency coefficients decreased, while the flow behaviour indexes and Casson plastic viscosities increased. There were also differences in the viscoelastic properties of the dispersions: for those heated at 65°C the storage and loss moduli increased with heating time whereas for those heated at 80°C both moduli decreased.

  17. Surface rheological observations on human plasma.

    PubMed

    Matrai, A; Warburton, B; Dormandy, J A

    1984-01-01

    The weak interactions between plasma proteins are of possible importance both in haemorheology and in the pathology of several diseases. The use of surface rheology is a convenient way to study the forces arising between surface adsorbed protein molecules. A surface rheological measuring head has been designed for the Contraves LS-30 viscometer. Plasma samples of healthy human subjects showed a rapidly developing viscous surface layer with a mean peak value of 2.10(-3) Ns/m surface viscosity at 30- 60 seconds. After that the viscosity of the surface layer gradually decreased to zero between 8-20 minutes. The rate of the observed decrease was not related to shearing. There was no difference between samples anticoagulated with heparin or EDTA. The time course of the described phenomenon coincides with that of thrombocyte and white cell adherence to solid surfaces exposed to plasma. PMID:6591960

  18. Rheological Properties of Iron Oxide Based Ferrofluids

    NASA Astrophysics Data System (ADS)

    Devi, M.; Mohanta, D.

    2009-06-01

    In the present work, we report synthesis and magneto-viscous properties of cationic and anionic surfactant coated, iron oxide nanoparticles based ferrofluids. Structural and morphological aspects are revealed by x-ray diffraction (XRD) and transmission electron microscopy (TEM) studies. We compare the rheological/magneto-viscous properties of different ferrofluids for various shear rates (2-450 sec-1) and applied magnetic fields (0-100 gauss). In the absence of a magnetic field, and under no shear case, the ferrofluid prepared with TMAH coated particle is found to be 12% more viscous compared to its counterpart. The rheological properties are governed by non-Newtonian features, and for a definite shear rate, viscosity of a given ferrofluid is found to be strongly dependent on the applied magnetic field as well as nature of the surfactant.

  19. Rheology of weakly vibrated granular materials

    NASA Astrophysics Data System (ADS)

    Dijksman, J. A.; Wortel, G.; van Hecke, M.

    2009-06-01

    We show how weak vibrations substantially modify the rheology of granular materials. We experimentally probe dry granular flows in a weakly vibrated split bottom shear cell—the weak vibrations modulate gravity and act as an agitation source. By tuning the applied stress and vibration strength, and monitoring the resulting strain as a function of time, we uncover a rich phase diagram in which non-trivial transitions separate a jammed phase, a creep flow case, and a steady flow case.

  20. A new rheology for dense granular flows

    NASA Astrophysics Data System (ADS)

    Jop, Pierre

    2005-11-01

    Recent experiments and numerical simulations of dry and dense granular flows suggest that a simple rheological description, in terms of a shear rate dependent friction coefficient, may be sufficient to capture the major flow properties [1,2]. In this work we generalize this approach by proposing a tensorial form of this rheology leading to 3D hydrodynamic equations for granular flows. We show that quantitative predictions can be obtained with this model by studying the flow of grains on a pile confined between two lateral walls. In this configuration we have experimentally measured the free surface velocity profile, the flowing thickness for different flow rates and channel widths. The results are compared with numerical simulations of the hydrodynamic model and quantitative agreement is observed. This study strongly supports the relevance of the proposed rheology. 1. F. da Cruz, S. Emam, M. Prochnow, J.-N. Roux and F. Chevoir, cond-mat/ 0503682 (2005)2. G.D.R. Midi, EPJE14 367-371 (2004)

  1. Rheology of a Polymeric Bicontinuous Microemulsion

    NASA Astrophysics Data System (ADS)

    Krishnan, Kasiraman; Lodge, Timothy P.; Bates, Frank S.; Burghardt, Wesley R.

    2002-03-01

    We have investigated the rheological properties of a model polymeric bicontinuous microemulsion. The microemulsion consists of a ternary blend of poly(ethyl ethylene) (PEE), poly(dimethyl siloxane) (PDMS) and the diblock copolymer PEE-PDMS. Steady shear measurements reveal four regimes as a function of shear rate. Newtonian behavior is observed at low shear rates (regime I), whereas shear thinning occurs in regime II. The striking feature is a stress plateau in regime III, independent of shear rate; the stress increases with shear rate again in regime IV. The morphologies in different regimes were characterized by neutron scattering, x-ray scattering, light scattering and microscopy, and these provide evidence for the occurrence of flow-induced phase separation. Transient rheological measurements reveal a behavior similar to worm-like micelles. Transient measurements for step changes in shear rate between different regimes confirm the proposed morphologies. Equilibrium rheological measurements show similarities with diblock copolymer lamellar phases just above the order-disorder transition.

  2. The rheology of two-phase magmas

    NASA Astrophysics Data System (ADS)

    Llewellin, E. W.; Mader, H. M.; Mueller, S.

    2012-12-01

    Great advances in our understanding of the rheology of two-phase magmatic suspensions (magma with either bubbles or crystals in it) have been made in recent years. These advances are based on laboratory experiments with both magma and analogue materials, and on analytical and numerical modelling. The current state-of-the-art is the culmination of scores of studies undertaken by scores of research groups and presented in scores of publications. Consequently, whilst it is possible to construct a sophisticated rheological description of a two-phase magma based on a few easily-measured properties (melt composition, crystal/vesicle volume fraction, CSD/VSD, etc.) the task of determining how best to do this is daunting to the non-specialist. We present a straightforward, practical, algorithmic approach to determining the rheology of two-phase magma to the degree of sophistication appropriate to most modelling applications. The approach is based on a broad synthesis of the literature, on new experimental data, and on new theoretical analysis.

  3. Time domain analysis of the weighted distributed order rheological model

    NASA Astrophysics Data System (ADS)

    Cao, Lili; Pu, Hai; Li, Yan; Li, Ming

    2016-05-01

    This paper presents the fundamental solution and relevant properties of the weighted distributed order rheological model in the time domain. Based on the construction of distributed order damper and the idea of distributed order element networks, this paper studies the weighted distributed order operator of the rheological model, a generalization of distributed order linear rheological model. The inverse Laplace transform on weighted distributed order operators of rheological model has been obtained by cutting the complex plane and computing the complex path integral along the Hankel path, which leads to the asymptotic property and boundary discussions. The relaxation response to weighted distributed order rheological model is analyzed, and it is closely related to many physical phenomena. A number of novel characteristics of weighted distributed order rheological model, such as power-law decay and intermediate phenomenon, have been discovered as well. And meanwhile several illustrated examples play important role in validating these results.

  4. Rheological studies of tautomerization kinetics in supercooled glibenclamide drug.

    PubMed

    Wojnarowska, Z; Wang, Y; Sokolov, A P; Paluch, M

    2012-12-01

    Rheological measurements have been applied to study the tautomerization of the pharmaceutically active compound glibenclamide. The rate constant and activation energy of the imidic-acid-amide transformation have been successfully determined by monitoring the evolution of shear viscosity. The kinetic parameters from rheological measurements agree reasonably well with the data previously obtained from dielectric spectroscopy. The present Brief Report demonstrates that rheology can provide a fast and precise way to characterize the reaction kinetics of tautomerization. PMID:23368084

  5. Rheological studies of tautomerization kinetics in supercooled glibenclamide drug

    NASA Astrophysics Data System (ADS)

    Wojnarowska, Z.; Wang, Y.; Sokolov, A. P.; Paluch, M.

    2012-12-01

    Rheological measurements have been applied to study the tautomerization of the pharmaceutically active compound glibenclamide. The rate constant and activation energy of the imidic-acid-amide transformation have been successfully determined by monitoring the evolution of shear viscosity. The kinetic parameters from rheological measurements agree reasonably well with the data previously obtained from dielectric spectroscopy. The present Brief Report demonstrates that rheology can provide a fast and precise way to characterize the reaction kinetics of tautomerization.

  6. Effects of Lateral Heterogeneity and Power Law Rheology on Glacially Induced Surface Motion and Gravity Rate of Change

    NASA Astrophysics Data System (ADS)

    Wu, P.; Wang, H.; van der Wal, W.

    2006-12-01

    Modern geodetic measurements from GPS, satellite altimetry, tide-gauges, Satellite Laser Ranging (SLR) and space-borne gravimetry (such as GRACE) have been used to monitor global change. Since these measurements contain contributions from glacial isostatic adjustment (GIA) and other tectonic processes, they must be modeled and removed in order to observe current climate change. In the past, most GIA models assumed that the earth is laterally homogeneous and the rheology is linear. The aim of this paper is to investigate the effects of lateral heterogeneity and Power-Law rheology on GIA induced land uplift rate, horizontal velocities, relative sealevels, J-dot and the secular gravity rate of change in the southern part of Hudson Bay, which is detected by the GRACE mission. Here, GIA is modeled with a spherical, self-gravitating, compressible viscoelastic, laterally heterogeneous earth using the Finite-Element Method. The effect of gravitationally self-consistent sea levels in realistic oceans is also included. Lateral variations in mantle viscosities and lithospheric thickness are inferred from the seismic tomography model S20A using well known scaling relationships. Power-Law rheologies in the whole mantle or in combination with linear rheologies in the upper or lower mantle are also investigated. Both ICE-5G and ICE-4G deglaciation models are used to investigate their effect on the pattern of rebound. Preliminary results show that both lateral heterogeneity and power-law rheology have strong effects on the direction and magnitude of horizontal velocities. The effects of lateral heterogeneity and power-law rheology are also large enough to be detected in land uplift rate, relative sealevels, J-dot and gravity rate of change. Their implication on observing the effects of global warming will also be discussed.

  7. Adsorption of superplasticizer admixtures on alkali-activated slag pastes

    SciTech Connect

    Palacios, M. Houst, Y.F.; Bowen, P.; Puertas, F.

    2009-08-15

    Alkali-activated slag (AAS) binders are obtained by a manufacturing process less energy-intensive than ordinary Portland cement (OPC) and involves lower greenhouse gasses emission. These alkaline cements allow the production of high mechanical strength and durable concretes. In the present work, the adsorption of different superplasticizer admixtures (naphthalene-based, melamine-based and a vinyl copolymer) on the slag particles in AAS pastes using alkaline solutions with different pH values have been studied in detail. The effect of the superplasticizers on the yield stress and plastic viscosity of the AAS and OPC pastes have been also evaluated. The results obtained allowed us to conclude that the adsorption of the superplasticizers on AAS pastes is independent of the pH of the alkaline solutions used and lower than on OPC pastes. However, the effect of the admixtures on the rheological parameters depends directly on the type and dosage of the superplasticizer as well as of the binder used and, in the case of the AAS, on the pH of the alkaline activator solution. In 11.7-pH NaOH-AAS pastes the dosages of the superplasticizers required to attain similar reduction in the yield stress are ten-fold lower than for Portland cement. In this case the superplasticizers studied show a fluidizing effect considerably higher in 11.7-pH NaOH-AAS pastes than in OPC pastes. In 13.6-pH NaOH-AAS pastes, the only admixture observed to affect the rheological parameters is the naphthalene-based admixture due to its higher chemical stability in such extremely alkaline media.

  8. Measurement of the Rheological Properties of High Performance Concrete: State of the Art Report

    PubMed Central

    Ferraris, Chiara F.

    1999-01-01

    The rheological or flow properties of concrete in general and of high performance concrete (HPC) in particular, are important because many factors such as ease of placement, consolidation, durability, and strength depend on the flow properties. Concrete that is not properly consolidated may have defects, such as honeycombs, air voids, and aggregate segregation. Such an important performance attribute has triggered the design of numerous test methods. Generally, the flow behavior of concrete approximates that of a Bingham fluid. Therefore, at least two parameters, yield stress and viscosity, are necessary to characterize the flow. Nevertheless, most methods measure only one parameter. Predictions of the flow properties of concrete from its composition or from the properties of its components are not easy. No general model exists, although some attempts have been made. This paper gives an overview of the flow properties of a fluid or a suspension, followed by a critical review of the most commonly used concrete rheology tests. Particular attention is given to tests that could be used for HPC. Tentative definitions of terms such as workability, consistency, and rheological parameters are provided. An overview of the most promising tests and models for cement paste is given.

  9. Glacial isostatic adjustment model with composite 3-D Earth rheology for Fennoscandia

    NASA Astrophysics Data System (ADS)

    van der Wal, Wouter; Barnhoorn, Auke; Stocchi, Paolo; Gradmann, Sofie; Wu, Patrick; Drury, Martyn; Vermeersen, Bert

    2013-07-01

    Models for glacial isostatic adjustment (GIA) can provide constraints on rheology of the mantle if past ice thickness variations are assumed to be known. The Pleistocene ice loading histories that are used to obtain such constraints are based on an a priori 1-D mantle viscosity profile that assumes a single deformation mechanism for mantle rocks. Such a simplified viscosity profile makes it hard to compare the inferred mantle rheology to inferences from seismology and laboratory experiments. It is unknown what constraints GIA observations can provide on more realistic mantle rheology with an ice history that is not based on an a priori mantle viscosity profile. This paper investigates a model for GIA with a new ice history for Fennoscandia that is constrained by palaeoclimate proxies and glacial sediments. Diffusion and dislocation creep flow law data are taken from a compilation of laboratory measurements on olivine. Upper-mantle temperature data sets down to 400 km depth are derived from surface heatflow measurements, a petrochemical model for Fennoscandia and seismic velocity anomalies. Creep parameters below 400 km are taken from an earlier study and are only varying with depth. The olivine grain size and water content (a wet state, or a dry state) are used as free parameters. The solid Earth response is computed with a global spherical 3-D finite-element model for an incompressible, self-gravitating Earth. We compare predictions to sea level data and GPS uplift rates in Fennoscandia. The objective is to see if the mantle rheology and the ice model is consistent with GIA observations. We also test if the inclusion of dislocation creep gives any improvements over predictions with diffusion creep only, and whether the laterally varying temperatures result in an improved fit compared to a widely used 1-D viscosity profile (VM2). We find that sea level data can be explained with our ice model and with information on mantle rheology from laboratory experiments

  10. Rheological Properties of Aqueous Nanometric Alumina Suspensions

    SciTech Connect

    Chuanping Li

    2004-12-19

    Colloidal processing is an effective and reliable approach in the fabrication of the advanced ceramic products. Successful colloidal processing of fine ceramic powders requires accurate control of the rheological properties. The accurate control relies on the understanding the influences of various colloidal parameters on the rheological properties. Almost all research done on the rheology paid less attention to the interactions of particle and solvent. However, the interactions of the particles are usually built up through the media in which the particles are suspended. Therefore, interactions of the particle with the media, the adsorbed layers on the particle surface, and chemical and physical properties of media themselves must influence the rheology of the suspension, especially for the dense suspensions containing nanosized particles. Relatively little research work has been reported in this area. This thesis addresses the rheological properties of nanometric alumina aqueous suspensions, and paying more attention to the interactions between particle and solvent, which in turn influence the particle-particle interactions. Dense nanometric alumina aqueous suspensions with low viscosity were achieved by environmentally-benign fructose additives. The rheology of nanometric alumina aqueous suspensions and its variation with the particle volume fraction and concentration of fructose were explored by rheometry. The adsorptions of solute (fructose) and solvent (water) on the nanometric alumina particle surfaces were measured and analyzed by TG/DSC, TOC, and NMR techniques. The mobility of water molecules in the suspensions and its variation with particle volume fractions and fructose additive were determined by the {sup 17}O NMR relaxation method. The interactions between the nanometric alumina particles in water and fructose solutions were investigated by AFM. The results indicated that a large number of water layers were physically bound on the particles' surfaces

  11. Rheological properties of a vesicle suspension.

    PubMed

    Guedda, M; Benlahsen, M; Misbah, C

    2014-11-01

    The rheological behavior of a dilute suspension of vesicles in linear shear flow at a finite concentration is analytically examined. In the quasispherical limit, two coupled nonlinear equations that describe the vesicle orientation in the flow and its shape evolution were derived [Phys. Rev. Lett. 96, 028104 (2006)PRLTAO0031-900710.1103/PhysRevLett.96.028104] and serve here as a starting point. Of special interest is to provide, for the first time, an exact analytical prediction of the time-dependent effective viscosity η_{eff} and normal stress differences N_{1} and N_{2}. Our results shed light on the effect of the viscosity ratio λ (defined as the inner over the outer fluid viscosities) as the main controlling parameter. It is shown that η_{eff},N_{1}, and N_{2} either tend to a steady state or describe a periodic time-dependent rheological response, previously reported numerically and experimentally. In particular, the shear viscosity minimum and the cusp singularities of η_{eff},N_{1}, and N_{2} at the tumbling threshold are brought to light. We also report on rheology properties for an arbitrary linear flow. We were able to obtain a constitutive law in a closed form relating the stress tensor to the strain rate tensor. It is found that the resulting constitutive markedly contrasts with classical laws known for other complex fluids, such as emulsions, capsule suspensions, and dilute polymer solutions (Oldroyd B model). We highlight the main differences between our law and classical laws. PMID:25493791

  12. Flexure and rheology of Pacific oceanic lithosphere

    NASA Astrophysics Data System (ADS)

    Hunter, Johnny; Watts, Tony

    2016-04-01

    The idea of a rigid lithosphere that supports loads through flexural isostasy was first postulated in the late 19th century. Since then, there has been much effort to investigate the spatial and temporal variation of the lithosphere's flexural rigidity, and to understand how these variations are linked to its rheology. We have used flexural modelling to first re-assess the variation in the rigidity of oceanic lithosphere with its age at the time of loading, and then to constrain mantle rheology by testing the predictions of laboratory-derived flow laws. A broken elastic plate model was used to model trench-normal, ensemble-averaged profiles of satellite-derived gravity at the trench-outer rise system of circum-Pacific subduction zones, where an inverse procedure was used to find the best-fit Te and loading conditions. The results show a first-order increase in Te with plate age, which is best fit by the depth to the 400 ± 35°C plate-cooling isotherm. Fits to the observed gravity are significantly improved by an elastic plate that weakens landward of the outer rise, which suggests that bending-induced plate weakening is a ubiquitous feature of circum-Pacific subduction zones. Two methods were used to constrain mantle rheology. In the first, the Te derived by modelling flexural observations was compared to the Te predicted by laboratory-derived yield strength envelopes. In the second, flexural observations were modelled using elastic-plastic plates with laboratory-derived, depth-dependent yield strength. The results show that flow laws for low-temperature plasticity of dry olivine provide a good fit to the observations at circum-Pacific subduction zones, but are much too strong to fit observations of flexure in the Hawaiian Islands region. We suggest that this discrepancy can be explained by differences in the timescale of loading combined with moderate thermal rejuvenation of the Hawaiian lithosphere.

  13. Blood rheology in general medicine and surgery.

    PubMed

    Lowe, G D

    1987-09-01

    Traditionally, blood rheology tests have been used in diagnosis and monitoring of infection, rheumatic diseases and malignancy, and are still of clinical value in these conditions. In the last twenty years, clinical and epidemiological studies have shown that the haematological determinants of blood flow resistance (haematocrit, fibrinogen, white cell count and altered red and white cell rigidity) are also associated with nutritional, metabolic, endocrine and vascular disorders. Decreased red cell deformability may contribute to reduced red cell survival and anaemia in burns, malaria, liver disease and kidney failure. In trauma and inflammatory disease, overt hyperviscosity is usually prevented by vasodilatation and reduction in the haematocrit. However, low-flow states may arise systemically from haemoconcentration (contracted plasma volume, Chapter 3) in severe burns, inappropriate red cell transfusion, or dehydration due to illness; systemically in circulatory shock; and locally in venous thrombosis or arterial disease. In such circumstances, the intrinsic flow resistance of blood may perpetuate flow disturbance, ischaemia and thrombosis. Conversely, optimal levels of haematocrit, fibrinogen and white cell count may be lower than normal in low-flow states. Haemodilution by colloid infusion is beneficial in burns, shock, major surgery, prevention of postoperative venous thrombosis, chronic stable claudication and possibly in acute stroke and retinal vein thrombosis. Plasma exchange may be beneficial in severe Raynaud's phenomenon. Defibrination with ancrod is effective in prevention and treatment of venous thrombosis but its role in arterial disease is unproven. The benefits of streptokinase therapy in venous thrombo-embolism and acute myocardial infarction may be partly rheological, due to fibrinogen depletion. Drugs with rheological effects may be beneficial in intermittent claudication. PMID:3327567

  14. Influence of interfacial rheology on stabilization of the tear film

    NASA Astrophysics Data System (ADS)

    Bhamla, M. Saad; Fuller, Gerald G.

    2014-11-01

    The tear film that protecting the ocular surface is a complex, thin film comprised of a collection of proteins and lipids that come together to provide a number of important functions. Of particular interest in this presentation is meibum, an insoluble layer that is spread from glands lining our eyelids. Past work has focussed on the role of this layer in reducing evaporation, although conflicting evidence on its ability to reduce evaporative loss has been published. We present here the beneficial effects that are derived through the interfacial viscoelasticity of the meibomian lipid film. This is a duplex film is comprised of a rich mixture of phospholipids, long chain fatty esters, and cholesterol esters. Using interfacial rheology measurements, meibum has been shown to be highly viscoelastic. By measuring the drainage and dewetting dynamics of thin aqueous films from hemispherical surfaces where those films are laden with insoluble layers of lipids at controlled surface pressure, we offer evidence that these layers strongly stabilize the films because of their ability to support surface shearing stresses. This alternative view of the role of meibum can help explain the origin of meibomian gland dysfunction, or dry eye disease, where improper compositions of this lipid mixture do not offer the proper mechanical resistance to breakage and dewetting of the tear film.

  15. Rheological and biochemical properties of Solanum lycocarpum starch.

    PubMed

    Di-Medeiros, Maria Carolina B; Pascoal, Aline M; Batista, Karla A; Bassinello, Priscila Z; Lião, Luciano M; Leles, Maria Inês G; Fernandes, Kátia F

    2014-04-15

    This study was conducted to evaluate the rheological and physicochemical properties of Solanum lycocarpum starch. The thermogravimetric analysis of S. lycocarpum starch showed a typical three-step weight loss pattern. Microscopy revealed significant changes in the granule morphology after hydrothermal treatment. Samples hydrothermally treated at 50°C for 10 min lost 52% of their crystallinity, which was recovered after storage for 7 days at 4°C. However, samples hydrothermally treated at 65°C were totally amorphous. This treatment was sufficient to completely disrupt the starch granule, as evidenced by the absence of an endothermic peak in the DSC thermogram. The RVA of S. lycocarpum starch revealed 4440.7cP peak viscosity, 2660.5cP breakdown viscosity, 2414.1cP final viscosity, 834.3cP setback viscosity, and a pasting temperature of 49.6°C. The low content of resistant starch (10.25%) and high content of digestible starch (89.78%) in S. lycocarpum suggest that this starch may be a good source for the production of hydrolysates, such as glucose syrup and its derivatives. PMID:24607161

  16. Rheological behavior of Slide Ring Gels.

    NASA Astrophysics Data System (ADS)

    Sharma, Vivek; Park, Jong Seung; Park, Jung O.; Srinivasarao, Mohan

    2006-03-01

    Slide ring gels were synthesized by chemically crosslinking, sparsely populated α-cyclodextrin (α-CD) present on the polyrotaxanes consisting of α-CD and polyethylene glycol (PEG). [1] Unlike physically or chemically crosslinked gels, slide ring gels are topological gels where crosslinks can slide along the chain. [2] We investigate the rheological behavior of these gels swollen in water and compare their viscoelastic properties to those of physical and chemical gels. We also study the equilibrium swelling behavior of these gels. [1] Okumura and Ito, Adv. Mater. 2001, 13, 485 [2] C. Zhao et al, J. Phys. Cond. Mat. 2005, 17, S2841

  17. Rheology and dynamics of repulsive clathrates

    NASA Astrophysics Data System (ADS)

    Eroshenko, V. A.; Lazarev, Yu. F.

    2012-01-01

    The physical and thermodynamic properties of a repulsive clathrate used as a working body for the dissipation, storage, and conversion of energy in thermomechanical systems are studied. In repulsive clathrates, use is made for the first time of the molecular repulsive forces acting in large interfacial areas in a system consisting of a fluid and a capillary-porous matrix not wetted by this fluid. Based on experimental studies of a car damper with a repulsive clathrate, a rheological model of energy dissipation was developed which can be used to design compact high-performance dampers for different purposes and anti-seismic systems of new generation.

  18. Rheology of the sickle cell disorders.

    PubMed

    Stuart, J; Johnson, C S

    1987-09-01

    The sickling process causes secondary changes in cell shape, size, cation and water content, and membrane structure that contribute to the impairment of intrinsic cell deformability (Figure 2). This rheological defect is partially compensated by a low haematocrit, which moderates the rise in whole-blood viscosity, and by a rise in cardiac output which increases capillary flow velocity (Berger and King, 1982). A delicate balance exists between these mechanisms and any local disturbance of this balance by pathological changes in factors extrinsic to the sickle cell (Figure 2) can precipitate vaso-occlusion. There is still considerable controversy over the site (arteriolar, capillary, or venular) of vaso-occlusion, the type of sickle cell (reversibly sickled or irreversibly sickled) that is primarily involved, and the relative importance of extra-erythrocytic precipitating factors such as stasis, hypoxia, hyperosmolality, acidosis, alteration in temperature, acute-phase rise in plasma proteins and leukocytes, prothrombotic changes in coagulation factors and platelets, and adhesion of blood cells to vascular endothelium (Figure 2). A low-grade hypercoagulable state has been described in patients with SS (Leichtman and Brewer, 1978; Richardson et al, 1979) which may be related to the procoagulant effect of the shift of phosphatidyl serine to the outer lipid bilayer of the sickle cell (Chiu et al, 1981; Franck et al, 1985). Platelets appear to accumulate at sites of vaso-occlusion (Siegel et al, 1985) and their migration to the vessel wall may be enhanced by the presence of poorly deformable erythrocytes (Aarts et al, 1984). Endothelial cell damage in the arterial or venous circulation may also contribute (Klug et al, 1982). Thus vaso-occlusion appears to result from a complex interaction between blood cells, plasma proteins and endothelium and any one of several precipitating factors may disturb the fragile steady state and cause a painful crisis. The study of sickle

  19. Magneto-rheological defects and failures: A review

    NASA Astrophysics Data System (ADS)

    Wahid, SA; Ismail, I.; Aid, S.; Rahim, MSA

    2016-02-01

    Magneto-rheological fluid is the colloidal suspension of micron sized magnetic particles in a carrier fluid where defects and failures occur at many circumstances. This paper presents a review on defects and failures of magneto-rheological fluid in engineering applications. The most significant defect is hard cake which developed due to re-dispersion difficulties of remnant particles magnetization, leaving the magneto-rheological fluid ineffective. Clumping effect on the other hand is a separation of carrier fluid from the magnetic particles when magneto-rheological fluid is being exposed to higher magnetic field for an extended period of time. As clumping occurred, it leads to Fluid Particle Separation (FPS) which is believed altering the strength distribution of magneto-rheological fluid and therefore reducing the squeezing force. Another significant failure is magnetic particles oxidation of the magneto-rheological fluid. This paper also will discuss on stability problems which is the most challenged issue in magneto-rheological fluid technology. With the comprehensive review in this paper, researcher can design materials of magneto-rheological fluid for better properties.

  20. SOME RHEOLOGICAL PROPERTIES OF AQUEOUS PEANUT FLOUR DISPERSIONS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The rheological behaviors of aqueous peanut flour dispersions were characterized across a range of conditions, including controlled heating and cooling rates under both large and small-strain deformations. Fat content of the dry flours influenced rheological characteristics, as dispersions of highe...

  1. Western Canadian coking coals -- Thermal rheology and coking quality

    SciTech Connect

    Leeder, W.R.; Price, J.T.; Gransden, J.F.

    1997-12-31

    Methods of predicting coke strength developed from the thermal rheological properties of Carboniferous coals frequently indicate that Cretaceous coals would not make high quality coke -- yet both types of coals produce coke suitable for the iron blast furnace. This paper will discuss the reasons why Western Canadian coals exhibit lower rheological values and how to predict the strength of coke produced from them.

  2. Rheological properties of heavy oils and heavy oil emulsions

    SciTech Connect

    Khan, M.R.

    1996-06-01

    In this study, the author investigated the effects of a number of process variables such as shear rate, measurement temperature, pressure, the influence of pretreatment, and the role of various amounts of added water on the rheology of the resulting heavy oil or the emulsion. Rheological properties of heavy oils and the corresponding emulsions are important from transportation and processing standpoints.

  3. Physicochemical, thermal and rheological properties of starches isolated from malting barley varieties.

    PubMed

    Pycia, Karolina; Gałkowska, Dorota; Juszczak, Lesław; Fortuna, Teresa; Witczak, Teresa

    2015-08-01

    The aim of this work was to characterize physicochemical, thermal and rheological properties of starches isolated from malting barley varieties. The analyzed starches contained 19.6-25.2 g of amylose, 42.47-70.67 mg of phosphorus, 0.50-1.26 g of protein and 0.10-0.61 g of fat per 100 g of starch dry mass. The clarity of the 1 % (w/w) starch pastes ranged from 5.4 to 9.8 %. Values of the characteristic gelatinization temperatures were in the ranges of 56.5-58.5 °C, 61.2-63.0 °C and 66.7-68.7 °C, respectively for TO, TP and TE, whereas values of gelatinization enthalpy were from 6.49 to 9.61 J/g. The barley starches showed various tendency to retrogradation, from 24.52 to 44.22 %, measured as R = ∆HR/∆HG value. The pasting curves showed differences in pasting characteristics of the barley starches, where values of peak (PV) and final (FV) viscosities were 133-230 mPa·s and 224-411 mPa·s, respectively. The barley starch pastes exhibited non-Newtonian, shear thinning flow behaviour and thixotropy phenomenon. After cooling the starch gels showed different viscoelastic properties, however, most of them behaved like weak gels (tan δ = G″/G' > 0.1). Significant linear correlations between the parameters of pasting characteristic and some rheological parameters were found. PMID:26243900

  4. Ion tunable of rheology of supramolecular metallogels

    NASA Astrophysics Data System (ADS)

    Clarke, Nigel; Steed, Jonathan; Piepenbrock, Marc-Oliver

    2011-03-01

    A bis(pyridylurea) ligand forms metallogels in methanol in the presence of up to 0.5 equiv of copper(II) chloride. The addition of further copper(II) chloride gives an unusual crystalline 4:3 coordination polymer, whereas in the presence of 0.5 equiv of copper(II) nitrate, a 2:1 crystalline coordination polymer arises. The latter represents a possible model for supramolecular gelators and highlights key interactions with counteranions that suggest a means to tune gel properties using anion binding. The influence of chloride and acetate anions on the rheological properties of the copper(II) chloride metallogels are investigated. The rheology of the anion-containing mixtures shows complex behavior with the gel structure evolving over time. We also observe shear-induced gelation, where vigorous shaking, rather than sonication, transforms a weak jelly like aggregate into a robust gel, exhibiting clear structural changes within the gel fibres. Reversible anion tuning allows these compounds to as responsive soft materials.

  5. Rheology of rock glaciers: a preliminary assessment

    SciTech Connect

    Giardino, J.R.; Vitek, J.D.; Hoskins, E.R.

    1985-01-01

    Movement of rock debris under the influence of gravity, i.e., mass movement, generates a range of phenomena from soil creep, through solifluction,debris flows and rock glaciers to rock falls. Whereas the resultant forms of these phenomena are different, common elements in the mechanics of movement are utilized in the basic interpretation of the processes of formation. Measurements of morphologic variables provide data for deductive analyses of processes that operate too slowly to observe or for processes that generated relict phenomena. External and internal characteristics or rock glacier morphometry and measured rates of motion serve as the basis for the development of a rheological model to explain phenomena classified as rock glaciers. A rock glacier in the Sangre de Cristo Mountains of Southern Colorado, which exhibits a large number of ridges and furrows and lichen bare fronts of lobes, suggests present day movement. A strain-net established on the surface provides evidence of movement characteristics. These data plus morphologic and fabric data suggest two rheological models to explain the flow of this rock glacier. Model one is based upon perfect plastic flow and model two is based upon stratified fluid movement with viscosity changing with depth. These models permit a better understanding of the movement mechanics and demonstrate that catastrophic events and slow creep contribute to the morphologic characteristics of this rock glacier.

  6. Rheology of asphaltene-toluene/water interfaces.

    PubMed

    Sztukowski, Danuta M; Yarranton, Harvey W

    2005-12-01

    The stability of water-in-crude oil emulsions is frequently attributed to a rigid asphaltene film at the water/oil interface. The rheological properties of these films and their relationship to emulsion stability are ill defined. In this study, the interfacial tension, elastic modulus, and viscous modulus were measured using a drop shape analyzer for model oils consisting of asphaltenes dissolved in toluene for concentrations varying from 0.002 to 20 kg/m(3). The effects of oscillation frequency, asphaltene concentration, and interface aging time were examined. The films exhibited viscoelastic behavior. The total modulus increased as the interface aged at all asphaltene concentrations. An attempt was made to model the rheology for the full range of asphaltene concentration. The instantaneous elasticity was modeled with a surface equation of state (SEOS), and the elastic and viscous moduli, with the Lucassen-van den Tempel (LVDT) model. It was found that only the early-time data could be modeled using the SEOS-LVDT approach; that is, the instantaneous, elastic, and viscous moduli of interfaces aged for at most 10 minutes. At longer interface aging times, the SEOS-LVDT approach was invalid, likely because of irreversible adsorption of asphaltenes on the interface and the formation of a network structure. PMID:16316096

  7. Rheological changes in irradiated chicken eggs

    NASA Astrophysics Data System (ADS)

    Ferreira, Lúcia F. S.; Del Mastro, Nélida L.

    1998-06-01

    Pathogenic bacteria may cause foodborne illnesses. Humans may introduce pathogens into foods during production, processing, distribution and or preparation. Some of these microorganisms are able to survive conventional preservation treatments. Heat pasteurization, which is a well established and satisfactory means of decontamination/disinfection of liquid foods, cannot efficiently achieve a similar objective for solid foods. Extensive work carried out worldwide has shown that irradiation is efficient in eradicating foodborne pathogens like Salmonella spp. that can contaminate poultry products. In this work Co-60 gamma irradiation was applied to samples of industrial powder white, yolk and whole egg at doses between 0 and 25 kGy. Samples were rehydrated and the viscosity measured in a Brookfield viscosimeter, model DV III at 5, 15 and 25°C. The rheological behaviour among the various kinds of samples were markedly different. Irradiation with doses up to 5 kGy, known to reduced bacterial contamination to non-detectable levels, showed almost no variation of viscosity of irradiated egg white samples. On the other hand, whole or yolk egg samples showed some changes in rheological properties depending on the dose level, showing the predominance of whether polimerization or degradation as a result of the irradiation. Additionally, irradiation of yolk egg powder reduced yolk color as a function of the irradiation exposure implemented. The importance of these results are discussed in terms of possible industrial applications.

  8. Rheology of bubble-bearing magmas

    NASA Astrophysics Data System (ADS)

    Lejeune, A. M.; Bottinga, Y.; Trull, T. W.; Richet, P.

    1999-02-01

    The physical effects of air or argon bubbles on the rheology of a calcium aluminosilicate melt have been measured at temperatures ranging from 830° to 960°C, at 1 bar pressure. The melt composition is SiO 2:64, Al 2O 3:23, and CaO:13 (wt%), while bubble volume fractions are: 0, 0.06, 0.13, 0.32, 0.41 and 0.47. Measured Newtonian viscosities range from 10 10 to 10 14 dPa s. Melts with bubble fractions of 0.06 and 0.13 show with increasing temperature ( T) an increasing relative viscosity for T < 850°C. However at T > 850°C, for all bubble fractions the viscosity decreases markedly with temperature. The observed maximum decrease of the relative viscosity is 75% for a bubble fraction of 0.47 at 907°C. At all bubble fractions the viscosity is independent of the applied stress, which ranged from 11 to 677 bars. No clear indications were observed of non-Newtonian rheological behavior. Under our experimental conditions the relative viscosity of the two phase liquid depends primarily on the bubble fraction. Physical and volcanological implications of these measurements are discussed.

  9. Rheology of blood cells as soft tissues.

    PubMed

    Skalak, R; Chien, S

    1982-01-01

    Erythrocytes are unusual in that the cell membrane plays a large and direct role in observed rheological properties. The cell membrane is not a three dimensional material or tissue in the usual sense but being only two molecules thick. It behaves like a liquid sheet of constant thickness and surface area with some elastic properties due in part to protein networks of spectrin and actin on the interior face of the cell membrane. Packed red cells form a viscoelastic fluid which can be sheared, but exhibits a considerable elastic response. The elastic component decreases as the hematocrit is reduced, but is present at all hematocrits. Leukocytes also exhibit viscoelasticity but the properties are primarily dependent on the cell cytoplasm. The cell membrane plays a role only when it is stretched taut. The normal white cell properties have been explored over a wide range of osmolarities, becoming much less viscous and less elastic as the fluid content of the cell increases. White cells also may show spontaneous deformation during which the rheological properties become much stiffer than in the normal passive state. PMID:7104483

  10. Ultrasound image velocimetry for rheological measurements

    NASA Astrophysics Data System (ADS)

    Gurung, A.; Haverkort, J. W.; Drost, S.; Norder, B.; Westerweel, J.; Poelma, C.

    2016-09-01

    Ultrasound image velocimetry (UIV) allows for the non-intrusive measurement of a wide range of flows without the need for optical transparency. In this study, we used UIV to measure the local velocity field of a model drilling fluid that exhibits yield stress flow behavior. The radial velocity profile was used to determine the yield stress and the Herschel–Bulkley model flow index n and the consistency index k. Reference data were obtained using the conventional offline Couette rheometry. A comparison showed reasonable agreement between the two methods. The discrepancy in model parameters could be attributed to inherent differences between the methods, which cannot be captured by the three-parameter model used. Overall, with a whole flow field measurement technique such as UIV, we were able to quantify the complex rheology of a model drilling fluid. These preliminary results show that UIV can be used as a non-intrusive diagnostic for in situ, real-time measurement of complex opaque flow rheology.

  11. Pasting and rheological properties of oat products dry-blended with ground chia seeds

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Oat products containing ß-glucan are documented for lowering blood cholesterol that could be beneficial for preventing coronary heart disease. Oat products (oat flour, oat bran concentrate, and Nutrim) were dry-blended with ground chia (Salvia hispanica L.) that contains omega-3 polyunsaturated fatt...

  12. Effect of corn bran particle size on rheology and pasting characteristics of flour gels

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Dietary fiber in corn bran is known for its beneficial effects on human health and nutrition. Corn bran substitution has shown to affect batter viscosity, and volume, crumb grain, color, and texture of cakes. Purified food-grade corn bran was milled to pass through 80, 100 and 120 mesh sieve, resu...

  13. Development of Alternative Rheological Measurements for DWPF Slurry Samples (U)

    SciTech Connect

    Koopman, D. c.

    2005-09-01

    Rheological measurements are used to evaluate the fluid dynamic behavior of Defense Waste Processing Facility, DWPF, slurry samples. Measurements are currently made on non-radioactive simulant slurries using two state-of-the-art rheometers located at the Aiken County Technical Laboratory, ACTL. Measurements are made on plant samples using a rheometer in the Savannah River National Laboratory, SRNL, Shielded Cells facility. Low activity simulants or plant samples can be analyzed using a rheometer located in a radioactive hood in SRNL. Variations in the rheology of SB2 simulants impacted the interpretation of results obtained in a number of related studies. A separate rheological study was initiated with the following four goals: (1) Document the variations seen in the simulant slurries, both by a review of recent data, and by a search for similar samples for further study. (2) Attempt to explain the variations in rheological behavior, or, failing that, reduce the number of possible causes. In particular, to empirically check for rheometer-related variations. (3) Exploit the additional capabilities of the rheometers by developing new measurement methods to study the simulant rheological properties in new ways. (4) Formalize the rheological measurement process for DWPF-related samples into a series of protocols. This report focuses on the third and fourth goals. The emphasis of this report is on the development and formalization of rheological measurement methods used to characterize DWPF slurry samples. The organization is by rheological measurement method. Progress on the first two goals was documented in a concurrent technical report, Koopman (2005). That report focused on the types and possible causes of unusual rheological behavior in simulant slurry samples. It was organized by the sample being studied. The experimental portion of this study was performed in the period of March to April 2004. A general rheology protocol for routine DWPF slurry samples, Koopman

  14. Rheological evaluations and in vitro studies of injectable bioactive glass-polycaprolactone-sodium alginate composites.

    PubMed

    Borhan, Shokoufeh; Hesaraki, Saeed; Behnamghader, Ali-Asghar; Ghasemi, Ebrahim

    2016-09-01

    Composite pastes composed of various amounts of melt-derived bioactive glass 52S4 (MG5) and polycaprolactone (PCL) microspheres in sodium alginate solution were prepared. Rheological properties in both rotatory and oscillatory modes were evaluated. Injectability was measured as injection force versus piston displacement. In vitro calcium phosphate precipitation was also studied in simulated body fluid (SBF) and tracked using scanning electron microscopy, X-ray diffraction and FTIR analyses. All composite pastes were thixotropic in nature and exhibited shear thinning behavior. The magnitude of thixotropy decreased by adding 10-30 wt% PCL, while further amounts of PCL increased it again. Moreover, the composites were viscoelastic materials in which the elastic modulus was higher than viscous term. The pastes which were just made of MG5 or PCL had poor injectability, whereas the composites containing both of these constituents exhibited reasonable injectability. All pastes revealed adequate structural stability in contact with SBF solution. In vitro calcium phosphate precipitation was well observed on the paste made of MG5 and somewhat on the pastes with 10-40 wt% PCL, however the precipitated layer was amorphous in nature. Overall, the produced composites may be appropriate as injectable biomaterials for non-invasive surgeries but more biological evaluations are essential. PMID:27432416

  15. Thermal interface pastes nanostructured for high performance

    NASA Astrophysics Data System (ADS)

    Lin, Chuangang

    Thermal interface materials in the form of pastes are needed to improve thermal contacts, such as that between a microprocessor and a heat sink of a computer. High-performance and low-cost thermal pastes have been developed in this dissertation by using polyol esters as the vehicle and various nanoscale solid components. The proportion of a solid component needs to be optimized, as an excessive amount degrades the performance, due to the increase in the bond line thickness. The optimum solid volume fraction tends to be lower when the mating surfaces are smoother, and higher when the thermal conductivity is higher. Both a low bond line thickness and a high thermal conductivity help the performance. When the surfaces are smooth, a low bond line thickness can be even more important than a high thermal conductivity, as shown by the outstanding performance of the nanoclay paste of low thermal conductivity in the smooth case (0.009 mum), with the bond line thickness less than 1 mum, as enabled by low storage modulus G', low loss modulus G" and high tan delta. However, for rough surfaces, the thermal conductivity is important. The rheology affects the bond line thickness, but it does not correlate well with the performance. This study found that the structure of carbon black is an important parameter that governs the effectiveness of a carbon black for use in a thermal paste. By using a carbon black with a lower structure (i.e., a lower DBP value), a thermal paste that is more effective than the previously reported carbon black paste was obtained. Graphite nanoplatelet (GNP) was found to be comparable in effectiveness to carbon black (CB) pastes for rough surfaces, but it is less effective for smooth surfaces. At the same filler volume fraction, GNP gives higher thermal conductivity than carbon black paste. At the same pressure, GNP gives higher bond line thickness than CB (Tokai or Cabot). The effectiveness of GNP is limited, due to the high bond line thickness. A

  16. Relating Single Crystal Rheology to Polyphase Aggregate Rheology - the Importance of Stress Percolation

    NASA Astrophysics Data System (ADS)

    Burnley, P. C.

    2014-12-01

    Percolation theory is used to describe the behavior of a large number of disordered systems including the passage of fluid through porous materials, the spread of forest fires, and the mechanical behavior of granular materials. By virtue of both variations in elastic and plastic properties between different rock forming minerals as well as the plastic and elastic anisotropy of individual mineral grains, polycrystalline rocks are elastically and plastically disordered systems. Using 2D finite element models I have shown that stress transmission in rocks can also be described as a percolation problem and that the modulation of stress states within a rock can in some cases, reach levels comparable to the differential load on the rock. The presence of such modulations in the internal stress state of a rock has many implications for understanding how the rock's rheology arises from the rheology of its constituent crystals. A first order result of stress percolation is the formation of shear localization. Depending on the degree of mechanical heterogeneity of the rock's mechanical components (including grain interiors and grain boundaries), the nature of the shear localization may be highly concentrated - and therefore observable or widely distributed and "cryptic" in nature. The modulations in stress states created by stress percolation create small regions (yield nuclei) distributed throughout the rock that yield well before the bulk of the rock has reached the yield criterion. Local yielding leads to percolation of yielded regions and shear localization. Whether the shear localization remains cryptic or is observable by virtue of the development of large offsets, is a function of the density and distribution of yield nuclei. The spatial distribution of yield nuclei is a function of the nature of the stress percolation pattern, the variation in yield strength of the mechanical components and their spatial distribution. The presence of shear localization changes the

  17. Rheological Characterization of Isabgol Husk, Gum Katira Hydrocolloids, and Their Blends

    PubMed Central

    Sharma, Vipin Kumar; Mazumder, Bhaskar; Nautiyal, Vinod

    2014-01-01

    The rheological parameters of Isabgol husk, gum katira, and their blends were determined in different media such as distilled water, 0.1 N HCl, and phosphate buffer (pH 7.4). The blend properties of Isabgol husk and gum katira were measured for four different percentage compositions in order to understand their compatibility in dispersion form such as 00 : 100, 25 : 50, 50 : 50, 75 : 25, and 100 : 00 in the gel strength of 1 mass%. The miscibility of blends was determined by calculating Isabgol husk-gum katira interaction parameters by Krigbaum and Wall equation. Other rheological properties were analyzed by Bingham, Power, Casson, Casson chocolate, and IPC paste analysis. The study revealed that the power flow index “p” was less than “1” in all concentrations of Isabgol husk, gum katira, and their blends dispersions indicating the shear-thinning (pseudoplastic) behavior. All blends followed pseudoplastic behavior at thermal conditions as 298.15, 313.15, and 333.15°K and in dispersion media such as distilled water, 0.1 N HCl, and phosphate buffer (pH 7.4). Moreover, the study indicated the applicability of these blends in the development of drug delivery systems and in industries, for example, ice-cream, paste, nutraceutical, and so forth. PMID:26904636

  18. Effect of heat-moisture treatment on the structural, physicochemical, and rheological characteristics of arrowroot starch.

    PubMed

    Pepe, Larissa S; Moraes, Jaqueline; Albano, Kivia M; Telis, Vânia R N; Franco, Célia M L

    2016-04-01

    The effect of heat-moisture treatment on structural, physicochemical, and rheological characteristics of arrowroot starch was investigated. Heat-moisture treatment was performed with starch samples conditioned to 28% moisture at 100 ℃ for 2, 4, 8, and 16 h. Structural and physicochemical characterization of native and modified starches, as well as rheological assays with gels of native and 4 h modified starches subjected to acid and sterilization stresses were performed. Arrowroot starch had 23.1% of amylose and a CA-type crystalline pattern that changed over the treatment time to A-type. Modified starches had higher pasting temperature and lower peak viscosity while breakdown viscosity practically disappeared, independently of the treatment time. Gelatinization temperature and crystallinity increased, while enthalpy, swelling power, and solubility decreased with the treatment. Gels from modified starches, independently of the stress conditions, were found to have more stable apparent viscosities and higher G' and G″ than gels from native starch. Heat-moisture treatment caused a reorganization of starch chains that increased molecular interactions. This increase resulted in higher paste stability and strengthened gels that showed higher resistance to shearing and heat, even after acid or sterilization conditions. A treatment time of 4 h was enough to deeply changing the physicochemical properties of starch. PMID:26163566

  19. Forward into the Past

    ERIC Educational Resources Information Center

    Housden, Sarah

    2007-01-01

    Key themes in the development of adult and community learning over the past 10 years have included widening participation, inclusive learning and partnership working. In her 2007 book, "Reminiscence and Lifelong Learning," the author used the example of reminiscence work to illustrate how drawing on learners' memories of past experiences can…

  20. Past Tense Route Priming

    ERIC Educational Resources Information Center

    Cohen-Shikora, Emily R.; Balota, David A.

    2013-01-01

    The present research examined whether lexical (whole word) or more rule-based (morphological constituent) processes can be locally biased by experimental list context in past tense verb inflection. In Experiment 1, younger and older adults completed a past tense inflection task in which list context was manipulated across blocks containing regular…

  1. Rheology of Dense Granular Mixtures and Slurries

    NASA Astrophysics Data System (ADS)

    Tewoldebrhan, Bereket Yohannes

    Dense granular flows, characterized by multiple contacts between grains, are common in many industrial processes and natural events, such as debris flows. Understanding the characteristics of these flows is crucial to predict quantities such as bedrock erosion and distance traveled by debris flows. However, the rheological properties of these flows are complicated due to wide particle size distribution and presence of interstitial fluids. Models for dense sheared granular materials indicate that their rheological properties depend on particle size, but the representative particle size for mixtures is not obvious. Using the discrete element method (DEM) we study sheared granular binary mixtures in a Couette cell to determine the relationship and rheological parameters such as stress and effective coefficient of friction and particle size distribution. The results indicate that the stress does not depend monotonically on the average particle size as it does in models derived from simple dimensional consideration. The stress has an additional dependence on a measure of the effective free volume per particle that is adapted from an expression for packing of monosized particles near the jammed state. The effective friction also has a complicated dependence on particle size distribution. For these systems of relatively hard particles, these relationships are governed largely by the ratio between average collision times and mean-free-path times. The characteristics of shallow free surface flows, important for applications such as debris flows, are different from confined systems. To address this, we also study shallow granular flows in a rotating drum. The stress at the boundary, height profiles and segregation patterns from DEM simulations are quantitatively similar to the results obtained from physical experiments of shallow granular flows in rotating drums. Individual particle-bed impacts rather than enduring contacts dominate the largest forces on the drum bed, which

  2. Rheology and interfacial tension of biopolymers

    NASA Astrophysics Data System (ADS)

    Kandadai, Madhuvanthi A.

    The rheology and interfacial tension of biomaterials are important factors governing their potential use in biomedical applications. This dissertation presents a study of the rheology and interfacial tension of three very different biomaterials: (1) A hydrophobically modified Hyaluronic acid (HA) with polypeptide side chains, (2) Actin fibers and (3) a highly hydrophobic fluoroalkane, Perfluoropentane, and the effect of various surfactants and their mixtures on lowering its interfacial tension in an aqueous interface. In Chapter 1, we present a description of the properties and applications of these materials and a detailed literature review relevant to our studies to better understand the motivation of our work. In Chapter 2 we describe the techniques used for our studies. In Chapter 3, we present our studies on the hydrophobically modified HA with polyleucine side chains and compare them to unmodified HA of same or similar backbone molecular weights. We found a significantly enhanced viscosity for the modified HA compared to unmodified HA at the same concentration. We also found a viscoelastic behavior that was dependent on the concentration of the solution and grafting ratio of the hydrophobic side chains. The associative thickening properties of modified HA investigated with various rheological experiments and simulation results are presented in this chapter. In Chapter 4, we present our studies on the properties of actin fibers. We used a novel microrheometer VROC(TM) (Viscometer-rheometer-on-a-chip) for studying actin fibers at very high shear rates. We show that at very high shear rats, the actin filaments show irreversible network breakdown. We also studied the surface tension of actin filaments and monomer solutions at the interface with air and report induction times of these materials. In Chapter 5, we study the interfacial tension of a highly hydrophobic fluoroalkane, Perfluoropentane, in the presence of different surfactants and their mixtures. The

  3. Experimental Investigation of Orthoenstatite Single Crystal Rheology

    NASA Astrophysics Data System (ADS)

    fraysse, G.; Girard, J.; Holyoke, C. W.; Raterron, P.

    2013-12-01

    The plasticity of enstatite, upper mantle second most abundant mineral, is still poorly constrained, mostly because of its high-temperature (T) transformation into proto- and clino-enstatite at low pressure (P). Mackwell (1991, GRL, 18, 2027) reports a pioneer study of protoenstatite (Pbcn) single-crystal rheology, but the results do not directly apply to the orthorhombic (Pbca) mantle phase. Ohuchi et al. (2011, Contri. Mineral. Petrol , 161, 961) carried out deformation experiments at P=1.3 GPa on oriented orthoenstatite crystals, investigating the activity of [001](100) and [001](010) dislocation slip systems; they report the first rheological laws for orthoenstatite crystals. However, strain and stress were indirectly constrained in their experiments, which questioned whether steady state conditions of deformation were achieved. Also, data reported for [001](100) slip system were obtained after specimens had transformed by twinning into clinoenstatite. We report here new data from deformation experiments carried out at high T and P ranging from 3.5 to 6.2 GPa on natural Fe-bearing enstatite single crystals, using the Deformation-DIA apparatus (D-DIA) that equipped the X17B2 beamline of the NSLS (NY, USA). The applied stress and specimen strain rates were measured in situ by X-ray diffraction and imaging techniques (e.g., Raterron & Merkel, 2009, J. Sync. Rad., 16, 748; Raterron et al., 2013, Rev. Sci. Instr., 84, 043906). Three specimen orientations were tested: i) with the compression direction along [101]c crystallographic direction, which forms a 45° angle with both [100] and [001] axes, to investigate [001](100) slip-system activity; ii) along [011]c direction to investigate [001](010) system activity; iii) and along enstatite [125] axis, to activate both slip systems together. Crystals were deformed two by two, to compare slip system activities, or against enstatite aggregates or orientated olivine crystals of known rheology for comparison. Run products

  4. Physicochemical and rheological properties of starch and flour from different durum wheat varieties and their relationships with noodle quality.

    PubMed

    Kaur, Amritpal; Shevkani, Khetan; Katyal, Mehak; Singh, Narpinder; Ahlawat, Arvind Kumar; Singh, Anju Mahendru

    2016-04-01

    Starch and flour properties of different Indian durum wheat varieties were evaluated and related to noodle-making properties. Flours were evaluated for pasting properties, protein characteristics (extractable as well as unextractable monomeric and polymeric proteins) and dough rheology (farinographic properties), while starches were evaluated for granule size, thermal, pasting, and rheological properties. Flour peak and final viscosities related negatively to the proportion of monomeric proteins but positively to that of polymeric proteins whereas opposite relations were observed for dough rheological properties (dough-development time and stability). Starches from varieties with higher proportion of large granules showed the presence of less stable amylose-lipids and had more swelling power, peak viscosity and breakdown viscosity than those with greater proportion of small granules. Noodle-cooking time related positively to the proportion of monomeric proteins and starch gelatinization temperatures but negatively to that of polymeric proteins and amylose content. Varieties with more proteins resulted in firmer noodles. Noodle-cohesiveness related positively to the proportion of polymeric proteins and amylose-lipids complexes whereas springiness correlated negatively to amylose content and retrogradation tendency of starches. PMID:27413243

  5. Shear History Extensional Rheology Experiment II (SHERE II) Microgravity Rheology with Non-Newtonian Polymeric Fluids

    NASA Technical Reports Server (NTRS)

    Jaishankar, Aditya; Haward, Simon; Hall, Nancy Rabel; Magee, Kevin; McKinley, Gareth

    2012-01-01

    The primary objective of SHERE II is to study the effect of torsional preshear on the subsequent extensional behavior of filled viscoelastic suspensions. Microgravity environment eliminates gravitational sagging that makes Earth-based experiments of extensional rheology challenging. Experiments may serve as an idealized model system to study the properties of lunar regolith-polymeric binder based construction materials. Filled polymeric suspensions are ubiquitous in foods, cosmetics, detergents, biomedical materials, etc.

  6. Essence of disposing the excess sludge and optimizing the operation of wastewater treatment: rheological behavior and microbial ecosystem.

    PubMed

    Tang, Bing; Zhang, Zi

    2014-06-01

    Proper disposal of excess sludge and steady maintenance of the high bioactivity of activated sludge in bioreactors are essential for the successful operation of wastewater treatment plants (WWTPs). Since sludge is a non-Newtonian fluid, the rheological behavior of sludge can therefore have a significant impact on various processes in a WWTP, such as fluid transportation, mixing, oxygen diffusion, mass transfer, anaerobic digestion, chemical conditioning and mechanical dewatering. These are key factors affecting the operation efficiency and the energy consumption of the entire process. In the past decade-due to the production of large quantities of excess sludge associated with the extensive construction of WWTPs and the emergence of some newly-developed techniques for wastewater purification characterized by high biomass concentrations-investigations into the rheology of sludge are increasingly important and this topic has aroused considerable interests. We reviewed a number of investigations into the rheology of sludge, with the purpose of providing systematic and detailed analyses on the related aspects of the rheological behavior of sludge. It is clear that, even though considerable research has focused on the rheology of sludge over a long time period, there is still a need for further thorough investigation into this field. Due to the complex process of bio-treatment in all WWTPs, biological factors have a major influence on the properties of sludge. These influences are however still poorly understood, particularly with respect to the mechanisms involved and magnitude of such impacts. When taking note of the conspicuous biological characteristics of sludge, it becomes important that biological factors, such as the species composition and relative abundance of various microorganisms, as well as the microbial community characteristics that affect relevant operating processes, should be considered. PMID:24462086

  7. Influence of Plasticizer Amount on Rheological and Hydration Properties of CEM II Type Portland Cements

    NASA Astrophysics Data System (ADS)

    Šeputytė-Juciké, J.; Pundienė, I.; Kičaitė, A.; Pranckevičienė, J.

    2015-11-01

    The article analyzes the effect of plasticizer (based on polycarboxilates) amount (0.3 - 1.2% wt. of cement) on the rheological and hydration properties of two Portland cements pastes: CEM II/A-S 42.5N and CEM II/A-LL 42.5N. Increase of plasticizer amount reduces viscosity of CEM II/A-LL 42.5N cement paste from 3 to 12 times, where viscosity of CEM II/A-S 42.5N cement paste reduces from 5 to 20 times. The optimum plasticizer dose (0.3%) in case of CEM II/A-S 42.5N and (1.2%) in case of CEM II/A-LL 42.5N was established. Calorimetry studies have shown that plasticizer reduces the wetting heat release rate in CEM II/A-LL 42.5N cement twice and in CEM II/A-S 42.5N cement - by 25%. Plasticizer prolongs the maximum heat release rate time by 16 h in CEM II/A-LL 42.5N samples and reduces heat release rate by 19%. In CEM II/A-S 42.5N cement samples plasticizer prolongs maximum heat release rate time by 14.5 h and increases heat release rate by 15%. The goal of this study is to analyze the effect of the dosage of the most widely used plasticizer on solubility characteristics, rheological and hydration properties of two cements CEM II/A-S 42.5N and CEM II/A-LL 42.5N to establish the optimum dose of plasticizer in cements pastes.

  8. Rheological effects on friction in elastohydrodynamic lubrication

    NASA Technical Reports Server (NTRS)

    Trachman, E. G.; Cheng, H. S.

    1973-01-01

    An analytical and experimental investigation is presented of the friction in a rolling and sliding elastohydrodynamic lubricated contact. The rheological behavior of the lubricant is described in terms of two viscoelastic models. These models represent the separate effects of non-Newtonian behavior and the transient response of the fluid. A unified description of the non-Newtonian shear rate dependence of the viscosity is presented as a new hyperbolic liquid model. The transient response of viscosity, following the rapid pressure rise encountered in the contact, is described by a compressional viscoelastic model of the volume response of a liquid to an applied pressure step. The resulting momentum and energy equations are solved by an iterative numerical technique, and a friction coefficient is calculated. The experimental study was performed, with two synthetic paraffinic lubricants, to verify the friction predictions of the analysis. The values of friction coefficient from theory and experiment are in close agreement.

  9. Rheological properties of sulfoacetate derivatives of cellulose.

    PubMed

    Chauvelon, Gaëlle; Doublier, Jean-Louis; Buléon, Alain; Thibault, Jean-François; Saulnier, Luc

    2003-04-01

    Water-soluble cellulose acetate sulfate derivatives (CAS) have been prepared through chemical reaction involving sulfuric acid as a catalyst. These CAS have been obtained from cellulosic materials of different origins (pure cellulose, wheat bran, maize bran) and their rheological behavior in salt-free aqueous solution has been estimated in dilute and semi-dilute regime using dynamic viscoelastic and viscosity measurements. Influence of concentration, temperature of solubilization and temperature of measurement has been investigated. Weak gel-like properties were exhibited at elevated concentration (typically above 7-8 g/L). These systems also exhibited thixotropic properties: the structure was partly broken down upon shearing and recovered at rest. They also displayed thermoreversibility with large hysteresis, the melting temperature being approximately 15 degrees C higher than the temperature at which gelation took place. These overall observations clearly indicate that these distinctive properties arise from intermolecular association of the macromolecular chains of the cellulose derivative. PMID:12668095

  10. Nanoparticles in Polymers: Assembly, Rheology and Properties

    NASA Astrophysics Data System (ADS)

    Rao, Yuanqiao

    Inorganic nanoparticles have the potential of providing functionalities that are difficult to realize using organic materials; and nanocomposites is an effective mean to impart processibility and construct bulk materials with breakthrough properties. The dispersion and assembly of nanoparticles are critical to both processibility and properties of the resulting product. In this talk, we will discuss several methods to control the hierarchical structure of nanoparticles in polymers and resulting rheological, mechanical and optical properties. In one example, polymer-particle interaction and secondary microstructure were designed to provide a low viscosity composition comprising exfoliated high aspect ratio clay nanoparticles; in another example, the microstructure control through templates was shown to enable unique thermal mechanical and optical properties. Jeff Munro, Stephanie Potisek, Phillip Hustad; all of the Dow Chemical Company are co-authors.

  11. Impact of Helicobacter Pylori on Mucus Rheology

    NASA Astrophysics Data System (ADS)

    Celli, Jonathan; Keates, Sarah; Kelly, Ciaran; Turner, Bradley; Bansil, Rama; Erramilli, Shyamsunder

    2006-03-01

    It is well known that the viscoelastic properties of gastric mucin are crucial to the protection of the lining of the stomach against its own acidic secretions and other agents. Helicobacter Pylori, a rod shaped, gram-negative bacteria that dwells in the mucus layer of approximately 50% of the world's population is a class I carcinogen and is associated with gastric ulcers and severe gastritis. The structural damage to the mucus layer caused by H. Pylori is an important aspect of infection with this bacteria. We are examining the impact of H. Pylori on mucin and mucus rheology quantitatively using a combination of dynamic light scattering and multiple particle tracking experiments. Video microscopy data will also be presented on the motility of this bacteria in mucin at different pH and in other viscoelastic gels.

  12. Rheology and lubricity of hyaluronic acid

    NASA Astrophysics Data System (ADS)

    Liang, Jing; Krause, Wendy E.

    2007-03-01

    The polyelectrolyte hyaluronic acid (HA, hyaluronan) is an important component in synovial fluid (i.e., the fluid that lubricates our freely moving joints). Its presence results in highly viscoelastic solutions. In comparison to healthy synovial fluid, diseased fluid has a reduced viscosity and loss of lubricity. In osteoarthritis the reduction in viscosity results from a decline in both the molecular weight and concentration of HA. In our investigation, we attempt to correlate the rheological properties of HA solutions to changes in lubrication and wear. A nanoindenter will be used to evaluate the coefficient of friction and wear properties between the nanoindenter tip and ultrahigh molecular weight polyethylene in both the presence and absence of a thin film of HA solution.

  13. Rheology of the upper mantle: a synthesis.

    PubMed

    Karato, S; Wu, P

    1993-05-01

    Rheological properties of the upper mantle of the Earth play an important role in the dynamics of the lithosphere and asthenosphere. However, such fundamental issues as the dominant mechanisms of flow have not been well resolved. A synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the Earth's upper mantle. The hot and shallow upper mantle flows by dislocation creep, whereas cold and shallow or deep upper mantle may flow by diffusion creep. When the stress increases, grain size is reduced and the upper mantle near the transition between these two regimes is weakened. Consequently, deformation is localized and the upper mantle is decoupled mechanically near these depths. PMID:17746109

  14. New applications for cellulose nanofibers: Rheological challenges

    NASA Astrophysics Data System (ADS)

    Nazari-Nasrabad, Behzad

    Cellulose nanofibers (CNF) are an exciting new renewable material produced from wood fibers. Even at low solids content, CNF-water suspensions have a complex rheology that includes extreme shear-thinning as well as viscoelastic properties and a yield stress. In the rheology of CNF suspensions, the measurement method may influence the results due to wall-slippage, but it is unclear how the behavior near walls influences the measurement method and what process equipment can manipulate this material. Parallel-plate and vane geometries were utilized to compare yielding and flow of CNF suspensions obtained by steady-state shear and oscillatory rheological measurements. Four different methods were compared as techniques to obtain a yield stress. The results are compared to pressure driven flow in a tube. Cone and plate geometries were found to lead to sample ejection at low shear rates: floc-floc interactions can explain this ejection. The suspensions violated the Cox-Merz rule in a significant manner as a sign of containing weak gel structures and the formation of a water-rich layer near the solid boundaries. For suspensions lower than 3% solids, the yield stress measured with different procedures were within 20% of each other, but for high solids suspensions, differences among the methods could be as large as 100%; the water-rich layer formation likely is the cause of these results. Oscillatory methods are suggested as a technique to obtain yield stress values. The pressure driven flow results were consistent with the power-law line fitted to the parallel-plate geometry data from steady shear. The capability of the extrusion process was investigated for pumping CNF suspensions through different dies. The extrusion process resulted in acceptable pumping rates which was in good agreement with the mathematical model. However, attributable to the extreme shear-thinning behavior of CNF, the pressure counter-flow dominates the drag flow along the screw channel and does not

  15. Metamorphic probing of subduction dynamics and rheology

    NASA Astrophysics Data System (ADS)

    Agard, Philippe

    2015-04-01

    Understanding subduction dynamics and rheology, and particularly the role of fluids and deformation, strongly relies on integrated tectonic, petrological and geochemical studies able to retrieve from our most direct and reliable natural probes (i.e., preserved metamorphic assemblages) their pressure-temperature-time (P-T-t) evolution. I first provide two examples of such integrated studies that allow tracking rock trajectories and exhumation dynamics in subduction zones -- thanks to the considerable progress made over the last ten years on estimating P-T-t conditions. The Oman example shows how EPMA mapping and the detailed study of local, low-temperature equilibria help constrain the behaviour and dynamics of upper crustal units during continental subduction, demonstrating the importance of slicing, accretion at depths of ~30 km and short-lived tectonic expulsion. In the Western Alps, the extensive coverage of field exposures by means of the Raman Spectrometry of carbonaceous matter and by dedicated pseudosection modelling allows to identify the existence of tens of km long, fairly continuous slices of downgoing slab exhumed from similar eclogitic depths (~80 km), and to assess the role of the overall fluid content in enabling their exhumation/preservation. I then illustrate how metamorphic rocks can provide ideal probes (though still partly to be improved) to address key, large-scale tectonic processes and not 'simply' histories, and do stress the importance of adequate field-based data acquisition. Three examples (and present-day limitations) are reviewed here: (1) The regional-scale exhumation of blueschists from the downdip end of the seismogenic zone across thousands of kilometers along the Neotethys (at ~1-1.5 GPa, 350°C) is a major geodynamic event providing insights into changes in interplate mechanical coupling and subduction dynamics. (2) Eclogite breccias recently reported in the Monviso area (W. Alps) allow constraining short-term processes involving

  16. Rheological characterization of addition polyimide matrix resins and prepregs

    NASA Technical Reports Server (NTRS)

    Maximovich, M. G.; Galeos, R. M.

    1984-01-01

    Although graphite-reinforced polyimide matrix composites offer outstanding specific strength and stiffness, together with high thermal oxidative stability, processing problems connected with their rheological behavior remain to be addressed. The present rheological studies on neat polyimide resin systems encountered outgassing during cure. A staging technique has been developed which can successfully handle polyimide samples, and novel methods were applied to generate rheological curves for graphite-reinforced prepregs. The commercial graphite/polyimide systems studied were PRM 15, LARC 160, and V378A.

  17. Development of a model colloidal system for rheology simulation.

    SciTech Connect

    Schunk, Peter Randall; Tallant, David Robert; Piech, Martin; Bell, Nelson Simmons; Frischknecht, Amalie Lucile

    2008-10-01

    The objective of the experimental effort is to provide a model particle system that will enable modeling of the macroscopic rheology from the interfacial and environmental structure of the particles and solvent or melt as functions of applied shear and volume fraction of the solid particles. This chapter describes the choice of the model particle system, methods for synthesis and characterization, and results from characterization of colloidal dispersion, particle film formation, and the shear and oscillatory rheology in the system. Surface characterization of the grafted PDMS interface, dispersion characterization of the colloids, and rheological characterization of the dispersions as a function of volume fraction were conducted.

  18. Rheology of coal slurries. Final report

    SciTech Connect

    Ulbrecht, J.J.; Ryan, M.E.

    1982-01-01

    Experimental investigations of suspensions of three size distributions of glass spheres in a solution of tetralin and tetrabromoethane were made using a Haake viscometer. The values of viscosity were determined over a range of shear rates from 1 to 1000 sec/sup -1/. The suspending medium is Newtonian with a viscosity of about 9.66 centipoise at 25 +- 1/sup 0/C. At phi less than or equal to 20%, the suspension exhibited Newtonian behavior but at phi greater than or equal to 30%, the suspension exhibited pronounced non-Newtonian behavior. Experimental studies of these three size distributions were also conducted in aqueous solutions of polyvinylpyrrolidone using a pipe loop apparatus. Viscosity was measured over the shear rate range from 600 to 6000 sec./sup -1/. These suspensions having non-Newtonian suspending media, exhibit non-Newtonian behavior at all concentration levels of the solid particles. In the limit of very high shear rates, the suspension viscosity was found to be independent of tube diameter over the range of shear rates and concentrations studied. The rheological behavior of slurries of irregularly-shaped anthracite coal particles was also systematically investigated. The suspending medium consisted of a mixture of anthracene oil and tetrabromoethane. The shear rate was varied from 0.01 to 1000 sec./sup -1/. Volume concentrations range from 0 to 34%. At volume concentrations greater than 29% the slurries exhibited a yield stress and pronounced thixotropic behavior. The relative viscosities of both the model and the coal slurries were found to be dependent on both the shear rate and the particle size. In the case of the coal slurries caution must be exercised with regard to the proper interpretation of the rheological data due to the influences of the measured apparent density of the coal particles, viscometric flow geometry, and time dependent effects.

  19. Rheological Characterization of Ethanolamine Gel Propellants

    NASA Astrophysics Data System (ADS)

    V. S Jyoti, Botchu; Baek, Seung Wook

    2016-07-01

    Ethanolamine is considered to be an environmentally friendly propellant system because it has low toxicity and is noncarcinogenic in nature. In this article, efforts are made to formulate and prepare ethanolamine gel systems, using pure agarose and hybrids of paired gelling agents (agarose + polyvinylpyrrolidine (PVP), agarose + SiO2, and PVP + SiO2), that exhibit a measurable yield stress, thixotropic behavior under shear rate ranges of 1-1,000 s-1 and a viscoelastic nature. To achieve these goals, multiple rheological experiments (including flow and dynamic studies) are performed. In this article, results are presented from experiments measuring the apparent viscosity, yield stress, thixotropy, dynamic strain, frequency sweep, and tan δ behaviors, as well as the effects of the test temperature, in the gel systems. The results show that the formulated ethanolamine gels are thixotropic in nature with yield stress between 30 and 60 Pa. The apparent viscosity of the gel decreases as the test temperature increases, and the apparent activation energy is the lowest for the ethanolamine-(PVP + SiO2) gel system. The dynamic rheology study shows that the type of gellant, choice of hybrid gelling materials and their concentration, applied frequencies, and strain all vitally affect the viscoelastic properties of the ethanolamine gel systems. In the frequency sweep experiment, the ethanolamine gels to which agarose, agarose + PVP, and agarose + SiO2 were added behave like linear frequency-dependent viscoelastic liquids, whereas the ethanolamine gel to which PVP + SiO2 was added behaves like a nearly frequency-independent viscoelastic solid. The variation in the tan δ of these gelled propellants as a function of frequency is also discussed.

  20. Performance comparison of front-side silver pastes using polyalkylene carbonates for cleaner burning binder system

    NASA Astrophysics Data System (ADS)

    Stephenson, Richard; Ferraro, Peter

    2015-09-01

    Clean-burning binder systems used in paste formulations for front side solar cell applications offer advantages of reduced residual carbon, improved conductive feature density, and overall performance and reliability. This paper presents the technical advantages of employing polyalkylene carbonates (QPAC®) as the principle binder for paste formulations used in front side solar screen printing applications. Thermal and rheological characteristics are presented and compared with standard or conventional pastes currently employed in production lines producing solar cell front side geometry. Microstructural comparisons of conductive features of the front side geometry are examined and related to aspects of adhesion performance and resistive losses.

  1. Anomalous rheological behavior of long glass fiber reinforced polypropylene

    NASA Astrophysics Data System (ADS)

    Kim, Dong Hak; Lee, Young Sil; Son, Younggon

    2012-12-01

    Dynamic rheological properties of PP-based long glass fiber-reinforced thermoplastics (LFT) were investigated. Weight fractions of the glass fibers investigated in the present study ranged from 0.15 to 0.5, which are higher than those of previous studies. We observed very abnormal rheological behavior. Complex viscosity (η*) of the LFT increased with the glass fiber content up to 40 wt. %. However, the η* with a weight fraction of 0.5 is observed to be lower than that of LFT with a weight fraction of 0.4 in spite of higher glass fiber content. From various experiments, we found that this abnormal behavior is analogous to the rheological behavior of a lyotropic liquid crystalline polymer solution and concluded that the abnormal rheological behavior for the LFT is attributed to the formation of a liquid crystal- like structure at high concentrations of long glass fibers.

  2. Rheology of Carbon Fibre Reinforced Cement-Based Mortar

    SciTech Connect

    Banfill, Phillip F. G.; Starrs, Gerry; McCarter, W. John

    2008-07-07

    Carbon fibre reinforced cement based materials (CFRCs) offer the possibility of fabricating 'smart' electrically conductive materials. Rheology of the fresh mix is crucial to satisfactory moulding and fresh CFRC conforms to the Bingham model with slight structural breakdown. Both yield stress and plastic viscosity increase with increasing fibre length and volume concentration. Using a modified Viskomat NT, the concentration dependence of CFRC rheology up to 1.5% fibre volume is reported.

  3. Rheology of Carbon Fibre Reinforced Cement-Based Mortar

    NASA Astrophysics Data System (ADS)

    Banfill, Phillip F. G.; Starrs, Gerry; McCarter, W. John

    2008-07-01

    Carbon fibre reinforced cement based materials (CFRCs) offer the possibility of fabricating "smart" electrically conductive materials. Rheology of the fresh mix is crucial to satisfactory moulding and fresh CFRC conforms to the Bingham model with slight structural breakdown. Both yield stress and plastic viscosity increase with increasing fibre length and volume concentration. Using a modified Viskomat NT, the concentration dependence of CFRC rheology up to 1.5% fibre volume is reported.

  4. Dynamic and rheological properties of soft biological cell suspensions

    PubMed Central

    Yazdani, Alireza; Li, Xuejin

    2016-01-01

    Quantifying dynamic and rheological properties of suspensions of soft biological particles such as vesicles, capsules, and red blood cells (RBCs) is fundamentally important in computational biology and biomedical engineering. In this review, recent studies on dynamic and rheological behavior of soft biological cell suspensions by computer simulations are presented, considering both unbounded and confined shear flow. Furthermore, the hemodynamic and hemorheological characteristics of RBCs in diseases such as malaria and sickle cell anemia are highlighted. PMID:27540271

  5. Rheology of Melt-bearing Crustal Rocks

    NASA Astrophysics Data System (ADS)

    Rosenberg, C. L.; Medvedev, S.; Handy, M. R.

    2006-12-01

    A review and reinterpretation of previous experimental data on the deformation of melt-bearing crustal rocks (Rosenberg and Handy, 2005) revealed that the relationship of aggregate strength to melt fraction is non-linear, even if plotted on a linear ordinate and abscissa. At melt fractions, Φ 0.07, the dependence of aggregate strength on Φ is significantly greater than at Φ > 0.07. This melt fraction (Φ= 0.07) marks the transition from a significant increase in the proportion of melt-bearing grain boundaries up to this point to a minor increase thereafter. Therefore, we suggest that the increase of melt-interconnectivity causes the dramatic strength drop between the solidus and a melt fraction of 0.07. A second strength drop occurs at higher melt fractions and corresponds to the breakdown of the solid (crystal) framework, corresponding to the well-known "rheologically critical melt percentage" (RCMP; Arzi, 1978). Although the strength drop at the RCMP is about 4 orders of magnitude, the absolute value of this drop is small compared to the absolute strength of the unmelted aggregate, rendering the RCMP invisible in a linear aggregate strength vs. melt fraction diagram. Predicting the rheological properties and thresholds of melt-bearing crust on the basis of the results and interpretations above is very difficult, because the rheological data base was obtained from experiments performed at undrained conditions in the brittle field. These conditions are unlikely to represent the flow of partially melted crust. The measured strength of most of the experimentally deformed, partially-melted samples corresponds to their maximum differential stress, before the onset of brittle failure, not to their viscous strength during "ductile" (viscous) flow. To overcome these problems, we extrapolated a theoretically-derived flow law for partially melted granite deforming by diffusion-accommodated grain-boundary sliding (Paterson, 2001) and an experimentally-derived flow law for

  6. Past tense route priming.

    PubMed

    Cohen-Shikora, Emily R; Balota, David A

    2013-03-01

    The present research examined whether lexical (whole word) or more rule-based (morphological constituent) processes can be locally biased by experimental list context in past tense verb inflection. In Experiment 1, younger and older adults completed a past tense inflection task in which list context was manipulated across blocks containing regular past tense verbs (e.g. REACH-REACHED) or irregular past tense verbs (TEACH-TAUGHT). Critical targets, consisting of half regular and half irregular verbs, were embedded within blocks and participants' inflection response latency and accuracy were assessed. The results yielded a cross-over interaction in response latencies for both young and older adults. In the regular context there was a robust regularity effect: regular target verbs were conjugated faster than irregular target verbs. In contrast, in the irregular context, irregular target verbs were conjugated faster than regular target verbs. Experiment 2 used the same targets but in the context of either standard nonwords or nonwords ending in "-ED" to test the possibility of a phonological basis for the effect. The effect of context was eliminated. The results support the notion that distinct processes in past tense verb production can be locally biased by list context and, as shown in Experiment 2, this route priming effect was not due to phonological priming. PMID:23291293

  7. Review Of Rheology Models For Hanford Waste Blending

    SciTech Connect

    Koopman, D. C.; Stone, M.

    2013-09-26

    The area of rheological property prediction was identified as a technology need in the Hanford Tank Waste - waste feed acceptance initiative area during a series of technical meetings among the national laboratories, Department of Energy-Office of River Protection, and Hanford site contractors. Meacham et al. delivered a technical report in June 2012, RPP-RPT-51652 ''One System Evaluation of Waste Transferred to the Waste Treatment Plant'' that included estimating of single shell tank waste Bingham plastic rheological model constants along with a discussion of the issues inherent in predicting the rheological properties of blended wastes. This report was selected as the basis for moving forward during the technical meetings. The report does not provide an equation for predicting rheological properties of blended waste slurries. The attached technical report gives an independent review of the provided Hanford rheological data, Hanford rheological models for single tank wastes, and Hanford rheology after blending provided in the Meacham report. The attached report also compares Hanford to SRS waste rheology and discusses some SRS rheological model equations for single tank wastes, as well as discussing SRS experience with the blending of waste sludges with aqueous material, other waste sludges, and frit slurries. Some observations of note: Savannah River Site (SRS) waste samples from slurried tanks typically have yield stress >1 Pa at 10 wt.% undissolved solids (UDS), while core samples largely have little or no yield stress at 10 wt.% UDS. This could be due to how the waste has been processed, stored, retrieved, and sampled or simply in the differences in the speciation of the wastes. The equations described in Meacham's report are not recommended for extrapolation to wt.% UDS beyond the available data for several reasons; weak technical basis, insufficient data, and large data scatter. When limited data are available, for example two to three points, the equations

  8. Rheology and structure of thermoreversible hydrogels

    NASA Astrophysics Data System (ADS)

    Jiang, Jun

    2007-12-01

    Highly concentrated solutions of non-ionic amphiphilic triblock copolymer poly(ethylene oxide)99-poly(propylene oxide)67-poly(ethylene oxide)99 (Pluronic F127) are widely used in numerous biomedical applications, such as drug delivery vehicles, and surfactants for emulsification of food and personal care products. The Pluronic copolymers are popular for these applications, since their gelation properties are thermoreversible and easily controlled by varying the concentration. They are liquid below room temperature and gel at body temperature. Hence they are great injectable biomaterials for tissue engineering and implantation. In this dissertation, thermal gelation and structure of high concentration triblock copolymer Pluronic F127-clay (Cloisite Na+ and Lucentite SWN) aqueous solutions were characterized by rheological measurements, differential scanning calorimetry (DSC) and small angle X-ray/neutron scattering. Small angle neutron scattering (SANS), under shear using a Couette cell in radial and tangential scattering geometry, was performed to examine the structural evolution of the polymeric micellar macro-lattice formed by concentrated aqueous solutions of triblock copolymer-Pluronic F127, as a function of the shear rate. The micellar gel showed a shear thinning, i.e., a reduction of the resistance to shear, by forming a layered stacking of two-dimensional hexagonally close packed (HCP) polymer micelles. A theoretical model was developed to calculate 2D SANS scattering patterns that can be compared with the experimental data. In order to improve the mechanical properties of the gel, while still maintaining the thermo-reversibility, we synthesized multiblock structures, where the F127 construct would be repeated several times. In this manner, physical interconnections between the micelles could occur as the multiblock copolymers formed interlocking loops and tails, thereby greatly increasing the mechanical strength of the gels. The rheological and structural

  9. Rheological Characterization of Foamy Oils under Pressure

    NASA Astrophysics Data System (ADS)

    Abivin, Patrice; Henaut, Isabelle; Moan, Michel; Argillier, Jean-Francois

    2008-07-01

    Heavy oils are a strategic source of hydrocarbons due to the large amount of reserves located mainly in Venezuela and Canada. They distinguish from conventional oils by their higher density and viscosity. When a reservoir is depleted, the lightest components (methane, ethane, etc.) can exsolve from the crude oil and create a gaseous phase. In conventional oils, bubbles grow and coalesce quickly. On the contrary, in heavy oils, bubbles are small and remain dispersed within the oil for a long time. This "foamy oil" phenomenon changes drastically the flow properties of the crude oil. This article is devoted to the characterization of the heavy oil foamy behavior through a rheological study. Our objectives are to study the kinetics of bubble evolution in heavy oil and to measure their influence on viscosity. A new experimental method was developed, based upon rheological measurements under pressure. Several heavy oils containing dissolved gas have been depleted inside the pressure cells of controlled stress rheometers to create foamy oils. Viscoelastic properties have been continuously measured using both oscillatory and continuous tests from the nucleation up to the total disengagement of bubbles from oil. The occurrence of bubbles was visualized using X-ray scanning experiments. Results demonstrate that foamy oil kinetics is mostly related to the oil viscosity. They also reveal that under low shear rates, the presence of bubbles leads to an increase in heavy oil viscosity, as predicted by the Hard Sphere Model or by Taylor's one. A theoretical model describing the viscosity of foamy oil was then established. It takes into account both first-order kinetics of appearance and release of bubbles in oil and a basic suspension model. Good agreement was obtained between experimental data and model predictions. Finally, several tests reveal the strong influence of the shear rate on the foamy oil behavior and point out the major role of bubble deformation on the viscosity of

  10. Using Ultrasound to Measure Mud Rheological Properties

    NASA Astrophysics Data System (ADS)

    Maa, P. Y. P. Y.; Kwon, J. I.; Park, K. S.

    2015-12-01

    In order to predict the dynamic responses of newly consolidated cohesive sediment beds, a better understanding of the material rheological properties (bulk density, ρ, kinematic viscosity, ν, and shear modulus, G, assuming mud is a simple Voigt viscoelastic model) of these sediment beds is needed. An acoustic approach that uses a commercially available 250 kHz shear wave transducer and tone-burst waves has been developed to measure those properties. This approach uses a 86.3 mm long delay-line (DL) to separate the generated pressure and shear waves, and measures the reflected shear waves as well as the reflected pressure waves caused at the interface between the delay line and the mud to interpret these properties. By using materials (i.e., air, water, olive oil, and honey) with available rheological properties to establish a calibration relationship between the information carried by the measured reflected waves and those given material properties, the mud properties as well as thνe change of these properties during consolidation can be interpreted. Using jelly pudding as a check, a value of G ≈ 12310 N/m2 and ν ≈ 5 x 10-5 m2/s were estimated. For the consolidating kaolinite bed (with zero salinity and initial suspended sediment concentration about 420 g/cm3), the measurements show that the shear modulus developed after about 40 hours and approached a value on the order of 15000 N/m2 after about 100 hours. The initial kinematic viscosity was about 5 x 10-4 m2/s, and it decreased slowly with time and approached a low plateau between 10-6 and 10-7 m2/s after 300 hours. The measured bulk density showed a small increasing rate during the entire consolidation period, except at a short period between 80 and 90 hours after consolidation. Results from this study suggest a promising approach for developing an in-situ instrument to measure mud properties, as well as many other materials in other industries.

  11. Integrative Analysis of Mantle Lithosphere Rheology

    NASA Astrophysics Data System (ADS)

    Hirth, G.; Collins, J. A.; Molnar, P. H.; Kelemen, P. B.

    2014-12-01

    We will present an analysis of the rheology of mantle lithosphere based on extrapolation of lab-based flow laws, microstructural characterization of mantle shear zones and xenoliths, and the spatial distribution of mantle earthquakes and seismic anisotropy. As a starting point, we illustrate the similarity in the evolution of olivine lattice preferred orientation (LPO) for cm-scale lab samples (e.g., Zhang et al., 2000) and 100 meter-scale shear zones (e.g., Warren et al., 2008; Skemer et al., 2010). This correlation provides strong support for the extrapolation of lab data in both time and scale. The extrapolation of these results to plate-scale processes is supported by the analysis of shear wave splitting across the Alpine Fault on the South Island of New Zealand and its surrounding ocean basins (Zietlow et al., 2014). For the same region, the similarity in the fast Pn azimuth with the fast shear wave polarization directions indicates high strain deformation of relatively cold (~500-700oC) mantle lithosphere across a region 100-200 km wide (Collins and Molnar, 2014). This latter observation suggests that the lithosphere is significantly weaker than predicted by the extrapolation of dislocation creep or Peierls creep flow laws. Weakening via promotion of grain size sensitive creep mechanisms (diffusion creep and DisGBS) is likely at these conditions; however, studies of exhumed mantle shear zones generally indicate that the activation of these processes leads to strain localization at scales <<200 km. These observations motivate us to consider rheological constraints derived from geodetic studies and earthquake depths in regions where deformation of the lithosphere occurs at similar conditions. At face value, these data provide additional support for the extrapolation of lab data; the depth extent of earthquakes is consistent with estimates for the conditions where a transition from stable to unstable frictional sliding occurs (e.g., Boettcher et al., 2007) - and

  12. Microfluidic Rheology of Soft Colloidal Suspensions

    NASA Astrophysics Data System (ADS)

    Nordstrom, Kerstin; Arratia, Paulo; Verneuil, Emilie; Gollub, Jerry; Durian, Douglas

    2008-11-01

    The rheology of a suspension of soft colloidal particles is investigated using a pressure-driven flow in a deep 25 μm wide microchannel. The system is composed of N-isopropylacrylamide (NIPA), colloidal microgel particles, suspended in aqueous solution. NIPA is temperature-sensitive in that the hydrodynamic radius of a particle decreases as temperature increases [1]. Therefore, colloidal suspensions of different packing fraction can be obtained simply by varying the temperature using a temperature-controlled stage. We determine the velocity profile and the local shear rate of the suspension using particle image velocimetry (PIV). We have developed methods to accurately infer the suspension shear viscosity and shear stress as a function of shear rate. The dynamical range of shear rates probed is approximately 5 orders of magnitude, ranging from 10-3 to 10^2 s-1. Results show that as the packing fraction is increased towards the jamming point, the velocity profiles are markedly non-Newtonian. Further, near the jamming point, the stress versus shear rate curves show yield stress behavior. [1] Alsayed, A.M., Islam, M.F., Zhang, J., Collings, P.J., Yodh, A.J., Science 309, 1207.-1210 (2005)

  13. Rheology of Soft Suspensions near Jamming

    NASA Astrophysics Data System (ADS)

    Nordstrom, Kerstin; Verneuil, Emilie; Arratia, Paulo; Gollub, Jerry; Durian, Douglas

    2009-03-01

    The rheology of a suspension of soft colloidal particles is investigated using a pressure-driven flow in a deep 25 μm wide microchannel. The system is composed of N-isopropylacrylamide (NIPA) colloidal microgel particles, suspended in aqueous solution. NIPA is temperature-sensitive in that the hydrodynamic radius decreases as temperature increases [1]. Therefore, colloidal suspensions of different packing fraction can be obtained simply by varying the temperature using a temperature-controlled stage. We determine the velocity profile and the local shear rate of the suspension using particle image velocimetry (PIV). We have developed methods to accurately infer the suspension shear viscosity and shear stress as a function of shear rate. The dynamical range of shear rates probed is approximately 5 orders of magnitude, ranging from 10-4 to 10^1 s-1. Results show that as the packing fraction is increased towards the jamming point, the velocity profiles are markedly non-Newtonian. Further, above the jamming point, the stress versus shear rate curves show yield stress behavior. [1] Alsayed, A.M.;Islam, M.F.;Zhang, J.;Collings, P.J.;Yodh, A.J., Science 2005.

  14. Rheological Properties and Transfer Phenomena of Nanofluids

    NASA Astrophysics Data System (ADS)

    Jung, Kang-min; Kim, Sung Hyun

    2008-07-01

    This study focused on the synthesis of stable nanofluids and investigation of their rhelogical properties and transfer phenomena. Nanofluids of diamond/ethylene glycol, alumina/transformer oil and silica/water were made to use in this study. Rheological properties of diamond nanofluids were determined at constant temperature (25 °C) using a viscometer. For the convective heat transfer experiment, alumina nanofluid passed through the plate heat exchanger. CO2 absorption experiment was conducted in a bubble type absorber containing silica nanofluid. Diamond nanofluid showed non-Newtonian behaviors under a steady-shear flow except the case of very low concentration of solid nanoparticles. The heat transfer coefficient of alumina nanofluid was higher than that of base fluid. One possible reason is that concentration of nanoparticles at the wall side is higher than that of microparticles. Silica nanofluid showed that both average CO2 absorption rate and total absorption amount enhanced than those of base fluid. The stably suspended nanoparticles create a mesh-like structure. That structure arrangement cracks the gas bubble and increases the surface area.

  15. Rheological characterization of nephila spidroin solution.

    PubMed

    Chen, Xin; Knight, David P; Vollrath, Fritz

    2002-01-01

    We report the results of an investigation into the rheology of solutions of natural spider silk dope (spinning solution). We demonstrate that dilute dope solutions showed only shear thinning as the shear rate increased while more concentrated solutions showed an initial shear thinning followed by a shear thickening and a subsequent decline in viscosity. The critical shear rate for shear thickening depended on dope concentration and was very low in concentrated solutions. This helps to explain how spiders are able to spin silk at very low draw rates and why they use a very concentrated dope solution. We also show that the optimum shear rate for shear thickening in moderately concentrated solutions occurred at pH 6.3 close to the observed pH at the distal end of the spider's spinning duct. Finally, we report that the addition of K(+) ions to dilute dope solutions produced a spontaneous formation of nanofibrils that subsequently aggregated and precipitated. This change was not seen after the addition of other common cations. Taken together, these observations support the hypothesis that the secretion of H(+) and K(+) by the spider's duct together with moderate strain rates produced during spinning induce a phase separation in the silk dope in which the silk protein (spidroin) molecules are converted into insoluble nanofibrils. PMID:12099805

  16. Ex vivo rheology of spider silk.

    PubMed

    Kojić, N; Bico, J; Clasen, C; McKinley, G H

    2006-11-01

    We investigate the rheological properties of microliter quantities of the spinning material extracted ex vivo from the major ampullate gland of a Nephila clavipes spider using two new micro-rheometric devices. A sliding plate micro-rheometer is employed to measure the steady-state shear viscosity of approximately 1 microl samples of silk dope from individual biological specimens. The steady shear viscosity of the spinning solution is found to be highly shear-thinning, with a power-law index consistent with values expected for liquid crystalline solutions. Calculations show that the viscosity of the fluid decreases 10-fold as it flows through the narrow spinning canals of the spider. By contrast, measurements in a microcapillary extensional rheometer show that the transient extensional viscosity (i.e. the viscoelastic resistance to stretching) of the spinning fluid increases more than 100-fold during the spinning process. Quantifying the properties of native spinning solutions provides new guidance for adjusting the spinning processes of synthetic or genetically engineered silks to match those of the spider. PMID:17050850

  17. Mudflow rheology in a vertically rotating flume

    USGS Publications Warehouse

    Holmes, Jr., Robert R.; Westphal, Jerome A.; Jobson, Harvey E.

    1990-01-01

    Joint research by the U.S. Geological Survey and the University of Missouri-Rolla currently (1990) is being conducted on a 3.05 meters in diameter vertically rotating flume used to simulate mudflows under steady-state conditions. Observed mudflow simulations indicate flow patterns in the flume are similar to those occurring in natural mudflows. Variables such as mean and surface velocity, depth, and average boundary shear stress can be measured in this flume more easily than in the field or in a traditional tilting flume. Sensitive variables such as sediment concentration, grain-size distribution, and Atterberg limits also can be precisely and easily controlled. A known Newtonian fluid, SAE 30 motor oil, was tested in the flume and the computed value for viscosity was within 12.5 percent of the stated viscosity. This provided support that the data from the flume can be used to determine the rheological properties of fluids such as mud. Measurements on mud slurries indicate that flows with sediment concentrations ranging from 81 to 87 percent sediment by weight can be approximated as Bingham plastic for strain rates greater than 1 per second. In this approximation, the yield stress and Bingham viscosity were extremely sensitive to sediment concentration. Generally, the magnitude of the yield stress was large relative to the change in shear stress with increasing mudflow velocity.

  18. Biodegradable compounds: Rheological, mechanical and thermal properties

    NASA Astrophysics Data System (ADS)

    Nobile, Maria Rossella; Lucia, G.; Santella, M.; Malinconico, M.; Cerruti, P.; Pantani, R.

    2015-12-01

    Recently great attention from industry has been focused on biodegradable polyesters derived from renewable resources. In particular, PLA has attracted great interest due to its high strength and high modulus and a good biocompatibility, however its brittleness and low heat distortion temperature (HDT) restrict its wide application. On the other hand, Poly(butylene succinate) (PBS) is a biodegradable polymer with a low tensile modulus but characterized by a high flexibility, excellent impact strength, good thermal and chemical resistance. In this work the two aliphatic biodegradable polyesters PBS and PLA were selected with the aim to obtain a biodegradable material for the industry of plastic cups and plates. PBS was also blended with a thermoplastic starch. Talc was also added to the compounds because of its low cost and its effectiveness in increasing the modulus and the HDT of polymers. The compounds were obtained by melt compounding in a single screw extruder and the rheological, mechanical and thermal properties were investigated. The properties of the two compounds were compared and it was found that the values of the tensile modulus and elongation at break measured for the PBS/PLA/Talc compound make it interesting for the production of disposable plates and cups. In terms of thermal resistance the compounds have HDTs high enough to contain hot food or beverages. The PLA/PBS/Talc compound can be, then, considered as biodegradable substitute for polystyrene for the production of disposable plates and cups for hot food and beverages.

  19. Extensional Rheology of Fire Ant Aggregates

    NASA Astrophysics Data System (ADS)

    Franklin, Scott; Kern, Matthew; Phonekeo, Sulisay; Hu, David

    We explore the extensional rheology and self-healing of fire ant (Solenopsis invicta) aggregations, mechanically entangled ensembles used to form rafts, bivouacs or bridges. Macroscopic experiments create quasi-two dimensional piles and measure the force required to impose a constant end-velocity. This force fluctuates, reminiscent of similar experiments on geometrically cohesive granular materials. Heterogeneous chains develop, with isolated ants often the sole link between top and bottom. Finally, the maximum pile strength scales sub-linearly with the number of ants, with the maximum force per ant decreasing as the pile grows. We reproduce these behaviors with a simple model that represents ants feet as discs connected by a spring (the ''leg''). Discs move randomly, and stick to one another when in contact. Discs in contact un-stick at random with a probability that decreases as the spring (leg) is stretched, modeling an ant's tendency to hold on longer when stretched. Simulations qualitatively reproduces the fluctuating force, chain formation and sublinear scaling of maximum force with particle number and give insight into underlying mechanisms that govern the ants' behaviors. Funded in part by NSF DMR #1133722.

  20. Rheological Characterization of Bioinspired Mineralization in Hydrogels

    NASA Astrophysics Data System (ADS)

    Regitsky, Abigail; Holten-Andersen, Niels

    With increasing amounts of CO2 in the atmosphere linked to potentially catastrophic climate change, it is critical that we find methods to permanently sequester and store CO2. Inspired by the natural biomineralization of calcium carbonate (CaCO3), one future goal of this project is to understand the mechanisms of CaCO3 mineralization in order to ultimately optimize a bioinspired hydrogel system, which produces high value industrial powders that consume CO2 as a feedstock. Along the way, we are developing a rheological technique to study mineral nucleation and growth events by measuring the modulations in mechanical properties of a hydrogel system during mineralization. Our initial system consists of a gelatin hydrogel matrix, which is preloaded with calcium ions, and an aqueous solution of carbonate ions, which are allowed to diffuse through the gel to initiate the mineralization process. In order to monitor how the growth of minerals affects the mechanical properties of the gel network, we measure the storage (G') and loss (G'') moduli of the system in situ. Future work will focus on modifying the properties of the minerals formed by changing the polymer used in the hydrogel network and adding other organic molecules into the system.

  1. Mesophase behavior and rheology of polyhedral particles

    NASA Astrophysics Data System (ADS)

    Agarwal, Umang; Escobedo, Fernando

    2011-03-01

    Translational and orientational excluded volume fields can guide assembly of particles with anisotropic shape to diverse morphologies. A roadmap elucidating correlations between phase behavior and particle shape may help devising efficient strategies for self-assembly of desired nanocrystal superlattices. To explore these complex correlations we performed detailed Monte Carlo simulations of six convex multi-faceted shapes belonging to the diverse class of space-filling polyhedrons. Simulations predict formation of various novel liquid-crystalline and plastic-crystalline phases at intermediate volume fractions. By correlating these findings with particle anisotropy and order of rotational symmetry, simple guidelines for predicting phase behavior of polyhedral particles are proposed. Moreover, detailed analysis of the structures of mesophases reveals importance of dynamical order in defining these phases and preliminary information about kinetics of these transitions is also obtained. Finally, to elucidate the effect of particle shape anisotropy on rheology, preliminary results will be reported from non equilibrium molecular dynamics simulations of the isotropic and cubatic(LC) phase of cuboidal particles. This work was supported by a Department of Energy Basic Energy Science Grant ER46517.

  2. Influence of Fat Content on Chocolate Rheology

    NASA Astrophysics Data System (ADS)

    Gabriele, D.; Migliori, M.; Baldino, N.; de Cindio, B.

    2008-07-01

    Molten chocolate is a suspension having properties strongly affected by particle characteristics including not only the dispersed particles but also the fat crystals formed during chocolate cooling and solidification. Even though chocolate rheology is extensively studied, mainly viscosity at high temperature was determined and no information on amount and type of fat crystals can be detected in these conditions. However chocolate texture and stability is strongly affected by the presence of specific crystals. In this work a different approach, based on creep test, was proposed to characterize chocolate samples at typical process temperatures (approximately 30 °C). The analysis of compliance, as time function, at short times enable to evaluate a material "elasticity" related to the solid-like behavior of the material and given by the differential area between the Newtonian and the experimental compliance. Moreover a specific time dependent elasticity was defined as the ratio between the differential area, in a time range, and total area. Chocolate samples having a different fat content were prepared and they were conditioned directly on rheometer plate by applying two different controlled cooling rate; therefore creep were performed by applying a low stress to ensure material linear behavior. Experimental data were analyzed by the proposed method and specific elasticity was related to single crystal properties. It was found that fat crystal amount and properties depend in different way on fat content and cooling rate; moreover creep proved to be able to detect even small differences among tested samples.

  3. Rheological and fractal hydrodynamics of aerobic granules.

    PubMed

    Tijani, H I; Abdullah, N; Yuzir, A; Ujang, Zaini

    2015-06-01

    The structural and hydrodynamic features for granules were characterized using settling experiments, predefined mathematical simulations and ImageJ-particle analyses. This study describes the rheological characterization of these biologically immobilized aggregates under non-Newtonian flows. The second order dimensional analysis defined as D2=1.795 for native clusters and D2=1.099 for dewatered clusters and a characteristic three-dimensional fractal dimension of 2.46 depicts that these relatively porous and differentially permeable fractals had a structural configuration in close proximity with that described for a compact sphere formed via cluster-cluster aggregation. The three-dimensional fractal dimension calculated via settling-fractal correlation, U∝l(D) to characterize immobilized granules validates the quantitative measurements used for describing its structural integrity and aggregate complexity. These results suggest that scaling relationships based on fractal geometry are vital for quantifying the effects of different laminar conditions on the aggregates' morphology and characteristics such as density, porosity, and projected surface area. PMID:25836036

  4. Rheological, thermo-mechanical, and baking properties of wheat-millet flour blends.

    PubMed

    Aprodu, Iuliana; Banu, Iuliana

    2015-07-01

    Millet has long been known as a good source of fiber and antioxidants, but only lately started to be exploited by food scientists and food industry as a consequence of increased consumer awareness. In this study, doughs and breads were produced using millet flour in different ratios (10, 20, 30, 40, and 50%) to white, dark, and whole wheat flour. The flour blends were evaluated in terms of rheological and thermo-mechanical properties. Fundamental rheological measurements revealed that the viscosity of the flour formulations increases with wheat flour-extraction rate and decreases with the addition of millet flour. Doughs behavior during mixing, overmixing, pasting, and gelling was established using the Mixolab device. The results of this bread-making process simulation indicate that dough properties become critical for the flour blends with millet levels higher than 30%. The breads were evaluated for volume, texture, and crumb-grain characteristics. The baking test and sensory evaluation results indicated that substitution levels of up to 30% millet flour could be used in composite bread flour. High levels of millet flour (40 and 50%) negatively influenced the loaf volume, crumb texture, and taste. PMID:24837596

  5. Is the Past Irrelevant?

    ERIC Educational Resources Information Center

    Banowsky, William S.

    1972-01-01

    Author sees a cultish emphasis on the new and the now" sweeping this country and believes we must avoid the cut-flower syndrome of being beautiful but rootless by not severing ties with the past. History is germane and so are many areas of the high school curriculum now under attack for their irrelevance. (Editor/RB)

  6. Exploring the Earth's Past

    ERIC Educational Resources Information Center

    Lindaman, Arnold D.; And Others

    1972-01-01

    Describes three approaches to a study of the earth's past: (1) development of a time line of the ages; (2) a study of rocks and how each was formed; and (3) a study of fossils as found in certain kinds of stone. (Editor)

  7. Paradigms Past and Future.

    ERIC Educational Resources Information Center

    Oates, Maureen

    1980-01-01

    Evaluates past paradigms (conceptual frameworks) such as the belief in the unlimited resources of the earth for humanity's particular benefit and the paradigm of the infallibility of technology. Illustrates how we are generally moving toward the new paradigm that small and simple is not only beautiful, but also more efficient, reliable, practical,…

  8. Influence of rheology and tectonic loading on postseismic creep

    NASA Astrophysics Data System (ADS)

    Montési, L. G.

    2003-12-01

    Postseismic creep, as observed by GPS, indicates probably transient deformation of the lower crust or upper mantle triggered by earthquake-induced stress perturbations. In these regions, deformation can be localized on a frictional surface or on a ductile shear zone. These two hypotheses imply specific rheologies and therefore time dependence of postseismic creep. Hence, postseismic creep may constitute a probe into the rheology of aseismic regions of the lithosphere. I derive an analytical general relaxation law for a power law rheology which can be used to model postseismic creep in the absence of reloading of the proposed shear zone. The stress exponent, n, is diagnostic of the deformation mechanism. The rheology appropriate for frictional sliding produces a relaxation law similar to the power law case in the limit 1/n=0. GPS data following several earthquakes are adequately modeled using the generalized relaxation law. However, for at least three examples (1997 Kronotsky, 1999 Izmit, and 2001 Peru earthquakes), the inferred stress exponent is negative. Rather than the shear zone rheology, these negative exponents indicate that reloading of the shear zone by tectonic forces is important. Numerical simulations of postseismic deformation with non-negligible reloading produces curves that are well fit by the generalized relaxation laws with negative stress exponent, although the actual stress exponent of the rheology is positive. Although this prevents rheology from being well constrained by the studied GPS records, it is clear that reloading is important in the postseismic time interval. In other words, the stress perturbation induced by earthquake is not much larger than the ambient stress field.

  9. The rheology, degradation, processing, and characterization of renewable resource polymers

    NASA Astrophysics Data System (ADS)

    Conrad, Jason David

    Renewable resource polymers have become an increasingly popular alternative to conventional fossil fuel based polymers over the past couple decades. The push by the government as well as both industrial and consumer markets to go "green" has provided the drive for companies to research and develop new materials that are more environmentally friendly and which are derived from renewable materials. Two polymers that are currently being produced commercially are poly-lactic acid (PLA) and polyhydroxyalkanoate (PHA) copolymers, both of which can be derived from renewable feedstocks and have shown to exhibit similar properties to conventional materials such as polypropylene, polyethylene, polystyrene, and PET. PLA and PHA are being used in many applications including food packaging, disposable cups, grocery bags, and biomedical applications. In this work, we report on the rheological properties of blends of PLA and PHA copolymers. The specific materials used in the study include Natureworks RTM 7000D grade PLA and PHA copolymers of poly(3-hydroxybutyrate-co-3-hydroxyvalerate). Blends ranging from 10 to 50 percent PHA by weight are also examined. Shear and extensional experiments are performed to characterize the flow behavior of the materials in different flow fields. Transient experiments are performed to study the shear rheology over time in order to determine how the viscoelastic properties change under typical processing conditions and understand the thermal degradation behavior of the materials. For the blends, it is determined that increasing the PHA concentration in the blend results in a decrease in viscosity and increase in degradation. Models are fit to the viscosity of the blends using the pure material viscosities in order to be able to predict the behavior at a given blend composition. We also investigate the processability of these materials into films and examine the resultant properties of the cast films. The mechanical and thermal properties of the

  10. Analyses of fine paste ceramics

    SciTech Connect

    Sabloff, J A

    1980-01-01

    Four chapters are included: history of Brookhaven fine paste ceramics project, chemical and mathematical procedures employed in Mayan fine paste ceramics project, and compositional and archaeological perspectives on the Mayan fine paste ceramics. (DLC)

  11. Tackiness and cohesive failure of granular pastes: mechanistic aspects.

    PubMed

    Abdelhaye, Y O Mohamed; Chaouche, M; Chapuis, J; Charlaix, E; Hinch, J; Roux, S; Van Damme, H

    2012-06-01

    Granular pastes are dense dispersions of non-colloidal grains in a simple or a complex fluid. Typical examples are the coating, gluing or sealing mortars used in building applications. We study the rupture of a thick layer of mortar paste in a simple pulling test where the paste is confined between two flat surfaces. It is shown that, depending on the rheological properties of the paste and the plate separation velocity, two main failure modes are obtained. The first mode is the inwards shear flow of the paste with viscous fingering instabilities, similarly to what has been observed with Newtonian fluids and with non-Newtonian colloidal suspensions or polymer solutions. The second failure mode is stemming from the expansion of bubbles, similarly to what has been observed in soft adhesive polymer layers and, more recently, in highly viscous fluids. It is shown that the crossover between the two failure modes is determined by the conditions required to generate a pressure drop able to trigger the growth of pre-existing micro-bubbles smaller than the inter-granular distance. PMID:22692685

  12. The non-isothermal rheology of low viscosity magmas.

    NASA Astrophysics Data System (ADS)

    Kolzenburg, Stephan; Giordano, Daniele; Dingwell, Donald B.

    2016-04-01

    Accurate prediction of the run-out distance of lava flows, as well as the understanding of magma migration in shallow dyke systems is hampered by an incomplete understanding of the transient, sub-liquidus rheology of crystallizing melts. This sets significant limits to physical property based modelling of lava flow (especially flow width, length and advancement rate) and magma migration behaviour and the resulting accuracy of volcanic hazard assessment The importance of the dynamic rheology of a lava / magma on its emplacement style becomes especially apparent in towards later stages of flow and dyke emplacement, where the melt builds increasing resistance to flow, entering rheologic regimes that determine the halting of lava flows and sealing of dykes. Thermal gradients between the interior of a melt body and the contact with air or the substratum govern these rheologic transitions that give origin to flow directing or impeding features like levees, tubes and chilled margins. Besides the critical importance of non-isothermal and sub-liquidus processes for the understanding of natural systems, accurate rheologic data at these conditions are scarce and studies capturing the transient rheological evolution of lavas at conditions encountered during emplacement virtually absent. We describe the rheologic evolution of a series of natural, re-melted lava samples during transient and non-equilibrium crystallization conditions characteristic of lava flows and shallow magmatic systems in nature. The sample suite spans from foidites to basalts; the dominant compositions producing low viscosity lava flows. Our data show that all melts undergo one or more change zones in effective viscosity when subjected to sub liquidus temperatures. The apparent viscosity of the liquid-crystal suspension increases drastically from the theoretical temperature-viscosity relationship of a pure liquid once cooled below the liquidus temperature. We find that: 1) Both cooling rate and shear rate

  13. Impact of Rheological Modifiers on Various Slurries Supporting DOE Waste Processing

    SciTech Connect

    Chun, Jaehun; Bredt, Paul R.; Hansen, Erich; Bhosale, Prasad S.; Berg, John C.

    2010-03-11

    Controlling the stability and subsequent rheological properties of slurries has been an important but challenging issue in nuclear waste treatment, one that previous research has yet to sufficiently address. At the Hanford and Savannah River sites, operation of the waste treatment facilities at increased solids loading reduces the evaporative load on the melter systems and thereby increases waste processing rates. However, at these higher solids loadings, increased slurry rheology becomes a significant processing issue. The current study evaluates the use of several rheological modifiers to alleviate increased slurry rheology at high waste solids concentrations. Rheological modifiers change particle interactions in slurry. For colloidal slurries, modifiers mainly alter the electrostatic and steric interactions between particles, leading to a change in slurry rheology. Weak organic acid type rheological modifiers strengthen electrostatic repulsion whereas nonionic/polymer surfactant type rheological modifiers introduce a steric repulsion. We investigated various rheological modifiers using high level waste (HLW) nuclear waste simulants characterized typically by high ionic strength and a wide range of pH from 4 to 13. Using rheological analysis, it was found that citric acid and polyacrylic acid would be good rheological modifiers for the HLW simulants tested, effectively reducing slurry rheology by 40% or more. Physical insights into the mechanisms driving stabilization by these rheological modifiers will be discussed.

  14. Rheology of Halogen-Rich Magmas

    NASA Astrophysics Data System (ADS)

    Webb, S. L.

    2010-12-01

    The degassing of magma as it rises through the volcanic conduit to the surface affects the viscosity and rate of movement of the magma. While the production of bubbles in the magma decreases the density of the magma and thus increases its rate of ascent, the loss of volatiles from the magma, in general, results in an increase in the viscosity. This is the ideal scenario for the deformation rate of the magma crossing the relaxation timescale of the increasingly viscous magma which can result in the shattering of the magma in its unrelaxed (glassy) state; which results in an explosive eruption and pyroclastic flow. The effect of the volatiles H2O and F on magma viscosity and relaxation timescale have been extensively studied; with 1 mol% F2O-1 or H2O causing a 4 to 5 order of magnitude decrease in viscosity at ca. 800 C. Early determinations of the effect of chlorine on melt viscosity, however, indicated that chlorine increases the viscosity of Al-bearing melts (but decreases the viscosity of Al-free synthetic melts). Thus the degassing of chlorine would result in a decrease in magma viscosity and a distancing of the physical condition of the magma from the shattering of the magma as it rises to the surface. The viscosity of chlorine-bearing peralkaline Na2O-CaO-Al2O3-SiO2 melts has been investigated using micro-penetration techniques in the 108 - 1013 Pa s viscosity range. The presence of 0.5 mol% (0.6 wt%) Cl2O-1 increases viscosity by 0.5 log10 units. A similar amount of H2O or F2O-1 would decrease viscosity by 2.5 orders of magnitude in this viscosity range. More information about the relative solubility of Cl, F and H2O as a function of composition, temperature and pressure is needed before one can model the relative effects of degassing volatiles on the rheology of magmas. Very little is known about the structural role of chlorine in silicate melts. NMR studies of Na2O-CaO-Al2O3-SiO2 glasses have shown that chlorine does not bond to Al (in contrast to fluorine

  15. Rheology of the Northern Apennines: Lateral variations of lithospheric strength

    NASA Astrophysics Data System (ADS)

    Pauselli, Cristina; Ranalli, Giorgio; Federico, Costanzo

    2010-03-01

    A thermorheological WSW-ENE profile along the Northern Apennines is presented. The variations in rheology are estimated using two different models: the conventional model in which only frictional sliding and power-law creep are taken into account, and a new model in which in addition to the previous two mechanisms, a high-pressure brittle fracture mechanism is included. Upper and lower bounds for the rheology are considered: a hard case where the lower crust is mafic granulite and the lithospheric mantle is dry peridotite, and a soft case where the lower crust is felsic granulite and the lithospheric mantle is wet peridotite. Important differences in lithospheric rheological structure are inferred between the western and the eastern sectors of the chain. In the former a "crème brulée" structure generally applies; in the latter a "jelly-sandwich" structure applies. These rheological models, therefore, are not alternative but end members of a continuous spectrum of rheological behaviours.

  16. Complex rheological behaviors of loach (Misgurnus anguillicaudatus) skin mucus

    SciTech Connect

    Wang, Xiang Su, Heng Lv, Weiyang Du, Miao Song, Yihu Zheng, Qiang

    2015-01-15

    The functions and structures of biological mucus are closely linked to rheology. In this article, the skin mucus of loach (Misgurnus anguillicaudatus) was proved to be a weak hydrogel susceptible to shear rate, time, and history, exhibiting: (i) Two-region breakdown of its gel structure during oscillatory strain sweep; (ii) rate-dependent thickening followed by three-region thinning with increased shear rate, and straight thinning with decreased shear rate; and (iii) time-dependent rheopexy at low shear rates, and thixotropy at high shear rates. An interesting correlation between the shear rate- and time-dependent rheological behaviors was also revealed, i.e., the rheopexy-thixotropy transition coincided with the first-second shear thinning region transition. Apart from rheology, a structure of colloidal network was observed in loach skin mucus using transmission electron microscopy. The complex rheology was speculated to result from inter- and intracolloid structural alterations. The unique rheology associated with the colloidal network structure, which has never been previously reported in vertebrate mucus, may play a key role in the functions (e.g., flow, reannealing, lubrication, and barrier) of the mucus.

  17. Moho, seismogenesis, and rheology of the lithosphere

    NASA Astrophysics Data System (ADS)

    Chen, Wang-Ping; Yu, Chun-Quan; Tseng, Tai-Lin; Yang, Zhaohui; Wang, Chi-yuen; Ning, Jieyuan; Leonard, Tiffany

    2013-12-01

    The Moho is not always a sharp interface; but seismic phase SsPmp yields robust, physically averaged estimates of crustal thickness (virtual deep seismic sounding, VDSS). In S. Tibet where the Moho is as deep as 75 km, bimodal distribution of earthquake depths, with one peak in the upper crust and the other below the Moho, generated much interest in how lithological contrast affects seismicity and rheology. Generally seismicity is limited by distinct temperatures (Tc): 350 ± 50 °C in the crust and 700 ± 100 °C in the mantle (Earthquake Thermometry). Laboratory experiments show that distinct Tc reflect the onset of substantial crystal plasticity in major crustal and mantle minerals, respectively. Above these Tc, frictional instability ends due to velocity weakening of slip. So the seismic to aseismic transition is closely linked with brittle-ductile transitions in the crust and in the uppermost mantle, where the strength of the continental lithosphere is expected to peak (“Jelly Sandwich”). Plasticity depends exponentially on temperature (which evolves over time), so interplay between the geotherm and crustal thickness could result in concentrated seismicity in the upper crust - the only portion of a very warm lithosphere where temperature is below ~ 350 °C (“Crème Brûlée”). Conversely, where the entire crust is below ~ 350 °C (and the uppermost mantle is also below ~ 700 °C), then earthquakes could occur over a wide range of depths, including the entire crust and the uppermost mantle (“Caramel Slab”).

  18. Antigorite rheology? Experimental challenges and complicating observations

    NASA Astrophysics Data System (ADS)

    Proctor, B.; Hirth, G.

    2015-12-01

    Characterizing the rheology of antigorite remains a challenge due to its strongly anisotropic structure and relatively low dehydration temperature. The efficacy of trading off temperature for strain-rate is limited and to date it remains unclear if antigorite can deform by fully plastic flow and, if so, by what rate-limiting mechanism(s). We present results from general shear experiments on antigorite gouge conducted in a Griggs-rig at 1-2 GPa confining pressure, 300-500 °C and strain-rates from 10^-5/s to 10^-7/s. We observe a peculiar behavior in which strain becomes increasingly localized at higher temperatures. At 300 °C gouge samples are macroscopically ductile with strain accommodated by a dense network of small fractures. At 500 °C strain is fully localized to a single ~10 μm wide fracture. Fractures contained finer-grained foliated antigorite. Increasing pressure from 1-2 GPa had no effect on localization. The apparent friction associated with slip along the fractures decreased from 0.23 to 0.07 at 300 °C and 500 °C respectively. The rate-dependence was relatively low (with an effective stress exponent of ~36) and decreased with increasing temperature. These findings are consistent with previous observations on talc (Escartin et al., 2008) and further complicate to the proposed Peierls creep and power law creep flow laws for antigorite (e.g., Amiguet et al., 2012). The 'thermal' embrittlement observed in our experiments may explain some occurrences of seismicity in serpentinized rock at temperatures too cold for dehydration.

  19. Molecular dynamics simulations of supramolecular polymer rheology

    NASA Astrophysics Data System (ADS)

    Li, Zhenlong; Djohari, Hadrian; Dormidontova, Elena E.

    2010-11-01

    Using equilibrium and nonequilibrium molecular dynamics simulations, we studied the equilibrium and rheological properties of dilute and semidilute solutions of head-to-tail associating polymers. In our simulation model, a spontaneous complementary reversible association between the donor and the acceptor groups at the ends of oligomers was achieved by introducing a combination of truncated pseudo-Coulombic attractive potential and Lennard Jones repulsive potential between donor, acceptor, and neighboring groups. We have calculated the equilibrium properties of supramolecular polymers, such as the ring/chain equilibrium, average molecular weight, and molecular weight distribution of self-assembled chains and rings, which all agree well with previous analytical and computer modeling results. We have investigated shear thinning of solutions of 8- and 20-bead associating oligomers with different association energies at different temperatures and oligomer volume fractions. All reduced viscosity data for a given oligomer length can be collapsed into one master curve, exhibiting two power-law regions of shear-thinning behavior with an exponent of -0.55 at intermediate ranges of the reduced shear rate β and -0.8 (or -0.9) at larger shear rates. The equilibrium viscosity of supramolecular solutions with different oligomer lengths and associating energies is found to obey a power-law scaling dependence on oligomer volume fraction with an exponent of 1.5, in agreement with the experimental observations for several dilute or semidilute solutions of supramolecular polymers. This implies that dilute and semidilute supramolecular polymer solutions exhibit high polydispersity but may not be sufficiently entangled to follow the reptation mechanism of relaxation.

  20. 2012 SRNL-EM VANE RHEOLOGY RESULTS

    SciTech Connect

    Hansen, E.; Marzolf, A.; Hera, K.

    2012-08-31

    The vane method has been shown to be an effective tool in measuring the yield stress of both settled and mixed slurries in laboratory bench scale conditions in supporting assessments of both actual and simulant waste slurries. The vane has also been used to characterize dry powders and granular solids, the effect of non-cohesive solids with interstitial fluids and used as a guide to determine if slip is present in the geometries typically used to perform rheological flow curve measurements. The vane has been extensively characterized for measuring the shear strength in soils in both field and laboratory studies. The objectives for this task are: Fabricate vane instrument; Bench top testing to further characterize the effect of cohesive, non-cohesive, and blends of cohesive/non-cohesive simple simulants; Data from measurement of homogenized and settled bed of Kaolin sludge and assessment of the technology. In this document, the assessment using bench scale measurements of non-cohesive materials (beads) and cohesive materials (kaolin) is discussed. The non-cohesive materials include various size beads and the vane was assessed for depth and deaeration (or packing) via tapping measurements. For the cohesive (or non-Newtonian) materials, flow curves and yield stress measurements are performed using the vane and this data is compared to the traditional concentric cylinder flow curve measurement. Finally, a large scale vane was designed, fabricated, and tested with the cohesive (or non-Newtonian) materials to determine how a larger vane performs in measuring the yield stress and flow curve of settled cohesive solids.

  1. Ice rheology and tidal heating of Enceladus

    NASA Astrophysics Data System (ADS)

    Shoji, D.; Hussmann, H.; Kurita, K.; Sohl, F.

    2013-09-01

    For the saturnian satellite Enceladus, the possible existence of a global ocean is a major issue. For the stability of an internal ocean, tidal heating is suggested as an effective heat source. However, assuming Maxwell rheology ice, it has been shown that a global scale ocean on Enceladus cannot be maintained (Roberts, J.F., Nimmo, F. [2008]. Icarus 194, 675-689). Here, we analyze tidal heating and the stability of a global ocean from the aspect of anelastic behavior. The Maxwell model is the most typical and widely used viscoelastic model. However, in the tidal frequency domain, energy is also dissipated by the anelastic response involving time-dependent or transient creep mechanisms, which is different from the viscoelastic response caused by steady-state creep. The Maxwell model cannot adequately address anelasticity, which has a large effect in the high viscosity range. Burgers and Andrade models are suggested as suitable models for the creep behavior of ice in the frequency domain. We calculate tidal heating in the ice layer and compare it with the radiated heat assuming both convection and conduction of the ice layer. Though anelastic behavior increases the heating rate, it is insufficient to maintain a global subsurface ocean if the ice layer is convecting, even though a wide parameter range is taken into account. One possibility to maintain a global ocean is that Enceladus’ ice shell is conductive and its tidal response is similar to that of the Burgers body with comparatively small transient shear modulus and viscosity. If the surface ice with large viscosity is dissipative by anelastic response, the heat produced in the ice layer would supersede the cooling rate and a subsurface ocean could be maintained without freezing.

  2. Effect of inulin on rheological and thermal properties of gluten-free dough.

    PubMed

    Juszczak, Lesław; Witczak, Teresa; Ziobro, Rafał; Korus, Jarosław; Cieślik, Ewa; Witczak, Mariusz

    2012-09-01

    The aim of the study was to evaluate the influence of inulins with varying degree of polymerization on rheological and thermal properties of gluten-free starch-based dough. The share of inulin reduced the values of consistency coefficient, as well as storage and loss moduli, and increased creep compliance. Inulin preparation with the highest average degree of polymerization had the strongest impact on viscoelastic properties of the obtained dough. The presence of inulin also caused a significant decrease of viscosity upon pasting, and an increase of gelatinization temperatures TOg, TP1g, TP2g, and TEg. Addition of inulin had no effect on gelatinization enthalpy (ΔHg), while it strongly reduced the enthalpies of retrograded amylopectin after storage. Water binding properties of inulin seem to be the key factor, responsible for modification of dough properties, because they influence solvent availability for other constituents of such system. PMID:24751052

  3. Effect of whey and casein protein hydrolysates on rheological, textural and sensory properties of cookies.

    PubMed

    Gani, Adil; Broadway, A A; Ahmad, Mudasir; Ashwar, Bilal Ahmad; Wani, Ali Abas; Wani, Sajad Mohd; Masoodi, F A; Khatkar, Bupinder Singh

    2015-09-01

    Milk proteins were hydrolyzed by papain and their effect on the rheological, textural and sensory properties of cookies were investigated. Water absorption (%) decreased significantly as the amount of milk protein concentrates and hydrolysates increased up to a level of 15 % in the wheat flour. Dough extensibility decreased with inrease in parental proteins and their hydrolysates in wheat flour, significantly. Similarly, the pasting properties also varied significantly in direct proportion to the quantity added in the wheat flour. The colour difference (ΔE) of cookies supplemented with milk protein concentrates and hydrolysates were significantly higher than cookies prepared from control. Physical and sensory characteristics of cookies at 5 % level of supplementation were found to be acceptable. Also the scores assigned by the judges for texture and colour were in good agreement with the measurements derived from the physical tests. PMID:26344985

  4. Steady and Dynamic Shear Rheological Properties of Buckwheat Starch-galactomannan Mixtures

    PubMed Central

    Choi, Dong Won; Chang, Yoon Hyuk

    2012-01-01

    This study investigated the effects of galacomannans (guar gum, tara gum, and locust bean gum) on the rheological properties of buckwheat starch pastes under steady and dynamic shear conditions. The power law and Casson models were applied to describe the flow behavior of the buckwheat starch and galactomannan mixtures. The values of the apparent viscosity (ηa,100), consistency index (K), and yield stress (σoc) for buckwheat starch-galactomannan mixtures were significantly greater than those for the control, indicating that there was a high synergism of the starch with galactomannans. The magnitudes of storage modulus (G′) and loss modulus (G″) for the starch-galactomannan mixtures increased with increasing frequency (ω). The dynamic moduli (G′, G″), and complex viscosity (η*) for the buckwheat starch-galactomannan mixtures were significantly higher than those for the control. PMID:24471083

  5. Meharry's past presidents.

    PubMed Central

    Hansen, Axel C.

    2004-01-01

    The author spent many years at Meharry as medical student, resident physician, faculty member, and member of the Board of Trustees. Those roles allowed him to become well-acquainted with six of the eight past presidents: Drs. Turner, Clawson, West, Elam, Lester, and Satcher. He also served as medical director of Hubbard Hospital for a period of six years (1960-1966). PMID:15233498

  6. Nonlinear rheology of entangled polymers at turning point.

    PubMed

    Wang, Shi-Qing

    2015-02-28

    Thanks to extensive observations of strain localization upon startup or after stepwise shear, a conceptual framework for nonlinear rheology of entangled polymers appears to have emerged that has led to discovery of many new phenomena, which were not previously predicted by the standard tube model. On the other hand, the published theoretical and experimental attempts to test the limits of the tube model have largely demonstrated that the most experimental data appear consistent with the tube-model based theoretical calculations. Therefore, the field of nonlinear rheology of entangled polymers is at a turning point and is thus a rather crucial area in which further examinations are needed. In particular, more molecular dynamics simulations are needed to delineate the detailed molecular mechanisms for the various nonlinear rheological phenomena. PMID:25606850

  7. Rheological controls on the development of the convergent margins

    NASA Astrophysics Data System (ADS)

    Burov, Evgueni; Francois, Thomas; Duretz, Thibault; Agard, Philippe; Meyer, Bertrand; Yamato, Philippe

    2013-04-01

    We use thermo-mechanical numerical models to explore the impact of rheological structure, brittle-elastic-ductile rheology and metamorphic reactions on localization and style of deformation in convergent contexts, during ocean-continent or continent-continent interactions. Even though continental subduction may occur in most cases of strong lithospheres with competent mantle at sufficiently high initial convergence rates (>1-1.5 cm/y), the subduction/collision styles and topography evolution are quite different depending on the initial configuration and preceding tectonic history but also on the particular structure of the continental crust, eventually affected by tectonic heritage, and localising properties of the subduction channel. Depending on lower and intermediate crustal rheology, the entire (upper, intermediate, lower) crust, intermediate or only the lower crust can deform independently of the mantle lithosphere. This results in different characteristic tectonic styles (leading, for example, to development of thin-sheet to thick-sheet tectonics structures), wavelengths, altitudes of surface topography and slab geometries. Certain rheological structures of the continental crust, while looking plausible from the geological and experimental rock mechanics point of view, are not compatible with the development of continental subduction, resulting in either blockage of the subduction channel and transition to folding and collision, or in gravitationally instable behaviours. Phase changes leading to material softening significantly improve chances for stable subduction, which is marked by exhumation of UHP-HP rocks to the surface that is particularly favoured if the crustal rheological profile has internal ductile decolement levels between the upper and lower or intermediate crust and the lower crust and mantle lithosphere. Pure shear or unstable RT-type collision is dominant when the mantle is rheologically weak or at convergence rates lower than 1-1.5 cm/yr. In

  8. Molecular rheological analysis on binary blends of perfluoropolyether lubricants

    NASA Astrophysics Data System (ADS)

    Seung Chung, Pil; Hari Vemuri, Sesha; Park, Sejoon; Jhon, Myung S.

    2014-05-01

    The molecular rheology of PFPE becomes critically important in designing optimal lubricants that control the friction/wear and air-bearing by tuning elastic or viscous shear/elongation deformations, which affect the performance and reliability of the hard disk drive. In this paper, we examine the rheological responses of nano blended PFPEs including storage (elastic) and loss (viscous) moduli (G' and G″), by monitoring the time-dependent-stress-strain relationship via non-equilibrium molecular dynamics simulations. By introducing binary blend of nonfunctional and functional PFPEs, we control the degree of liquid/solid-like behavior using the rheology as a complementary tool for design criteria by tuning molecular conformation and diffusion with nano blend ratio.

  9. Local rheological measurements in the granular flow around an intruder

    NASA Astrophysics Data System (ADS)

    Seguin, A.; Coulais, C.; Martinez, F.; Bertho, Y.; Gondret, P.

    2016-01-01

    The rheological properties of granular matter within a two-dimensional flow around a moving disk is investigated experimentally. Using a combination of photoelastic and standard tessellation techniques, the strain and stress tensors are estimated at the grain scale in the time-averaged flow field around a large disk pulled at constant velocity in an assembly of smaller disks. On the one hand, one observes inhomogeneous shear rate and strongly localized shear stress and pressure fields. On the other hand, a significant dilation rate, which has the same magnitude as the shear strain rate, is reported. Significant deviations are observed with local rheology that justify the need of searching for a nonlocal rheology.

  10. A unified description of the rheology of hard particles

    NASA Astrophysics Data System (ADS)

    Hermes, Michiel; Guy, Ben; Poon, Wilson

    The rheology of suspensions of Brownian, or colloidal, particles (diameter d <~ 1 μ m) differs markedly from that of larger grains (d >~ 50 μ m). Each of these two regimes has been separately studied, but the flow of suspensions with intermediate particle sizes (1 μm <~ d <~ 50 μ m), which occur ubiquitously in applications, remains poorly understood. By measuring the rheology of suspensions of hard spheres with a wide range of sizes, we show experimentally that shear thickening drives the transition from colloidal to granular flow across the intermediate size regime. This insight makes possible a unified description of the (non-inertial) rheology of hard spheres over the full size spectrum. Moreover, we are able to test a new theory of friction-induced shear thickening, showing that our data can be well fitted using expressions derived from it.

  11. Morphology and Rheology of Polymer/Liquid Crystal Blends

    NASA Astrophysics Data System (ADS)

    Yu, Wei; Wu, Youjun; Zhou, Chixing

    2008-07-01

    The morphology and rheology of immiscible polymer blends has been the subjects of many researches. It is well known that the properties of blends depend on the rheology of components fluids as well as the properties of interface. For blends composed of isotropic fluids, the capillary number, defined as the ratio between the shear stress and the interfacial stress, controls the behaviors of dispersed droplet under flow field. When one component becomes an anisotropic fluid, it is expected that the anisotropic interfacial properties would greatly affect the properties of the blends. The effect of anisotropic properties of interface between a polymer and a liquid crystal (LC) on the steady and transient behavior of morphological evolution and rheology properties is the main interest of the present work. The deformation and relaxation behavior of a LC droplet immersed in a polymer matrix is investigated and compared with the predictions of our recent model.

  12. Dielectric Relaxation and Rheological Behavior of Supramolecular Polymeric Liquid

    SciTech Connect

    Lou, Nan; Wang, Yangyang; Li, Xiaopeng; Li, Haixia; Wang, Ping

    2013-01-01

    A model self-complementary supramolecular polymer based on thymine and diamidopyridine triple hydrogen-bonding motifs has been synthesized, and its dielectric and rheological behavior has been investigated. The formation of supramolecular polymers has been unequivocally demonstrated by nuclear magnetic resonance, electrospray ionization mass spectrometry with traveling wave ion mobility separation, dielectric spectroscopy, and rheology. The dynamical behaviors of this associating polymer generally conform to those of type-A polymers, with a low-frequency chain relaxation and a high-frequency relaxation visible in both rheological and dielectric measurements. The dielectric chain relaxation shows the ideal symmetric Debye-like shape, resembling the peculiar features of hydrogen-bonding monoalcohols. Detailed analysis shows that there exists a weak decoupling between the mechanical terminal relaxation and dielectric Debye-like relaxation. The origin of the Debye-like dielectric relaxation is further discussed in the light of monoalcohols.

  13. Weakly sheared active suspensions: hydrodynamics, stability, and rheology.

    PubMed

    Cui, Zhenlu

    2011-03-01

    We present a kinetic model for flowing active suspensions and analyze the behavior of a suspension subjected to a weak steady shear. Asymptotic solutions are sought in Deborah number expansions. At the leading order, we explore the steady states and perform their stability analysis. We predict the rheology of active systems including an activity thickening or thinning behavior of the apparent viscosity and a negative apparent viscosity depending on the particle type, flow alignment, and the anchoring conditions, which can be tested on bacterial suspensions. We find remarkable dualities that show that flow-aligning rodlike contractile (extensile) particles are dynamically and rheologically equivalent to flow-aligning discoid extensile (contractile) particles for both tangential and homeotropic anchoring conditions. Another key prediction of this work is the role of the concentration of active suspensions in controlling the rheological behavior: the apparent viscosity may decrease with the increase of the concentration. PMID:21517529

  14. Weakly sheared active suspensions: Hydrodynamics, stability, and rheology

    NASA Astrophysics Data System (ADS)

    Cui, Zhenlu

    2011-03-01

    We present a kinetic model for flowing active suspensions and analyze the behavior of a suspension subjected to a weak steady shear. Asymptotic solutions are sought in Deborah number expansions. At the leading order, we explore the steady states and perform their stability analysis. We predict the rheology of active systems including an activity thickening or thinning behavior of the apparent viscosity and a negative apparent viscosity depending on the particle type, flow alignment, and the anchoring conditions, which can be tested on bacterial suspensions. We find remarkable dualities that show that flow-aligning rodlike contractile (extensile) particles are dynamically and rheologically equivalent to flow-aligning discoid extensile (contractile) particles for both tangential and homeotropic anchoring conditions. Another key prediction of this work is the role of the concentration of active suspensions in controlling the rheological behavior: The apparent viscosity may decrease with the increase of the concentration.

  15. Rheological properties of simulated debris flows in the laboratory environment

    USGS Publications Warehouse

    Ling, Chi-Hai; Chen, Cheng-lung; Jan, Chyan-Deng

    1990-01-01

    Steady debris flows with or without a snout are simulated in a 'conveyor-belt' flume using dry glass spheres of a uniform size, 5 or 14 mm in diameter, and their rheological properties described quantitatively in constants in a generalized viscoplastic fluid (GVF) model. Close agreement of the measured velocity profiles with the theoretical ones obtained from the GVF model strongly supports the validity of a GVF model based on the continuum-mechanics approach. Further comparisons of the measured and theoretical velocity profiles along with empirical relations among the shear stress, the normal stress, and the shear rate developed from the 'ring-shear' apparatus determine the values of the rheological parameters in the GVF model, namely the flow-behavior index, the consistency index, and the cross-consistency index. Critical issues in the evaluation of such rheological parameters using the conveyor-belt flume and the ring-shear apparatus are thus addressed in this study.

  16. Native Silk Feedstock as a Model Biopolymer: A Rheological Perspective.

    PubMed

    Laity, Peter R; Holland, Chris

    2016-08-01

    Variability in silk's rheology is often regarded as an impediment to understanding or successfully copying the natural spinning process. We have previously reported such variability in unspun native silk extracted straight from the gland of the domesticated silkworm Bombyx mori and discounted classical explanations such as differences in molecular weight and concentration. We now report that variability in oscillatory measurements can be reduced onto a simple master-curve through normalizing with respect to the crossover. This remarkable result suggests that differences between silk feedstocks are rheologically simple and not as complex as originally thought. By comparison, solutions of poly(ethylene-oxide) and hydroxypropyl-methyl-cellulose showed similar normalization behavior; however, the resulting curves were broader than for silk, suggesting greater polydispersity in the (semi)synthetic materials. Thus, we conclude Nature may in fact produce polymer feedstocks that are more consistent than typical man-made counterparts as a model for future rheological investigations. PMID:27315508

  17. High-throughput rheology in a microfluidic device

    NASA Astrophysics Data System (ADS)

    Furst, Eric; Schultz, Kelly; Han, Hyejin; Kim, Chongyoup

    2011-11-01

    High-throughput rheological measurements in a microfluidic device are demonstrated. A series of microrheology samples is generated as droplets in an immiscible spacer fluid using a microfluidic T-junction. The compositions of the sample droplets are continuously varied over a wide range. Rheology measurements are made in each droplet using multiple particle tracking microrheology. We review critical design and operating parameters, including the droplet size, flow rates and rapid fabrication methods. Validation experiments are performed by measuring the solution viscosity of glycerine and the biopolymer heparin as a function of concentration. Finally, an analysis of droplet mixing is performed in order to optimize the device performance. Overall, the combination of microrheology with microfluidics maximizes the number of rheological measurements while simultaneously minimizing the sample preparation time and amount of material, and should be particularly suited to the characterization of scarce or expensive materials. We acknowledge financial support from the NSF (CBET-0730292).

  18. Rheological behavior of magnetic powder mixtures for magnetic PIM

    NASA Astrophysics Data System (ADS)

    Kim, Sung Hun; Kim, See Jo; Park, Seong Jin; Mun, Jun Ho; Kang, Tae Gon; Park, Jang Min

    2012-06-01

    Powder injection molding (PIM) is a promising manufacturing technology for the net-shape production of small, complex, and precise metal or ceramic components. In order to manufacture high quality magnets using PIM, the magneto-rheological (MR) properties of the PIM feedstock, i.e. magnetic powder-binder mixture, should be investigated experimentally and theoretically. The current research aims at comprehensive understanding of the rheological characteristics of the PIM feedstock. The feedstock used in the experiment consists of strontium ferrite powder and paraffin wax. Steady and oscillatory shear tests have been carried out using a plate-and-plate rheometer, under the influence of a uniform magnetic field applied externally. Rheological properties of the PIM feedstock have been measured and characterized for various conditions by changing the temperature, the powder fraction and the magnetic flux density.

  19. Tidal dissipation in heterogeneous bodies: Maxwell vs Andrade rheology

    NASA Astrophysics Data System (ADS)

    Behounkova, M.; Cadek, O.

    2014-04-01

    The tremendous volcanism on Jupiter's moon Io as well as the huge activity at the south pole of Saturn's moon Enceladus show that tidal dissipation is a very strong source of energy for some bodies in the Solar System. Outside the Solar System, tidal heating in short-period exoplanets may cause Io-like volcanism, large-scale melting and even thermal runaways [1-4]. Here we further develop the method to compute tidal heating in heterogeneous bodies [5]. Especially, we concentrate on the Andrade rheology implementation. We study the impact of the improved model on bodies with large lateral viscosity variation such as Enceladus and tidally locked exoEarth with a large surface temperature contrast due to uneven insolation [6]. We discuss the influence of empirical parameters describing the Andrade rheology and compare the tidal heating and tidal stress obtained for the Andrade rheology with frequently used Maxwell models for different forcing frequencies.

  20. A dynamic rheological model for thin-film lubrication

    NASA Astrophysics Data System (ADS)

    Zhang, Xiang-Jun; Huang, Ying; Guo, Yan-Bao; Tian, Yu; Meng, Yong-Gang

    2013-01-01

    In this study, the effects of the non-Newtonian rheological properties of the lubricant in a thin-film lubrication regime between smooth surfaces were investigated. The thin-film lubrication regime typically appears in Stribeck curves with a clearly observable minimum coefficient of friction (COF) and a low-COF region, which is desired for its lower energy dissipation. A dynamic rheology of the lubricant from the hydrodynamic lubrication regime to the thin-film lubrication regime was proposed based on the convected Maxwell constitutive equation. This rheology model includes the increased relaxation time and the yield stress of the confined lubricant thin film, as well as their dependences on the lubricant film thickness. The Deborah number (De number) was adopted to describe the liquid-solid transition of the confined lubricant thin film under shearing. Then a series of Stribeck curves were calculated based on Tichy's extended lubrication equations with a perturbation of the De number. The results show that the minimum COF points in the Stribeck curve correspond to a critical De number of 1.0, indicating a liquid-to-solid transition of the confined lubricant film. Furthermore, the two proposed parameters in the dynamic rheological model, namely negative slipping length b (indicating the lubricant interfacial effect) and the characteristic relaxation time λ0, were found to determine the minimum COF and the width of the low-COF region, both of which were required to optimize the shape of the Stribeck curve. The developed dynamic rheological model interprets the correlation between the rheological and interfacial properties of lubricant and its lubrication behavior in the thin-film regime.

  1. Rheological Models of Blood: Sensitivity Analysis and Benchmark Simulations

    NASA Astrophysics Data System (ADS)

    Szeliga, Danuta; Macioł, Piotr; Banas, Krzysztof; Kopernik, Magdalena; Pietrzyk, Maciej

    2010-06-01

    Modeling of blood flow with respect to rheological parameters of the blood is the objective of this paper. Casson type equation was selected as a blood model and the blood flow was analyzed based on Backward Facing Step benchmark. The simulations were performed using ADINA-CFD finite element code. Three output parameters were selected, which characterize the accuracy of flow simulation. Sensitivity analysis of the results with Morris Design method was performed to identify rheological parameters and the model output, which control the blood flow to significant extent. The paper is the part of the work on identification of parameters controlling process of clotting.

  2. Rheological Study of Mutarotation of Fructose in Anhydrous State

    SciTech Connect

    Wang, Yangyang; Wlodarczyk, Patryk; Sokolov, Alexei P; Paluch, Marian W

    2013-01-01

    Rheological measurement was employed to study the mutarotation of D-fructose in anhydrous state. By monitoring the evolution of shear viscosity with time, rate constants for mutarotation were estimated, and two different stages of this reaction were identified. One of the mutarotation stages is rapid and has a low activation energy, whereas the other is much slower and has a much higher activation energy. Possible conversions corresponding to these two phases are discussed. This work demonstrates that, in addition to the routine techniques such polarimetry and gas liquid chromatography, rheological measurement can be used as an alternative method to continuously monitor the mutarotation of sugars.

  3. Electrical conductivity and rheology of carbon black composites under elongation

    NASA Astrophysics Data System (ADS)

    Starý, Zdeněk

    2015-04-01

    Electrical properties of conductive polymer composites are governed by filler particle structures which are formed in the material during the mixing. Therefore, knowledge of the behavior of conductive particle structures under defined conditions of deformation is necessary to produce materials with balanced electrical and rheological properties. Whereas the electrical conductivity evolution under shear can be nowadays studied even with the commercial rheometers, the investigations under elongation were not performed up to now. In this work simultaneous electrical and rheological measurements in elongation on polystyrene/carbon black composites are introduced. Such kind of experiment can help in understanding the relationships between processing conditions and properties of conductive polymer composites.

  4. Rheology of Savannah River site tank 42 HLW radioactive sludge

    SciTech Connect

    Ha, B.C.

    1997-11-05

    Knowledge of the rheology of the radioactive sludge slurries at the Savannah River Site is necessary in order to ensure that they can be retrieved from waste tanks and processed for final disposal. At Savannah River Site, Tank 42 sludge represents on of the first HLW radioactive sludges to be vitrified in the Defense Waste Processing Facility. The rheological properties of unwashed Tank 42 sludge slurries at various solids concentrations were measured remotely in the Shielded Cells at the Savannah River Technology Center using a modified Haake Rotovisco viscometer.

  5. Seismic velocity, attenuation and rheology of the upper mantle

    NASA Technical Reports Server (NTRS)

    Anderson, D. L.; Minster, J. B.

    1980-01-01

    Seismic and rheological properties of the upper mantle in the vicinity of the low-velocity zone are expressed in terms of relaxation by dislocation glide. Dislocation bowing in the glide plane explains seismic velocities and attenuation. Climbing at higher stresses for longer periods of time give the observed viscosity, and explain the low velocity and high temperature attenuation found at seismic frequencies. Due to differing parameters, separate terms for thermal, seismic and rheological lithospheres are proposed. All three lithospheres, however, are related and are functions of temperature, and must be specified by parameters such as period, stress, and stress duration.

  6. Rheological Study of Dextran-Modified Magnetite Nanoparticle Water Suspension

    NASA Astrophysics Data System (ADS)

    Józefczak, A.; Hornowski, T.; Rozynek, Z.; Skumiel, A.; Fossum, J. O.

    2013-04-01

    The aim of this work is to investigate the effect of surface modification of superparamagnetic magnetite nanoparticles (sterically stabilized by sodium oleate) by the dextran biocompatible layer on the rheological behavior of water-based magnetic fluids. The flow curves were measured as a function of the magnetic field strength by means of rheometry. The measured viscosity is generally dependent on both the particle concentration and the geometrical factors such as the particle shape and thickness of the adsorbed layers. The rheological properties of the magnetic fluids studied show the effect of the magnetic field strength and the presence of the surfactant second layer (dextran) on their viscosity.

  7. The rheology and composition of cryovolcanic flows on icy satellites

    NASA Technical Reports Server (NTRS)

    Kargel, Jeffrey S.

    1993-01-01

    The rheologic properties of terrestrial lavas have been related to morphologic features of their flows, such as levees, banked surfaces, multilobate structures, and compressible folds. These features also have been used to determine rheologies and constrain the compositions of extraterrestrial flows. However, with rare exceptions, such features are not resolvable in Voyager images of the satellites of outer planets. Often only flow length and edge thickness of cryovolcanic flows can be measured reasonably accurately from Voyager images. The semiempirical lava-flow model presented here is a renewed effort to extract useful information from such measurements.

  8. Stabilizers: indispensable substances in dairy products of high rheology.

    PubMed

    Tasneem, Madiha; Siddique, Farzana; Ahmad, Asif; Farooq, Umar

    2014-01-01

    The functionality of stabilizers is apparent in many food applications including dairy products. The role of stabilizers like gelatin, pectins, alginates, carboxymethylcellulose, gums, ispghol, sago starch, and chitosan in the development of dairy products of high rheology, like yoghurt, ice cream, and flavored milk, is discussed in this review. Attention is also paid to comprehend on interactions among milk proteins, minerals, and other milk constituents with the reactive sites of stabilizers to get the desirable properties such as appearance, body and texture, mouthfeel, consistency. The role played by stabilizers in the control of syneresis and overrun problems in the high-rheology dairy products is also the topic of discussion. PMID:24499066

  9. Longevity and rheology of cratons: key constraints from surface topography

    NASA Astrophysics Data System (ADS)

    Francois, T.; Burov, E. B.; Meyer, B.; Agard, P.

    2011-12-01

    Archean cratons are stable remnants of Earth's early continental lithosphere. Their structure, composition and survival over geological time spans make them ones of the most unique and enigmatic features of the Earth's surface. It has become evident from both geophysical and petrological studies that cratons exhibit deep lithospheric roots, which remained stable ever since their formation in the early Archean. The question of how some of the cratons survived destruction over timescales of billions of years remains a subject of vigorous debate. In order to understand what controls the long-term stability of the cratons, we investigated the impact of the thermo-rheological structure of the lithosphere on the evolution of both surface topography and cratonic roots using fully coupled thermo-mechanical numerical models (600*3000 km, free upper surface topography, layered lithospheric structure). Our model has a particular focus on the Canadian Shield, where considerable structural and thermal data are available from both geological and geophysical studies. In particular, we compare the implications of the "Cratonic" "Jelly-Sandwich" rheology (JS; strong dry olivine mantle, strong crust, cold geotherm with Moho temperature of 400°C, thermal lithosphere thickness of 250 km) with those of the "Crème Brûlée" rheology (CB; strong crust, weak wet olivine mantle, Moho temperature of 600°C, thermal lithosphere thickness of 150 km) (Figure 1). Our experiments show that, in the case of a laterally homogeneous lithosphere and in the absence of tectonic shortening or extension (blocked borders), both JS and CB rheologies may account for the stability of the shield and its surface topography. In this case continental lithosphere remains stable over large time spans, even for the weakest wet olivine mantle (but for "cold" thermal gradients). Nevertheless, for a laterally heterogeneous crust, as is the case for the Canadian Shield and most cratons, dry olivine mantle JS rheology

  10. Rheological Properties of Enzymatically Isolated Tomato Fruit Cuticle.

    PubMed Central

    Petracek, P. D.; Bukovac, M. J.

    1995-01-01

    Rheological properties were determined for cuticular membranes (CMs) enzymatically isolated from mature tomato (Lycopersicon esculentum Mill. cv Pik Red) fruit. The cuticle responded as a viscoelastic polymer in stress-strain studies. Both CM and dewaxed CM expanded and became more elastic and susceptible to fracture when hydrated, suggesting that water plasticized the cuticle. Dewaxing of the CM caused similar changes in elasticity and fracturing, indicating that wax may serve as a supporting filler in the cutin matrix. Exposure of the cuticle to the surfactant Triton X-100 did not significantly affect its rheological properties. PMID:12228622

  11. Critical scaling in the rheology of damped random spring networks

    NASA Astrophysics Data System (ADS)

    Tighe, Brian

    2011-11-01

    Physical, biological, and engineered materials ranging from foams and emulsions to bioppolymer and bar-joint networks can be modelled as random networks of springs. We study the oscillatory rheology of random networks immersed in a viscous background fluid, and show how their response is intimately tied to the presence or absence of floppy modes in the zero frequency limit. The rheology displays dynamic critical scaling with three different regimes: viscous fluid, elastic solid, and shear thinning power law fluid. We give scaling arguments to explain all of the critical exponents and confirm our predictions with numerics. Supported by the Dutch Organization for Scientific Research (NWO).

  12. REAL WASTE TESTING OF SLUDGE BATCH 5 MELTER FEED RHEOLOGY

    SciTech Connect

    Reboul, S.; Stone, M.

    2010-03-17

    Clogging of the melter feed loop at the Defense Waste Processing Facility (DWPF) has reduced the throughput of Sludge Batch 5 (SB5) processing. After completing a data review, DWPF attributed the clogging to the rheological properties of the Slurry Mix Evaporator (SME) project. The yield stress of the SB5 melter feed material was expected to be high, based on the relatively high pH of the SME product and the rheological results of a previous Chemical Process Cell (CPC) demonstration performed at the Savannah River National Laboratory (SRNL).

  13. Rheology of composite solid propellants during motor casting

    NASA Technical Reports Server (NTRS)

    Klager, K.; Rogers, C. J.; Smith, P. L.

    1978-01-01

    Results of casting studies are reviewed so as to define the viscosity criteria insuring the fabrication of defect-free grains. The rheology of uncured propellants is analyzed showing that a realistic assessment of a propellant's flow properties must include measurement of viscosity as a function of shear stress and time after curing agent. Methods for measuring propellant viscosity are discussed, with particular attention given to the Haake-Rotovisko rotational viscometer. The effects of propellant compositional and processing variables on apparent viscosity are examined, as are results relating rheological behavior to grain defect formation during casting.

  14. Blood rheology in vitro and in vivo.

    PubMed

    Lowe, G D

    1987-09-01

    Blood rheology tests are traditionally used for detection of organic disease and for monitoring disease activity. More recently they have been used for prediction of blood flow in vivo, not only in overt hyperviscosity syndromes but also in the covert hyperviscosity of low-flow states. The traditional ESR test result increases with red cell aggregation induced by increases in large, asymmetrical plasma globulins. However, small increases in haematocrit and large increases in plasma viscosity each decrease the ESR, reducing both its diagnostic utility and its ability to predict blood flow in vivo. The ESR should be corrected to a standard haematocrit, or else replaced by the ZSR or plasma viscosity, which are more rapid, simple, sensitive and independent of haematocrit. For prediction of blood flow in vivo, these tests can be supplemented by measurement of whole-blood viscosity, which can be performed simply and cheaply in capillary viscometers at high shear rates. Whole-blood viscosity is determined by plasma viscosity, haematocrit and red cell deformability at high shear rates. Its measurement is useful in overt hyperviscosity syndromes, particularly in estimating the effect of red cell transfusion in anaemic patients with plasma hyperviscosity, hyperleukocytic leukaemias or sickling disorders. Blood viscosity should be related to the haematocrit or haemoglobin concentration in order to estimate oxygen delivery to tissues. Changes in blood viscosity can be compensated readily in the normal circulation but not in the compromised, low-flow circulation. In these circumstances, systemic increases in plasma viscosity, haematocrit, whole-blood viscosity, red cell aggregation and in the numbers of circulating rigid red or white blood cells can perpetuate low-flow states and ischaemia. Red cell deformability in narrow vessels is best measured by micropore filtration systems, in which the effect of white cells has been eliminated. Red cell deformability is reduced by

  15. Gas slug ascent through rheologically stratified conduits

    NASA Astrophysics Data System (ADS)

    Capponi, Antonio; James, Mike R.; Lane, Steve J.

    2016-04-01

    Textural and petrological evidence has indicated the presence of viscous, degassed magma layers at the top of the conduit at Stromboli. This layer acts as a plug through which gas slugs burst and it is thought to have a role in controlling the eruptive dynamics. Here, we present the results of laboratory experiments which detail the range of slug flow configurations that can develop in a rheologically stratified conduit. A gas slug can burst (1) after being fully accommodated within the plug volume, (2) whilst its base is still in the underlying low-viscosity liquid or (3) within a low-viscosity layer dynamically emplaced above the plug during the slug ascent. We illustrate the relevance of the same flow configurations at volcanic-scale through a new experimentally-validated 1D model and 3D computational fluid dynamic simulations. Applied to Stromboli, our results show that gas volume, plug thickness, plug viscosity and conduit radius control the transition between each configuration; in contrast, the configuration distribution seems insensitive to the viscosity of magma beneath the plug, which acts mainly to deliver the slug into the plug. Each identified flow configuration encompasses a variety of processes including dynamic narrowing and widening of the conduit, generation of instabilities along the falling liquid film, transient blockages of the slug path and slug break-up. All these complexities, in turn, lead to variations in the slug overpressure, mirrored by changes in infrasonic signatures which are also associated to different eruptive styles. Acoustic amplitudes are strongly dependent on the flow configuration in which the slugs burst, with both acoustic peak amplitudes and waveform shapes reflecting different burst dynamics. When compared to infrasonic signals from Stromboli, the similarity between real signals and laboratory waveforms suggests that the burst of a slug through a plug may represent a viable first-order mechanism for the generation of

  16. Introducing Students to Rheological Classification of Foods, Cosmetics, and Pharmaceutical Excipients Using Common Viscous Materials

    ERIC Educational Resources Information Center

    Faustino, Ce´lia; Bettencourt, Ana F.; Alfaia, Anto´nio; Pinheiro, Lídia

    2015-01-01

    Rheological measurements are very important tools for the characterization of the flow and deformation of a material, as well as for optimization of the rheological parameters. The application and acceptance of pharmaceutical formulations, cosmetics, and foodstuffs depends upon their rheological characteristics, such as texture, consistency, or…

  17. Triamcinolone Acetonide Oromucoadhesive Paste for Treatment of Aphthous Stomatitis

    PubMed Central

    Hamishehkar, Hamed; Nokhodchi, Ali; Ghanbarzadeh, Saeed; Kouhsoltani, Maryam

    2015-01-01

    Purpose: The aim of this study was to prepare the optimized oral paste formulation of Triamcinolone acetonide intended to be used in aphtous stomatitis. Methods: Plastibases were prepared using mineral oil and polyethylene (95:5). Oral paste formulations were prepared with different mixtures of three hydrocolloids solids, including gelatin, pectin and sodium carboxymethylcellulose, with different ratios, as well as Plastibase. Long-term and short-term stability of prepared formulations were studied in the case of color and consistency of pastes. Franz diffusion cell and dialysis membrane were employed for release study. Release data were fitted in the kinetic models to find out the mechanism of drug release. Results: Formulation containing 60% plastibase, 3.3% pectin, 6.6% gelatin and 30% carboxymethylcellulose showed desired durability of adhesion, spreadability and rheology property in healthy volunteers and was compared with reference formulation (Adcortyl®) in the case of release profile. Although, optimized formulation and Adcortyl followed the Higuchi and first order release kinetics respectively, optimized formulation showed similar release profile to reference formulation. Conclusion: Optimized oral paste formulation of Triamcinolone Acetonide showed similar characteristics with reference formulation and could be used as an effective drug delivery system for the treatment of recurrent aphthous stomatitis. PMID:26236668

  18. Water Past and Present

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This image of sulfate and water ice deposits in the Olympia Undae region of Mars was taken by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) at 2213 UTC on October 2, 2006 (6:13 p.m. EDT) near 81.6 degrees north latitude, 188.9 degrees east longitude. CRISM's image was taken in 544 colors covering 0.36-3.92 micrometers, and shows features as small as 20 meters (66 feet) across.

    Olympia Undae is a large dune field that stretches some 1,100 kilometers (684 miles) across the northern polar region of Mars, just south of the ice cap. The region holds a vast expanse of complex, shifting dunes and is best described as a sand sea or erg similar to the Sahara.

    The two images above provide interesting clues into Mars' history by revealing the planet's wet past and frozen present. The left image is an infrared, false-color image that reveals dark-colored dunes overlying a lighter substrate. Spectral data from CRISM and its sister instrument OMEGA suggest similar compositions of these dunes and the dark basal, or lowermost, unit of the north polar layered deposits. HIRISE images revealed cross-bedding (crossed layers that are oriented at a different angle to the main layer) in this dark unit. On Earth, cross-bedded sediments can form in both windy and watery environments. The dark polar basal unit on Mars is interpreted as a sand sheet underlying and pre-dating the ice, and now being eroded to dunes by the Martian winds.

    The mineralogy of the Olympia Undae region holds a record of past water. CRISM spectral data (right image) shows that the darker dunes are rich in polyhydrated sulfate (sulfates with more than one water molecule incorporated into each molecule of the mineral). The mineral gypsum is a polyhydrated sulfate, and the most likely constituent in these dunes. The gypsum probably formed by evaporation of ancient, saline water or by aqueous alteration of the silicate portion of the dune material. Areas shaded in red are cover by

  19. Microwave heating effect on rheology and microstructure of white sauces.

    PubMed

    Guardeño, Luis M; Sanz, Teresa; Fiszman, Susana M; Quiles, Amparo; Hernando, Isabel

    2011-10-01

    The microstructure and rheological properties of white sauces formulated with different starches were analyzed after being microwave-heated for different times. Significant differences (P < 0.05) in rheological parameters analyzed-storage modulus (G'), loss modulus (G″), and loss tangent (tanδ)-were obtained for sauces made with different starches. Microwave reheating did not affect G' and G″ values until water evaporation became significant. In addition, tanδ values did not change significantly (P < 0.05) even during long reheating times showing that sauce viscoelastic properties did not change after microwave irradiation. However, microstructure assessed by confocal laser scanning microscopy showed changes in fat globule and protein. These microstructural changes did not seem to have a significant effect on rheological measurements since starch and ι-carrageenan are mainly responsible for the viscoelastic behavior of the sauces. Practical Application:  The development of products appropriate to microwave heating is constantly rising in food industry. It is necessary to understand the behavior of the ingredients and the final product to microwave heating in order to choose those ingredients which will develop the best performance. Starches are common ingredients in industrial sauces, and rheological and microstructural techniques have shown their usefulness in characterization of starch-based systems. PMID:21913921

  20. Rheology and structure of surface crosslinked surfactant-activated microgels.

    PubMed

    Li, Dongcui; Hsu, Raymond; Figura, Brian; Jacobs, Robert; Li, Sinan; Horvath, Steve; Clifford, Ted; Chari, Krishnan

    2016-09-14

    Nonionic surfactant-activated microgels (SAMs), composed of hydrophobic alkyl acrylates and hydrophilic hydroxyalkyl esters that utilize the effects of surfactant mediated swelling and interaction to provide pH-independent rheological properties, were previously reported as a new pathway to the rheology modification of surfactant solutions. Crosslinking was shown to play an important role in the properties of these soft microgel systems. To understand the impact of crosslinking chemistry on SAM polymers, we have compared two types of SAM polymers: a conventionally crosslinked SAM polymer via allyl pentaerythritol and a novel SAM polymer, where the surface is self-crosslinked via a reactive surfactant. We have systematically characterized the polymer's swelling, rheology and microstructure in a model system containing the polymer, sodium dodecyl sulfate (SDS) and water. Surface self-crosslinking is demonstrated to be a more effective crosslinking approach to create surfactant-mediated interactions between the microgel particles, resulting in more effective rheology modification. Internal crosslinking hinders both the full swelling of the SAM polymer as well as inter-particle bridging interactions, and is therefore less effective. To our best knowledge, this is the first report on creating a novel surface self-crosslinked microgel via a dual-functional reactive surfactant that interacts with a non-reactive surfactant to create a yield stress fluid. PMID:27470971

  1. The Rheology of Three-Phase Basaltic Magma

    NASA Astrophysics Data System (ADS)

    Llewellin, E. W.; Truby, J.; Mueller, S. P.; Mader, H. M.

    2014-12-01

    The transport of magma is controlled by its rheology which, in turn, is a function of its crystal and bubble content. We develop the first empirically-validated model for the rheology of a three-phase magma (i.e. one containing both bubbles and crystals). The model is valid at low bubble capillary number (where bubble deformation is small) which is typical of basaltic magma. We adopt an 'effective-medium' approach in which the bubbly melt is treated as a continuous medium which suspends the crystals. The resulting three-phase model combines separate two-phase models for bubble suspension rheology and crystal suspension rheology, which are taken from the literature. The model is validated against new analogue experimental data for three-phase suspensions of bubbles and spherical particles, collected in the low bubble capillary number regime. Good agreement is found across the experimental range of particle volume fraction (0 ≤ Фp ≤0.5) and bubble volume fraction (0 ≤ Фb ≤ 0.3). Consistent with model predictions, experimental results demonstrate that, at low capillarity, bubble growth in a crystal-poor magma increases its viscosity, whilst bubble growth in a crystal-rich magma decreases its viscosity. The validity range of the model makes it particularly applicable to the transport of magma in the sub-volcanic plumbing system. The model is trivially extended to account for variations in crystal shape, and for the high capillarity regime; these extended models await experimental validation.

  2. Rheology of defatted ultrafiltration-diafiltration soy proteins

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The linear and non-linear rheological properties of defatted soy proteins produced by ultrafiltration-diafiltration were investigated at three temperatures. Five concentrations ranging from 10% to 30% of the defatted ultrafiltered-diafiltered (DUD) soy proteins were prepared. The properties of DUD...

  3. Rheological and microstructural changes in Queso Fresco during storage

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Queso Fresco is a traditional Hispanic cheese that is increasing in popularity in the United States. Rheological and microstructural studies were performed on samples refrigerated at 4 and 10 deg C for up to 8 wk. The hardness of all cheeses as measured by texture profile analysis (TPA) was low a...

  4. Flow and Thixotropic Parameters for Rheological Characterization of Hydrogels.

    PubMed

    Ghica, Mihaela Violeta; Hîrjău, Mircea; Lupuleasa, Dumitru; Dinu-Pîrvu, Cristina-Elena

    2016-01-01

    The goal of this paper was to design several sodium carboxymethylcellulose hydrogels containing a BCS class II model drug and to evaluate their flow and thixotropic properties. The rheological measurements were performed at two temperatures (23 °C and 37 °C), using a rotational viscometer. The hydrogels were stirred at different time intervals (10 s, 2, 5, 10 and 20 min at 23 °C, and 10 s, 2 and 5 min at 37 °C), with a maximum rotational speed of 60 rpm, and the corresponding forward and backward rheograms were recorded as shear stress vs. shear rate. For all hydrogels, the rheological data obtained at both temperatures showed a decrease of viscosity with the increase of the shear rate, highlighting a pseudoplastic behaviour. The flow profiles viscosity vs. shear rate were quantified through power law model, meanwhile the flow curves shear stress vs. shear rate were assessed by applying the Herschel-Bulkley model. The thixotropic character was evaluated through different descriptors: thixotropic area, thixotropic index, thixotropic constant and destructuration thixotropic coefficient. The gel-forming polymer concentration and the rheological experiments temperature significantly influence the flow and thixotropic parameters values of the designed hydrogels. The rheological characteristics described have an impact on the drug release microenvironment and determine the stasis time at the application site. PMID:27322222

  5. Analysis improves selection of rheological model for slurries

    SciTech Connect

    Moftah, K. )

    1993-10-25

    The use of a statistical index of determination can help select a fluid model to describe the rheology of oil well cement slurries. The closer the index is to unity, the better the particular model will describe the actual fluid behavior. Table 1 lists a computer program written in Quick Basic to calculate rheological parameters and an index of determination for the Bingham plastic and power law models. The points used for the calculation of the rheological parameters can be selected from the data set. The skipped points can then be introduced and the calculations continued, not restarted, to obtain the parameters for the full set of data. The two sets of results are then compared for the decision to include or exclude the added points in the regression. The program also calculates the apparent viscosity to help determine where turbulence or high gross error occurred. In addition, the program calculates the confidence interval of the rheological parameters for a 90% level of confidence.

  6. THERMAL AND RHEOLOGICAL PROPERTIES OF LUPINUS ALBUS FLOUR MEAL

    Technology Transfer Automated Retrieval System (TEKTRAN)

    There is very little research done in the area of structure and function relationships of lupin meal or lupin native protein. The scope of this work is to study lupin's native proteins thermal and rheological properties in whole meal. The effect of pH and heat treatment on the thermal properties o...

  7. Using Modeling to Design new Rheology Modifiers for Paints

    NASA Astrophysics Data System (ADS)

    Ginzburg, Valeriy

    2013-03-01

    Since their invention in 1970-s, hydrophobically ethoxylated urethanes (HEUR) have been actively used as rheology modifiers for paints. Thermodynamic and rheological behavior of HEUR molecules in aqueous solutions is now very well understood and is based on the concept of transient network (TN), where the association of hydrophobic groups into networks of flower micelles causes viscosity to increase dramatically as function of polymer concentration. The behavior of complex mixtures containing water, HEUR, and latex (``binder'') particles, however, is understood less well, even though it has utmost importance in the paint formulation design. In this talk, we discuss how the adsorption of HEUR chains onto latex particles results in formation of complex viscoelastic networks with temporary bridges between particles. We then utilize Self-Consistent Field Theory (SCFT) model to compute effective adsorption isotherms (thickener-on-latex) and develop a rheological theory describing steady-shear viscosity of such mixtures. The model is able to qualitatively describe many important features of the water/latex/HEUR mixtures, such as strong shear thinning. The proposed approach could potentially lead to the design of new HEUR structures with improved rheological performance. This work was supported by Dow Chemical Company

  8. QUESO CHIHUAHUA:EFFECTS OF SEASONALITY OF CHEESEMILK ON RHEOLOGY

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Fresh semi-hard raw milk (RM) and pasteurized milk (PM) cheeses made by Mennonite communities in Chihuahua, Mexico were sampled in early winter, mid-spring, and late summer and evaluated during storage to determine if rheological properties were affected by the season the cheese was produced. The r...

  9. Rheology and Structure of Molten, Olefin Multiblock Copolymers

    SciTech Connect

    Park, Heon E.; Dealy, John M.; Marchand, Gary R.; Wang, Jian; Li, Sheng; Register, Richard A.

    2010-12-07

    Several samples of a recently developed olefin multiblock copolymer were studied by means of rheology, differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS). The synthesis involves a chain shuttling agent (CSA) that switches the growing chain between two catalysts, one that favors the incorporation of an {alpha}-olefin comonomer and one that suppresses incorporation. The data were used to determine the effect of octene comonomer content and CSA level on rheological behavior and the occurrence of mesophase separation transition (MST) in the melt. To distinguish between crystallization and MST, we made calorimetry scans and measured the density and rheological properties over a range of temperatures. Small angle X-ray scattering analysis of a sample that had undergone planar extensional flow revealed strong alignment of lamellar mesodomains, which maintained their alignment after annealing. This result confirmed the hypothesis based on rheological evidence that a lamellar mesophase is present in the melt at temperatures well above the melting point.

  10. THERMAL AND RHEOLOGICAL PROPERTIES OF LUPINUS ALBUS FLOUR MEAL

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Research on the structure and function relationships of lupin meal or lupin native protein is limited. The scope of this work is to study lupin's native proteins' thermal and rheological properties in whole meal. The effect of pH and heat treatment on the thermal properties of lupin meal was studi...

  11. Continuum-mechanics-based rheological formulation for debris flow

    USGS Publications Warehouse

    Chen, Cheng-lung; Ling, Chi-Hai

    1993-01-01

    This paper aims to assess the validity of the generalized viscoplastic fluid (GVF) model in the light of both the classical relative-viscosity versus concentration relation and the dimensionless stress versus shear-rate squared relations based on kinetic theory, thereby addressing how to evaluate the rheological parameters of the GVF model using Bagnold's data.

  12. Historical evolution of oil painting media: A rheological study

    NASA Astrophysics Data System (ADS)

    de Viguerie, Laurence; Ducouret, Guylaine; Lequeux, François; Moutard-Martin, Thierry; Walter, Philippe

    2009-09-01

    Rheology is the science of flow, which is a phenomenon found in every painting operation, such as decorative paintings or protective coatings. In this article, the principles of rheology as applied to paintings and coatings are recalled in a first part and the rheological criteria required in the paint industry presented. Indeed, different flow behaviours leads to different finishes. The same procedure and techniques as in industry can be employed to explain some evolutions in oil painting aspects over the centuries. The first recipes for oil painting indicate the use of treated oil, resins and spirits. This article deals with the evolution of the composition of these systems as media for oil painting, according to rheological clues. During the Renaissance period, the media used were Newtonian or slightly shear thinning and allowed one a perfect levelling. Then techniques changed, paints became more opaque with less addition of oil/resin media, and brushstrokes appeared visible. Some preparations containing lead, oil and mastic resin, whose flow behaviour is closed to those required in industry, may have appeared during the 17th century and are still used and sold today. To cite this article: L. de Viguerie et al., C. R. Physique 10 (2009).

  13. Rheological Properties of Liquid and Particle Stabilized Foam

    NASA Astrophysics Data System (ADS)

    Özarmut, A. Ö.; Steeb, H.

    2015-04-01

    In Earth-Pressure-Balance (EPB) tunnelling the excavated ground is used as face support medium to prevent surface settlements. In general, the excavated ground (e.g. for cohesionless soils) does not exhibit suitable conditions to support the tunnelling face. This technical challenge can be solved by adding conditioning agents that are mainly foams. In order to physically understand the rheological properties of the (added) liquid foam and the foam-soil (foam-particle) mixture and to comprehend its influence on the soil, advanced rheological investigations are necessary. Therefore, rheological experiments such as flow curve tests have been performed to determine the effective yield stress. Since the morphology, i.e. the microstructure of the foam accounts for effective rheological properties, size, shape and distribution of the cells of the foam and particle-laden foam were characterized in detail applying imaging techniques. In order to perform the above mentioned experiments, polymer- stabilised shaving foam seems to be a good replacement of tunnelling foam and suitable for laboratory tests due to its time stability, characteristic length scales of the microstructure and accessibility. Glass beads (of different diameter and volume fractions, i.e. specific surface areas) are used to investigate the effective material behaviour of foam-particle mixtures. The experimental results are compared with yield stress models of modified Herschel-Bulkley- Papanastasiou type.

  14. Activation energy measurements in rheological analysis of cheese

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Activation energy of flow (Ea) was calculated from temperature sweeps of cheeses with contrasting characteristics to determine its usefulness in predicting rheological behavior upon heating. Cheddar, Colby, whole milk Mozzarella, low moisture part skim Mozzarella, Parmesan, soft goat, and Queso Fre...

  15. Rheology of crumb-rubber modified asphalt binders and mixes

    NASA Astrophysics Data System (ADS)

    Sheth, Vikas Rameshchandra

    Laboratory test procedures are presented to determine the rheological properties of crumb rubber modified asphalt (CRMA) binders and mixes. These tests provide simple, fast, and cost-effective alternatives to evaluate the performance (rutting and cracking potential) of binders and mixes used for pavement construction. Viscoelastic properties of CRMA binders are measured using dynamic shear analysis. Master curves were generated using the principle of time-temperature superposition to evaluate the effects of aging, rubber concentration, and curing conditions on the rheology of the modified binder. Results indicate that the rheology of CRMA binders can be divided into three regions of viscoelasticity: glassy region at high frequencies, transition/viscoelastic region at intermediate frequencies, and viscous region at low frequencies. Modification of the asphalt by addition of rubber leads to an improvement in both the high and low temperature properties, as reflected by changes in Gsp' and Gsp{''}, which causes the binder to have a greater resistance to specific pavement failure mechanisms. Both transient and dynamic properties of CRMA mixes were measured in the laboratory using the creep and recovery, direct tension, and frequency sweep tests. Rheological properties of the mix generated from the test data were compared to those of the binder to evaluate the effect of aging, rubber concentration, and curing conditions on mix performance. Several rheological parameters have been identified to characterize the rutting and cracking potential of mixes. A power law equation was found to give good correlations between several mix rheological parameters. Analysis of binder and mix failure energies show that work of cohesion of the binder is negligible compared to the failure energies. A unique relationship between Paris law material parameters has been confirmed. It is also shown that mix failure properties bear a one-to-one correlation with binder failure properties. Based

  16. Sorption and Interfacial Rheology Study of Model Asphaltene Compounds.

    PubMed

    Pradilla, Diego; Simon, Sébastien; Sjöblom, Johan; Samaniuk, Joseph; Skrzypiec, Marta; Vermant, Jan

    2016-03-29

    The sorption and rheological properties of an acidic polyaromatic compound (C5PeC11), which can be used to further our understanding of the behavior of asphaltenes, are determined experimentally. The results show that C5PeC11 exhibits the type of pH-dependent surface activity and interfacial shear rheology observed in C6-asphaltenes with a decrease in the interfacial tension concomitant with the elastic modulus when the pH increases. Surface pressure-area (Π-A) isotherms show evidence of aggregation behavior and π-π stacking at both the air/water and oil/water interfaces. Similarly, interactions between adsorbed C5PeC11 compounds are evidenced through desorption experiments at the oil/water interface. Contrary to indigenous asphaltenes, adsorption is reversible, but desorption is slower than for noninteracting species. The reversibility enables us to create layers reproducibly, whereas the presence of interactions between the compounds enables us to mimic the key aspects of interfacial activity in asphaltenes. Shear and dilatational rheology show that C5PeC11 forms a predominantly elastic film both at the liquid/air and the liquid/liquid interfaces. Furthermore, a soft glassy rheology model (SGR) fits the data obtained at the liquid/liquid interface. However, it is shown that the effective noise temperature determined from the SGR model for C5PeC11 is higher than for indigenous asphaltenes measured under similar conditions. Finally, from a colloidal and rheological standpoint, the results highlight the importance of adequately addressing the distinction between the material functions and true elasticity extracted from a shear measurement and the apparent elasticity measured in dilatational-pendant drop setups. PMID:26949974

  17. Viscoelastic silicone oils in analog modeling - a rheological benchmark

    NASA Astrophysics Data System (ADS)

    Rudolf, Michael; Boutelier, David; Rosenau, Matthias; Schreurs, Guido; Oncken, Onno

    2016-04-01

    Tectonic analog models frequently use silicone oils to simulate viscous flow in the lower crust and mantle. Precise knowledge of the model rheology is required to ensure dynamic similarity with the prototype. We assessed the rheological properties of various silicone oils using rotational and oscillatory tests. Resulting viscosities are in the range of 2 - 3 ×104 Pa s with a transition from Newtonian viscous to power-law, shear-thinning, around shear rates of 10‑2 to 10‑1 s‑1. Maxwell relaxation times are in the range of 10‑1 s. Comparing the rheological properties of chemically similar silicone oils from different laboratories shows that they differ from laboratory to laboratory. Furthermore, we characterized the temperature dependency of viscosity and aging effects. The samples show a reduction in zero-shear viscosity over time. This stabilizes at a certain value over several months. The dynamic moduli decrease as well, but other viscoelastic constants, such as the Maxwell relaxation time, are not affected by aging. We conclude that the aging is mainly controlled by the storage conditions and that a silicone shows no further aging when it has equilibrated with the ambient laboratory conditions. We consider all these differences as minor compared to the much larger uncertainties for estimating the lithosphere rheology. Nevertheless, it is important that the rheological properties of the experimental materials are monitored during an experimental series that spans over several weeks to months. Additionally, the viscoelastic properties may be scaled using dimensionless parameters (Deborah number) and show a dynamically similar change from Newtonian to power-law flow, like the natural prototype. In consequence, the viscoelasticity of these silicone oils is able to mimic the change in deformation mechanism from diffusion to dislocation creep.

  18. Valuing (and Teaching) the Past

    ERIC Educational Resources Information Center

    Peart, Sandra J.; Levy, David M.

    2005-01-01

    There is a difference between the private and social cost of preserving the past. Although it may be privately rational to forget the past, the social cost is significant: We fail to see that classical political economy is analytically egalitarian. The past is a rich source of surprises and debates, and resources on the Web are uniquely suited to…

  19. Extensional Rheology Experiment Developed to Investigate the Rheology of Dilute Polymer Solutions in Microgravity

    NASA Technical Reports Server (NTRS)

    Logsdon, Kirk A.

    2001-01-01

    A fundamental characteristic of fluid is viscosity; that is, the fluid resists forces that cause it to flow. This characteristic, or parameter, is used by manufacturers and end-users to describe the physical properties of a specific material so that they know what to expect when a material, such as a polymer, is processed through an extruder, a film blower, or a fiber-spinning apparatus. Normally, researchers will report a shear viscosity that depends on the rate of an imposed shearing flow. Although this type of characterization is sufficient for some processes, simple shearing experiments do not provide a complete picture of what a processor may expect for all materials. Extensional stretching flows are common in many polymer-processing operations such as extrusion, blow molding, and fiber spinning. Therefore, knowledge of the complete rheological (ability to flow and be deformed) properties of the polymeric fluid being processed is required to accurately predict and account for the flow behavior. In addition, if numerical simulations are ever able to serve as a priori design tools for optimizing polymer processing operations such as those described above, an accurate knowledge of the extensional viscosity of a polymer system and its variation with temperature, concentration, molecular weight, and strain rate is critical.

  20. PAA/PEO comb polymer effects on the rheological property evolution in concentrated cement suspensions

    NASA Astrophysics Data System (ADS)

    Kirby, Glen Harold

    We have studied the behavior of polyelectrolyte-based comb polymers in dilute solution and on the rheological property evolution of concentrated Portland cement suspensions. These species consisted of charge-neutral, poly(ethylene oxide) (PEO) "teeth" grafted onto a poly(acrylic acid) (PAA) "backbone" that contains one ionizable carboxylic acid group (COOH) per monomer unit. As a benchmark, our observations were compared to those obtained for pure cement pastes and systems containing pure polyelectrolyte species, i.e., sulfonated naphthalene formaldehyde (SNF) and poly(acrylic acid) (PAA). The behavior of PAA/PEO comb polymers, SNF, and PAA in dilute solution was studied as a function of pH in the absence and presence of mono-, di-, and trivalent counterions. Light scattering and turbidity measurements were carried out to assess their hydrodynamic radius and stability in aqueous solution, respectively. PAA experienced large conformational changes as a function of solution pH and ionic strength. Moreover, dilute solutions of ionized SNF and PAA species became unstable in the presence of multivalent counterions due to ion-bridging interactions. PAA/PEO solutions exhibited enhanced stability relative to pure polyelectrolytes under analogous conditions. The charge neutral PEO teeth shielded the underlying PAA backbone from ion-bridging interactions. In addition, such species hindered conformational changes in solution due to steric interactions between adjacent teeth. A new oscillatory shear technique was developed to probe the rheological property evolution of concentrated cement systems. The rheological property evolution of ordinary and white Portland cement systems were studied in the absence and presence of pure polyelectrolytes and PAA/PEO comb polymers with a wide range of PAA backbone molecular weight, PEO teeth molecular weight, and acid:imide ratio. Cement-PAA suspensions experienced rapid irreversible stiffening and set at 6 min due to ion

  1. Role of viscoelastic rheologies on heterogeneous stress fields in dynamic rupture models.

    NASA Astrophysics Data System (ADS)

    Radiguet, Mathilde; Kammer, David S.; Molinari, Jean-François

    2014-05-01

    Understanding how past ruptures will affect the propagation of the following ruptures, and how stress heterogeneities develop on faults are fundamental to a better comprehension of earthquake behavior. In that sense, numerical simulations provide a useful tool to study slip dynamics. In this study, we show, using dynamic rupture simulations, the importance of viscoelastic rheologies on the persistence of heterogeneous stress states along a frictional interface. The modeled set-up is a system used in laboratory friction experiments [Rubinstein et al., 2007; Ben-David et al. 2010]. Using a finite-element code, we model two 2D blocks of viscoelastic material (PMMA), with a slip-weakening friction law at the interface between the two solids. The system is loaded from the side of the upper block, resulting in a sequence of precursory slip events, which initiate at the trailing edge and stop before propagating over the entire interface. Their length increases with increasing loading, and high stress concentrations are generated at the tip of each arrested rupture. We analyze the evolution of these stress concentrations when the following slip events take place. We show that due to the viscous properties of the bulk material, the stress concentrations created by the arrest of precursory slip are not erased by the propagation of the following rupture, but reappear with the relaxation of the material, with a smaller amplitude. The amplitude of the stress concentrations follows an exponential decrease rate with successive rupture, which is controlled by by the material properties, and in particular by the ratio of the viscous over instantaneous Young's moduli. We extend this analysis by using rheological parameters relevant for rocks. Our results highlight the importance of viscous relaxation mechanisms in the persistence of heterogeneous stress states along a frictional interface. This study also provides a mechanism to explain how previous slip history will influence the

  2. Textural, Rheological and Sensory Properties and Oxidative Stability of Nut Spreads—A Review

    PubMed Central

    Shakerardekani, Ahmad; Karim, Roselina; Ghazali, Hasanah Mohd; Chin, Nyuk Ling

    2013-01-01

    Tree nuts are rich in macro and micronutrients, phytochemicals, tocopherols and phenolic compounds. The development of nut spreads would potentially increase the food uses of nuts and introduce consumers with a healthier, non-animal breakfast snack food. Nut spreads are spreadable products made from nuts that are ground into paste. Roasting and milling (particle size reduction) are two important stages for the production of nut spreads that affected the textural, rheological characteristic and overall quality of the nut spread. Textural, color, and flavor properties of nut spreads play a major role in consumer appeal, buying decisions and eventual consumption. Stability of nut spreads is influenced by its particle size. Proper combination of ingredients (nut paste, sweetener, vegetable oil and protein sources) is also required to ensure a stable nut spread product is produced. Most of the nut spreads behaved like a non-Newtonian pseudo-plastic fluid under yield stress which help the producers how to start pumping and stirring of the nut spreads. Similar to other high oil content products, nut spreads are susceptible to autoxidation. Their oxidation can be controlled by application of antioxidants, using processing techniques that minimize tocopherol and other natural antioxidant losses. PMID:23429239

  3. Rheological and functional properties of heat moisture treated pearl millet starch.

    PubMed

    Sharma, Monika; Yadav, Deep N; Singh, Ashish K; Tomar, Sudhir K

    2015-10-01

    Pearl millet (Pennisetum typhoides) starch was subjected to heat moisture treatment (HMT) at different moisture levels i.e., 20 % (HMT-20), 25 % (HMT-25) & 30 % (HMT-30) for 8 h at 110 °C and evaluated for changes in rheological, thermal, functional and morphological properties. Peak, breakdown, cool paste and setback viscosity decreased, while pasting temperature increased after HMT. Shear stability of HMT-30 sample was maximum (stability ratio 0.54). Highest (33.5 Pa) G' value was observed for native and lowest (14.8 Pa) for HMT-25 sample. Yield and flow point of starch gels also decreased after HMT, indicating softer gels and higher spreadability. HMT increased gelatinization temperature from 62.59 °C for native to 84.05 °C for HMT-30. Resistant starch content increased about three times in HMT-30 sample (7.07 %) as compared to native. Swelling power and solubility decreased after HMT. HMT also induced cavity and some dents on starch granules surface. PMID:26396395

  4. Spectrophotometry: Past and Present

    NASA Astrophysics Data System (ADS)

    Adelman, Saul J.

    2009-01-01

    I describe the rise of optical region spectrophotometry in the 1960's and 1970's when it achieved a status as a major tool in stellar research through its decline and near demise at present. With absolutely calibrated fluxes and Balmer profiles usually of H-gamma, astronomers used model atmospheres predictions to find both the effective temperatures and surface gravities of many stars. Spectrophotometry as I knew it was photometrically calibrated low dispersion spectroscopy with a typical resolution of order 25 A. A typical data set consists of 10 to 15 values covering most of the optical spectral region. The strengths and shortcomings of the rotating grating scanners are discussed. The accomplishments achieved using spectrophotometric data, which were obtained with instruments using photomultipliers, are reviewed. Extensions to other spectral regions are noted and attempts to use observations from space to calibrate the optical region will be discussed. There are two steps to fully calibrate flux data. The first requires the calibration of the fluxes of one or more standard stars against sources calibrated absolutely in a laboratory. The use of Vega as the primary standard has been both a blessing as it is so bright and a curse especially as modeling it correctly requires treating it as a fast rotating star seen nearly pole-on. At best its calibration has errors of about 1%. The other step is to apply extinction corrections for the Earth's atmosphere and then calibrate the fluxes using the fluxes of standard stars. Now the ASTRA Spectrophotometer promises a revitalization of the use and availability of optical flux data. Its design specifications included solutions to the problems of past optical spectrophotometric instruments.

  5. Rheology of lava flows on Mercury: an experimental study

    NASA Astrophysics Data System (ADS)

    Sehlke, A.; Whittington, A. G.

    2014-12-01

    The morphology of lava flows is controlled by the physical properties of the lava and its effusion rates, as well as environmental influences such as surface medium, slope and ambient temperature and pressure conditions. The important rheological properties of lavas include viscosity (η) and yield strength (σy), strongly dependent on temperature (T), composition (X), crystal fraction (φc) and vesicularity (φb). The crystal fraction typically increases as temperature decreases, and also influences the residual liquid composition. The rheological behavior of multi-phase lava flows is expressed as different flow morphologies, for example basalt flows transition from smooth pahoehoe to blocky `a`a at higher viscosities and/or strain rates. We have previously quantified the rheological conditions of this transition for Hawaiian basalts, but lavas on Mercury are very different in composition and expected crystallization history. Here we determine experimentally the temperature and rheological conditions of the pahoehoe-`a`a transition for two likely Mercury lava compositions using concentric cylinder viscometry. We detect first crystals at 1302 ºC for an enstatite basalt and 1317 ºC for a basaltic komatiite composition representative of the northern volcanic plains (NVP). In both cases, we observe a transition from Newtonian to pseudo-plastic response at crystal fractions > 10 vol%. Between 30 to 40 vol%, a yield strength (τ0) around 26±6 and 110±6 Pa develops, classifying the two-phase suspensions as Herschel-Bulkley fluids. The measured increase in apparent viscosity (ηapp) ranges from 10 Pa s to 104 Pa s. This change in rheological properties occurs only in a temperature range up to 100 ºC below the liquidus. By analogy with the rheological conditions of the pahoehoe-`a`a transition for Hawaiian basalts, we can relate the data for Mercury to lava flow surface morphology as shown in Figure 1, where the onset of the transition threshold zone (TTZ) for the

  6. In situ rheology of Staphylococcus epidermidis bacterial biofilms

    PubMed Central

    Pavlovsky, Leonid

    2014-01-01

    We developed a method to grow Staphylococcus epidermidis bacterial biofilms and characterize their rheological properties in situ in a continuously fed bioreactor incorporated into a parallel plate rheometer. The temperature and shear rates of growth modeled bloodstream conditions, a common site of S. epidermidis infection. We measured the linear elastic (G′) and viscous moduli (G″) of the material using small-amplitude oscillatory rheology and the yield stress using non-linear creep rheology. We found that the elastic and viscous moduli of the S. epidermidis biofilm were 11 ± 3 Pa and 1.9 ± 0.5 Pa at a frequency of 1 Hz (6.283 rad per s) and that the yield stress was approximately 20 Pa. We modeled the linear creep response of the biofilm using a Jeffreys model and found that S. epidermidis has a characteristic relaxation time of approximately 750 seconds and a linear creep viscosity of 3000 Pa s. The effects on the linear viscoelastic moduli of environmental stressors, such as NaCl concentration and extremes of temperature, were also studied. We found a non-monotonic relationship between moduli and NaCl concentrations, with the stiffest material properties found at human physiological concentrations (135 mM). Temperature dependent rheology showed hysteresis in the moduli when heated and cooled between 5 °C and 60 °C. Through these experiments, we demonstrated that biofilms are rheologically complex materials that can be characterized by a combination of low modulus (~10 Pa), long relaxation time (~103 seconds), and a finite yield stress (20 Pa). This suggests that biofilms should be viewed as soft viscoelastic solids whose properties are determined in part by local environmental conditions. The in situ growth method introduced here can be adapted to a wide range of biofilm systems and applied over a broad spectrum of rheological and environmental conditions because the technique minimizes the risk of irreversible, non-linear deformation of the microbial

  7. Rheology and TIC/TOC results of ORNL tank samples

    SciTech Connect

    Pareizs, J. M.; Hansen, E. K.

    2013-04-26

    The Savannah River National Laboratory (SRNL)) was requested by Oak Ridge National Laboratory (ORNL) to perform total inorganic carbon (TIC), total organic carbon (TOC), and rheological measurements for several Oak Ridge tank samples. As received slurry samples were diluted and submitted to SRNL-Analytical for TIC and TOC analyses. Settled solids yield stress (also known as settled shear strength) of the as received settled sludge samples were determined using the vane method and these measurements were obtained 24 hours after the samples were allowed to settled undisturbed. Rheological or flow properties (Bingham Plastic viscosity and Bingham Plastic yield stress) were determined from flow curves of the homogenized or well mixed samples. Other targeted total suspended solids (TSS) concentrations samples were also analyzed for flow properties and these samples were obtained by diluting the as-received sample with de-ionized (DI) water.

  8. Microstructure and rheology of microfibril-polymer networks.

    PubMed

    Veen, Sandra J; Versluis, Peter; Kuijk, Anke; Velikov, Krassimir P

    2015-12-14

    By using an adsorbing polymer in combination with mechanical de-agglomeration, the microstructure and rheological properties of networks of microfibrils could be controlled. By the addition of sodium carboxymethyl cellulose during de-agglomeration of networks of bacterial cellulose, the microstructure could be changed from an inhomogeneous network with bundles of microfibrils and voids to a more homogeneous spread and alignment of the particles. As a result the macroscopic rheological properties were altered. Although still elastic and gel-like in nature, the elasticity and viscous behavior of the network as a function of microfibril concentration is altered. The microstructure is thus changed by changing the surface properties of the building blocks leading to a direct influence on the materials macroscopic behavior. PMID:26434637

  9. Modeling lava lake heat loss, rheology, and convection

    NASA Astrophysics Data System (ADS)

    Harris, Andrew J. L.

    2008-04-01

    Measurements at Erta Ale's lava lake and theoretical equations for lake rheology, density driven convection and thermally-driven plume ascent allow the constraint of lake dynamics. Cooling and crystallization expected from surface heat losses imply a viscosity increase from 150 Pa s to 300-1800 Pa s for cooled surface layers. Convection is expected to proceed vigorously under low viscosity conditions driving rapid (0.1-0.4 m s-1) surface motions and sluggishly under moderate-to-high viscosity conditions to drive slower motions (<0.08 m s-1). Convection is likely driven by small (~6 kg m-3) density differences, where surface cooling can influence lake rheology and explain variable rates of surface convective motion.

  10. Rheology evolution of sludge through high-solid anaerobic digestion.

    PubMed

    Dai, Xiaohu; Gai, Xin; Dong, Bin

    2014-12-01

    The main purpose of this study was to investigate the rheology evolution of sludge through high-solid anaerobic digestion (AD) and its dependency on sludge retention time (SRT) and temperature of AD reactor. The operation performance of high-solid AD reactors were also studied. The results showed that sludge became much more flowable after high-solid AD. It was found that the sludge from reactors with long SRT exhibited low levels of shear stress, viscosity, yield stress, consistency index, and high value of flow behaviour index. While the flowability of sludge from thermophilic AD reactors were better than that of sludge from mesophilic AD reactors though the solid content of the formers were higher than that of the latters, which could be attributed to the fact that the formers had more amount of free and interstitial moisture. It might be feasible to use sludge rheology as an AD process controlling parameter. PMID:25463776

  11. Rheological and thermal properties of PP-based WPC

    NASA Astrophysics Data System (ADS)

    Mazzanti, V.; Mollica, F.; El Kissi, N.

    2014-05-01

    Wood Plastic Composite (WPC) has attracted great interest in outdoor building products for the reduced cost and the possibility of using recycled materials. Nevertheless the material shows two problems: the large viscosity due to the presence of high concentrations of filler and the degradation of cellulose during processing The aim of this work was to investigate the rheological and thermal properties of WPC. The material used for the experiments was a commercial PP-based WPC compound, with different concentrations of natural fibers (30, 50, 70% wt.). The thermal properties were studied to check for degradation of natural fibers during the subsequent rheological tests. Analyzing the storage and loss moduli and the complex viscosity curves obtained using a parallel plate rheometer it was possible to observe some features related to the viscoelastic nature of the composite.

  12. Estimate of Hanford Waste Rheology and Settling Behavior

    SciTech Connect

    Poloski, Adam P.; Wells, Beric E.; Tingey, Joel M.; Mahoney, Lenna A.; Hall, Mark N.; Thomson, Scott L.; Smith, Gary Lynn; Johnson, Michael E.; Meacham, Joseph E.; Knight, Mark A.; Thien, Michael G.; Davis, Jim J.; Onishi, Yasuo

    2007-10-26

    The U.S. Department of Energy (DOE) Office of River Protection’s Waste Treatment and Immobilization Plant (WTP) will process and treat radioactive waste that is stored in tanks at the Hanford Site. Piping, pumps, and mixing vessels have been selected to transport, store, and mix the high-level waste slurries in the WTP. This report addresses the analyses performed by the Rheology Working Group (RWG) and Risk Assessment Working Group composed of Pacific Northwest National Laboratory (PNNL), Bechtel National Inc. (BNI), CH2M HILL, DOE Office of River Protection (ORP) and Yasuo Onishi Consulting, LLC staff on data obtained from documented Hanford waste analyses to determine a best-estimate of the rheology of the Hanford tank wastes and their settling behavior. The actual testing activities were performed and reported separately in referenced documentation. Because of this, many of the required topics below do not apply and are so noted.

  13. Dynamics of diffuse oceanic plate boundaries: insensitivity to rheology

    NASA Astrophysics Data System (ADS)

    Zatman, Stephen; Gordon, Richard G.; Mutnuri, Kartik

    2005-07-01

    Diffuse plate boundaries, which are zones of deformation hundreds to thousands of kilometres wide, occur in both continental and oceanic lithosphere. Here, we build on our prior work in which we described analytic approximations to simple dynamical models that assume that the vertically averaged viscous force resisting deformation in diffuse oceanic plate boundaries (DOPBs) is described by either a linear Newtonian viscous rheology or a yield-stress (high-exponent power-law) rheology. An important observation is that the poles of relative rotation of adjacent component plates tend to lie in the diffuse plate boundary that separates them. A key cause of this tendency is that a faster spin is needed to balance a component of torque through the middle of a diffuse plate boundary than to balance an equal component of torque lying 90° from the middle of the diffuse boundary. The strength of that tendency depends on rheology, however, with the tendency being stronger for a yield-stress rheology than for a Newtonian viscous rheology. For the special case of the pole of rotation lying outside of and along the strike of the boundary, these large differences can be simply explained in terms of the distribution of boundary-perpendicular normal forces acting across the boundary. In the Newtonian case, the distribution of forces has an along-strike gradient that can balance a component of torque about the middle of the boundary, while in the yield-stress case, the distribution of forces has zero along-strike gradient and cannot balance a component of torque about the middle of the diffuse plate boundary. To expand our analysis to intermediate power laws of geophysical interest (i.e. power-law exponents of 3 to 30), as well as to investigate more thoroughly the behaviour for a high-exponent power law, we numerically integrate the force distribution to obtain the torques. Results for intermediate power laws resemble the yield-stress rheology much more than they resemble the

  14. Rheology of fluids measured by correlation force spectroscopy

    NASA Astrophysics Data System (ADS)

    Radiom, Milad; Robbins, Brian; Honig, Christopher D. F.; Walz, John Y.; Paul, Mark R.; Ducker, William A.

    2012-04-01

    We describe a method, correlation force spectrometry (CFS), which characterizes fluids through measurement of the correlations between the thermally stimulated vibrations of two closely spaced micrometer-scale cantilevers in fluid. We discuss a major application: measurement of the rheological properties of fluids at high frequency and high spatial resolution. Use of CFS as a rheometer is validated by comparison between experimental data and finite element modeling of the deterministic ring-down of cantilevers using the known viscosity of fluids. The data can also be accurately fitted using a harmonic oscillator model, which can be used for rapid rheometric measurements after calibration. The method is non-invasive, uses a very small amount of fluid, and has no actively moving parts. It can also be used to analyze the rheology of complex fluids. We use CFS to show that (non-Newtonian) aqueous polyethylene oxide solution can be modeled approximately by incorporating an elastic spring between the cantilevers.

  15. The Rheological Properties of the Biopolymers in Synovial Fluid

    NASA Astrophysics Data System (ADS)

    Krause, Wendy E.; Klossner, Rebecca R.; Wetsch, Julie; Oates, Katherine M. N.; Colby, Ralph H.

    2005-03-01

    The polyelectrolyte hyaluronic acid (HA, hyaluronan), its interactions with anti-inflammatory drugs and other biopolymers, and its role in synovial fluid are being studied. We are investigating the rheological properties of sodium hyaluronate (NaHA) solutions and an experimental model of synovial fluid (comprised of NaHA, and the plasma proteins albumin and γ-globulins). Steady shear measurements on bovine synovial fluid and the synovial fluid model indicate that the fluids are highly viscoeleastic and rheopectic (stress increases with time under steady shear). In addition, the influence of anti-inflammatory agents on these solutions is being explored. Initial results indicate that D-penicillamine and hydroxychloroquine affect the rheology of the synovial fluid model and its components. The potential implications of these results will be discussed.

  16. Novel Rheology in a Structured Food Product—Marmite™

    NASA Astrophysics Data System (ADS)

    White, David E.; Moggridge, Geoff D.; Wilson, D. Ian

    2008-07-01

    The rheology of Marmite™, a yeast extract spread containing ˜70-75 wt% colloidal protein and NaCl solids in water, was studied using a number of shear rheology techniques. The material was found to be thixotropic in steady shear with no wall-slip. Creep data and the occurrence of jamming in controlled-stress mode further illustrate the presence of a structure and both solid and liquid flow regimes. Steady-state data acquired at low shear rates suggest a zero-shear plateau at shear stresses that are of the same order of magnitude as those found for the transition between flow regimes observed in the creep data. This transition has been the subject of recent discussion, e.g. [1],[2].

  17. Rheological properties of polyolefin composites highly filled with calcium carbonate

    NASA Astrophysics Data System (ADS)

    Nobile, Maria Rossella; Fierro, Annalisa; Jakubowska, Paulina; Sterzynski, Tomasz

    2016-05-01

    In this paper the rheological properties of highly filled polyolefin composites (HFPCs) have been investigated. Calcium carbonate (CaCO3), with stearic acid modified surface, was used as filler. Ternary compounds have been obtained by the inclusion of a CaCO3/polypropylene master batch into the high density polyethylene matrix. The highly filled polyolefin composites with CaCO3 content in the range between 40 and 64 wt% have been prepared in the molten state using a single-screw extruder, the temperature of the extrusion die was set at 230°C. The melt rheological properties of the HFPCs have been extensively investigated both in oscillatory and steady shear flow.

  18. Fabricating mesostructed thin films by Marangoni and rheology effects

    NASA Astrophysics Data System (ADS)

    Lee, Chang; Shen, Amy

    2004-11-01

    Thin films with self-assembled mesostructures are important in applications such as catalysis, synthesis, and biosensor technology. A major technique used to prepare such films is sol-gel processing. This technique involves depositing a complex fluid containing colloids, alcohol, and surfactants on a substrate by coating, followed by allowing the film to evaporate and form self-assembled mesostructures. The fundamental mechanisms underlying this process are poorly understood. By dip coating a plate through wormlike micellar solutions, we are able to synthesize self-assembled mesoporous films under the proper combinations of coating speed, surface tension gradients, and rheological properties of the fluids. The experiments exhibit that the surface morphology of the mesoporous films is highly dependent on the rheological properties of the sol solution and the Marangoni effects induced both thermally (by evaporation) and chemically (effective surfactant concentration change during solvent evaporation).

  19. Structure factor and rheology of chain molecules from molecular dynamics

    NASA Astrophysics Data System (ADS)

    Castrejón-González, Omar; Castillo-Tejas, Jorge; Manero, Octavio; Alvarado, Juan F. J.

    2013-05-01

    Equilibrium and non-equilibrium molecular dynamics were performed to determine the relationship between the static structure factor, the molecular conformation, and the rheological properties of chain molecules. A spring-monomer model with Finitely Extensible Nonlinear Elastic and Lennard-Jones force field potentials was used to describe chain molecules. The equations of motion were solved for shear flow with SLLOD equations of motion integrated with Verlet's algorithm. A multiple time scale algorithm extended to non-equilibrium situations was used as the integration method. Concentric circular patterns in the structure factor were obtained, indicating an isotropic Newtonian behavior. Under simple shear flow, some peaks in the structure factor were emerged corresponding to an anisotropic pattern as chains aligned along the flow direction. Pure chain molecules and chain molecules in solution displayed shear-thinning regions. Power-law and Carreau-Yasuda models were used to adjust the generated data. Results are in qualitative agreement with rheological and light scattering experiments.

  20. Time-dependent rheological behaviour of bacterial cellulose hydrogel.

    PubMed

    Gao, Xing; Shi, Zhijun; Kuśmierczyk, Piotr; Liu, Changqing; Yang, Guang; Sevostianov, Igor; Silberschmidt, Vadim V

    2016-01-01

    This work focuses on time-dependent rheological behaviour of bacterial cellulose (BC) hydrogel. Due to its ideal biocompatibility, BC hydrogel could be employed in biomedical applications. Considering the complexity of loading conditions in human body environment, time-dependent behaviour under relevant conditions should be understood. BC specimens are produced by Gluconacetobacter xylinus ATCC 53582 at static-culture conditions. Time-dependent behaviour of specimens at several stress levels is experimentally determined by uniaxial tensile creep tests. We use fraction-exponential operators to model the rheological behaviour. Such a representation allows combination of good accuracy in analytical description of viscoelastic behaviour of real materials and simplicity in solving boundary value problems. The obtained material parameters allow us to identify time-dependent behaviour of BC hydrogel at high stress level with sufficient accuracy. PMID:26478298

  1. Can rheologic variables be of prognostic relevance in arteriosclerotic diseases?

    PubMed

    Resch, K L; Ernst, E; Matrai, A; Buhl, M; Schlosser, P; Paulsen, H F

    1991-12-01

    The hypothesis that blood rheology is of prognostic value in patients with arteriosclerotic diseases was tested in a prospective study of 843 patients at a rehabilitation clinic. They were tested for blood serum and plasma viscosity, hematocrit, fibrinogen, red cell aggregation and deformability, erythrocyte sedimentation rate, white cell count, cholesterol, and triglycerides. End points were defined as a second stroke or myocardial infarction or cardiovascular death within two years of the initial examination. Patients suffering such end points as compared with matched pairs (n = 74; matching criteria: identical manifestation of arteriosclerosis, identical sex and similar age and risk factors) had significantly higher native blood viscosity (p = 0.002), red cell aggregation (p = 0.01), serum viscosity (p = 0.01), fibrinogen (p = 0.02), and cholesterol (p = 0.01). It is concluded that rheologic factors are associated with the prognosis in patients with arteriosclerotic diseases. PMID:1763830

  2. Impaired blood rheology: a risk factor after stroke?

    PubMed

    Ernst, E; Resch, K L; Matrai, A; Buhl, M; Schlosser, P; Paulsen, H F

    1991-05-01

    The hypothesis that blood rheology is of prognostic value in stroke patients was tested in a prospective study. A total of 523 patients in the rehabilitation phase of stroke (outside the acute phase reaction after stroke) were tested for blood, serum and plasma viscosity, haematocrit, fibrinogen, red cell aggregation and deformability, ESR, white cell count, cholesterol and triglycerides. Endpoints were defined as a second stroke (lethal or not) within 2 years after the initial examination. Patients suffering such endpoints exhibit elevated blood viscosity, red cell aggregation, plasma and serum viscosity, fibrinogen and cholesterol levels, compared to patients without endpoints. It is concluded that rheological factors are associated with the prognosis after a first stroke. PMID:2040872

  3. Rheology of Foam Near the Order-Disorder Phase Transition

    NASA Technical Reports Server (NTRS)

    Holt, R. Glynn; McDaniel, J. Gregory

    1999-01-01

    Foams are extremely important in a variety of industrial applications. Foams are widely used in fire-fighting applications, and are especially effective in fighting flammable liquid fires. In fact the Fire Suppression System aboard the Space Shuttle utilizes cylinders of Halon foam, which, when fired, force a rapidly expanding foam into the convoluted spaces behind instrument panels. Foams are critical in the process of enhanced oil recovery, due to their surface-active and highly viscous nature. They are also used as drilling fluids in underpressurized geologic formations. They are used as transport agents, and as trapping agents. They are also used as separation agents, where ore refinement is accomplished by froth flotation of the typically lighter and hydrophobic contaminants. The goal of the proposed investigation is the determination of the mechanical and rheological properties of foams, utilizing the microgravity environment to explore foam rheology for foams which cannot exist, or only exist for a short time, in 1g.

  4. Empirical rheological model for rough or grooved bonded interfaces.

    PubMed

    Belloncle, Valentina Vlasie; Rousseau, Martine

    2007-12-01

    In the industrial sector, it is common to use metal/adhesive/metal structural bonds. The cohesion of such structures can be improved by preliminary chemical treatments (degreasing with solvents, alkaline, or acid pickling), electrochemical treatments (anodising), or mechanical treatments (abrasion, sandblasting, grooving) of the metallic plates. All these pretreatments create some asperities, ranging from roughnesses to grooves. On the other hand, in damage solid mechanics and in non-destructive testing, rheological models are used to measure the strength of bonded interfaces. However, these models do not take into account the interlocking of the adhesive in the porosities. Here, an empirical rheological model taking into account the interlocking effects is developed. This model depends on a characteristic parameter representing the average porosity along the interface, which considerably simplifies the corresponding stress and displacement jump conditions. The paper deals with the influence of this interface model on the ultrasonic guided modes of the structure. PMID:17659313

  5. Shape Oscillations of Gas Bubbles With Newtonian Interfacial Rheological Properties

    NASA Technical Reports Server (NTRS)

    Nadim, Ali

    1996-01-01

    The oscillation frequency and damping rate for small-amplitude axisymmetric shape modes of a gas bubble in an ideal liquid are obtained, in the limit when the bubble interface possesses Newtonian interfacial rheology with constant surface shear and dilatational viscosities. Such results permit the latter surface properties to be measured by analyzing experimental data on frequency shift and damping rate of specific shape modes of suspended bubbles in the presence of surfactants.

  6. Mafic granulite rheology: Implications for a weak continental lower crust

    NASA Astrophysics Data System (ADS)

    Wang, Y. F.; Zhang, J. F.; Jin, Z. M.; Green, H. W.

    2012-11-01

    The “jelly sandwich” model of continental rheology, long the consensus model, has recently been challenged. The controversy is based on the rheology of mafic granulite that is thought to make up most of the lower continental crust. However, because of technical issues in experimental rock deformation, there are very few data on this problem. Here we report the rheology and fabrics of a reconstituted, fine-grained nominally dry (i.e., no hydrous mineral) mafic granulite (57% plagioclase+24% clinopyroxene+14% orthopyroxene+5% opaque minerals, 0.16-0.28 wt% H2O) deformed at 1.1-1.2 GPa pressure in a modified Griggs-type deformation apparatus. The rheology of this mafic granulite can be described by the constitutive equation of ε˙=Aσexp(-(244±35 kJ/mol)/RT) where ε˙ is in s-1, σ in MPa, T in Kelvin and A=10-2.0±1.6 MPa-3.2 s-1. Our results provide new experimental evidence in support of the “jelly sandwich” lithosphere strength model and imply that mafic granulite with a moderate amount of water (>0.05-0.08 wt% H2O) is likely to be a weak layer in the lithosphere. Both pyroxenes and plagioclase develop pronounced fabrics in responding to axial deformation. The deformation mechanism is dislocation creep with (100)[001], and (001)[100]/(010)[100] being the dominant slip systems for pyroxenes and plagioclase, respectively. The low strength of mafic granulite is ascribed largely to the significant weakening effect of dissolved water in pyroxenes and plagioclase. A weak continental lower crust has many important implications for geodynamics of crust-mantle interactions, such as lower crust channel flow and delamination.

  7. Sludge Batch 2 (Macrobatch 3) Rheology Studies with Simulants

    SciTech Connect

    Koopman, D.C.

    2001-05-02

    Non-radioactive sludge-only process simulations of the DWPF Sludge Receipt and Adjustment Tank (SRAT) and the Slurry Mix Evaporator (SME) cycles were conducted for a 50:50 blend of Tank 8 and Tank 40 washed sludge and Tank 40 washed sludge by itself. Rheological characterization of the sludge, SRAT product, and SME product material was requested as part of the simulant program.

  8. Rheology and Wetting Properties of Fluxes for Flip Chip Packages

    NASA Astrophysics Data System (ADS)

    Wang, Jinlin

    2008-07-01

    The rheological properties, wettability, and fluxability of fluxes for flip chip packages were studied. The flux viscosity showed significant decrease from room temperature to the peak reflow temperature. The viscosity of fluxes decreased after kneading process. One of the reasons of the viscosity decrease for some fluxes during the kneading is the moisture uptake. The tackiness of the fluxes increased with both applied load and retraction speed.

  9. Jamming, Yielding, and Rheology of Weakly Vibrated Granular Media

    NASA Astrophysics Data System (ADS)

    Dijksman, Joshua A.; Wortel, Geert H.; van Dellen, Louwrens T. H.; Dauchot, Olivier; van Hecke, Martin

    2011-09-01

    We establish that the rheological curve of dry granular media is nonmonotonic, both in the presence and absence of external mechanical agitations. In the presence of weak vibrations, the nonmonotonic flow curves govern a hysteretic transition between slow but steady and fast, inertial flows. In the absence of vibrations, the nonmonotonic flow curve governs the yielding behavior of granular media. Finally, we show that nonmonotonic flow curves can be seen in at least two different flow geometries and for several granular materials.

  10. Hydrodynamics and rheology of active liquid crystals: a numerical investigation.

    PubMed

    Marenduzzo, D; Orlandini, E; Yeomans, J M

    2007-03-16

    We report numerical studies of the hydrodynamics and rheology of an active liquid crystal. We confirm the existence of a transition between a passive and an active phase, with spontaneous flow in steady state. We explore how the velocity profile changes with activity, and we point out the difference in behavior for flow-aligning and tumbling materials. We find that an active material can thicken or thin under a flow, or even exhibit both behaviors as the forcing changes. PMID:17501095

  11. Effect of Fluoropolymer Antidripping Agent on Rheological Behavior of LLDPE

    NASA Astrophysics Data System (ADS)

    Obr, Aleš; Zatloukal, Martin

    2011-07-01

    In this work, high molecular weight polytetrafluoroethylene based antidripping agent was blended with Ziegler-Natta based LLDPE in different concentrations. Rheological characterization was consequently performed for all the blends and the obtained results were compared with the pure LLDPE. It has been found that high molecular weight PTFE based melt modifier MM 5935 EF significantly enhancing the shear viscosity/elasticity and especially the extensional viscosity of the LLDPE melt.

  12. Rheological study of clay-kaolin aqueous suspensions

    NASA Technical Reports Server (NTRS)

    Lapasin, R.; Lucchini, F.

    1984-01-01

    Rheological characteristics of clay-kaolin aqueous suspensions were studied by a rotational viscometer to correlate their behavior with the properties of ceramic slips for casting containing quartz, feldspars, and other nonplastic materials. In particular, the effects of the different amounts of dry materials and deflocculant (mixture 1:1 of Na2CO3 and Na2SiO3) and of temperatures on the shear-time-dependent properties of suspensions were examined.

  13. Evaluation for rheological constitutive relations, using the indentation technique

    NASA Astrophysics Data System (ADS)

    Fang, Lei

    1992-01-01

    A simple experimental method of determining the rheological constitutive relations is proposed. The method relies upon an analysis of the frictionless contact of a rigid spherical indenter and the rheological materials. The proposal addresses problems in two fields: rheological constitutive models and contact mechanics. It attempts to evaluate the rheological constitutive relations using an indentation technique. A systematic, optimization-based material parameter/function indentation model is proposed. The identification algorithm is based on a modified Marquardt-Levenberg method. A new integral constitutive equation for viscoelastic materials is derived. The derivation is carried out so that a damage function is included in the model in a relatively convenient form. Inclusion of damage effects makes this constitutive equation considerably more general than the widely accepted K-BKZ integral model. The single-step and double-step stress relaxation indentation experiments on asphalt materials were performed. The K-BKZ, Wagner, and nonlinear Volterra models were evaluated. It is demonstrated that the new integral constitutive model shows a very good agreement with the experimental data. The idea of damage function is introduced not only to have a better fit of data, but the damage (or irreversibility) is observed experimentally. Also, the creep indentation tests on composites were presented. A multiaxial theory of creep deformation for particle-strengthened metal matrix composites (Zhu-Weng Theory) was evaluated. The goal of the proposed research is to develop the indentation technique for use in basic mechanical studies. From the indentation test, material response is measured. The data are used in conjunction with the material parameter identification model to optimally back calculate the constitutive relations.

  14. Lava flow rheology: A comparison of morphological and petrological methods

    NASA Astrophysics Data System (ADS)

    Chevrel, M. O.; Platz, T.; Hauber, E.; Baratoux, D.; Lavallée, Y.; Dingwell, D. B.

    2013-12-01

    In planetary sciences, the emplacement of lava flows is commonly modelled using a single rheological parameter (apparent viscosity or apparent yield strength) calculated from morphological dimensions using Jeffreys' and Hulme's equations. The rheological parameter is then typically further interpreted in terms of the nature and chemical composition of the lava (e.g., mafic or felsic). Without the possibility of direct sampling of the erupted material, the validity of this approach has remained largely untested. In modern volcanology, the complex rheological behaviour of lavas is measured and modelled as a function of chemical composition of the liquid phase, fractions of crystals and bubbles, temperature and strain rate. Here, we test the planetary approach using a terrestrial basaltic lava flow from the Western Volcanic Zone in Iceland. The geometric parameters required to employ Jeffreys' and Hulme's equations are accurately estimated from high-resolution HRSC-AX Digital Elevation Models. Samples collected along the lava flow are used to constrain a detailed model of the transient rheology as a function of cooling, crystallisation, and compositional evolution of the residual melt during emplacement. We observe that the viscosity derived from the morphology corresponds to the value estimated when significant crystallisation inhibits viscous deformation, causing the flow to halt. As a consequence, the inferred viscosity is highly dependent on the details of the crystallisation sequence and crystal shapes, and as such, is neither uniquely nor simply related to the bulk chemical composition of the erupted material. This conclusion, drawn for a mafic lava flow where crystallisation is the primary process responsible for the increase of the viscosity during emplacement, should apply to most of martian, lunar, or mercurian volcanic landforms, which are dominated by basaltic compositions. However, it may not apply to felsic lavas where vitrification resulting from

  15. Interfacial shear rheology of DPPC under physiologically relevant conditions.

    PubMed

    Hermans, Eline; Vermant, Jan

    2014-01-01

    Lipids, and phosphatidylcholines in particular, are major components in cell membranes and in human lung surfactant. Their ability to encapsulate or form stable layers suggests a significant role of the interfacial rheological properties. In the present work we focus on the surface rheological properties of dipalmitoylphosphatidylcholine (DPPC). Literature results are confusing and even contradictory; viscosity values have been reported differ by several orders of magnitude. Moreover, even both purely viscous and gel-like behaviours have been described. Assessing the literature critically, a limited experimental window has been explored correctly, which however does not yet include conditions relevant for the physiological state of DPPC in vivo. A complete temperature and surface pressure analysis of the interfacial shear rheology of DPPC is performed, showing that the monolayer behaves as a viscoelastic liquid with a domain structure. At low frequencies and for a thermally structured monolayer, the interaction of the molecules within the domains can be probed. The low frequency limit of the complex viscosity is measured over a wide range of temperatures and surface pressures. The effects of temperature and surface pressure on the low frequency viscosity can be analysed in terms of the effects of free molecular area. However, at higher frequencies or following a preshear at high shear rates, elasticity becomes important; most probably elasticity due to defects at the edge of the domains in the layer is probed. Preshearing refines the structure and induces more defects. As a result, disagreeing interfacial rheology results in various publications might be due to different pre-treatments of the interface. The obtained dataset and scaling laws enable us to describe the surface viscosity, and its dependence under physiological conditions of DPPC. The implications on functioning of lung surfactants and lung surfactant replacements will be discussed. PMID:24651838

  16. Olivine Slip-system Activity at High Pressure: Implications for Upper-Mantle Rheology and Seismic Anisotropy (Invited)

    NASA Astrophysics Data System (ADS)

    Raterron, P.; Castelnau, O.; Geenen, T.; Merkel, S.

    2013-12-01

    The past decade abounded in technical developments allowing the investigation of materials rheology at high pressure (P > 3 GPa) [1]. This had a significant impact on our understanding of olivine rheology in the Earth asthenosphere, where P is in the range 3 - 13 GPa. A dislocation slip-system transition induced by pressure has been documented in dry Fe-bearing olivine [2]; it induces changes in olivine aggregate lattice preferred orientation (LPO) [3,4], which may explain the seismic velocity anisotropy attenuation observed at depths > 200 km in the upper mantle [5]. Deformation experiments carried out on olivine single crystals at high pressure allowed quantifying the effect of P on individual slip system activities [6]. Integration of these data, together with data on lattice friction arising from computational models (e.g., [7]), into analytical or mean-field numerical models for aggregate plasticity gave insight on the viscosity and LPO of olivine aggregates deformed at geological conditions in the dislocation creep regime [8,9]. We will review these recent findings and their implications for upper mantle rheology and seismic anisotropy. [1] Raterron & Merkel, 2009, J. Sync. Rad., 16, 748 ; [2] Raterron et al., 2009, PEPI, 172, 74 ; [3] Jung et al., 2009, Nature Geoscience, 2, 73 ; [4] Ohuchi et al., 2011, EPSL, 304, 55 ; [5] Mainprice et al., 2005, Nature, 433, 731 ; [6] Raterron et al., 2012, PEPI, 200-201, 105 ; [7] Durinck et al., 2007, EJM, 19, 631 ; [8] Castelnau et al., 2010, C.R. Physique, 11, 304 ; [9] Raterron et al., 2011, PEPI, 188, 26

  17. Super-strong magneto-rheological fluids

    NASA Astrophysics Data System (ADS)

    Tao, R.

    2001-03-01

    A typical MR fluid is a suspension of magnetic particles of micrometer size in a liquid. Upon application of a strong magnetic field, the fluid turns into a solid. This process is reversible and the response time is of milliseconds. MR fluids presently have a yield shear stress around 80 kPa, which is adequate for applications in shock absorbers and vibration dampers, but is inadequate for automobile clutch etc. Efforts in searching for new materials in the past decades came with limited results. Thus we have developed a new approach to change the microstructure of MR fluids and make them super-strong. It is well known that under a strong magnetic field, the ideal structure of MR fluids is a body-centered tetragonal (bct) lattice. The mechanical strength of MR fluids strongly depends on the microstructure. A bct-lattice based thick column has a much higher yield stress than a single-chain structure. When a magnetic field is applied to a MR fluid, the particles first form chains. With time, the chains may aggregate into columns. However, the unassisted aggregation is not very useful, as it is slow and produces columns with a limited thickness. Our method is based on assisted aggregations. Immediately after a magnetic field is applied, we compress the MR fluid in the field direction before a shear force is applied. The compression pushes the induced chains together to form thick columns. This microstructure change greatly enhances the yield stress. The experiment on an iron-based MR fluid finds 800 kPa for the yield stress, ten times stronger than that without the compression. When the magnetic field is removed, the MR fluid still returns to the liquid state quickly. The upper limit of this structure-enhanced yield stress seems well above 800 kPa. The super-strong MR fluids are suitable for many industrial applications. *Supported by NSF Grant 0196022

  18. Aging and nonlinear rheology of thermoreversible colloidal gels

    NASA Astrophysics Data System (ADS)

    Wagner, Norman; Gordon, Melissa; Kloxin, Christopher

    Colloidal dispersions are found in a wide variety of consumer products such as paint, food and pharmaceuticals. We investigate gel formation and aging in a thermoreverible gel consisting of octadecyl-coated silica nanoparticles suspended in n-tetradecane. In this system, the octadecyl brush can undergo a phase change allowing the attractions between particles to be tuned by temperature (1,2). By probing the system with steady shear and large amplitude oscillatory shear, we have studied the effect of thermal history and shear history on gel formation and gel mechanical properties during aging. Gels were formed by approaching a common temperature from above and below to determine a reference state from which creep tests were conducted. Creep ringing was observed as expected for the viscoelastic gel. The rheological aging is interpreted in terms of the gel microstructure formed with differing thermal and shear histories to determine how processing affects structure. Recently proposed scaling laws for the rheology and structure under flow are explored within the context of gel aging (3). Through rheological and microstructural measurements, we will further the understanding of gel formation and aging in this model system which may be applied to processing conditions in an industrial setting.

  19. Rheological Properties of Quasi-2D Fluids in Microgravity

    NASA Technical Reports Server (NTRS)

    Stannarius, Ralf; Trittel, Torsten; Eremin, Alexey; Harth, Kirsten; Clark, Noel; Maclennan, Joseph; Glaser, Matthew; Park, Cheol; Hall, Nancy; Tin, Padetha

    2015-01-01

    In recent years, research on complex fluids and fluids in restricted geometries has attracted much attention in the scientific community. This can be attributed not only to the development of novel materials based on complex fluids but also to a variety of important physical phenomena which have barely been explored. One example is the behavior of membranes and thin fluid films, which can be described by two-dimensional (2D) rheology behavior that is quite different from 3D fluids. In this study, we have investigated the rheological properties of freely suspended films of a thermotropic liquid crystal in microgravity experiments. This model system mimics isotropic and anisotropic quasi 2D fluids [46]. We use inkjet printing technology to dispense small droplets (inclusions) onto the film surface. The motion of these inclusions provides information on the rheological properties of the films and allows the study of a variety of flow instabilities. Flat films have been investigated on a sub-orbital rocket flight and curved films (bubbles) have been studied in the ISS project OASIS. Microgravity is essential when the films are curved in order to avoid sedimentation. The experiments yield the mobility of the droplets in the films as well as the mutual mobility of pairs of particles. Experimental results will be presented for 2D-isotropic (smectic-A) and 2D-nematic (smectic-C) phases.

  20. Investigating the rheological properties of native plant latex.

    PubMed

    Bauer, Georg; Friedrich, Christian; Gillig, Carina; Vollrath, Fritz; Speck, Thomas; Holland, Chris

    2014-01-01

    Plant latex, the source of natural rubber, has been of interest to mankind for millennia, with much of the research on its rheological (flow) properties focused towards industrial application. However, little is known regarding the rheology of the native material as produced by the plant, a key factor in determining latex's biological functions. In this study, we outline a method for rheological comparison between native latices that requires a minimum of preparatory steps. Our approach provides quantitative insights into the coagulation mechanisms of Euphorbia and Ficus latex allowing interpretation within a comparative evolutionary framework. Our findings reveal that in laboratory conditions both latices behave like non-Newtonian materials with the coagulation of Euphorbia latex being mediated by a slow evaporative process (more than 60 min), whereas Ficus appears to use additional biochemical components to increase the rate of coagulation (more than 30 min). Based on these results, we propose two different primary defensive roles for latex in these plants: the delivery of anti-herbivory compounds (Euphorbia) and rapid wound healing (Ficus). PMID:24173604

  1. Rheology of Savannah River Site Tank 51 HLW radioactive sludge

    SciTech Connect

    Ha, B.C.

    1993-01-01

    Savannah River Site (SRS) Tank 51 HLW radioactive sludge represents a major portion of the first batch of sludge to be vitrified in the Defense Waste Processing Facility (DWPF) at SRS. The rheological properties of Tank 51 sludge will determine if the waste sludge can be pumped by the current DWPF process cell pump design and the homogeneity of melter feed slurries. The rheological properties of Tank 51 sludge and sludge/frit slurries at various solids concentrations were measured remotely in the Shielded Cells Operations (SCO) at the Savannah River Technology Center (SRTC) using a modified Haake Rotovisco viscometer system. Rheological properties of Tank 51 radioactive sludge/Frit 202 slurries increased drastically when the solids content was above 41 wt %. The yield stresses of Tank 51 sludge and sludge/frit slurries fall within the limits of the DWPF equipment design basis. The apparent viscosities also fall within the DWPF design basis for sludge consistency. All the results indicate that Tank 51 waste sludge and sludge/frit slurries are pumpable throughout the DWPF processes based on the current process cell pump design, and should produce homogeneous melter feed slurries.

  2. Hanford Waste Physical and Rheological Properties: Data and Gaps - 12078

    SciTech Connect

    Kurath, D.E.; Wells, B.E.; Huckaby, J.L.; Mahoney, L.A.; Daniel, R.C.; Burns, C.A.; Tingey, J.M.; Cooley, S.K.

    2012-07-01

    The retrieval, transport, treatment and disposal operations associated with Hanford Tank Wastes involve the handling of a wide range of slurries. Knowledge of the physical and rheological properties of the waste is a key component to the success of the design and implementation of the waste processing facilities. Previous efforts to compile and analyze the physical and rheological properties were updated with new results including information on solids composition and density, particle size distributions, slurry rheology, and particle settling behavior. The primary source of additional data is from a recent series of tests sponsored by the Hanford Waste Treatment and Immobilization Plant (WTP). These tests involved an extensive suite of characterization and bench-scale process testing of 8 waste groups representing approximately 75% of the high-level waste mass expected to be processed through the WTP. Additional information on the morphology of the waste solids was also included. Based on the updated results, a gap analysis to identify gaps in characterization data, analytical methods and data interpretation was completed. (authors)

  3. Rheological assessment of nanofluids at high pressure high temperature

    NASA Astrophysics Data System (ADS)

    Kanjirakat, Anoop; Sadr, Reza

    2013-11-01

    High pressure high temperature (HPHT) fluids are commonly encountered in industry, for example in cooling and/or lubrications applications. Nanofluids, engineered suspensions of nano-sized particles dispersed in a base fluid, have shown prospective as industrial cooling fluids due to their enhanced rheological and heat transfer properties. Nanofluids can be potentially utilized in oil industry for drilling fluids and for high pressure water jet cooling/lubrication in machining. In present work rheological characteristics of oil based nanofluids are investigated at HPHT condition. Nanofluids used in this study are prepared by dispersing commercially available SiO2 nanoparticles (~20 nm) in a mineral oil. The basefluid and nanofluids with two concentrations, namely 1%, and 2%, by volume, are considered in this investigation. The rheological characteristics of base fluid and the nanofluids are measured using an industrial HPHT viscometer. Viscosity values of the nanofluids are measured at pressures of 100 kPa to 42 MPa and temperatures ranging from 25°C to 140°C. The viscosity values of both nanofluids as well as basefluid are observed to have increased with the increase in pressure. Funded by Qatar National Research Fund (NPRP 08-574-2-239).

  4. Mechanically modified xanthan gum: Rheology and polydispersity aspects.

    PubMed

    Eren, Necla Mine; Santos, Paulo H S; Campanella, Osvaldo

    2015-12-10

    Xanthan gum solutions were treated with high-pressure homogenization (HPH) in order to provide alternative treatments to enzymatic and chemical modification of this carbohydrate. Rheological properties of the treated and control samples were investigated in detail to gain an understanding of functional consequences of physical modification. The molecular structural properties were investigated via Size exclusion chromatography (SEC) coupled with Multi-angle laser light scattering (MALLS) and Circular dichroism (CD). Structured network of xanthan gum solutions was lost gradually depending on the severity of the HPH treatment as evidenced by the observed changes in the viscosity and viscoelasticity of the treated solutions. Reduction in molecular weight and a significant increase in polydispersity of the polymer were the expected causes of these rheological changes. Observed increase in hydrodynamic volume upon HPH treatment was not surprising and attributed to the loss of structured networks. Changes in the rheological and structural characteristics of biopolymer were irreversible and significant recovery was not detected over a period of 11 weeks. PMID:26428149

  5. Hanford Waste Physical and Rheological Properties: Data and Gaps

    SciTech Connect

    Kurath, Dean E.; Wells, Beric E.; Huckaby, James L.; Mahoney, Lenna A.; Daniel, Richard C.; Burns, Carolyn A.; Tingey, Joel M.; Cooley, Scott K.

    2012-03-01

    The retrieval, transport, treatment and disposal operations associated with Hanford Tank Wastes involve the handling of a wide range of slurries. Knowledge of the physical and rheological properties of the waste is a key component to the success of the design and implementation of the waste processing facilities. Previous efforts to compile and analyze the physical and rheological properties were updated with new results including information on solids composition and density, particle size distributions, slurry rheology, and particle settling behavior. The primary source of additional data is from a recent series of tests sponsored by the Hanford Waste Treatment and Immobilization Plant. These tests involved an extensive suite of characterization and bench-scale process testing of 8 waste groups representing approximately 75% of the high-level waste mass expected to be processed through the WTP. Additional information on the morphology of the waste solids was also included. Based on the updated results, a gap analysis to identify gaps in characterization data, analytical methods and data interpretation was completed.

  6. The effect of temperature on rheological properties of endodontic sealers

    PubMed Central

    Rai, Roshni U.; Singbal, Kiran P.; Parekh, Vaishali

    2016-01-01

    Aim: The purpose of this study was to investigate temperature-dependent rheological properties of three endodontic sealers MTA Fillapex (Angelus, Brazil), AH Plus (Dentsply, Germany), and EndoREZ (Ultradent, USA). Materials and Methods: Five samples of each group of endodontic sealers (n = 30) were freshly mixed and placed on the plate of a rheometer (MCR 301, AntonPaar, Physica) and examined at 25°C and 37°C temperature, respectively. Rheological properties of the sealers were calculated according to the loss modulus (G″), storage modulus (G′), loss factor (Tan δ), and complex viscosity (η*) using dynamic oscillatory shear tests. Results: Statistical analysis (Wilcoxon signed-rank test) demonstrated that MTA Fillapex exhibited higher loss modulus (G″ > G′) and a crossover region. AH Plus and EndoREZ had a higher storage modulus (G′ > G″) at both temperatures. Loss factor (Tan δ) of MTA Fillapex was the highest compared to AH Plus, followed by EndoREZ. With a temperature change from 25°C to 37°C, MTA Fillapex exhibited a decrease while AH Plus exhibited an increase and, EndoREZ exhibited the least change, in complex viscosity (η*). Conclusions: EndoREZ exhibited better rheological properties compared to the other two test sealers. PMID:27099414

  7. Recent Advances in High Pressure and Temperature Rheological Studies

    SciTech Connect

    Wang, Yanbin; Hilairet, Nadege; Dera, Przemyslaw

    2012-01-20

    Rheological studies at high pressure and temperature using in-situ X-ray diffraction and imaging have made significant progresses in recent years, thanks to a combination of recent developments in several areas: (1) advances in synchrotron X-ray techniques, (2) advances in deformation devices and the abilities to control pressure, temperature, stress, strain and strain rates, (3) theoretical and computational advances in stress determination based on powder and single crystal diffraction, (4) theoretical and computational advances in modeling of grain-level micromechanics based on elasto-plastic and visco-plastic self-consistent formulations. In this article, we briefly introduce the experimental techniques and theoretical background for in-situ high pressure, high temperature rheological studies, and then review recent studies of rheological properties of major mantle materials. Some currently encountered issues have prompted developments in single-crystal quasi-Laue diffraction for complete stress tensor determination and textural evolution of poly-phased composites based on X-ray microtomography. Future prospects are discussed.

  8. Current Progress in Rheology of Cellulose Nanofibril Suspensions.

    PubMed

    Nechyporchuk, Oleksandr; Belgacem, Mohamed Naceur; Pignon, Frédéric

    2016-07-11

    Cellulose nanofibrils (CNFs) are produced and commonly used in the form of aqueous suspensions or gels. A number of studies have focused lately on rheological properties of CNF suspensions, which gives insight into properties of such materials and can reflect their behavior during handling. This Review summarizes the recent progress in rheological studies on CNF aqueous suspensions using rotational rheometry. Here, we discuss linear viscoelastic properties, i.e., frequency-dependent storage and loss moduli; shear flow behavior, i.e., apparent viscosity and shear stress as a function of shear rate; local flow characteristics, etc. In this Review, we point out that the rheological behavior of at least two types of CNF suspensions should be distinguished: (i) ones produced using mechanical fibrillation with or without enzymatic pretreatment (no surface chemical modification), which possess highly flocculated structure, and (ii) ones produced involving chemical modification pretreatments, e.g., carboxylation, carboxymethylation, quaternization, or sulfonation, which possess better colloidal stability and do not evidently flocculate. PMID:27310523

  9. Shear History Extensional Rheology Experiment: A Proposed ISS Experiment

    NASA Technical Reports Server (NTRS)

    Hall, Nancy R.; Logsdon, Kirk A.; Magee, Kevin S.

    2007-01-01

    The Shear History Extensional Rheology Experiment (SHERE) is a proposed International Space Station (ISS) glovebox experiment designed to study the effect of preshear on the transient evolution of the microstructure and viscoelastic tensile stresses for monodisperse dilute polymer solutions. Collectively referred to as Boger fluids, these polymer solutions have become a popular choice for rheological studies of non-Newtonian fluids and are the non-Newtonian fluid used in this experiment. The SHERE hardware consists of the Rheometer, Camera Arm, Interface Box, Cabling, Keyboard, Tool Box, Fluid Modules, and Stowage Tray. Each component will be described in detail in this paper. In the area of space exploration, the development of in-situ fabrication and repair technology represents a critical element in evolution of autonomous exploration capability. SHERE has the capability to provide data for engineering design tools needed for polymer parts manufacturing systems to ensure their rheological properties have not been impacted in the variable gravity environment and this will be briefly addressed.

  10. Patient-specific blood rheology in sickle-cell anaemia.

    PubMed

    Li, Xuejin; Du, E; Lei, Huan; Tang, Yu-Hang; Dao, Ming; Suresh, Subra; Karniadakis, George Em

    2016-02-01

    Sickle-cell anaemia (SCA) is an inherited blood disorder exhibiting heterogeneous cell morphology and abnormal rheology, especially under hypoxic conditions. By using a multiscale red blood cell (RBC) model with parameters derived from patient-specific data, we present a mesoscopic computational study of the haemodynamic and rheological characteristics of blood from SCA patients with hydroxyurea (HU) treatment (on-HU) and those without HU treatment (off-HU). We determine the shear viscosity of blood in health as well as in different states of disease. Our results suggest that treatment with HU improves or worsens the rheological characteristics of blood in SCA depending on the degree of hypoxia. However, on-HU groups always have higher levels of haematocrit-to-viscosity ratio (HVR) than off-HU groups, indicating that HU can indeed improve the oxygen transport potential of blood. Our patient-specific computational simulations suggest that the HVR level, rather than the shear viscosity of sickle RBC suspensions, may be a more reliable indicator in assessing the response to HU treatment. PMID:26855752

  11. The Rheology and Processing of Renewable Resource Polymers

    NASA Astrophysics Data System (ADS)

    Conrad, Jason D.; Harrison, Graham M.

    2008-07-01

    Bio-based polymers offer an alternative to conventional fossil fuel-based materials, in particular for commodity applications such as single-use products. In this work, we report on the rheology and processing of two bio-based polymers, namely poly-hydroxyalkanoate (PHA) copolymers and poly-lactic acid (PLA), and their blends. These materials are derived from renewable resources, and can degrade under the appropriate conditions. The rheology is investigated in shear, elongation, and transient modes. Of particular importance is the degradation of these materials at typical processing conditions, and the impact of polymer architecture on the extensional properties. Using results from these rheological investigations, appropriate thermal and flow conditions are employed in a DSM Xplore microcompounder, with the cast film attachment, to produce films of PHA copolymers blended with PLA. The resultant films are characterized, as a function of both material composition and processing history, using DSC, WAXD, tensile testing, and SEM, to investigate the effect of varying PHA content on the final properties.

  12. Non-local rheology for dense granular flows in avalanches

    NASA Astrophysics Data System (ADS)

    Izzet, Adrien; Clement, Eric; Andreotti, Bruno

    A local constitutive relation was proposed to describe dense granular flows (GDR MiDi, EPJE 2004). It provides a rather good prediction of the flowing regime but does not foresee the existence of a ``creep regime'' as observed by Komatsu et al. (PRL 2001). In the context of a 2D shear cell, a relaxation length for the velocity profile was measured (Bouzid et al., PRL 2013) which confirmed the existence of a flow below the standard Coulomb yield threshold. A correction for the local rheology was proposed. To test further this non-local constitutive relation, we built an inclined narrow channel within which we monitor the flow from the side. We managed to observe the ``creep regime'' over five orders of magnitude in velocity and fit the velocity profiles in the depth with an asymptotic solution of the non-local equation. However, the boundary condition at the free surface needs to be selected in order to calibrate the non-local rheology over the whole range of stresses in the system. In this perspective, we complement the experimental results with 2D simulations of hard and frictional discs on an inclined plane in which we introduce a surface friction force proportional to the effective pressure in the granular. We analyze these results in the light of the non-local rheology.

  13. Rheological properties of kaolin and chemically simulated waste

    SciTech Connect

    Selby, C.L.

    1981-12-01

    The Savannah River Laboratory is conducting tests to determine the best operating conditions of pumps used to transfer insoluble radioactive sludges from old to new waste tanks. Because it is not feasible to conduct these tests with real or chemically simulated sludges, kaolin clay is being used as a stand-in for the solid waste. The rheology tests described herein were conducted to determine whether the properties of kaolin were sufficiently similar to those of real sludge to permit meaningful pump tests. The rheology study showed that kaolin can be substituted for real waste to accurately determine pump performance. Once adequately sheared, kaolin properties were found to remain constant. Test results determined that kaolin should not be allowed to settle more than two weeks between pump tests. Water or supernate from the waste tanks can be used to dilute sludge on an equal volume basis because they identically affect the rheological properties of sludge. It was further found that the fluid properties of kaolin and waste are insensitive to temperature.

  14. Investigating the rheological properties of native plant latex

    PubMed Central

    Bauer, Georg; Friedrich, Christian; Gillig, Carina; Vollrath, Fritz; Speck, Thomas; Holland, Chris

    2014-01-01

    Plant latex, the source of natural rubber, has been of interest to mankind for millennia, with much of the research on its rheological (flow) properties focused towards industrial application. However, little is known regarding the rheology of the native material as produced by the plant, a key factor in determining latex's biological functions. In this study, we outline a method for rheological comparison between native latices that requires a minimum of preparatory steps. Our approach provides quantitative insights into the coagulation mechanisms of Euphorbia and Ficus latex allowing interpretation within a comparative evolutionary framework. Our findings reveal that in laboratory conditions both latices behave like non-Newtonian materials with the coagulation of Euphorbia latex being mediated by a slow evaporative process (more than 60 min), whereas Ficus appears to use additional biochemical components to increase the rate of coagulation (more than 30 min). Based on these results, we propose two different primary defensive roles for latex in these plants: the delivery of anti-herbivory compounds (Euphorbia) and rapid wound healing (Ficus). PMID:24173604

  15. Instructional Architecture for Teaching Past and Past Participle Verb Forms.

    ERIC Educational Resources Information Center

    Cronnell, Bruce

    Noting that using correct verb forms is a problem for many elementary school students, and especially for those who are speakers of nonstandard English, this paper presents an instructional program for teaching past and past participle verb forms in writing to students in grade 3 through 6. The paper outlines the content of the instructional…

  16. The shear dependence of the methylcellulose gelation phenomena in aqueous solution and in ceramic paste.

    PubMed

    Knarr, Matthias; Bayer, Roland

    2014-10-13

    The gelation temperature of methylcellulose (MC) in aqueous solutions as well as in aqueous ceramic paste depends on the applied shear. Rheological investigations in oscillation vs. shear mode show lower gelation temperature at low shear rates as for the corresponding angular frequencies. Above a critical shear rate the gelation temperature is shifted to higher temperatures. The paste extrusion process uses MC as a plasticizer and runs under high shear conditions. When extruding close to the gelation temperature of the MC in the paste, crack formation and other defects can occur. The upwards shift of the gelation temperature with increasing applied shear gives a larger temperature window during the extrusion process. The understanding of the shear influence on the gelation temperature is important to design the optimal process conditions. PMID:25037332

  17. Lithospheric thermal structure and rheology of the eastern China

    NASA Astrophysics Data System (ADS)

    Wang, Yang; Cheng, Su-Hua

    2012-03-01

    Temperature distributions of the lithosphere beneath the eastern China were estimated by local isostasy equilibrium constrained geothermal calculation in this study. Maps of the lateral temperature variation at depths of 50 and 100 km as well as Moho boundary are presented for the eastern China continent, and the 600 °C and 1100 °C isotherm depth maps are also given. Meanwhile, the thermal thickness of lithosphere is calculated as the depth of 1350 °C isotherm. The rheological strength of lithosphere is calculated based on a four-layer model, which consists of the upper, lower, lowermost crust layers and a wet lithospheric mantle layer. The results show that, the lithosphere of 160-180 km thick exists under Sichuan basin in the western part of Yangtze Craton, but keel is absent beneath the entire North China Craton. It is notable that the lithospheric thickness is only 130-140 km beneath Ordos basin in the western part of North China Craton; accordingly, there is no lithospheric keel beneath Ordos basin. These geothermal modeling results are in good agreement with those of seismic tomography and other geothermal studies. The temperatures in the lower crust of the North China Craton estimated are in range of 500-600 °C. Consequently, the composition of lower crust of the North China Craton should be more mafic than that of previous estimation based on much cooler geotherms. The spatial variation of lithospheric rheology in the eastern China is influenced by local geotherms and crustal compositions. The "crème brûlée" model, which is represent by a strong crust portion but a weak lithospheric mantle portion in vertical strength profile, approximates the lithospheric rheological layering for the regions of the western half of North China Craton and the northern part of NE China, which has thicker crust or moderate-to-high geotherm. On the other hand, the "jelly sandwich" model demonstrates the rheological layering of the western part of the Yangtze Craton and

  18. Rheological and dielectric properties of different gold nanoparticle sizes

    PubMed Central

    2011-01-01

    Background Gold nanoparticles (GNPs) have found themselves useful for diagnostic, drug delivery and biomedicine applications, but one of the important concerns is about their safety in clinical applications. Nanoparticle size has been shown to be an extremely important parameter affecting the nanoparticle uptake and cellular internalization. The rheological properties assume to be very important as it affects the pressure drop and hence the pumping power when nano-fluids are circulated in a closed loop. The rheological and dielectric properties have not been documented and identified before. The aim of the present study was to investigate the rheology and the dielectric properties of different GNPs sizes in aqueous solution. Methods 10, 20 and 50 nm GNPs (Product MKN-Au, CANADA) was used in this study. The rheological parameters were viscosity, torque, shear stress, shear rate, plastic viscosity, yield stress, consistency index, and activation energy. These rheological parameters were measured using Brookfield LVDV-III Programmable rheometer supplied with temperature bath and controlled by a computer. Results The shear stress and shear rate of GNPs have shown a linear relationship and GNPs exhibited Newtonian behaviour. The GNPs with larger particle size (50 nm) exhibited more viscosity than those with smaller particle sizes (10 and 20 nm). Viscosity decreased with increasing the temperature for all the examined GNP sizes. The flow behaviour index (n) values were nearly ≤ 1 for all examined GNP sizes. Dielectric data indicated that the GNPs have strong dielectric dispersion in the frequency range of 20-100 kHz. The conductivity and relaxation time decreased with increasing the GNP size. Conclusions This study indicates that the GNP size has considerable influence on the viscosity of GNPs. The strong dielectric dispersion was GNP size dependent. The decrease in relaxation time might be attributed to increase in the localized charges distribution within the medium

  19. UNDERSTANDING THE EFFECTS OF SURFACTANT ADDITION ON RHEOLOGY USING LASER SCANNING CONFOCAL MICROSCOPY

    SciTech Connect

    White, T

    2007-05-08

    The effectiveness of three dispersants to modify rheology was examined using rheology measurements and laser scanning confocal microscopy (LSCM) in simulated waste solutions. All of the dispersants lowered the yield stress of the slurries below the baseline samples. The rheology curves were fitted reasonably to a Bingham Plastic model. The three-dimensional LSCM images of simulants showed distinct aggregates were greatly reduced after the addition of dispersants leading to a lowering of the yield stress of the simulated waste slurry solutions.

  20. Using natural laboratories and modeling to decipher lithospheric rheology

    NASA Astrophysics Data System (ADS)

    Sobolev, Stephan

    2013-04-01

    Rheology is obviously important for geodynamic modeling but at the same time rheological parameters appear to be least constrained. Laboratory experiments give rather large ranges of rheological parameters and their scaling to nature is not entirely clear. Therefore finding rheological proxies in nature is very important. One way to do that is finding appropriate values of rheological parameter by fitting models to the lithospheric structure in the highly deformed regions where lithospheric structure and geologic evolution is well constrained. Here I will present two examples of such studies at plate boundaries. One case is the Dead Sea Transform (DST) that comprises a boundary between African and Arabian plates. During the last 15- 20 Myr more than 100 km of left lateral transform displacement has been accumulated on the DST and about 10 km thick Dead Sea Basin (DSB) was formed in the central part of the DST. Lithospheric structure and geological evolution of DST and DSB is rather well constrained by a number of interdisciplinary projects including DESERT and DESIRE projects leaded by the GFZ Potsdam. Detailed observations reveal apparently contradictory picture. From one hand widespread igneous activity, especially in the last 5 Myr, thin (60-80 km) lithosphere constrained from seismic data and absence of seismicity below the Moho, seem to be quite natural for this tectonically active plate boundary. However, surface heat flow of less than 50-60mW/m2 and deep seismicity in the lower crust ( deeper than 20 km) reported for this region are apparently inconsistent with the tectonic settings specific for an active continental plate boundary and with the crustal structure of the DSB. To address these inconsistencies which comprise what I call the "DST heat-flow paradox", a 3D numerical thermo-mechanical model was developed operating with non-linear elasto-visco-plastic rheology of the lithosphere. Results of the numerical experiments show that the entire set of

  1. Rheological and Tribological Properties of Complex Biopolymer Solutions

    NASA Astrophysics Data System (ADS)

    Klossner, Rebecca Reese

    2011-12-01

    The rheological and tribological properties of an experimental synovial fluid model were investigated in order to determine the solution dynamics of the three most abundant macromolecules present in synovial fluid, the fluid that lubricates freely moving (synovial) joints. These components, hyaluronic acid (HA) and the plasma proteins, albumin and gamma-globulins are combined in a phosphate buffered saline solution (PBS) and subjected to steady shear rheology testing, as well as nanoindenter-based scratch testing, which allows for the study of the lubrication properties of the experimental synovial fluid model. Steady shear experiments, where the shear rate was increased from low to high, and then decreased from high to low, showed hysteresis in only protein containing solutions, whereas samples of HA in PBS behaved as a "typical" polyelectrolyte in solution. Subsequent rheological experiments on the synovial fluid model exhibited an increase in viscosity at low shear stresses, indicating that a structure was present at these low shear stresses, which was not found at higher shear stresses. This result is in agreement with studies conducted on the same model which show unusual rheological behavior at low shear rates. Low shear stresses can cause modifications to the external protein surface, resulting in their unfolding and creating many opportunities for the molecules to reorder themselves. As the proteins reorder themselves, the newly exposed hydrophobic patches will have a tendency to aggregate together, creating a network within the fluid, and, in turn causing the observed increased viscosity at low shear stresses. Additionally, an anti-inflammatory drug, hydroxychloroquine (HCQ) was added to the solutions. This addition diminishes the protein aggregation process substantially. Finally, the HA component of the synovial fluid model was replaced with a neutral polymer in order to examine the role of HA in synovial fluid. As suspected, the HA appears to have

  2. In situ Rheological Measurements at Extreme Pressure and Temperature using Synchrotron X-ray Diffraction and Radiography

    SciTech Connect

    Raterron, P.; Merkel, S

    2009-01-01

    Dramatic technical progress seen over the past decade now allows the plastic properties of materials to be investigated under extreme pressure and temperature conditions. Coupling of high-pressure apparatuses with synchrotron radiation significantly improves the quantification of differential stress and specimen textures from X-ray diffraction data, as well as specimen strains and strain rates by radiography. This contribution briefly reviews the recent developments in the field and describes state-of-the-art extreme-pressure deformation devices and analytical techniques available today. The focus here is on apparatuses promoting deformation at pressures largely in excess of 3 GPa, namely the diamond anvil cell, the deformation-DIA apparatus and the rotational Drickamer apparatus, as well as on the methods used to carry out controlled deformation experiments while quantifying X-ray data in terms of materials rheological parameters. It is shown that these new techniques open the new field of in situ investigation of materials rheology at extreme conditions, which already finds multiple fundamental applications in the understanding of the dynamics of Earth-like planet interior.

  3. Influence of Wheat-Milled Products and Their Additive Blends on Pasta Dough Rheological, Microstructure, and Product Quality Characteristics

    PubMed Central

    Dhiraj, B.; Prabhasankar, P.

    2013-01-01

    This study is aimed to assess the suitability of T. aestivum wheat milled products and its combinations with T. durum semolina with additives such as ascorbic acid, vital gluten and HPMC (Hydroxypropyl methyl cellulose) for pasta processing quality characteristics such as pasta dough rheology, microstructure, cooking quality, and sensory evaluation. Rheological studies showed maximum dough stability in Comb1 (T. aestivum wheat flour and semolina). Colour and cooking quality of Comb2 (T. durum semolina and T. aestivum wheat flour) and Comb3 (T. aestivum wheat semolina and T. durum semolina) were comparable with control. Pasting results indicated that T. aestivum semolina gave the lowest onset gelatinization temperature (66.9°C) but the highest peak viscosity (1.053 BU). Starch release was maximum in Comb1 (53.45%) when compared with control (44.9%) as also proved by microstructure studies. Firmness was seen to be slightly high in Comb3 (2.430 N) when compared with control (2.304 N), and sensory evaluations were also in the acceptable range for the same. The present study concludes that Comb3 comprising 50% T. durum semolina and 50% T. aestivum refined wheat flour with additives would be optimal alternate for 100% T. durum semolina for production of financially viable pasta. PMID:26904601

  4. Phonological Priming and Irregular Past

    ERIC Educational Resources Information Center

    Stemberger, Joseph Paul

    2004-01-01

    It has been shown that the processing of irregular past-tense forms is affected by phonological factors that are inherent in the relationship of the past-tense forms to other words in the lexicon (rhyming families of irregulars) or to their base forms (vowel dominance effects). This paper addresses more ephemeral phonological effects. In a…

  5. Biodiversity: past, present, and future

    NASA Technical Reports Server (NTRS)

    Sepkoski, J. J. Jr; Sepkoski JJ, J. r. (Principal Investigator)

    1997-01-01

    Data from the fossil record are used to illustrate biodiversity in the past and estimate modern biodiversity and loss. This data is used to compare current rates of extinction with past extinction events. Paleontologists are encouraged to use this data to understand the course and consequences of current losses and to share this knowledge with researchers interested in conservation and ecology.

  6. Constraints on the mantle and lithosphere dynamics from the observed geoid with the effect of visco-elasto-plastic rheology in the upper 300 km

    NASA Astrophysics Data System (ADS)

    Osei Tutu, Anthony; Steinberger, Bernhard; Rogozhina, Irina; Sobolev, Stephan

    2015-04-01

    Over the past decades rheological properties of the Earth's mantle and lithosphere have been extensively studied using numerical models calibrated versus a range of surface observations (e.g., free-air-gravity anomaly/geoid, dynamic topography, plate velocity, etc.).The quality of model predictions however strongly depends on the simplifying assumptions, spatial resolution and parameterizations adopted by numerical models. The geoid is largely (Hager & Richards, 1989) determined by both the density anomalies driving the mantle flow and the dynamic topography at the Earth surface and the core-mantle boundary. This is the effect of the convective processes within the Earth's mantle. The remainder is mostly due to strong heterogeneities in the lithospheric mantle and the crust, which also need to be taken into account. The surface topography caused by density anomalies both in the sub-lithospheric mantle and within the lithosphere also depends on the lithosphere rheology. Here we investigate the effects of complex lithosphere rheology on the modelled dynamic topography, geoid and plate motion using a spectral mantle flow code (Hager & O'Connell, 1981) considering radial viscosity distribution and a fully coupled code of the lithosphere and mantle accounting for strong heterogeneities in the upper mantle rheology in the 300 km depths (Popov & Sobolev, 2008). This study is the first step towards linking global mantle dynamics with lithosphere dynamics using the observed geoid as a major constraint. Here we present the results from both codes and compare them with the observed geoid, dynamic topography and plate velocities from GPS measurements. This method allows us to evaluate the effects of plate rheology (e.g., strong plate interiors and weak plate margins) and stiff subducted lithosphere on these observables (i.e. geoid, topography, plate boundary stresses) as well as on plate motion. This effort will also serve as a benchmark of the two existing numerical methods

  7. Rheological and microstructural properties of porcine gastric digesta and diets containing pectin or mango powder.

    PubMed

    Wu, Peng; Dhital, Sushil; Williams, Barbara A; Chen, Xiao Dong; Gidley, Michael J

    2016-09-01

    Hydrated polysaccharides and their assemblies are known to modulate gastric emptying rate due to their capacity to change the structural and rheological properties of gastric contents (digesta). In the present study, we investigated the rheological and microstructural properties of gastric digesta from pigs fed with diets incorporating mango powder or pectin, and compared results with those from hydrated diets of the same water content, in order to investigate the origins for rheological changes in the pig stomach. All of the hydrated diets and gastric digesta were particle-dominated suspensions, generally showing weak gel or more solid-like behavior with the storage modulus (G') always greater than loss modulus (G") under small deformation oscillatory measurements, and with small deformation viscosity greater than steady shear viscosity (i.e. non-Cox-Merz superposition). Although significant rheological differences were observed between the hydrated diets, rheological parameters for gastric digesta were similar for all diets, indicative of a rheological homeostasis in the pig stomach. Whilst the addition of gastric mucin (20mg/mL) to control and mango diets altered the rheology to match the gastric digesta rheology, the effect of mucin on the pectin-containing diet was negligible. The viscous effect of pectin also hindered the action of alpha amylase as observed from relatively less damaged starch granules in pectin digesta compared to mango and control digesta. Based on the experimental findings that the rheology of gastric digesta differs from hydrated diets of the same water content, the current study revealed composition-dependent complex behavior of gastric digesta in vivo, suggesting that the rheology of food products or ingredients may not necessarily reflect the rheological effect when ingested. PMID:27185134

  8. Structure and rheology of associative triblocks in microemulsion solutions

    NASA Astrophysics Data System (ADS)

    Bhatia, Surita Rani

    This thesis describes our theoretical and experimental work on the rheology, static structure, and phase behavior of associative solutions. Our theoretical efforts have centered on solving the diffusion equation model of Dolan and Edwards for ideal associative triblocks between surfaces to yield the segment density profile and free energy. We have shown that polymers between two spheres cause an O(kT) attraction, similar to that calculated by Milner and Witten for associative polymer brushes between flat plates. The attraction we calculate is weaker than that given by the Derjaguin approximation, and excluded volume moderates the attraction and softens the repulsion between spheres. The free energy was used to estimate an interparticle potential, which in turn was used to compute structure factors for solutions of associative polymers via Monte Carlo simulations. As a model system for our experiments, we have chosen PEO-PI-PEO triblocks in an AOT/water/decane microemulsion. Upon dilution with decane, the solutions phase separate into a dense, high viscosity phase and a dilute, low viscosity phase. We have performed both small-angle neutron scattering (SANS) and rheology on these solutions. Structure factors derived from our SANS data agree fairly well with those predicted by our theory and indicate that the droplets reside in an attractive minimum. The rheology of these solutions shows several interesting features that are not predicted by classical reversible network theory. Data from oscillatory experiments indicate a single relaxation time at low polymer concentrations but show evidence of a slower relaxation for higher concentrations. In addition, some solutions exhibit a maximum in the high shear viscosity. Some of our observations are predicted by the flowerlike micelle theory developed by Semenov and co-workers; however, our data is not completely consistent with the theoretical predictions. The high frequency modulus scales roughly quadratically with

  9. Shear and effective elongational rheology and polymer molecular characteristics

    NASA Astrophysics Data System (ADS)

    Wei, Xiaoling

    Extensional deformations play a significant role in many processing operations which involve a rapid change of shape such as fiber spinning, film blowing, blow molding, and nonwoven melt processing. To develop real time, on-line process and quality control analysis in these operations, knowledge of the molecular weight (MW) and molecular weight distribution (MWD), effects of molecular characteristics and processing conditions on the elongational rheology, and orientation of polymeric materials in these operations is essential. In this work, shear rheology of six polyethylenes (PE), one polyisobutylene (PIB), and five cellulose solutions was measured at different temperatures using a rotational rheometer. Effective elongational viscosity of polyethylenes and polyisobutylene was also measured at different Hencky strains and temperatures using a capillary rheometer by replacing the capillary cylindrical die with a hyperbolic converging die. The hyperbolic shape of the dies establishes a purely elongational flow field at a constant elongational strain rate throughout the die. The effect of molecular characteristics such as MW, MWD, and long chain branches and the processing conditions such as temperature and Hencky strain on the elongational rheology of PE and PIB samples was studied. The results from the hyperbolic dies were compared with results from other techniques, namely Rheometrics Extensional Rheometer (RER) and Elongational Rheometer for Melts (RME). Good master curves were generated for the temperature and Hencky strain shifting, and simultaneous shifting with respect to both temperature and Hencky strain. The enthalpy and entropy changes were calculated from the effective elongational and shear viscosities to investigate flow induced orientation of the polymer melts in hyperbolic dies. The enthalpy and entropy changes increase in magnitude with higher elongational strain rate and higher Hencky strain. The storage and loss moduli were used to determine and

  10. Rheology and phase behavior of dense casein micelle dispersions

    NASA Astrophysics Data System (ADS)

    Bouchoux, A.; Debbou, B.; Gésan-Guiziou, G.; Famelart, M.-H.; Doublier, J.-L.; Cabane, B.

    2009-10-01

    Casein micelle dispersions have been concentrated through osmotic stress and examined through rheological experiments. In conditions where the casein micelles are separated from each other, i.e., below random-close packing, the dispersions have exactly the flow and dynamic properties of the polydisperse hard-sphere fluid, demonstrating that the micelles interact only through excluded volume effects in this regime. These interactions cause the viscosity and the elastic modulus to increase by three orders of magnitude approaching the concentration of random-close packing estimated at Cmax≈178 g/l. Above Cmax, the dispersions progressively turn into "gels" (i.e., soft solids) as C increases, with elastic moduli G' that are nearly frequency independent. In this second regime, the micelles deform and/or deswell as C increases, and the resistance to deformation results from the formation of bonds between micelles combined with the intrinsic mechanical resistance of the micelles. The variation in G' with C is then very similar to that observed with concentrated emulsions where the resistance to deformation originates from a set of membranes that separate the droplets. As in the case of emulsions, the G' values at high frequency are also nearly identical to the osmotic pressures required to compress the casein dispersions. The rheology of sodium caseinate dispersions in which the caseins are not structured into micelles is also reported. Such dispersions have the behavior of associative polymer solutions at all the concentrations investigated, further confirming the importance of structure in determining the rheological properties of casein micelle systems.

  11. Modeling of craton stability using a viscoelastic rheology

    NASA Astrophysics Data System (ADS)

    Beuchert, Marcus; Podladchikov, Yuri; Simon, Nina; Rüpke, Lars

    2010-05-01

    Archean cratons belong to the most remarkable features of our planet, since they represent continental crust that has avoided reworking for several billions of years. Even more, it has become evident from both geophysical and petrological studies that cratons exhibit deep lithospheric keels which equally remained stable ever since the formation of the cratons in the Archean. Dating of inclusions in diamonds from kimberlite pipes give Archean ages, showing that the Archean lithosphere must have been cold soon after its formation in the Archean, in order to allow for the existence of diamonds, and must have stayed in that state ever since. Yet, whereas the stability of Archean cratonic lithosphere for billions of years is a fact, some numerical models failed to reproduce this observed long-term stability (see review by King, 2005). We devised a viscoelastic mantle convection model for exploring cratonic stability. Our modeling results indicate that the application of sufficiently high temperature-dependent viscosity ratio can provide for the observed cratonic stability for billions of years. From our numerical simulations, we derived a relation between Rayleigh number, viscosity ratio, size of the model craton and time to instability of the cratonic root. The comparison between simulations with viscous and viscoelastic rheology indicates no significant influence of elasticity on craton stability. Yet, stress distributions within the model craton differ significantly between viscous and viscoelastic rheologies. This has important implications for future models that include stress-dependent processes like plasticity, power law creep and shear heating. If those processes are to be modeled accurately in mantle convection models that include the lithosphere, a viscoelastic rheology would have to be applied.

  12. Rheological and thermal properties of polylactide/silicate nanocomposites films.

    PubMed

    Ahmed, Jasim; Varshney, Sunil K; Auras, Rafeal

    2010-03-01

    Polylactide (DL)/polyethylene glycol/silicate nanocomposite blended biodegradable films have been prepared by solvent casting method. Rheological and thermal properties were investigated for both neat amorphous polylactide (PLA-DL form) and blend of montmorillonite (clay) and poly (ethylene glycol) (PEG). Melt rheology of the PLA individually and blends (PLA/clay; PLA/PEG; PLA/PEG/clay) were performed by small amplitude oscillation shear (SAOS) measurement. Individually, PLA showed an improvement in the viscoelastic properties in the temperature range from 180 to 190 degrees C. Incorporation of nanoclay (3% to 9% wt) was attributed by significant improvements in the elastic modulus (G') of PLA/clay blend due to intercalation at higher temperature. Both dynamic modulii of PLA/PEG blend were significantly reduced with addition of 10% PEG. Rheometric measurement could not be conducted while PLA/PEG blends containing 25% PEG. A blend of PLA/PEG/clay (68/23/9) showed liquid-like properties with excellent flexibility. Thermal analysis of different clay loading films indicated that the glass transition temperatures (T(g)) remained unaffected irrespective of clay concentration due to immobilization of polymer chain in the clay nanocomposite. PEG incorporation reduced the T(g) of the blend (PLA/PEG and PLA/PEG/clay) significantly. Both rheological and thermal analysis data supported plasticization and flexibility of the blended films. It is also interesting to study competition between PLA and PEG for the intercalation into the interlayer spacing of the clay. This study indicates that PLA/montmorillonite blend could serve as effective nano-composite for packaging and other applications. PMID:20492249

  13. Foam rheology: A model of viscous effects in shear flow

    SciTech Connect

    Kraynik, A.M.; Reinelt, D.A.

    1988-01-01

    Foams consisting of gas bubbles dispersed in a continuous network of thin liquid films display a remarkable range of rheological characteristics that include a finite shear modulus, yield stress, non-Newtonian viscosity, and slip at the wall. Progress in developing micromechanical theories to describe foam rheology has depended upon two-dimensional models, which in most cases are assumed to have perfectly ordered structure. Princen accounted for surface tension and geometrical effects, and analyzed the nonlinear elastic response of a spatially periodic foam in simple shear. His analysis has been extended to account for more general deformations. Khan and Armstrong and Kraynik and Hansen have proposed ad hoc models for viscous effects in foam rheology. Their models capture numerous qualitative phenomena but incorporate relaxation mechanisms based upon overly simplified assumptions of liquid flow in the thin films. Mysels, Shinoda, and Frankel considered soap films with interfaces that are inextensible due to the presence of surfactants. They analyzed the primary flow that occurs when such films are slowly withdrawn from or recede into essentially static junction regions such as the Plateau borders in a foam. Adopting this mechanism, Schwartz and Princen considered small periodic deformations of a foam and calculated the energy dissipation due to viscous flow in the thin films. In the following, we also adopt the basic interfacial and viscous mechanisms introduced by Mysels et al. and analyze simple shearing deformations of finite amplitude. The configuration and effective stress of the foam are determined. Under these deformation conditions, the foam is a nonlinear viscoelastic material. Results for the uniform expansion of a foam are also presented. 11 refs., 3 figs.

  14. Heat transfer and Rheological behavior of nanoparticle compound microencapsulated phase change material suspensions

    NASA Astrophysics Data System (ADS)

    Wang, L.; Lin, G. P.; Ding, Y. L.

    2010-03-01

    Addition of microencapsulated phase change materials (MPCM) have been used for enhance the heat transfer of fluids because of the large latent heat during the phase change period of particles. However low thermal conductivity of phase change material diminishes the heat transfer performance of the fluid partially. In the past decade, significant enhancements of nanofluids on the enhancement of thermal conductivity and convective heat transfer were observed in comparison with the base fluids. To improve the thermal conductivity of MPCM suspensions, the additive nanoparticles were used to formulate a novel thermal fluid—nanoparticle compound microencapsulated phase change material suspensions were formulated. The rheology measurements shows that such suspensions are Newtonian fluids at the shear rate of 5-500s-1 and the shear viscosities depend strongly on temperature. Experimental investigations were conducted on the laminar convective heat transfer characteristic of the nanoparticle compound MPCM suspensions in a vertical circular tube with 0.5% TiO2 nanoparticles and various MPCM mass concentrations ranging from 5%-20%. The results exhibit that the convective heat transfer performance of nanoparticle compound MPCM suspensions are significantly improved in comparison of the MPCM suspensions and this enhancement increases with the increasing of the MPCM concentration, the modified Nusselt number can be improved by 27.0% for MPCM concentration of 20 wt%.

  15. Evaluation of rheological, bioactives and baking characteristics of mango ginger (curcuma amada) enriched soup sticks.

    PubMed

    Crassina, K; Sudha, M L

    2015-09-01

    Wheat flour was replaced with mango ginger powder (MGP) at 0, 5, 10 and 15 %. Influence of MGP on rheological and baking characteristics was studied. Farinograph was used to study the mixing profile of wheat flour-MGP blend. Pasting profile of the blends namely gelatinization and retrogradation were carried out using micro-visco-amylograph. Test baking was done to obtain the optimum level of replacement and processing conditions. Sensory attributes consisting texture, taste, overall quality and breaking strength were assessed. Nutritional characterization of the soup sticks in terms of protein and starch in vitro digestibility, dietary fiber, minerals, polyphenols and antioxidant activity were determined using standard methods. With the increasing levels of MGP from 0 to 15 %, the farinograph water absorption increased from 60 to 66.7 %. A marginal increase in the gelatinization temperature from 65.4 to 66.2 °C was observed. Retrogradation of gelatinized starch granules decreased with the addition of MGP. The results indicated that the soup stick with 10 % MG had acceptable sensory attributes. The soup stick showed further improvement in terms of texture and breaking strength with the addition of gluten powder, potassium bromate and glycerol monostearate. The total dietary fiber and antioxidant activity of the soup sticks having 10 % MGP increased from 3.31 to 8.64 % and 26.83 to 48.06 % respectively as compared to the control soup sticks. MGP in soup sticks improved the nutritional profile. PMID:26345009

  16. Some physicochemical and rheological properties of starch isolated from avocado seeds.

    PubMed

    Chel-Guerrero, Luis; Barbosa-Martín, Enrique; Martínez-Antonio, Agustino; González-Mondragón, Edith; Betancur-Ancona, David

    2016-05-01

    Seeds from avocado (Persea americana Miller) fruit are a waste byproduct of fruit processing. Starch from avocado seed is a potential alternative starch source. Two different extraction solvents were used to isolate starch from avocado seeds, functional and rheological characteristics measured for these starches, and comparisons made to maize starch. Avocado seed powder was suspended in a solution containing 2 mM Tris, 7.5 mM NaCl and 80 mM NaHSO3 (solvent A) or sodium bisulphite solution (1500 ppm SO2, solvent B). Solvent type had no influence (p>0.05) on starch properties. Amylose content was 15-16%. Gelatinization temperature range was 56-74 °C, peak temperature was 65.7 °C, and transition enthalpy was 11.4-11.6J/g. At 90 °C, solubility was 19-20%, swelling power 28-30 g water/g starch, and water absorption capacity was 22-24 g water/g starch. Pasting properties were initial temperature 72 °C; maximum viscosity 380-390 BU; breakdown -2 BU; consistency 200 BU; and setback 198 BU. Avocado seed starch dispersions (5% w/v) were characterized as viscoelastic systems, with G'>G″. Avocado seed starch has potential applications as a thickening and gelling agent in food systems, as a vehicle in pharmaceutical systems and an ingredient in biodegradable polymers for food packaging. PMID:26800900

  17. Bacillus thuringiensis fermentation of hydrolyzed sludge--rheology and formulation studies.

    PubMed

    Brar, Satinder K; Verma, M; Tyagi, R D; Valéro, J R; Surampalli, R Y

    2007-03-01

    Rheology of Bacillus thuringiensis fermentation of hydrolyzed sludge was investigated in bench scale fermenter. Stable liquid formulations were developed and optimized for two-year based studies comprising various physical/chemical (viscosity, particle size, corrosion and suspendibility) and biological (microbial contamination, viable spores and entomotoxicity) parameters at different pHs and temperatures. The hydrolyzed sludge depicted non-Newtonian and pseudoplastic behaviour during fermentation with 90% to 96% confidence of fits into Casson, Power and IPC paste models. Higher values of consistency and flow index during exponential growth and stationary phase, respectively, affected downstream processing. The power law was also followed by stable formulations. Sorbitol, sodium monophosphate and sodium metabisulfite (2.2:1:1) as suspending agents produced suspendibility ranging from 69% to 94%. The stable formulation (FH-4) comprising sorbitol, sodium monophosphate and sodium metabisulfite deteriorated at pHs 6, 6.5 and temperatures, 40 and 50 degrees C, with no signs of corrosion and microbial contamination. The viscosity of FH-4 formulations decreased with shear rate which could improve handling and consequent spraying. PMID:17184817

  18. Prevention of Peritoneal Adhesions Using Polymeric Rheological Blends

    PubMed Central

    Hoare, Todd; Yeo, Yoon; Bellas, Evangelia; Bruggeman, Joost P.

    2014-01-01

    The effectiveness of rheological blends of high molecular weight hyaluronic acid (HA) and low molecular weight hydroxypropyl methylcellulose (HPMC) in the prevention of peritoneal adhesions post-surgery is demonstrated. The physical mixture of the two carbohydrates increased the dwell time in the peritoneum while significantly improving the injectability of the polymer compared to hyaluronic acid alone. HA-HPMC treatment decreased the total adhesion area by ~70% relative to a saline control or no treatment in a repeated cecal injury model in the rabbit. No significant cytotoxicity and minimal inflammation was associated with the blend, and no chemical or physical processing was required prior to their use beyond simple mixing. PMID:24365709

  19. Preparation of Magnetorheological Fluid and Study on Its Rheological Properties

    NASA Astrophysics Data System (ADS)

    Kolekar, Shreedhar

    2014-04-01

    The present paper focuses on preparation and process of the magnetorheological (MR) fluid whose carrier fluid is silicone-based oil and its additive is the commercial grease with different concentration of iron particles. General properties of MR fluid are discussed and rheological properties like shear rate, shear stress, viscosity of MR fluid can be found by using cone-and-plate sensor system-type rheometer. The result shows that shear stress as a function of magnetic flux density and viscosity does not strictly scale with iron loading.

  20. The ball bearing as a rheological test device

    NASA Technical Reports Server (NTRS)

    Kingsbury, E.

    1984-01-01

    An angular-contact ball bearing provides an easily obtainable, precise mechanical system for rheological tests on thin films under high pressure. The test conditions are by definition similar to those found in practice. Accessible independent variables include size, pressure, bulk temperature, roughness, adsorbed surfactant, fluid type, fluid quantity, fluid supply rate, film thickness, entrainment velocity, transit time, and combined strain. Easily measured or inferred variables include slip, changes in film thickness with time (transients), strain rate, lubricant elastic modulus (thin film, high pressure), tractive force, lubricant chemical degradation rate, and lubricant degradation product. Methods for setting and obtaining these quantities in a bearing are discussed, together with experimental limitations on them.

  1. Effect of aging on rheology of ball clay suspensions

    NASA Astrophysics Data System (ADS)

    Tonthai, Tienchai

    2002-01-01

    The behaviors of clay-water suspensions such as deflocculation or rheological properties are not constant but change with time. Aging has been recognized for changing the rheological properties of clay suspensions. This work provided information about the effects of the moisture contents in ball clay lumps and clay air exposure time on their processability. Dynamic oscillatory rheometry using a vane-in-cup geometry was used to characterize the rheological behavior of ball clay suspensions in terms of elastic modulus, viscous modulus and yield stress as a function of aging time. A light scattering size analyzer was used to examine the agglomerate size distribution of ball clay suspensions which affected the rheological behavior. Soluble ion release (both cations and anions) in the filtrate of suspensions was measured by ion chromatography. Low and high lignitic ball clay suspensions were dispersed with sodium silicate (Na2SiO3) or sodium polyacrylate at specific gravity 1.3 and 1.6 in two dispersion states: fully deflocculated (minimum viscosity) and under deflocculated. Suspensions prepared using freshly mined ball clays required more dispersant than suspensions prepared using dry ball clays to achieve minimum viscosity due to a difference in agglomerate size distribution. The agglomerate size distribution of suspensions prepared using dry clays was broader than that of suspensions prepared using freshly mined clays. In suspensions prepared using freshly mined clays, there were many uniformly small agglomerates having loose water inside, while in suspensions prepared using dry clays, the capillary effect and bonding between clay particles resulting from drying broke clay aggregates apart into agglomerate structures composed of a few to many clay particles. For suspensions prepared using dry clays after one day suspension aging, the elastic modulus and yield stress decreased due to the change in agglomerate size distribution of suspensions but increased for

  2. Rheology of the 2006 eruption at Tungurahua volcano, Ecuador

    NASA Astrophysics Data System (ADS)

    Hanson, J. B.; Lavallée, Y.; Hess, K.-U.; von Aulock, F. W.; Dingwell, D. B.

    2009-04-01

    During August 16th to 18th 2006, the eruptive crisis at Tungurahua volcano (Ecuador) culminated in VEI 2 eruption with tens of pyroclastic flows and the extrusion of a lava flow. The nearly simultaneous occurrence of a lava flow and a pyroclastic flow from a single vent deserves attention. Generally, the rheology is a chief determinant of eruption style. Specifically, magmas are ductile (effusive) at low strain rates whereas they are brittle (explosive) at high strain rates. Although this distinction has been extensively described for single-phase magmas, there remain many questions as to the rheological implications of crystals and bubbles present in magmas. Here we present preliminary characterizations of the complex rheology of the magma involved in the 2006 eruption at Tungurahua volcano. The magma present in this eruption was andesitic with an interstitial melt composition averaging ~58 wt.% SiO2. The bombs present in the pyroclastic deposit show an open porosity ranging from 15 to 35 vol.% and a crystallinity generally greater than ~30 vol.% and occasionally up to 60 vol.% in samples affected by microlite growth. Petrographic analyses revealed magma batches with different crystallization histories. In high-porosity samples containing microlites, a recrystallization rim around clinopyroxene and resorption of the plagioclase were observed. In contrast, the dense samples show pristine, euhedral crystals and a near absence of microlites. The heterogeneous petrographic structures suggest the possibilities of mingling in the conduit or of magma batches with different decompression rates. Dilatometric analyses suggest glass transition temperatures (Tg) of ~974 °C for the dense material (porosity~15 vol.%) and as high as ~1060 °C for the high-porosity bombs (porosity~35 vol.%). Successive series of heating and cooling of the glass reveal an increase of Tg by as much as 60 °C indicative of significant water left in the melt. Preliminary analyses of images obtained

  3. Rheology and microstructure of magmatic emulsions - Theory and experiments

    NASA Technical Reports Server (NTRS)

    Stein, Daniel J.; Spera, Frank J.

    1992-01-01

    The rheological properties of a dilute mixture of melt plus vapor bubbles, referred to as emulsion, are investigated theoretically and in rheometric experiments on dilute viscous germanium dioxide emulsions at temperatures between 1100 and 1175 C and at 100 kPa pressure in a rotating rod rheometer at shear rates between 0.05/s and 7/s. The results indicate that the emulsions may be described by a power-law constitutive relation when observations cover a sufficient range of shear rates to resolve nonlinear flow.

  4. Some comments on the rheologically critical melt percentage

    NASA Astrophysics Data System (ADS)

    Takeda, Yoshi-Taka; Obata, Masaaki

    2003-05-01

    The concept of rheologically critical melt percentage (RCMP) originally proposed by Arzi [Tectonophysics 44 (1978) 173-184] for partially molten granitic rocks is re-examined. It is shown that there is no experimental support to show the presence of RCMP. The published experimental data suggest that the effective viscosity of partially molten granitic rocks is reduced rapidly and continuously with increasing melt fraction. It is also shown that the experimental data may be modeled by means of the upper bound behavior (the Voigt bound) of two-phase material by assuming a melt localization, which implies that there is no partitioning of strain between the solid and the melt.

  5. Jamming, Yielding and Rheology of Weakly Vibrated Granular Media

    NASA Astrophysics Data System (ADS)

    Wortel, Geert; Dijksman, Joshua; Dauchot, Olivier; van Hecke, Martin

    2012-02-01

    We establish that the rheological curve of dry granular media is nonmonotonic, both in the presence and absence of external mechanical agitations. In the absence of vibrations, the nonmonotonic flow curve governs the yielding behavior of granular media. In the presence of weak vibrations, the nonmonotonic flow curves govern a hysteretic transition between slow but steady and fast, inertial flows. For large agitations, the transition becomes non-hysteretic. We probe the fluctuations near the point where the 1st order transition becomes of 2nd order.

  6. A nonequilibrium molecular dynamics study of the rheology of alkanes

    SciTech Connect

    Gupta, S.A.; Cui, S.T.; Cummings, P.T.; Cochran, H.D. |

    1996-05-01

    We examine the rheological properties of four different alkanes: n-decane, n-hexadecane, n-tetracosane, and squalane. Simulations of Couette flow are performed for a range of shear rates with 100 molecules in each case using a replicated data version of our code. Number of interaction sites ranges from 1000 to 3000. We have performed extremely long simulations required to obtain acceptable statistics at low shear rates. The alkanes show a transition from non-Newtonian to Newtonian behavior as the shear rate decreases to low values. 1 tab, 1 fig, 17 refs.

  7. Determining lava rheology using video velocimetry and flow models (Invited)

    NASA Astrophysics Data System (ADS)

    Lev, E.; Spiegelman, M. W.; Wysocki, R.; Karson, J. A.

    2013-12-01

    Flowing lava is one of the most common surface expressions of magmatic and volcanic processes, and thus provides an opportunity for measuring the physical properties of magma. However, direct and accurate field measurements are difficult to carry out, and thus flow models rely on estimates based from measurements of velocity and temperature made at the flow's surface. We demonstrate here how lava rheology can be assessed remotely using video velocimetry. We apply our method on lava flows of both laboratory and natural scales. Our experimental setup, part of the Syracuse University Lava Project (http://lavaproject.syr.edu) includes a large furnace capable of melting up to 450 kg of basalt. The lava is poured onto tilted planes or channels made of sand or steel to produce meters-long flows. This experimental setup is probably the only facility that allows such large scale controlled lava flows made of natural basaltic material. We document the lava using a high-resolution video camera, a forward-looking infrared (FLIR) camera and thermocouples. We employ Differential Optical Flow to extract surface velocity fields from video recordings of the experimental and natural flows. This technique uses the time-variations of the spatial gradients of the image intensity to estimate velocity between consecutive frames. An important benefit for using optical flow, compared with other velocimetry methods, is that it outputs a spatially coherent flow field rather than point measurements. We demonstrate that the optical flow results agree with other measures of the flow velocity, and estimate the error due to noise and time-variability to be under 30 percent of the measured velocity. Our forward flow models are obtained by solving the Stokes flow equations using the finite-element method. We explore a range of rheological parameters, including the lava's apparent viscosity, the power-law exponent m and the thermal activation energy. We find that for the high-temperature portion of

  8. The role of surface rheology in liquid film formation

    NASA Astrophysics Data System (ADS)

    Scheid, B.; Delacotte, J.; Dollet, B.; Rio, E.; Restagno, F.; van Nierop, E. A.; Cantat, I.; Langevin, D.; Stone, H. A.

    2010-04-01

    The role of surface rheology in fundamental fluid dynamical systems, such as liquid coating flows and soap film formation, is poorly understood. We investigate the role of surface viscosity in the classical film-coating problem. We propose a theoretical model that predicts film thickening based on a purely surface-viscous theory. The theory is supported by a set of new experimental data that demonstrates slight thickening even at very high surfactant concentrations for which Marangoni effects are irrelevant. The model and experiments represent a new regime that has not been identified before.

  9. RHEOLOGICAL PROPERTIES & MOLECULAR WEIGHT DISTRIBUTIONS OF FOUR PERFLUORINATED THERMOPLASTIC POLYMERS

    SciTech Connect

    Hoffman, D M; Shields, A L

    2009-02-24

    Dynamic viscosity measurements and molecular weight estimates have been made on four commercial, amorphous fluoropolymers with glass transitions (Tg) above 100 C: Teflon AF 1600, Hyflon AD 60, Cytop A and Cytop M. These polymers are of interest as binders for the insensitive high explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) because of their high density and Tg above ambient, but within a suitable processing range of TATB. As part of this effort, the rheological properties and molecular weight distributions of these polymers were evaluated.

  10. Rheology of Coating Materials and Their Coating Characteristics

    NASA Astrophysics Data System (ADS)

    Grabsch, C.; Grüner, S.; Otto, F.; Sommer, K.

    2008-07-01

    Lots of particles used in the pharmaceutical and the food industry are coated to protect the core material. But almost no investigations about the coating material behavior do exist. In this study the focus was on the rheological material properties of fat based coating materials. Rotational shear experiments to determine the viscosity of a material were compared to oscillatory shear tests to get information about the vicoelastic behavior of the coating materials. At the liquid state the viscosity and the viscoelastic properties showed a good analogy. The viscoelastic properties of the solid coating materials yielded differences between materials that have the same properties at the liquid state.

  11. Terahertz correlation spectroscopy infers particle velocity and rheological properties.

    PubMed

    Rees, Eric J; Su, Ke; Zeitler, Axel

    2016-07-15

    Correlation spectroscopy is an analytical technique that can identify the residence time of reflective or fluorescent particles in a measurement spot, allowing particle velocity or diffusion to be inferred. We show that the technique can be applied to data measured with a time-domain terahertz sensor. The speed of reflectors such as silica ballotini or bubbles can thus be measured in fluid samples. Time-domain terahertz sensors can therefore be used, for the first time, to measure rheological properties of optically opaque fluids that contain entrained reflectors, such as polyethylene beads. PMID:27420517

  12. Abstention from chronic cigarette smoking normalizes blood rheology.

    PubMed

    Ernst, E; Matrai, A

    1987-03-01

    Smokers differ in terms of blood rheology from non-smokers. Ex-smokers differ from smokers but not from non-smokers. When investigated while abstaining from nicotine for 8 weeks, chronic cigarette smokers show a gradual normalization of blood and plasma viscosities, haematocrit, blood cell filterability, plasma fibrinogen levels as well as total white cell count. Those smokers who did not manage to abstain, reveal no such changes. The findings suggest that haemorheological alterations caused by smoking are reversible. This might play a role in the reduction of cardiovascular risk and in the elevation of tissue perfusion. PMID:3593464

  13. Applying modern measurements of Pleistocene loads to model lithospheric rheology

    NASA Astrophysics Data System (ADS)

    Beard, E. P.; Hoggan, J. R.; Lowry, A. R.

    2011-12-01

    The remnant shorelines of Pleistocene Lake Bonneville provide a unique opportunity for building a dataset from which to infer rheological properties of the lower crust and upper mantle. Multiple lakeshores developed over a period of around 30 kyr which record the lithosphere's isostatic response to a well-constrained load history. Bills et al. (1994) utilized a shoreline elevation dataset compiled by Currey (1982) in an attempt to model linear (Maxwell) viscosity as a function of depth beneath the basin. They estimated an effective elastic thickness (Te) for the basin of 20-25 km which differs significantly from the 5-15 km estimates derived from models of loading on geologic timescales (e.g., Lowry and Pérez-Gussinyé, 2011). We propose that the discrepancy in Te modeled by these two approaches may be resolved with dynamical modeling of a common rheology, using a more complete shoreline elevation dataset applied to a spherical Earth model. Where Currey's (1982) dataset was compiled largely from observations of depositional shoreline features, we are developing an algorithm for estimating elevation variations in erosional shorelines based on cross-correlation and stacking techniques similar to those used to automate picking of seismic phase arrival times. Application of this method to digital elevation models (DEMs) will increase the size and accuracy of the shoreline elevation dataset, enabling more robust modeling of the rheological properties driving isostatic response to unloading of Lake Bonneville. Our plan is to model these data and invert for a relatively small number of parameters describing depth- and temperature-dependent power-law rheology of the lower crust and upper mantle. These same parameters also will be used to model topographic and Moho response to estimates of regional mass variation on the longer loading timescales to test for inconsistencies. Bills, B.G., D.R. Currey, and G.A. Marshall, 1994, Viscosity estimates for the crust and upper

  14. The rheology of crystal-rich magmas (Kuno Award Lecture)

    NASA Astrophysics Data System (ADS)

    Huber, Christian; Aldin Faroughi, Salah; Degruyter, Wim

    2016-04-01

    The rheology of magmas controls not only eruption dynamics but also the rate of transport of magmas through the crust and to a large extent the rate of magma differentiation and degassing. Magma bodies stalled in the upper crust are known to spend most of their lifespan above the solidus at a high crystal content (Cooper and Kent, 2014; Huber et al., 2009), where the probability of melt extraction (crystal fractionation) is the greatest (Dufek and Bachmann, 2010). In this study, we explore a new theoretical framework to study the viscosity of crystal bearing magmas. Since the seminal work of A. Einstein and W. Sutherland in the early 20th century, it has been shown theoretically and tested experimentally that a simple self-similar behavior exist between the relative viscosity of dilute (low crystal content) suspensions and the particle volume fraction. The self-similar nature of that relationship is quickly lost as we consider crystal fractions beyond a few volume percent. We propose that the relative viscosity of crystal-bearing magmas can be fully described by two state variables, the intrinsic viscosity and the crowding factor (a measure of the packing threshold in the suspension). These two state variables can be measured experimentally under different conditions, which allows us to develop closure relationships in terms of the applied shear stress and the crystal shape and size distributions. We build these closure equations from the extensive literature on the rheology of synthetic suspensions, where the nature of the particle shape and size distributions is better constrained and apply the newly developed model to published experiments on crystal-bearing magmas. We find that we recover a self-similar behavior (unique rheology curve) up to the packing threshold and show that the commonly reported break in slope between the relative viscosity and crystal volume fraction around the expected packing threshold is most likely caused by a sudden change in the state

  15. Rheology of composite solid propellants during motor casting

    NASA Technical Reports Server (NTRS)

    Rogers, C. J.; Smith, P. L.; Klager, K.

    1978-01-01

    In a study conducted to evaluate flow parameters of uncured solid composite propellants during motor casting, two motors (1.8M-lb grain wt) were cast with a PBAN propellant exhibiting good flow characteristics in a 260-in. dia solid rocket motor. Attention is given to the effects of propellant compositional and processing variables on apparent viscosity as they pertain to rheological behavior and grain defect formation during casting. It is noted that optimized flow behavior is impaired with solid propellant loading. Non-Newtonian pseudoplastic flow is observed, which is dependent upon applied shear stress and the age of the uncured propellant.

  16. Pre-cooked Fiber-enriched Wheat Flour Obtained by Extrusion: Rheological and Functional Properties

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Functional and rheological properties of different process conditions of extruded wheat flour with 0%, 10%, 20% and 30% fiber levels were studied in the production of cookies and tortillas. Functional and rheological properties were evaluated using Rapid Visco Analyzer and Mixograph equipment. Resul...

  17. Waxy soft white wheat: extrusion characteristics and thermal and rheological properties

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Waxy wheat flour was analyzed for its thermal and rheological properties and extruded to understand its processing characteristics. Comparisons were made with normal soft white wheat flour to identify extrusion differences under the same conditions. The thermal and rheological properties through Rap...

  18. Dynamic light scattering for measuring microstructure and rheological properties of food

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In recent years there has been significant interest in the determination of microstructural and rheological properties of viscoelastic food materials and their formulations. This is because the arrangement (architecture) of the micro­ and nano­components, size distribution, and rheological (mechanic...

  19. Rheological Changes in Refrigerated Dough During Storage in Relation to Proteins

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Refrigerated dough is a flour-based, unbaked product that is stored between 4-7 ºC. The aim of this work was to study the rheological properties of refrigerated dough during storage and determine their correlations with dough proteins. Rheological properties were determined using texture analyzer an...

  20. Impact of superplasticizer concentration and of ultra-fine particles on the rheological behaviour of dense mortar suspensions

    SciTech Connect

    Artelt, C. Garcia, E.

    2008-05-15

    This work aims at investigating the impact of the addition of superplasticizer and of ultra-fine particles, namely of silica fume and of precipitated titania, on the rheological behaviour of water-lean mortar pastes. The pastes are characterised in terms of their spread, their flowing behaviour and by means of performing a shear test, giving access to viscosity/shear gradient correlations. Adding superplasticizer is shown to shift the onset of shear thickening of the referring pastes to higher shear rates and to attenuate its otherwise rapid evolution, possibly by means of favouring steric particle-particle interactions. The workability of these mortars, which is characterised in terms of spread values and draining, is also improved. For the case of fly ash based mortars, adding ultra-fine particles is another way of (slightly) 'retarding' shear thickening and of attenuating its evolution, possibly because of resulting in - on the average - lower hydrodynamic forces and reduced attractive Van der Waals interactions between particles. However, at the same time these mortars are characterised by a worsening in workability which is attributed to the huge amount of surface area provided by the ultra-fines.

  1. Rheological anisotropy of the Earth's mantle and attenuation of seismic waves

    NASA Astrophysics Data System (ADS)

    Birger, B. I.

    2006-11-01

    The nonlinear integral (having memory) model previously proposed by the author for the description of the dislocation rheology of mantle rocks is generalized to the case of crystals with anisotropic rheology. The latter is caused by a large difference between the effective viscosities associated with dislocation glide and dislocation climb (in the crystallographic coordinate system, the dislocation glide governs simple shear, whereas the dislocation climb governs pure shear). Since the mantle is polycrystalline and crystal grains an order of a millimeter in size are oriented chaotically, anisotropy vanishes with volume averaging. However, convective flows in the mantle produce large strains and lead to a preferred orientation of grains and, thereby, anisotropy of the upper mantle. The lower mantle is dominated by diffusion rheology, which cannot cause anisotropy. The mantle rheological anisotropy gives rise to anisotropic attenuation of seismic waves. It is shown that the attenuation depends on the polarization and direction of seismic waves and on the parameters of the rheological model.

  2. Structural analysis of gluten-free doughs by fractional rheological model

    NASA Astrophysics Data System (ADS)

    Orczykowska, Magdalena; Dziubiński, Marek; Owczarz, Piotr

    2015-02-01

    This study examines the effects of various components of tested gluten-free doughs, such as corn starch, amaranth flour, pea protein isolate, and cellulose in the form of plantain fibers on rheological properties of such doughs. The rheological properties of gluten-free doughs were assessed by using the rheological fractional standard linear solid model (FSLSM). Parameter analysis of the Maxwell-Wiechert fractional derivative rheological model allows to state that gluten-free doughs present a typical behavior of viscoelastic quasi-solid bodies. We obtained the contribution dependence of each component used in preparations of gluten-free doughs (either hard-gel or soft-gel structure). The complicate analysis of the mechanical structure of gluten-free dough was done by applying the FSLSM to explain quite precisely the effects of individual ingredients of the dough on its rheological properties.

  3. 77 FR 25406 - Consortium on “Concrete Rheology: Enabling Metrology (CREME)”: Membership Fee Update

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-04-30

    ... National Institute of Standards and Technology Consortium on ``Concrete Rheology: Enabling Metrology (CREME... NIST/Industry Consortium on Concrete Rheology: Enabling Metrology (CREME)''. The notice stated that... consortium is to predict the pumpability of a grout/mortar or a concrete from the rheological properties...

  4. Phase behavior and rheological characterization of silica nanoparticle gel

    NASA Astrophysics Data System (ADS)

    Metin, Cigdem O.; Rankin, Kelli M.; Nguyen, Quoc P.

    2014-01-01

    Preferential injection into high permeability thief zones or fractures can result in early breakthrough at production wells and large unswept areas of high oil saturation, which impact the economic life of a well. A variety of conformance control techniques, including polymer and silica gel treatments, have been designed to block flow through the swept zones. Over a certain range of salinities, silica nanoparticle suspensions form a gel in bulk phase behavior tests. These gels have potential for in situ flow diversion, but in situ flow tests are required to determine their applicability. To determine the appropriate scope of the in situ tests, it is necessary to obtain an accurate description of nanoparticle phase behavior and gel rheology. In this paper, the equilibrium phase behavior of silica nanoparticle solutions in the presence of sodium chloride (NaCl) is presented with four phase regions classified as a function of salinity and nanoparticle concentration. Once the gelation window was clearly defined, rheology experiments of silica nanoparticle gels were also carried out. Gelation time decreases exponentially as a function of silica concentration, salinity, and temperature. Following a power law behavior, the storage modulus, G', increases with particle concentration. Steady shear measurements show that silica nanoparticle gels exhibit non-Newtonian, shear thinning behavior. This comprehensive study of the silica nanoparticle gels has provided a clear path forward for in situ tests to determine the gel's applicability for conformance control operations.

  5. Correlation of chitosan's rheological properties to its ability to electrospin

    NASA Astrophysics Data System (ADS)

    Krause, Wendy E.; Queen, Hailey A.; Klossner, Rebecca R.; Coughlin, Andrew J.

    2007-03-01

    Chitosan, derived from chitin found in the exoskeleton of crustaceans, has been investigated extensively for use in biomedical applications ranging from drug delivery to scaffolds for tissue engineering. Therefore, forming nanofibers of this linear polysaccharide is desirable for use in such applications, because the nanofibers can be tailored to mimic the size and porosity of the extracellular matrix. Electrostatic spinning (electrospinning) is a convenient method to produce nonwoven mats of nanofibers. The ability of the solutions to successfully electospin is closely correlated with the rheological properties of the solutions. Chitosan is challenging to electrospin due to its relatively high viscosity at modest concentrations. Solutions of chitosan blended with poly(ethylene oxide) (PEO) have been electrospun successfully with freshly prepared solutions. If the blended solutions are stored, they do not readily electrospin. Moreover, chitosan/PEO blend solutions show a drastic decrease in zero shear rate viscosity over time, which can be attributed to phase separation. The challenges associated with electrospinning charged biopolymers (chitosan is cationic) will be discussed in terms of their rheological properties. Successes and failures will be highlighted and compared results for readily electrospun neutral polymers.

  6. Forced unfolding of protein domains determines cytoskeletal rheology

    NASA Astrophysics Data System (ADS)

    Crocker, John

    2005-03-01

    Cells have recently been shown to have a power-law dynamic shear modulus over wide frequency range; the value of the exponent being non-universal, varying from 0.1-0.25 depending on cell type. This observation has been interpreted as evidence for the Soft Glassy Rheology (SGR) model, a trap-type glass model with an effective granular temperature. We propose a simple, alternative model of cytoskeletal mechanics based on the thermally activated, forced unfolding of domains in proteins cross-linking a stressed semi-flexible polymer gel. It directly relates a cell’s mechanical response to biophysical parameters of the cytoskeleton’s molecular constituents. Simulations indicate that unfolding events in a random network display a collective self-organization, giving rise to an exponential distribution of crosslink stress that can reproduce cell viscoelasticity. The model suggests natural explanations for the observed correlation between cell rheology and intracellular static stress, including those previously explained using the tensegrity concept. Moreover, our model provides insight into potential mechanisms of mechanotransduction as well as cell shape sensing and maintenance.

  7. Interplay between electrical and rheological properties of viscoelastic inks

    NASA Astrophysics Data System (ADS)

    Yu, Milim; Ahn, Kyung Hyun; Lee, Seung Jong

    2016-04-01

    We investigated the effect of the interaction between the electrical and rheological properties of the ink in electrodydrodynamic (EHD) printing process by designing model systems that control both the electrical conductivity and the viscoelasticity of the ink to observe how they affect the Taylor cone jet formation. The results demonstrate that the initial voltage at which the Taylor cone jet first appears and the final voltage at which the jet becomes unstable increase at higher electrical conductivity as the conical shape with large surface area is formed and grants stability at higher conductivity. Increased viscosity and elasticity also lead to the similar result: increase in the initial and final voltages, which can be attributed to the slower charge transport that minimizes the stabilizing effect of the inks' electrical conductivity. In addition, we use two dimensionless variables (dimensionless flow rate and dimensionless voltage) to make an operating window map of the EHD process. Through this map, the processing condition for the Taylor cone jet zone can be predicted with respect to the effect of the interplay between the electrical and rheological properties of the ink.

  8. Rheology of cubic particles suspended in a Newtonian fluid.

    PubMed

    Cwalina, Colin D; Harrison, Kelsey J; Wagner, Norman J

    2016-05-18

    Many real-world industrial processes involve non-spherical particles suspended in a fluid medium. Knowledge of the flow behavior of these suspensions is essential for optimizing their transport properties and designing processing equipment. In the present work, we explore and report on the rheology of concentrated suspensions of cubic-shaped colloidal particles under steady and dynamic shear flow. These suspensions exhibit a rich non-Newtonian rheology that includes shear thickening and normal stress differences at high shear stresses. Scalings are proposed to connect the material properties of these suspensions of cubic particle to those measured for suspensions of spherical particles. Negative first normal stress differences indicate that lubrication hydrodynamic forces dominate the stress in the shear-thickened state. Accounting for the increased lubrication hydrodynamic interactions between the flat surfaces of the cubic particles allows for a quantitative comparison of the deviatoric stress in the shear-thickened state to that of spherical particles. New semi-empirical models for the viscosity and normal stress difference coefficients are presented for the shear-thickened state. The results of this study indicate that cubic particles offer new and unique opportunities to formulate colloidal dispersions for field-responsive materials. PMID:27112791

  9. Rheology of Imidazolium-Based Ionic Liquids with Aromatic Functionality.

    PubMed

    Tao, Ran; Simon, Sindee L

    2015-09-01

    A series of imidazolium-based ionic liquids with cyclic and aromatic groups and a bis[(trifluoromethane)sulfonyl]amide anion were characterized using dynamic and steady shear rheology in a wide temperature range. The cations investigated include 1-(cyclohexylmethyl)-3-methylimidazolium ([CyhmC1im](+)), 1-benzyl-3-methylimidazolium ([BnzC1im](+)), 1,3-dibenzylimidazolium ([(Bnz)2im](+)), and 1-(2-naphthylmethyl)-3-methylimidazolium ([NapmC1im](+)). Rheological properties are reported from terminal flow to the glassy state. All ionic liquids show very similar flow behavior with a glassy modulus approaching 1 GPa. The temperature dependences of the shift factors used for time-temperature superposition and the viscosity both follow the same VFT or WLF relationship, and the dynamic fragility at Tg ranges from 117 to 130 for the aromatic ionic liquids investigated, considerably more fragile, in the Angell sense, than the aliphatic analogs. Additionally, an anomalous aging effect in the dynamic viscosity response (i.e., a maximum observed at intermediate frequencies) was found using a strain-controlled rheometer but not using a stress-controlled rheometer. PMID:26230926

  10. The influence of additives on rheological properties of limestone slurry

    NASA Astrophysics Data System (ADS)

    Jaworska, B.; Bartosik, A.

    2014-08-01

    Limestone slurry appears in the lime production process as the result of rinsing the processed material. It consists of particles with diameter smaller than 2 mm and the water that is a carrier of solid fraction. Slurry is directed to the settling tank, where the solid phase sediments and the excess water through the transfer system is recovered for re-circulation. Collected at the bottom of the tank sludge is deposited in a landfill located on the premises. Rheological properties of limestone slurry hinder its further free transport in the pipeline due to generated flow resistance. To improve this state of affairs, chemical treatment of drilling fluid, could be applied, of which the main task is to give the slurry properties suitable for the conditions encountered in hydrotransport. This treatment consists of applying chemical additives to slurry in sufficient quantity. Such additives are called as deflocculants or thinners or dispersants, and are chemical compounds which added to aqueous solution are intended to push away suspended particles from each other. The paper presents the results of research allowing reduction of shear stress in limestone slurry. Results demonstrate rheological properties of limestone slurry with and without the addition of modified substances which causes decrease of slurry viscosity, and as a consequence slurry shear stress for adopted shear rate. Achieving the desired effects increases the degree of dispersion of the solid phase suspended in the carrier liquid and improving its ability to smooth flow with decreased friction.

  11. Rheological and structural studies of carboxymethyl derivatives of chitosan

    SciTech Connect

    Winstead, Cherese; Katagumpola, Pushpika

    2014-05-15

    The degrees of substitution of chitosan derivatives were varied and the viscoelastic behavior of these biopolymer solutions was studied using rheology. Chitosan is a cationic copolymer of glucosamine and N-acetylglucosamine obtained by alkaline deacetylation of chitin. Due to its inherent non-toxicity, biocompatibility, and biodegradability, chitosan has gained much interest. However, the poor solubility of the biopolymer in water and most common organic solvents limits its applications. Therefore, the focus of this work is the chemical modification of chitosan via carboxymethylation as well as studying the viscoelastic behavior of these polymer solutions. Varying degrees of substitution (DS) of carboxymethyl chitosan derivatives were synthesized by treating chitosan with monochloroacetic acid under alkylated medium varying the reaction time and temperature. The effect of degree of substitution on the rheology of these polymer solutions was studied as a function of concentration. The viscosity of chitosan derivatives sharply increased with increase in degree of substitution. G' and G' dependence on strain and angular frequency were studied and were found to exhibit predominantly viscous behavior. Additional characterization of the derivatized products were further studied using Fourier transform infrared (FT-IR), {sup 1}H Nuclear Magnetic Resonance ({sup 1}H NMR) spectroscopy, X-ray diffraction (XRD), and thermal gravimetric analysis as well as differential scanning calorimetry (DSC). Degree of substitution (DS) was calculated by titrimetric method.

  12. Low-temperature plastic rheology of olivine determined by nanoindentation

    NASA Astrophysics Data System (ADS)

    Kranjc, Kelly; Rouse, Zachary; Flores, Katharine M.; Skemer, Philip

    2016-01-01

    Low-temperature plasticity is a deformation mechanism that occurs mainly at high stress and low temperatures and may be important in the shallow lithosphere, at the tips of cracks, and in laboratory experiments. Previous studies investigating the low-temperature plasticity of the mineral olivine have exhibited wide variability in their extrapolations to the athermal flow strength or Peierls stress. To better constrain the rheology of olivine, nanoindentation tests were performed on samples in the temperature range of 0-175°C. The indentation properties were converted to uniaxial properties using a finite element-based method. The data were fit to a standard flow law for low-temperature plasticity, and Peierls stresses between 5.32 and 6.45 GPa were obtained. These results provide increased confidence in the extrapolation of high-pressure and high-temperature laboratory experiments to low-temperature conditions and illustrate the applicability of nanoindentation methods to the study of mineral rheology.

  13. Advanced rheological characterization of soft colloidal model systems

    NASA Astrophysics Data System (ADS)

    Gupta, S.; Kundu, S. K.; Stellbrink, J.; Willner, L.; Allgaier, J.; Richter, D.

    2012-11-01

    The complex flow behavior of polymer-based soft colloidal model systems was investigated using steady and oscillatory shear to prove new concepts for advanced rheological characterization. In the very dilute regime we investigated high molecular weight polybutadiene star polymers to quantify the internal relaxation time arising from the polymeric nature of these ultra-soft colloids. The observed shear-induced brush deformation is interpreted in terms of the internal Zimm time τz. The observed dependence of τz on matrix viscosity can be explained by shrinkage of the star polymer due to an increasing incompatibility with increasing matrix molecular weight. The influence of the polymeric nature on the characteristic structural relaxation time in the concentrated regime was investigated using non-linear rheology following Wyss et al (SRFS) (2007 Phys. Rev. Lett. 98 238303). Here we used star-like block copolymer micelles to systematically tune the ‘softness’ of the colloids by variation of the block ratio. A master curve with proper scaling parameters could be generated independent of the degree of colloidal ‘softness’. However, the obtained strain-rate independent structural relaxation time τ0 was not observed in the linear regime. In addition, a high frequency discrepancy was clearly found in all our experimental data. Both reflect the shortcomings of the SRFS approach.

  14. Pressure cycle rheology of nanofluids at ambient temperature

    NASA Astrophysics Data System (ADS)

    Kanjirakat, Anoop; Sadr, Reza; Yrac, Rommel; Amani, Mahmood

    2015-11-01

    Colloidal suspensions of particles dispersed in a base fluid (or drilling fluid) are commonly used in oil industry to aid the drilling of oil well into the ground. Nanofluids, the colloidal suspensions of nano-sized particles dispersed in a basefluid, have also shown potentials as cooling and abrasive fluids. Utilizing them along with drilling fluids under cyclic high-pressure loadings have not been investigated so far. In the present work, rheological characteristics of silicon oil based nanofluids (prepared with alumina nanoparticles) under pressures up to 1000 bar are investigated using a high-pressure viscometer. The rheological characteristics of nanofluids are measured and are compared with that of the basefluid under increasing and decreasing pressures. Relative viscosity variations of nanofluids were observed to have influenced by the shear rate. In addition, under cyclic high-pressure loading viscosity values of nanofluids are observed to have reduced. This reduction in viscosity at the second pressure cycle could have been caused by the de-agglomeration of particles in the first cycle while working a high-pressure and high-shear condition.

  15. Mesoscale Characterization of Supramolecular Transient Networks Using SAXS and Rheology

    PubMed Central

    Pape, A. C. H.; Bastings, Maartje M. C.; Kieltyka, Roxanne E.; Wyss, Hans M.; Voets, Ilja K.; Meijer, E. W.; Dankers, Patricia Y. W.

    2014-01-01

    Hydrogels and, in particular, supramolecular hydrogels show promising properties for application in regenerative medicine because of their ability to adapt to the natural environment these materials are brought into. However, only few studies focus on the structure-property relationships in supramolecular hydrogels. Here, we study in detail both the structure and the mechanical properties of such a network, composed of poly(ethylene glycol), end-functionalized with ureido-pyrimidinone fourfold hydrogen bonding units. This network is responsive to triggers such as concentration, temperature and pH. To obtain more insight into the sol-gel transition of the system, both rheology and small-angle X-ray scattering (SAXS) are used. We show that the sol-gel transitions based on these three triggers, as measured by rheology, coincide with the appearance of a structural feature in SAXS. We attribute this feature to the presence of hydrophobic domains where cross-links are formed. These results provide more insight into the mechanism of network formation in these materials, which can be exploited for tailoring their behavior for biomedical applications, where one of the triggers discussed might be used. PMID:24441567

  16. Probing polyethylene crystallization via simultaneous Raman scattering, rheology and microscopy

    NASA Astrophysics Data System (ADS)

    Migler, Kalman; Kotula, Anthony; Hight Walker, Angela

    The structure and rheology of polyolefins during crystallization is of critical importance to the polymer processing industry. Here we present simultaneous Raman scattering, rheological and optical microscopy measurements of crystallizing high density polyethylenes during quiescent and slow flow conditions. Raman scattering measurements during quiescent crystallization allow us to quantify three different mass fractions of chain conformers: an amorphous fraction, an orthorhombic crystalline fraction, and a fraction of chains that contain many consecutive trans bonds but are not part of the orthorhombic crystal. These non-crystalline consecutive trans (NCCT) conformers are generated as a precursor to crystallinity. Slow steady shear rates (1 s 1) applied during isothermal crystallization experiments dramatically increase the crystallization rate as well as the amount of NCCT conformers produced. Optical measurements of sheared samples during crystallization reveal the formation of fiber structures that compositionally contain more NCCT conformers than the surrounding melt. The increase in the complex shear modulus commonly measured for crystallizing polyethylenes correlates with the growth of chain conformers and the appearance of spherulites within the melt.

  17. Synthesis, physicochemical, structural and rheological characterizations of carboxymethyl xanthan derivatives.

    PubMed

    Yahoum, Madiha M; Moulai-Mostefa, Nadji; Le Cerf, Didier

    2016-12-10

    The aim of this work was to synthesize a carboxymethylated xanthan (CMXG) via an etherification reaction between different ratios (2, 4, and 6) of xanthan gum (XG) and monochloroacetic acid (MCAA) using the Williamson synthesis method. The synthetized products were characterized in terms of their physico-chemical and rheological properties. Both FTIR and proton nuclear magnetic resonance (H(1) NMR) analyses confirmed the grafting of carboxymethyl groups on xanthan hydroxyl groups. The obtained results demonstrated that the degree of substitution was proportional to the chloroacetic acid and xanthan gum ratios. The obtained carboxymethyl derivatives presented greater hydrophilicity and lower molecular weights with increasing degrees of substitution than native xanthan gum. The rheological study revealed that the viscosity of the CMXG derivatives decreased with the degree of substitution and with the conservation of the shear-thinning and weak gel behaviours. The flow curves suggested the existence of two different populations of particles consisting of CMXG particles with a smaller average size and a second population formed by the residual fractions of native XG particles. It was also found that the elastic modulus of XG was largely higher than that of the CMXG derivatives and decreased with increasing DS. For the CMXG derivatives, two regions of viscoelastic behaviour were observed, which were separated by a crossover point corresponding to the critical frequency and relaxation time, i.e., the time required for stress relaxation. PMID:27577918

  18. Tribological and Rheological Properties of a Synovial Fluid Model

    NASA Astrophysics Data System (ADS)

    Klossner, Rebecca; Liang, Jing; Krause, Wendy

    2010-03-01

    Hyaluronic acid (HA) and the plasma proteins, albumin and globulins, are the most abundant macromolecules in synovial fluid, the fluid that lubricates freely moving joints. In previous studies, bovine synovial fluid, a synovial fluid model (SFM) and albumin in phosphate buffered saline (PBS) were observed to be rheopectic---viscosity increases over time under constant shear. Additionally, steady shear experiments have a strong shear history dependence in protein-containing solutions, whereas samples of HA in PBS behaved as a ``typical'' polyelectrolyte. The observed rheopexy and shear history dependence are indicative of structure building in solution, which is most likely caused by protein aggregation. The tribology of the SFM was also investigated using nanoindenter-based scratch tests. The coefficient of frictions (μ) between the diamond nanoindenter tip and a polyethylene surface was measured in the presence of the SFM and solutions with varied protein and HA concentrations. The lowest μ is observed in the SFM, which most closely mimics a healthy joint. Finally, an anti-inflammatory drug, hydroxychloroquine, was shown to inhibit protein interactions in the SFM in rheological studies, and thus the tribological response was examined. We hypothesize that the rheopectic behavior is important in lubrication regimes and therefore, the rheological and tribological properties of these solutions will be correlated.

  19. Protein adsorption and interfacial rheology interfering in dilatational experiment

    NASA Astrophysics Data System (ADS)

    Rühs, P. A.; Scheuble, N.; Windhab, E. J.; Fischer, P.

    2013-05-01

    The static and dilatational response of β-lactoglobulin fibrils and native β-lactoglobulin (monomers) at water-air and water-oil interfaces (pH 2) was measured using the pendant drop method. The resulting adsorption behavior and viscoelasticity is dependent of concentration and adsorption time. The interfacial pressure of the β-lactoglobulin fibrils obtained in static measurements was 16-18 mN/m (against air) and 7 mN/m (against oil) for all concentrations. With higher concentrations, faster adsorption kinetics and slightly higher interfacial and surface pressure is achieved but did not lead to higher viscoelastic moduli. The transient saturation of the interface is similar for both the fibril solution and the monomers, however the fibril solution forms a strong viscoelastic network. To evaluate the superimposed adsorption behavior and rheological properties, the formed interfacial layer was subjected to dilatational experiments, which were performed by oscillating the surface area of the drop in sinusoidal and sawtooth (diagonal) deformation manner. The sinusoidal oscillations (time depended area deformation rate) result in a complex interfacial tension behavior against air and oil interfaces and show remarkable differences during compression and expansion as emphasized by Lissajous figures. For diagonal (constant area deformation rate) experiments, a slight bending of the interfacial tension response was observed at low frequencies emphasizing the influence of protein adsorption during rheological measurements.

  20. How does interfacial rheology govern soap bubble cluster dynamics?

    NASA Astrophysics Data System (ADS)

    Cohen-Addad, Sylvie; Biance, Anne-Laure; Hohler, Reinhard

    2009-11-01

    Aqueous foams are concentrated dispersions of gas bubbles in a soapy solution. These complex fluids exhibit solid-like or liquid-like mechanical behaviors, depending on the applied shear. When it is increased beyond a yield strain, neighbor switching bubble rearrangements called T1 events are triggered and plastic flow sets in. We study experimentally the dynamics of such strain induced T1s in 3D bubble clusters that we consider as model systems of 3D foams. To determine the hydrodynamics and physico-chemistry that set the duration of T1s, we use foaming solutions of a wide range of well characterized bulk and interfacial rheological properties. At low shear rates, the T1 duration is set by a balance between surface tension and surface viscous forces in qualitative agreement with previous studies of T1s in 2D foams [1] and we present a simple physical model that explains our 3D findings. Moreover, above a characteristic shear rate, rearrangement dynamics are driven by the applied strain. By combining all our results, we link the transition from intermittent to continous flow dynamics in foams to the rheology of the gas-liquid interfaces. [4pt] [1] M. Durand, H. A. Stone, Phys. Rev. Lett. 97, 2226101 (2006).

  1. A modification of Murray's law for shear-thinning rheology.

    PubMed

    McGah, Patrick M; Capobianchi, Massimo

    2015-05-01

    This study reformulates Murray's well-known principle of minimum work as applied to the cardiovascular system to include the effects of the shear-thinning rheology of blood. The viscous behavior is described using the extended modified power law (EMPL), which is a time-independent, but shear-thinning rheological constitutive equation. The resulting minimization problem is solved numerically for typical parameter ranges. The non-Newtonian analysis still predicts the classical cubic diameter dependence of the volume flow rate and the cubic branching law. The current analysis also predicts a constant wall shear stress throughout the vascular tree, albeit with a numerical value about 15-25% higher than the Newtonian analysis. Thus, experimentally observed deviations from the cubic branching law or the predicted constant wall shear stress in the vasculature cannot likely be attributed to blood's shear-thinning behavior. Further differences between the predictions of the non-Newtonian and the Newtonian analyses are highlighted, and the limitations of the Newtonian analysis are discussed. Finally, the range and limits of applicability of the current results as applied to the human arterial tree are also discussed. PMID:25565456

  2. Growth Kinetics and Mechanics of Hydrate Films by Interfacial Rheology.

    PubMed

    Leopércio, Bruna C; de Souza Mendes, Paulo R; Fuller, Gerald G

    2016-05-01

    A new approach to study and understand the kinetics and mechanical properties of hydrates by interfacial rheology is presented. This is made possible using a "double wall ring" interfacial rheology cell that has been designed to provide the necessary temperature control. Cyclopentane and water are used to form hydrates, and this model system forms these structures at ambient pressures. Different temperature and water/hydrocarbon contact protocols are explored. Of particular interest is the importance of first contacting the hydrocarbon against ice crystals in order to initiate hydrate formation. Indeed, this is found to be the case, even though the hydrates may be created at temperatures above the melting point of ice. Once hydrates completely populate the hydrocarbon/water interface, strain sweeps of the interfacial elastic and viscous moduli are conducted to interrogate the mechanical response and fragility of the hydrate films. The dependence on temperature, Tf, by the kinetics of formation and the mechanical properties is reported, and the cyclopentane hydrate dissociation temperature was found to be between 6 and 7 °C. The formation time (measured from the moment when cyclopentane first contacts ice crystals) as well as the elastic modulus and the yield strain increase as Tf increases. PMID:27076092

  3. Effect of Amphiphiles on the Rheology of Triglyceride Networks

    NASA Astrophysics Data System (ADS)

    Seth, Jyoti

    2014-11-01

    Networks of aggregated crystallites form the structural backbone of many products from the food, cosmetic and pharmaceutical industries. Such materials are generally formulated by cooling a saturated solution to yield the desired solid fraction. Crystal nucleation and growth followed by aggregation leads to formation of a space percolating fractal-network. It is understood that microstructural hierarchy and particle-particle interactions determine material behavior during processing, storage and use. In this talk, rheology of suspensions of triglycerides (TAG, like tristearin) will be explored. TAGs exhibit a rich assortment of polymorphs and form suspensions that are evidently sensitive to surface modifying additives like surfactants and polymers. Here, a theoretical framework will be presented for suspensions containing TAG crystals interacting via pairwise potentials. The work builds on existing models of fractal aggregates to understand microstructure and its correlation with material rheology. Effect of amphiphilic additives is derived through variation of particle-particle interactions. Theoretical predictions for storage modulus will be compared against experimental observations and data from the literature and micro structural predictions against microscopy. Such a theory may serve as a step towards predicting short and long-term behavior of aggregated suspensions formulated via crystallization.

  4. Rheological and structural studies of carboxymethyl derivatives of chitosan

    NASA Astrophysics Data System (ADS)

    Winstead, Cherese; Katagumpola, Pushpika

    2014-05-01

    The degrees of substitution of chitosan derivatives were varied and the viscoelastic behavior of these biopolymer solutions was studied using rheology. Chitosan is a cationic copolymer of glucosamine and N-acetylglucosamine obtained by alkaline deacetylation of chitin. Due to its inherent non-toxicity, biocompatibility, and biodegradability, chitosan has gained much interest. However, the poor solubility of the biopolymer in water and most common organic solvents limits its applications. Therefore, the focus of this work is the chemical modification of chitosan via carboxymethylation as well as studying the viscoelastic behavior of these polymer solutions. Varying degrees of substitution (DS) of carboxymethyl chitosan derivatives were synthesized by treating chitosan with monochloroacetic acid under alkylated medium varying the reaction time and temperature. The effect of degree of substitution on the rheology of these polymer solutions was studied as a function of concentration. The viscosity of chitosan derivatives sharply increased with increase in degree of substitution. G' and G" dependence on strain and angular frequency were studied and were found to exhibit predominantly viscous behavior. Additional characterization of the derivatized products were further studied using Fourier transform infrared (FT-IR), 1H Nuclear Magnetic Resonance (1H NMR) spectroscopy, X-ray diffraction (XRD), and thermal gravimetric analysis as well as differential scanning calorimetry (DSC). Degree of substitution (DS) was calculated by titrimetric method.

  5. A Maxwell elasto-brittle rheology for sea ice modelling

    NASA Astrophysics Data System (ADS)

    Dansereau, Véronique; Weiss, Jérôme; Saramito, Pierre; Lattes, Philippe

    2016-07-01

    A new rheological model is developed that builds on an elasto-brittle (EB) framework used for sea ice and rock mechanics, with the intent of representing both the small elastic deformations associated with fracturing processes and the larger deformations occurring along the faults/leads once the material is highly damaged and fragmented. A viscous-like relaxation term is added to the linear-elastic constitutive law together with an effective viscosity that evolves according to the local level of damage of the material, like its elastic modulus. The coupling between the level of damage and both mechanical parameters is such that within an undamaged ice cover the viscosity is infinitely large and deformations are strictly elastic, while along highly damaged zones the elastic modulus vanishes and most of the stress is dissipated through permanent deformations. A healing mechanism is also introduced, counterbalancing the effects of damaging over large timescales. In this new model, named Maxwell-EB after the Maxwell rheology, the irreversible and reversible deformations are solved for simultaneously; hence drift velocities are defined naturally. First idealized simulations without advection show that the model reproduces the main characteristics of sea ice mechanics and deformation: strain localization, anisotropy, intermittency and associated scaling laws.

  6. Influence of cell properties on rheological characterization of microalgae suspensions.

    PubMed

    Zhang, Xinru; Jiang, Zeyi; Chen, Liang; Chou, Aihui; Yan, Hai; Zuo, Yi Y; Zhang, Xinxin

    2013-07-01

    The influences of algal cell size and surface charge on rheological properties of microalgae suspensions were investigated. The effective viscosity of two microalgae suspensions, i.e., the freshwater Chlorella sp. and the marine Chlorella sp., was measured as a function of their volume fractions in the range of 0.70-4.31%. The hydrodynamic diameters of the freshwater Chlorella sp. and the marine Chlorella sp. were measured to be 3.13 and 6.00 μm, respectively. The Zeta potentials of these two algal cells were measured to be -23.73 and -81.81 mV, respectively. The intrinsic viscosities of these two microalgae suspensions were further determined to be 24.7 and 16.1, respectively. Combining with theoretical models, these results indicated that the algal cell size has a predominant effect over cell surface charge in affecting rheological properties of microalgae suspensions. Smaller algal cells result in a higher effective viscosity of the microalgae suspension. PMID:23665517

  7. Structure and rheological properties in alkali aluminosilicate melts

    NASA Astrophysics Data System (ADS)

    Le Losq, Charles; Neuville, Daniel

    2010-05-01

    Rheological properties of silicate melts govern both magma ascension from the mantle to the surface of the earth and volcanological eruptions styles and behaviors. In this mind, it is very important to understand which parameters influence these properties. Up to now, we know for example that viscosity of silicate melts is dependent of temperature, pressure and chemical composition. In this work, we will focus on the Na2O-K2O-Al2O3-SiO2 system, which is of a prime importance because it deals with a non-negligible part of natural melts like haplogranitic rhyolitic alkali magmas. We will first present our viscosity measurements and some modelisation concepts based on the Adam and Gibbs theory. From configurational entropy theory we obtain some macroscopic information's that we can link to the structure of glasses and melts. In this mind, we have investigated them with Raman and NMR spectroscopies. These spectroscopies provide information on speciation and polymerization of glasses and melts. We will present and discuss structural and rheological variations as a function of temperature and chemical change.

  8. Particle size dependent rheological property in magnetic fluid

    NASA Astrophysics Data System (ADS)

    Wu, Jie; Pei, Lei; Xuan, Shouhu; Yan, Qifan; Gong, Xinglong

    2016-06-01

    The influence of the particle size on the rheological property of magnetic fluid was studied both by the experimental and computer simulation methods. Firstly, the magnetic fluids were prepared by dispersing Fe3O4 nanospheres with size varied from 40 nm to 100 nm and 200 nm in the solution. Then, the rheological properties were investigated and it was found that the relative magnetorheological effects increased with increasing the particle size. Finally, the molecular dynamic simulation was used to analyze the mechanical characteristics of the magnetic fluid and the chain-like model agreed well with the experimental result. The authentic chain-like structure observed by a microscope agreed with the simulation results. The three particles composed of the similar cluster nanostructure, thus they exhibited similar magnetic property. To this end, the unique assembling microstructures was the origination of the mechanical difference. And it was found that the higher MR (magnetorheological) effects of the large particle based magnetic fluid was originated from the stronger assembling microstructure under the applying magnetic field.

  9. CFD simulation of anaerobic digester with variable sewage sludge rheology.

    PubMed

    Craig, K J; Nieuwoudt, M N; Niemand, L J

    2013-09-01

    A computational fluid dynamics (CFD) model that evaluates mechanical mixing in a full-scale anaerobic digester was developed to investigate the influence of sewage sludge rheology on the steady-state digester performance. Mechanical mixing is provided through an impeller located in a draft tube. Use is made of the Multiple Reference Frame model to incorporate the rotating impeller. The non-Newtonian sludge is modeled using the Hershel-Bulkley law because of the yield stress present in the fluid. Water is also used as modeling fluid to illustrate the significant non-Newtonian effects of sewage sludge on mixing patterns. The variation of the sewage sludge rheology as a result of the digestion process is considered to determine its influence on both the required impeller torque and digester mixing patterns. It was found that when modeling the fluid with the Hershel-Bulkley law, the high slope of the sewage stress-strain curve at high shear rates causes significant viscous torque on the impeller surface. Although the overall fluid shear stress property is reduced during digestion, this slope is increased with sludge age, causing an increase in impeller torque for digested sludge due to the high strain rates caused by the pumping impeller. Consideration should be given to using the Bingham law to deal with high strain rates. The overall mixing flow patterns of the digested sludge do however improve slightly. PMID:23764598

  10. Effect of water on the rheology of enstatite

    NASA Astrophysics Data System (ADS)

    Zhang, G.; Mei, S.; Song, M.; Kohlstedt, D. L.

    2015-12-01

    The influence of water on the rheological properties of enstatite, the second principal constituent of the upper mantle, was investi­gated by performing high-temperature creep experiments under both hydrous and anhydrous conditions. Samples were fabricated from fine powered Bamble enstatite (Mg0.85Fe0.15SiO3) from Norway. Deformation experiments were carried out using a gas-medium apparatus at a confining pressure of 300 MPa and temperatures between 1123 and 1473 K. For experiments conducted under hydrous conditions, samples were encapsulated with a talc sleeve, which supplied water by the dehydration near 1075 K. Under our experimental conditions, deformation was dominated by diffusion creep as indicated by a stress exponent of ~1 for both anhydrous and hydrous conditions. Furthermore, our data yields activation energies of ~200 and ~400 kJ/mol for hydrous and anhydrous conditions, respectively. These values are smaller than those reported for enstatite deformed in the dislocation creep regime (820 kJ/mol, Mackwell, 1992; 600 kJ/mol, Lawlis, 1997). Importantly, our results demonstrate a strong influence of water on the diffusion creep of enstatite. Samples deformed under hydrous conditions crept ~1.5 order of magnitude faster than those deformed under anhydrous conditions at similar differential stresses and temperatures. This water-weakening effect is more than ten times greater than determined for olivine. Such results provide critical constraints needed for understanding the rheological behavior of Earth's interior.

  11. Microfluidic viscometers for shear rheology of complex fluids and biofluids.

    PubMed

    Gupta, Siddhartha; Wang, William S; Vanapalli, Siva A

    2016-07-01

    The rich diversity of man-made complex fluids and naturally occurring biofluids is opening up new opportunities for investigating their flow behavior and characterizing their rheological properties. Steady shear viscosity is undoubtedly the most widely characterized material property of these fluids. Although widely adopted, macroscale rheometers are limited by sample volumes, access to high shear rates, hydrodynamic instabilities, and interfacial artifacts. Currently, microfluidic devices are capable of handling low sample volumes, providing precision control of flow and channel geometry, enabling a high degree of multiplexing and automation, and integrating flow visualization and optical techniques. These intrinsic advantages of microfluidics have made it especially suitable for the steady shear rheology of complex fluids. In this paper, we review the use of microfluidics for conducting shear viscometry of complex fluids and biofluids with a focus on viscosity curves as a function of shear rate. We discuss the physical principles underlying different microfluidic viscometers, their unique features and limits of operation. This compilation of technological options will potentially serve in promoting the benefits of microfluidic viscometry along with evincing further interest and research in this area. We intend that this review will aid researchers handling and studying complex fluids in selecting and adopting microfluidic viscometers based on their needs. We conclude with challenges and future directions in microfluidic rheometry of complex fluids and biofluids. PMID:27478521

  12. Studies on blood rheology in patients with primary pulmonary hypertension.

    PubMed

    Persson, S U; Gustavsson, C G; Larsson, H; Persson, S

    1991-10-01

    The rheologic properties of blood were studied in 6 patients with primary pulmonary hypertension (PPH) and compared with those of a control group of 10 healthy subjects. Blood viscosity was studied with a rotational viscometer and blood cell deformability with a filtrometer giving values for clogging particles (CP) and red cell transit time (RCTT). Blood viscosity at varying shear rates was found to be increased both at natural (p less than 0.025-0.005) and standardized hematocrit, 45% (p less than 0.05 at 40 s-1) in patients with PPH. Red cell deformability was reduced as indicated by a significant increase of RCTT (p less than 0.01). Increased values for hematocrit (p less than 0.001), hemoglobin concentration (p less than 0.001), and erythrocyte count (p less than 0.005) were found and decreased values for mean corpuscular hemoglobin concentration (MCHC) (p less than 0.025) and HDL cholesterol (p less than 0.005). Plasma viscosity, white cell deformability, white cell count, mean corpuscular volume (MCV), and plasma fibrinogen concentration did not significantly differ from the values found in the control group. It is concluded that patients with PPH have impaired blood rheology. The hemorheologic abnormalities in these patients may be of hemodynamic significance. PMID:1952272

  13. Dynamically-Tunable Smart Composites Featuring Electro-Rheological Fluids

    NASA Astrophysics Data System (ADS)

    Gandhi, Mukesh V.; Thompson, Brian S.

    1990-02-01

    A new generation of revolutionary multi-functional, dynamically-tunable, intelligent, ultra-advanced composite materials featuring electro-rheological fluids is proposed herein for the active continuum vibrational-control of structural systems. This paper reports on pioneering proof-of-concept experimental investigations focused on evaluating the elastodynamic transient and also the forced response characteristics of beams fabricated in this new class of materials. The results of these investigations clearly demonstrate the ability to dramatically change the vibrational characteristics of beam-like specimens fabricated in ultra-advanced composite materials by changing the electrical field imposed on the fluid domains. In addition, experimental results are presented which characterize the elastodynamic response of a connecting rod of a slider-crank mechanism fabricated in these ultra-advanced composite materials. Again, the combined forced and parametric responses are controlled by the voltage imposed on the electro-rheological fluid domain in the structure. The capability of these materials to interface with modern solid-state electronics can be exploited by extending the fundamental phenomenological work presented herein through the successful incorporation of intelligent sensor technologies and modern control strategies in order to significantly accelerate the evolution of these novel composite materials for the military and aerospace industries.

  14. Rheology of Indian Honey: Effect of Temperature and Gamma Radiation

    PubMed Central

    Panicker, Lata; Gautam, Satyendra

    2014-01-01

    Honey brands commonly available in Indian market were characterized for their rheological and thermal properties. Viscosity of all the honey samples belonging to different commercial brands was found to decrease with increase in temperature (5–40°C) and their sensitivity towards temperature varied significantly as explained by calculating activation energy based on Arrhenius model and ranged from 54.0 to 89.0 kJ/mol. However, shear rate was not found to alter the viscosity of honey indicating their Newtonian character and the shear stress varied linearly with shear rate for all honey samples. Honey is known to contain pathogenic microbial spores and in our earlier study gamma radiation was found to be effective in achieving microbial decontamination of honey. The effect of gamma radiation (5–15 kGy) on rheological properties of honey was assessed, and it was found to remain unchanged upon radiation treatment. The glass transition temperatures (Tg) of these honey analyzed by differential scanning calorimetry varied from −44.1 to −54.1°C and remained unchanged upon gamma radiation treatment. The results provide information about some key physical properties of commercial Indian honey. Radiation treatment which is useful for ensuring microbial safety of honey does not alter these properties. PMID:26904655

  15. Effect of confinement induced structures on suspension rheology

    NASA Astrophysics Data System (ADS)

    Ramaswamy, Meera; Leahy, Brian; Lin, Yen-Chih; Cohen, Itai

    2015-11-01

    Understanding the flow behavior of confined colloidal systems is important in many industrial settings ranging from inkjet printers to pharmaceuticals. Confined colloidal suspensions under shear demonstrate many fascinating responses including vorticity-aligned strings in colloidal liquids and buckled phases in crystals. Despite the extensive studies of these confinement induced structures, the interplay between these exotic structural responses and the suspension rheology remains poorly understood. Here, we use a confocal rheoscope to image the suspension particle configuration while simultaneously measuring its stress responses. The confocal rheoscope has two precisely-aligned parallel plates that can confine the suspension with a variable gap size ranging from 3 to 20 particle diameters, allowing us to measure the response of the system as a function of the gap size. Moreover, we alter the rheological properties of the sample by adding a small amount of dimers. The dimers undergo Jeffery orbits at large strains and deform the confinement induced structures of the spheres, leading to a viscosity change. We discuss the results of these experiments and their implications in the areas of micro and nanofluidics.

  16. Rheology of zirconia suspensions in a nonpolar organic medium

    SciTech Connect

    Moloney, V.M.B.; Parris, D.; Edirisinghe, M.J.

    1995-12-01

    Three dispersants (stearic acid, oleic acid, and poly-(12-hydroxystearic acid)) are compared for their ability to produce low-viscosity suspensions of zirconia in kerosene. Rheological measurements and sediment packing density measurements show that poly(12-hydroxystearic acid) is a better dispersant than stearic acid or oleic acid; this is explained in terms of the longer tail of the poly-(12-hydroxystearic acid) surfactant molecule. The amount of dispersant can be optimized to reduce viscosity and yield point of the suspension, and to eliminate thixotropic hysteresis. The use of a dispersion medium of lower viscosity than the dispersant makes it easy to detect when complete monolayer coverage has been achieved. The loss of pseudoplasticity, brought about by a higher degree of deflocculation, can be recovered by increasing the volume fraction of solids of a suspension and this is beneficial in the plastic forming of ceramics. Rheological measurements showed that these suspensions reach a critical state above a critical shear stress ({tau}{sub c}). This critical state is described by several parameters, i.e., the Bingham yield stress ({tau}{sub B}), the plastic viscosity ({eta}{sub PL}), and the critical shear rate ({dot {gamma}}{sub c}), which are dependent on the volume fraction of solids.

  17. Physicochemical, rheological and structural characteristics of starch in maize tortillas.

    PubMed

    Hernández-Uribe, Juan P; Ramos-López, Gonzalo; Yee-Madeira, Hernani; Bello-Pérez, Luis A

    2010-06-01

    Fresh and stored maize (white and blue) tortillas were evaluated for physicochemical, rheological and structural characteristics assessed by calorimetry, x-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, dynamic viscoelastic tests, and high-performance size-exclusion chromatography. Two endotherms were found in studies of fresh and stored tortillas. The low temperature endotherm (50-56 degrees C) was due to reorganized (retrograded) amylopectin, while the high temperature endotherm (105-123 degrees C) was attributed to retrograded amylose. The enthalpy value for the lower temperature transition was minor than that of the high temperature transition. Fresh tortillas showed an amorphous starch arrangement by x-ray diffraction study. Stored samples showed the presence of peaks at 2theta = 17 masculine and 23 masculine, indicating re-crystallization of starch components. FTIR results confirmed the development of higher levels of starch crystals during storage. Differences in the viscoelastic parameters were also observed between fresh and stored samples. At the longest storage times, white tortillas were more rigid than blue tortillas. Molar mass values for starch increased for both white and blue tortillas as storage time progressed, though relatively higher values were obtained for white tortillas. More starch reorganization occurred in white tortillas, in accordance to calorimetric, x-ray diffraction, FTIR and rheological results. These results corroborate that changes occurring in tortillas during storage are related to reorganization of starch components, and the maize variety more than the color plays an important role. PMID:20396953

  18. Blood rheology effect of submaximal exercise on young subjects.

    PubMed

    Romagnoli, Marco; Alis, Rafael; Martinez-Bello, Vladimir; Sanchis-Gomar, Fabian; Aranda, Rafael; Gómez-Cabrera, Mari-Carmen

    2014-01-01

    Nowadays cardiac and metabolic diseases are a matter of concern. Exercise is a valid treatment and method of prevention for not only adults, but also young subjects. Physical activity causes transient blood rheology impairment in adults. However little is known about the effects of exercise on blood flow characteristics in young subjects. The aim of the study was to assess the effects of a light aerobic exercise session on blood rheology in young subjects. Ten young subjects (aged 12-16 years) performed 1 hour of submaximal aerobic exercise (70% HRmax). Blood samples were drawn just before and after exercise. We determined blood and plasma viscosity, fibrinogen, erythrocyte deformability and aggregability. No changes in blood viscosity (p > 0.05), erythrocyte aggregation (p > 0.05) and fibrinogen (p > 0.05) were observed. Hematocrit (p = 0.025) and plasma viscosity (p = 0.018) rose with exercise, while erythrocyte elongation index lowered (p < 0.001). Plasma volume slightly reduced which may explain the lack of changes in blood viscosity. The results of the present study indicate a similar hemorheological response to submaximal exercise in both young people and adults. PMID:23302596

  19. Evolutionary models of the Earth with a grain size-dependent rheology

    NASA Astrophysics Data System (ADS)

    Rozel, Antoine; Golabek, Gregor; Tackley, Paul

    2015-04-01

    Thermodynamically consistent models of single phase grain size evolution have been proposed in the past years [Austin and Evans (2007), Ricard and Bercovici (2009), Rozel et al. (2011), Rozel (2012)]. Following the same physical approach, the mechanics of two-phase grain aggregates has been formulated [Bercovici and Ricard (2012a)]. Several non-linear mechanisms such as dynamic recrystallization or Zener pinning are now available in a single non-equilibrium formulation of grain size distributions evolution. The self-consistent generation of localized plate boundaries is predicted in [Bercovici and Ricard (2012b)] using this model, but it has not been tested in a dynamically consistent way. Our preliminary results have shown that out of equilibrium grain size dynamics leads to localization of deformation below the lithosphere rather than subduction initiation. Yet this result was obtained assuming indealized conditions. We study here, for the first time, the evolution of grain size in the mantle and lithosphere in evolutionary models, starting from a just-frozen magma ocean until the present day situation. Following complexities are considered in these models: melting, phase transitions, compressible convection, and different pressure-temperature-dependent composite rheologies in upper and lower mantles. We use a visco-plastic rheology in which the viscous strain rate is obtained by summation of dislocation and diffusion creep. Pressure and velocity fields are solved on a staggered grid using a SIMPLER-like method. Multigrid W-cycles and extra coarse-grid relaxations are employed to enhance the convergence of Stokes and continuity equations. The grain size is stored on a large number of tracers advected through the computational domain (a 2D spherical annulus), which prevent numerical diffusion and allows a high resolution. We also describe the physical formalism itself and derive a set of free parameters for the model. The results show that Normal growth, dynamic

  20. Impact of lithosphere rheology on the dynamic topography

    NASA Astrophysics Data System (ADS)

    Burov, Evgueni; Gerya, Taras; Koptev, Alexander

    2014-05-01

    Dynamic topography is a key observable signature of the Earth's and planetary (e.g. Venus) mantle dynamics. In general view, it reflects complex mantle flow patterns, and hence is supposed to correlate at different extent with seismic tomography, SKS fast orientations, geodetic velocity fields and geoid anomalies. However, identification of dynamic topography had no systematic success, specifically in the Earth's continents. Here we argue that lithosphere rheology, in particular, rheological stratification of continents, results in modulation of dynamic topography, converting commonly expected long-wavelength/small amplitude undulations into short-wavelength surface undulations with wide amplitude spectrum, superimposed onto "tectonic" topography. These ideas are explored in 3D using unprecedentedly high resolution numerical experiments (grid step size 2-3 km for 1500x1500x600 km computational area) incorporating realistic rheologically stratified lithosphere. Such high resolution is actually needed to resolve small-scale crustal faulting and inter-layer coupling/uncoupling that shape surface topography. The results reveal strikingly discordant, counterintuitive features of 3D dynamic topography, going far beyond the inferences from previous models. In particular, even weak anisotropic tectonic stress field results both in large-scale small-amplitude dynamic topography and in strongly anisotropic short-wavelength (at least in one direction) dynamic topography with wide amplitude range (from 100 to 2000-3000 m), including basins and ranges and large-scale linear normal and strike-slip faults. Even very slightly pre-stressed strong lithosphere yields and localizes deformation much easier , than un-prestressed one, in response to plume impact and mantle flow. The results shed new light on the importance of lithosphere rheology and active role of lithosphere in mantle-lithosphere interactions as well as on the role of mantle flow and far-field stresses in tectonic

  1. Magma rheology and eruption style at Volcán Fuego, Guatemala

    NASA Astrophysics Data System (ADS)

    Whittington, A. G.; Magaldi, T.; Calderas, A.; Chigna, G.; Escobar-Wolf, R. P.; Lyons, J. J.; Mathias, O.; Robert, G.; Seaman, S. J.

    2013-12-01

    Volcán Fuego, Guatemala, is a basaltic andesitic stratovolcano that has been in semi-continuous eruption for more than 500 years. The past decade has been characterized by vulcanian explosions with minor ash emission, punctuated by strombolian episodes with extrusions of lava flows and rare larger eruptions with pyroclastic flows, most recently in September 2012. We have investigated 10 samples (4 lava flows, 2 air-cooled bombs, and 4 blocks transported in pyroclastic flows) erupted or deposited in 2003 and in 2008-9, and all collected from the Barranca Santa Teresa on Fuego's western flank, to see if the type of activity (lava flow vs pyroclastic flow generation) can be correlated with varying physical and chemical properties of the magma. In particular we test the hypothesis that magma rheology controls eruptive style, i.e. blocks and bombs should be more viscous than lava flows. All the samples are highly crystalline, with similar basaltic andesite bulk compositions (52-53 wt.% SiO2) comprising matrix glass of andesitic to dacitic composition (62-67 wt.% SiO2) with abundant plagioclase, olivine and pyroxene phenocrysts together with minor Fe-Ti oxides. One lava flow "2003c" has a rhyolitic matrix glass (74 wt.% SiO2). Phenocryst compositions vary little, and show no systematic variation with eruption style. The matrix (dense-rock) density of the samples also varies little, from 2810-2850 kgm-3), while bulk density varies from 1480 to 2680 kgm-3, due to porosity. Lava flow samples contain 11-16 vol.% vesicles, while the bomb contains 16 vol.% and blocks range from 5 vol.% (dense) to 48 vol.% (vesicular). Water contents of matrix glasses vary from 0.25 wt.% (bomb) to less than 500 ppm (breadcrust block in a pyroclastic flow). The rheology of all samples was measured by uniaxial compression at 1020°C and 1 atm. In all experiments, regardless of porosity, the viscosity increased from 1010 to 1012 Pa.s in a few hours, then increased only slightly for the next 80

  2. Rheological and morphological properties of graphene-epoxy nanocomposites

    NASA Astrophysics Data System (ADS)

    Nobile, Maria Rossella; Raimondo, Marialuigia; Lafdi, Khalid; Guadagno, Liberata

    2016-05-01

    In this paper the rheological and morphological properties of an epoxy resin filled with graphene-based nanoparticles have been investigated. Two samples of partially exfoliated graphite (pEG) and carboxylated partially exfoliated graphite (CpEG), differing essentially for the content of carboxylated groups, are used. The percentage of exfoliated graphite is slightly different for the two samples: 56% for pEG and and 60% for CpEG. Exfoliated graphite is prepared using traditional acid intercalation followed by a sudden treatment at high temperature (900°C). The epoxy matrix is prepared by mixing a tetrafunctional precursor with a reactive diluent which produces a significant decrease in the viscosity of the epoxy precursor so that the dispersion step of nanofillers in the matrix can easily occur. The hardener agent, the 4,4-diaminodiphenyl sulfone (DDS), is added at a stoichiometric concentration with respect to all the epoxy rings. The inclusion of the pEG and CpEG samples in the formulated epoxy mixture significantly modifies the rheological behaviour of the mixture itself. The epoxy mixture, indeed, shows a Newtonian behavior; on the contrary the complex viscosity of the nanocomposites clearly shows a shear thinning behavior at 3 wt % of pEG content and at 0.75 wt% of CpEG content. The increase in complex viscosity with the increasing of pEG and CpEG content is mostly caused by a dramatic increase in the storage modulus of the nanocomposites. All the graphene-based epoxy mixtures are cured by a two-stage curing cycles: a first isothermal stage is carried out at the lower temperature of 125°C for 1 hour and, then, a second isothermal stage at the higher temperature of 200°C for 3 hours. The different morphology shown by the two pEG and CpEG samples is consistent with the difference in the percentage of exfoliation degree and well correlates with the rheological behavior of investigated graphene-epoxy nanocomposites.

  3. Thermo-Rheological Feedbacks in Silicic Lavas and Ignimbrites

    NASA Astrophysics Data System (ADS)

    Whittington, A. G.; Robert, G.; Andrews, G. D.; Avard, G.; Romine, W. L.; Ye, J.

    2012-12-01

    The rheology of lava is highly dependent on temperature, both directly (via non-Arrhenian temperature dependence of melt viscosity) and indirectly (via increasing crystal content). Rheology feeds back to temperature, because rapidly sheared melts can undergo viscous heating (heat production = viscosity × [strain rate]2), and rapid disequilibrium crystallization can cause heating due to latent heat release (ΔHxt). The heat budget of partially crystalline lava balances these gains with conductive losses controlled by thermal diffusivity (D) and conductivity (k = DρCP, where ρ is density and CP is heat capacity). We measured the apparent viscosity of several crystalline dacitic lavas from Santiaguito, Guatemala and Bezymianny, Kamchatka. At conditions appropriate to lava flows (shear stress ~0.1 to 0.4 MPa, strain rate ~10-8 to 10-5s-1), apparent viscosity is best modeled as a power-law with no yield strength. Viscosity of the flow core, at ~850°C, is estimated ~5×1010 Pa.s. There is no evidence for significant crystallization during flow emplacement at Santiaguito, but viscous heating may be significant ongoing heat source within these flows (~100Wm-3 if most shearing is restricted to a ~1m wide zone), enabling highly viscous lava to travel long distances (~4 km in ~2 yrs for Santiaguito). Extremely high-grade, lava-like welded ignimbrites are deposited by many of the largest explosive eruptions in Earth history with volumes typically ranging between 10 to 1000 km3 and volcanic explosivity indices of 8 to 9. The lava-like and rheomorphic Grey's Landing ignimbrite, Idaho, provides abundant field evidence supporting the upward-migration of a transient, 1 - 2 m thick, sub-horizontal ductile shear zone at the interface between the pyroclastic density current and deposit, through which all of the deposit passed. We test the syn-depositional shear zone model through a combination of rheological experiments and thermo-mechanical modeling. Our results demonstrate that

  4. Local rheology of human neutrophils investigated using atomic force microscopy.

    PubMed

    Lee, Yong J; Patel, Dipika; Park, Soyeun

    2011-01-01

    During the immune response, neutrophils display localized mechanical events by interacting with their environment through the micro-vascular transit, trans-endothelial, and trans-epithelial migration. Nano-mechanical studies of human neutrophils on localized nano-domains could provide the essential information for understanding their immune responsive functions. Using the Atomic Force Microscopy (AFM)-based micro-rheology, we have investigated rheological properties of the adherent human neutrophils on local nano-domains. We have applied the modified Hertz model to obtain the viscoelastic moduli from the relatively thick body regions of the neutrophils. In addition, by using more advanced models to account for the substrate effects, we have successfully characterized the rheological properties of the thin leading and tail regions as well. We found a regional difference in the mechanical compliances of the adherent neutrophils. The central regions of neutrophils were significantly stiffer (1,548 ± 871 Pa) than the regions closer to the leading edge (686 ± 801 Pa), while the leading edge and the tail (494 ± 537 Pa) regions were mechanically indistinguishable. The frequency-dependent elastic and viscous moduli also display a similar regional difference. Over the studied frequency range (100 to 300 Hz), the complex viscoelastic moduli display the partial rubber plateau behavior where the elastic moduli are greater than the viscous moduli for a given frequency. The non-disparaging viscous modulus indicates that the neutrophils display a viscoelastic dynamic behavior rather than a perfect elastic behavior like polymer gels. In addition, we found no regional difference in the structural damping coefficient between the leading edge and the cell body. Thus, we conclude that despite the lower loss and storage moduli, the leading edges of the human neutrophils display partially elastic properties similar to the cell body. These results suggest that the lower elastic moduli

  5. Molecular order, miscibility, and rheology of molten polyethylenes

    NASA Astrophysics Data System (ADS)

    Hussein, Ibnelwaleed Ali

    New evidence of high-temperature transitions and molecular order in molten polyethylenes is presented, and its influence on the miscibility of polyethylenes is discussed. Thermal and rheological techniques were used to investigate commercial HDPE, LDPE and Ziegler-Natta and Metallocene LLDPEs. Adequate amounts of extra antioxidants were added to the polyethylenes during melt conditioning, following a separate investigation. Polystyrene was utilized to demonstrate the typical behavior of isotropic polymer melts. Temperature sweeps during torque measurements in a melt blender, and when using a rheometer and DSC, showed thermal transitions at about 208°C and 227°C. Torque in the blender over the temperature range 208°--227°C showed a flat profile or an increase in torque near 227°C, unique behavior associated with thermotropic liquid crystal polymers (LCP). Additional support for the liquid-state order that agree with theoretical predictions for a LCP is found. These include indications of an approach to a sign change in the first normal stress difference, N1( ġ ), at low values of the steady shear rate, ġ , and a kink in the non-Newtonian viscosity eta( ġ ). A rheological investigation found no evidence of the attainment of the isotropic state at high temperature and suggested the persistence of order above these transitions. However, highly branched metallocene LLDPE ( ˜ 40 CH3/1000 C) did not show transitions or any evidence of molecular order. It is suggested that polyethylenes possess different molecular conformation in the melt state ranging from the chain-folded HDPE to the amorphous highly-branched LLDPE. It is this molecular order and mismatch of the molecular conformations of different polyethylene structures that provide an explanation for the immiscibility of polyethylenes, as revealed by the dependence of their rheological properties on blend composition. The influence of molecular weight, comonomer type, and mixing temperature on the miscibility

  6. Past presidents I have known.

    PubMed Central

    Keys, T E

    1975-01-01

    This paper is an account of the accomplishments of some of the early past presidents of the Medical Library Association known personally to the author in his career as a medical librarian. It demonstrates the qualities that made these librarians leaders of our profession and also indicates their personal attributes that contributed to the advancement of medical librarianship. It is hoped that the historical presentation of some of the giants of our profession will inspire present and future presidents and other medical librarians with an understanding of some of the qualities necessary to the continuing success of our profession. Sir William Osler, who was a great believer in libraries and librarians and himself a Past President of MLA, summed up four qualities in his advice to medical students equally applicable to past and present leadership in the library profession-(1) the art of detachment, (2) the virtue of method, (3) the quality of thoroughness, (4) the grace of humility (Osler, Sir William. Teacher and Student. In his Aequanimitas: with Other Addresses to Medical Students. 3d ed. Philadelphia, Blakiston Company, 1904. p. 27-31.). It is thought that our past presidents possessed all of these qualities. Images PMID:1089017

  7. Past presidents I have known.

    PubMed Central

    Keys, T E

    1998-01-01

    This paper is an account of the accomplishments of some of the early past presidents of the Medical Library Association known personally to the author in his career as a medical librarian. It demonstrates the qualities that made these librarians leaders of our profession and also indicates their personal attributes that contributed to the advancement of medical librarianship. It is hoped that the historical presentation of some of the giants of our profession will inspire present and future presidents and other medical librarians with an understanding of some of the qualities necessary to the continuing success of our profession. Sir William Osler, who was a great believer in libraries and librarians and himself a past president of MLA, summed up four qualities in his advice to medical students equally applicable to past and present leadership in the library profession--(1) the art of detachment, (2) the virtue of method, (3) the quality of thoroughness, and (4) the grace of humility (Osler, Sir William. Teacher and Student. In his Aequanimitas: with Other Addresses to Medical Students. 3d ed. Philadelphia, Blakiston Company, 1904. p. 27-31). It is thought that our past presidents possessed all of these qualities. Images PMID:9578938

  8. Healing the Past through Story

    ERIC Educational Resources Information Center

    Mullet, Judy H.; Akerson, Nels M. K.; Turman, Allison

    2013-01-01

    Stories matter, and the stories we tell ourselves matter most. Truth has many layers and narrative helps us makes senses of our multilayered reality. We live a personal narrative that is grounded in our past experience, but embodied in our present. As such, it filters what we see and how we interpret events. Attachment theorists tell us our early…

  9. The influence of selected excipients on the rheological behaviour of chitosan based ocular pharmaceutical systems

    NASA Astrophysics Data System (ADS)

    Budai, L.; Szabadi, E.; Hajdú, M.; Budai, M.; Klebovich, I.; Antal, I.

    2015-04-01

    Aims: Chitosan, a modified natural carbohydrate polymer, has received great attention in diverse scientific fields including pharmaceutical and biomedical research areas. Besides its low toxicity, mucoadhesiveness and biodegradability its special favourable rheological feature makes it a unique gelling agent for the design of ocular systems. Chitosan based (2.0 w/v %) ocular systems containing selected excipients were formulated in order to investigate the rheological influence of applied auxiliary materials. Rotational and oscillatory rheological properties of propylene glycol (1.0-20.0 w/v %), glycerin (1.0-5.0 w/v %) and castor oil (1.0-5.0 w/v %) containing chitosan gels were evaluated. The rheological behaviour of formulated ocular gels were compared before and after steam sterilization. Methods: Rotational and oscillatory rheological measurements were carried out with Kinexus Pro Rheometer. Comparison of flow curves and oscillatory frequency sweep measurements in the linear viscoelastic region made possible the evaluation of rheological effect of selected excipients. Results: In the applied concentration range the effect of propylene glycol among the selected excipients presents the most significant impact on rheology of chitosan formulations. Steam sterilization results in reduced viscosity in most of chitosan gels. However, the presence of polyols appears to prevent the degradation of chitosan after steam sterilization.

  10. Gelatins as rock analog in laboratory models: a rheological study and preliminary applications

    NASA Astrophysics Data System (ADS)

    Corbi, F.; di Giuseppe, E.; Funiciello, F.; Ranalli, G.; Faccenna, C.

    2009-12-01

    A laboratory model is a simplified scaled representation of nature. Thereby, according to ‘similarity criteria’, both rheological and physical parameters involved in the modeling must be properly scaled to natural conditions. In this work we systematically investigated the rheological and physical properties of a wide range of gelatins as functions of their temperature, composition, concentration, ageing and strain rate, in both gel- (i.e. solid) and sol-state (i.e. solution). Our results show that the complex mechanical behavior of gelatins reproduces gradually the full range of rheological behavior from purely elastic to visco-elasto-brittle to purely viscous (nonlinear) rheology going from the gel- to the sol-state. The handiness of the manipulation of the gelatins’ microstructure by calibrating the setting parameters and their resulting rheological variability appear promising for the potential use of these analog materials to simulate crustal and lithospheric rheological behavior. In particular, we found that pig skin 2.5 wt.% at 10 °C has the required rheological properties for a suitable experimental set-up to model crustal deformations.

  11. Effect of Particle Size Distribution on Slurry Rheology: Nuclear Waste Simulant Slurries

    SciTech Connect

    Chun, Jaehun; Oh, Takkeun; Luna, Maria L.; Schweiger, Michael J.

    2011-07-05

    Controlling the rheological properties of slurries has been of great interest in various industries such as cosmetics, ceramic processing, and nuclear waste treatment. Many physicochemical parameters, such as particle size, pH, ionic strength, and mass/volume fraction of particles, can influence the rheological properties of slurry. Among such parameters, the particle size distribution of slurry would be especially important for nuclear waste treatment because most nuclear waste slurries show a broad particle size distribution. We studied the rheological properties of several different low activity waste nuclear simulant slurries having different particle size distributions under high salt and high pH conditions. Using rheological and particle size analysis, it was found that the percentage of colloid-sized particles in slurry appears to be a key factor for rheological characteristics and the efficiency of rheological modifiers. This behavior was shown to be coupled with an existing electrostatic interaction between particles under a low salt concentration. Our study suggests that one may need to implement the particle size distribution as a critical factor to understand and control rheological properties in nuclear waste treatment plants, such as the U.S. Department of Energy’s Hanford and Savannah River sites, because the particle size distributions significantly vary over different types of nuclear waste slurries.

  12. Rheology as a tool for evaluation of melt processability of innovative dosage forms.

    PubMed

    Aho, Johanna; Boetker, Johan P; Baldursdottir, Stefania; Rantanen, Jukka

    2015-10-30

    Future manufacturing of pharmaceuticals will involve innovative use of polymeric excipients. Hot melt extrusion (HME) is an already established manufacturing technique and several products based on HME are on the market. Additionally, processing based on, e.g., HME or three dimensional (3D) printing, will have an increasingly important role when designing products for flexible dosing, since dosage forms based on compacting of a given powder mixture do not enable manufacturing of optimal pharmaceutical products for personalized treatments. The melt processability of polymers and API-polymer mixtures is highly dependent on the rheological properties of these systems, and rheological measurements should be considered as a more central part of the material characterization tool box when selecting suitable candidates for melt processing by, e.g., HME or 3D printing. The polymer processing industry offers established platforms, methods, and models for rheological characterization, and they can often be readily applied in the field of pharmaceutical manufacturing. Thoroughly measured and calculated rheological parameters together with thermal and mechanical material data are needed for the process simulations which are also becoming increasingly important. The authors aim to give an overview to the basics of rheology and summarize examples of the studies where rheology has been utilized in setting up or evaluating extrusion processes. Furthermore, examples of different experimental set-ups available for rheological measurements are presented, discussing each of their typical application area, advantages and limitations. PMID:25666026

  13. Rheological characterization of levan polysaccharides from Microbacterium laevaniformans.

    PubMed

    Bae, In Young; Oh, Im-Kyung; Lee, Suyong; Yoo, Sang-Ho; Lee, Hyeon Gyu

    2008-01-01

    Levan polysaccharides were produced from Microbacterium laevaniformans and its rheological behaviors were characterized as a function of concentration and temperature. The intrinsic viscosity of the purified levan was determined to be 0.38dL/g at 25 degrees C which was relatively higher than that of levans from other microbial sources. The flow behaviors of the levan solutions were characterized by the increase in the shear stress, giving more increments in the shear rate. Thus, the levan solutions exhibited the pseudoplastic behavior, which was characterized by the power law model. In addition, the flow behaviors of the levans were satisfactorily fitted to the Arrhenius equation where the activation energy of flow (Ea) decreased from 24.07 to 13.53kJ/mol (R2=0.98-0.99) with increasing concentrations. Moreover, the exponential equation was favorably applied to describe the effect of concentration on the apparent viscosity of the levan polysaccharides. PMID:17931701

  14. Rheology and Relaxation Timescales of ABA Triblock Polymer Gels

    NASA Astrophysics Data System (ADS)

    Peters, Andrew; Lodge, Timothy

    When dissolved in a midblock selective solvent, ABA polymers form gels composed of aggregated end block micelles bridged by the midblocks. While much effort has been devoted to the study of the structure of these systems, the dynamics of these systems has received less attention. We examine the underlying mechanism of shear relaxation of ABA triblock polymer gels, especially as a function of chain length, composition, and concentration. Recent work using time-resolved small-angle neutron scattering of polystyrene (PS)-block-poly(ethylene-alt-propylene) (PEP) in squalane has elucidated many aspects of the dynamics of diblock chain exchange. By using rheology to study bulk relaxation phenomena of the triblock equivalent, PS-PEP-PS, we apply the knowledge gained from the chain exchange studies to bridge the gap between the molecular and macroscopic relaxation phenomena in PS-PEP-PS triblock gels.

  15. Comparing the rheology of native spider and silkworm spinning dope.

    PubMed

    Holland, C; Terry, A E; Porter, D; Vollrath, F

    2006-11-01

    Silk production has evolved to be energetically efficient and functionally optimized, yielding a material that can outperform most industrial fibres, particularly in toughness. Spider silk has hitherto defied all attempts at reproduction, despite advances in our understanding of the molecular mechanisms behind its superb mechanical properties. Spun fibres, natural and man-made, rely on the extrusion process to facilitate molecular orientation and bonding. Hence a full understanding of the flow characteristics of native spinning feedstock (dope) will be essential to translate natural spinning to artificial silk production. Here we show remarkable similarity between the rheologies for native spider-dragline and silkworm-cocoon silk, despite their independent evolution and substantial differences in protein structure. Surprisingly, both dopes behave like typical polymer melts. This observation opens the door to using polymer theory to clarify our general understanding of natural silks, despite the many specializations found in different animal species. PMID:17057700

  16. Rheological investigation of highly filled polymers: Effect of molecular weight

    NASA Astrophysics Data System (ADS)

    Hnatkova, Eva; Hausnerova, Berenika; Hales, Andrew; Jiranek, Lukas; Vera, Juan Miguel Alcon

    2015-04-01

    The paper deals with rheological properties of highly filled polymers used in powder injection molding. Within the experimental framework seven PIM feedstocks based on superalloy Inconel 718 powder were prepared. Each feedstock contains the fixed amount of powder loading and the same composition of binder system consisting of three components: polyethylene glycol (PEG) differing in molecular weight, poly (methyl methacrylate) (PMMA) and stearic acid (SA). The aim is to investigate the influence of PEG's molecular weight on the flow properties of feedstocks. Non-Newtonian indices, representing the shear rate sensitivity of the feedstocks, are obtained from a polynomial fit, and found to vary within measured shear rates range from 0.2 to 0.8. Temperature effect is considered via activation energies, showing decreasing trend with increasing of molecular weight of PEG (except of feedstock containing 1,500 g.mol-1 PEG).

  17. New insights on the rheological properties of a rocksalt

    NASA Astrophysics Data System (ADS)

    Speranza, G.; Vinciguerra, S.; Di Genova, D.; Romano, C.; Vona, A.; Mollo, S.; Iarocci, A.

    2013-12-01

    The importance and economic interest on rocksalt deposits and salt bodies are well known and extensively studied. The physical and mechanical properties of salt have a profound influence on the tectonics as well as they are considered to be vital for applicative purposes such as mining, petroleum and nuclear waste storage. However, previous scientific works have mainly focused on synthetic rocksalt or commercial salt, whereas natural salt facies have been scarcely investigated. In this view, we present new data on the role of natural heterogeneities (i.e., relative abundance of primary salt crystals and impurities) on the rheological parameters of a rocksalt. This rock belongs to the Saline di Volterra formation (Volterra basin, Tuscany, central Italy) that was deposited during the Messinian Salinity Crisis. The 49-metre-thick salt sequence (intersected by the S1113 borehole of the Solvay company) is characterized by a high salt facies variability. In particular, three end-members have been recognized: the first contains abundant primary salt crystals, with minor or no recrystallizazion; the second member is extensively recrystallized, with scarce primary crystal remnants; the third shows a great abundance of clay impurities. Rheological parameters, such as static and dynamic Young's Modulus and coefficient of linear expansion, were measured for the three rocksalt end-members throughout P and S seismic velocities, uniaxial compressive strength and thermal expansion measurements. Seismic velocity has been measured on cubic samples with a side ranging from 4 to 7 cm. A clear effect of the salt facies was found: the average velocity is faster in mostly recrystallized salt samples (4500 m/s), slower in primary salt-rich samples (4300 m/s), and intermediate (4350 m/s) in presence of clay impurities. Dynamic Young's Modulus calculated on velocities (average value ≈ 38 GPa) mirrors this behavior, with lowest values related to primary salt. The anisotropic effect induced

  18. Effect of friction on the rheology of dense suspensions

    NASA Astrophysics Data System (ADS)

    Gallier, Stany; Lemaire, Elisabeth; Peters, François; Lobry, Laurent

    2014-11-01

    This work reports three-dimensional numerical simulations of sheared non-Brownian concentrated suspensions using a fictitious domain method. Contacts between particles are modeled using a DEM-like approach (Discrete Element Method), which allows for a more physical description, including roughness and friction. This study emphasizes the effect of friction between particles and its role on rheological properties, especially on normal stress differences. Friction is shown to notably increase viscosity and second normal stress difference | N2 | and decrease | N1 | , in better agreement with experiments. The hydrodynamic and contact contributions to the overall particle stress are particularly investigated and this shows that the effect of friction is mostly due to the additional contact stress since the hydrodynamic stress remains unaffected by friction. Simulation results are also compared with experiments and the agreement is improved when friction is accounted for: this suggests that friction is operative in actual suspensions.

  19. Rheological characterization of digested sludge by solid sphere impact.

    PubMed

    Jiang, Jiankai; Wu, Jing; Poncin, Souhila; Li, Huai Z

    2016-10-01

    An impact method was applied to investigate the rheological characteristics of digested sludge and reveal its transient dynamics. A high-speed camera allowed visualizing the dynamic impact process and observing interaction between impacting sphere and targeted sludge. A damping oscillation was observed after the impact. The crater diameter followed an exponential function, while the crater depth varied as a logarithmic function of both sphere diameter and free fall height. Furthermore, the viscosity and elasticity of digested sludge were evaluated by establishing a simplified impact drag force model. The impact elastic modulus was consistent with the Young's modulus measured by a penetrometer. The impact viscosity was reasonable as the estimated impact shear stress was greater than the yield stress of digested sludge resulting in the formation of crater. The impact method offers an alternative way to reveal the viscoelasticity of digested sludge through a dynamic process. PMID:27372010

  20. Rheology, tectonics, and the structure of the Venus lithosphere

    NASA Technical Reports Server (NTRS)

    Zuber, M. T.

    1994-01-01

    Given the absence of ground truth information on seismic structure, heat flow, and rock strength, or short wavelength gravity or magnetic data for Venus, information on the thermal, mechanical and compositional nature of the shallow interior must be obtained by indirect methods. Using pre-Magellan data, theoretical models constrained by the depths of impact craters and the length scales of tectonic features yielded estimates on the thickness of Venus' brittle-elastic lithosphere and the allowable range of crustal thickness and surface thermal gradient. The purpose of this study is to revisit the question of the shallow structure of Venus based on Magellan observations of the surface and recent experiments that address Venus' crustal rheology.

  1. Low temperature rheological studies of hydrocarbon base lubricants

    SciTech Connect

    Venerus, D.C.; Klaus, E.E.; Duda, J.L.

    1987-01-01

    This study is designed to evaluate the rheological properties of samples of waxy mineral oil, a wax-free hydrocarbon solvent, wax-free polymer-thickened oils and fully formulated lubricants containing wax and polymer in hydrocarbon solvents. A mechanical spectrometer (cone and plate rotational viscometer) and the mini rotary viscometer were used in these studies. The cooling rate and cold soak times were computer programmed using a mechanical system. A compromise system using a cooling rate of 0.56/sup 0/C/min and a cold soak time of one hour was used in order to produce data in a reasonable time. These values were chosen from the information gained on wax crystal growth and equilibration from the low temperature dewaxing studies conducted at this laboratory.

  2. Rheological decoupling at the Moho and implication to Venusian tectonics.

    PubMed

    Azuma, Shintaro; Katayama, Ikuo; Nakakuki, Tomoeki

    2014-01-01

    Plate tectonics is largely responsible for material and heat circulation in Earth, but for unknown reasons it does not exist on Venus. The strength of planetary materials is a key control on plate tectonics because physical properties, such as temperature, pressure, stress, and chemical composition, result in strong rheological layering and convection in planetary interiors. Our deformation experiments show that crustal plagioclase is much weaker than mantle olivine at conditions corresponding to the Moho in Venus. Consequently, this strength contrast may produce a mechanical decoupling between the Venusian crust and interior mantle convection. One-dimensional numerical modeling using our experimental data confirms that this large strength contrast at the Moho impedes the surface motion of the Venusian crust and, as such, is an important factor in explaining the absence of plate tectonics on Venus. PMID:24638113

  3. Novel reversible and switchable electrolytes based on magneto-rheology

    PubMed Central

    Ding, Jie; Peng, Gangrou; Shu, Kewei; Wang, Caiyun; Tian, Tongfei; Yang, Wenrong; Zhang, Yuanchao; Wallace, Gordon G.; Li, Weihua

    2015-01-01

    Replacing organic liquid electrolytes with solid electrolytes has led to a new perspective on batteries, enabling high-energy battery chemistry with intrinsically safe cell designs. However, most solid/gel electrolytes are easily deformed; under extreme deformation, leakage and/or short-circuiting can occur. Here, we report a novel magneto-rheological electrolyte (MR electrolyte) that responds to changes in an external magnetic field; the electrolyte exhibits low viscosity in the absence of a magnetic field and increased viscosity or a solid-like phase in the presence of a magnetic field. This change from a liquid to solid does not significantly change the conductivity of the MR electrolyte. This work introduces a new class of magnetically sensitive solid electrolytes that can enhance impact resistance and prevent leakage from electronic devices through reversible active switching of their mechanical properties. PMID:26493967

  4. Rheological measurements in titania gels synthesized from reverse micelles

    NASA Astrophysics Data System (ADS)

    Romano, S. D.; Kurlat, D. H.

    2000-06-01

    TiO 2 sol and gel systems have been synthesized by hydrolysis of titanium butoxide in microemulsions W/O. Different systems compositions were prepared at constant Wo=[H 2O]/[AOT] and changing R=[H 2O]/[Ti(BuO) 4]. Experimental measurements show a progressive increase of the viscosity with time, characteristic of a sol-gel transition. The rheology of the transition was studied by following the behavior of viscoelastic parameters ( G', G″ and η*) as a function of time at different frequencies. The possibility to apply standard percolation theory was discussed. The application of two alternative growth models — either `fractal growth model' or `nearly linear growth model' — has been analysed.

  5. Rheology of a Twist-bend Nematic Liquid Crystal

    NASA Astrophysics Data System (ADS)

    Salili, Seyyed Muhammad; Kim, Chanjoong; Sprunt, Samuel; Gleeson, James; Parri, Owain; Jakli, Antal; Kim Lab Team; Merck Lab Team

    2015-03-01

    First detailed flow shear alignment studies and rheological measurements in the twist-bend nematic (Ntb) liquid crystalline phase of odd numbered flexible dimer molecules is presented. It is found that the Ntb phase is strongly shear-thinning. At shear stresses below 1 Pa the apparent viscosity of the Ntb phase is 1000 times larger than in the nematic phase. At stresses above 10 Pa the Ntb viscosity drops by two orders of magnitude and the material exhibits Newtonian fluid behavior. The results are consistent with the behavior of a system with pseudo-layer structure with layer spacing determined by the heliconical pitch. From the measurements of dynamic modulus we estimate the compression modulus of the pseudo-layers to be B ~ 2 kPa this value is discussed within the context of a simple theoretical model based upon a coarse-grained elastic free energy. www.jakligroup.com.

  6. Rheology of Deformable Particle Suspensions by Dissipative Particle Dynamics

    NASA Astrophysics Data System (ADS)

    Chaudhri, Anuj; Lukes, Jennifer R.

    2007-03-01

    Understanding the behavior of colloidal suspensions, emulsions, and other complex fluids under shear flow is important in liquid crystal switching, lab-on-chip processing of biological fluids, self-assembly of polymer structures, and other areas of soft matter physics. Various analytical and computational approaches, including Brownian dynamics, dissipative particle dynamics, and Stokesian dynamics, have been applied to study the rheology of rigid particle suspensions. Still lacking are methods capable of treating suspensions containing deformable particles such as blood cells or macromolecules. Here we present a new, dissipative particle dynamics-based computational method with this capability. This method is used to calculate the shear rate dependence of viscosity for suspensions of deformable particles with varying stiffnesses.

  7. The Rheological Structure of the East Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Jiang, X.; Jin, Y.

    2012-04-01

    The Rheological Structure of the East Tibetan Plateau Xiaodian Jiang1, and Yu Jin2 1. Ocean University of China, Qingdao 266003, China 2. Chevron Exploration & Production, Beijing 100004, China The rheological structure of the lithosphere can be calibrated with seismic activities. We intensively use the seismic focal depths from 2072 events occurring in Longmenshan Fold Belt (LFB) area to identify the transition from brittle failure to ductile with depth in the lithosphere. The earthquakes were monitored by China Earthquake Network Center (CENC) from 01/07/1970 through 31/08/2010 with magnitude larger than 3.5 at 88 earthquake stations with a depth error bar of ±2km. Among the 2072 seismic events, 82 of them have a magnitude larger than 5 and were recorded simultaneously by the NEIC and CENC since January 1, 1990. The parameters of the 82 events recorded by both institutions are in close agreement. Most of the earthquakes in LFB and its vicinity occurred at depths from 2 to 36 km. However, there are 3 extras with focal depth at 39, 44 and 60 km respectively. All these three events occurred in Sichuan Basin where the lithosphere is not decouple between the crust and the upper mantle so that the brittle failure is able to propagate all the way from the crust to the upper mantle lithosphere. Because all of the seismic events in the eastern Tibetan plateau occurred at the depths less than or equal to 36±2 km deep, the 36±2 km should be a good statistical number to define the lower boundary of the elastically strong, brittle upper/middle crust. The Moho depth across LFB calculated by the 3D flexural modeling in space domain constrained by the gridded gravity database and merged our new measurement data varies considerably from about 38 km in Sichuan Basin to about 58 km beneath the eastern plateau. The Moho depths in the eastern plateau are in lower to mid 50 km deep. In the other words, the thermally depending ductile, weak lower crust is rheologically defined the

  8. Molecular simulation of rheological properties using massively parallel supercomputers

    SciTech Connect

    Bhupathiraju, R.K.; Cui, S.T.; Gupta, S.A.; Cummings, P.T.; Cochran, H.D.

    1996-11-01

    Advances in parallel supercomputing now make possible molecular-based engineering and science calculations that will soon revolutionize many technologies, such as those involving polymers and those involving aqueous electrolytes. We have developed a suite of message-passing codes for classical molecular simulation of such complex fluids and amorphous materials and have completed a number of demonstration calculations of problems of scientific and technological importance with each. In this paper, we will focus on the molecular simulation of rheological properties, particularly viscosity, of simple and complex fluids using parallel implementations of non-equilibrium molecular dynamics. Such calculations represent significant challenges computationally because, in order to reduce the thermal noise in the calculated properties within acceptable limits, large systems and/or long simulated times are required.

  9. Novel reversible and switchable electrolytes based on magneto-rheology

    NASA Astrophysics Data System (ADS)

    Ding, Jie; Peng, Gangrou; Shu, Kewei; Wang, Caiyun; Tian, Tongfei; Yang, Wenrong; Zhang, Yuanchao; Wallace, Gordon G.; Li, Weihua

    2015-10-01

    Replacing organic liquid electrolytes with solid electrolytes has led to a new perspective on batteries, enabling high-energy battery chemistry with intrinsically safe cell designs. However, most solid/gel electrolytes are easily deformed; under extreme deformation, leakage and/or short-circuiting can occur. Here, we report a novel magneto-rheological electrolyte (MR electrolyte) that responds to changes in an external magnetic field; the electrolyte exhibits low viscosity in the absence of a magnetic field and increased viscosity or a solid-like phase in the presence of a magnetic field. This change from a liquid to solid does not significantly change the conductivity of the MR electrolyte. This work introduces a new class of magnetically sensitive solid electrolytes that can enhance impact resistance and prevent leakage from electronic devices through reversible active switching of their mechanical properties.

  10. Rheological profile of boron nitride–ethylene glycol nanofluids

    SciTech Connect

    Żyła, Gaweł; Witek, Adam; Gizowska, Magdalena

    2015-01-07

    The paper presents the complete rheological profile of boron nitride (BN)–ethylene glycol (EG) nanofluids. Nanofluids have been produced by two-step method on the basis of commercially available powder of plate-like grains of nanometrical thickness. Viscoelastic structure has been determined in oscillatory measurements at a constant frequency and temperature. Viscosity and flow curves for these materials have been measured. Studies have shown that the Carreau model can be used for the modeling of dynamic viscosity curves of the material. The samples were tested for the presence of thixotropy. The dependence of viscosity on temperature was also examined. The effect of temperature on the dynamic viscosity of BN-EG nanofluids can be modelled with the use of Vogel-Fulcher-Tammann expression.

  11. Rheological behavior of cellulose nanowhisker suspension under magnetic field.

    PubMed

    Kim, Dah Hee; Song, Young Seok

    2015-08-01

    We investigated the influence of a magnetic field on the rheology of cellulose nanowhisker (CNW) suspension. The morphology of CNWs was analyzed by using polarized optical microscopy (POM) and transmission electron microscopy (TEM). The findings show that the application of the magnetic field leads to an increase in shear viscosity and viscoelastic properties such as the storage and loss moduli. A mesoscale constitutive model was adopted to provide better understanding of the effect of particle concentration on the orientation of CNWs. As the concentration increases, the steric interaction between particles becomes significant and the effect of the applied magnetic field on the internal structure of the CNW suspension was reduced. In addition, the size distribution of CNWs was characterized using a light scattering method. PMID:25933545

  12. Rheological decoupling at the Moho and implication to Venusian tectonics

    PubMed Central

    Azuma, Shintaro; Katayama, Ikuo; Nakakuki, Tomoeki

    2014-01-01

    Plate tectonics is largely responsible for material and heat circulation in Earth, but for unknown reasons it does not exist on Venus. The strength of planetary materials is a key control on plate tectonics because physical properties, such as temperature, pressure, stress, and chemical composition, result in strong rheological layering and convection in planetary interiors. Our deformation experiments show that crustal plagioclase is much weaker than mantle olivine at conditions corresponding to the Moho in Venus. Consequently, this strength contrast may produce a mechanical decoupling between the Venusian crust and interior mantle convection. One-dimensional numerical modeling using our experimental data confirms that this large strength contrast at the Moho impedes the surface motion of the Venusian crust and, as such, is an important factor in explaining the absence of plate tectonics on Venus. PMID:24638113

  13. Bread dough rheology: Computing with a damage function model

    NASA Astrophysics Data System (ADS)

    Tanner, Roger I.; Qi, Fuzhong; Dai, Shaocong

    2015-01-01

    We describe an improved damage function model for bread dough rheology. The model has relatively few parameters, all of which can easily be found from simple experiments. Small deformations in the linear region are described by a gel-like power-law memory function. A set of large non-reversing deformations - stress relaxation after a step of shear, steady shearing and elongation beginning from rest, and biaxial stretching, is used to test the model. With the introduction of a revised strain measure which includes a Mooney-Rivlin term, all of these motions can be well described by the damage function described in previous papers. For reversing step strains, larger amplitude oscillatory shearing and recoil reasonable predictions have been found. The numerical methods used are discussed and we give some examples.

  14. Rheological properties of ovalbumin hydrogels as affected by surfactants addition.

    PubMed

    Hassan, Natalia; Messina, Paula V; Dodero, Veronica I; Ruso, Juan M

    2011-04-01

    The gel properties of ovalbumin mixtures with three different surfactants (sodium perfluorooctanoate, sodium octanoate and sodium dodecanoate) have been studied by rheological techniques. The gel elasticities were determined as a function of surfactant concentration and surfactant type. The fractal dimension of the formed structures was evaluated from plots of storage modulus against surfactant concentration. The role of electrostatic, hydrophobic and disulfide SS interactions in these systems has been demonstrated to be the predominant. The viscosity of these structures tends to increase with surfactant concentration, except for the fluorinated one. Unfolded ovalbumin molecules tend to form fibrillar structures that tend to increase with surfactant concentration, except for the fluorinated one. This fact has been related to the particular nature of this molecule. PMID:21262258

  15. The rheology of collapsing zeolites amorphized by temperature and pressure.

    PubMed

    Greaves, G N; Meneau, F; Sapelkin, A; Colyer, L M; ap Gwynn, I; Wade, S; Sankar, G

    2003-09-01

    Low-density zeolites collapse to the rigid amorphous state at temperatures that are well below the melting points of crystals of the same composition but of conventional density. Here we show, by using a range of experimental techniques, how the phenomenon of amorphization is time dependent, and how the dynamics of order-disorder transitions in zeolites under temperature and pressure are equivalent. As a result, thermobaric regions of instability can be charted, which are indicative of polyamorphism. Moreover, the boundaries of these zones depend on the rate at which temperature or pressure is ramped. By directly comparing the rheology of collapse with structural relaxation in equivalent melts, we conclude that zeolites amorphize like very strong liquids and, if compression occurs slowly, this is likely to lead to the synthesis of perfect glasses. PMID:12942072

  16. Comparing the rheology of native spider and silkworm spinning dope

    NASA Astrophysics Data System (ADS)

    Holland, C.; Terry, A. E.; Porter, D.; Vollrath, F.

    2006-11-01

    Silk production has evolved to be energetically efficient and functionally optimized, yielding a material that can outperform most industrial fibres, particularly in toughness. Spider silk has hitherto defied all attempts at reproduction, despite advances in our understanding of the molecular mechanisms behind its superb mechanical properties. Spun fibres, natural and man-made, rely on the extrusion process to facilitate molecular orientation and bonding. Hence a full understanding of the flow characteristics of native spinning feedstock (dope) will be essential to translate natural spinning to artificial silk production. Here we show remarkable similarity between the rheologies for native spider-dragline and silkworm-cocoon silk, despite their independent evolution and substantial differences in protein structure. Surprisingly, both dopes behave like typical polymer melts. This observation opens the door to using polymer theory to clarify our general understanding of natural silks, despite the many specializations found in different animal species.

  17. Novel reversible and switchable electrolytes based on magneto-rheology.

    PubMed

    Ding, Jie; Peng, Gangrou; Shu, Kewei; Wang, Caiyun; Tian, Tongfei; Yang, Wenrong; Zhang, Yuanchao; Wallace, Gordon G; Li, Weihua

    2015-01-01

    Replacing organic liquid electrolytes with solid electrolytes has led to a new perspective on batteries, enabling high-energy battery chemistry with intrinsically safe cell designs. However, most solid/gel electrolytes are easily deformed; under extreme deformation, leakage and/or short-circuiting can occur. Here, we report a novel magneto-rheological electrolyte (MR electrolyte) that responds to changes in an external magnetic field; the electrolyte exhibits low viscosity in the absence of a magnetic field and increased viscosity or a solid-like phase in the presence of a magnetic field. This change from a liquid to solid does not significantly change the conductivity of the MR electrolyte. This work introduces a new class of magnetically sensitive solid electrolytes that can enhance impact resistance and prevent leakage from electronic devices through reversible active switching of their mechanical properties. PMID:26493967

  18. Fault zone rheology and length scales of frictional failure

    NASA Astrophysics Data System (ADS)

    Fagereng, A.

    2011-12-01

    Faults have a finite thickness and commonly contain fault rocks of heterogeneous composition, leading to rheological contrasts between intermingled lithologies (at the macroscale) and minerals (at the microscale) within the fault zone. The distribution and volumetric ratio of materials with different viscosity, frictional behavior, and preferred deformation mechanism, may therefore be a critical factor controlling the bulk rheology of heterogeneous fault zones. For example, at subgreenschist facies metamorphic conditions, fine-grained phyllosilicate-dominated mudstones tend to experience viscous shearing flow by dissolution-precipitation creep, whereas coarse grained quartz-dominated sandstones tend to act like competent, brittle volumes. In the rock record, deformation of mixed lithologies is well represented in tectonic mélanges. The subgreenschist facies (P < 550 MPa, T ~ 300°C) Chrystalls Beach Complex accretionary mélange, New Zealand, is an example of a well-exposed shear zone where relatively competent lenses of chert, sandstone, and basalt are distributed within a cleaved pelitic matrix. Whereas the pelitic matrix deformed predominantly by viscous shearing flow accommodated by dissolution-precipitation creep, the more competent lenses commonly contain extension fractures. The complex is cross-cut by an anastomosing fault-fracture mesh, defined by slickenfibre-coated shear surfaces linked by quartz-calcite extension veins. The frequency-size distribution of competent lenses (phacoids) in the Chrystalls Beach Complex follows a power-law distribution and is scale-invariant. The exponent of the power-law distribution varies with dominant deformation style, and is high in zones of dominantly continuous deformation - relating to a high matrix fraction, predominance of small phacoids, and small phacoid aspect ratios, whereas a low power-law exponent relates to a small matrix fraction and localized deformation accommodated on shear discontinuities. This

  19. Novel formulations of ballistic gelatin. 1. Rheological properties.

    PubMed

    Zecheru, Teodora; Său, Ciprian; Lăzăroaie, Claudiu; Zaharia, Cătălin; Rotariu, Traian; Stănescu, Paul-Octavian

    2016-06-01

    Ballistic gelatin is the simulant of the human body during field tests in forensics and other related fields, due to its physical and mechanical similarities to human trunk and organs. Since the ballistic gelatin used in present has important issues to overcome, an alternative approach is the use of gelatin-polymer composites, where a key factor is the insertion of biocompatible materials, which replicate accurately the human tissues. In order to be able to obtain an improved material in terms of mechanical performances by an easy industrial-scale technology, before the verification of the ballistic parameters by shooting in agreement with military standards, one of the best and cheapest solutions is to perform a thorough check of their rheological properties, in standard conditions. PMID:27139038

  20. Comparing the rheology of mulberry and "wild" silkworm spinning dopes.

    PubMed

    Holland, C; Porter, D; Vollrath, F

    2012-06-01

    Lepidoperan silks provide a superb opportunity for comparative studies of spinning and fiber characteristics. Comparing the four species, Bombyx mori (China), Actias selene (India), Antheraea yamamai (Japan), Gonometa postica (Africa), allows us to examine differences on the family, species, and race levels. Measured rheological properties were consistent with phylogenetic relationships and in the context of resource allocation and gland morphology. We propose that the thorough domestication of the mulberry silkworm B. mori for high silk yield has resulted in a compensatory optimization for spinning efficiency. This is in stark contrast to the wild silkworms, where Saturnids appear to minimize their energetic input toward silk output and G. postica seems to balance both. We conclude that comparative studies provide valuable baseline information for future biomimetic applications and modeling, as well as illuminating biologically important details of silk processing. PMID:22161905

  1. Dynamic elastic properties of magneto-rheological slurries

    NASA Astrophysics Data System (ADS)

    Donado, F. F.; Mendoza, M. E. M. E.; Carrillo, J. L.

    2001-06-01

    We study the propagation of elastic perturbations in magneto-rheological slurries of iron particles dispersed in glycerine. The complexity of these systems is revealed in the fibrillar structure acquired under the application of a magnetic field. Recently, it has been reported the observation of two different low frequency modes of propagation. One of these modes has been associated to the propagation of the perturbation through the fluid medium. The other one has been qualitatively explained as the propagation of the elastic perturbation through the suspended particles. This second mode appears when a magnetic field is applied to the slurry. The propagation speed for both modes depends on the field intensity and on the properties of the magnetic particles. Theoretically, we analyze these modes and calculate the sound velocity. We obtain a quantitative good agreement with the experimental results.

  2. Rheological properties of living cytoplasm: endoplasm of Physarum plasmodium.

    PubMed

    Sato, M; Wong, T Z; Allen, R D

    1983-10-01

    Magnetic sphere viscoelastometry, video microscopy, and the Kamiya double chamber method (Kamiya, N., 1940, Science [Wash. DC], 92:462-463.) have been combined in an optical and rheological investigation of the living endoplasm of Physarum polycephalum. The rheological properties examined were yield stress, viscosity (as a function of shear), and elasticity. These parameters were evaluated in directions perpendicular; (X) and parallel (Y) to the plasmodial vein. Known magnetic forces were used for measurements in the X direction, while the falling ball technique was used in the Y direction (Cygan, D.A., and B. Caswell, 1971, Trans. Soc. Rheol. 15:663-683; MacLean-Fletcher, S.D., and T.D. Pollard, 1980, J. Cell Biol., 85:414-428). Approximate yield stresses were calculated in the X and Y directions of 0.58 and 1.05 dyn/cm2, respectively. Apparent viscosities measured in the two directions (eta x and eta y) were found to fluctuate with time. The fluctuations in eta x and eta y were shown, statistically, to occur independently of each other. Frequency correlation with dynamoplasmograms indicated that these fluctuations probably occur independently of the streaming cycle. Viscosity was found to be a complex function of shear, indicating that the endoplasm is non-Newtonian. Plots of shear stress vs. rate of shear both parallel and perpendicular to the vein, showed that endoplasm is not a shear thinning material. These experiments have shown that living endoplasm of Physarum is an anisotropic viscoelastic fluid with a yield stress. The endoplasm appears not to be a homogeneous material, but to be composed of heterogeneous domains. PMID:6619187

  3. Rheological characterization of a magnetorheological ferrofluid using iron nitride nanoparticles

    NASA Astrophysics Data System (ADS)

    Armijo, Leisha M.; Ahuré-Powell, Louise A.; Wereley, Norman M.

    2015-05-01

    Magnetorheology of a magnetorheological ferrofluid (MRFF) was investigated to study the role of a ferromagnetic nanoparticle (NP) additive in magnetorheological fluids (MRFs). Iron nitride (Fe16N2) NPs, nominally within the diameter range of ˜16-45 nm (spherical NPs) and ˜30-66 nm (cubic NPs), were coated with carboxy-polyethylene glycol (carboxy-PEG) and dispersed in silicone oil in order to produce a magnetic carrier fluid or ferrofluid for two solids loadings: 2 vol. % and 5 vol. %. Conventional spherical carbonyl iron (CI) particles, varying in diameter from 6 to 10 μm, were suspended in the ferrofluid at 25 vol. % solids loading. Rheological properties of the MRFF synthesized with the carboxy-PEG-based ferromagnetic carrier fluid were compared to the MRF synthesized with silicone oil to determine how ferrofluid can influence dynamic viscosity and yield stress. Rheological measurements of both MRF and MRFF samples were carried out using a Paar Physica 300 rheometer to estimate the field-off viscosity and to measure flow curves (i.e., shear stress vs. shear rate) as a function of magnetic field. A Bingham-plastic model was used to characterize the flow curves, and results show that there is an increase in the dynamic viscosity of the MRFF over the MRF. The ferromagnetic carrier fluid greatly increases yield stress as only 2 vol. % of added carboxy-PEG NPs improves the yield stress performance by almost 5%. A second MRFF sample synthesized with 5 vol. % of added carboxy-PEG NPs contained in the ferrofluid significantly enhanced the yield stress performance by 13% over the MRF at the same CI solids loading (25 vol. %).

  4. Experiments on the rheology of vesicle-bearing magmas

    NASA Astrophysics Data System (ADS)

    Vona, Alessandro; Ryan, Amy G.; Russell, James K.; Romano, Claudia

    2016-04-01

    We present a series of high temperature uniaxial deformation experiments designed to investigate the effect of bubbles on the magma bulk viscosity. Starting materials having variable vesicularity (φ = 0 - 66%) were synthesized by high-temperature foaming (T = 900 - 1050 ° C and P = 1 bar) of cores of natural rhyolitic obsidian from Hrafntinnuhryggur, Krafla, Iceland. These cores were subsequently deformed using a high-temperature uniaxial press at dry atmospheric conditions. Each experiment involved deforming vesicle-bearing cores isothermally (T = 750 ° C), at constant displacement rates (strain rates between 0.5-1 x 10‑4 s‑1), and to total strains (ɛ) of 10-40%. The viscosity of the bubble-free melt (η0) was measured by micropenetration and parallel plate methods and establishes a baseline for comparing data derived from experiments on vesicle rich cores. At the experimental conditions, the presence of vesicles has a major impact on the rheological response, producing a marked decrease of bulk viscosity (maximum decrease of 2 log units Pa s) that is best described by a two-parameter empirical equation: log ηBulk = log η0 - 1.47 * [φ/(1-φ)]0.48. Our model provides a means to compare the diverse behaviour of vesicle-bearing melts reported in the literature and reflecting material properties (e.g., analogue vs. natural), geometry and distribution of pores (e.g. foamed/natural vs. unconsolidated/sintered materials), and flow regime. Lastly, we apply principles of Maxwell relaxation theory, combined with our parameterization of bubble-melt rheology, to map the potential onset of non-Newtonian behaviour (strain localization) in vesiculated magmas and lavas as a function of melt viscosity, vesicularity, strain rate, and geological condition. Increasing vesicularity in magmas can initiate non-Newtonian behaviour at constant strain rates. Lower melt viscosity sustains homogeneous Newtonian flow in vesiculated magmas even at relatively high strain rates.

  5. Serum zinc and blood rheology in sportsmen (football players).

    PubMed

    Khaled, S; Brun, J F; Micallel, J P; Bardet, L; Cassanas, G; Monnier, J F; Orsetti, A

    1997-01-01

    We aimed at investigating relationships between zinc status, blood rheology and blood glucose during exercise. Twenty-one professional football players underwent a triangular maximal exercise test on cycloergometer, with progressively increasing work loads until VO2max. On the whole these subjects had a low serum zinc because nine of them had a hypozincemia (0.54 +/- 0.01 mg/l) which suggested a zinc deficiency. Subjects with low serum zinc were able to perform a lower power output (123 +/- 8.71 vs. 166.27 +/- 14.84 watts, p = 0.029) and exhibited a higher increase in blood lactate during exercise (7.51 +/- 0.81 vs. 5.57 +/- 0.33 mmol/l, p = 0.024) resulting in a lower 2 mmol lactate threshold (44.7 +/- 3.9% vs. 58.9 +/- 4.8% of maximal power output, p = 0.04). They were less able to maintain their plasma glucose and exhibited a tendency towards hypoglycemia (p = 0.0153). Hypozincemia was associated with a higher viscometric RBC rigidity index (p = 0.0009), and this index was negatively correlated to serum zinc (r = -0.68, p = 0.7 x 10(-3)). Blood viscosity at high shear rate (MT90 viscosimeter) corrected for hematocrit (45%) remained higher during exercise in these hypozincemic subjects (p = 0.003). This study suggests that zinc status may influence blood rheology during exercise, either by its direct action on RBC flexibility (demonstrated in vitro) or by its effect on lactate accumulation which may in turn modify erythrocyte fexibility. PMID:9181758

  6. Bottlebrush Polymers: Synthesis, Rheology, and Self-Assembly

    NASA Astrophysics Data System (ADS)

    Dalsin, Samuel J.

    Bottlebrush polymers are comb-like molecules with a high density of side chains grafted along a central backbone. Due to their unique conformational properties, bottlebrush polymers have become attractive candidates for developing new photonic bandgap materials, nanotubes and nanowires, or drug delivery vehicles, to name a few. This dissertation primarily investigates the rheological properties and self-assembly behavior of bottlebrush polymer molecules made using a variety of different polymerization routes. A considerable portion of the work is directed towards the linear rheology of model, polyolefin-based bottlebrush polymers with independently varied branch and backbone lengths. These studies demonstrate how the tight spacing between branch points effectively precludes backbone entanglement in the polymer melts, but it does not inhibit the formation of entanglements among the branched side chains. Furthermore, the relaxation profiles reveal transient scaling behavior in which the dynamics transition from Zimm-like to Rouse-like at increasing relaxation times. These results highlight the distinct conformational character of bottlebrushes at different length scales. The latter parts of this work report on the self-assembly behavior of bottlebrush diblock polymers composed of atactic polypropylene and polystyrene side chains. The diblock samples are analyzed using small-angle X-ray scattering and atomic force microscopy. Nearly all of the samples display strong segregation between the two blocks, owing to the large molar mass of typical bottlebrush polymers. Consequently, only one experimental sample displays an accessible order-disorder transition temperature. The strong segregation is also shown to affect the ability of large bottlebrush diblocks to readily achieve well-ordered nanostructures by self-assembly. Finally, results of the most symmetric (by volume fraction) diblock samples are compared with predictions of a newly developed self-consistent field

  7. Dynamic rupture in a damage-breakage rheology model

    NASA Astrophysics Data System (ADS)

    Lyakhovsky, Vladimir; Ben-Zion, Yehuda; Ilchev, Assen; Mendecki, Aleksander

    2016-05-01

    We present a thermodynamically-based formulation for modeling dynamic rupture processes in the brittle crust using a continuum damage-breakage rheology. The model combines aspects of a continuum viscoelastic damage framework for brittle solids with a continuum breakage mechanics for granular flow within dynamically generated slip zones. The formulation accounts for the density of distributed cracking and other internal flaws in damaged rocks with a scalar damage parameter, and addresses the grain size distribution of a granular phase in the slip zone with a breakage parameter. A dynamic brittle instability is associated with a critical level of damage in the solid, leading to loss of convexity of the solid strain energy, localization, and transition to a granular phase associated with lower energy level. The continuum damage-breakage rheology model treats the localization to a slip zone at the onset of dynamic rupture and post-failure recovery process as phase transitions between solid and granular states. The model generates sub- and super-shear rupture velocities and pulse-type ruptures seen also in frictional models, and additional important features such as strong dynamic changes of volumetric strain near the rupture front and diversity of nucleation mechanisms. The propagation of rupture front and slip accumulation at a point are correlated with sharp dynamic dilation followed by a gradual decay to a level associated with the final volumetric change associated with the granular phase transition in the slipping zone. The local brittle failure process associated with the solid-granular transition is expected to produce isotropic radiation in addition to the deviatoric terms. The framework significantly extends the ability to model brittle processes in complex geometrical structures and allows analyzing the roles of gouge thickness and other parameters on nucleation, rupture and radiation characteristics.

  8. Yoghurt with candied chestnut: freeze drying, physical, and rheological behaviour.

    PubMed

    Sakin-Yilmazer, Melike; Dirim, S Nur; Di Pinto, Davide; Kaymak-Ertekin, Figen

    2014-12-01

    As a novel product, yoghurt powder was produced by freeze drying and with added candied chestnut puree at ratios of 5, 10, and 20 % by weight. During the freeze drying process, mass loss, water activity, and the moisture content of the samples were determined and the colour (Hunter L, a, b) of the yoghurt powder products was measured. Results showed that increasing the percentage of candied chestnut puree resulted in an increase in water activity, moisture content, and colour change values of the end product. The drying behaviour, drying rate versus free moisture content, was also investigated. It was observed that yoghurt with or without added candied chestnut puree could be satisfactorily freeze-dried. Moreover, the performance of the dried product was observed in a ready-to-use, reconstituted form. For this purpose, the obtained powders were reconstituted to their original moisture contents. Shear stress and apparent viscosity against shear rate in a range of 1-1,000 (1/sec) was then measured by a Haake-Mars rotary viscometer. According to the results, the apparent viscosities of reconstituted products, as plain yoghurt and the one with an added 5 % chestnut puree were lower than that of fresh yoghurt. However, reconstituted yoghurts containing 10 % and 20 % chestnut puree had apparent viscosities higher than fresh yoghurt. Power Law explained well the rheological behaviour of reconstituted yoghurt samples for the applied shear rate range. Based on rheological data and sensory analysis, it was concluded that the freeze dried yoghurt containing 10 % (w/w) candied chestnut puree was an acceptable novel product. PMID:25477665

  9. Filamin-A and Rheological Properties of Cultured Melanoma Cells

    PubMed Central

    Coughlin, Mark F.; Puig-de-Morales, Marina; Bursac, Predrag; Mellema, Matthew; Millet, Emil; Fredberg, Jeffrey J.

    2006-01-01

    Here we report the rheological properties of cultured hsFLNa (filamin-A)-expressing (FIL+) and hsFLNa-deficient (FIL−) melanoma cells. Using magnetic twisting cytometry over a wide range of probing frequencies, and targeting either cortical or deeper cytoskeletal structures, we found that differences in stiffness of FIL+ versus FIL− cells were remarkably small. When probed through deep cytoskeletal structures, FIL+ cells were, at most, 30% stiffer than FIL− cells, whereas when probed through more peripheral cytoskeletal structures FIL− cells were not different except at very high frequencies. The loss tangent, expressed as an effective cytoskeletal temperature, was systematically greater in FIL− than FIL+ cells, but these differences were small and showed that the FIL+ cells were only slightly closer to a solidlike state. To quantify cytoskeletal remodeling, we measured spontaneous motions of beads bound to cortical cytoskeletal structures and found no difference in FIL+ versus FIL− cells. Although mechanical differences between FIL+ and FIL− cells were evident both in cortical and deeper structures, these differences were far smaller than expected based on measurements of the rheology of purified actin-filamin solutions. These findings do not rule out an important contribution of filamin to the mechanical properties of the cortical cytoskeleton, but suggest that effects of filamin in the cortex are not exerted on the length scale of the probe used here. These findings would appear to rule out any important contribution of filamin to the bulk mechanical properties of the cytoplasm, however. Although filamin is present in the cytoplasm, it may be inactive, its mechanical effects may be small compared with other crosslinkers, or mechanical properties of the matrix may be dominated by an overriding role of cytoskeletal prestress. PMID:16387775

  10. The Application of Powder Rheology in Additive Manufacturing

    NASA Astrophysics Data System (ADS)

    Clayton, Jamie; Millington-Smith, Doug; Armstrong, Brian

    2015-03-01

    Additive manufacturing (AM) is sensitive to powder variability when applying fine layers in a uniform manner. This demands a high degree of consistency and repeatability in the feedstock. Particle size is often used as a critical quality attribute, but this is not sufficient to fully qualify a feedstock. Indeed, it is inadequate to suggest that any parameter from a single test, e.g., Hall flowmeter or Hausner ratio, can comprehensively describe a powder's characteristics. This article uses four case studies to demonstrate the limitations of single parameter characterization and how the rheological properties of several metal powders used in AM applications are used to establish in-process performance. In the first study, the significantly reduced permeability and increased specific energy of a one batch of powder demonstrate a clear link to poor layer uniformity. The second study investigates the impact of metal powder manufacturing methods and suppliers, and it shows how shear properties alone cannot be relied on to identify properties that influence the process. The effect of additives on the processability of polymer blends used in AM is also evaluated, and the results show that even small quantities can have a significant effect on the permeability and basic flowability energy of feedstocks. The final study demonstrates the how rheological measurements can be used to identify the optimum blend of fresh and used material when reusing metal powders to manufacture components. These case studies illustrate the ability of a modern powder rheometer to detect minor variations in powders that are directly relevant to performance in AM processes in a way that traditional characterization methods cannot.

  11. Dynamic rupture in a damage-breakage rheology model

    NASA Astrophysics Data System (ADS)

    Lyakhovsky, Vladimir; Ben-Zion, Yehuda; Ilchev, Assen; Mendecki, Aleksander

    2016-08-01

    We present a thermodynamically based formulation for modelling dynamic rupture processes in the brittle crust using a continuum damage-breakage rheology. The model combines aspects of a continuum viscoelastic damage framework for brittle solids with a continuum breakage mechanics for granular flow within dynamically generated slip zones. The formulation accounts for the density of distributed cracking and other internal flaws in damaged rocks with a scalar damage parameter, and addresses the grain size distribution of a granular phase in the slip zone with a breakage parameter. A dynamic brittle instability is associated with a critical level of damage in the solid, leading to loss of convexity of the solid strain energy, localization and transition to a granular phase associated with lower energy level. The continuum damage-breakage rheology model treats the localization to a slip zone at the onset of dynamic rupture and post-failure recovery process as phase transitions between solid and granular states. The model generates sub- and supershear rupture velocities and pulse-type ruptures seen also in frictional models, and additional important features such as strong dynamic changes of volumetric strain near the rupture front and diversity of nucleation mechanisms. The propagation of rupture front and slip accumulation at a point are correlated with sharp dynamic dilation followed by a gradual decay to a level associated with the final volumetric change associated with the granular phase transition in the slipping zone. The local brittle failure process associated with the solid-granular transition is expected to produce isotropic radiation in addition to the deviatoric terms. The framework significantly extends the ability to model brittle processes in complex geometrical structures and allows analysing the roles of gouge thickness and other parameters on nucleation, rupture and radiation characteristics.

  12. Flow properties of MK-based geopolymer pastes. A comparative study with standard Portland cement pastes.

    PubMed

    Favier, Aurélie; Hot, Julie; Habert, Guillaume; Roussel, Nicolas; d'Espinose de Lacaillerie, Jean-Baptiste

    2014-02-28

    Geopolymers are presented in many studies as alternatives to ordinary Portland cement. Previous studies have focused on their chemical and mechanical properties, their microstructures and their potential applications, but very few have focussed on their rheological behaviour. Our work highlights the fundamental differences in the flow properties, which exist between geopolymers made from metakaolin and Ordinary Portland Cement (OPC). We show that colloidal interactions between metakaolin particles are negligible and that hydrodynamic effects control the rheological behaviour. Metakaolin-based geopolymers can then be described as Newtonian fluids with the viscosity controlled mainly by the high viscosity of the suspending alkaline silicate solution and not by the contribution of direct contacts between metakaolin grains. This fundamental difference between geopolymers and OPC implies that developments made in cement technology to improve rheological behaviour such as plasticizers will not be efficient for geopolymers and that new research directions need to be explored. PMID:24795966

  13. Volcanologists and the geologic past

    USGS Publications Warehouse

    Swanson, D.A.

    1991-01-01

    Were volcanologists to be asked why they study active volcanoes, they would list many reasons: to understand their dynamics, to use them as windows into the earth, to warn of hazards, to provide nearly real-time information on rates of various physical and chemical processes, and many others. Near the bottom of the list would be "to understand the Earth's past." Generally, that task has been left to other corners of the earth sciences, and volcanologists have kept their sights on the present or near present without worrying much about what happened millions of years ago. But much can be gained from applying a volcanologic perspective to the interpretation of old rocks, and this gain enhances our understanding of both the past and the present. 

  14. Ebolavirus Evolution: Past and Present.

    PubMed

    de La Vega, Marc-Antoine; Stein, Derek; Kobinger, Gary P

    2015-01-01

    The past year has marked the most devastating Ebola outbreak the world has ever witnessed, with over 28,000 cases and over 11,000 deaths. Ebola virus (EBOV) has now been around for almost 50 years. In this review, we discuss past and present outbreaks of EBOV and how those variants evolved over time. We explore and discuss selective pressures that drive the evolution of different Ebola variants, and how they may modify the efficacy of therapeutic treatments and vaccines currently being developed. Finally, given the unprecedented size and spread of the outbreak, as well as the extended period of replication in human hosts, specific attention is given to the 2014-2015 West African outbreak variant (Makona). PMID:26562671

  15. Past and Current Climate Change

    NASA Astrophysics Data System (ADS)

    Mercedes Rodríguez Ruibal, Ma

    2014-05-01

    In 1837 the Swiss geologist and palaeontologist Louis Agassiz was the first scientist to propose the existence of an ice age in the Earth's past. Nearly two centuries after discussing global glacial periods... while the average global temperature is rising very quickly because of our economic and industrial model. In tribute to these pioneers, we have selected a major climate change of the past as the Snowball Earth and, through various activities in the classroom, compared to the current anthropogenic climate change. First, we include multiple geological processes that led to a global glaciation 750 million years ago as the decrease in the atmospheric concentration of greenhouse gases such as CO2 and CH4, the effect of climate variations in solar radiation due to emissions of volcanic dust and orbital changes (Milankovitch cycles), being an essential part of this model the feedback mechanism of the albedo of the ice on a geological scale. Moreover, from simple experiments and studies in the classroom this time we can compare the past with the current anthropogenic global warming we are experiencing and some of its consequences, highlighting that affect sea level rise, increased extreme and effects on health and the biosphere weather.

  16. Effects of nonlinear rheology and anisotropy on the relationship between age and depth at ice divides

    NASA Astrophysics Data System (ADS)

    Martin, C.; Gudmundsson, G. H.

    2012-04-01

    Ice-cores need to be accurately dated to reveal, in detail, past environmental conditions. The ice-core chronology is always incomplete because of ice stratigraphy thinning and distortion due to flow, and timeline extraction is often reliant on simplified models to predict the age of ice. Through numerical modelling using a full Stokes solver and a non-linear anisotropic rheology, we investigate the effects of ice flow on the age versus depth relationship at ice divides. We compare our results with analytical approximations commonly employed in age-depth prediction. Our main findings are: Firstly, once the ice has developed a significant single maximum or vertical girdle fabric, the analytical approximations tend to underestimate the age of ice. Secondly, ice fabric enhance the effect of the bedrock topography on the ice flow. We show that the presence of single maximum fabric close to the bedrock affects strongly the ice stratigraphy and the age-depth relationship. We also study the coupling between anisotropic viscosity and internal heating. It does produce a warm spot and softer ice at the base of the divide when compared with surrounding areas. Finally we study the age-depth distribution in divides that show double-peaked Raymond bump in their radar stratigraphy. They provide ideal locations fore ice-core drilling as they have been stable for a long time when compared with their characteristic time (ice thickness divide by accumulation). Our model shows that the ice in these areas can be up to one order of magnitude older that ice at the same depth both at the flanks of the divide area or on similar divides that have not been stable for that long.

  17. Rheology, Morphology and Temperature Dependency of Nanotube Networks in Polycarbonate/Multiwalled Carbon Nanotube Composites

    SciTech Connect

    Abbasi, Samaneh; Carreau, Pierre J.; Derdouri, Abdessalem

    2008-07-07

    We present several issues related to the state of dispersion and rheological behavior of polycarbonate/multiwalled carbon nanotube (MWCNT) composites. The composites were prepared by diluting a commercial masterbatch containing 15 wt% nanotubes using optimized melt-mixing conditions. The state of dispersion was then analyzed by scanning and transmission electron microscopy (SEM, TEM). Rheological characterization was also used to assess the final morphology. Further, it was found that the rheological percolation threshold decreased significantly with increasing temperature and finally reached a constant value. This is described in terms of the Brownian motion, which increases with temperature. However, by increasing the nanotube content, the temperature effects on the complex viscosity at low frequency decreased significantly. Finally, the percolation thresholds were found to be approximately equal to 0.3 and 2 wt% for rheological and electrical conductivity measurements, respectively.

  18. SOLUTION RHEOLOGY OF HYPERBRANCHED POLYESTERS AND THEIR BLENDS WITH LINEAR POLYMERS

    EPA Science Inventory

    In this study, the rheological properties of different generations of hyperbranched polyesters in 1-methyl-2-pyrrolidinone solvent and their blends with poly(2-hydroxyethyl methacrylate) have ben investigated. All the hyperbranched polyester solutions exhibited Newtonian behavior...

  19. The Compatibility Effect Of Coupling Agent On Rheological-Morphological Relationship Of Banana Fibre Reinforced Polypropylene

    SciTech Connect

    Chang, S. Y.; Shamsudin, Z.

    2009-06-01

    The rheological properties of banana fibre reinforced polypropylene (PP/BF) composites at different composition were analysed using Shimadzu capillary rheometer. The effect of coupling agent concentration on the rheological properties was studied and followed by drawing a relationship of rheological-morphological properties of PP/BF composites. It was found that all composite system exhibits pseudoplasticity and incorporation of treated fibres consequents enhanced viscosity due to improved interfacial adhesion at fibre-matrix interface. However, it was observed that PP/BF composite with 2 wt% silane concentration does not yield further enhancement in the rheological properties when compared to that of 1 wt%. Composites with 1 wt% silane concentration were found to yield most promising compatibility effect with well-oriented and uniformly dispersed fibre morphology.

  20. Rheological study of feed stock for NiTi alloy molded parts

    NASA Astrophysics Data System (ADS)

    Subuki, I.; Abdullah, Z.; Razali, R.; Ismail, M. H.

    2015-12-01

    A rheological behaviour of the powder-binder mixture is one of essential analysis upon to success of Metal Injection Moulding (MIM) process. The purpose of this experimental work is to investigate the rheological behavior of feedstock containing mixtures of elemental Ni and Ti powders mixed with composite binder of palm stearin (PS) and polyethylene (PE) binder system. An equiatomic Ni-Ti (50-50) ratio was used in the present work for all formulations owing to excellent shape memory behaviour. The experimental rheological result indicated that all the feedstocks exhibited pseudo plastic flow behaviour; viscosity decreasing with temperature and shear rate. Increasing the powder loading resulted in higher viscosity, particularly at the low-range of shear rate. Owing to pseudo-plastic flow, it was found that the feedstock prepared exhibit promising rheological properties, thus resulting successfully injection moulding at an optimum temperature of 130°C.

  1. Thermal destruction of erythrocyte spectrin: Rheology, deformability, and stability with respect to detergents

    NASA Astrophysics Data System (ADS)

    Yamaikina, M. V.; Mansurov, V. A.; Ivashkevich, É. V.

    1996-05-01

    By means of blood heating in the region of the thermal denaturation transition of spectrin (50°C) the relationship between the stability of erythrocytes with respect to detergents and their deformability and rheological parameters of blood was studied.

  2. Enhancement of Hydrodynamic Processes in Oil Pipelines Considering Rheologically Complex High-Viscosity Oils

    NASA Astrophysics Data System (ADS)

    Konakhina, I. A.; Khusnutdinova, E. M.; Khamidullina, G. R.; Khamidullina, A. F.

    2016-06-01

    This paper describes a mathematical model of flow-related hydrodynamic processes for rheologically complex high-viscosity bitumen oil and oil-water suspensions and presents methods to improve the design and performance of oil pipelines.

  3. Rheological monitoring of phase separation induced by chemical reaction in thermoplastic-modified epoxy

    SciTech Connect

    Vinh-Tung, C.; Lachenal, G.; Chabert, B.

    1996-12-31

    The phase separation induced by chemical reaction in blends of tetraglycidyl-diaminodiphenylmethane epoxy resin with an aromatic diamine hardener and a thermoplastic was monitored. Rheological measurements and morphologies are described.

  4. [Molecular Dynamics of Self-assembling and Rheology of Superhelical Structure of Protofiber of Spider Web].

    PubMed

    Shaitan, K V; Orshanskiy, I A

    2015-01-01

    In this study we suggested a dynamics simulation for the formation of protofiber of spider web nanofiber. It was shown that a bundle of parallel polyalanine β-strands of sufficient length is arranged through self-assembly into a stable right-handed super helix. By numerical analysis we investigated the rheological properties and provided in nonlinear regime a generalization of the model of Singer for description of the rheological behaviour of super helix. PMID:26394464

  5. Different macro- and micro-rheological properties of native porcine respiratory and intestinal mucus.

    PubMed

    Bokkasam, Harish; Ernst, Matthias; Guenther, Marco; Wagner, Christian; Schaefer, Ulrich F; Lehr, Claus-Michael

    2016-08-20

    Aim of this study was to investigate the similarities and differences at macro- and microscale in the viscoelastic properties of mucus that covers the epithelia of the intestinal and respiratory tract. Natural mucus was collected from pulmonary and intestinal regions of healthy pigs. Macro-rheological investigations were carried out through conventional plate-plate rheometry. Microrheology was investigated using optical tweezers. Our data revealed significant differences both in macro- and micro-rheological properties between respiratory and intestinal mucus. PMID:27311353

  6. Rheology of dense suspensions of non colloidal spheres in yield-stress fluids

    NASA Astrophysics Data System (ADS)

    Guazzelli, Elisabeth; Dagois-Bohy, Simon; Hormozi, Sarah; Pouliquen, Olivier; Aix-Marseille Université, Cnrs, Iusti Umr 7343 Team; Department Of Mechanical Engineering, Ohio University Team

    2015-11-01

    Pressure-imposed rheometry is used to study the rheological properties of suspensions of non colloidal spheres in yield stress fluids. Accurate measurements for both the shear stress and particle normal stress are obtained in the dense regime. The rheological measurements are favourably compared to a model based on scaling arguments and homogenisation methods. The detailed account of this study can be found in. ANR-13-IS09-0005-01, Etudes et Productions Schlumberger, NSERC Postdoctoral Fellowships Program PDF-439036-2013.

  7. Chemical and rheological aspects of gel formation in the California Mastitis Test.

    PubMed

    Whyte, David; Walmsley, Michael; Liew, Alvin; Claycomb, Rod; Mein, Graeme

    2005-02-01

    The rheological properties of the CMT gel were analysed. Data are presented to demonstrate that the gel is a non-homogenous, visco-elastic, non-Newtonian fluid with rheopectic, and rheodestructive behaviour. The fundamental chemistry of the CMT is reviewed and a modified theory of gel formation is presented. The implications of the rheological properties and modified theory of gel formation for an automatic sensor are discussed. PMID:15747739

  8. Rheologically stable, nontoxic, high-temperature, water-based drilling fluid

    SciTech Connect

    Elward-Berry, J.; Darby, J.B.

    1997-09-01

    An exceptionally stable, high-temperature, water-based drilling fluid has been developed based on a fundamental redesign of drilling fluid components and functions, while still using commercially available materials. Rheological stability was characterized by extensive Fann 50C low-shear-rate viscosity vs. temperature studies and supporting viscoelastic rheological data. The fluid has been used in offshore and land applications, at temperatures as high as 420 F and densities as high as 15.5 lbm/gal.

  9. In vitro/in vivo and analytical evaluation of sunless tanning formulations containing different rheology modifiers.

    PubMed

    Dueva-Koganov, Olga V; Mandalia, Yamini; Brito, Juan; Rocafort, Colleen; Orofino, Steven; Vazquez, Gustavo

    2010-01-01

    In vitro data suggest that different in vivo performances are expected for two dihydroxyacetone (DHA)-containing formulations with similar concentrations of DHA and excipients but different commercially available rheology modifiers: one with a cationic polymer-based rheology modifier (blend) [dimethylacrylamide/ethyltrimonium chloride methacrylate copolymer (and) propylene glycol dicaprylate/dicaprate (and) PPG-1 trideceth-6 (and) C10-11 isoparaffin]; and the other with a polyacrylamide-based rheology modifier (blend) [polyacrylamide (and) C13-14 isoparaffin (and) laureth-7]. Both rheology modifiers (blends) contained comparable levels of polymers and were used at 3% w/w (as supplied). Differences in color development were illustrated in vitro with respect to the yellow/red and lightness/chroma parameters, which were confirmed in the followup in vivo studies. The test article with the cationic polymer-based rheology modifier produced a more natural sunless tan, comparable to a desirable sun-induced tan, for all panelists, one that was more uniform and lasted longer compared with the sunless tan generated by the test article with the polyacrylamide-based rheology modifier. A method for HPLC analysis of DHA in sunless tanning formulations was established and utilized to confirm concentrations of DHA in test articles. PMID:20447361

  10. Simulation and experimental study of rheological properties of CeO2-water nanofluid

    NASA Astrophysics Data System (ADS)

    Loya, Adil; Stair, Jacqueline L.; Ren, Guogang

    2015-10-01

    Metal oxide nanoparticles offer great merits over controlling rheological, thermal, chemical and physical properties of solutions. The effectiveness of a nanoparticle to modify the properties of a fluid depends on its diffusive properties with respect to the fluid. In this study, rheological properties of aqueous fluids (i.e. water) were enhanced with the addition of CeO2 nanoparticles. This study was characterized by the outcomes of simulation and experimental results of nanofluids. The movement of nanoparticles in the fluidic media was simulated by a large-scale molecular thermal dynamic program (i.e. LAMMPS). The COMPASS force field was employed with smoothed particle hydrodynamic potential (SPH) and discrete particle dynamics potential (DPD). However, this study develops the understanding of how the rheological properties are affected due to the addition of nanoparticles in a fluid and the way DPD and SPH can be used for accurately estimating the rheological properties with Brownian effect. The rheological results of the simulation were confirmed by the convergence of the stress autocorrelation function, whereas experimental properties were measured using a rheometer. These rheological values of simulation were obtained and agreed within 5 % of the experimental values; they were identified and treated with a number of iterations and experimental tests. The results of the experiment and simulation show that 10 % CeO2 nanoparticles dispersion in water has a viscosity of 2.0-3.3 mPas.

  11. Neonatal blood rheological parameters at delivery in healthy neonates and in those with morbidities.

    PubMed

    Soliman, Amr A; Csorba, Roland; Tsikouras, Pagnaioti; Wieg, Christian; Harnack, Harald; von Tempelhoff, Georg-Friedrich

    2013-03-26

    Rheological blood parameters of neonates are different form those of adults. Many authors have studied changes in blood rheology in neonates in different clinical disorders. To-date, no one set the normal values for blood rheological parameters in healthy neonates. The aim of this study is to set the norm for rheological blood parameters in healthy newborns and to describe the changes in those parameters in common clinical disorders that affect the newborns. We recruited all the neonates born to mothers experiencing un eventful pregnancies, blood was taken from the umbilical cord right after the delivery. In this time period we recruited 4985 neonate. From this huge database we were able to set the standards for blood rheology in neonates, namely plasma viscosity of 1.06 ± 0.072 mPa, erythrocyte aggregation at stasis of 2.41 ± 2.74 s-1 and erythrocyte aggregation under low shear forces of 8.51 ± 6.38 s-1. These values changed significantly in some diseased neonates. This is the largest study investigating normal rheological parameters and deviations from the norm in common clinical disorders occurring in this early stage of life. PMID:23532177

  12. Preliminary investigations on the rheology and boundary stresses associated with granular mixtures

    NASA Astrophysics Data System (ADS)

    Yohannes, B.; Hill, K. M.

    2010-05-01

    Recent advances in rheological models for monodisperse dense granular materials are exciting. However, they do not account for the effect of local particle size distributions on the rheology mixtures of particles. It is well-known that particulate mixtures tend to unmix, and their rheological properties are dependent on species concentration. Typically, expressions for the rheology of dense granular flows are explicitly dependent on particle size. However, there is no indication of what may be used for a representative size in a mixture of particles of different sizes. We find, in the absence of gravity, plane Couette cells present an effective geometry for investigating the rheology of binary mixtures of different sized particles. Unlike the behavior of more sparse systems, we find that the dense systems do not segregate much, indicating the usefulness of the geometry for studying the dependence of the mixture rheology on particle sized distribution systematically. In our preliminary studies we find that the pressure at the boundary has a skewed probability distribution function (pdf). We also find that the pdf of the boundary pressure for a particular mixture scales according to the inertial stress.

  13. Rheological Models in the Time-Domain Modeling of Seismic Motion

    NASA Astrophysics Data System (ADS)

    Moczo, P.; Kristek, J.

    2004-12-01

    The time-domain stress-strain relation in a viscoelastic medium has a form of the convolutory integral which is numerically intractable. This was the reason for the oversimplified models of attenuation in the time-domain seismic wave propagation and earthquake motion modeling. In their pioneering work, Day and Minster (1984) showed the way how to convert the integral into numerically tractable differential form in the case of a general viscoelastic modulus. In response to the work by Day and Minster, Emmerich and Korn (1987) suggested using the rheology of their generalized Maxwell body (GMB) while Carcione et al. (1988) suggested using the generalized Zener body (GZB). The viscoelastic moduli of both rheological models have a form of the rational function and thus the differential form of the stress-strain relation is rather easy to obtain. After the papers by Emmerich and Korn and Carcione et al. numerical modelers decided either for the GMB or GZB rheology and developed 'non-communicating' algorithms. In the many following papers the authors using the GMB never commented the GZB rheology and the corresponding algorithms, and the authors using the GZB never related their methods to the GMB rheology and algorithms. We analyze and compare both rheologies and the corresponding incorporations of the realistic attenuation into the time-domain computations. We then focus on the most recent staggered-grid finite-difference modeling, mainly on accounting for the material heterogeneity in the viscoelastic media, and the computational efficiency of the finite-difference algorithms.

  14. Recent advances in the GPUSPH model for the thermal and rheological evolution of lava flows

    NASA Astrophysics Data System (ADS)

    Zago, Vito; Bilotta, Giuseppe; Cappello, Annalisa; Dalrymple, Robert A.; Fortuna, Luigi; Ganci, Gaetana; Herault, Alexis; Del Negro, Ciro

    2016-04-01

    GPUSPH is a fully three-dimensional model for the simulation of the thermal and rheological evolution of lava flows that relies on the Smoothed Particle Hydrodynamics (SPH) numerical method. Thanks to the Lagrangian, meshless nature of SPH, the model incorporates a more complete physical description of the emplacement process and rheology of lava that considers the free surface, the irregular boundaries represented by the topography, the solidification fronts and the non-Newtonian rheology. Because of the very high degree of parallelism, GPUSPH is implemented very efficiently on high-performance graphics processing units (GPUs) employing the Compute Unified Device Architecture (CUDA), a parallel programming language developed by NVIDIA for GPU computing. GPUSPH follows the very general Herschel-Bulkley rheological model, which encompasses Newtonian, power-law and Bingham flow behaviour and can thus be used to explore in detail the impact of rheology on the behaviour of lava flows and on their emplacement. We present here the first validation tests of the GPUSPH model against well known analytical problems, considering the different rheological models, heat exchanges by thermal conduction and radiation, and providing the relative error estimates.

  15. Influence of large strain rheology on the peeling performances of Pressure Sensitive Adhesives

    NASA Astrophysics Data System (ADS)

    Villey, Richard; Ciccotti, Matteo; Creton, Costantino; Cortet, Pierre-Philippe; Yarusso, David J.

    2015-03-01

    The dependence of adhesion energy of Pressure Sensitive Adhesives (PSA) on peeling velocity reduces to a master curve using a time-temperature superposition principle, usually verified by the linear rheology of polymers. This result has guided models predicting peeling energy of PSA to consider the small strain rheology of the glue only, despite it can experience very large strains before debonding. The argument of the time-temperature superposition principle can actually also be applied to large strains and is thus not a stringent one. To clarify the role of large strain rheology during the peeling of PSA, we present experiments on commercial and custom-made tapes supplied by 3M Company. Small and large strain rheology differences are obtained by changing the glass transition temperature, the cross-linking density and the density of entanglements, yet remaining close to commercial PSA. The rheology influence is decoupled from geometrical effects, by examining the nontrivial dependence of the adhesion energy on the peeling angle. Finally, adhesion energy measurements and visualizations of the process zone, over a large range of peeling velocities, are discussed, in the perspective of building a model for the adherence considering the complete rheology of the glue.

  16. Life: past, present and future.

    PubMed

    Nealson, K H; Conrad, P G

    1999-12-29

    Molecular methods of taxonomy and phylogeny have changed the way in which life on earth is viewed; they have allowed us to transition from a eukaryote-centric (five-kingdoms) view of the planet to one that is peculiarly prokarote-centric, containing three kingdoms, two of which are prokaryotic unicells. These prokaryotes are distinguished from their eukaryotic counterparts by their toughness, tenacity and metabolic diversity. Realization of these features has, in many ways, changed the way we feel about life on earth, about the nature of life past and about the possibility of finding life elsewhere. In essence, the limits of life on this planet have expanded to such a degree that our thoughts of both past and future life have been altered. The abilities of prokaryotes to withstand many extreme conditions has led to the term extremophiles, used to describe the organisms that thrive under conditions thought just a few years ago, to be inconsistent with life. Perhaps the most extensive adaptation to extreme conditions, however, is represented by the ability of many bacteria to survive nutrient conditions not compatible with eukaryotic life. Prokaryotes have evolved to use nearly every redox couple that is in abundance on earth, filling the metabolic niches left behind by the oxygen-using, carbon-eating eukaryotes. This metabolic plasticity leads to a common feature in physically stratified environments of layered microbial communities, chemical indicators of the metabolic diversity of the prokaryotes. Such 'metabolic extremophily' forms a backdrop by which we can view the energy flow of life on this planet, think about what the evolutionary past of the planet might have been, and plan ways to look for life elsewhere, using the knowledge of energy flow on earth. PMID:10670014

  17. Life: past, present and future

    NASA Technical Reports Server (NTRS)

    Nealson, K. H.; Conrad, P. G.

    1999-01-01

    Molecular methods of taxonomy and phylogeny have changed the way in which life on earth is viewed; they have allowed us to transition from a eukaryote-centric (five-kingdoms) view of the planet to one that is peculiarly prokarote-centric, containing three kingdoms, two of which are prokaryotic unicells. These prokaryotes are distinguished from their eukaryotic counterparts by their toughness, tenacity and metabolic diversity. Realization of these features has, in many ways, changed the way we feel about life on earth, about the nature of life past and about the possibility of finding life elsewhere. In essence, the limits of life on this planet have expanded to such a degree that our thoughts of both past and future life have been altered. The abilities of prokaryotes to withstand many extreme conditions has led to the term extremophiles, used to describe the organisms that thrive under conditions thought just a few years ago, to be inconsistent with life. Perhaps the most extensive adaptation to extreme conditions, however, is represented by the ability of many bacteria to survive nutrient conditions not compatible with eukaryotic life. Prokaryotes have evolved to use nearly every redox couple that is in abundance on earth, filling the metabolic niches left behind by the oxygen-using, carbon-eating eukaryotes. This metabolic plasticity leads to a common feature in physically stratified environments of layered microbial communities, chemical indicators of the metabolic diversity of the prokaryotes. Such 'metabolic extremophily' forms a backdrop by which we can view the energy flow of life on this planet, think about what the evolutionary past of the planet might have been, and plan ways to look for life elsewhere, using the knowledge of energy flow on earth.

  18. Life: past, present and future.

    PubMed Central

    Nealson, K H; Conrad, P G

    1999-01-01

    Molecular methods of taxonomy and phylogeny have changed the way in which life on earth is viewed; they have allowed us to transition from a eukaryote-centric (five-kingdoms) view of the planet to one that is peculiarly prokarote-centric, containing three kingdoms, two of which are prokaryotic unicells. These prokaryotes are distinguished from their eukaryotic counterparts by their toughness, tenacity and metabolic diversity. Realization of these features has, in many ways, changed the way we feel about life on earth, about the nature of life past and about the possibility of finding life elsewhere. In essence, the limits of life on this planet have expanded to such a degree that our thoughts of both past and future life have been altered. The abilities of prokaryotes to withstand many extreme conditions has led to the term extremophiles, used to describe the organisms that thrive under conditions thought just a few years ago, to be inconsistent with life. Perhaps the most extensive adaptation to extreme conditions, however, is represented by the ability of many bacteria to survive nutrient conditions not compatible with eukaryotic life. Prokaryotes have evolved to use nearly every redox couple that is in abundance on earth, filling the metabolic niches left behind by the oxygen-using, carbon-eating eukaryotes. This metabolic plasticity leads to a common feature in physically stratified environments of layered microbial communities, chemical indicators of the metabolic diversity of the prokaryotes. Such 'metabolic extremophily' forms a backdrop by which we can view the energy flow of life on this planet, think about what the evolutionary past of the planet might have been, and plan ways to look for life elsewhere, using the knowledge of energy flow on earth. PMID:10670014

  19. Rheological flow laws for multiphase magmas: An empirical approach

    NASA Astrophysics Data System (ADS)

    Pistone, Mattia; Cordonnier, Benoît; Ulmer, Peter; Caricchi, Luca

    2016-07-01

    The physical properties of magmas play a fundamental role in controlling the eruptive dynamics of volcanoes. Magmas are multiphase mixtures of crystals and gas bubbles suspended in a silicate melt and, to date, no flow laws describe their rheological behaviour. In this study we present a set of equations quantifying the flow of high-viscosity (> 105 Pa·s) silica-rich multiphase magmas, containing both crystals (24-65 vol.%) and gas bubbles (9-12 vol.%). Flow laws were obtained using deformation experiments performed at high temperature (673-1023 K) and pressure (200-250 MPa) over a range of strain-rates (5 · 10- 6 s- 1 to 4 · 10- 3 s- 1), conditions that are relevant for volcanic conduit processes of silica-rich systems ranging from crystal-rich lava domes to crystal-poor obsidian flows. We propose flow laws in which stress exponent, activation energy, and pre-exponential factor depend on a parameter that includes the volume fraction of weak phases (i.e. melt and gas bubbles) present in the magma. The bubble volume fraction has opposing effects depending on the relative crystal volume fraction: at low crystallinity bubble deformation generates gas connectivity and permeability pathways, whereas at high crystallinity bubbles do not connect and act as "lubricant" objects during strain localisation within shear bands. We show that such difference in the evolution of texture is mainly controlled by the strain-rate (i.e. the local stress within shear bands) at which the experiments are performed, and affect the empirical parameters used for the flow laws. At low crystallinity (< 44 vol.%) we observe an increase of viscosity with increasing strain-rate, while at high crystallinity (> 44 vol.%) the viscosity decreases with increasing strain-rate. Because these behaviours are also associated with modifications of sample textures during the experiment and, thus, are not purely the result of different deformation rates, we refer to "apparent shear-thickening" and

  20. Transonic Flow Past Cone Cylinders

    NASA Technical Reports Server (NTRS)

    Solomon, George E

    1955-01-01

    Experimental results are presented for transonic flow post cone-cylinder, axially symmetric bodies. The drag coefficient and surface Mach number are studied as the free-stream Mach number is varied and, wherever possible, the experimental results are compared with theoretical predictions. Interferometric results for several typical flow configurations are shown and an example of shock-free supersonic-to-subsonic compression is experimentally demonstrated. The theoretical problem of transonic flow past finite cones is discussed briefly and an approximate solution of the axially symmetric transonic equations, valid for a semi-infinite cone, is presented.

  1. Acupuncture: Past, Present, and Future

    PubMed Central

    Mittelman, Michele

    2014-01-01

    During the past 40 years, acupuncture, a therapeutic technique of oriental medicine, has become more and more popular, evolving into one of the most utilized forms of complementary integrative medicine interventions in the United States. In fact, more than 10 million acupuncture treatments are administered annually in the United States alone.1 Its rise in popularity, particularly in the West, can be attributed in part to its effectiveness for pain relief and in part to the fact that scientific studies have begun to prove its efficacy. PMID:25105069

  2. Lead alloys past present future

    SciTech Connect

    Bagshaw, N.E.

    1995-03-01

    The most critical non-active component in the lead acid battery is the grid of substrate. A review of the work on and grid alloys in the period 1960-1993 has been carried out by by the Advanced Lead-Acid Consortium, (ALABC), and, in this paper, the results are analyzed in relation to the effort expended in different alloy systems. Lead-antimony alloys and the effects on them of additions of arsenic, tin, and grain-refining elements (selenium, sulfur, copper), together with lead-calcium alloys and the effect on them of tin additions have received the greatest attention in the past.

  3. Rheology, Structure, and Diffusion in Concentrated Colloidal Dispersions

    NASA Astrophysics Data System (ADS)

    Lionberger, Robert A.

    non-Newtonian rheology requires the distortion for strong flows. However, the conservation equation describing the nonequilibrium structure under shear is singularly perturbed for large separations. Therefore we solve the conservation equation and closure approximation non-perturbatively through a spherical harmonic expansion and a numerical calculation at finite shear rate. For steady shear flow this procedure determines the dependence of the rheological properties, including shear thinning and normal stresses, on shear rate.

  4. Structural relaxation and rheological response of a driven amorphous system.

    PubMed

    Varnik, F

    2006-10-28

    The interplay between the structural relaxation and the rheological response of a simple amorphous system {a 80:20 binary Lennard-Jones mixture [W. Kob and H. C. Andersen, Phys. Rev. Lett. 73, 1376 (1994)]} is studied via molecular dynamics simulations. In the quiescent state, the model is well known for its sluggish dynamics and a two step relaxation of correlation functions at low temperatures. An ideal glass transition temperature of Tc=0.435 has been identified in the previous studies via the analysis of the system's dynamics in the framework of the mode coupling theory of the glass transition [W. Kob and H. C. Andersen, Phys. Rev. E 51, 4626 (1995)]. In the present work, we focus on the question whether a signature of this ideal glass transition can also be found in the case where the system's dynamics is driven by a shear motion. Indeed, the following distinction in the structural relaxation is found: In the supercooled state, the structural relaxation is dominated by the shear at relatively high shear rates gamma, whereas at sufficiently low gamma the (shear-independent) equilibrium relaxation is recovered. In contrast to this, the structural relaxation of a glass is always driven by shear. This distinct behavior of the correlation functions is also reflected in the rheological response. In the supercooled state, the shear viscosity eta decreases with increasing shear rate (shear thinning) at high shear rates, but then converges toward a constant as the gamma is decreased below a (temperature-dependent) threshold value. Below Tc, on the other hand, the shear viscosity grows as eta proportional, etax 1/gamma, suggesting a divergence at gamma=0. Thus, within the accessible observation time window, a transition toward a nonergodic state seems to occur in the driven glass as the driving force approaches zero. As to the flow curves (stress versus shear rate), a plateau forms at low shear rates in the glassy phase. A consequence of this stress plateau for

  5. Percolation effects on entangled polymer rheology and the glass transition

    NASA Astrophysics Data System (ADS)

    Wool, Richard P.

    2012-07-01

    Current thinking on the fundamentals of entangled polymer melt rheology suggests that stress relaxation in the terminal zone occurs via Reptation, chain-end fluctuation and (convective) constraint release. This scenario is not correct. It is shown through a series of experiments with selectively deuterated model polymers that relaxation occurs through a percolation process which permits large clusters of entangled polymers to stress relax before their conformations are fully relaxed. The percolation model of entanglements (R.P. Wool, Macromolecules 26, 1564, 1993) makes unique predictions regarding the dynamics of polymer chains in the terminal relaxation zone. These include: (a) Reptating homopolymer chains with molecular weight M >> Mc appear to be non-Reptating as their ends and centers relax at the same rate in a Rouse-like manner during percolation. (b) The mechanical relaxation time τ(M) is related to the Reptation time Tr˜ M3 by τ(M) = Tr[(1-Mc/M)Me/Mc]2, which is the origin of the zero shear viscosity behaving as ηo˜M3.4 (c) The biggest surprise is that during stress relaxation, the random coil dimensions Rg(//) and Rg(⊥) are not fully relaxed when the stress and birefringence relax to zero. (d) Matrix molecular weight P effects on relaxation time τ(M) of the probe chain M are as follows: When the probe chain M>>P, the matrix P-chains percolate and Rouse-like dynamics is observed for the M-Reptating chains with τ(M) ˜ P1M2. (e) When the matrix P>>M, percolation does not occur for the M-chain and the relaxation time of the probe chain τ(M) ˜ PoM3 is in accord with DeGennes Reptation theory. These unusual results predicted by entanglement percolation are supported by extensive experimental data (NR, SANS, DSIMS, FTIR, BR) from selectively deuterated polystyrene chains HDH, DHD, HPS and DPS. These results clearly suggest that current notions of polymer rheology need to be reconsidered. Near Tg, a new perspective on the Glass Transition of amorphous

  6. On the dependence of stress states on viscoelastic rheologies.

    NASA Astrophysics Data System (ADS)

    Cornet, Jan; Dabrowski, Marcin; Schmid, Daniel

    2016-04-01

    According to the World Stress Map, stresses in the earth crust change as a function of location and depth. Explaining the origin of the stresses is usually done by referring to active tectonic processes and by assuming that the crust is critically stressed. Although this is true in many areas around the world, we believe that the rheology of the rocks can also have an impact on the stress situation observed at depth. Considering viscoelastic materials, we investigate how the viscous component can lead to changes in stress situations with time and depth. Our setup is taken to represent a succession of perfectly bonded horizontal layers with different material properties overlain on top of each other. We use MILAMIN, a fast finite element code, to numerically study the impact of different viscoelastic rheologies on the stress distribution as a function of time. The code is purely mechanical but assuming a constant temperature gradient with depth and an Arrhenius law for viscosity we also include a first degree approximation of the temperature dependence of viscosity. Using our numerical code, we consider two sets of boundary conditions for a setup where a low viscosity layer is surrounded by much viscous ones. In the first set, we prescribe velocities at the bottom boundary and we determine how low a low viscosity layer should be to decouple the deformations seen in the layers above and below for time scales much shorter than the tectonic ones. We provide orders of magnitude for these low viscosities. In the second set, we prescribe tractions along a vertical boundary and we study how the stresses away from this boundary get redistributed between layers as a function of time. The low viscosity layer quickly reaches a hydrostatic state and the neighboring layers have to support the extra deviatoric stresses. Both sets of boundary conditions show that viscoelasticity can have an impact on the stress situation even at short time scales compared to the tectonic ones. It

  7. Colloids on the frontier of ferrofluids. Rheological properties.

    PubMed

    López-López, Modesto T; Gómez-Ramírez, Ana; Rodríguez-Arco, Laura; Durán, Juan D G; Iskakova, Larisa; Zubarev, Andrey

    2012-04-17

    This paper is devoted to the steady-state rheological properties of two new kinds of ferrofluids. One of these was constituted by CoNi nanospheres of 24 nm in diameter, whereas the other by CoNi nanofibers of 56 nm in length and 6.6 nm in width. These ferrofluids were subjected to shear rate ramps under the presence of magnetic fields of different intensity, and the corresponding shear stress values were measured. From the obtained rheograms (shear stress vs shear rate curves) the values of both the static and the dynamic yield stresses were obtained as a function of the magnetic field. The magnetoviscous effect was also obtained as a function of both the shear rate and the magnetic field. The experimental results demonstrate that upon magnetic field application these new ferrofluids develop yield stresses and magnetoviscous effects much greater than those of conventional ferrofluids, based on nanospheres of approximately 10 nm in diameter. Besides some expected differences, such as the stronger magnetorheological effect in the case of ferrofluids based on nanofibers, some intriguing differences are found between the rheological behaviors of nanofiber ferrofluids and nanosphere ferrofluid. First, upon field application the rheograms of nanofiber ferrofluids present N-shaped dependence of the shear stress on the shear rate. The decreasing part of the rheograms takes place at low shear rate. These regions of negative differential viscosity, and therefore, unstable flow is not observed in the case of nanosphere ferrofluids. The second intriguing difference concerns the curvature of the yield stress vs magnetic field curves. This curvature is negative in the case of nanosphere ferrofluid, giving rise to saturation of the yield stress at medium field, as expected. However, in the case of nanofiber ferrofluid this curvature is positive, which means a faster increase of the yield stress with the magnetic field the higher the magnitude of the latter. These interesting

  8. A Model of Dislocation-Controlled Rheology for the Mantle

    NASA Astrophysics Data System (ADS)

    Minster, J. B.; Anderson, D. L.

    1981-02-01

    The dislocation microstructure of mantle materials can account simultaneously for long-term steady-state creep, and for stress wave attenuation at seismic frequencies. The hypothesis that a single microstructural model explains the rheology for characteristic times ranging from 1 to 1010 seconds can be used to restrict the class of permissible rheological models for the mantle. We review steady-state dislocation damping models in order of increasing complexity, and reject those which do not satisfy laboratory data or geophysical constraints. This elimination procedure leads us to consider an organized microstructure, in which most dislocations are found inside subgrain walls. The cells contain relatively few dislocation links. These are free to bow under small, i.e. seismic, stresses. The time constant of this mechanism is controlled either by the diffusion of kinks or of point defects bound to the dislocation line. The glide of intragrain dislocations explains the magnitude and frequency range of seismic attenuation. Steady-state creep is governed by recovery through climb and annihilation in cell walls. Under conditions of jog undersaturation, climb is controlled by jog formation in addition to self-diffusion, and the model requires a higher creep activation energy than for self-diffusion, in agreement with observations on olivine. Quantitative agreement with laboratory data is achieved if the density of cell-wall dislocations is one to two orders of magnitude higher than the density of intracell dislocations. Self-diffusion is probably controlled by silicon diffusion at low pressure and by oxygen diffusion at high pressure. The long-term tectonic stress is the dominant factor determining scale lengths; as a result, the total strength of the relaxation associated with bowing of intracell dislocation links is fixed by the geometry and is of the order of 10%. This limits the width of the seismic absorption band to 2-3 decades in frequency for each mantle mineral

  9. Rheological quality of pearl millet porridge as affected by grits size.

    PubMed

    Yadav, Deep N; Chhikara, Navnidhi; Anand, Tanupriya; Sharma, Monika; Singh, Ashish K

    2014-09-01

    Study was conducted to optimize pearl millet grits size for the preparation of acceptable porridge with skimmed milk powder (SMP). Pearl millet porridge was prepared with different grits size (1.410, 0.841, 0.595, and 0.420 mm). A positive (r = 0.904) correlation was observed between water absorption index and grits size. Porridge showed shear thinning behavior as, initially shear stress increased with increase in shear rate and later on decreased. Porridge prepared with larger grits (1.410 mm) exhibited higher firmness (38.4 ± 1.27 N) and viscosity (446 ± 3.9 cP), whereas smaller grits (0.420 mm) resulted in less viscous (118.8 ± 1.74 cP) and firm (20.4 ± 1.85 N) porridge. The medium grits (0.841 mm) produced porridge with acceptable firmness (30.7 ± 1.56 N) and viscosity (298.1 ± 8.81 cP) with moderate (6.0 ± 0.10) acceptability. To improve sensory quality of porridge (grits size 0.841 mm); skimmed milk powder at different levels (0, 5, 10 and 15 %) was added and its effect on various quality parameters was studied. SMP addition significantly (P ≤ 0.05) modified the gelatinization and gelling behavior of grits and decreased (P ≤ 0.05) all the pasting characteristics except pasting temperature, which increased from 77.1 ± 1.85 to 85.9 ± 3.46 °C. The peak (499 ± 6.6 cP) and final viscosity (450 ± 11.9 cP) of porridge (0.841 mm) prepared with 15 % SMP are quite similar. Hence, it maintains viscosity on cooling, similar to maximum viscosity attained during cooking. Keeping in view the rheological, firmness and sensory quality, 0.841 mm grits of pearl millet with 15 % SMP was found optimum for preparation of acceptable porridge. PMID:25190879

  10. Turbulent Flow Past Spinning Cylinders

    NASA Astrophysics Data System (ADS)

    Mehmedagic, Igbal; Carlucci, Donald; Carlucci, Pasquale; Thangam, Siva

    2009-11-01

    Flow past cylinders aligned along their axis where a base freely spins while attached to a non-spinning forebody is considered from a computational and experimental point of view. The time-averaged equations of motion and energy are solved using the modeled form of transport equations for the turbulence kinetic energy and the scalar form of turbulence dissipation with an efficient finite-volume algorithm. An anisotropic two-equation Reynolds-stress model that incorporates the effect of rotation-modified energy spectrum and swirl is used to perform computations for the flow past axially rotating cylinders. Both rigid cylinders as well as that of cylinders with free-spinning base are considered from a computational point of view. A subsonic wind tunnel with a forward-sting mounted spinning cylinder is used for experiments. Experiments are performed for a range of spin rates and free stream flow conditions. The experimental results of Carlucci & Thangam (2001) are used to benchmark flow over spinning cylinders. The data is extended to munitions spinning in the wake of other munitions. Applications involving the design of projectiles are discussed.

  11. Effects of corn fiber gum (CFG) on the pasting and thermal behaviors of maize starch.

    PubMed

    Qiu, Shuang; Yadav, Madhav P; Chen, Hao; Liu, Yan; Tatsumi, Eizo; Yin, Lijun

    2015-01-22

    Corn fiber gum (CFG) was a novel arabinoxylan hydrocolloid and recent researches showed its considerable potential in food processing. In this study, the interactions of maize starch and CFG were studied. Maize starch/CFG blend gels were prepared from maize starch suspension mixing with 0.1%, 0.25%, 0.5%, 1.0% (w/w) CFG. The pasting and thermal properties, rheological properties, microstructure, leached amylose and swelling power characteristics were evaluated. Compared with the reference, CFG addition lowered peak viscosity and breakdown of the composite system, but increased final viscosity in RVA measurement. The swelling power and the amount of leached amylose of maize starch gels were reduced as the addition concentration of CFG increased. The thermal characteristics of maize starch/CFG mixtures varied insignificantly as determined in DSC heating process. Rheological parameters, such as storage modulus (G') and loss modulus (G"), of the maize starches were observed to increase when CFG was present, supporting the hypothesis that the interaction between CFG and amylose could happen in the composite system. Confocal laser scanning microscopy (CLSM) confirmed changes in gels microstructure as starch components tended to be inhibited from leaching out of the granules when CFG was added, and the morphology of starch granule was more compact when CFG was added. PMID:25439892

  12. PREFACE: 1st International Conference on Rheology and Modeling of Materials

    NASA Astrophysics Data System (ADS)

    Gömze, László A.

    2015-04-01

    Understanding the rheological properties of materials and their rheological behaviors during their manufacturing processes and in their applications in many cases can help to increase the efficiency and competitiveness not only of the finished goods and products but the organizations and societies also. The more scientific supported and prepared organizations develop more competitive products with better thermal, mechanical, physical, chemical and biological properties and the leading companies apply more competitive knowledge, materials, equipment and technology processes. The idea to organize in Hungary the 1st International Conference on Rheology and Modeling of Materials we have received from prospective scientists, physicists, chemists, mathematicians and engineers from Asia, Europe, North and South America including India, Korea, Russia, Turkey, Estonia, France, Italy, United Kingdom, Chile, Mexico and USA. The goals of ic-rmm1 the 1st International Conference on Rheology and Modeling of Materials are the following: • Promote new methods and results of scientific research in the fields of modeling and measurements of rheological properties and behavior of materials under processing and applications. • Change information between the theoretical and applied sciences as well as technical and technological implantations. • Promote the communication between the scientists of different disciplines, nations, countries and continents. The international conference ic-rmm1 provides a platform among the leading international scientists, researchers, PhD students and engineers for discussing recent achievements in measurement, modeling and application of rheology in materials technology and materials science of liquids, melts, solids, crystals and amorphous structures. Among the major fields of interest are the influences of material structures, mechanical stresses temperature and deformation speeds on rheological and physical properties, phase transformation of

  13. Rheological Signature of Frictional Interactions in Shear Thickening Suspensions.

    PubMed

    Royer, John R; Blair, Daniel L; Hudson, Steven D

    2016-05-01

    Colloidal shear thickening presents a significant challenge because the macroscopic rheology becomes increasingly controlled by the microscopic details of short ranged particle interactions in the shear thickening regime. Our measurements here of the first normal stress difference over a wide range of particle volume fractions elucidate the relative contributions from hydrodynamic lubrication and frictional contact forces, which have been debated. At moderate volume fractions we find N_{1}<0, consistent with hydrodynamic models; however, at higher volume fractions and shear stresses these models break down and we instead observe dilation (N_{1}>0), indicating frictional contact networks. Remarkably, there is no signature of this transition in the viscosity; instead, this change in the sign of N_{1} occurs while the shear thickening remains continuous. These results suggest a scenario where shear thickening is driven primarily by the formation of frictional contacts, with hydrodynamic forces playing a supporting role at lower concentrations. Motivated by this picture, we introduce a simple model that combines these frictional and hydrodynamic contributions and accurately fits the measured viscosity over a wide range of particle volume fractions and shear stress. PMID:27203345

  14. Anisometric Particle Systems—from Shape Characterization to Suspension Rheology

    NASA Astrophysics Data System (ADS)

    Gregorová, Eva; Pabst, Willi; Vaněrková, Lucie

    2009-06-01

    Methods for the characterization of anisometric particle systems are discussed. For prolate particles, the aspect ratio determination via microscopic image analysis is recalled, and aspect ratio distributions as well as shape-size dependences are commented upon. For oblate particles a simple relation is recalled with can be used to determine an average aspect ratio when size distributions are available from two methods, typically from sedimentation analysis and laser diffraction. The connection between particle shape (aspect ratio) and suspension rheology is outlined and it is shown how a generic procedure, based on Brenner's theory, can be applied to predict the intrinsic viscosity when the aspect ratio is known. On the other hand it is shown, how information on the intrinsic viscosity and the critical solids volume fraction can be extracted from experiments, when the measured concentration dependence of the effective suspension viscosity is adequately interpreted (using the Krieger relation for fitting). The examples mentioned in this paper include systems with oblate or prolate ceramic particles (kaolins, pyrophyllite, wollastonite, silicon carbide) as well as (prolate) pharmaceuticals (mesalamine, ibuprofen, nifuroxazide, paracetamol).

  15. Morphology and Rheological Behaviour of Ag-SBS Nanocomposite Gels

    NASA Astrophysics Data System (ADS)

    Peponi, Laura; Torre, Luigi; Kenny, Josè M.; Mondragon, Iñaki

    2008-08-01

    Block copolymers are of both theoretical and practical importance because of their ability to self-assemble in nano-ordered structures. The self-assembly processes in these materials, are a consequence of the intermolecular micro phase separation between the dissimilar chains covalently linked together. Another important property of block copolymers is that, in solution with a selective solvent, they aggregate to form physical gels. Their technological importance is due to their ability to form elastic solids via self-assembly, with midblocks bridging aggregated end-block micelles. In our study poly(styrene-b-butadiene-b-styrene) (SBS), form, by its dissolution in a mid-block-selective solvent (THF) physical gels. So the morphology and the rheological behavior of the thermoreversible gels have been studied and characterized. Moreover, the gel behavior was also studied when Ag nanoparticles were added to the SBS matrix. The results of this study show that the gel stability is not affected by the presence of Ag nanoparticles.

  16. Mechanics of Single Cells: Rheology, Time Dependence, and Fluctuations

    PubMed Central

    Massiera, Gladys; Van Citters, Kathleen M.; Biancaniello, Paul L.; Crocker, John C.

    2007-01-01

    The results of mechanical measurements on single cultured epithelial cells using both magnetic twisting cytometry (MTC) and laser tracking microrheology (LTM) are described. Our unique approach uses laser deflection for high-performance tracking of cell-adhered magnetic beads either in response to an oscillatory magnetic torque (MTC) or due to random Brownian or ATP-dependent forces (LTM). This approach is well suited for accurately determining the rheology of single cells, the study of temporal and cell-to-cell variations in the MTC signal amplitude, and assessing the statistical character of the tracers' random motion in detail. The temporal variation of the MTC rocking amplitude is surprisingly large and manifests as a frequency-independent multiplicative factor having a 1/f spectrum in living cells, which disappears upon ATP depletion. In the epithelial cells we study, random bead position fluctuations are Gaussian to the limits of detection both in the Brownian and ATP-dependent cases, unlike earlier studies on other cell types. PMID:17693461

  17. Effect of thermal modification on rheological properties of polyethylene blends

    SciTech Connect

    Siriprumpoonthum, Monchai; Nobukawa, Shogo; Yamaguchi, Masayuki; Satoh, Yasuo; Sasaki, Hiroko

    2014-03-15

    We examined the effects of thermal modification under flow field on the rheological properties of linear low-density polyethylene (LLDPE) with high molecular weight, low-density polyethylene (LDPE), and their blends, without thermal stabilizer. Although structural changes during processing are not detected by size extrusion chromatography or nuclear magnetic resonance spectroscopy, linear viscoelastic properties changed greatly, especially for the LLDPE. A cross-linking reaction took place, leading to, presumably, star-shaped long-chain branches. Consequently, the modified LLDPE, having high zero-shear viscosity, became a thermorheologically complex melt. Moreover, it should be noted that the drawdown force, defined as the uniaxial elongational force at a constant draw ratio, was significantly enhanced for the blends. Enhancement of elongational viscosity was also detected. The drawdown force and elongational viscosity are marked for the thermally modified blend as compared with those for the blend of thermally modified pure components. Intermolecular cross-linking reactions between LDPE and LLDPE, yielding polymers with more than two branch points per chain, result in marked strain-hardening in the elongational viscosity behavior even at small strain. The recovery curve of the oscillatory modulus after the shear modification is further evidence of a branched structure.

  18. Reaction-induced rheological weakening enables oceanic plate subduction.

    PubMed

    Hirauchi, Ken-Ichi; Fukushima, Kumi; Kido, Masanori; Muto, Jun; Okamoto, Atsushi

    2016-01-01

    Earth is the only terrestrial planet in our solar system where an oceanic plate subducts beneath an overriding plate. Although the initiation of plate subduction requires extremely weak boundaries between strong plates, the way in which oceanic mantle rheologically weakens remains unknown. Here we show that shear-enhanced hydration reactions contribute to the generation and maintenance of weak mantle shear zones at mid-lithospheric depths. High-pressure friction experiments on peridotite gouge reveal that in the presence of hydrothermal water, increasing strain and reactions lead to an order-of-magnitude reduction in strength. The rate of deformation is controlled by pressure-solution-accommodated frictional sliding on weak hydrous phyllosilicate (talc), providing a mechanism for the 'cutoff' of the high peak strength at the brittle-plastic transition. Our findings suggest that infiltration of seawater into transform faults with long lengths and low slip rates is an important controlling factor on the initiation of plate tectonics on terrestrial planets. PMID:27562366

  19. Reaction-induced rheological weakening enables oceanic plate subduction

    PubMed Central

    Hirauchi, Ken-ichi; Fukushima, Kumi; Kido, Masanori; Muto, Jun; Okamoto, Atsushi

    2016-01-01

    Earth is the only terrestrial planet in our solar system where an oceanic plate subducts beneath an overriding plate. Although the initiation of plate subduction requires extremely weak boundaries between strong plates, the way in which oceanic mantle rheologically weakens remains unknown. Here we show that shear-enhanced hydration reactions contribute to the generation and maintenance of weak mantle shear zones at mid-lithospheric depths. High-pressure friction experiments on peridotite gouge reveal that in the presence of hydrothermal water, increasing strain and reactions lead to an order-of-magnitude reduction in strength. The rate of deformation is controlled by pressure-solution-accommodated frictional sliding on weak hydrous phyllosilicate (talc), providing a mechanism for the ‘cutoff' of the high peak strength at the brittle-plastic transition. Our findings suggest that infiltration of seawater into transform faults with long lengths and low slip rates is an important controlling factor on the initiation of plate tectonics on terrestrial planets. PMID:27562366

  20. Soft water-soluble microgel dispersions: structure and rheology.

    PubMed

    Omari, A; Tabary, R; Rousseau, D; Calderon, F Leal; Monteil, J; Chauveteau, G

    2006-10-15

    The size and structural characteristics of polyacrylamide-based water-soluble microgel dispersions were investigated by optical and rheological methods. Microgel hydrodynamic radii Rh were measured by light scattering and derived from intrinsic shear viscosity [eta]0. The variations of Rh3 and [eta]0 with the crosslink density Nx, follow the scaling law Rh3 congruent withNx(-alpha) with alpha close to 0.63, in good agreement with the simple structural model proposed in this paper showing how the exact value of alpha depends on inner structural details of the microgel. The plateau viscosity versus particle apparent volume fraction shows a monotonous change from hard sphere dispersions (high crosslink density of microgels) to flexible linear polymer solutions. Measurements of the first normal stress difference N1 show that increasing the microgel crosslink density affects the system viscosity more than its elasticity. Under oscillatory shear flow, loss and storage moduli undergo both qualitative and quantitative changes with crosslink density. At moderate concentrations, the elastic modulus is the most affected and its slope in low frequency regime decreases from two to less than one as Nx increases. We discuss the experimental results within the frame of knowledge on linear, branched polymer solutions and soft microgel suspensions. PMID:16928380