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Sample records for sand-blended-cement pastes rheology

  1. Pasting and rheological properties of quinoa-oat composites

    USDA-ARS?s Scientific Manuscript database

    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 ...

  2. 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

  3. Rheology and Extrusion of Cement-Fly Ashes Pastes

    NASA Astrophysics Data System (ADS)

    Micaelli, F.; Lanos, C.; Levita, G.

    2008-07-01

    The addition of fly ashes in cement pastes is tested to optimize the forming of cement based material by extrusion. Two sizes of fly ashes grains are examinated. The rheology of concentrated suspensions of ashes mixes is studied with a parallel plates rheometer. In stationary flow state, tested suspensions viscosities are satisfactorily described by the Krieger-Dougherty model. An "overlapped grain" suspensions model able to describe the bimodal suspensions behaviour is proposed. For higher values of solid volume fraction, Bingham viscoplastic behaviour is identified. Results showed that the plastic viscosity and plastic yield values present minimal values for the same optimal formulation of bimodal mixes. The rheological study is extended to more concentrated systems using an extruder. Finally it is observed that the addition of 30% vol. of optimized ashes mix determined a significant reduction of required extrusion load.

  4. 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.

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

    USDA-ARS?s Scientific Manuscript database

    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 ...

  6. Effect of ground granulated blast furnace slag particle size distribution on paste rheology: A preliminary model

    NASA Astrophysics Data System (ADS)

    Kashani, Alireza; Provis, John L.; van Deventer, Jannie S. J.

    2013-06-01

    Ground granulated blast furnace slag is widely combined with Portland cement as a supplementary material, and is also used in alkali-activated binders (geopolymers) and in supersulfated cements, which are potential replacements for Portland cement with significantly reduced carbon dioxide emissions. The rheology of a cementitious material is important in terms of its influence on workability, especially in self leveling concretes. The current research investigates the effects of different particle size distributions of slag particles on paste rheology. Rheological measurements results show a direct relationship between the modal particle size and the yield stress of the paste. An empirical model is introduced to calculate the yield stress value of each paste based on the particle size distribution, and applied to a range of systems at single water to solids ratio. The model gives a very good match with the experimental data.

  7. In situ measurement of the rheological properties and agglomeration on cementitious pastes

    SciTech Connect

    Kim, Jae Hong; Yim, Hong Jae; Ferron, Raissa Douglas

    2016-07-15

    Various factors influence the rheology of cementitious pastes, with the most important being the mixing protocol, mixture proportions, and mixture composition. This study investigated the influence of ground-granulated blast-furnace slag, on the rheological behavior of cementitious pastes. In tandem with the rheological measurements, fresh state microstructural measurements were conducted using three different techniques: A coupled stroboscope-rheometer, a coupled laser backscattering-rheometer, and a conventional laser diffraction technique. Laser diffraction and the coupled stroboscope-rheometer were not good measures of the in situ state of flocculation of a sample. Rather, only the laser backscattering technique allowed for in situ measurement on a highly concentrated suspension (cementitious paste). Using the coupled laser backscattering-rheometer technique, a link between the particle system and rheological behavior was determined through a modeling approach that takes into account agglomeration properties. A higher degree of agglomeration was seen in the ordinary Portland cement paste than pastes containing the slag and this was related to the degree of capillary pressure in the paste systems.

  8. Physicochemical, morphological and rheological properties of canned bean pastes "negro Queretaro" variety (Phaseolus vulgaris L.).

    PubMed

    Martínez-Preciado, A H; Estrada-Girón, Y; González-Álvarez, A; Fernández, V V A; Macías, E R; Soltero, J F A

    2014-09-01

    Proximate, thermal, morphological and rheological properties of canned "negro Querétaro" bean pastes, as a function of fat content (0, 2 and 3 %) and temperature (60, 70 and 85 °C), were evaluated. Raw and precooked bean pastes were characterized by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). Well-defined starch granules in the raw bean pastes were observed, whereas a gelatinized starch paste was observed for the canned bean pastes. The DSC analysis showed that the raw bean pastes had lower onset peak temperatures (79 °C, 79.1 °C) and gelatinization enthalpy (1.940 J/g), compared to that precooked bean pastes (70.4 °C, 75.7 °C and 1.314 J/g, respectively) thermal characteristics. Moreover, the dynamic rheological results showed a gel-like behavior for the canned bean pastes, where the storage modulus (G') was frequency independent and was higher than the loss modulus (G″). The non-linear rheological results exhibited a shear-thinning flow behavior, where the steady shear-viscosity was temperature and fat content dependent. For canned bean pastes, the shear-viscosity data followed a power law equation, where the power law index (n) decreased when the temperature and the fat content increased. The temperature effect on the shear-viscosity was described by an Arrhenius equation, where the activation energy (Ea) was in the range from 19.04 to 36.81 KJ/mol. This rheological behavior was caused by gelatinization of the starch during the cooking and sterilization processes, where starch-lipids and starch-proteins complex were formed.

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

    USDA-ARS?s Scientific Manuscript database

    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...

  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. Optimization of the functional characteristics, pasting and rheological properties of pearl millet-based composite flour.

    PubMed

    Awolu, Olugbenga Olufemi

    2017-02-01

    Optimisation of composite flour comprising pearl millet, kidney beans and tigernut with xanthan gum was evaluated for rheological evaluations. The functional properties of the composite flour were optimized using optimal design of response surface methodology. The optimum blends, defined as blends with overall best functional characteristics were run 3 (75.956% pearl millet, 17.692% kidney beans, 6.352% tigernut flours), run 7 (85.000% pearl millet, 10.000% kidney beans, 5.000% tigernut flours) and run 13 (75.000% pearl millet, 20.000% kidney beans, 5.000% tigernut flours). The pasting characteristics and rheological evaluation of the optimized blends were further evaluated in rapid visco units (RVU). Run 7 had the overall best pasting characteristics; peak viscosity (462 RVU), trough (442 RVU), breakdown viscosity (20 RVU), final viscosity (975 RVU), setback (533 RVU), peak time (5.47 min) and pasting temperature (89.60 °C). These values were found to be better than several composite flours consisting mixture of wheat and non-wheat crops. In addition, the rheological characteristics (measured by Mixolab) showed that run 7 is the best in terms of dough stability, swelling, water absorption and shelf stability. Composite flour with 85% pearl millet flour in addition to kidney beans and tigernut flours could therefore serve as a viable alternative to 100% wheat flour in bread production.

  12. Pasting and rheological properties of rice starch as affected by pullulan.

    PubMed

    Chen, Long; Tong, Qunyi; Ren, Fei; Zhu, Guilan

    2014-05-01

    Effect of pullulan (PUL) on the pasting, rheological properties of rice starch (RS) was investigated. The swelling power, amylose leaching, and confocal laser scanning microscopy (CLSM) observation of the samples were also conducted to explore the possible interaction between starch and pullulan. Rapid visco-analysis (RVA) showed that PUL significantly changed viscosity parameters of rice starch-pullulan (RS-PUL) mixtures. Dynamic rheological measurements revealed that the modulus (G', G″) of the mixtures increased with the increase of pullulan concentration from 0.01% to 0.07%, but then decreased with the increase of pullulan concentration from 0.07% to 0.50%. The pasting and rheological properties of samples indicated that pullulan could blend well with rice starch and promote the gelatinization of starch granules at low concentration of pullulan, but suppress the gelatinization of starch granules at high concentration of pullulan. The results of swelling power, leached amylose and CLSM observation of samples further suggest that the interaction between starch and pullulan occurred in the RS-PUL system and the interaction was hypothesized to be responsible for these results.

  13. 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.

  14. Studies on fish and pork paste gelation by dynamic rheology and circular dichroism.

    PubMed

    Liu, R; Zhao, S-M; Xiong, S-B; Xie, B-J; Liu, H-M

    2007-09-01

    The muscle paste of fish, pork, and their mixtures were prepared to study the gelling characteristics by dynamic rheological measurement. The gelation mechanisms of muscle paste were also investigated by circular dichroism. Gel formation of fish paste occurred in 2 steps of 5 to 35 and 51 to 90 degrees C respectively, while pork paste mainly in 1 step of 49 to 72 degrees C. Gel formation was relative to the alpha-helix unfolding of myosin, which responded the melting temperatures of 40 and 50 degrees C for fish myosin and 50 and 60 degrees C for pork myosin, respectively. Alpha-helix unfolding of myosin was beneficial for gel formation. During gel formation, G' of muscle paste was linearly related to alpha-helical content of myosin. The interactions of fish and pork proteins at high temperature (>35 degrees C) could change the gel forming characteristics of muscle paste. Mixed paste exhibited a similar gelation pattern to individual fish paste with 2 visible increases in G'. Addition of pork could suppress the breakdown of fish gel structure at approximately 50 degrees C. Mixing pork and silver carp in a certain ratio could improve the gel properties of silver carp products.

  15. 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.

  16. Effects of oligosaccharides on pasting, thermal and rheological properties of sweet potato starch.

    PubMed

    Zhou, Da-Nian; Zhang, Bao; Chen, Bo; Chen, Han-Qing

    2017-09-01

    Effects of sucrose, raffinose and stachyose on pasting, thermal, and rheological properties of sweet potato starch (SPS) were investigated. The results indicated that pasting temperature of SPS increased with increasing sugar concentration in the order of stachyose>raffinose>sucrose. Addition of sugars significantly decreased the peak, trough, and final viscosities as well as setback value. The gelatinization temperatures of SPS-sugar mixtures markedly increased with increasing sugar concentration in the order of stachyose>raffinose=sucrose, gelatinization enthalpy also increased when sugar was added at high concentration compared with native starch. The addition of sugars increased the yield stress and consistency coefficient of SPS-sugar mixed pastes. The SPS-sugar mixed pastes exhibited a pseudoplastic and shear-thinning behavior under yield stress condition. Moreover, storage moduli (G') of SPS-sugar mixed pastes decreased with addition of sugars. This study also showed that addition of sugars promoted liquid-like characteristics of SPS-sugar mixed pastes. Copyright © 2017 Elsevier Ltd. All rights reserved.

  17. 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.

  18. Influence of lamb rennet paste containing probiotic on proteolysis and rheological properties of pecorino cheese.

    PubMed

    Santillo, A; Albenzio, M

    2008-05-01

    Pecorino cheeses made from heat-treated ewes' milk using traditional lamb rennet paste (RP), lamb rennet paste containing Lactobacillus acidophilus (LA-5; RPL), and lamb rennet paste containing a mix of Bifidobacterium lactis (BB-12) and Bifidobacterium longum (BB-46; RPB) were characterized for proteolytic and rheological features during ripening. Consumer acceptance of cheeses at 60 d of ripening was evaluated. Lactobacillus acidophilus and Bifidobacterium mix displayed counts of 8 log(10) cfu/g and 9 log(10) cfu/g, respectively, in cheese during ripening. The RPB cheese displayed a greater degradation of casein (CN) matrix carried out by the enzymes associated to both Bifidobacterium mix and endogenous lactic acid microflora, resulting in the highest values of non-CN N and water-soluble N and the highest amount of alpha(s)-CN degradation products in cheese at 60 d of ripening. The RPL cheese displayed intermediate levels of lactic acid bacteria and of N fractions. The percentage of gamma-CN in RP and RPL cheeses at 60 d was 2-fold higher than in the cheese curd of the same groups, whereas the mentioned parameter was 3-fold higher in RPB cheese than in the corresponding fresh curd according to its highest plasmin content. The lower hardness in RPB at the end of ripening could be ascribed to the greater proteolysis observed in cheese harboring the Bifidobacterium mix. Although differences in proteolytic patterns were found among treatments, there were no differences in smell and taste scores.

  19. Physicochemical, pasting, rheological, thermal and morphological properties of horse chestnut starch.

    PubMed

    Rafiq, Syed Insha; Jan, Kulsum; Singh, Sukhcharn; Saxena, D C

    2015-09-01

    Indian Horse chestnuts contain high content of starch which can be explored to be used in various applications in food industry as encapsulating agent, stabilizer, binder, thickener, gelling agents and many more. Horse chest nut is locally available and can be a boon for food industry if the inherent properties are explored. Hence, horse chest nut starch can be a better option for the replacement of conventional starches to meet the industrial demand of starch. Physicochemical, pasting, rheological, thermal and morphological properties of starch isolated from Indian Horse chestnut (HCN) were determined. Amylose content was found to be 26.10 %. Peak viscosity obtained from RVA profile was 4110 cP. Hardness, cohesiveness, adhesiveness and gumminess were determined by Texture Profile Analyser. Particle size analysis showed a typical Uni modal size distribution profile with particle distribution ranging from 7.52 to 27.44 μm. The shape of starch granules varied from round, irregular, oval, and elliptical with smooth surface. X- ray diffraction revealed that HCN starch showed a typical C-type pattern with characteristic peaks at 5.7, 15.0, 17.3 and 22.3°. The transition temperatures (To, Tp, and Tc) and enthalpy of gelatinization (ΔH) values were 53.35, 58.81, 63.57 °C and 8.76 J/g, respectively. The rheological properties were determined in terms of variation of storage modulus (G (/)), loss modulus (G (//)) and loss factor (tan δ) at different temperatures. Peak G (/), peak G (//) and peak tan δ values were observed as 10,400 Pa, 1,710 Pa, and 0.164, respectively.

  20. 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

    2016-11-05

    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.

  1. Rheological and Pasting Properties of Naked Barley Flour as Modified by Guar, Xanthan, and Locust Bean Gums

    PubMed Central

    Yoon, Sung-Jin; Lee, Youngseung; Yoo, Byoungseung

    2016-01-01

    To understand the effects of adding different gums (guar, xanthan, and locust bean gums) on naked barley flour (NBF), the rheological and pasting properties of NBF-gum mixtures were measured at different gum concentrations (0, 0.3, and 0.6% w/w). Steady shear rheological properties were determined by rheological parameters for power law and Casson models. All samples showed a clear trend of shear-thinning behavior (n=0.16~0.48) and had a non-Newtonian nature with yield stress. Consistency index, apparent viscosity, and yield stress values increased with an increase in gum concentration. Storage modulus values were more predominant than loss modulus values with all concentrations of gums. There is a more pronounced synergistic effect of elastic properties of NBF in the presence of xanthan gum. Rapid visco analyser pasting properties showed that the addition of gums resulted in a significant increase in the peak, breakdown, setback, and final viscosities, whereas the pasting temperature decreased. PMID:28078260

  2. Rheological and Pasting Properties of Naked Barley Flour as Modified by Guar, Xanthan, and Locust Bean Gums.

    PubMed

    Yoon, Sung-Jin; Lee, Youngseung; Yoo, Byoungseung

    2016-12-01

    To understand the effects of adding different gums (guar, xanthan, and locust bean gums) on naked barley flour (NBF), the rheological and pasting properties of NBF-gum mixtures were measured at different gum concentrations (0, 0.3, and 0.6% w/w). Steady shear rheological properties were determined by rheological parameters for power law and Casson models. All samples showed a clear trend of shear-thinning behavior (n=0.16~0.48) and had a non-Newtonian nature with yield stress. Consistency index, apparent viscosity, and yield stress values increased with an increase in gum concentration. Storage modulus values were more predominant than loss modulus values with all concentrations of gums. There is a more pronounced synergistic effect of elastic properties of NBF in the presence of xanthan gum. Rapid visco analyser pasting properties showed that the addition of gums resulted in a significant increase in the peak, breakdown, setback, and final viscosities, whereas the pasting temperature decreased.

  3. 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.

  4. Effect of partially hydrolyzed guar gum on pasting, thermo-mechanical and rheological properties of wheat dough.

    PubMed

    Mudgil, Deepak; Barak, Sheweta; Khatkar, B S

    2016-12-01

    Partially hydrolyzed guar gum was prepared using enzymatic hydrolysis of native guar gum that can be utilized as soluble fiber source. The effect of partially hydrolyzed guar gum (PHGG) on pasting, thermo-mechanical and rheological properties of wheat flour was investigated using rapid visco-analyzer, Mixolab and Microdoughlab. Wheat flour was replaced with 1-5g PHGG per 100g of wheat flour on weight basis. PHGG addition decreased the peak, trough, breakdown, setback and final viscosity of wheat flour. Water absorption and amylase activity of wheat dough were increased whereas starch gelatinization and protein weakening of wheat dough were reduced as a result of PHGG addition to wheat flour. PHGG addition also increased the peak dough height, arrival time, dough development time, dough stability and peak energy of wheat dough system. However, dough softening was decreased after PHGG addition to wheat flour dough. Overall, it can be assumed that PHGG has influenced the properties of wheat flour dough system by decreasing the RVA viscosities and increasing the water absorption and starch gelatinization of wheat dough system. Copyright © 2016 Elsevier B.V. All rights reserved.

  5. 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.

  6. 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

  7. Assessing of the potential of extruded flour paste as fat replacer in O/W emulsion: A rheological and microstructural study.

    PubMed

    Román, Laura; Martínez, Mario M; Gómez, Manuel

    2015-08-01

    Extruded flour represents an economical and environmental friendly alternative as fat replacer. In this research, the potential use of an extruded flour-water paste as fat replacer in an oil-in-water emulsion was studied. The effect of flour-water ratio and level of oil replacement (30, 50 and 70%) on the microstructure, rheological properties and stability of mayonnaise-like emulsion was evaluated. Fat replacement by extruded flour gradually increased the number and reduced the size of oil droplets. All the emulsion samples showed a pseudoplastic behaviour. At low shear rates a Newtonian region characterised by Carreau model appeared (R(2)>0.99). In general, the limiting viscosity of the Newtonian region and the consistency index increased with the decreased water content of the paste and increased the level of oil substitution. A decrease in oil concentration led to a greater thixotropic behaviour. Oscillatory test revealed that predominance of the continuous or dispersed phase influenced viscoelastic behaviour. Reduction in oil content resulted in an increased freeze-thaw stability. Results suggested that if the flour-water ratio of the paste is controlled, extruded flour is appropriate for preparing reduced-fat oil-in-water emulsion with similar rheological properties to the full fat and greater freeze-thaw stability. Copyright © 2015 Elsevier Ltd. All rights reserved.

  8. The influence of polymeric component of bioactive glass-based nanocomposite paste on its rheological behaviors and in vitro responses: hyaluronic acid versus sodium alginate.

    PubMed

    Sohrabi, Mehri; Hesaraki, Saeed; Kazemzadeh, Asghar

    2014-04-01

    Different biocomposite pastes were prepared from a solid phase that was nanoparticles of sol-gel-derived bioactive glass and different liquid phases including 3% hyaluronic acid solution, sodium alginate solutions (3% and 10 %) or mixtures of hyaluronic acid and sodium alginate (3% or 10 %) solutions in 50:50 volume ratio. Rheological properties of the pastes were measured in both rotatory and oscillatory modes. The washout behavior and in vitro apatite formation of the pastes were determined by soaking them in simulated body fluid under dynamic situation for 14 days. The proliferation and alkaline phosphatase activity of MG-63 osteoblastic cells were also determined using extracts of the pastes. All pastes could be easily injected from the standard syringes with different tip diameters. All pastes exhibited visco-elastic character, but a nonthixotropic paste was obtained using hyaluronic acid in which the loss modulus was higher than the storage modulus. The thixotropy and storage modulus were increasingly improved by adding/using sodium alginate as mixing liquid. Moreover, the pastes in which the liquid phase was sodium alginate or mixture of hyaluronic acid and 10% sodium alginate solution revealed better apatite formation ability and washout resistance than that made of hyaluronic acid alone. No cytotoxicity effects were observed by extracts of the pastes on osteoblasts but better alkaline phosphatase activity was found for the pastes containing hyaluronic acid. Overall, injectable biocomposites can be produced by mixing bioactive glass nanoparticles and sodium alginate/hyaluronic acid polymers. They are potentially useful for hard and even soft tissues treatments.

  9. Specification of a new de-stoner machine: evaluation of machining effects on olive paste's rheology and olive oil yield and quality.

    PubMed

    Romaniello, Roberto; Leone, Alessandro; Tamborrino, Antonia

    2017-01-01

    An industrial prototype of a partial de-stoner machine was specified, built and implemented in an industrial olive oil extraction plant. The partial de-stoner machine was compared to the traditional mechanical crusher to assess its quantitative and qualitative performance. The extraction efficiency of the olive oil extraction plant, olive oil quality, sensory evaluation and rheological aspects were investigated. The results indicate that by using the partial de-stoner machine the extraction plant did not show statistical differences with respect to the traditional mechanical crushing. Moreover, the partial de-stoner machine allowed recovery of 60% of olive pits and the oils obtained were characterised by more marked green fruitiness, flavour and aroma than the oils produced using the traditional processing systems. The partial de-stoner machine removes the limitations of the traditional total de-stoner machine, opening new frontiers for the recovery of pits to be used as biomass. Moreover, the partial de-stoner machine permitted a significant reduction in the viscosity of the olive paste. © 2016 Society of Chemical Industry. © 2016 Society of Chemical Industry.

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

    USDA-ARS?s Scientific Manuscript database

    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...

  11. Optimum chopping conditions for Alaska pollock, Pacific whiting, and threadfin bream surimi paste and gel based on rheological and Raman spectroscopic analysis.

    PubMed

    Poowakanjana, Samanan; Mayer, Steven G; Park, Jae W

    2012-04-01

    Rheological and Raman spectroscopic properties of surimi from three species [Alaska pollock (AP) (cold water), Pacific whiting (temperate water), and threadfin bream (warm water)] were investigated as affected by various chopping conditions. Comminuting Alaska pollock surimi at 0 °C demonstrated superior gel hardness and cohesiveness when chopping time was extended to 15-18 min; however, long chopping time at higher temperatures resulted in a significantly decreased gel texture particularly at 20 °C. Warm water fish threadfin bream exhibited higher gel texture when chopping was done longer at higher temperature. Rheological properties were significantly affected by both chopping time and temperature. Species effect, based on their thermal stability, was readily apparent. Raman spectroscopy revealed a significant change in disulfide linkage and the reduction of secondary structure upon extended chopping. Dynamic oscillation rheology demonstrated the damage of light meromyoisn and lowering of onset of gelling temperature as the chopping time was extended. Chopping conditions to determine gel quality and manufacture surimi seafood are varied by all manufacturers. This paper covering three primary species for surimi with their suggested optimum chopping conditions: 15 min for Alaska pollock when chopped at 0 °C, 15 min for Pacific whiting at 15-20 °C, and 18 min for threadfin bream at 25-30 °C. The use of optimum chopping condition should maximize the value of each surimi and provide consistent quality to the end users. © 2012 Institute of Food Technologists®

  12. 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

    SciTech Connect

    Cohen, A.; Richon, D.

    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.

  13. Erythrocyte rheology.

    PubMed

    Stuart, J

    1985-09-01

    Erythrocyte deformability was formerly measured by its contribution to whole blood viscosity. It is now more commonly measured by filtration of erythrocytes through, or aspiration into, pores of 3-5 microns diameter and by the measurement of shear induced erythrocyte elongation using laser diffractometry. Recent improvements in the technology for erythrocyte filtration have included the removal of acute phase reactants from test erythrocyte suspensions, ultrasonic cleaning and reuse of filter membranes, awareness of the importance of mean cell volume as a determinant of flow through 3 microns diameter pores, and the ability to detect subpopulations of less deformable erythrocytes. Measurements of erythrocyte elongation by laser diffractometry, using the Ektacytometer, are also influenced by cell size and need to be corrected for mean cell volume. These advances have greatly improved the sensitivity and specificity of rheological methods for measuring the deformability of erythrocytes and for investigating the mode of action of rheologically active drugs.

  14. 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.

  15. Theory of rheology

    NASA Technical Reports Server (NTRS)

    Hutton, J. F.

    1973-01-01

    The structure of the modern theory of rheology is discussed to show the assumptions and limitations. Rheology is discussed as a branch of continuum mechanics to determine the relationships between stress, strain, and strain rate which will give a closer representation of lubricant properties than the Newtonian flow equation. Rheology is also investigated as a branch of chemical physics. Consideration is limited to those theories of nonpolymeric and polymeric fluids which can represent viscoelasticity in terms of identifiable and measureable molecular characteristics. The possibility that elastic liquids may rupture in shear and linear tension analogous to the failure of solids is proposed.

  16. Rheology of Structured Oils

    NASA Astrophysics Data System (ADS)

    Kelbaliev, G. I.; Rasulov, S. R.; Rzaev, A. G.; Mustafaeva, G. R.

    2017-07-01

    Rheological models of structured oils are proposed and compared with available experimental data on oils from different deposits. It is shown that structured oils can possess properties of Bingham and power-law non-Newtonian fluids.

  17. 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.

  18. 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.

  19. Rheology of concentrated biomass

    Treesearch

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

    2011-01-01

    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...

  20. 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"

  1. 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.

  2. Rheology in lubrication

    NASA Technical Reports Server (NTRS)

    Cheng, H. S.

    1973-01-01

    The rheological effects on lubrication are discussed. The types of lubrication considered are thick film hydrodynamic lubrication and thin film elastohydrodynamic lubrication. The temperature-viscosity, viscoelastic, shear-thinning, and normal stess effects on the lubrication of journal bearings are analyzed. A graph of the pressure distribution of viscoelastic liquids in journal bearings is provided. Mathematical models are developed to define the effects of various properties of the lubricants on friction reduction.

  3. Rheology in lubrication

    NASA Technical Reports Server (NTRS)

    Cheng, H. S.

    1973-01-01

    The rheological effects on lubrication are discussed. The types of lubrication considered are thick film hydrodynamic lubrication and thin film elastohydrodynamic lubrication. The temperature-viscosity, viscoelastic, shear-thinning, and normal stess effects on the lubrication of journal bearings are analyzed. A graph of the pressure distribution of viscoelastic liquids in journal bearings is provided. Mathematical models are developed to define the effects of various properties of the lubricants on friction reduction.

  4. Experiments on Paint Rheology

    NASA Astrophysics Data System (ADS)

    Hartranft, Thomas J.; Settles, Gary S.

    1998-11-01

    We seek a better understanding of the atomization of paints for purposes of limiting the environmental impact of spray painting. However, to do so one must confront both the shear and extensional rheology of mobile non-Newtonian fluids whose very composition is often complex and even unknown. A conventional Couette rheometer yields data on paint shear behavior, but no commercial instrument is available to measure the extensional viscosity, which is believed to govern ligamentary breakup in spray painting. Here a converging-flow extensional rheometer has been built for this purpose. Flow rate and orifice pressure drop are measured and related to the rheological properties of the fluid. At first, experience was gained by visualizing in this device the flow of clear aqueous solutions of both Newtonian (glycerol) and non-Newtonian (polyacrylamide) thickeners. Commercial latex and marine paints were then tested, with the goal of characterizing their extensional behavior and the hope that they might be replaceable by simpler aqueous rheological "substitute" fluids insofar as their atomization behavior is concerned. (Research supported by the US Navy via the Penn State Applied Research Laboratory.)

  5. Rheological properties of synovial fluids.

    PubMed

    Fam, H; Bryant, J T; Kontopoulou, M

    2007-01-01

    Synovial fluid is the joint lubricant and shock absorber [Semin. Arthritis Rheum. 32 (2002), 10-37] as well as the source of nutrition for articular cartilage. The purpose of the present paper is to provide a comprehensive review of the rheological properties of synovial fluid as they relate to its chemical composition. Given its importance in the rheology of synovial fluid, an overview of the structure and rheology of HA (hyaluronic acid) is presented first. The rheology of synovial fluids is discussed in detail, with a focus on the possible diagnosis of joint pathology based on the observed differences in rheological parameters and trends. The deterioration of viscoelastic properties of synovial fluid in pathological states due to effects of HA concentration and molecular weight is further described. Recent findings pertaining to the composition and rheology of periprosthetic fluid, the fluid that bathes prosthetic joints in vivo are reported.

  6. Rheological properties of soil: a review

    NASA Astrophysics Data System (ADS)

    Zhu, Guangli; Zhu, Long; Yu, Chao

    2017-05-01

    Recently rheological methods have been applied to investigate the mechanical properties of soil micro-structure. Rheological techniques have a number of quantitative physically based measurements and offer a better understanding of how soil micro-structure behaves when subject to stress. Rheological material is refers to deformation properties similar to the solid and flow properties similar to the liquid of bound water and colloidal substances under stress. Soil rheology is divided into fluid rheology and plasticity rheology. Fluid rheology is produced by rheological material. Plasticity rheology mainly refers to the sliding and peristaltic between soil solid particles under shear stress. It is generally believed that the soft soil rheology mainly belongs to fluid rheology, while the rheology of sand and other coarse grained soil mainly belongs to plasticity rheology. Thus, rheology mechanisms of soft soil and sand are different. This paper introduces the methods of the research progress on the rheology of soil, in the soil rheological mechanism, rheological model and rheological numerical aspects of the research at home and abroad were summarized and analysed, discussed the problems existed in related research, and puts forward some suggestions for the future study on the rheology of soil.

  7. Rheology of nanofluids: a review.

    PubMed

    Wang, Liang; Chen, Haisheng; Witharana, Sanjeeva

    2013-11-01

    The rheological behavior of nanofluids published in recent research papers and the relevant patents are reviewed in this article. Effects of various factors such as preparation, nanoparticle and base fluid properties, concentration, temperature, surface charge, and aggregation etc. on the rheological behavior of nanofluids are discussed. Brownian motion and nanoparticle aggregation are found to be the major mechanisms for rheological properties of nanofluids compared to the micro-sized suspensions. The importance of microstructure as means of understanding the mechanisms behind the rheological and heat transfer behavior of nanofluids is also disclosed.

  8. Thermal and rheological properties of breadfruit starch.

    PubMed

    Wang, Xueyu; Chen, Ling; Li, Xiaoxi; Xie, Fengwei; Liu, Hongshen; Yu, Long

    2011-01-01

    The thermal and rheological properties of breadfruit starch were studied using DSC and 2 different rheometers. It was found that the gelatinization temperature of starch with excess moisture content (>70%) was at approximately 75 °C. A new endotherm was detected at about 173 °C when the moisture content was lower than required for full gelatinization of the starch. A detailed examination revealed that this endotherm represented the melting of amylose-lipid complexes. Breadfruit starch paste exhibited shear-thinning fluid characteristics, and good thermal and pH stability. The setback viscosity of the breadfruit starch was lower than that of potato and corn starches. The rheological properties of the breadfruit starch paste was well described by the Herschel-Bulkley model at a shear rate of 0 to 100 s(-1), where R(2) is greater than 0.95, and it behaved like a yield-pseudoplastic fluid. Both the storage modulus and loss modulus of the paste initially increased sharply, then dropped after reaching the gelatinization peak. Breadfruit starch gel showed both flexibility and viscosity. Suspension with 6% starch content exhibited very weak gel rigidity; however, this increased significantly at starch contents above 20%.

  9. 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.

  10. 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

  11. 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

  12. Unifying suspension and granular rheology.

    PubMed

    Boyer, François; Guazzelli, Élisabeth; Pouliquen, Olivier

    2011-10-28

    Using an original pressure-imposed shear cell, we study the rheology of dense suspensions. We show that they exhibit a viscoplastic behavior similarly to granular media successfully described by a frictional rheology and fully characterized by the evolution of the friction coefficient μ and the volume fraction ϕ with a dimensionless viscous number I(v). Dense suspension and granular media are thus unified under a common framework. These results are shown to be compatible with classical empirical models of suspension rheology and provide a clear determination of constitutive laws close to the jamming transition.

  13. 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.

  14. Rheological behaviour of nanofluids

    NASA Astrophysics Data System (ADS)

    Chen, Haisheng; Ding, Yulong; Tan, Chunqing

    2007-10-01

    This work aims at a more fundamental understanding of the rheological behaviour of nanofluids and the interpretation of the discrepancy in the recent literature. Both experiments and theoretical analyses are carried out with the experimental work on ethylene glycol (EG)-based nanofluids containing 0.5-8.0 wt% spherical TiO2 nanoparticles at 20-60 °C and the theoretical analyses on the high shear viscosity, shear thinning behaviour and temperature dependence. The experimental results show that the EG-based nanofluids are Newtonian under the conditions of this work with the shear viscosity as a strong function of temperature and particle concentration. The relative viscosity of the nanofluids is, however, independent of temperature. The theoretical analyses show that the high shear viscosity of nanofluids can be predicted by the Krieger-Dougherty equation if the effective nanoparticle concentration is used. For spherical nanoparticles, an aggregate size of approximately 3 times the primary nanoparticle size gives the best prediction of experimental data of both this work and those from the literature. The shear thinning behaviour of nanofluids depends on the effective particle concentration, the range of shear rate and viscosity of the base liquid. Such non-Newtonian behaviour can be characterized by a characteristic shear rate, which decreases with increasing volume fraction, increasing base liquid viscosity, or increasing aggregate size. These findings explain the reported controversy of the rheological behaviour of nanofluids in the literature. At temperatures not very far from the ambient temperature, the relative high shear viscosity is independent of temperature due to negligible Brownian diffusion in comparison to convection in high shear flows, in agreement with the experimental results. However, the characteristic shear rate can have strong temperature dependence, thus affecting the shear thinning behaviour. The theoretical analyses also lead to a

  15. Rheological Modifiers and Wetting Agents

    SciTech Connect

    Chun, Jaehun; Hansen, Erich; Berg, John C.

    2009-10-01

    DOE tank waste treatment plants, the Waste Treatment Plant (WTP) at Hanford and Defense Waste Processing Facility (DWPF) at Savannah River, are designed to vitrify radioactive waste slurries for long-term storage. Plant throughput is currently limited by the waste solids loading. To increase waste throughput rates in the plant, an increase in the slurry solids concentration (or conversely, a reduction in the mass fraction of water in the waste) is being considered. However, the present mechanical designs used to mix and transport theses slurries are limited by the rheological properties. This reduction of water results in an increase in rheological properties that challenge plant design and performance. To support this increase in throughput, there is a need to reduce the rheological properties of these waste slurries. The objective of this project is to determine a small set of well-performing and commercially available rheological modifiers that allow control rheological properties of various simulated and actual waste slurries and to understand the physical mechanisms that govern modification of waste rheology. It is estimated that processing at a higher solids concentration will reduce the operating life of these plants by one year for both facilities, representing roughly $1B in lifecycle cost savings. In addition, this research is potentially important to sustainable operations of both WTP and DWPF

  16. Electro-rheological disk pump

    NASA Astrophysics Data System (ADS)

    Iorio, Vincent M.; Loy, Luke W.

    1993-02-01

    The invention is directed to a device for pumping electro-rheological fluids comprising a casing that defines an inner rotor chamber having a central inlet opening and a peripheral discharge opening. Rotatably disposed within said chamber is a rotor for imparting energy to the pumped electro-rheological fluid comprising of a plurality of non-conducting coaxial substantially parallel spaced disks. On one face of each disk are embedded one or more electrodes and on the opposing face of each disk are attached one or more conductive surfaces. By selectively applying an electric charge to the embedded electrodes, an electric field is produced between the electrodes and the conducting surfaces of adjacent disks. As a result, the viscosity of the electro-rheological fluid exposed to the applied electric field is increased thereby producing electro-rheological fluid vanes between adjacent disks. When the rotor is placed in rotation and a voltage is applied to the embedded electrodes, the electro-rheological fluid that is not exposed to the applied electric field, it is accelerated from the center of the rotor towards the outer periphery by the combined action of the electro-rheological fluid vanes and the friction force acting between the fluid and the rotating disks.

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

    USDA-ARS?s Scientific Manuscript database

    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 ...

  18. The synthesis and rheological characterization of a hydrophobically-modified acrylamide/acrylamide copolymer

    SciTech Connect

    Brady, T.A.; Davis, R.M.; Peiffer, D.G.

    1993-12-31

    The synthesis of a anionic, hydrophobically-modified acrylonitrile derivative is described, as the aqueous free-radical copolymerization of this monomer with acrylamide. The hydrophobic monomer contains a long-chain alkyl group and the pendant chain is terminated by a sulfonate group. Past rheological characterization has yielded viscosity profiles atypical for a conventional polyelectrolyte. Preliminary rheological data suggest that the copolymer in aqueous solution exhibits the polyelectrolyte effect, as well as interchain hydrophobic association.

  19. 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

  20. Rheology and hemodynamics

    SciTech Connect

    Cokelet, G.R.

    1980-01-01

    The mechanisms of red cell aggregation and cell deformation can impart viscoelastic behavior to blood: at very high hematocrits, the cell deformation mechanism dominates; at physiological and low hematocrits, red cell aggregation dominates at low shear rates. At physiological hematocrits, the viscoelastic behavior may be linear at low shear rates, where the elastic component of the complex viscosity may be comparable in magnitude to the viscous component; in the higher shear rate region, where red cell aggregation is less extensive or absent, blood behavior is nonlinear, and the elastic component becomes less significant. The nonadditivity of steady and oscillatory flow data for prediction of pulsatile flow behavior is indicative of the importance of the mean shear rate and the kinetics of the red cell aggregation-disaggregation processes in governing pulsatile blood flow. While oscillatory measurements will be useful in assessing rheological parameters that may give insight into the fundamental aspects of flow of normal and pathological bloods, it is not clear that the elastic component of the complex viscosity of blood will be of significance in physiological pulsatile flow. Many interesting questions remain to be answered, such as the question raised by the finding that normal stress differences were not detectable for blood under low shear rates. Judging from the number of papers presented at the Third International Congress of Biorheology, we can look forward to considerable activity in this area.

  1. 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.

  2. High-throughput method to predict extrusion pressure of ceramic pastes.

    PubMed

    Cao, Kevin; Liu, Yang; Tucker, Christopher; Baumann, Michael; Grit, Grote; Lakso, Steven

    2014-04-14

    A new method was developed to measure the rheology of extrudable ceramic pastes using a Hamilton MicroLab Star liquid handler. The Hamilton instrument, normally used for high throughput liquid processing, was expanded to function as a low pressure capillary rheometer. Diluted ceramic pastes were forced through the modified pipettes, which produced pressure drop data that was converted to standard rheology data. A known ceramic paste containing cellulose ether was made and diluted to various concentrations in water. The most dilute paste samples were tested in the Hamilton instrument and the more typical, highly concentrated, ceramic paste were tested with a hydraulic ram extruder fitted with a capillary die and pressure measurement system. The rheology data from this study indicates that the dilute high throughput method using the Hamilton instrument correlates to, and can predict, the rheology of concentrated ceramic pastes normally used in ceramic extrusion production processes.

  3. 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

  4. 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

  5. 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.

  6. Rheological characteristics of tooth bleaching materials.

    PubMed

    Wille, T; Combe, E C; Pesun, I J; Giles, D W

    2000-12-01

    Tooth bleaching materials need to flow easily on insertion but should have high viscosity at low stresses to stay in place on the teeth. Some degree of elasticity may also aid retention on the teeth thereby maximizing efficacy. The present work was undertaken to study the comparative rheology of three tooth bleaching systems: two gels (Opalescence, Ultradent; Perfecta Trio, American Dental Hygienics) and a paste (Colgate Platinum, Colgate). A dynamic stress rheometer (Rheometrics Scientific) with cone and plate geometry was used, with the materials maintained at 37.0+/-0.1 degrees C with a vapour hood to minimize volatilization. Stress creep and recovery experiments were carried out. Steady shear viscosity for all three systems was high (>10(6) Pa s(-1)) for stresses <20 Pa. Between 100 and 200 Pa stress, all three materials showed a large drop in viscosity and flowed readily. The recovery portion of the data showed a marked difference where the elasticity of the gels was nearly two orders of magnitude higher than that of the paste. It was concluded that all materials would flow readily on insertion into the mouth and all have desirable high viscosity at low stress, but the paste material had the lowest elasticity. The effect of elasticity on performance needs to be determined clinically.

  7. 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.

  8. Simple rheology of mixed proteins

    USDA-ARS?s Scientific Manuscript database

    Mixing different proteins to form strong gel networks for food applications may create synergistic increases in viscoelasticity that cannot be achieved with a single protein. In this study, small amplitude oscillatory shear analyses were used to investigate the rheology of calcium caseinate (CC), e...

  9. Paste mechanics for fine extrusion

    NASA Astrophysics Data System (ADS)

    Hurysz, Kevin Michael

    Lightweight metallic honeycomb structures having low density and high strength are potentially useful materials in a wide variety of applications. These materials can be employed as replacements for bearing and support structures, for impact and sound absorption, for thermal management, and in multifunctional capacities where the benefits of both metallic character and low density are required. Extrusion of these architectures represents a novel and economical alternative to conventional honeycomb fabrication. Extrusion is a material forming process that allows the shaping of cohesive plastic body into a linear form having constant cross section. The plastic body is a paste; well mixed material composed of solids, liquids, and processing aids. Control of paste rheology and optimization of flow and die variables are necessary to the extrusion of articles having complex geometry. By extruding paste compositions of raw material powders, mixed in the appropriate proportion to produce alloy materials upon reduction, lightweight ceramic honeycomb can be formed. The green ceramic honeycomb is then reduced to alloy in a controlled atmosphere heat treatment. In this investigation, high quality, green extruded honeycomb structures were fabricated. The model equations used to describe high viscosity suspension behavior were applied to paste formulations to predict properties. To accomplish the goals of this research, it was necessary to consider: (1) Raw material characterization, ensuring consistency between batches and allowing prediction of paste behavior; (2) Mechanics of the fluid phase and the paste, using capillary rheometry to determine paste properties; (3) Characteristics of the fluid phase and the paste, including methods to estimate and experimentally determine maximum solids content and the hydrodynamic constant; (4) Model development, applying the equations that describe high viscosity suspensions to pastes, allowing prediction of extrusion variables over a wide

  10. 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

  11. Rheology of vibrated granular suspensions

    NASA Astrophysics Data System (ADS)

    Kiesgen de Richter, Sebastien; Hanotin, Caroline; Gaudel, Naima; Louvet, Nicolas; Marchal, Philippe; Jenny, Mathieu

    2017-06-01

    In this work we investigate in details the flow behaviour of dense vibrated gravitational suspensions. We study the rheology in the stationary state by using a stress imposed rheometer (spectroscopy mechanics) coupled with a vibration cell, we show that applying well-controlled mechanical vibrations allows the control of the suspension viscosity by suppressing the apparent yield stress which is largely the cause of flow jamming. We show that the rheology in the stationary state is controlled by the competition between the reorganization time induced by the flow and the internal reorganization time induced by vibrations. We discuss the influence of particles size, suspending fluid viscosity and vibration parameters and demonstrate that the grains dynamics is controlled by the ratio between the lubrication stress and the granular pressure. This work evidences the major role played by the vibration induced lubrication stress on the liquefaction of vibrated granular suspensions.

  12. Microgravity Foam Structure and Rheology

    NASA Technical Reports Server (NTRS)

    Durian, Douglas J.

    1996-01-01

    The objective of this research was 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 was 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.

  13. Rheological properties of selected dairy products.

    PubMed

    Vélez-Ruiz, J F; Barbosa Cánovas, G V

    1997-06-01

    This article reviews rheological properties of milk, concentrated milk, cream, butter, ice cream, and yogurt, as well as the structure and some physicochemical properties of milk components. A brief description of basic rheological concepts related to liquids, solids, and viscoelasticity is presented, including those rheological models commonly used to characterize dairy products. Rheological behaviors exhibited by these dairy products, including Newtonian in milk and concentrated milk, nonNewtonian in concentrated milk, cream, and yogurt, thixotropy revealed by concentrated milk, cream, and yogurt, and the viscoelastic characteristics displayed by butter, ice cream, and yogurt, are analyzed, and relevant process variables affecting the rheological behavior of dairy products are discussed. Also, to facilitate the comparison of test methods and identify the typical instrumentation and models utilized in rheological characterization of dairy products, experimental conditions and equations used for modeling are included in a tabulated form.

  14. Improvement of rheological, thermal and functional properties of tapioca starch using gum arabic

    USDA-ARS?s Scientific Manuscript database

    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...

  15. Ice Rheology Beyond Planet Earth

    NASA Astrophysics Data System (ADS)

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

    2001-12-01

    Barclay Kamb is well known for his seminal work on the motions and internal flow of glaciers, but he was also a pioneer in research on the crystal structures, chemical bonding, and rheologies of the high-pressure phases of ice. In the flow and fracture of terrestrial materials, no rock is more studied than ice. Water ice also has an important presence on other solar system bodies, in particular the moons of the outer solar system, where its flow may extend to deep interiors. Most of these low-density (< 2 Mg/m3) moons have volume fractions of ice well above 0.5, and the largest moons, for example Ganymede, Callisto, and Titan, have sufficient internal pressures to stabilize the high-pressure phases II, III, V, VI, VII, and, possibly in early satellite history, ice VIII. The rheology of ice I has important influence on the surface morphologies of the moons, and the rheologies of all these phases (including ice I) can affect the thermal evolution of the moons by governing the rates of advection of internal radiogenic heat. Polycrystalline ice I under terrestrial conditions is far warmer than ice I in most planetary settings. The phenomenon of "premelting" in ice at T > 255 K leads to high grain-boundary mobility and much higher activation energy in warm ice than in cold ice under the same stress, so the flow of terrestrial ice may not be a good analog for that in the outer solar system. Phenomena from the rheological law itself to the development of lattice preferred orientation may be affected. Of the high-pressure phases through ice VI (all whose rheologies have been explored to date), ices III and VI are the weakest, an effect that, as Kamb has pointed out, parallels and draws explanation from the high rate of dielectric relaxation in those phases. Ice III is exceptionally weak and is stable over a very small part of the (P, T) phase diagram that is situated very close to possible planetary temperature profiles. This could lead to either self-regulation or

  16. 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.

  17. Nonequilibrium thermodynamics of the soft glassy rheology model

    NASA Astrophysics Data System (ADS)

    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.

  18. Rheological behaviour of lahar flow

    NASA Astrophysics Data System (ADS)

    Lafarge, N.; Chambon, G.; Thouret, J. C.; Laigle, D.

    2012-04-01

    Lahars are mixtures of water and debris flowing down the flanks of volcanoes. These flows generally occur after heavy rainfalls and carry sediments deposited by volcanic eruptions. They are among the most destructive volcanic phenomena, and were responsible, in the 20th century, for 40% of the fatalities associated with volcanic eruptions worldwide. However, the mechanical behaviour and the propagation of these particular debris flows still remain poorly understood. In the frame of the research project Laharisk, Mount Semeru in Java (Indonesia) was chosen as a test site to monitor lahar activity and flows properties owing to the frequent occurrence of lahars on its flanks during the monsoon rainy period. Two observation stations, situated 510 m apart, were installed in the Curah Lengkong Valley on the southeast flank of Semeru volcano. The relatively straight and box-shaped channel between the two stations represents a natural flume well suited to study the hydraulics of the flows. Both stations are equipped with video cameras, pore-pressure and load sensors, AFM geophones, and one broad-band seismometer to measure the evolution over time of lahar flow height, speed, and discharge. Bucket samples are also directly taken in the flows at regular time-intervals in order to provide sediment concentration and grain-size distribution. The rheological behaviour of the material is studied through laboratory vane tests at constant imposed shear rate conducted on the fine-sized fraction (< 400 µm) of the samples. The flows generally comprise several distinct pulses or 'packets' that can be traced between the two instrumented stations. Each pulse lasts between 5 and 30 minutes. Typical flow heights, peak velocities, and maximum discharges range between 0.5-2 m, 3-6 m.s-1, and 25-250 m3.s-1, respectively. The rheometrical tests indicate a mechanical behaviour of the frictional type, the shear stress being almost independent of the shear rate. In addition, the friction

  19. Rheological Properties of Aqueous Peanut Flour Dispersions

    USDA-ARS?s Scientific Manuscript database

    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 changes, as dispersions of higher fat fl...

  20. Using Greener Gels to Explore Rheology

    ERIC Educational Resources Information Center

    Garrett, Brendan; Matharu, Avtar S.; Hurst, Glenn A.

    2017-01-01

    A laboratory experiment was developed to investigate the rheological properties of a green calcium-cross-linked alginate gel as an alternative to the traditional borax-cross-linked poly(vinyl alcohol) gel. As borax is suspected of damaging fertility and the unborn child, a safe, green alternative is necessary. The rheological properties of a…

  1. 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.

  2. Rheological evolution of subducting slabs

    NASA Astrophysics Data System (ADS)

    Hirth, G.

    2016-12-01

    The mechanical behavior of subducting lithosphere depends on both the rheological evolution of the slab and how the slab is modified prior to subduction. Geophysical data demonstrate that the combination of thermal evolution and deformation lead to alteration of the slab at both mid-ocean ridges and the outer rise of subduction zones. In addition, the locations of earthquakes in these locations are generally consistent with both extrapolation of laboratory data that constrain the depth to the brittle-plastic transition, and deformation mechanisms inferred from microstructural analysis of mantle rocks recovered from the oceanic lithosphere. However, the frictional properties of both mantle aggregates and their alteration products suggest that linking the location of lithospheric earthquakes to regions that become hydrothermally altered is not straightforward. Furthermore, the inferred link between the location of intermediate-depth seismicity and the conditions of dehydration reactions is challenged by laboratory studies on dehydration embrittlement. In this presentation, I will introduce these apparent discrepancies; provide some possible resolutions for them based on scaling of laboratory data and discuss the implications for how an integrated understanding of slab rheology informs our understanding of the mechanical and geochemical evolution of the slab.

  3. 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.

  4. Rheology of welding: experimental constraints

    NASA Astrophysics Data System (ADS)

    Quane, S. L.; Russell, J. K.; Kennedy, L. A.

    2003-04-01

    The rheological behavior of pyroclastic deposits during welding is incompletely understood and is based on a surprisingly small number of experimental studies. Previous pioneering experimental studies were done on small (1 cm thick) samples of ash/crystal mixtures under constant load. They established minimum welding temperatures between 600 and 700^oC under loads of 0.7 MPa (˜40 m of ignimbrite) to 3.6 MPa (˜250 m depth of ignimbrite). However, these data are neither sufficiently comprehensive nor coherent enough to fully describe the rheology of pyroclastic mixtures. In addition, previous studies did not examine the microstructural and geometric changes associated with welding compaction. Our goal is to provide accurate and comprehensive constitutive relationships between material properties, temperature, load and strain rate for pyroclastic material undergoing welding. Here we present results from a newly designed experimental apparatus. The experimental apparatus consists of a LoadTrac II fully automated uniaxial compression load frame manufactured by Geocomp Corporation. The load frame has a built in displacement transducer and can run both constant strain rate (10-6 to 0.25 cm/s) and constant load (up to 1150 kg) tests to a maximum displacement of 7.5 cm. The sample assembly comprises 5 cm diameter cylindrical upper and lower pistons (insulating ceramic with steel conductive ends) housed in a copper jacket. Samples are 5 cm diameter cores and can vary in length from 1 to 15 cm depending on experimental needs. A fiber insulated tube furnace capable of reaching temperatures ≈1000^oC surrounds the sample assembly. Temperature is measured using a thermocouple located inside the sample through the bottom piston; the furnace controller is capable of maintaining temperature fluctuations to <5^oC. Deformation experiments are performed on pre-fabricated cylinders of soda-lime glass beads and rhyolitic volcanic ash, as well as, cores of pumiceous rhyodacite

  5. Study on Rheological Behavior of Konjac Glucomannan

    NASA Astrophysics Data System (ADS)

    Wang, Chao; Xu, Mei; Lv, Wen-ping; Qiu, Pei; Gong, Yuan-yuan; Li, Dong-sheng

    Konjac glucomannan (KGM) gum belongs to pseudoplastic fluid. Remarkable non-linear change tendencies of shear rheological behavior of KGM were detected through analysis of the correlation of viscosity (η)-shear rates and shear stress- shear rates respectively. The result shows that the sample concentration, sheer rate and temperature has great influence to its rheological property, and its shear rheological curves conformed to the Power Law (τ=KDn). When the concentration belows 0.55%, the hydrosol behaves approximate Newtonian fluid, and at higher concentration, it behaves pseudoplastically. When temperature changes from 0 to 85°, the viscosity declines remarkably.

  6. 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.

  7. Theory of rheology in confinement.

    PubMed

    Aerov, Artem A; Krüger, Matthias

    2015-10-01

    The viscosity of fluids is generally understood in terms of kinetic mechanisms, i.e., particle collisions, or thermodynamic ones as imposed through structural distortions upon, e.g., applying shear. Often the latter are more relevant, which allows a simpler theoretical description, and, e.g., (damped) Brownian particles can be considered good fluid model systems. We formulate a general theoretical approach for rheology in confinement, based on microscopic equations of motion and classical density functional theory. Specifically, we discuss the viscosity for the case of two parallel walls in relative motion as a function of the wall-to-wall distance, analyzing its relation to the slip length found for a single wall. The previously observed [A. A. Aerov and M. Krüger, J. Chem. Phys. 140, 094701 (2014).] deficiency of inhomogeneous (unphysical) stresses under naive application of shear in confinement is healed when hydrodynamic interactions are included.

  8. Theory of rheology in confinement

    NASA Astrophysics Data System (ADS)

    Aerov, Artem A.; Krüger, Matthias

    2015-10-01

    The viscosity of fluids is generally understood in terms of kinetic mechanisms, i.e., particle collisions, or thermodynamic ones as imposed through structural distortions upon, e.g., applying shear. Often the latter are more relevant, which allows a simpler theoretical description, and, e.g., (damped) Brownian particles can be considered good fluid model systems. We formulate a general theoretical approach for rheology in confinement, based on microscopic equations of motion and classical density functional theory. Specifically, we discuss the viscosity for the case of two parallel walls in relative motion as a function of the wall-to-wall distance, analyzing its relation to the slip length found for a single wall. The previously observed [A. A. Aerov and M. Krüger, J. Chem. Phys. 140, 094701 (2014)., 10.1063/1.4866450] deficiency of inhomogeneous (unphysical) stresses under naive application of shear in confinement is healed when hydrodynamic interactions are included.

  9. 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.

  10. 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.

  11. Microfluidic rheology of non-Newtonian liquids.

    PubMed

    Girardo, Salvatore; Cingolani, Roberto; Pisignano, Dario

    2007-08-01

    We investigate the rheological properties of a non-Newtonian glass-former liquid within lithographically defined microchannels in the range of temperatures above the vitrification region. The non-Newtonian behavior of the fluid, as evidenced by rotational rheology, is well described by a power law dependence of the viscosity on the shear rate. Taking into account such non-Newtonian character in the equations for the microfluidic motion, we relate the penetration dynamics into capillaries with the liquid rheological properties. The temperature dependence of the viscosity, determined over 1 order of magnitude in the temperature range 286-333 K and for shear rates between 0.07 and 1 s-1, can be described by a Vogel-Fulcher-Tamman law, consistent with the fragile nature of the investigated compound. Microfluidics is a promising analytical approach for the investigation of the rheology of non-Newtonian fluids within confined microenvironments.

  12. Investigation of interfacial rheology & foam stability.

    SciTech Connect

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

    2010-05-01

    The rheology at gas-liquid interfaces strongly influences the stability and dynamics of foams and emulsions. Several experimental techniques are employed to characterize the rheology at liquid-gas interfaces with an emphasis on the non-Newtonian behavior of surfactant-laden interfaces. The focus is to relate the interfacial rheology to the foamability and foam stability of various aqueous systems. An interfacial stress rheometer (ISR) is used to measure the steady and dynamic rheology by applying an external magnetic field to actuate a magnetic needle suspended at the interface. Results are compared with those from a double wall ring attachment to a rotational rheometer (TA Instruments AR-G2). Micro-interfacial rheology (MIR) is also performed using optical tweezers to manipulate suspended microparticle probes at the interface to investigate the steady and dynamic rheology. Additionally, a surface dilatational rheometer (SDR) is used to periodically oscillate the volume of a pendant drop or buoyant bubble. Applying the Young-Laplace equation to the drop shape, a time-dependent surface tension can be calculated and used to determine the effective dilatational viscosity of an interface. Using the ISR, double wall ring, SDR, and MIR, a wide range of sensitivity in surface forces (fN to nN) can be explored as each experimental method has different sensitivities. Measurements will be compared to foam stability.

  13. 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.

  14. 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

  15. Rheology of Granitic Magmas During Ascent and Emplacement

    NASA Astrophysics Data System (ADS)

    Petford, Nick

    Considerable progress has been made over the past decade in understanding the static rheological properties of granitic magmas in the continental crust. Changes in H2O content, CO2 content, and oxidation state of the interstitial melt phase have been identified as important compositional factors governing the rheodynamic behavior of the solid/fluid mixture. Although the strengths of granitic magmas over the crystallization interval are still poorly constrained, theoretical investigations suggest that during magma ascent, yield strengths of the order of 9 kPa are required to completely retard the upward flow in meter-wide conduits. In low Bagnold number magma suspensions with moderate crystal contents (solidosities 0.1 0.3), viscous fluctuations may lead to flow differentiation by shear-enhanced diffusion. AMS and microstructural studies support the idea that granite plutons are intruded as crystal-poor liquids ( 50%), with fabric and foliation development restricted to the final stages of emplacement. If so, then these fabrics contain no information on the ascent (vertical transport) history of the magma. Deformation of a magmatic mush during pluton emplacement can enhance significantly the pressure gradient in the melt, resulting in a range of local macroscopic flow structures, including layering, crystal alignment, and other mechanical instabilities such as shear zones. As the suspension viscosity varies with stress rate, it is not clear how the timing of proposed rheological transitions formulated from simple equations for static magma suspensions applies to mixtures undergoing shear. New theories of magmas as multiphase flows are required if the full complexity of granitic magma rheology is to be resolved.

  16. Rheological properties of elastomeric impression materials before and during setting.

    PubMed

    McCabe, J F; Arikawa, H

    1998-11-01

    In this study, we examined the rheological properties of elastomeric impression materials, both before and during setting, to assess the clinical significance of certain key characteristics such as viscosity, pseudoplasticity, and the rate of development of elasticity. The hypothesis to be tested was that monitoring the change in tan delta is the most appropriate means of monitoring the setting characteristics of elastomers. The loss tangent (tan delta) and the dynamic viscosity (eta') for five impression materials (both unmixed pastes and mixed/setting materials) were measured by means of a controlled-stress rheometer in a cone/plate configuration. For unmixed pastes, tests were performed at various frequencies (0.1 to 10 Hz) and torques (from 1 to 50 x 10(-4) Nm), while testing on setting materials was performed at constant frequency (1 Hz) and torque (3 x 10(-3) Nm). Most base and catalyst pastes were pseudoplastic before being mixed. Immediately after being mixed, the polyether (tan delta = 9.85) and polysulfide (tan delta = 9.54) elastomers showed tan delta markedly higher than those of other mixed materials (tan delta = 4.96 to 3.01). The polyvinylsiloxane elastomers showed lower initial tan delta, which rapidly reduced even further with time. This suggests that these materials should be used as soon as possible after being mixed. The polyether elastomer had a comparatively long induction period during which the tan delta remained at a high value. These characteristics are thought to be key factors in controlling clinical efficacy and therefore support the hypothesis that monitoring tan delta is an appropriate method for evaluating the setting characteristics of elastomers. One limitation was that the controlled-stress rheometer was unable to monitor rheological properties through to completion of setting.

  17. Rheology of welding: Field constraints

    NASA Astrophysics Data System (ADS)

    Russell, K.; Quane, S.

    2003-04-01

    Pyroclastic deposits emplaced at high temperature and having sufficient thickness become welded via sintering, compaction and flattening of hot glassy particles. The welding process is attended by pronounced changes in the physical properties of the deposit and welding intensity can be tracked by measuring the density, porosity, fabric or strength of samples. Ultimately, the intensity of welding reflects the aggregate effects of load and residence time at temperatures above the glass transition temperature (Tg). This results in welding intensity varying with stratigraphic depth; vertical sections through welded ignimbrite deposits commonly show maximum (e.g., density) or minimum (porosity) values in physical properties in the lower half (30--40% above the base) of the unit. Here we explore the extent to which these data, serving as proxies for strain, can be used constrain the rheological properties of the pyroclastic deposit during the welding process. Our data include measurements of density, porosity, fabric and rock strength as a function of stratigraphic position for 4 sections through the Bandelier tuff, New Mexico. These profiles record changes in physical properties and, thus, map the cumulative strain associated with welding as a function of depth (load). We have used simple conductive heat transfer models to estimate cooling curves for each sample. Essentially, these curves provide the residence time within the "welding window" for each sample. The curves are dependent on sample position, thickness of ignimbrite, emplacement temperature and the glass transition temperature of the material. The unknowns in the problem are a number of physical constants in a generalized power-law relationship between strain-rate (ɛ') and stress (σ) for steady-state creep at constant load: ɛ' = A σ^n e[-Q/R T]. Specifically, we adopt an inverse-model approach whereby the observations on the natural material are used to constrain the pre-exponential constant (A), stress

  18. 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

  19. 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

  20. Rheological characterization of hydroxypropylcellulose gels.

    PubMed

    Ramachandran, S; Chen, S; Etzler, F

    1999-02-01

    The present paper describes the rheological properties of hydroxypropylcellulose (HPC) gels formulated in propylene glycol (PG), water, ethanol, and mixtures of these components. The effects of molecular weight, polymer concentration, and solvent composition on the apparent viscosity and flow characteristics have been studied by continuous shear rheometry. The HPC gels are shear thinning and do not exhibit significant yield or hysteresis in their rheograms. The apparent viscosity increases with increasing molecular weight and concentration of the polymer, as expected. Although not so pronounced at lower concentrations (< or = 1.5%), HPC gels tend to become increasingly non-Newtonian with increasing molecular weight at higher polymer concentrations (3%). A mathematical model has been proposed for the prediction of viscosities of HPC gels. There exists a high degree of dependence on molecular interactions between various solvent molecules in the prediction of mixture viscosities in ternary systems. The effects of solvent composition on the viscoelastic behavior of these gels have also been examined by dynamic mechanical analysis. The HPC gels are highly viscoelastic and exhibit greater degrees of elasticity with increased PG content in ternary solvent mixtures with water and ethanol. The study also suggests that dynamic mechanical analysis could prove to be a useful tool in the determination of zero-shear viscosities, viscosities that are representative of most realistic situations.

  1. 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.

  2. Nicotine alters mucin rheological properties

    PubMed Central

    Chen, Eric Y.; Sun, Albert; Chen, Chi-Shuo; Mintz, Alexander J.

    2014-01-01

    Tobacco smoke exposure, the major cause of chronic obstructive pulmonary disease (COPD), instigates a dysfunctional clearance of thick obstructive mucus. However, the mechanism underlying the formation of abnormally viscous mucus remains elusive. We investigated whether nicotine can directly alter the rheological properties of mucin by examining its physicochemical interactions with human airway mucin gels secreted from A549 lung epithelial cells. Swelling kinetics and multiple particle tracking were utilized to assess mucin gel viscosity change when exposed to nicotine. Herein we show that nicotine (≤50 nM) significantly hindered postexocytotic swelling and hydration of released mucins, leading to higher viscosity, possibly by electrostatic and hydrophobic interactions. Moreover, the close association of nicotine and mucins allows airway mucus to function as a reservoir for prolonged nicotine release, leading to correlated pathogenic effects. Our results provide a novel explanation for the maltransport of poorly hydrated mucus in smokers. More importantly, this study further indicates that even low-concentration nicotine can profoundly increase mucus viscosity and thus highlights the health risks of secondhand smoke exposure. PMID:24838753

  3. Coal slurry rheology and chemistry

    SciTech Connect

    Lynch, A.W.; Cook, D.W.

    1987-09-01

    Three well-characterized, generic surfactants (nonionic, anionic and cationic) were used to modify coal/water mixtures by changing the interaction between several coals of different rank and the slurry liquor. Each experiment involved one coal and one surfactant per experiment. The analytical and rheological results from these experiments have been previously reported. The thrust of the current program is to extend the work to shear rates expected during atomization. The program consists of the following elements: (1) design, fabricate and test a helical screw rheometer capable of developing shear rates to 10,000 sec/sup -1/; (2) establish a capability to atomize slurries and monitor the spray using high speed photography; and (3) initiate a collaborative program with the Combustion Research Facility at Sandia National Laboratories Livermore for the purpose of analyzing particulates in atomized and burned sprays. The helical screw rheometer was designed using technology developed for polymer processing. The rheometer acts as an extrusion pump when there is discharge of fluid, but when flow is interrupted a differential pressure develops across the length of the screw. Using the mathematical analysis developed for screw pumps, the rotation rate of the screw may be translated to shear rate and the differential pressure translated to shear stress. 9 refs., 11 figs.

  4. 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.

  5. Binary mixtures of two anionic polysaccharides simulating the rheological properties of oxidised starch

    NASA Astrophysics Data System (ADS)

    Sikora, Marek; Dobosz, Anna; Adamczyk, Greta; Krystyjan, Magdalena; Kowalski, Stanisław; Tomasik, Piotra; Kutyła-Kupidura, Edyta M.

    2017-01-01

    Modifications of starches are carried out to improve their industrial usefulness. However, the consumers prefer natural products. For this reason, various methods of starch properties modification are applied to replace those requiring the use of chemical reagents. The aim of this study was to determine whether it is possible to use binary pastes, containing normal potato starch and xanthan gum, as substitutes of chemically modified starches (with oxidised starch E 1404 pastes as an example). Flow curves with hysteresis loops, apparent viscosity at constant shear rate of 50 s-1 and in-shear structural recovery test with pre-shearing were applied to study the rheological properties of the pastes. It was found that two anionic hydrocolloids, potato starch and xanthan gum, can form binary systems with thickening properties, provided that their proportions are adequately adjusted. Some of the binary pastes under investigation exhibited rheological properties resembling pastes of starch oxidised with hypochlorite (E 1404). The way of tailoring the binary pastes properties is presented.

  6. Intrusion rheology in grains and other flowable materials

    NASA Astrophysics Data System (ADS)

    Askari, Hesam; Kamrin, Ken

    2016-12-01

    The interaction of intruding objects with deformable materials arises in many contexts, including locomotion in fluids and loose media, impact and penetration problems, and geospace applications. Despite the complex constitutive behaviour of granular media, forces on arbitrarily shaped granular intruders are observed to obey surprisingly simple, yet empirical `resistive force hypotheses’. The physics of this macroscale reduction, and how it might play out in other media, has however remained elusive. Here, we show that all resistive force hypotheses in grains arise from local frictional yielding, revealing a novel invariance within a class of plasticity models. This mechanical foundation, supported by numerical and experimental validations, leads to a general analytical criterion to determine which rheologies can obey resistive force hypotheses. We use it to explain why viscous fluids are observed to perform worse than grains, and to predict a new family of resistive-force-obeying materials: cohesive media such as pastes, gels and muds.

  7. Intrusion rheology in grains and other flowable materials.

    PubMed

    Askari, Hesam; Kamrin, Ken

    2016-12-01

    The interaction of intruding objects with deformable materials arises in many contexts, including locomotion in fluids and loose media, impact and penetration problems, and geospace applications. Despite the complex constitutive behaviour of granular media, forces on arbitrarily shaped granular intruders are observed to obey surprisingly simple, yet empirical 'resistive force hypotheses'. The physics of this macroscale reduction, and how it might play out in other media, has however remained elusive. Here, we show that all resistive force hypotheses in grains arise from local frictional yielding, revealing a novel invariance within a class of plasticity models. This mechanical foundation, supported by numerical and experimental validations, leads to a general analytical criterion to determine which rheologies can obey resistive force hypotheses. We use it to explain why viscous fluids are observed to perform worse than grains, and to predict a new family of resistive-force-obeying materials: cohesive media such as pastes, gels and muds.

  8. Thixotropic properties of normal potato starch depending on the degree of the granules pasting.

    PubMed

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

    2015-05-05

    The aim of this paper was the study of the rheological instability (thixotropy and/or antithixotropy) of normal potato starch (NPS) pastes depending on their concentration (2-5%) and degree of pasting. Flow curves with hysteresis loops, apparent viscosity at constant shear rate and in-shear structural recovery tests were carried out. Granule size profiles, the pasting characteristic of corresponding starch suspensions and the transmittance of the pastes, the molecular weights and polydispersity of granular starch and its pastes prepared at 80, 95 and 121°C were also studied. The degree of pasting was dependent on the temperature and the concentration and influenced strongly the rheological behavior of the pastes. All pastes belonged to the non-Newtonian liquids thinned by shear and were rheologically unstable to the various extent. Thixotropic properties were connected to the size and the number of the starch granules in the pastes as well as depended on the measuring method used. In the 2 and 3% samples pasted at 80°C the swelling of the granules prevailed their destruction (thixotropy was observed). In the other samples the destruction predominated the swelling (antithixotropy observed).

  9. Dilational surface rheology of polymer solutions

    NASA Astrophysics Data System (ADS)

    Noskov, B. A.; Bykov, A. G.

    2015-06-01

    The review concerns main achievements in dilational rheology of polymer adsorption films at the gas/liquid interfaces reported in the last fifteen years. The theoretical foundations of methods of surface rheology and the key results obtained in studies of solutions of amphiphilic nonionic polymers, polyelectrolytes, proteins and their complexes with low-molecular-mass surfactants are discussed. Interest in the surface dilational rheology is mainly caused by a small number of available experimental methods for investigation of the surface of liquids, by the fact that traditional methods of measurement of the surface tension that are widely used in studies of solutions of low-molecular-mass surfactants provide little information when applied to polymer solutions owing to very slow establishment of equilibrium as well as by weak dependence of the surface tension on the polymer concentration. Progress in the surface rheology is driven by the recent studies of the stability of foams and emulsions that demonstrated a key role of the dilational surface rheological properties in the dynamics of liquid-phase disperse systems. The bibliography includes 191 references.

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

    SciTech Connect

    Green, Tim 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)2•8H2O 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.

  11. Laboratory Study of Till Rheology

    NASA Astrophysics Data System (ADS)

    Rathbun, A. P.; Marone, C. J.; Anandakrishnan, S.; Alley, R. B.

    2005-12-01

    Recent studies show that small-amplitude stress changes can trigger ice sheet motion and subglacial seismicity. Deformation in the subglacial region plays a key role in determining slip behavior, including creep, transient slip, stick-slip motion, and seismicity. However, progress in understanding these phenomena is limited by uncertainty in the rheology and frictional properties of glacial till. We report on detailed laboratory experiments to measure the creep and frictional constitutive properties of till sampled from the Matanuska Glacier, Alaska and Caesar Till from the Scioto Lobe of the Laurentide Ice Sheet, sampled in central Ohio. Experiments were conducted in a servo-controlled, double direct shear apparatus with air dried samples at a normal stresses ranging from 50 kPa to 5 MPa. Till was sheared in a three-block arrangement in which two layers are sandwiched between a central forcing block and two stationary blocks. We studied the effect of saturation, initial deformation fabric, stress history, and the boundary conditions of loading. The nominal frictional contact area is 100 cm2 and remains constant during shear. The layer thickness is 1 cm prior to shear. All blocks are grooved perpendicular to the shear direction to ensure that deformation occurs within the layer. The Matanuska till has grains ranging from 6.3 mm to finer than .063 mm with a mean of 2.67 mm whereas the Caesar till has a smaller mean grain size of 0.60 mm, but lacks silt and clay sized particles. We conducted both constant strain rate and constant stress tests. Constant shear stress experiments were employed to study frictional creep. In these tests, stress steps were conducted at 2 % and 5 % steps of the shear strength with strain rate calculated at 20 and 40 minute intervals after the stress steps. Strain rate was calculated by taking a linear fit of strain versus time over two minutes. The stress exponent, n was then calculated from the equation dɛ/dt = bτn. Where ɛ is strain,

  12. 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.

  13. Extensional rheology of active suspensions.

    PubMed

    Saintillan, David

    2010-05-01

    A simple model is presented for the effective extensional rheology of a dilute suspension of active particles, such as self-propelled microswimmers, extending previous classical studies on suspensions of passive rodlike particles. Neglecting particle-particle hydrodynamic interactions, we characterize the configuration of the suspension by an orientation distribution, which satisfies a Fokker-Planck equation including the effects of an external flow field and of rotary diffusion. Knowledge of this orientation distribution then allows the determination of the particle extra stress as a configurational average of the force dipoles exerted by the particles on the fluid, which involve contributions from the imposed flow, rotary diffusion, and the permanent dipoles resulting from activity. Analytical expressions are obtained for the stress tensor in uniaxial extensional and compressional flows, as well as in planar extensional flow. In all types of flows, the effective viscosity is found to increase as a result of activity in suspensions of head-actuated swimmers (pullers) and to decrease in suspensions of tail-actuated swimmers (pushers). In the latter case, a negative particle viscosity is found to occur in weak flows. In planar extensional flow, we also characterize normal stresses, which are enhanced by activity in suspensions of pullers but reduced in suspensions of pushers. Finally, an energetic interpretation of the seemingly unphysical decrease in viscosity predicted in suspensions of pushers is proposed, where the decrease is explained as a consequence of the active power input generated by the swimming particles and is shown not to be directly related to viscous dissipative processes.

  14. Extensional rheology of active suspensions

    NASA Astrophysics Data System (ADS)

    Saintillan, David

    2010-05-01

    A simple model is presented for the effective extensional rheology of a dilute suspension of active particles, such as self-propelled microswimmers, extending previous classical studies on suspensions of passive rodlike particles. Neglecting particle-particle hydrodynamic interactions, we characterize the configuration of the suspension by an orientation distribution, which satisfies a Fokker-Planck equation including the effects of an external flow field and of rotary diffusion. Knowledge of this orientation distribution then allows the determination of the particle extra stress as a configurational average of the force dipoles exerted by the particles on the fluid, which involve contributions from the imposed flow, rotary diffusion, and the permanent dipoles resulting from activity. Analytical expressions are obtained for the stress tensor in uniaxial extensional and compressional flows, as well as in planar extensional flow. In all types of flows, the effective viscosity is found to increase as a result of activity in suspensions of head-actuated swimmers (pullers) and to decrease in suspensions of tail-actuated swimmers (pushers). In the latter case, a negative particle viscosity is found to occur in weak flows. In planar extensional flow, we also characterize normal stresses, which are enhanced by activity in suspensions of pullers but reduced in suspensions of pushers. Finally, an energetic interpretation of the seemingly unphysical decrease in viscosity predicted in suspensions of pushers is proposed, where the decrease is explained as a consequence of the active power input generated by the swimming particles and is shown not to be directly related to viscous dissipative processes.

  15. 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

  16. 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.

  17. Interfacial Shear Rheology of Coffee Samples

    NASA Astrophysics Data System (ADS)

    Läuger, Jörg; Heyer, Patrick

    2008-07-01

    Both oscillatory and rotational measurements on the film formation process and on interfacial rheological properties of the final film of coffee samples with different concentrations are presented. As higher the concentration as faster the film formation process is, whereas the concentration does not have a large effect on the visco-elastic properties of the final films. Two geometries, a biconical geometry and a Du Noüy ring have been employed. The presented results show that interfacial shear rheology allows detailed investigations on coffee films. Although with a Du Noüy ring it is possible to measure the qualitative behavior and relative differences only the biconical geometry is sensitive enough to test weak films and to reveal real absolute values for the interfacial shear rheological quantities.

  18. Understanding rheological hysteresis in soft glassy materials.

    PubMed

    Radhakrishnan, Rangarajan; Divoux, Thibaut; Manneville, Sébastien; Fielding, Suzanne M

    2017-03-01

    Motivated by recent experimental studies of rheological hysteresis in soft glassy materials, we study numerically strain rate sweeps in simple yield stress fluids and viscosity bifurcating yield stress fluids. Our simulations of downward followed by upward strain rate sweeps, performed within fluidity models and the soft glassy rheology model, successfully capture the experimentally observed monotonic decrease of the area of the rheological hysteresis loop with sweep time in simple yield stress fluids, and the bell shaped dependence of hysteresis loop area on sweep time in viscosity bifurcating fluids. We provide arguments explaining these two different functional forms in terms of differing tendencies of simple and viscosity bifurcating fluids to form shear bands during the sweeps, and show that the banding behaviour captured by our simulations indeed agrees with that reported experimentally. We also discuss the difference in hysteresis behaviour between inelastic and viscoelastic fluids. Our simulations qualitatively agree with the experimental data discussed here for four different soft glassy materials.

  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. Effect of Admixtures on the Yield Stresses of Cement Pastes under High Hydrostatic Pressures

    PubMed Central

    Yim, Hong Jae; Kim, Jae Hong; Kwon, Seung Hee

    2016-01-01

    When cement-based materials are transported at a construction site, they undergo high pressures during the pumping process. The rheological properties of the materials under such high pressures are unknown, and estimating the workability of the materials after pumping is a complex problem. Among various influential factors on the rheology of concrete, this study investigated the effect of mineral and chemical admixtures on the high-pressure rheology. A rheometer was fabricated that could measure the rheological properties while maintaining a high pressure to simulate the pumping process. The effects of superplasticizer, silica fume, nanoclay, fly ash, or ground granulated blast furnace slag were investigated when mixed with two control cement pastes. The water-to-cement ratios were 0.35 and 0.50. PMID:28773273

  1. 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

  2. Advances in rheology. Volume 4: Applications

    SciTech Connect

    Mena, B.; Garcia-Rejon, A.; Rangel-Nafaile, C.

    1984-01-01

    This book contains over 50 selections. Some of the titles are: Rheology and mass transfer in a stationary or pulsatile two phase flow of suspended particles investigated by electrochemical techniques; The helical screw rheometer; Characterization of polymer solutions in flow through porous media; A discrete model for the recovery of oil from a reservoir; and Nonlinear creep characteristics of Devonian oil shale.

  3. From Reactor to Rheology in LDPE Modeling

    SciTech Connect

    Read, Daniel J.; Das, Chinmay; Auhl, Dietmar; McLeish, Tom C. B.; Kapnistos, Michael; Doelder, Jaap den; Vittorias, Iakovos

    2008-07-07

    In recent years the association between molecular structure and linear rheology has been established and well-understood through the tube concept and its extensions for well-characterized materials (e.g. McLeish, Adv. Phys. 2002). However, for industrial branched polymeric material at processing conditions this piece of information is missing. A large number of phenomenological models have been developed to describe the nonlinear response of polymers. But none of these models takes into account the underlying molecular structure, leading to a fitting procedure with arbitrary fitting parameters. The goal of applied molecular rheology is a predictive scheme that runs in its entirety from the molecular structure from the reactor to the non-linear rheology of the resin. In our approach, we use a model for the industrial reactor to explicitly generate the molecular structure ensemble of LDPE's, (Tobita, J. Polym. Sci. B 2001), which are consistent with the analytical information. We calculate the linear rheology of the LDPE ensemble with the use of a tube model for branched polymers (Das et al., J. Rheol. 2006). We then, separate the contribution of the stress decay to a large number of pompom modes (McLeish et al., J. Rheol. 1998 and Inkson et al., J. Rheol. 1999) with the stretch time and the priority variables corresponding to the actual ensemble of molecules involved. This multimode pompom model allows us to predict the nonlinear properties without any fitting parameter. We present and analyze our results in comparison with experimental data on industrial materials.

  4. Morphology and rheology in filamentous cultivations.

    PubMed

    Wucherpfennig, T; Kiep, K A; Driouch, H; Wittmann, C; Krull, R

    2010-01-01

    Because of their metabolic diversity, high production capacity, secretion efficiency, and capability of carrying out posttranslational modifications, filamentous fungi are widely exploited as efficient cell factories in the production of metabolites, bioactive substances, and native or heterologous proteins, respectively. There is, however, a complex relationship between the morphology of these microorganisms, transport phenomena, the viscosity of the cultivation broth, and related productivity. The morphological characteristics vary between freely dispersed mycelia and distinct pellets of aggregated biomass, every growth form having a distinct influence on broth rheology. Hence, the advantages and disadvantages for mycelial or pellet cultivation have to be balanced out carefully. Because of the still inadequate understanding of the morphogenesis of filamentous microorganisms, fungal morphology is often a bottleneck of productivity in industrial production. To obtain an optimized production process, it is of great importance to gain a better understanding of the molecular and cell biology of these microorganisms as well as the relevant approaches in biochemical engineering. In this chapter, morphology and growth of filamentous fungi are described, with special attention given to specific problems as they arise from fungal growth forms; growth and mass transfer in fungal biopellets are discussed as an example. To emphasize the importance of the flow behavior of filamentous cultivation broths, an introduction to rheology is also given, reviewing important rheological models and recent studies concerning rheological parameters. Furthermore, current knowledge on morphology and productivity in relation to the environom is outlined in the last section of this review. Copyright 2010 Elsevier Inc. All rights reserved.

  5. 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.

  6. 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.

  7. 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...

  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. Transport analogy for segregation and granular rheology

    NASA Astrophysics Data System (ADS)

    Liu, Siying; McCarthy, Joseph J.

    2017-08-01

    Here, we show a direct connection between density-based segregation and granular rheology that can lead to insight into both problems. Our results exhibit a transition in the rate of segregation during simple shear that occurs at I ˜0.5 and mimics a coincident regime change in flow rheology. We propose scaling arguments that support a packing fraction criterion for this transition that can both explain our segregation results as well as unify existing literature studies of granular rheology. By recasting a segregation model in terms of rheological parameters, we establish an approach that not only collapses results for a wide range of conditions, but also yields a direct relationship between the coordination number z and the segregation velocity. Moreover, our approach predicts the precise location of the observed regime change or saturation. This suggests that it is possible to rationally design process operating conditions that lead to significantly lower segregation extents. These observations can have a profound impact on both the study of granular flow or mixing as well as industrial practice.

  10. 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.

  11. Deformation and rheology of the Asian continent

    NASA Astrophysics Data System (ADS)

    Liu, Yongjiang; Liu, Junlai; Neubauer, Franz

    2017-05-01

    The plate tectonic theory has been developed and accepted by most geologists since the last century when Joseph Barrell (1914) first introduced the concept of a strong lithosphere that overlies a weak fluid asthenosphere. The plate tectonic theory led to a revolution in geosciences in the 1960s of the 20th century, and explains well the tectonic evolution of the global lithosphere, especially the rigid oceanic lithosphere. But there are many problems when we apply the plate tectonic theory to the study of continents due to the large strength contrasts between oceanic and continental lithospheres. Compared with the oceanic lithosphere, the continental lithosphere has heterogeneous compositions, more complicated structures, long history, distinct rheological properties and lower deformation strength (Burov, 2011; Chen et al., 2012; Kirby, 1983). The continent has horizontally both marginal and inner-plate deformations and different rheological layers with the depth (Brace and Kohlstedt, 1980; Burgmann and Dresen, 2008; Kirby, 1983), which control the behavior of the continental lithosphere (Jackson, 2002). These properties, especially the rheological behavior, block the plate tectonic theory applying to the not-rigid continent. In the last decade, the continental rheology has become one of the cutting-edge research directions for the continental geodynamics (Burov and Watts, 2006).

  12. The rheological properties of different GNPs.

    PubMed

    Abdelhalim, Mohamed Anwar K

    2012-01-24

    Rheological analysis can be employed as a sensitive tool in predicting the physical properties of gold nanoparticles (GNPs). Understanding the rheological properties of GNPs can help to develop a better therapeutic cancer product, since these physical properties often link material formulation and processing stages with the ultimate end use. The rheological properties of GNPs have not been previously documented. The present study attempted to characterize the rheological properties of different sizes of GNPs at: 1) fixed temperature and wide range of shear rates; 2) varied temperature and fixed shear rate. 10, 20 and 50 nm GNPs was used in this study. Several rheological parameters of GNPs such as viscosity, torque%, shear stress and shear rate were evaluated using Brookfield LVDV-III Programmable rheometer supplied with temperature bath and controlled by a computer. To measure fluid properties (viscosity as function of shear rate), e.g., to determine whether the flow is Newtonian or non-Newtonian flow behaviour, and viscoelasticity (viscosity as function of temperature), rheological parameters were firstly measured at starting temperature of 37°C and wide range of shear rates from 375 to 1875 s(-1), and secondly at a gradual increase of temperature from 37 to 42°C and fixed shear rate of 1875 s(-1). The 10, 20 and 50 nm GNPs showed mean size of 9.45 ± 1.33 nm, 20.18 ± 1.80 nm, and 50 nm GNPs, respectively. The 10 and 20 nm GNPs showed spherical morphology while 50 nm GNPs showed hexagonal morphology using the transmission electron microscope (TEM). The relation between viscosity (cp) and shear rate (s(-1)) for 10, 20 and 50 nm GNPs at a temperature of 37°C showed non-Newtonian behaviour. Although the relationship between SS (dyne/cm(2)) and SR (s(-1)) for 10, 20 and 50 nm GNPs was linearly related however their fluid properties showed non-Newtonian behaviour. The torque%, viscosity (cp) and SS (dyne/cm(2)) of all GNP sizes decreased with increasing the

  13. Atomic force microscopy for the examination of single cell rheology.

    PubMed

    Okajima, Takaharu

    2012-11-01

    Rheological properties of living cells play important roles in regulating their various biological functions. Therefore, measuring cell rheology is crucial for not only elucidating the relationship between the cell mechanics and functions, but also mechanical diagnosis of single cells. Atomic force microscopy (AFM) is becoming a useful technique for single cell diagnosis because it allows us to measure the rheological properties of adherent cells at any region on the surface without any modifications. In this review, we summarize AFM techniques for examining single cell rheology in frequency and time domains. Recent applications of AFM for investigating the statistical analysis of single cell rheology in comparison to other micro-rheological techniques are reviewed, and we discuss what specificity and universality of cell rheology are extracted using AFM.

  14. Shear rheology of molten crumb chocolate.

    PubMed

    Taylor, J E; Van Damme, I; Johns, M L; Routh, A F; Wilson, D I

    2009-03-01

    The shear rheology of fresh molten chocolate produced from crumb was studied over 5 decades of shear rate using controlled stress devices. The Carreau model was found to be a more accurate description than the traditional Casson model, especially at shear rates between 0.1 and 1 s(-1). At shear rates around 0.1 s(-1) (shear stress approximately 7 Pa) the material exhibited a transition to a solid regime, similar to the behavior reported by Coussot (2005) for other granular suspensions. The nature of the suspension was explored by investigating the effect of solids concentration (0.20 < phi < 0.75) and the nature of the particles. The rheology of the chocolate was then compared with the rheology of (1) a synthetic chocolate, which contained sunflower oil in place of cocoa butter, and (2) a suspension of sugar of a similar size distribution (volume mean 15 mum) in cocoa butter and emulsifier. The chocolate and synthetic chocolate showed very similar rheological profiles under both steady shear and oscillatory shear. The chocolate and the sugar suspension showed similar Krieger-Dougherty dependency on volume fraction, and a noticeable transition to a stiff state at solids volume fractions above approximately 0.5. Similar behavior has been reported by Citerne and others (2001) for a smooth peanut butter, which had a similar particle size distribution and solids loading to chocolate. The results indicate that the melt rheology of the chocolate is dominated by hydrodynamic interactions, although at high solids volume fractions the emulsifier may contribute to the departure of the apparent viscosity from the predicted trend.

  15. The relationship between particle morphology and rheological properties in injectable nano-hydroxyapatite bone graft substitutes.

    PubMed

    Ryabenkova, Y; Pinnock, A; Quadros, P A; Goodchild, R L; Möbus, G; Crawford, A; Hatton, P V; Miller, C A

    2017-06-01

    Biomaterials composed of hydroxyapatite (HA) are currently used for the treatment of bone defects resulting from trauma or surgery. However, hydroxyapatite supplied in the form of a paste is considered a very convenient medical device compared to the materials where HA powder and liquid need to be mixed immediately prior to the bone treatment during surgery. In this study we have tested a series of hydroxyapatite (HA) pastes with varying microstructure and different rheological behaviour to evaluate their injectability and biocompatibility. The particle morphology and chemical composition were evaluated using HRTEM, XRD and FTIR. Two paste-types were compared, with the HA particles of both types being rod shaped with a range of sizes between 20 and 80nm while differing in the particle aspect ratio and the degree of roundness or sharpness. The pastes were composed of pure HA phase with low crystallinity. The rheological properties were evaluated and it was determined that the pastes behaved as shear-thinning, non-Newtonian liquids. The difference in viscosity and yield stress between the two pastes was investigated. Surprisingly, mixing of these pastes at different ratios did not alter viscosity in a linear manner, providing an opportunity to produce a specific viscosity by mixing the two materials with different characteristics. Biocompatibility studies suggested that there was no difference in vitro cell response to either paste for primary osteoblasts, bone marrow mesenchymal stromal cells, osteoblast-like cells, and fibroblast-like cells. This class of nanostructured biomaterial has significant potential for use as an injectable bone graft substitute where the properties may be tailored for different clinical indications. Copyright © 2017 Elsevier B.V. All rights reserved.

  16. 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

  17. Analytical rheology of metallocene-catalyzed polyethylenes

    NASA Astrophysics Data System (ADS)

    Shanbhag, Sachin; Takeh, Arsia

    2011-03-01

    A computational algorithm that seeks to invert the linear viscoelastic spectrum of single-site metallocene-catalyzed polyethylenes is presented. The algorithm uses a general linear rheological model of branched polymers as its underlying engine, and is based on a Bayesian formulation that transforms the inverse problem into a sampling problem. Given experimental rheological data on unknown single-site metallocene- catalyzed polyethylenes, it is able to quantitatively describe the range of values of weight-averaged molecular molecular weight, MW , and average branching density, bm , consistent with the data. The algorithm uses a Markov-chain Monte Carlo method to simulate the sampling problem. If, and when information about the molecular weight is available through supplementary experiments, such as chromatography or light scattering, it can easily be incorporated into the algorithm, as demonstrated. Financial support from NSF DMR 0953002.

  18. Nonlinear and nonlocal rheology of jammed matter

    NASA Astrophysics Data System (ADS)

    Tighe, Brian

    Emulsions, foams, and grains all jam into a weakly elastic state when confined by pressure. By now the mechanics of jammed matter is well understood in the case of slow, weak, and homogeneous forcing - but in reality, it is rare for all three of these assumptions to hold. Here we demonstrate the complex rheology that results when jammed materials are forced at finite rate, finite amplitude, and finite wavelength. Using computer simulations, we subject dense soft sphere packings to a host of rheological tests, including stress relaxation, flow start-up, oscillatory shear, and standing wave forcing. These allow us to tease apart the influence of viscous, nonlinear, and nonlocal effects, and also to probe the link between particle dynamics and bulk response. We identify strain, time, and length scales that depend critically on the distance to the jamming transition, and which govern the onset of shear thinning, strain softening, and gradient elasticity.

  19. 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.

  20. On transient rheology and glacial isostasy

    NASA Technical Reports Server (NTRS)

    Yuen, David A.; Sabadini, Roberto C. A.; Gasperini, Paolo; Boschi, Enzo

    1986-01-01

    The effect of transient creep on the inference of long-term mantle viscosity is investigated using theoretical predictions from self-gravitating, layered earth models with Maxwell, Burgers' body, and standard linear solid rheologies. The interaction between transient and steady-state rheologies is studied. The responses of the standard linear solid and Burgers' body models to transient creep in the entire mantle, and of the Burgers' body and Maxwell models to creep in the lower mantle are described. The models' responses are examined in terms of the surface displacement, free air gravity anomaly, wander of the rotation pole, and the secular variation of the degree 2 zonal coefficient of the earth's gravitational potential field. The data reveal that transient creep cannot operate throughout the entire mantle.

  1. On transient rheology and glacial isostasy

    NASA Technical Reports Server (NTRS)

    Yuen, David A.; Sabadini, Roberto C. A.; Gasperini, Paolo; Boschi, Enzo

    1986-01-01

    The effect of transient creep on the inference of long-term mantle viscosity is investigated using theoretical predictions from self-gravitating, layered earth models with Maxwell, Burgers' body, and standard linear solid rheologies. The interaction between transient and steady-state rheologies is studied. The responses of the standard linear solid and Burgers' body models to transient creep in the entire mantle, and of the Burgers' body and Maxwell models to creep in the lower mantle are described. The models' responses are examined in terms of the surface displacement, free air gravity anomaly, wander of the rotation pole, and the secular variation of the degree 2 zonal coefficient of the earth's gravitational potential field. The data reveal that transient creep cannot operate throughout the entire mantle.

  2. Rheological Characterization of Oil Cement Suspensions

    NASA Astrophysics Data System (ADS)

    Abderrahmane, Mellak; Moh-Amokrane, Aitouche

    2015-04-01

    This study is a contribution to the study of the rheological behavior of cement suspensions. An oil well is drilled, cased, cemented and set completion. The well drilling is done in several phases then at various diameters to isolate the following problems like land fragile subsidence and poorly consolidated aquifer formations, loss of the movement in the porous and permeable formations. Therefore, it would go down a casing and cementing to work safely. The materials studied were chosen to satisfy the requirements and the problems encountered in real applications in the oil field (casing cementing wells). So it was used an oil hydraulic binder "G". This systematic study of rheological properties of cement Class "G" standardized API (American Petroleum Institute) deal with a formulation which is compatible with the surrounding environment taking account an optimal efficiency.

  3. 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.

  4. Rheological evaluation of pretreated cladding removal waste

    SciTech Connect

    McCarthy, D.; Chan, M.K.C.; Lokken, R.O.

    1986-01-01

    Cladding removal waste (CRW) contains concentrations of transuranic (TRU) elements in the 80 to 350 nCi/g range. This waste will require pretreatment before it can be disposed of as glass or grout at Hanford. The CRW will be pretreated with a rare earth strike and solids removal by centrifugation to segregate the TRU fraction from the non-TRU fraction of the waste. The centrifuge centrate will be neutralized with sodium hydroxide. This neutralized cladding removal waste (NCRW) is expected to be suitable for grouting. The TRU solids removed by centrifugation will be vitrified. The goal of the Rheological Evaluation of Pretreated Cladding Removal Waste Program was to evaluate those rheological and transport properties critical to assuring successful handling of the NCRW and TRU solids streams and to demonstrate transfers in a semi-prototypic pumping environment. This goal was achieved by a combination of laboratory and pilot-scale evaluations. The results obtained during these evaluations were correlated with classical rheological models and scaled-up to predict the performance that is likely to occur in the full-scale system. The Program used simulated NCRW and TRU solid slurries. Rockwell Hanford Operations (Rockwell) provided 150 gallons of simulated CRW and 5 gallons of simulated TRU solid slurry. The simulated CRW was neutralized by Pacific Northwest Laboratory (PNL). The physical and rheological properties of the NCRW and TRU solid slurries were evaluated in the laboratory. The properties displayed by NCRW allowed it to be classified as a pseudoplastic or yield-pseudoplastic non-Newtonian fluid. The TRU solids slurry contained very few solids. This slurry exhibited the properties associated with a pseudoplastic non-Newtonian fluid.

  5. Rheological behavior on treated Malaysian crude oil

    NASA Astrophysics Data System (ADS)

    Chandran, Krittika; Sinnathambi, Chandra Mohan

    2016-11-01

    Crude oil is always produced with water. This association causes many problems during oil production, arising from the formation of emulsion. Emulsion is an undesirable substance that increases operational and capital cost in the pipeline and processing equipment. To overcome this issue, demulsifiers are formulated to break the emulsion, where they are able to separate the water-oil emulsions to their respective phases. The emulsifier's main function is to reduce the interfacial tension properties of the emulsion. For this research, both the EOR and natural water-in-oil emulsions were treated with low a concentration demulsifier. The main objective of this paper is to determine the dynamic viscosity and rheological properties of the treated EOR and natural emulsion. The dynamic viscosity was obtained using the Brook-field Digital Viscometer. The components that influence the emulsion's rheological properties are the temperature, shear rate and shear stress. The results obtained demonstrate that the viscosity of the treated crude decreases and portrays the Non-Newtonian shear thinning "pseudo-plastic" behavior. Besides that, to determine the interfacial film of the treated crude, the spinning drop tensiometer was used. With the addition of demulsifier, the thinning rate of the oil film accelerates whereby there is a linear decrease in the interfacial tension with an increase in time. Therefore, from the results, it can be observed that the rheology study plays a significant role in the demulsification test. Furthermore, both the rheology approaches showed that time, temperature, shear rate and shear stress have a great impact on the viscosity behavior as well as the IFT.

  6. Viscous rheology of soft particles near jamming

    NASA Astrophysics Data System (ADS)

    Woldhuis, Erik; Tighe, Brian; van Hecke, Martin

    2013-03-01

    We investigate the effect of changing the exact nature of the viscous interaction in simulations of sheared soft, viscous, repulsive disks, which are considered to be a good model for foams and emulsions. We determine the way in which the power-law exponent of the rheological curve, in other words the shear-thinning or shear-thickening part, depends on the microscopic viscous interaction around the jamming density. We attempt to find a model that describes and predicts this dependence.

  7. Rheology, microrheology and structure of soft materials

    NASA Astrophysics Data System (ADS)

    Oppong, Felix K.

    We study the relationship between the bulk rheological properties and the micron-scale structure and rheology of different types of soft materials. The materials studied are Laponite, a colloidal clay suspension; Carbopol, a dispersion of microgel particles; hydroxyethyl cellulose, a linear polymer solution; and hydrophobically modified hydroxyethyl cellulose, an associative polymer. Bulk properties are measured using conventional shear rheometry. The micron-scale measurements are performed using techniques based on multiple particle tracking and dynamic light scattering. From the thermal motion of suspended tracer particles, we obtain information about the local structure and viscoelastic properties of the materials. We investigate the evolution of Laponite from a liquid to a gel and find that the process is length-scale dependent. We study the properties of Carbopol as a function of microgel concentration and find that as concentration increases, a jamming transition occurs which is related to the onset of yield stress on the bulk scale. We compare the viscoelastic properties of hydroxyethylcellulose and its associative derivative and observe that the hydrophobic interactions in the latter lead to much slower dynamics than in the unmodified polymer. A study of the stress relaxation in hydroxyethylcellulose showed that it depended on both the wait time after the application and removal of a large strain and on the type and magnitude of the deformation applied. Our work exploits the unique ability of microrheological techniques to probe both the rheology and structure of soft materials on the microscopic scale, which enables a better understanding of the relationship between bulk scale properties and microscopic structure in these systems. Keywords. Rheology, microrheology, soft materials, particle tracking, dynamic light scattering, viscoelasticity, yield stress, gelation, polymers.

  8. Physiochemical/Rheological Control of Nonmetallic Materials.

    DTIC Science & Technology

    1982-08-01

    Temperature Tge Temperature at Gel T Glass Transition Temperature rl Viscosity t gel Time to Gel G’ Storage Modulus G" Loss Modulus til Enthalpy...standards were obtained and the amounts of the volatiles were determined by gas chromotography . Where applicable, the thermal and rheological properties...aluminum powder and the fillers. The filtrate , which contained th two epoxies and DICY, cured without any foaming. Attempts to separate the exact blowing

  9. Rheological properties of Cubic colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Boromand, Arman; Maia, Joao

    2016-11-01

    Colloidal and non-colloidal suspensions are ubiquitous in many industrial application. There are numerous studies on these systems to understand and relate their complex rheological properties to their microstructural evolution under deformation. Although most of the experimental and simulation studies are centered on spherical particles, in most of the industrial applications the geometry of the colloidal particles deviate from the simple hard sphere and more complex geometries exist. Recent advances in microfabrication paved the way to fabricate colloidal particles with complex geometries for applications in different areas such as drug delivery where the fundamental understanding of their dynamics has remained unexplored. In this study, using dissipative particle dynamics, we investigate the rheological properties of cubic (superball) particles which are modeled as the cluster of core-modified DPD particles. Explicit representation of solvent particles in the DPD scheme will conserve the full hydrodynamic interactions between colloidal particles. Rheological properties of these cubic suspensions are investigated in the dilute and semi-dilute regimes. The Einstein and Huggins coefficients for these particles with different superball exponent will be calculate which represent the effect of single particle's geometry and multibody interactions on viscosity, respectively. The response of these suspensions is investigated under simple shear and oscillatory shear where it is shown that under oscillation these particles tend to form crystalline structure giving rise to stronger shear-thinning behavior recently measured experimentally.

  10. Soft glassy rheology of supercooled molecular liquids

    PubMed Central

    Zondervan, Rob; Xia, Ted; van der Meer, Harmen; Storm, Cornelis; Kulzer, Florian; van Saarloos, Wim; Orrit, Michel

    2008-01-01

    We probe the mechanical response of two supercooled liquids, glycerol and ortho-terphenyl, by conducting rheological experiments at very weak stresses. We find a complex fluid behavior suggesting the gradual emergence of an extended, delicate solid-like network in both materials in the supercooled state—i.e., above the glass transition. This network stiffens as it ages, and very early in this process it already extends over macroscopic distances, conferring all well known features of soft glassy rheology (yield-stress, shear thinning, aging) to the supercooled liquids. Such viscoelastic behavior of supercooled molecular glass formers is difficult to observe because the large stresses in conventional rheology can easily shear-melt the solid-like structure. The work presented here, combined with evidence for long-lived heterogeneity from previous single-molecule studies [Zondervan R, Kulzer F, Berkhout GCG, Orrit M (2007) Local viscosity of supercooled glycerol near Tg probed by rotational diffusion of ensembles and single dye molecules. Proc Natl Acad Sci USA 104:12628–12633], has a profound impact on the understanding of the glass transition because it casts doubt on the widely accepted assumption of the preservation of ergodicity in the supercooled state. PMID:18362347

  11. Structure and rheology of organoclay suspensions

    SciTech Connect

    King, H. E. Jr.; Milner, Scott T.; Lin, Min Y.; Singh, John P.; Mason, T. G.

    2007-02-15

    We have characterized a montmorillonite-based organoclay dispersed in three different nonaqueous solvents using a combination of x-ray scattering, small-angle neutron scattering (SANS), and ultrasmall angle neutron scattering (USANS), together with rheological measurements. Consistent with these measurements, we present a structural model for the incompletely dispersed clay as consisting of randomly oriented tactoids made of partially overlapping clay sheets, with transverse dimensions of several microns. Intersheet correlation peaks are visible in x-ray scattering, and quantitatively fit by our model structure factor. SANS and USANS together show a power law of about -3 over a wide range of wave numbers below the intersheet correlation peak. Our model relates this power law to a power law distribution of the number of locally overlapping layers in a tactoid. The rheology data show that both storage and loss moduli, as well as yield stress, scale with a power law in volume fraction of about three. Equating the gel onset composition with the overlap of randomly oriented tactoids and taking into account the large transverse dimensions of the tactoids, we predict the gel point to be at or below 0.006 volume fraction organoclay. This is consistent with the rheology data.

  12. Evolution of the rheological structure of Mars

    NASA Astrophysics Data System (ADS)

    Azuma, Shintaro; Katayama, Ikuo

    2017-01-01

    The evolution of Mars has been greatly influenced by temporal changes in its rheological structure, which may explain the difference in tectonics between Mars and Earth. Some previous studies have shown the rheological structures of Mars calculated from the flow law of rocks and the predicted thermal structure. However, the Peierls mechanism, which is the dominant deformation mechanism at relatively low temperature, and the evolution of water reservoirs on Mars were not considered in such studies. In this paper, we apply the Peierls mechanism to refine the rheological structure of Mars to show a new history of the planet that considers the most recent reports on its evolution of water reservoirs. Considering the Peierls creep and the evolution of water reservoirs, we attempt to explain why the tectonics of Mars is inactive compared with that of Earth. On early Mars, the lithospheric thickness inferred from the brittle-ductile transition was small, and the lithospheric strength was low ( 200-300 MPa) under wet conditions at 4 Gya. This suggests that plate boundaries could have developed on the early "wet" Mars, which is a prerequisite for the operation of plate tectonics. Our results also imply that the lithospheric strength had significantly increased in the Noachian owing to water loss. Therefore, plate tectonics may have ceased or could no longer be initiated on Mars. At the least, the tectonic style of Mars would have dramatically changed during the Noachian.[Figure not available: see fulltext.

  13. 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.

  14. Rheological properties of aging thermosensitive suspensions

    NASA Astrophysics Data System (ADS)

    Purnomo, Eko H.; van den Ende, Dirk; Mellema, Jorrit; Mugele, Frieder

    2007-08-01

    Aging observed in soft glassy materials inherently affects the rheological properties of these systems and has been described by the soft glassy rheology (SGR) model [S. M. Fielding , J. Rheol. 44, 323 (2000)]. In this paper, we report the measured linear rheological behavior of thermosensitive microgel suspensions and compare it quantitatively with the predictions of the SGR model. The dynamic moduli [ G'(ω,t) and G″(ω,t) ] obtained from oscillatory measurements are in good agreement with the model. The model also predicts quantitatively the creep compliance J(t-tw,tw) , obtained from step stress experiments, for the short time regime [(t-tw)

  15. Rheological and boundary effects on microswimmers

    NASA Astrophysics Data System (ADS)

    Montenegro-Johnson, Thomas; Loghin, Daniel; Smith, David

    2013-11-01

    Two important environmental factors impacting cell motility are the rheological properties of the surrounding fluid and the presence of boundaries. In this talk we will present simulations that explore the relationship between microswimmer, fluid rheology and boundary features, with a particular emphasis on the example of human sperm. Human sperm must navigate the labyrinthine structure of human fallopian tubes, actively bending their flagella in order to propel themselves through physiological mucus. Sperm trajectories are greatly affected by boundaries, scattering over features such as steps and ripples. We present simulations of scattering sperm-like swimmers in confined geometries, comparing these results to experiments of swimmers in microchannels. The rheological properties of mucus also affect sperms' ability to penetrate. Using the method of femlets, a new finite element technique entailing an immersed force representation of the swimmer with a body-fitted mesh, we present novel physical mechanisms through which shear-thinning, an important property of physiological mucus affects microscopic swimmers. In particular, we show that these effects are sensitive to the swimming stroke employed, and present example reciprocal swimmers that violate Purcell's Scallop Theorem.

  16. Rheological properties of a vesicle suspension

    NASA Astrophysics Data System (ADS)

    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), 10.1103/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 ηeff and normal stress differences N1 and N2. 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 ηeff,N1 , and N2 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 ηeff,N1 , and N2 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.

  17. Rheology of nanocrystalline cellulose aqueous suspensions.

    PubMed

    Shafiei-Sabet, Sadaf; Hamad, Wadood Y; Hatzikiriakos, Savvas G

    2012-12-11

    The rheological properties and microstructure of nanocrystalline cellulose (NCC) aqueous suspensions have been investigated at different concentrations. The suspension is isotropic up to 3 wt %, and phase separates to liquid crystalline and isotropic domains at higher concentrations where the samples exhibit a fingerprint texture and the viscosity profile shows a three-region behavior, typical of liquid crystals. The suspension behaves as a rheological gel at even higher concentrations where the viscosity profile shows a single shear thinning behavior over the whole range of shear rates investigated. The effects of ultrasound energy and temperature on the rheological properties and structure of these suspensions were studied using polarized optical microscopy and rheometry. Our results indicate that the amount of applied ultrasound energy affects the microstructure of the suspensions and the pitch of the chiral nematic domains. The viscosity profile is changed significantly at low shear rates, whereas the viscosity of biphasic suspensions at intermediate and high shear rates decreased with increasing temperature. This suggests that, between 30 and 40 °C, structural rearrangement takes place. At higher concentrations of about 10 wt %, the temperature has no significant effect on viscosity; however, a marked increase in viscosity has been observed at around 50 °C. Finally, the Cox-Merz rule was found to fail after a critical concentration, thereby implying significant structural formation. This critical concentration is much higher for sonicated compared to unsonicated suspensions.

  18. Effect of micellar topology on shear rheology

    NASA Astrophysics Data System (ADS)

    Rogers, Simon; Calabrese, Michelle; Wagner, Norman

    2014-03-01

    Micellar topology affects the nonlinear shear rheology of self-assembled surfactant solutions. Segmental alignment of wormlike micelles (WLMs) exhibiting varying degrees of branching was investigated under shear in the flow-gradient and flow-vorticity planes using new small angle neutron scattering (SANS) sample environments. The degree of branching in mixed cationic/anionic surfactant (CTAT/SDBS) WLMs is controlled via the addition of the hydrotropic salt sodium tosylate. Shear-induced segmental alignment of the micelles is characterized by spatially-resolved flow-small angle neutron scattering (flow-SANS). Our ability to resolve structural projections in both planes provides insight to branch behavior and kinematics under shear flows. Local segmental orientation and alignment in the flow-gradient plane is a non-monotonic function of branching level and radial position. Alignment in the flow-gradient plane is significantly higher than that observed in the flow-vorticity plane, suggesting that branches may simultaneously migrate into the vorticity direction and inhibit spatially localized flows. Shear and normal stresses calculated from micellar alignment using the stress-SANS law are favorably compared with rheological measurements under identical conditions. The results provide evidence for the effects of micellar topology on the nonlinear shear rheology of WLM solutions.

  19. Arresting dissolution by interfacial rheology design.

    PubMed

    Beltramo, Peter J; Gupta, Manish; Alicke, Alexandra; Liascukiene, Irma; Gunes, Deniz Z; Baroud, Charles N; Vermant, Jan

    2017-09-26

    A strategy to halt dissolution of particle-coated air bubbles in water based on interfacial rheology design is presented. Whereas previously a dense monolayer was believed to be required for such an "armored bubble" to resist dissolution, in fact engineering a 2D yield stress interface suffices to achieve such performance at submonolayer particle coverages. We use a suite of interfacial rheology techniques to characterize spherical and ellipsoidal particles at an air-water interface as a function of surface coverage. Bubbles with varying particle coverages are made and their resistance to dissolution evaluated using a microfluidic technique. Whereas a bare bubble only has a single pressure at which a given radius is stable, we find a range of pressures over which bubble dissolution is arrested for armored bubbles. The link between interfacial rheology and macroscopic dissolution of [Formula: see text] 100 [Formula: see text]m bubbles coated with [Formula: see text] 1 [Formula: see text]m particles is presented and discussed. The generic design rationale is confirmed by using nonspherical particles, which develop significant yield stress at even lower surface coverages. Hence, it can be applied to successfully inhibit Ostwald ripening in a multitude of foam and emulsion applications.

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

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

    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.

  1. Dry granular flows - rheological measurements of the μ(I) - Rheology

    NASA Astrophysics Data System (ADS)

    Fall, Abdoulaye; Badetti, Michel; Ovarlez, Guillaume; Chevoir, François; Roux, Jean-Noël

    2017-06-01

    Granular materials do not always flow homogeneously like fluids when submitted to external stress, but often form rigid regions that are separated by narrow shear bands where the material yields and flows. This shear localization impacts their apparent rheology, which makes it difficult to infer a constitutive behavior from conventional rheometric measurements. Moreover, they present a dilatant behavior, which makes their study in classical fixed-volume geometries difficult. These features led numerous groups to perform extensive studies with inclined plane flows, which were of crucial importance for the development and the validation of the μ(I)-rheology. Our aim is to develop a method to characterize granular materials with rheometrical tools. Using rheometry measurements in an annular shear cell, dense granular flows of 0.5mm spherical and monodisperse beads are studied. A focus is placed on the comparison between the present results and the μ(I)-rheology.

  2. Modification of the rheological properties of screen printing ceramic paints containing gold

    NASA Astrophysics Data System (ADS)

    Izak, P.; Mastalska-Poplawska, J.; Lis, J.; Stempkowska, A.

    2017-01-01

    This work presents the results of modification of rheological properties of screen printing paints containing gold. 15 wt% glossy gold paste and 15 wt% glossy liquid gold were used as modifiers containing gold. The study showed that the gold paint for screen printing can be obtained by evaporation of the 15 wt% liquid gold and the golden luster. The compaction process of liquid gold by evaporation is slow and easy to perform in industrial conditions. The second way to adapt the 15 wt% gold ceramic paint for screen printing application depended on adding the aniseed oil and the pine oil. The course of the flow curve of the gold paste without modification indicates that it is shear thinning and shows the desired effect of thixotropy, and even anti-thixotropy, at low shear rates (<50-1 s-1). The introduction of the essential oils eliminates this phenomenon and the paste converts itself from the non-rheostable to the rheostable liquid.

  3. Rheological Predictions of Network Systems Swollen with Entangled Solvent

    DTIC Science & Technology

    2014-04-01

    solvent was previously studied experimentally. In this article, we use the discrete slip-link model to predict its linear and nonlinear rheology ...Model parameters are obtained from the dynamic modulus data of pure solvent. Network rheology predictions also require an estimate of the fraction and...Triangle Park, NC 27709-2211 rheology ;polymer properties;gels, networks;mathematical modeling;multiscale modeling REPORT DOCUMENTATION PAGE 11. SPONSOR

  4. 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.

  5. Another word on the rheology of silicone putty: Bingham

    NASA Astrophysics Data System (ADS)

    Dixon, John M.; Summers, John M.

    Silicone putty, a material commonly used as a rock-analog in tectonic scale-model studies, exhibits rheological behavior that is similar to the Bingham rheological model over a wide range of strain rate. Nevertheless, at low strain rates a power law is a useful approximation. Similarly, at high strain rates a linear viscous model can be applied. Thus, the choice of rheologic expression can be based on knowledge of the range of stress levels that are achieved in a given model. Conversely, models can be designed to develop appropriate stress levels so that the rheological formulation appropriate to the relevant prototype material will be applicable.

  6. Rheological characterization of hyaluronic acid derivatives as injectable materials toward nucleus pulposus regeneration.

    PubMed

    Gloria, Antonio; Borzacchiello, Assunta; Causa, Filippo; Ambrosio, Luigi

    2012-02-01

    Nucleus pulposus (NP) is the soft center of the intervertebral disc (IVD), able to resist compressive loads, while the annulus fibrosus withstands tension and gives mechanical strength. NP function may be altered as consequence of several pathologies or injury and when a damaged IVD does not properly play its role. In the past years, a great effort has been devoted to the design of injectable systems as NP substitutes. The different synthetic- and natural hydrogel-based materials proposed, present many drawbacks and, in particular, they do not seem to mimic the required behavior. In the search for natural-based systems a dodecylamide of hyaluronic acid (HA), HYADD3®, has been proved as bioactive and suitable vehicle to carry cells for NP tissue engineering, while a crosslinked HA ester, HYAFF120® showed interesting results if used as injectable acellular material. Even though these derivatives showed appropriate biological behavior up to now, data on mechanical behavior of these derivatives are still missing. In this frame, the aim of this study was to provide a rheological characterization of these HA derivatives to asses their biomechanical compatibility with the NP tissue. To this, the rheological properties of these derivatives were studied through dynamic shear tests before and after injection through needles used in the current surgical procedure. Both HA derivatives showed a 'gel-like' rheological behavior similar to the native NP tissue and this behavior was not altered by injection. © The Author(s), 2010.

  7. Polymer melt rheology and flow simulations applied to cast film extrusion die design: An industrial perspective

    NASA Astrophysics Data System (ADS)

    Catherine, Olivier

    2017-05-01

    This article is an overview of the techniques used today in the area of rheology and flow simulation, on the industrial level, for cast film extrusion die design. This industry has made significant progress over the past three decades and die and feedblock design and optimization certainly have been instrumental in the overall improvement. Dies and coextrusion feedblocks are a critical aspect of the process due to the layering and forming function, which drive the final product economics and properties. Polymer melt rheology is a key aspect to consider when optimizing the flow patterns in the extrusion equipment. Not only is rheology critical for the flow channel design when aiming at obtaining a uniform flow distribution at the die exit, but also it is playing a major role in the thermal aspect of the flow due to the strong mechanical and thermal coupling. This coupling comes, on one hand, from the occurrence of viscous dissipation in the flow and on the other hand from the significant temperature dependency of melt viscosity. Viscous dissipation is due to relatively high melt viscosities and strain rates, especially with today's processes which involve formidable extrusion speeds. The third aspect discussed in this paper is the complexity of residence time distribution in modern flow channels, which is evaluated with advanced three-dimensional flow simulation and particle tracking.

  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. Rheological properties of typical chernozems (Kursk oblast) under different land uses

    NASA Astrophysics Data System (ADS)

    Khaidapova, D. D.; Chestnova, V. V.; Shein, E. V.; Milanovskii, E. Yu.

    2016-08-01

    Rheological parameters of humus horizons from typical chernozems under different land use—on a virgin land (unmown steppe) and under an oak forest, long-term black fallow, and agricultural use—have been studied by the amplitude sweep method with an MCR-302 modular rheometer at water contents corresponding to swelling limit and liquid limit. From the curves of elastic and viscous moduli, the ranges of elastic and viscoelastic (plastic) behavior of soil pastes—as well as that of transition from viscoelastic to viscous behavior—have been determined. It has been shown that the rheological behavior is largely determined by the content of organic matter, which can act as a binding agent structuring the interparticle bonds and as a lubricant in the viscous-flow (plastic) state of soil pastes. Soil samples enriched with organic matter (virgin land, oak forest, forest belt) have a more plastic behavior and a higher resistance to loads. Soil samples with the lower content of organic matter (long-term fallow, plowland) are characterized by a more rigid cohesion of particles and a narrower range of load resistance. Soil pastes at the water content of liquid limit have a stronger interparticle cohesion and a more brittle behavior than at the water content of swelling limit. Methodological aspects of testing soil pastes at the constant sample thickness and the controlled normal load have been considered. For swelling soil samples, tests under controlled normal load are preferred.

  10. Influence of ultrasonication and Fenton oxidation pre-treatment on rheological characteristics of wastewater sludge.

    PubMed

    Pham, T T H; Brar, S K; Tyagi, R D; Surampalli, R Y

    2010-01-01

    The effect of ultrasonication and Fenton oxidation as physico-chemical pre-treatment processes on the change of rheology of wastewater sludge was investigated in this study. Pre-treated and raw sludges displayed non-Newtonian rheological behaviour with shear thinning as well as thixotropic properties for total solids ranging from 10 g/L to 40 g/L. The rheological models, namely, Bingham plastic, Casson law, NCA/CMA Casson, IPC Paste, and power law were also studied to characterize flow of raw and pre-treated sludges. Among all rheological models, the power law was more prominent in describing the rheology of the sludges. Pre-treatment processes resulted in a decrease in pseudoplasticity of sludge due to the decrease in consistency index K varying from 42.4 to 1188, 25.6 to 620.4 and 52.5 to 317.9; and increase in flow behaviour index n changing from 0.5 to 0.35, 0.62 to 0.55 and 0.63 to 0.58, for RS, UlS and FS, respectively at solids concentration 10-40 g/L. The correlation between improvement of biodegradability and dewaterability, decrease in viscosity, and change in particle size as a function of sludge pre-treatment process was also investigated. Fenton oxidation facilitated sludge filterability resulting in capillary suction time values which were approximately 50% of the raw sludges, whereas ultrasonication with high input energy deteriorated the filterability. Biodegradability was also enhanced by the pre-treatment processes and the maximum value was obtained (64%, 77% and 73% for raw, ultrasonicated and Fenton oxidized sludges, respectively) at total solids concentration of 25 g/L. Hence, pre-treatment of wastewater sludge modified the rheological properties so that: (1) the flowability of sludge was improved for transport through the treatment train (via pipes and pumps); (2) the dewaterability of wastewater sludge was enhanced for eventual disposal and; (3) the assimilation of nutrients by microorganisms for further value-addition was increased.

  11. In-Situ Lithospheric Rheology Measurement Using Isostatic Response and Geophysical State

    NASA Astrophysics Data System (ADS)

    Lowry, A. R.; Becker, T. W.; Buehler, J. S.; ma, X.; Miller, M. S.; Perez-Gussinye, M.; Ravat, D.; Schutt, D.

    2013-12-01

    Measurements of effective elastic thickness, Te, from flexural isostatic modeling are sensitive to flow rheology of the lithosphere. Nevertheless, Te has not been widely used to estimate in-situ rheology. Past methodological controversies regarding Te measurement are partly to blame for under-utilization of isostatic response in rheology studies, but these controversies are now largely resolved. The remaining hurdles include uncertainties in properties of geophysical state such as temperature, lithology, and water content. These are ambiguous in their relative contributions to total strength, and the unknown state-of-stress adds to ambiguity in the rheology. Dense seismic and other geophysical arrays such as EarthScope's USArray are providing a wealth of new information about physical state of the lithosphere, however, and these data promise new insights into rheology and deformation processes. For example, new estimates of subsurface mass distributions derived from seismic data enable us to examine controversial assumptions about the nature of lithospheric loads. Variations in crustal lithology evident in bulk crustal velocity ratio, vP/vS, contribute a surprisingly large fraction of total loading. Perhaps the most interesting new information on physical state derives from imaging of uppermost mantle velocities using refracted mantle phases, Pn and Sn, and depths to negative velocity gradients imaged as converted phases in receiver functions (so-called seismic lithosphere-asthenosphere boundary, 'LAB', and mid-lithosphere discontinuity, 'MLD'). Imaging of the ~580°C isotherm associated with the phase transition from alpha- to beta-quartz affords another exciting new avenue for investigation, in part because the transition closely matches the Curie temperature thought to control magnetic bottom in some continental crust. Reconciling seismic estimates of temperature variations with measurements of Te and upper-mantle negative velocity gradients in the US requires

  12. Physico-chemical and rheological properties of gelatinized/freeze-dried cereal starches

    NASA Astrophysics Data System (ADS)

    Krystyjan, Magdalena; Ciesielski, Wojciech; Gumul, Dorota; Buksa, Krzysztof; Ziobro, Rafał; Sikora, Marek

    2017-07-01

    The influence of gelatinization and freeze-drying process on the physico-chemical and rheological properties of cereal starches was evaluated, and it was observed that modified starches revealed an increased water binding capacity and solubility when compared to dry starches, while exhibiting the same amylose and fat contents. The molecular weights of starches decreased after modification which resulted in the lower viscosity of dissolved modified samples in comparison to native starch pastes. As it was observed by scanning electron microscopy modified starches were characterized by an expanded surface, a uniform structure and high porosity.

  13. The effect of artificial saliva on the rheological properties of tooth whitening systems.

    PubMed

    Castellon, R G; Combe, E C; Pesun, I J

    2004-12-01

    This work was undertaken to explore the effect of saliva addition on the rheological properties of two contrasting tooth bleaching systems, one of which was a paste (Colgate Platinum) and the other a gel (Zaris, 3M ESPE). Using a dynamic stress rheometer with cone and plate geometry, it was shown that addition of artificial saliva reduced the apparent viscosity of each material. However, in some cases this was accompanied by an increase in elasticity. It is suggested that saliva may not have a deleterious effect on the ability of the materials to remain in the bleaching tray.

  14. Rheological characterization of human brain tissue.

    PubMed

    Budday, S; Sommer, G; Haybaeck, J; Steinmann, P; Holzapfel, G A; Kuhl, E

    2017-09-15

    The rheology of ultrasoft materials like the human brain is highly sensitive to regional and temporal variations and to the type of loading. While recent experiments have shaped our understanding of the time-independent, hyperelastic response of human brain tissue, its time-dependent behavior under various loading conditions remains insufficiently understood. Here we combine cyclic and relaxation testing under multiple loading conditions, shear, compression, and tension, to understand the rheology of four different regions of the human brain, the cortex, the basal ganglia, the corona radiata, and the corpus callosum. We establish a family of finite viscoelastic Ogden-type models and calibrate their parameters simultaneously for all loading conditions. We show that the model with only one viscoelastic mode and a constant viscosity captures the essential features of brain tissue: nonlinearity, pre-conditioning, hysteresis, and tension-compression asymmetry. With stiffnesses and time constants of μ∞=0.7kPa, μ1=2.0kPa, and τ1=9.7s in the gray matter cortex and μ∞=0.3kPa, μ1=0.9kPa and τ1=14.9s in the white matter corona radiata combined with negative parameters α∞ and α1, this five-parameter model naturally accounts for pre-conditioning and tissue softening. Increasing the number of viscoelastic modes improves the agreement between model and experiment, especially across the entire relaxation regime. Strikingly, two cycles of pre-conditioning decrease the gray matter stiffness by up to a factor three, while the white matter stiffness remains almost identical. These new insights allow us to better understand the rheology of different brain regions under mixed loading conditions. Our family of finite viscoelastic Ogden-type models for human brain tissue is simple to integrate into standard nonlinear finite element packages. Our simultaneous parameter identification of multiple loading modes can inform computational simulations under physiological conditions

  15. Rheological Properties of Aqueous Nanometric Alumina Suspensions

    SciTech Connect

    Li, Chuanping

    2004-01-01

    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 17O 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

  16. 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.

  17. Functional and rheological properties of cold plasma treated rice starch.

    PubMed

    Thirumdas, Rohit; Trimukhe, A; Deshmukh, R R; Annapure, U S

    2017-02-10

    The present work deals with aimed to study the effect of cold plasma treatment on the functional and rheological properties of rice starch using two different power levels (40 and 60W). The changes in amylose content, turbidity, pH, water and fat absorption due to plasma treatment were evaluated. Where decrease in the turbidity and pH after the treatment was observed. Gel hydration properties and syneresis study revealed that there is an increase in leaching of amylose molecules after the treatment. Rapid Visco Analyzer examination showed an increase in pasting and final viscosities. From G' and G″ moduli determination we observed that there is decrease in retrogradation tendency of starch gels. XRD did not show any change in A-type pattern but decrease in the relative crystallinity was observed due to depolymerization caused by active plasma species. FTIR shows some of the additional functional groups after treatment. SEM showed formation of fissures on the surface of starch granules due to etching caused by the plasma species. Thus, plasma treatment can be one of the methods for physical modification of starch.

  18. 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.

  19. 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.

  20. Mass Transfer and Rheology of Fiber Suspensions

    NASA Astrophysics Data System (ADS)

    Wang, Jianghui

    Rheological and mass transfer properties of non-Brownian fiber suspensions are affected by fiber characteristics, fiber interactions, and processing conditions. In this thesis we develop several simulation methods to study the dynamics of single fibers in simple shear flow, as well as the rheology and mass transfer of fiber suspensions. Isolated, rigid, neutrally-buoyant, non-Brownian, slightly curved, nonchiral fibers in simple shear flow of an incompressible Newtonian fluid at low Reynolds number can drift steadily in the gradient direction without external forces or torques. The average drift velocity and direction depend on the fiber aspect ratio, curvature and initial orientation. The drift results from the coupling of rotational and translational dynamics, and the combined effects of flipping, scooping, and spinning motions of the fiber. Irreversible fiber collisions in the suspensions cause shear-induced diffusion. The shear-induced self-diffusivity of dilute suspensions of fibers increases with increasing concentration and increasing static friction between contacts. The diffusivities in both the gradient and vorticity directions are larger for suspensions of curved fibers than for suspensions of straight fibers. For suspensions of curved fibers, significant enhancements in the diffusivity in the gradient direction are attributed to fiber drift in the gradient direction. The shear-induced self-diffusivity of concentrated suspensions of fibers increases with increasing concentration before fiber networks or flocs are formed, after which the diffusivity decreases with increasing concentration. The diffusivity increases with increasing fiber equilibrium bending angle, effective stiffness, coefficient of static friction, and rate of collisions. The specific viscosity of fiber suspensions increases with increasing fiber curvature, friction coefficient between mechanical contacts, and solids concentration. The specific viscosity increases linearly with

  1. Rheology of dense granular mixtures: boundary pressures.

    PubMed

    Hill, K M; Yohannes, B

    2011-02-04

    Models for dense sheared granular materials indicate that their rheological properties depend on particle size, but the representative size for mixtures is not obvious. Here, we computationally study pressure on a boundary due to sheared granular mixtures to determine its dependence on particle size distribution. We find that the pressure does not depend monotonically on average particle size. Instead it has an additional dependence on a measure of the effective free volume per particle we adapt from an expression for packing of monosized particles near the jammed state.

  2. Hydrodynamics and Rheology of Active Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Cui, Zhenlu

    2012-02-01

    Active liquid crystals such as swimming bacteria, active gels and assemblies of motors and filaments are active complex fluids. Such systems differ from their passive counterparts in that particles absorb energy and generate motion. They are interesting from a more fundamental perspective as their dynamic phenomenons are both physically fascinating and potentially of great biological significance. In this talk, I will present a continuum model for active liquid crystals and analyze the behavior of a suspension subjected to a weak Poiseuille flow. Hydrodynamics, stability and rheology will also be discussed.

  3. 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.

  4. The rheological behavior of HDPE/coal blends

    SciTech Connect

    Zhou Anning; Ge Lingmei; Guo Shucai

    1997-12-31

    The antistatic functional material of HDPE/coal [high density polyethylene mixed with coal fines] has a higher tensile strength, higher resistance and stability. The rheological properties of the blends are important for their processing and practical use. It was necessary to study the rheological behavior of the blends. P. Ujas et al (1994) had studied the rheology of HDPE/nylon-11 blends and the effect of nylon-11 on the rheological behavior of HDPE. If Shenfu coal is used as a special polymer, it has necessarily an important affect on the rheological behavior of HDPE. In this paper, the rheological behavior of HDPE/coal blends were investigated to study the effect of the coal polymer on the rheology of HDPE. The rheological behavior of the blends were found to be very different from that of HDPE. The curves of shear viscosity for the blends at different temperatures (478, 488, and 498K) reveal that HDPE and the blends are characteristic of pseudoplastic fluid, that is, there is a decrease of shear viscosity with an increase of shearing rate.

  5. Rheological modification of corn stover biomass at high solids concentrations

    Treesearch

    Joseph R. Samaniuk; C. Tim Scott; Thatcher W. Root; Daniel J. Klingenberg

    2012-01-01

    Additives were tested for their ability to modify the rheology of lignocellulosic biomass. Additive types included water-soluble polymers (WSPs), surfactants, and fine particles. WSPs were the most effective rheological modifiers, reducing yield stresses of concentrated biomass by 60–80% for additive concentrations of 1–2 wt. % (based on mass of dry biomass solids)....

  6. 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.

  7. Sharing the World's Advanced Rheology Knowledge through Rheo-Hub

    NASA Astrophysics Data System (ADS)

    Winter, H. Henning

    2008-07-01

    Recent advances in rheometer design and rheology theory have led to an abundance of rheological information, both experimental and theoretical. In response to this wonderful opportunity, many of the world's leading rheologists began to share their expert software codes with the wider community of materials researchers and practitioners. This became possible through "Rheo-Hub", a central computer platform from which the user interrogates rheological expert codes ("engines") and rheological data by comparing, merging, and funneling these into further interrogations and explorations. In this virtual environment, results are returned to the computer screen as visuals so that the visual intelligence of the user gets involved in the cognition process. Rheological explorations may be repeated in different ways (using different expert codes for answering the same research question) and viewed from different graphical viewpoints. This creates the multi-scale and multi-expertise workspace that is needed to support quantitative rheological explorations and to prepare for discovery. The virtual environment technology will be presented and examples will be shown. Rheo-Hub's strengths are data analysis, integration of experimental results with theoretically predicted rheology, visuals for communicating results, and introduction of a rheological data standard.

  8. 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

  9. 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.

  10. 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

  11. Improving feed slurry rheology by colloidal techniques

    SciTech Connect

    Heath, W.O.; Ternes, R.L.

    1984-06-01

    Pacific Northwest Laboratory (PSN) has investigated three colloidal techniques in the laboratory to improve the sedimentation and flowability of Hanford simulated (nonradioactive) current acid waste (CAW) melter feed slurry: polymer-induced bridging flocculation; manipulating glass former (raw SiO/sub 2/ or frit) particle size; and alteration of nitric acid content. All three methods proved successful in improving the rheology of the simulated CAW feed. This initially had exhibited nearly worst-case flow and clogging properties, but was transformed into a flowable, resuspendable (nonclogging) feed. While each has advantages and disadvantages, the following three specific alternatives proved successful: addition of a polyelectrolyte in 2000 ppM concentration to feed slurry; substitution of a 49 wt % SiO/sub 2/ colloidal suspension (approx. 10-micron particle size) for the -325 mesh (less than or equal to 44-micron particle size) raw-chemical SiO/sub 2/; and increase of nitric acid content from the reference 1.06 M to optimum 1.35 M. The first method, polymer-induced bridging flocculation, results in a high sediment volume, nonclogging CAW feed. The second method, involving the use of colloidal silica particles results in a nonsedimenting feed that when left unagitated forms a gel. The third method, increase in feed acidity, results in a highly resuspendable (nonclogging) melter feed. Further research is therefore required to determine which of the three alternatives is the preferred method of achieving rheological control of CAW melter feeds.

  12. 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.

  13. Investigation on cell assemblies for mantle rheology

    NASA Astrophysics Data System (ADS)

    Long, H.; Li, L.; Chen, J.; Leinenweber, K.; Wang, L.; Liu, Z.; Vaughan, M. T.; Yang, Y.; Weidner, D. J.

    2004-12-01

    Several types of cell assemblies are being tested on large volume press apparatus at Sam85, NSLS to determine their suitability for high pressure rheology experiments, with present focus on the influence of different cells on water fugacity and the thermal efficiency. SanCarlos olivine, both lab dry and super dry, is being used as the testing material. Three types of pressure media including mullite, MgO and boron:epoxy (BE) are used for both DIA and T-cup apparatus in the test. For lab dry sample assemblies, 2¡ª3 hours heating at 130C in the vacuum environment is applied before experiment in order to drive off the absorptive water. Different pressure media in each apparatus are carried out at the same P-T path. After experiments the recovered samples are examined on the synchrotron infrared (IR) spectrometer at U2A beamline of NSLS to evaluate the water concentration. IR results suggest that mullite cell offers an acceptable dry environment for the rheology study. Among the tested cell assemblies, mullite cell has a comparable thermal efficiency as BE cell does. Both of them show much higher heating efficiency than MgO cell does. This preliminary study suggests that mullite has great potential as the pressure medium for the high pressure and high temperature experiment.

  14. 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.

  15. Rheological events following laparoscopic and conventional laparotomy.

    PubMed

    Beilin, Benzion; Mayburd, Eduard; Yardeni, Israel-Zeev; Bessler, Hanna

    2005-01-01

    Laparoscopic surgery has become a widely used procedure with many advantages compared to conventional laparotomy. Although rare, this technique is not entirely absent from clinical hazards and particularly thromboembolic events. This complication is due to activation of the coagulation cascade, as well as factors that may cause alterations in blood rheology. Apart from high hematocrit, presence of abnormal proteins and elevated fibrinogen level, the type of anesthesia, temperature, and increased intra-abdominal pressure following CO(2) insufflation may affect blood viscosity. Therefore, the objective of the study was to compare rheological events in 17 patients undergoing laparoscopic surgery to those in 15 patients who underwent laparotomy. Both groups of patients did not show any complications during the early and late post-operative period. The values of whole blood viscosity in patients undergoing laparoscopy did not differ from those in patients treated by laparotomy. A slight, although significant decrease in plasma viscosity and red blood cell aggregation was observed in patients who underwent laparotomy. The results suggest that the benefits of laparoscopic surgery in the present series were not affected by alterations in blood and plasma viscosity, as well as in red blood cell aggregation.

  16. Study of rheological behaviour of wines

    NASA Astrophysics Data System (ADS)

    Trávníček, Petr; Burg, Patrik; Krakowiak-Bal, Anna; Junga, Petr; Vítěz, Tomáš; Ziemiańczyk, Urszula

    2016-10-01

    This study deals with rheological properties of various wine varieties. Samples of the following wines were used for this experiment: André, Cabernet Moravia, Laurot, Saint Laurent, Gruner Veltliner, Pinot Blanc, Müller Thurgau, and Riesling Italico. These samples were obtained from wine produced from the grapes collected in the Czech Republic (Morava region, subregion Velke Pavlovice). In the first phase, the chemical composition of the samples was determined. The following chemical parameters were determined: total acidity, pH, content of the alcohol, reduced sugars, free SO2, total SO2, and volatile acids. In the second phase of the study, the physical properties of the samples were determined and the samples of the wines were subjected to rheological tests. These tests consisted in determination of apparent viscosity in relation to temperature, hysteresis loop tests, and apparent viscosity related to time. The dependence of the shear rate on the shear stress was described with the Herschel-Bulkley mathematical model. The experiment yielded the following findings: seven out of the eight samples behaved as non-Newtonian fluids at low temperature (5°C); non-Newtonian behaviour was changed into Newtonian at the temperature higher than 10°C; non-Newtonian behaviour was characterised as thixotropic behaviour; the degree of thixotropy is relatively small and reaches 1.85 Pa s-1 ml-1.

  17. Rheology and dynamics of colloidal superballs.

    PubMed

    Royer, John R; Burton, George L; Blair, Daniel L; Hudson, Steven D

    2015-07-28

    Recent advances in colloidal synthesis make it possible to generate a wide array of precisely controlled, non-spherical particles. This provides a unique opportunity to probe the role that particle shape plays in the dynamics of colloidal suspensions, particularly at higher volume fractions, where particle interactions are important. We examine the role of particle shape by characterizing both the bulk rheology and micro-scale diffusion in a suspension of pseudo-cubic silica superballs. Working with these well-characterized shaped colloids, we can disentangle shape effects in the hydrodynamics of isolated particles from shape-mediated particle interactions. We find that the hydrodynamic properties of isolated superballs are marginally different from comparably sized hard spheres. However, shape-mediated interactions modify the suspension microstructure, leading to significant differences in the self-diffusion of the superballs. While this excluded volume interaction can be captured with a rescaling of the superball volume fraction, we observe qualitative differences in the shear thickening behavior of moderately concentrated superball suspensions that defy simple rescaling onto hard sphere results. This study helps to define the unknowns associated with the effects of shape on the rheology and dynamics of colloidal solutions.

  18. In situ rheology of yeast biofilms.

    PubMed

    Brugnoni, Lorena I; Tarifa, María C; Lozano, Jorge E; Genovese, Diego

    2014-01-01

    The aim of the present work was to investigate the in situ rheological behavior of yeast biofilms growing on stainless steel under static and turbulent flow. The species used (Rhodototula mucilaginosa, Candida krusei, Candida kefyr and Candida tropicalis) were isolated from a clarified apple juice industry. The flow conditions impacted biofilm composition over time, with a predominance of C. krusei under static and turbulent flow. Likewise, structural variations occurred, with a tighter appearance under dynamic flow. Under turbulent flow there was an increase of 112 μm in biofilm thickness at 11 weeks (p < 0.001) and cell morphology was governed by hyphal structures and rounded cells. Using the in situ growth method introduced here, yeast biofilms were determined to be viscoelastic materials with a predominantly solid-like behavior, and neither this nor the G'0 values were significantly affected by the flow conditions or the growth time, and at large deformations their weak structure collapsed beyond a critical strain of about 1.5-5%. The present work could represent a starting point for developing in situ measurements of yeast rheology and contribute to a thin body of knowledge about fungal biofilm formation.

  19. Rheology of asphaltene-toluene/water interfaces.

    PubMed

    Sztukowski, Danuta M; Yarranton, Harvey W

    2005-12-06

    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.

  20. Rheological behavior and the SPF of sunscreens.

    PubMed

    Gaspar, L R; Maia Campos, P M B G

    2003-01-02

    Due to a large variety of sunscreens, it is important to study among other things, the effect of the vehicle on the thickness and uniformity of sunscreen films. In this study, we determined the physical stability of five sunscreens SPF 15 (FA to FG), containing or not PVP/eicosene crosspolymer (PVP/EC), and two different self-emulsifying bases (SEB), and also evaluated the influence of the vehicle in their SPF. In the study of physical stability, formulations were stored at 25, 37 and 45 degrees C, for 28 days. Viscosity and rheological behavior of the formulations were determined using a Brookfield rheometer. Investigations of the SPF were carried out in a group of 30 volunteers (COLIPA methodology). The FC samples (phosphate-based SEB), with a lower thixotropy, showed statistically higher SPF (13.6) when compared with FB (non-ionic SEB), which presented higher thixotropy and a SPF of 9.84. The FE sample (phosphate-based SEB+PVP/EC) presented the same SPF as the FC, but had a higher thixotropy. The FB formulation (stable with higher thixotropy) showed the lowest SPF while FC (an unstable formulation with lower thixotropy) presented a higher SPF. We concluded that FE was the best formulation showing a higher SPF and stability and the study of rheology can help the development of sunscreens.

  1. Rheological Behavior of Bentonite-Polyester Dispersions

    NASA Astrophysics Data System (ADS)

    Abu-Jdayil, Basim; Al-Omari, Salah Addin

    2013-07-01

    The rheological behavior of a bentonite clay dispersed in unsaturated polyester was investigated. The effects of the solid content and particle size on the steady and transient rheological properties of the dispersions were studied. In addition, two types of bentonite with different Na+/Ca+2 ratio were used in this study. The Herschel-Bulkley and the Weltman models were used to describe the apparent viscosity of the bentonite-polyester composite in relation to the shear rate and shearing time. The bentonite-polyester dispersions were found to exhibit both Newtonian and non-Newtonian behavior. The transition from a Newtonian to a Bingham plastic and then to a shear-thinning material with a yield stress was found to depend on the solid concentration, the particle size, and the type of bentonite. At a low solid content, the apparent viscosity of the bentonite dispersion increased linearly with solid concentration. But a dramatic increase in the apparent viscosity beyond a solid content of 20 wt.% was observed. On the other hand, a thixotropic behavior was detected in bentonite-polyester dispersions with a high solid content and a low particle size. However, this behavior was more pronounced in dispersions with a high Na+/Ca+2 ratio.

  2. Chinese Lithosphere Rheology and Geodynamic Modeling

    NASA Astrophysics Data System (ADS)

    Shi, Y.; Zhang, H.; Cao, J.; Zhang, C.; Sun, L.

    2009-04-01

    Rock rheology is of critical importance to affect lithosphere deformation. Laboratory experiments show that viscosity of rocks strongly depends on temperature. Therefore, reliable estimation of geotherm is the first step for understanding lithospheric rheology. Deduction of geotherm from surface heat flow and thermal conductivity has been applied widely. However, error in temperature estimated this way increases with depth. In our study, we use seismic tomographic data to estimate mantle temperature ranges 50 to 200 km depth, and get a better constraint of temperature at depth. We use new petrology data to construct the crustal structure and viscosity model of China. To test the validity of extrapolation of flow law of rock from laboratory sample size and higher strain rate to large field scale and much lower strain rate, we use post seismic GPS deformation observation to invert lower crust viscosity for comparison. We then apply the viscosity model to simulate a number of tectonic problems in China, such as GPS velocity clockwise rotation around the eastern syntax of the Himalaya and uplift of the Tibetan plateau, decoupling of stress indicated by compression in the upper crust and extensional normal fault earthquake in the upper mantle in Taiwan southwest coast, and different stress accumulation rate in the upper and lower crust in Longmenshan area, Sichuan Province to estimate the reccurence time of large earthquakes.

  3. A predictive, nonlocal rheology for granular flows

    NASA Astrophysics Data System (ADS)

    Kamrin, Ken; Henann, David

    2013-11-01

    We propose a continuum model for flowing granular matter and demonstrate that it quantitatively predicts flow and stress fields in many different geometries. The model is constructed in a step-by-step fashion. First we compose a relation based on existing granular rheological approaches (notably the ``inertial'' granular flow rheology) and point out where the resulting model succeeds and where it does not. The clearest missing ingredient is shown to be the lack of an intrinsic length-scale. To tie flow features more carefully to the characteristic grain size, we compose a nonlocal model that includes a new size-dependent term (with only one new material parameter). This new nonlocal model resolves some outstanding questions in the granular flow literature--of note, it is the first model to predict all features of flows in split-bottom cell geometries, a decade-long open question in the field. In total, we will show that this new model, using three material parameters, quantitatively matches the flow and stress data from over 160 experiments in several different geometries.

  4. 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.

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

    USDA-ARS?s Scientific Manuscript database

    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...

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

    USDA-ARS?s Scientific Manuscript database

    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...

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

    PubMed

    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.

  8. 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

  9. 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.

  10. 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…

  11. Past Is Prologue

    ERIC Educational Resources Information Center

    Clement, Mary C.

    2008-01-01

    Behavior-based interviewing (BBI) has been used in the business world for decades as a way to select new hires whose past behaviors indicate future success. Behavior-based interviews are based on the premise that past behavior is the best predictor of future performance and that interview questions should evaluate the knowledge, skills, and…

  12. Past Is Prologue

    ERIC Educational Resources Information Center

    Clement, Mary C.

    2008-01-01

    Behavior-based interviewing (BBI) has been used in the business world for decades as a way to select new hires whose past behaviors indicate future success. Behavior-based interviews are based on the premise that past behavior is the best predictor of future performance and that interview questions should evaluate the knowledge, skills, and…

  13. 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.

  14. 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. Copyright © 2014 Elsevier Ltd. All rights reserved.

  15. 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.

  16. 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.

  17. 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.

  18. Structural rheological model of two-phase interlayer shear flow

    NASA Astrophysics Data System (ADS)

    Altoiz, B. A.; Aslanov, S. K.; Kiriyan, S. V.

    2011-04-01

    This paper presents a study of an epitropic liquid crystal layer formation at a metal substrate. Such layer structurization leads to non-Newtonian flow of thin interlayer with wall-adjacent orientation-ordered layers. Rheological characteristics of micron interlayers of n-hexadecane and Vaseline oil with surfactant addition are investigated. The features of structural "variable viscosity" layer are defined within the framework of a proposed rheological model. An increase in the rate of shear deformation leads to a reduction in near-surface layer viscosity due to molecular reorientation. Estimation of model parameters, performed on basis of the experimental rheological data, is carried out.

  19. Sensory and rheological properties of Polish commercial mayonnaise.

    PubMed

    Juszczak, Lesław; Fortuna, Teresa; Kośla, Aneta

    2003-08-01

    Sensory and rheological analyses were performed to compare seven commercial mayonnaises having various fat contents and containing, or not, thickening and stabilizing agents. It was found that mayonnaise samples differed in their sensory and rheological properties. The samples with a higher fat content scored higher in sensory analysis than the low-fat ones. The mayonnaises studied showed non-Newtonian, pseudoplastic flow with yield stress and thixotropy. All mayonnaises, although to a different degree, exhibited a decrease in the apparent viscosity at constant shear. The mayonnaise samples which contained thickeners and stabilizers had a greater rheological stability.

  20. 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.

  1. Rheological properties of dairy cattle manure.

    PubMed

    El-Mashad, Hamed M; van Loon, Wilko K P; Zeeman, Grietje; Bot, Gerard P A

    2005-03-01

    Rheological properties are important for the design and modelling of handling and treating fluids. In the present study, the viscosity of liquid manure (about 10% total solids) was measured at different shear rates (2.38-238 s(-1)). The effect of temperature on the viscosity at different shear rates was also studied. The results showed that manure has non-Newtonian flow properties, because the viscosity strongly depended on the applied shear rate. The results showed also that manure behaves like real plastic materials. The power-law model of the shear stress and the rate of shear showed that the magnitude of the consistency coefficient decreased while increasing the temperature, with high values of the determination coefficient. Moreover, the results showed that the Arrhenius-type model fitted the temperature effect on manure viscosity very well (R2 at least 0.95) with calculated activation energy of 17.0+/-0.3 kJ mol(-1).

  2. Nonlinear Rheology in a Model Biological Tissue

    NASA Astrophysics Data System (ADS)

    Matoz-Fernandez, D. A.; Agoritsas, Elisabeth; Barrat, Jean-Louis; Bertin, Eric; Martens, Kirsten

    2017-04-01

    The rheological response of dense active matter is a topic of fundamental importance for many processes in nature such as the mechanics of biological tissues. One prominent way to probe mechanical properties of tissues is to study their response to externally applied forces. Using a particle-based model featuring random apoptosis and environment-dependent division rates, we evidence a crossover from linear flow to a shear-thinning regime with an increasing shear rate. To rationalize this nonlinear flow we derive a theoretical mean-field scenario that accounts for the interplay of mechanical and active noise in local stresses. These noises are, respectively, generated by the elastic response of the cell matrix to cell rearrangements and by the internal activity.

  3. 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

  4. Rheology Of Suspensions Derived From Numerical Simulation

    NASA Astrophysics Data System (ADS)

    Ahamadi, M.; Harlen, O. G.

    2007-05-01

    In many polymer processing applications filler particles such as glass beads are added to the polymer matrix. To study the rheology of such multiphase systems we perform direct simulations of the motion of the suspended particles when subjected to an external linear flow, such as simple shear or planar extensional flow. The method uses a Lagrangian finite element grid that deforms with fluid combined with a quotient representation of the periodic computational domain. For shear flow we show that one can predict the viscometric properties of the suspension for shear thining fluid by using a simple shifting model. For planar extensional flow it is found that adding particle suppressed the extend of strain hardening in strongly strain-hardening fluids.

  5. Blood rheology near a stagnation point.

    PubMed

    Niimi, H; Sugihara, M

    1982-01-01

    Blood rheology at a stagnation point is studied in views of microhemorheology. Special emphasis is put on the effect of both non-Newtonian and unhomogeneous properties of blood on the fine structure of blood flow impinging on the wall. It is shown that "non-flow" region exists just at the stagnation point due to the non-Newtonian viscosity when its yield stress is large enough, compared with the viscous stress far from the wall. When the yield stress becomes negligibly small, RBC and plasma behave individually near the stagnation point; RBC is deviated from the plasma streamline and impinges on the wall. Finally, a microhemorheological factor of legional metabolic disorder is discussed on basis of the fine structure near a stagnation point.

  6. 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.

  7. 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.

  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 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.

  10. Vane Rheology of Cohesionless Glass Beads

    SciTech Connect

    Daniel, Richard C.; Poloski, Adam P.; Saez, Avelino E.

    2008-02-12

    The rheology of a single coarse granular powder has been studied with shear vane rotational viscometry. The torque required to maintain constant rotation of a vane tool in a confined bed of glass beads (with a mean particle size of 203 micrometers) is measured as a function of vane immersion depth and rotational speed. The resulting torque profiles exhibit both Coulombic behavior at low rotational rates and fluid-like behavior at high rotational rates. Analyzing vane shaft and end effects allows the flow dynamics at the cylindrical and top and bottom disk surfaces of vane rotation to be determined. Disk surfaces show a uniform torque profile consistent with Coulombic friction over most of the rotational rates studied. In contrast, cylindrical surfaces show both frictional and collisional torque contributions, with significant dynamic torque increases at deep immersion depths and fast vane rotation. A recently proposed constitutive equation is used to model the flow behavior. Semi-quantitative prediction is achieved at rotational rates both below 0.5 rad/s and above 10 rad/s. At slow vane speeds, the bed appears to be governed by a Janssen type normal stress distribution such that pressure saturates at deep immersions. This occurs because internal stresses are transmitted to the vane and container walls. For fast vane rotation, the particles in the vicinity of the vane behave as if they were fully fluidized, and the normal stress distributions influencing granular rheology are primarily lithostatic. Prediction at rotational rates from 0.5 rad/s to 10 rad/s is complicated by changes in the granular microstructure and stress fields resulting from partial fluidization of the bed. Overall, it is possible to characterize the quasi-static and partially fluidized flow regimes with a vane rheometer. Knowledge of how the granular normal stress profile changes as the granular material is fluidized could enable prediction in the intermediate flow regime.

  11. Rheological Behavior, Granule Size Distribution and Differential Scanning Calorimetry of Cross-Linked Banana (Musa paradisiaca) Starch.

    NASA Astrophysics Data System (ADS)

    Núñez-Santiago, María C.; Maristany-Cáceres, Amira J.; Suárez, Francisco J. García; Bello-Pérez, Arturo

    2008-07-01

    Rheological behavior at 60 °C, granule size distribution and Differential Scanning Calorimetry (DSC) tests were employed to study the effect of diverse reaction conditions: adipic acid concentration, pH and temperature during cross-linking of banana (Musa paradisiaca) starch. These properties were determined in native banana starch pastes for the purpose of comparison. Rheological behavior from pastes of cross-linked starch at 60 °C did not show hysteresis, probably due the cross-linkage of starch that avoided disruption of granules, elsewhere, native starch showed hysteresis in a thixotropic loop. All pastes exhibited non-Newtonian shear thinning behavior. In all cases, size distribution showed a decrease in the median diameter in cross-linked starches. This condition produces a decrease in swelling capacity of cross-linked starch. The median diameter decreased with an increase of acid adipic concentration; however, an increase of pH and Temperature produced an increase in this variable. Finally, an increase in gelatinization temperature and entalphy (ΔH) were observed as an effect of cross-linkage. An increase in acid adipic concentration produced an increase in Tonset and a decrease in ΔH. pH and temperature. The cross-linked of banana starch produced granules more resistant during the pasting procedure.

  12. Rheological behavior of Phanerochaete chrysosporium broth during lignin degradation.

    PubMed

    Hernández-Peñaranda, A M; Salazar-Montoya, J A; Rodriguez-Vázquez, R; Ramos-Ramirez, E G

    2001-01-01

    Rheological behavior of a lignin-degrading culture of Phanerochaete chrysosporium CDBB-H-298 was determined. Rheological characteristics revealed a Newtonian behavior in the culture medium without fungi, and a non-Newtonian dilatant behavior with fungi. In addition, the rheological behavior of the lignin-containing culture medium was complex, and changed from dilatant to pseudoplastic. During fungal growth without lignin in Kirk media rheological behavior exhibited a parabolic profile, and thixotropy showed a tendency to increase. Results indicated a small increase in the apparent viscosity in the presence of lignin; however, this may not affect the oxygen and mass transfer coefficients. The present findings can be applied to bioreactor desing for waste water treatment.

  13. An examination of the rheology of flocculated clay suspensions

    NASA Astrophysics Data System (ADS)

    Spearman, Jeremy

    2017-03-01

    A dense cohesive sediment suspension, sometimes referred to as fluid mud, is a thixotropic fluid with a true yield stress. Current rheological formulations struggle to reconcile the structural dynamics of cohesive sediment suspensions with the equilibrium behaviour of these suspensions across the range of concentrations and shear. This paper is concerned with establishing a rheological framework for the range of sediment concentrations from the yield point to Newtonian flow. The shear stress equation is based on floc fractal theory, put forward by Mills and Snabre (1988). This results in a Casson-like rheology equation. Additional structural dynamics is then added, using a theory on the self-similarity of clay suspensions proposed by Coussot (1995), giving an equation which has the ability to match the equilibrium and time-dependent viscous rheology of a wide range of suspensions of different concentration and mineralogy.

  14. Rheological aspects of mucin-containing solutions and saliva substitutes.

    PubMed

    Mellema, J; Holterman, H J; Waterman, H A; Blom, C; Gravenmade, E J

    1992-01-01

    In this study rheological properties of aqueous solutions of mucin, albumin and mucin-albumin have been investigated in search for saliva substitutes. They were compared with commercially available saliva substitutes on the one hand and natural human saliva on the other hand. For the latter a few measurements on saliva are reported here in addition to previously reported measurements done in our laboratory. Proteins absorb at the interface and saliva proteins do so strongly and rapidly. Therefore rheological measurements were carried out on the interface and on the bulk underneath the layer. In both cases the flow curve and the complex viscosity was determined. The results show that specific mucin-albumin solutions were rheologically similar to human whole saliva with respect to both bulk liquid and surface properties. The rheological properties of commercial saliva substitutes were essentially different from those of human saliva. It is concluded that mucin-albumin solutions have good perspectives as saliva substitutes.

  15. An examination of the rheology of flocculated clay suspensions

    NASA Astrophysics Data System (ADS)

    Spearman, Jeremy

    2017-04-01

    A dense cohesive sediment suspension, sometimes referred to as fluid mud, is a thixotropic fluid with a true yield stress. Current rheological formulations struggle to reconcile the structural dynamics of cohesive sediment suspensions with the equilibrium behaviour of these suspensions across the range of concentrations and shear. This paper is concerned with establishing a rheological framework for the range of sediment concentrations from the yield point to Newtonian flow. The shear stress equation is based on floc fractal theory, put forward by Mills and Snabre (1988). This results in a Casson-like rheology equation. Additional structural dynamics is then added, using a theory on the self-similarity of clay suspensions proposed by Coussot (1995), giving an equation which has the ability to match the equilibrium and time-dependent viscous rheology of a wide range of suspensions of different concentration and mineralogy.

  16. Rheological characterization of polyolefin composites with reduced flammability

    NASA Astrophysics Data System (ADS)

    Habrova, Veronika; Kalendova, Alena; Paravanova, Gordana

    2012-07-01

    In this work, the low-flammability halogen-free polyolefin composites were characterized with three rheological methods. In the extrusion process of the studied materials the end-products with a dissimilar surface quality were produced. Therefore, the diverse melt flow behaviours evaluated with common rheological techniques were also expected. Nevertheless, the conventional rotational and capillary rheometries were not able to describe the differences between investigated flame retarded composites in optimal way. Thus, the non-conventional rheological die Shark skin, originally designed to detect flow instabilities, was tested as a third possibility in order to better understand rheology of the filled polymer melts. It was found that the Shark skin technique is able to characterize the studied two kind flame retardants composites and can also be helpful to qualify the production bathes with identical additives/polymer formulation.

  17. 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

  18. 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.

  19. 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

  20. 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

  1. 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.

  2. 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

  3. Rheological behaviors of the fresh SFRCC extrudate: Experimental, theoretical and numerical investigations

    NASA Astrophysics Data System (ADS)

    Zhou, Xiangming

    Short fiber reinforced cementitious composites (SFRCC) manufactured by the extrusion technique exhibit significant improvements in physical, mechanical and durable properties as compared with the fiber-reinforced cementitious composites made by traditional manufacturing techniques. In the present study, first, various promising rheology and plasticity methods, including ram extrusion, orifice extrusion, capillary extrusion and upsetting, have been examined to investigate constitutive characteristics of the fresh SFRCC pastes for extrusion. In these experimental works, the traditional ram extrusion and orifice extrusion theories have been further developed and the capillary extrusion theory has been modified by taking the rate and the slip effects. The upsetting theory has been corrected to include the effects of boundary friction and strain rate. It has been found that the fresh SFRCC pastes show pseudo-plasticity and significant strain rate hardening behavior. Only by combing rheology and plasticity methods could it give a full description of the constitutive behavior of such pastes. Second, based on experimental and theoretical investigations, an elasto-viscoplastic constitutive model has been proposed for the fresh SFRCC paste, which considers the von Mises yield criterion, the associated flow rule and nonlinear isotropic strain rate-hardening. The model is formulated by introducing a strain rate-dependent yield function. The associated material parameters in the proposed constitutive model could be identified from material tests without the help of numerical methods. These parameters have been determined for the fresh SFRCC paste for extrusion in this study. Third, the proposed elasto-viscoplasticy constitutive model has been formulated in a computational form and implemented into the explicit finite element code ANSYS/LS-DYNA for simulation purposes. Various forming processes of the fresh SFRCC pastes, including upsetting and ram extrusion, have been simulated

  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.

  5. Determination of the mineral fraction and rheological properties of microwave modified starch from Canna edulis.

    PubMed

    Lares, Mary; Pérez, Elevina

    2006-09-01

    The goal of this study was to evaluate the effect of the physical modification by microwave irradiation on the mineral fraction and rheological properties of starch isolated from Canna edulis rhizomes. Phosphorus, sodium, potassium, magnesium, iron, calcium and zinc were evaluated using atomic absorption spectrophotometry. Rheological properties were determined using both the Brabender amylograph and Brookfield viscosimeter. Except for the calcium concentration, mineral contents decreased significantly (p < 0.05) after microwave treatment. The amylographic profile was also modified, showing increased pasting temperature range and breakdown index, whereas the viscosity peak, viscosity at holding (95 degrees C) and cooling periods (50 degrees C), setback and consistency decreased as compared to the native starch counterpart. Although viscosity decreased in the microwaved sample, presumably due to starch changes at molecular level, it retained the general pseudo plastic behavior of native starch. It is concluded that canna starch may be modified by microwave irradiation in order to change its functional properties. This information should be considered when using microwave irradiation for food processing. Furthermore, the altered functional attributes of canna modified starch could be advantageous in new product development.

  6. Rheology of Film-Forming Solutions Prepared with Modified Banana Starch and Plasticizer

    NASA Astrophysics Data System (ADS)

    Flores-Gómez, Yaritza; Sánchez-Rivera, Mirna; Romero-Bastida, Claudia; González-Soto, Rosalía; Bello-Pérez, Arturo; Solorza-Feria, Javier

    2008-07-01

    The physical properties of edible films depend to a great extent on those of their components; the biopolymer and the plasticizer, which define its physical changes during heat processing and handling. The aim of this work was to determine the rheological profile of film forming solutions (FFS) composed of native and modified (oxidized) banana starch and the plasticizer glycerol. Samples of FFS, composed by 4%(w/w) of native and oxidized banana starch and glycerol (4%(w/w) were prepared. Two types of rheological tests were undertaken using a strain controlled Rheometer TA Instruments, model AR1000, with a cone and plate system, 60 mm of diameter and angle of 2°: a) isothermal oscillatory (amplitude and frequency) tests at 25 °C, 90 °C and once cooled down, at 25 °C. b) temperature sweeps, run as the samples were heated up from 25 °C to 90 °C and also when cooled down to 25 °C. The isothermal tests showed that all pastes produced, behaved as weak viscoelastic gel-like materials, with the elastic modulus (G')> the viscous modulus (G″) over the entire frequency range. The temperature sweeps also showed that all viscoelastic FFS, behaved as mainly elastic materials over the temperature range. Overall, FFS from native starch yielded gels with higher moduli values than those of the oxidized ones.

  7. Effects of locust bean gum on the structural and rheological properties of resistant corn starch.

    PubMed

    Hussain, Raza; Singh, Ajaypal; Vatankhah, Hamed; Ramaswamy, Hosahalli S

    2017-03-01

    In this study, interactions between resistant corn starch (RS) (5% w/w) and locust bean gum (LBG) (0, 0.125, 0.25, 0.50 and 1.0% w/v) on the viscoelastic, pasting and morphological characteristics of aqueous dispersions were evaluated. Results showed that the storage modulus (G'), loss modulus (G''), and apparent viscosity values of starch/gum (RS/LBG) mixtures were enhanced with the addition of LBG, and the rheograms demonstrated a biphasic behavior. RS/LBG samples were predominantly either solid like (G' > G'') or viscous (G'' > G'), depending on the added concentration level of LBG. Gum addition also caused higher peak viscosity, breakdown and total set back of RS/LBG mixtures. A strong correlation between rheological and structural properties was found. Confocal laser scanning microscopy (CLSM) images confirmed the transition of starch particles from a scattered angular shape to clustered structures cross-linked by dense aggregate junction zones justifying the observed changes in rheological properties.

  8. Rheological characterization of hydraulic fracturing slurries

    SciTech Connect

    Shah, S.N. . Research and Engineering Dept.)

    1993-05-01

    Few studies have dealt with the flow behavior of concentrated suspensions or slurries prepared with non-Newtonian carrier fluids. Therefore, the purpose of this investigation is to present experimental results obtained by pumping various hydraulic fracturing slurries into a fracture model and gathering data on differential pressure vs. flow rate. Several concentrations of hydroxypropyl guard (HPG), a wide range of proppant concentrations, and three test temperatures were studies. The effects of such variables as polymer gelling-agent concentration, proppant concentration, test temperature, and fracture-flow shear rate on the rheological properties of slurries were investigated. The correlations for predicting the relative slurry viscosity for these HPG fluids are presented. Substantial increases in viscosity of fracturing gels were observed, and results are discussed in light of several affecting variables. Results also are compared with those available for Newtonian and non-Newtonian concentrated suspensions. Applications of these correlations to estimate the hindered particle-settling velocity in the fracture caused by the presence of surrounding particles also is discussed. The correlations presented can easily be included in any currently available 2D or 3D fracture-design simulators; thus, the information can be applied directly to predict fracture geometry and extension.

  9. The extrudate swell of HDPE: Rheological effects

    NASA Astrophysics Data System (ADS)

    Konaganti, Vinod Kumar; Ansari, Mahmoud; Mitsoulis, Evan; Hatzikiriakos, Savvas G.

    2017-05-01

    The extrudate swell of an industrial grade high molecular weight high-density polyethylene (HDPE) in capillary dies is studied experimentally and numerically using the integral K-BKZ constitutive model. The non-linear viscoelastic flow properties of the polymer resin are studied for a broad range of large step shear strains and high shear rates using the cone partitioned plate (CPP) geometry of the stress/strain controlled rotational rheometer. This allowed the determination of the rheological parameters accurately, in particular the damping function, which is proven to be the most important in simulating transient flows such as extrudate swell. A series of simulations performed using the integral K-BKZ Wagner model with different values of the Wagner exponent n, ranging from n=0.15 to 0.5, demonstrates that the extrudate swell predictions are extremely sensitive to the Wagner damping function exponent. Using the correct n-value resulted in extrudate swell predictions that are in excellent agreement with experimental measurements.

  10. 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.

  11. 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.

  12. 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.

  13. Rheological studies of polysaccharides for skin scaffolds.

    PubMed

    Almeida, Nalinda; Mueller, Anja; Hirschi, Stanley; Rakesh, Leela

    2014-05-01

    Polysaccharide hydrogels are good candidates for skin scaffolds because of their inherent biocompatibility and water transport properties. In the current study, hydrogels were made from a mixture of four polysaccharides: xanthan gum, konjac gum, iota-carrageenan, and kappa-carrageenan. Gel formation, strength, and structure of these polysaccharides were studied using rheological and thermal techniques. All gel samples studied were strong gels at all times because of the gradual water loss. However, after 12 h of storage, elastic (G') and loss (G'') moduli of hydrogel mixture containing all the ingredients is of one to two orders of magnitude greater than that of mixtures not containing either xanthan gum or iota-carrageenan, which confirmed the varied levels of gel strength. This is mainly due to the rate of water loss in each of these mixtures, resulting in gels of varying structures and dynamic moduli over a period of time. Iota-carrageenan and xanthan gum differ in their effect on gel strength and stability in combination with konjac gum and kappa-carrageenan.

  14. Rheological properties of asphalts with particulate additives

    SciTech Connect

    Shashidhar, N.; Chollar, B.H.

    1996-12-31

    The Superpave asphalt binder specifications are performance-based specifications for purchasing asphalt binders for the construction of roads. This means that the asphalt is characterized by fundamental material (rheological) properties that relate to the distress modes of the pavements. The distress modes addressed are primarily rutting, fatigue cracking and low temperature cracking. For example, G*/sin({delta}) is designed to predict the rutting potential of pavements, where G* is the magnitude of the complex shear modulus and 6 is the phase angle. The binder for a road that is situated in a certain climatic zone requires the binder to have a minimum G*/sin({delta}) of 2200 Pa at the highest consecutive 7-day average pavement temperature the road had experienced. Implicit in such a performance based specification is that the fundamental property, G*/sin({delta}), of the binder correlates with rutting potential of the pavement regardless of the nature of the binder. In other words, the specification is transparent to the fact that the binder can simply be an asphalt, or an asphalt modified by polymers, particulates and other materials that can form a two-phase mixture. This paper discusses the asphalt-particulate system.

  15. 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.

  16. 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.

  17. Effect of Confinement on Suspension Rheology

    NASA Astrophysics Data System (ADS)

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

    Confined systems are ubiquitous in nature and occur at widely separated length scales from the atomic to granular. While the flow properties of both atomic and granular systems has been well studied, examining the rheology of the intermediate length scale in colloidal suspensions is challenging. We use a confocal rheoscope to image the particle configuration in a suspension of silica microspheres 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 30 particle diameters, allowing us to measure the response of the system as a function of the gap size. We find that the viscosity of the system decreases with confinement in sharp contrast to the increase reported in atomic and granular systems. The microscopy images indicate that this decrease in viscosity is due to the formation of particle layers in this shear regime where hydrodynamic forces dominate particle interactions. We discuss these results and their implications.

  18. 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.

  19. Controlling Stability and Rheology of Organic Foams

    NASA Astrophysics Data System (ADS)

    Kropka, Jamie; Celina, Mathew

    2009-03-01

    It is often important to understand the stability and flow properties of polymeric foams in order to optimize industrial processing conditions or design new materials. The fact that foaming, polymerization and temperature rise are often coupled in these systems makes it difficult to even characterize existing materials, much less model behaviors to optimize formulations and processing conditions. To make progress in this area, we have developed model foaming systems that decouple these processes and allow us to characterize the physical properties of liquid foams. We are specifically interested in understanding the controlling factors of foam persistence, shear stability, and rheological behavior. We show both chemical (e.g., partial polymerization) and physical (e.g., particulate additives) means of tuning foam persistence as well as both small strain deformation flow and the less understood liquid-like flow at high applied stresses. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

  20. 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.

  1. Weird Past Tense Forms.

    ERIC Educational Resources Information Center

    Xu, Fei; Pinker, Steven

    1995-01-01

    Presents an analysis of past tense and participle usages by children, focusing on overapplications of irregular vowel-change patterns, as in "brang"; blends, as in "branged"; productive suffixations of "-en," as in "walken"; gross distortions, as in "mail-membled"; and double-suffixation, as in "walkeded." Findings indicate that these errors are…

  2. 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)

  3. 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)

  4. 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)

  5. The rheological behavior of a fast-setting calcium phosphate bone cement and its dependence on deformation conditions.

    PubMed

    Şahin, Erdem; Kalyon, Dilhan M

    2017-08-01

    Calcium phosphate cements are osteoconductive biomaterials that are widely used for bone repair and regeneration applications, including spinal fusion, vertebroplasty, khyphoplasty, cranioplasty and periodontal surgeries. The flow and deformation behavior (rheology) and injectability of the calcium phosphate bone cements to the treatment site are governed by the setting kinetics of the cement during which the initially flowable, viscous cement paste transforms into a rigid elastic solid. Here time-dependent development of the linear viscoelastic properties of a brushite-forming calcium phosphate cement are characterized and linked to the mechanism and kinetics of the setting reaction and to the injectability window available during the surgical applications of the cement. The setting kinetics is shown to be a function of the deformation conditions that are utilized in rheological characterization, emphasizing the intimate relationships between setting kinetics, particle to particle network formation and deformation history. Furthermore, the preshearing of the calcium phosphate cement prior to injection and temperature are shown to alter the kinetics of the setting reaction and thus to provide additional degrees of freedom for the tailoring of the rheological behavior and injectability of the calcium phosphate cement. Copyright © 2017 Elsevier Ltd. All rights reserved.

  6. 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

  7. Rheological properties of polyvinylsiloxane impression materials before mixing and during setting related to handling characteristics

    NASA Astrophysics Data System (ADS)

    Lee, Hyang-Ok; Lee, In-Bog

    2012-09-01

    The purpose of this study is to determine and compare the handling and rheological properties of polyvinylsiloxane impression pastes before mixing and during setting, and to investigate the effect of its constituents on the properties of the materials. Five polyvinylsiloxane impression materials (Examixfine, Extrude, Honigum, Imprint II, and Express) were used. A flow test and a drip test were performed to determine the handling characteristics. The rheological properties of each impression material prior to mixing (shear stress, viscosity) and during setting (storage modulus G'), loss modulus G″), loss tangent tanδ) were measured with a stress-controlled rheometer at 25°C and 32°C, respectively. Inorganic filler content of each impression material was measured and observed with a SEM. The molecular weight distribution of polymer matrix was determined with a gel permeation chromatography (GPC). Express and Honigum display lower flow compared to the other materials, due to their high yield-stress values. Examixfine exhibits the greatest flow. All materials display pseudoplastic behavior, excluding the Examixfine catalyst. The viscosities at low shear rate are greatest for Express and Honigum; however, under high shear conditions, the viscosities of Extrude and Honigum are the lowest. Following mixing, each material show an increase in G', finally reaching a plateau, and the tanδ rapidly decreases with time. Imprint II shows the highest final G' as well as the most rapid decrease in tanδ. Express and Imprint II present the highest filler content and rough filler surface, while Honigum shows the lowest filler content and small filler particles. Most products are composed of polymers over 30 kDa and oligomers less than 1 kDa. Each impression material possesses different rheological properties, which significantly affect the handling characteristics. The yield stress of the impression material minimizes unnecessary flow prior to and after seating. Viscoelastic

  8. 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.

  9. Rheological behavior or bauxite- and alumina-based castables

    NASA Astrophysics Data System (ADS)

    Ye, Fangbao

    In this cooperative work between Ecole Polytechnique, Canada and Zhengzhou University, China initiated in 2000, the following subjects have been studied: (1) the rheological properties of the matrix part of bauxite-based castables; (2) the rheological properties of SiC containing bauxite-based castables; (3) the high temperature mechanical properties of the SiC containing bauxite-based castables; (4) the rheological behavior of low cement alumina-based castable with and without graphite addition; (5) the rheological behavior of zero cement alumina-based castable with and without MgO and/or graphite addition. At first it was intended to optimize the factors affecting the rheological behaviour of a slurry containing up to 80% solids (such as super-fine silica and alumina addition, water/cement ratio, type and content of dispersants and powder particle-size), to use them in later work on the rheology of castables. The second and third subjects were tackled to understand the relationship between rheological behavior and high temperature properties and to optimize these properties for conventional castable used in iron making industry. The fourth and fifth subjects were initiated to contribute to the understanding of rheological properties of new alumina-based castables, containing magnesia and carbon. The goals in each case are to identify the parameters which influence the most shear thinning or the shear thickening of mixes by measuring the rheological characteristics, torque viscosity and yield stress (from rheometer) for self-flow and pumpable castables, and to assess the optimal conditions in the formulation of different mixes, including these newly developed carbon-containing castables, yet to be commercialized, at least those containing graphite. In total, more than 200 different mixes have been prepared and their rheological behaviour studied. For this purpose, three methods have been used: (1) Rotational viscometer---for study on rheology of matrix slurry; (2

  10. 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

  11. A rheological constitutive model for semiconcentrated rod suspensions in Bingham fluids

    NASA Astrophysics Data System (ADS)

    Férec, J.; Bertevas, E.; Khoo, B. C.; Ausias, G.; Phan-Thien, N.

    2017-07-01

    A rheological constitutive law is developed for a suspension of rigid rods in a Bingham fluid for volume fractions ranging up to the semiconcentrated regime. Based on a cell model approach, which allows expressing the shear stress on the particle surface, the particle stress contribution is derived and involves additional yield stress terms related to an ensemble average orientation distribution of the rods. As a first approach, a von Mises criterion is used to describe the composite flow threshold, which is found to be anisotropic in the sense that it depends on the rod orientation. A rod dynamics equation is also proposed and incorporates some diffusion/perturbation due to yielded regions encountered throughout the suspension. In parallel, an equivalent kinetic theory is also developed. The model provides good agreement with shear stress experiments for kaolin pastes filled with steel fibers of two different aspect ratios.

  12. 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.

  13. Assessment of chapatti quality of wheat varieties based on physicochemical, rheological and sensory traits.

    PubMed

    Kundu, Manju; Khatkar, Bhupendar Singh; Gulia, Neelam

    2017-07-01

    Fifty wheat varieties were assessed for chapatti quality using grain characteristics, dough rheological properties and pasting characteristics. Results revealed that 88% of wheat varieties studied were medium-hard to hard based on kernel texture. Water absorption and damaged starch were found to be important parameters for chapatti quality as both parameters had significant positive effect on the pliability and puffing height of chapatti. Protein content and gluten strength parameters like SDS sedimentation volume, dough stability and gluten index were found to have a negative impact on chapatti quality. Based on chapatti quality assessment the wheat varieties were classified into four distinct clusters viz. good, acceptable, fair and poor for chapatti making. It was elucidated that 46% of the varieties studied were good to acceptable for chapatti making, while 54% resulted in fair or poor chapatti quality thereby clearly indicating the need to establish and substantiate the development of product-specific varieties.

  14. [Determination of the gelatinization temperature of starches via thermoanalytical and rheological methods].

    PubMed

    Szepes, Aniko; Fehér, András; Eros, István; Szabóné, Révész Piroska

    2007-01-01

    This work provides a short review concerning the measuring techniques frequently applied to characterize the gelatinization behaviour of starches. The aim of the experiments was to determine the gelatinization temperatures of maize (A-type) and potato (B-type) starches via isothermal microcalorimetry and rheological methods (rotational viscosimetry and dynamic oscillatory testing). A significant difference was observed between the gelatinization temperatures of the aqueous starch suspensions, which can be attributed to the structural differences between A-type and B-type starches. Comparison of the applied measuring methods revealed a close correlation between the experimental data obtained by isothermal microcalorimetry and oscillatory testing, while rotational viscosimetry overestimated the gelatinization temperature. Additionally dynamic oscillatory tests provided valuable information not only on the gelatinization point, but also on the pasting temperature of the starch suspensions.

  15. 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

  16. Numerical Simulation of Rheology Character of Polymer Extrusion Flow in the Micro Channel

    NASA Astrophysics Data System (ADS)

    Ren, Zhong; Huang, Xing-Yuan; Liu, He-Sheng

    2016-05-01

    In this study, to study the rheology characteristic of polymer melt in the micro-channel, the apparent viscosity, entrance pressure and shear stress under the same shear rate were analyzed by mean of CFD numerical simulation method. The Phan-Thien and Tanner (PTT) viscoelastic model was used as the constructive equation of polymer melt. To verify the change situation of apparent viscosity and entrance pressure in the flow of channel, two sets of channels with different diameters and ratios of length-to-diameter were compared with each other. The research results verified that the entrance pressure increase and apparent viscosity decrease with decreasing of diameter of channel, which is in good agreement with the results of past reported.

  17. Concentration dependence of rheological properties of telechelic associative polymer solutions

    NASA Astrophysics Data System (ADS)

    Uneyama, Takashi; Suzuki, Shinya; Watanabe, Hiroshi

    2012-09-01

    We consider concentration dependence of rheological properties of associative telechelic polymer solutions. Experimental results for model telechelic polymer solutions show rather strong concentration dependence of rheological properties. For solutions with relatively high concentrations, linear viscoelasticity deviates from the single Maxwell behavior. The concentration dependence of characteristic relaxation time and moduli is different in high- and low-concentration cases. These results suggest that there are two different concentration regimes. We expect that densely connected (well percolated) networks are formed in high-concentration solutions, whereas sparsely connected (weakly percolated) networks are formed in low-concentration solutions. We propose single chain type transient network models to explain experimental results. Our models incorporate the spatial correlation effect of micellar cores and average number of elastically active chains per micellar core (the network functionality). Our models can reproduce nonsingle Maxwellian relaxation and nonlinear rheological behavior such as the shear thickening and thinning. They are qualitatively consistent with experimental results. In our models, the linear rheological behavior is mainly attributable to the difference of network structures (functionalities). The nonlinear rheological behavior is attributable to the nonlinear flow rate dependence of the spatial correlation of micellar core positions.

  18. Toothpaste microstructure and rheological behaviors including aging and partial rejuvenation

    NASA Astrophysics Data System (ADS)

    Liu, Zhiwei; Liu, Lei; Zhou, Huan; Wang, Jiali; Deng, Linhong

    2015-08-01

    Toothpastes are mainly composed of a dense suspension of abrasive substances, flavors, and therapeutic ingredients in a background liquid of humectants and water, and usually exhibit complex rheological behaviors. However, the relationship between the rheology and microstructure of toothpaste remains to be studied. In this paper, three commonly used toothpastes, namely Colgate, Darlie and Yunnan Baiyao (Ynby), were qualitatively and quantitatively studied as soft glassy materials. We found that although the three toothpastes generally behaved in similar fashion in terms of rheology, each particular one was distinct from others in terms of the quantitative magnitude of the rheologcial properties including thixotropy, creep and relaxation, yield stress, and power-law dependence of modulus on frequency. In addition, the history-dependent effects were interpreted in terms of aging and rejuvenation phenomena, analogous to those existing in glassy systems, and Ynby seemed to result in greater extent of aging and rejuvenation as compared to the other two. All these differences in toothpaste rheology may well be attributed to the different microscopic network microstructures as observed in this study. Therefore, this study provides first evidence of microstructurebased rheological behaviors of toothpaste, which may be useful for optimizing its composition, manufacturing processing as well as end-user applications.

  19. 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.

  20. Factors That Influence the Extensional Rheological Property of Saliva

    PubMed Central

    Vijay, Amrita; Inui, Taichi; Dodds, Michael; Proctor, Gordon; Carpenter, Guy

    2015-01-01

    The spinnbarkeit of saliva reflects the ability of saliva to adhere to surfaces within the mouth, thereby serving as a protective role and aiding in lubrication. Therefore, alterations in the extensional rheology of saliva may result in the loss in adhesiveness or the ability to bind onto surfaces. Mucin glycoproteins and their structures are known to be important factors for the extensional rheological properties of saliva. The conformation of mucin depends on factors such as pH and ionic strength. Chewing is one of the main stimuli for salivary secretion but creates significant sheer stress on the salivary film which could influence mouthfeel perceptions. The current study investigates the possible factors which affect the extensional rheological properties of saliva by comparing submandibular/sublingual saliva with different oral stimuli within the same group of subjects. Unstimulated and stimulated saliva (chew, smell and taste) salivas were collected primarily from submandibular/sublingual glands. The saliva samples were measured for Spinnbarkeit followed by the measuring mucin, total protein, total calcium and bicarbonate concentrations. The results indicated correlations between rheological properties and mucin/ion concentrations. However, chewing stimulated submandibular/sublingual saliva is shown to have significantly lower Spinnbarkeit, but factors such as mucin, protein and calcium concentrations did not account for this variation. Analysis of the concentration of bicarbonate and pH appears to suggest that it has a prominent effect on extensional rheology of saliva. PMID:26305698

  1. Relation between sensory analysis and rheology of body lotions.

    PubMed

    Moravkova, T; Filip, P

    2016-12-01

    Evaluation of sensory attributes of cosmetic products is traditionally based on sensory panels. However, in some cases, a suitable candidate method that can reduce time and costs is the use of instrumental analysis that can detect relatively very small changes of entry ingredients. Such approach has been already applied for emollients, salt content, stabilizers, etc. The aim of this contribution is to apply the relations between sensory analysis and rheology to a series of body lotions differing in the contents of emulsifiers and viscosity regulators. Sensory and rheological analyses are related. Rheological analysis can represent a good alternative to basic orientation in chosen customer's feelings. A rotational rheometer is the only instrumental device required for the measurements. An empirical rheological model was proposed by means of which the selected sensory attributes were evaluated using the numerical values of adjustable model parameters. This approach exhibited a very good agreement with the results obtained by the sensory panel. It was shown that a description of chosen sensory attributes can be responsibly carried out by rheological measurements, that is through the attained numerical values of the parameters appearing in a proposed empirical model characterizing shear viscosity of body lotions. © 2016 Society of Cosmetic Scientists and the Société Française de Cosmétologie.

  2. Factors That Influence the Extensional Rheological Property of Saliva.

    PubMed

    Vijay, Amrita; Inui, Taichi; Dodds, Michael; Proctor, Gordon; Carpenter, Guy

    2015-01-01

    The spinnbarkeit of saliva reflects the ability of saliva to adhere to surfaces within the mouth, thereby serving as a protective role and aiding in lubrication. Therefore, alterations in the extensional rheology of saliva may result in the loss in adhesiveness or the ability to bind onto surfaces. Mucin glycoproteins and their structures are known to be important factors for the extensional rheological properties of saliva. The conformation of mucin depends on factors such as pH and ionic strength. Chewing is one of the main stimuli for salivary secretion but creates significant sheer stress on the salivary film which could influence mouthfeel perceptions. The current study investigates the possible factors which affect the extensional rheological properties of saliva by comparing submandibular/sublingual saliva with different oral stimuli within the same group of subjects. Unstimulated and stimulated saliva (chew, smell and taste) salivas were collected primarily from submandibular/sublingual glands. The saliva samples were measured for Spinnbarkeit followed by the measuring mucin, total protein, total calcium and bicarbonate concentrations. The results indicated correlations between rheological properties and mucin/ion concentrations. However, chewing stimulated submandibular/sublingual saliva is shown to have significantly lower Spinnbarkeit, but factors such as mucin, protein and calcium concentrations did not account for this variation. Analysis of the concentration of bicarbonate and pH appears to suggest that it has a prominent effect on extensional rheology of saliva.

  3. Osteoarthritic synovial fluid rheology and correlations with protein concentration.

    PubMed

    Madkhali, Anwar; Chernos, Michael; Grecov, Dana; Kwok, Ezra

    2016-11-09

    Osteoarthritis is a common, localized joint disease that causes pain, stiffness and reduced mobility. Osteoarthritis is particularly common in the knees. The effects of osteoarthritis on the rheology of synovial fluid in the knees are not fully understood and consequently require further study. The purpose of this study is to investigate the effects of protein content on synovial fluid shear rheology. A secondary study outcome will include study of the temperature dependence of synovial fluid behaviour. 38 osteoarthritic synovial fluid samples were studied under shear flow. Shear properties were correlated with protein concentration. Viscosupplement was used as a comparison and to verify measurement reliability. The effects of temperature were investigated at 20, 29 and 37°C. Shear rheological properties were found to vary widely between samples, however all samples demonstrated clear non-Newtonian shear thinning behaviour. In general viscoelastic properties were lower in osteoarthritic samples than previously studied healthy synovial fluid. A moderate correlation was observed between synovial fluid dynamic moduli at a frequency of 2.5 Hz and protein concentration. Temperature was found to affect the rheology of osteoarthritic synovial fluid and was fitted with the Arrhenius model. Increased protein concentration has been correlated with decreased shear rheological parameters. Temperature dependence of synovial fluid was also demonstrated and modelled for use in Part 2 of this article.

  4. 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

  5. Rheological evolution of a Mediterranean subduction complex

    NASA Astrophysics Data System (ADS)

    Behr, Whitney Maria; Platt, John Paul

    2013-09-01

    We use field and microstructural observations, coupled to previously published P-T-time histories, to track the rheological evolution of an intracontinental subduction complex exposed in the Betic Cordillera in the western Mediterranean region. The body of rock we focus on, known as the Nevado-Filabride Complex (NFC), was originally part of the upper crust of the Iberian margin. It was subducted into hot asthenospheric mantle, then exhumed back toward the surface in two stages: an early stage of fast exhumation along the top of the subducting slab in a subduction channel, and a late stage of slower exhumation resulting from capture by a low-angle detachment fault rooted at the brittle-ductile transition. Each stage of deformation in the NFC was punctuated by changes in the dominant deformation mechanism. Deformation during initial subduction of the complex was accommodated by pressure-solution creep in the presence of a fluid phase - the grain sizes, stress magnitudes, and estimated strain rates for this stage are most consistent with a thin-film model for pressure solution in which the diffusion length scale is controlled by the grain size. During the early stages of exhumation within the subduction channel, deformation transitioned from pressure solution to dislocation creep due to increases in temperature, which resulted in increases in both water fugacity and grain size, each of which favor the dislocation creep mechanism. Differential stress magnitudes for this stage were ˜10 MPa, and are consistent with simple models of buoyancy-driven channel flow. With continuing subduction-channel exhumation, deformation remained within the dislocation creep field because sequestration of free water into hydrous, retrogressive minerals suppressed the pressure-solution mechanism. Differential stresses progressively increased to ˜100 MPa near the mouth of the channel during cooling as the rocks moved into mid-crustal levels. During the final, core-complex stage of

  6. 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

  7. 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.

  8. Coating Of Model Rheological Fluids In Microchannels

    NASA Astrophysics Data System (ADS)

    Koelling, Kurt; Boehm, Michael

    2008-07-01

    Researchers have strived to understand and quantify the dynamics within the myriad micro/nano-devices proposed and developed within the last decade. Concepts such as fluid flow, mass transfer, molecule manipulation, and reaction kinetics must be understood in order to intelligently design and operate these devices. In addition to general engineering principles, intelligent design should also focus on material properties (e.g. density, viscosity, conductivity). One key property, viscosity, will play a large part of any fluidic device, including biomedical devices, because the fluids used will, most likely, be non-Newtonian and therefore highly dependent upon the shear rate. Be it a biomedical or macromolecule separation device, or simply the processing of polymeric material, select model polymers and simple flow schemes can be used to investigate the dynamics within micro-devices. Here, we present results for the processing of Newtonian and non-Newtonian polymeric fluids in micro-channels during two-phase penetrating flow. The system investigated is a circular capillary 100 microns in diameter, which is pre-filled with a polymeric liquid. The polymeric liquid is either of Newtonian viscosity, or the same liquid with dispersed high molecular weight polystyrene, which exhibits viscoelastic behavior. A second, immiscible phase, silicone oil of low Newtonian viscosity, is pumped into the system and subsequently cores the polymeric liquid. The dynamics of bubble flow (e.g. bubble velocity and bubble shape) as well as the influence of rheology on coating will be investigated. By studying these model systems, we will learn how complex fluids behave on progressively smaller size scales.

  9. 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”).

  10. 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.

  11. Rheology of fetal and maternal blood.

    PubMed

    Reinhart, W H; Danoff, S J; King, R G; Chien, S

    1985-01-01

    Rheological parameters were measured in 10 pairs of mothers and newborns. Whole blood viscosity was similar despite a higher fetal hematocrit (47.0 +/- 5.1 versus 35.5 +/- 12.0%, mean +/- SD, p less than 0.05). When the hematocrit of the suspension of red cells in plasma was adjusted to 45%, the viscosity was significantly lower in the fetal blood over a wide range of shear rates (0.52-208 S-1). The main reason for the lower viscosity in the fetal blood was the lower plasma viscosity as compared to the maternal blood (1.08 +/- 0.05 versus 1.37 +/- 0.08 centipoise, p less than 0.05); this in turn was attributable to a lower total plasma protein concentration (4.74 +/- 0.71 versus 6.47 +/- 0.64 g/dl, p less than 0.05). All protein fractions were lower in the fetal plasma. The assessment of red cell deformability by filtration through polycarbonate sieves revealed that the resistance of a fetal red cell was three times higher than that of a maternal red cell in a 2.6-micron pore, but there was no significant difference in resistance for these red cells in 6.9-micron pores. This higher filtration resistance of fetal red cells through the small pores was mainly due to their large volume (115.4 +/- 10.8 versus 93.5 +/- 5.9 fl, p less than 0.001). Measurements on membrane-free hemoglobin solutions indicated that the internal viscosity of these two types of red cells was not different.(ABSTRACT TRUNCATED AT 250 WORDS)

  12. Linking enclave formation to magma rheology

    NASA Astrophysics Data System (ADS)

    Hodge, K. F.; Jellinek, A. M.

    2012-10-01

    Magmatic enclaves record the history of deformation and disaggregation (i.e., fragmentation) of relatively hot, compositionally more mafic magmas injected into actively convecting silicic magma chambers through dikes. Enclave size distributions may provide crucial clues for understanding the nature of this mechanical mixing process. Accordingly, we conduct a comprehensive field study to measure enclave size distributions in six Cascade lava flows. Using results from recent fluid dynamics experiments along with thermodynamic and modeling constraints on key physical properties of the injected and host magmas (i.e., temperature, density and effective viscosity), we use the size distributions of enclaves to characterize the magmatic flow regime governing enclave formation. Scaling arguments suggest that the viscous stresses related to magma chamber flow acting against the yield strength of a crystallizing injected magma control the breakup of 1 m-wide mafic dikes into millimeter- to centimeter-scale enclaves. Our data analysis identifies a characteristic length scale of breakup that constrains the yield strength of the injected magmas in a more restrictive way than existing empirical models for yield strength based on crystal content. In all six lava flows, we show that the progressive fragmentation of the injected magma is self-similar and characterized by a fractal dimensionDf ˜ 2, which is comparable to previous studies on enclaves. We also find a small but statistically significant dependence of Df on the effective viscosity ratio between host and enclave magmas, such that large variations in effective viscosity enhance breakup. This work demonstrates that field observations of enclave size distributions can reliably constrain the rheological and flow conditions in which enclaves form.

  13. Study of effect of excipient source variation on rheological behavior of diltiazem HCl-HPMC wet masses using a mixer torque rheometer.

    PubMed

    Chatlapalli, Ramarao; Rohera, Bhagwan D

    2002-05-15

    In the wet massing of powders and powder blends, the rheological behavior of the wet powder masses not only plays a critical role in the unit process but also influences the attributes of the product. The physical properties of the powder excipients, such as particle size and size distribution, shape, surface area, bulk and tapped density and surface morphology, are a major source of variability in the rheological behavior of wet powder masses and the quality attributes of the final product. The objective of the present investigations was to study the rheological behavior of wet masses containing hydroxypropyl methylcellulose (HPMC) obtained from two sources (Methocel from Dow and Pharmacoat from Shin-Etsu) using a mixer torque rheometer. In order to simulate a real formulation, diltiazem HCl (DTZ) (40% loading) was used as part of the substrate powder mass. Hydroxypropyl cellulose (HPC) was used as the binder. Since HPMC is water-soluble, isopropyl alcohol (IPA) was used as the wet massing liquid. The rheological behavior of the wet powder masses was studied as a function of mixing time and amount of wet massing liquid (IPA). The rheological profiles obtained for DTZ-Methocel and DTZ-Pharmacoat exhibited same magnitude for mean torque, however, for DTZ-Pharmacoat the peak was more extended than that for DTZ-Methocel. The extended peak for DTZ-Pharmacoat indicated that the wet mass will stay suitable during the process for larger quantities of the wet massing liquid before turning into paste and becoming unsuitable for the process as compared with the DTZ-Methocel system. The mixing kinetics of the two powder systems appeared to be quite different. These differences in the rheological behavior of the wet masses may be attributed to the difference in the particulate and surface properties of the two HPMCs. Some of the properties of the two HPMCs, such as particle size and size distribution, surface area, surface morphology and DSC thermograms, explain the difference

  14. Impact Features on Europa: Rheological and Thermal States of the Icy Crust

    NASA Astrophysics Data System (ADS)

    Mevel, L.; Grasset, O.; Mercier, E.

    2001-03-01

    Rheological and thermal characteristics of Europa icy crust are studied in the two impact features Tyre and Callanish. The importance of grain size, composition, and deformation rates, on the rheological structure of the icy crust are investigated.

  15. Gap Dependent Rheology in Type I Collagen Gels

    NASA Astrophysics Data System (ADS)

    Arevalo, Richard; Urbach, Jeffrey; Blair, Daniel

    2010-03-01

    Branched type I collagen fiber networks provide extracellular support in mammalian tissues. The intricate network structure can succumb to partial or complete tearing under sufficient applied strain. Under small shear strains, in vitro collagen gels exhibit strain-stiffening while maintaining overall network integrity. Higher shear strains lead to network failure through discrete yielding events. We perform rheology and confocal-rheology experiments to fully elucidate the strain-stiffening and yielding behavior in these highly nonlinear materials. We apply continuous shear strains to collagen gels confined within the rheometer at fixed gaps. We observe that sheared collagen in the strain-stiffening and yielding regime has an apparent modulus that is strongly dependent on the collagen thickness. Moreover, we demonstrate that network yielding is universally controlled by the ratio of the collagen thickness to the mesh size. These results have broad implications for the interpretation of rheological data of extracellular matrix proteins and for the design of biomimetic scaffolds.

  16. 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.

  17. Rheology of semiflexible bundle networks with transient linkers.

    PubMed

    Müller, Kei W; Bruinsma, Robijn F; Lieleg, Oliver; Bausch, Andreas R; Wall, Wolfgang A; Levine, Alex J

    2014-06-13

    We present a theoretical and computational analysis of the rheology of networks made up of bundles of semiflexible filaments bound by transient cross-linkers. Such systems are ubiquitous in the cytoskeleton and can be formed in vitro using filamentous actin and various cross-linkers. We find that their high-frequency rheology is characterized by a scaling behavior that is quite distinct from that of networks of the well-studied single semiflexible filaments. This regime can be understood theoretically in terms of a length-scale-dependent bending modulus for bundles. Next, we observe new dissipative dynamics associated with the shear-induced disruption of the network at intermediate frequencies. Finally, at low frequencies, we encounter a region of non-Newtonian rheology characterized by power-law scaling. This regime is dominated by bundle dissolution and large-scale rearrangements of the network driven by equilibrium thermal fluctuations.

  18. 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.

  19. 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.

  20. 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.

  1. Numerical Implementation of Ice Rheology for Europa's Shell

    NASA Technical Reports Server (NTRS)

    Barr, A. C.; Pappalardo, R. T.

    2004-01-01

    We present a discussion of approximations to the temperature dependent part of the rheology of ice. We have constructed deformation maps using the superplastic rheology of Goldsby & Kohlstedt and find that the rheologies that control convective flow in the Europa's are likely grain boundary sliding and basal slip for a range of grain sizes 0.1 mm < d < 1 cm. We compare the relative merits of two different approximations to the temperature dependence of viscosity and argue that for temperature ranges appropriate to Europa, implementing the non-Newtonian, lab-derived flow law directly is required to accurately judge the onset of convection in the ice shell and temperature gradient in the near-surface ice.

  2. 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.

  3. Rheological Characterization of Unusual DWPF Slurry Samples (U)

    SciTech Connect

    Koopman, D. C.

    2005-09-01

    A study was undertaken to identify and clarify examples of unusual rheological behavior in Defense Waste Processing Facility (DWPF) simulant slurry samples. Identification was accomplished by reviewing sludge, Sludge Receipt and Adjustment Tank (SRAT) product, and Slurry Mix Evaporator (SME) product simulant rheological results from the prior year. Clarification of unusual rheological behavior was achieved by developing and implementing new measurement techniques. Development of these new methods is covered in a separate report, WSRC-TR-2004-00334. This report includes a review of recent literature on unusual rheological behavior, followed by a summary of the rheological measurement results obtained on a set of unusual simulant samples. Shifts in rheological behavior of slurries as the wt. % total solids changed have been observed in numerous systems. The main finding of the experimental work was that the various unusual DWPF simulant slurry samples exhibit some degree of time dependent behavior. When a given shear rate is applied to a sample, the apparent viscosity of the slurry changes with time rather than remaining constant. These unusual simulant samples are more rheologically complex than Newtonian liquids or more simple slurries, neither of which shows significant time dependence. The study concludes that the unusual rheological behavior that has been observed is being caused by time dependent rheological properties in the slurries being measured. Most of the changes are due to the effect of time under shear, but SB3 SME products were also changing properties while stored in sample bottles. The most likely source of this shear-related time dependence for sludge is in the simulant preparation. More than a single source of time dependence was inferred for the simulant SME product slurries based on the range of phenomena observed. Rheological property changes were observed on the time-scale of a single measurement (minutes) as well as on a time scale of hours

  4. Numerical Implementation of Ice Rheology for Europa's Shell

    NASA Technical Reports Server (NTRS)

    Barr, A. C.; Pappalardo, R. T.

    2004-01-01

    We present a discussion of approximations to the temperature dependent part of the rheology of ice. We have constructed deformation maps using the superplastic rheology of Goldsby & Kohlstedt and find that the rheologies that control convective flow in the Europa's are likely grain boundary sliding and basal slip for a range of grain sizes 0.1 mm < d < 1 cm. We compare the relative merits of two different approximations to the temperature dependence of viscosity and argue that for temperature ranges appropriate to Europa, implementing the non-Newtonian, lab-derived flow law directly is required to accurately judge the onset of convection in the ice shell and temperature gradient in the near-surface ice.

  5. Mantle Rheology and Plate Tectonics: Damage and Inheritance

    NASA Astrophysics Data System (ADS)

    Ricard, Y. R.; Bercovici, D.; Schubert, G.

    2014-12-01

    The specific rheology of the lithosphere that allows the existence of plate tectonics on Earth is poorly understood. This rheology must explain why plate tectonics initiated on Earth but not on Venus, which has very similar size and gravity, but also how changes in plate motion can occur on time scales more rapid than that of the deeper convection (~100 myrs). We suggest that a key ingredient of this rheology is the coupling of the grain size evolution of the polycrystalline rocks that constitute the mantle, with the flow. We demonstrate this process using a grain evolution and damage mechanism (Bercovici and Ricard, 2012) with a composite rheology, which are compatible with field and laboratory observations. Our model predicts that the grain size is controlled by an dynamic equilibrium where deformation tends to reduce the grain sizes which otherwise would spontaneously increase. The presence of secondary phases is crucial as it eases the grain size reduction and inhibits their too fast recoveries. The resulting time-dependent rheology is non-linear, leads to localisation on time scales much shorter than those of the typical transit time of mantle convection but has also a long healing time. These characteristics of fast damage and long term memory is shown in simple models to spontaneously generate plates on a planet with Earth's parameters. For Venus hotter surface conditions, accumulation and inheritance of damage is negligible; hence only subduction zones survive and plate tectonics does not spread. This rheology also explains how subducting slabs can be rapidly detached when a buoyant crust is drawn into subduction and therefore how rapid plate changes can occur.

  6. The Past Earth Network

    NASA Astrophysics Data System (ADS)

    Haywood, A.; Voss, J.; Dolan, A. M.; Yorke, E.

    2016-12-01

    Forecasts of climate rely on model projections, but derivation of sophisticated climate models from first principles is not currently feasible. Therefore, evaluating climate models with observations is essential. The development and improvement of global climate models is currently only based on comparison with and tuning to historical observations of climate (the instrumental record). Models show a range of sensitivities when predicting the future climate response to the emission of greenhouse gases. This indicates that the evaluation of models using observations of historical climate is insufficient. A wide variety of different climate states are recorded in the geological record (spanning greenhouse to icehouse scenarios). The modelling of past climates, in combination with data from the geological record, provides a unique laboratory to evaluate the ability of models to forecast global change. The Past Earth Network is developing a shared, multi-disciplinary vision for addressing the challenges encompassed by the following four network themes: (1) Quantification of error and uncertainty of data: The uncertainties inherent in different forms of climate data must be well-understood. (2) Quantification of uncertainty in complex models: The uncertainties in the output of the (complex and high-dimensional) models in use must be well-understood. (3) Methodologies which enable robust model-data comparison: Appropriate methods for model-data comparison must be used. (4) Forecasting and future climate projections: This theme synthesizes the results from the first three themes in order to assess and ultimately improve the ability of climate models to forecast climate change. By addressing these four challenges, results produced by the Past Earth Network will help to better understand and reduce the uncertainties in climate forecasts and ultimately will contribute to the development of better climate forecasts.

  7. Repeating the Past

    NASA Astrophysics Data System (ADS)

    Moore, John W.

    1998-05-01

    As part of the celebration of the Journal 's 75th year, we are scanning each Journal issue from 25, 50, and 74 years ago. Many of the ideas and practices described are so similar to present-day "innovations" that George Santayana's adage (1) "Those who cannot remember the past are condemned to repeat it" comes to mind. But perhaps "condemned" is too strong - sometimes it may be valuable to repeat something that was done long ago. One example comes from the earliest days of the Division of Chemical Education and of the Journal.

  8. Rheological Transition of Sheared Frictionless Disks with Rotational Motion

    NASA Astrophysics Data System (ADS)

    Olsson, Peter; Teitel, Steve

    We consider the massive Durian bubble model for sheared bidisperse disks, but modified so as to include the rotational motion of particles due to dissipative collisional torques. In such a model, particles possess a viscous tangential dissipation, though no elastic tangential friction. As the packing fraction is increased, we find a discontinuous transition from Bagnoldian to Newtonian rheology, at a packing fraction that lies below the jamming transition. At this transition we find a region of coexisting shear bands of Bagnoldian and Newtonian rheology, and suggestions of discontinuous shear thickening upon increasing the shear strain rate. This work has been supported by NSF Grant No. DMR-1205800.

  9. 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.

  10. Size-dependent rheology of type-I collagen networks.

    PubMed

    Arevalo, Richard C; Urbach, Jeffrey S; Blair, Daniel L

    2010-10-20

    We investigate the system size-dependent rheological response of branched type I collagen gels. When subjected to a shear strain, the highly interconnected mesh dynamically reorients, resulting in overall stiffening of the network. When a continuous shear strain is applied to a collagen network, we observe that the local apparent modulus, in the strain-stiffening regime, is strongly dependent on the gel thickness. In addition, we demonstrate that the overall network failure is determined by the ratio of the gel thickness to the mesh size. These findings have broad implications for cell-matrix interactions, the interpretation of rheological tissue data, and the engineering of biomimetic scaffolds.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Investigations of lubricant rheology as applied to elastohydrodynamic lubrication

    NASA Technical Reports Server (NTRS)

    Bair, S.; Winer, W. O.

    1978-01-01

    Measurements of lubricant shear rheological behavior in the amorphous solid region and near the liquid-solid transition are reported. Elastic, plastic and viscous behavior was observed. A shear rheological model based on primary laboratory data is proposed for concentrated contact lubrication. The model is a Maxwell model modified with a limiting shear stress. Three material properties are required: low shear stress viscosity, limiting elastic shear modulus, and the limiting shear stress the material can withstand. All three are functions of temperature and pressure. In applying the model to EHD contacts the predicted response possesses the characteristics expected from several experiments reported in the literature.

  16. 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.

  17. Rheological properties of saliva substitutes containing mucin, carboxymethylcellulose or polyethylenoxide.

    PubMed

    Vissink, A; Waterman, H A; s-Gravenmade, E J; Panders, A K; Vermey, A

    1984-02-01

    Apparent viscosities at different shear rates were measured for 3 types of saliva substitutes: (a) mucin-containing saliva; (b) substitutes based upon carboxymethylcellulose (CMC), and (c) solution of polyethylenoxide (PEO). The apparent viscosities were compared with those of human whole saliva. Human whole saliva and mucin-containing saliva substitutes appeared to be similar in their rheological properties. Both types of solution are viscoelastic solutions and adjust their apparent viscosities to their biological functions. Preparations containing CMC or PEO are non-Newtonian liquids. From this study it is concluded that mucin-containing saliva substitutes appear to be the best substitutes for natural saliva, as far as rheological properties are concerned.

  18. 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.

  19. Microscale rheology of a soft glassy material close to yielding.

    PubMed

    Jop, Pierre; Mansard, Vincent; Chaudhuri, Pinaki; Bocquet, Lydéric; Colin, Annie

    2012-04-06

    Using confocal microscopy, we study the flow of a model soft glassy material: a concentrated emulsion. We demonstrate the micro-macro link between in situ measured movements of droplets during the flow and the macroscopic rheological response of a concentrated emulsion, in the form of scaling relationships connecting the rheological "fluidity" with local standard deviation of the strain-rate tensor. Furthermore, we measure correlations between these local fluctuations, thereby extracting a correlation length which increases while approaching the yielding transition, in accordance with recent theoretical predictions.

  20. Rheological Properties of Enzymatically Isolated Tomato Fruit Cuticle.

    PubMed

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

    1995-10-01

    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.

  1. Rheology enhanced transport in Non-Newtonian porous media flows

    NASA Astrophysics Data System (ADS)

    Seybold, Hansjoerg; Dias Araujo, Ascanio; Lima, Roberto; Andrade, Roberto; Soares de Andrade, Jose, Jr.

    2017-04-01

    Flow and transport in porous media is of great interest in Earth Science, including oil extraction and groundwater hydrology. The disordered pore-structure leads heterogeneous flow patterns and preferential flow paths. Here we show how the fluid's rheology can be used to control the transport properies inside a porous medium. We find that for a Bingham type rheology, the fluid has a characteristic Reynolds number for which the flow is least localized, resulting in enhanced channelized transport. The increased channelization of the flow leads to a corresponding maximum in permeability. This result has important consequences for the design of chemical reactors, heat transfer and reactive transport in porous media in general.

  2. 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…

  3. 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…

  4. Effects of rheology and viscosity of biobased adhesives on bonding performance

    USDA-ARS?s Scientific Manuscript database

    Rheology is the science of deformation and flow of the matter due to the application of a force. Most rheological tests involve applying a force to a material and measuring its flow or change in shape. Rheological characterization is useful to study the flowability and viscoelastic properties of adh...

  5. The Rheology of Acoustically Fluidized Sand

    NASA Astrophysics Data System (ADS)

    Conrad, J. W.; Melosh, J.

    2013-12-01

    The collapse of large craters and the formation of central peaks and peak rings is well modeled by numerical computer codes that incorporate the acoustic fluidization mechanism to temporarily allow the fluid-like flow of rock debris immediately after crater excavation. Furthermore, long runout landslides require a similar mechanism to explain their almost frictionless movement, which is probably also a consequence of their granular composition coupled with internal vibrations. Many different investigators have now confirmed the ability of vibrations to fluidize granular materials. Yet it still remains to fully describe the rheology of vibrated sand as a function of stress, frequency and amplitude of the vibrations in the sand itself. We constructed a rotational viscometer to quantitatively investigate the relation between the stress and strain rate in a horizontal bed of strongly vibrated sand. In addition to the macroscopic stain rate, the amplitude and frequency of the vibrations produced by a pair of pneumatic vibrators were also measured with the aid of miniaturized piezoelectric accelerometers (B&K 4393) whose output was recorded on a digital storage oscilloscope. The initial gathering of the experimental data was difficult due to granular memory, but by having the sand compacted vibrationally for 8 minutes before each run the scatter of data was reduced and we were able to obtain consistent results. Nevertheless, our major source of uncertainty was variations in strain rate from run to run. We find that vibrated sand flows like a highly non-Newtonian fluid, in which the shear strain rate is proportional to stress to a power much greater than one, where the precise power depends on the amplitude and frequency of the applied vibrations. Rapid flow occurs at stresses less than half of the static yield stress (that is, the yield stress when no vibration is applied) when strong vibrations are present. For a Newtonian fluid, such as water, the relation between

  6. The rheology of chain molecules under shear

    NASA Astrophysics Data System (ADS)

    Moore, Jonathan David

    The rheology of chain molecules is a subject that comprises a wide variety of complex physical phenomena, challenging scientific questions, and fundamentally important practical applications. In this work, nonequilibrium molecular dynamics (NEMD) is employed to study linear and branched alkane chains in the melt state under transient and steady-state shearing conditions. This study focuses on three isomers of C30H62 (n- triacontane, squalane, and 9-n- octyldocosane) as well as a linear short-chain polyethylene (C100H202). A transferable united atom potential is used to model these alkane chains, and the simulations of planar Couette flow are performed using the SLLOD algorithm and a multi- timestep, simulation technique. The strain rates studied in this work (108-10 12 s-1) are extremely difficult to study experimentally yet typical of the severe conditions commonly found in engines and other machinery. NEMD and the united atom model underpredict the kinematic viscosities of n-triacontane and 9- n-octyldocosane but accurately predict the values for squalane (within 15%) at temperatures of 311 and 372 K. The predicted kinematic viscosity index values for both 9- n-octyldocosane and squalane are in quantitative agreement with experiment and represent the first such predictions by molecular simulation. Thus, this same general potential model and computational approach can be used to predict this important lubricant property for potential lubricants prior to their synthesis, offering the possibility of simulation-guided lubricant design. Simulations of C100H202 under steady-state shearing conditions reveal a pronounced minimum in the hydrostatic pressure at an intermediate strain rate that is associated with a minimum in the intermolecular potential energy as well as transitions in the strain-rate-dependent behavior of several other viscous and structural properties of the system. Upon onset of shear, the stress overshoot curves calculated for C100 are in good

  7. Treating inertia in passive microbead rheology.

    PubMed

    Indei, Tsutomu; Schieber, Jay D; Córdoba, Andrés; Pilyugina, Ekaterina

    2012-02-01

    The dynamic modulus G(*) of a viscoelastic medium is often measured by following the trajectory of a small bead subject to Brownian motion in a method called "passive microbead rheology." This equivalence between the positional autocorrelation function of the tracer bead and G(*) is assumed via the generalized Stokes-Einstein relation (GSER). However, inertia of both bead and medium are neglected in the GSER so that the analysis based on the GSER is not valid at high frequency where inertia is important. In this paper we show how to treat both contributions to inertia properly in one-bead passive microrheological analysis. A Maxwell fluid is studied as the simplest example of a viscoelastic fluid to resolve some apparent paradoxes of eliminating inertia. In the original GSER, the mean-square displacement (MSD) of the tracer bead does not satisfy the correct initial condition. If bead inertia is considered, the proper initial condition is realized, thereby indicating an importance of including inertia, but the MSD oscillates at a time regime smaller than the relaxation time of the fluid. This behavior is rather different from the original result of the GSER and what is observed. What is more, the discrepancy from the GSER result becomes worse with decreasing bead mass, and there is an anomalous gap between the MSD derived by naïvely taking the zero-mass limit in the equation of motion and the MSD for finite bead mass as indicated by McKinley et al. [J. Rheol. 53, 1487 (2009)]. In this paper we show what is necessary to take the zero-mass limit of the bead safely and correctly without causing either the inertial oscillation or the anomalous gap, while obtaining the proper initial condition. The presence of a very small purely viscous element can be used to eliminate bead inertia safely once included in the GSER. We also show that if the medium contains relaxation times outside the window where the single-mode Maxwell behavior is observed, the oscillation can be

  8. Flow Birefringence in Polymer Melt Rheology.

    NASA Astrophysics Data System (ADS)

    Subramanian, Ramesh Mani

    Optical techniques that are sensitive to structural changes induced by a flow field applied to polymers during processing have been used to study the fundamental relationships between applied deformation, mechanical stresses, and flow -induced molecular orientation. But most of the work done so far has used opto-mechanical techniques (i.e. mechanical measurement of stress and deformation, and optical measurement of flow-induced molecular orientation). This thesis reports the development and application of non-intrusive, opto-electronic techniques for rheo-optical studies on a 300 Pa.s polydimethylsiloxane (PDMS) melt flowing through a 5.00 cm wide converging wedge cell at room temperature. The two techniques used as tools of rheological characterization in the present study are laser doppler anemometry (LDA) to compute strain rate from local velocity measurements, and flow birefringence (double refraction) for measurement of the anisotropic refractive index tensor which, for flexible polymer solutions and melts, provides information the state of stress in the material via the stress-optical law. Birefringence measurements in extensional flow up to a pressure drop of 689 kPa across the converging wedge cell indicated that stress tensor and polarizability or anisotropic refractive index tensor were linearly related for the polymer over a range of strain rate that extended well into the non-Newtonian region. Along the cell centerline, the extensional flow behaviour of the polymer was studied via birefringence measurements in the linear stress-optical region, and it was found to be extension-thinning in nature. Assuming no boundary layer error, the optical techniques used in the present study provide a valuable test for constitutive relations between stress and deformation in the polymer by comparing predicted orientation angles with experimental measurements in combined shear and extension flows. The two constitutive equations tested were the Power-law model and the

  9. 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

  10. Formwork pressure of self-consolidating concrete: Influence of flocculation mechanisms, structural rebuilding, thixotropy and rheology

    NASA Astrophysics Data System (ADS)

    Ferron, Raissa Patricia Douglas

    While self-consolidating concrete (SCC) may no longer be considered a "new concrete", there are still significant challenges to overcome before there is broader acceptance of SCC. One of these challenges concerns the formwork pressure exerted by SCC. A major advantage of SCC is the accelerated casting process due to the elimination of external vibration. However, faster casting rates may induce higher formwork pressure; this is a major concern for cast-in place applications, especially when casting tall elements. It has been reported that the formwork pressure of SCC can be less than hydrostatic pressure. This is due to the build-up of a three-dimensional structure when the concrete is left at rest. The development of this structure and the mechanisms behind it are of particular interest to users of SCC. The research presented in this manuscript was carried out at the Center for Advanced Cement-Based Materials at Northwestern University and the Universidad Complutense de Madrid. This dissertation focuses on the structural rebuilding SCC and its implications for formwork pressure. Special emphasis was given to the influence of flocculation mechanisms and the impact of material constituents. A rheological protocol to characterize structural rebuilding was developed. This protocol can be used to assess the contributions from irreversible structural build-up from hydration and reversible structural rebuilding from thixotropic effects. The impact of various mixture ingredients, including cement type, mineral admixtures, chemical admixtures and clays, on the structural rebuilding was examined. The results showed that the rheological properties of the paste matrix and its evolution over time can be used as an indication of the formwork pressure behavior. Formwork pressure is highly impacted by the structural rebuilding that occurs in the paste matrix, and the results showed that formwork pressure is related to the rate at which structural rebuilding occurs and the total

  11. 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

  12. 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

  13. Periodontology: past, present, perspectives.

    PubMed

    Slots, Jørgen

    2013-06-01

    Periodontitis is an infectious disease that affects the tooth-supporting tissues and exhibits a wide range of clinical, microbiological and immunological manifestations. The disease is associated with and is probably caused by a multifaceted dynamic interaction of specific infectious agents, host immune responses, harmful environmental exposure and genetic susceptibility factors. This volume of Periodontology 2000 covers key subdisciplines of periodontology, ranging from etiopathogeny to therapy, with emphasis on diagnosis, classification, epidemiology, risk factors, microbiology, immunology, systemic complications, anti-infective therapy, reparative treatment, self-care and affordability issues. Learned and unlearned concepts of periodontitis over the past 50 years have shaped our current understanding of the etiology of the disease and of clinical practice.

  14. Hydrogel Nanocomposites with Independently Tunable Rheology and Mechanics.

    PubMed

    Unterman, Shimon; Charles, Lyndon F; Strecker, Sara E; Kramarenko, Denis; Pivovarchik, Dmitry; Edelman, Elazer R; Artzi, Natalie

    2017-03-28

    Hydrogels are an attractive class of biomaterials for minimally invasive local drug delivery given their injectability, tunability, high water content, and biocompatibility. Broad applicability though is challenged: relatively modest mechanical properties restrict use to soft tissues, while flow properties necessary for injectability limit implantation to dried, enclosed tissues to minimize material migration during gelation. To address these dual concerns, we designed an injectable nanocomposite hydrogel based on dextran aldehyde and a poly(amido amine) dendrimer doped with phyllosilicate nanoplatelet fillers. Balance of components allows for exfoliation of nanoplatelets, significantly changing macromer solution flow, facilitating injection and manipulation in a wide variety of implantation contexts while enhancing compressive modulus of hydrogels at low loading. Importantly, rheological and mechanical effects were dependent on aspect ratio, with high aspect ratio nanoplatelets having much stronger effects on mechanics and low aspect ratio nanoplatelets having stronger effects on rheology, enabling nearly independent control of rheological and mechanical properties. Nanoplatelets enhanced hydrogel properties at a filler loading substantially lower than that of comparably sized nanoparticles. We present a model to explain the role that aspect ratio plays in control of rheology and mechanics in nanoplatelet-containing hydrogels, with lessons for further nanocomposite hydrogel development. This low-cost biocompatible material may be useful as a drug delivery platform in challenging implantation environments.

  15. Rheology and extrusion of low-grade paper and sludge

    Treesearch

    C. Tim. Scott; Stefan. Zauscher; Daniel J. Klingenberg

    1999-01-01

    This paper discusses efforts to characterize the rheological properties of pulps that include low-grade wastepapers and papermill sludges to determine their potential for extrusion and conversion into useful products. We investigated apparent changes in viscosity associated with the addition of typical inorganic paper fillers (calcium carbonate, kaolin clay, and...

  16. 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).

  17. Rheological and microstructural changes in Queso Fresco during storage

    USDA-ARS?s Scientific Manuscript database

    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...

  18. Particle laden fluid interfaces: dynamics and interfacial rheology.

    PubMed

    Mendoza, Alma J; Guzmán, Eduardo; Martínez-Pedrero, Fernando; Ritacco, Hernán; Rubio, Ramón G; Ortega, Francisco; Starov, Victor M; Miller, Reinhard

    2014-04-01

    We review the dynamics of particle laden interfaces, both particle monolayers and particle+surfactant monolayers. We also discuss the use of the Brownian motion of microparticles trapped at fluid interfaces for measuring the shear rheology of surfactant and polymer monolayers. We describe the basic concepts of interfacial rheology and the different experimental methods for measuring both dilational and shear surface complex moduli over a broad range of frequencies, with emphasis in the micro-rheology methods. In the case of particles trapped at interfaces the calculation of the diffusion coefficient from the Brownian trajectories of the particles is calculated as a function of particle surface concentration. We describe in detail the calculation in the case of subdiffusive particle dynamics. A comprehensive review of dilational and shear rheology of particle monolayers and particle+surfactant monolayers is presented. Finally the advantages and current open problems of the use of the Brownian motion of microparticles for calculating the shear complex modulus of monolayers are described in detail.

  19. 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.

  20. Debris flow rheology: Experimental analysis of fine-grained slurries

    USGS Publications Warehouse

    Major, Jon J.; Pierson, Thomas C.

    1992-01-01

    The rheology of slurries consisting of ≤2-mm sediment from a natural debris flow deposit was measured using a wide-gap concentric-cylinder viscometer. The influence of sediment concentration and size and distribution of grains on the bulk rheological behavior of the slurries was evaluated at concentrations ranging from 0.44 to 0.66. The slurries exhibit diverse rheological behavior. At shear rates above 5 s−1 the behavior approaches that of a Bingham material; below 5 s−1, sand exerts more influence and slurry behavior deviates from the Bingham idealization. Sand grain interactions dominate the mechanical behavior when sand concentration exceeds 0.2; transient fluctuations in measured torque, time-dependent decay of torque, and hysteresis effects are observed. Grain rubbing, interlocking, and collision cause changes in packing density, particle distribution, grain orientation, and formation and destruction of grain clusters, which may explain the observed behavior. Yield strength and plastic viscosity exhibit order-of-magnitude variation when sediment concentration changes as little as 2–4%. Owing to these complexities, it is unlikely that debris flows can be characterized by a single rheological model.

  1. Rheological Properties of Calcium Hydroxylapatite With Integral Lidocaine.

    PubMed

    Meland, Melissa; Groppi, Chris; Lorenc, Z Paul

    2016-09-01

    Calcium hydroxylapatite with integral lidocaine, CaHA (+), received FDA approval in 2015 and CE mark approval in 2016. This formulation has been associated with significant pain reduction compared to CaHA. In a previous rheometry study, CaHA without lidocaine demonstrated higher viscosity and elasticity when compared with hyaluronic acid fillers. To compare the rheological properties of CaHA (+) lidocaine to CaHA without lidocaine and to compare the rheological measures of CaHA (+) to 5 cross-linked hyaluronic acid (HA) fillers with integral 0.3% lidocaine.
    The rheological properties of complex viscosity (η*) and elastic modulus (G') were measured for 2 types of CaHA fillers [CaHA without lidocaine and CaHA (+) with integral 0.3% lidocaine] and 5 HA fillers using an oscillation frequency sweep at a sheer stress of 5 pascal tau (Pa) and an interpolation of 0.7 Hz.
    CaHA with and without integral lidocaine demonstrate similar η* and G' measurements. CaHA with and without integral lidocaine demonstrates higher η* and G' compared with HA fillers with integral lidocaine.
    CaHA with integral lidocaine has a similar rheological profile to CaHA without lidocaine: the highest η* and G' compared with available HA fillers with integral lidocaine.

    J Drugs Dermatol. 2016;15(9):1107-1110.

  2. Rheology of defatted ultrafiltration-diafiltration soy proteins

    USDA-ARS?s Scientific Manuscript database

    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. Inverting Glacial Isostatic Adjustment beyond linear viscoelasticity using Burgers rheology

    NASA Astrophysics Data System (ADS)

    Caron, L.; Greff-Lefftz, M.; Fleitout, L.; Metivier, L.; Rouby, H.

    2014-12-01

    In Glacial Isostatic Adjustment (GIA) inverse modeling, the usual assumption for the mantle rheology is the Maxwell model, which exhibits constant viscosity over time. However, mineral physics experiments and post-seismic observations show evidence of a transient component in the deformation of the shallow mantle, with a short-term viscosity lower than the long-term one. In these studies, the resulting rheology is modeled by a Burgers material: such rheology is indeed expected as the mantle is a mixture of materials with different viscosities. We propose to apply this rheology for the whole viscoelastic mantle, and, using a Bayesian MCMC inverse formalism for GIA during the last glacial cycle, study its impact on estimations of viscosity values, elastic thickness of the lithosphere, and ice distribution. To perform this inversion, we use a global dataset of sea level records, the geological constraints of ice-sheet margins, and present-day GPS data as well as satellite gravimetry. Our ambition is to present not only the best fitting model, but also the range of possible solutions (within the explored space of parameters) with their respective probability of explaining the data. Our first results indicate that compared to the Maxwell models, the Burgers models involve a larger lower mantle viscosity and thicker ice over Fennoscandia and Canada.

  4. Rheological properties of silica suspensions in aqueous cellulose derivatives solutions

    NASA Astrophysics Data System (ADS)

    Ryo, Y.; Kawaguchi, M.

    1992-05-01

    The rheological properties of the silica suspensions in aqueous solutions of hydroxypropylmethylcellulose (HPMC) were investigated in terms of the shear stress and storage and loss moduli (G' and G`) as a function of silica content, HPMC concentration, and HPMC molecular weight by using a coaxial cylinder rheometer.

  5. Activation energy measurements in rheological analysis of cheese

    USDA-ARS?s Scientific Manuscript database

    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...

  6. Laboratory procedure for the rheological characterization of slurry suspensions

    SciTech Connect

    Chang, C.Y.

    1996-02-01

    This procedure provides rheology measurements that are more reliable and accurate than those described in the technical procedure PNL-(WTC-006-4). Methods are provided to measure the sweep rheogram and steady shear viscosity with concentric cylinders, to measure the yield stress directly with a shear vane, and to measure the sweep rheogram with parallel plates.

  7. Rheology of the Active Cell Cortex in Mitosis.

    PubMed

    Fischer-Friedrich, Elisabeth; Toyoda, Yusuke; Cattin, Cedric J; Müller, Daniel J; Hyman, Anthony A; Jülicher, Frank

    2016-08-09

    The cell cortex is a key structure for the regulation of cell shape and tissue organization. To reach a better understanding of the mechanics and dynamics of the cortex, we study here HeLa cells in mitosis as a simple model system. In our assay, single rounded cells are dynamically compressed between two parallel plates. Our measurements indicate that the cortical layer is the dominant mechanical element in mitosis as opposed to the cytoplasmic interior. To characterize the time-dependent rheological response, we extract a complex elastic modulus that characterizes the resistance of the cortex against area dilation. In this way, we present a rheological characterization of the cortical actomyosin network in the linear regime. Furthermore, we investigate the influence of actin cross linkers and the impact of active prestress on rheological behavior. Notably, we find that cell mechanics values in mitosis are captured by a simple rheological model characterized by a single timescale on the order of 10 s, which marks the onset of fluidity in the system. Copyright © 2016 Biophysical Society. Published by Elsevier Inc. All rights reserved.

  8. Sediment Formation in Nearshore Environments: Strength, Rheology, Microstructure, and Stability

    DTIC Science & Technology

    2006-01-01

    Sediment Formation in Nearshore Environments: Strength, Rheology, Microstructure, and Stability Homa Lee U.S. Geological Survey 345 Middlefield ...ES) U.S. Geological Survey,345 Middlefield Road,Menlo Park,CA,94025 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S

  9. Rheology and extrusion of high-solids biomass

    Treesearch

    Tim Scott; Joseph R. Samaniuk; Daniel J. Klingenberg

    2011-01-01

    Economical biorefining of lignocellulosic biomass (LCB) requires processing high-solids particulate streams. We have developed new techniques and testing protocols to measure the rheological properties of high-solids LCB using a modified torque rheometer (TR). The flow field in the TR is similar to that of a twin-screw extruder and for modeling purposes can be...

  10. Effect of condensed tannin profile on wheat flour dough rheology

    USDA-ARS?s Scientific Manuscript database

    Proanthocyanidins (PA) crosslink proteins and could expand wheat gluten functionality. Effect PA MW profile (sorghum versus grape seed PA) on rheology of flours with different gluten composition (high versus low insoluble polymeric protein, IPP) was evaluated using mixograph, large (TA.XT2i) and sm...

  11. The influence of propolis on rheological properties of lipstick.

    PubMed

    Goik, U; Ptaszek, A; Goik, T

    2015-08-01

    The aim of this work was to study the effect of propolis on the rheological and textural properties of lipsticks. The studied lipsticks were based on raw materials and contained no synthetic compounds, preservatives, fragrances or dyes. The rheological and textural properties of the prepared lipsticks, both with and without propolis, were studied as a function of temperature and storage period. Measurements were taken using an RS6000 rheometer (Haake, Germany) with a cone-plate sensor. The cone parameters were as follows: diameter 35 mm and angle 2°. Textural tests were performed using the same cone-plate geometry. The research results of rheological and textural properties of lipsticks, with and without the addition of propolis, indicate the possibility of application of propolis as a beneficial additive to such type of cosmetics. The presence of propolis does not significantly alter the viscoelastic properties of the lipsticks. The courses of flow curves indicate shear thinning, which is very advantageous from an application point of view. From the rheological point of view, the properties of lipsticks tested in low deformation conditions show some structural changes, most likely due to consolidation of the structure. The analysis of textural properties indicates that lipsticks with added propolis are more brittle and prone to crushing. However, the temperature increase (30°C) does not cause significant changes to the textural characteristics of these lipsticks. © 2015 Society of Cosmetic Scientists and the Société Française de Cosmétologie.

  12. Instrument and methods for surface dilatational rheology measurements

    NASA Astrophysics Data System (ADS)

    Russev, Stoyan C.; Alexandrov, Nikola; Marinova, Krastanka G.; Danov, Krassimir D.; Denkov, Nikolai D.; Lyutov, Lyudmil; Vulchev, Vassil; Bilke-Krause, Christine

    2008-10-01

    We describe an instrument combining the advantages of two methods, axisymmetric drop shape analysis for well-deformed drops and capillary pressure tensiometry for spherical drops, both used for measuring the interfacial tension and interfacial rheological parameters. The rheological parameters are the complex interfacial elasticity, and the surface elasticity and viscosity of Kelvin-Voigt and Maxwell rheological models. The instrument is applicable for investigation of the effect of different types of surfactants (nonionic, ionic, proteins, and polymers) on the interfacial rheological properties both of air/water and oil/water interfaces, and of interfaces between liquids with equal mass densities. A piezodriven system and a specially designed interface unit, implemented in the instrument, ensure precise control for standard periodic waveforms of surface deformation (sine, square, triangle, and sawtooth) at a fixed frequency, or produce surface deformation at constant rate. The interface unit ensures accurate synchronization between the pressure measurement and the surface control, which is used for real-time data processing and feedback control of drop area in some of the applications.

  13. Rheological behavior and structural interpretation of waxy crude oil gels.

    PubMed

    Visintin, Ruben F G; Lapasin, Romano; Vignati, Emanuele; D'Antona, Paolo; Lockhart, Thomas P

    2005-07-05

    A waxy crude oil which gels below a threshold temperature has been investigated under static and dynamic conditions, using a combination of rheological methods, optical microscopy, and DSC. Particular attention is given in this work to the influence of the mechanical history on gel strength and to describing the time-dependent rheological behavior. The gels display a strong dependence of the yield stress and moduli on the shear history, cooling rate, and stress loading rate. Of particular interest is the partial recovery of the gel structure after application of small stress or strain (much smaller than the critical values needed for flow onset) during cooling, which can be used to reduce the ultimate strength of the crude oil gel formed below the pour point. A second focus of this study is to further develop the physical interpretation of the mechanism by which wax crystallization produces gelation. Gelation of the waxy crude oil studied is suggested to be the result of the association between wax crystals, which produces an extended network structure, and it is shown that the system displays features common to attractive colloidal gels, for one of which, fumed silica (Aerosil 200) in paraffin oil, rheological data are reported. The colloidal gel model provides a simple and economical basis for explaining the response of the gelled oil to various mechanical perturbations and constitutes a fruitful basis from which to develop technologies for controlling the gelation phenomenon, as suggested by the rheological results reported.

  14. 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

  15. Rheology of bauxite-based low-cement shotcreting castables

    NASA Astrophysics Data System (ADS)

    Zhou, Xianxin

    Continuous research efforts on castable technology since two decades have lead to the transformation of placement mode from vibrating to self-flow to pumping and shotcreting. Shotcreting (an installation process of self-flow castables by combining pumping and shooting), as a high efficient installation technique, has demanded castable composition with specific characteristics in terms of rheology. Though, the understanding on self-low castable technology is appreciable, the state-of-art on shotcreting has not yet been revealed and the literature on this area is scarce. This demands an in-depth research on this particular subject. The goal of the current investigation is to develop a predictive method of shotcreting castable with good pumpability and self-flowability through rheological approach and to validate the approach through shotcreting trial. A bauxite-based low-cement self-flow castable has been chosen for this purpose. Basically, three test methods have been adopted to fulfill the stated purpose: flow table test, viscometer and a new rheometer. A rheometer has been used to measure the rheological behavior of chosen castables. Through this, two rheological constants are obtained which are used to predict the pumpability of chosen system. This approach has overcome the drawback of measuring rheology of fine matrix portion only to predict the castable behaviors. Fine matrix rheology has also been evaluated using viscometer for comparison purpose. The relationship between viscometer and rheometer measurement are analysed. To support the results of rheometer and viscometer, conductivity measurement on fine matrix portion, exothermic profile measurement on castable mix, mechanical and physical properties measurements after drying and the appearance of castable green bodies are also carried out. The whole work is divided into four stages. In stage I, all raw materials used in this work, including bauxites, cements, microsilicas, reactive aluminas, have been

  16. [Study of relationship between the onset time of sudden deafness and blood rheology].

    PubMed

    Chen, Xiu-Mei; Zhang, Qing-Quan; Xie, Guang

    2007-03-01

    To investigate the correlation of the onset time of sudden deafness and blood rheology using a large-scale retrospective study. One hundred and ninety-eight patients of sudden deafness were examined with blood rheology and compared with 60 healthy people. Thirty patients were as subjects to study the circadian of blood rheology in order to search whether the blood rheology of morning was the highest. By divided 24 hours into twelve groups, each group contained two hours. Then the 198 patients were separated into twelve groups according to the time of onset. The blood rheology of each group was analyzed and compared with each other to observe which group was the highest. Most blood rheology index of the patients were higher than that of the healthy people. The onset time in most of the patients was during 4 am-8 am, but 45 patients during 4 am-6 am and 40 patients during 6 am-8 am. By analyzing and comparing the blood rheology of each group, the results showed that the blood rheology index in the group of 4 am-8 am was highest. And the blood rheology index of sudden deafness was highest in the morning. There was a close relation between blood rheology and sudden deafness. The peak time of onset was 4 am-8 am, and the patients whose blood rheology were the highest should be more predisposed to sudden deafness than the other patients.

  17. Numerical analysis of temperature and torque in a Magneto-rheological clutch

    NASA Astrophysics Data System (ADS)

    Bosioc, A. I.; Stuparu, A.; Susan-Resiga, R.

    2017-07-01

    The paper focuses on numerical analysis of temperature field into a magneto-rheological clutch. The magneto-rheological fluid is used for a clutch operated at different speeds. The magneto-rheological clutch application was developed due to the magnetic control and fast response. The two dimensional axi-symmetric computational domain corresponds to the experimental magneto-rheological clutch. The numerical simulations have been performed for seven speed values with zero magnetic fields. Firstly, the temperature map for magneto-rheological clutch is computed. Secondly, the temperature value obtained on the outside casing wall is validated against experimental data. Next, the maximum temperature value was identified based on numerical simulation in all domain of the magneto-rheological fluid. The numerical results will be used to improve the magneto-rheological clutch operation/design.

  18. Interfacial rheology: an overview of measuring techniques and its role in dispersions and electrospinning.

    PubMed

    Pelipenko, Jan; Kristl, Julijana; Rošic, Romana; Baumgartner, Saša; Kocbek, Petra

    2012-06-01

    Interfacial rheological properties have yet to be thoroughly explored. Only recently, methods have been introduced that provide sufficient sensitivity to reliably determine viscoelastic interfacial properties. In general, interfacial rheology describes the relationship between the deformation of an interface and the stresses exerted on it. Due to the variety in deformations of the interfacial layer (shear and expansions or compressions), the field of interfacial rheology is divided into the subcategories of shear and dilatational rheology. While shear rheology is primarily linked to the long-term stability of dispersions, dilatational rheology provides information regarding short-term stability. Interfacial rheological characteristics become relevant in systems with large interfacial areas, such as emulsions and foams, and in processes that lead to a large increase in the interfacial area, such as electrospinning of nanofibers.

  19. Normal force controlled rheology applied to agar gelation

    NASA Astrophysics Data System (ADS)

    Mao, Bosi; Divoux, Thibaut; Snabre, Patrick

    2016-05-01

    A wide range of thermoreversible gels are prepared by cooling down to ambient temperature hot aqueous polymer solutions. During the sol-gel transition, such materials may experience a volume contraction which is traditionally overlooked as rheological measurements are usually performed in geometries of constant volume. In this article, we revisit the formation of 1.5\\% wt. agar gels through a series of benchmark rheological experiments performed with a plate-plate geometry. We demonstrate on that particular gel of polysaccharides that the contraction associated with the sol/gel transition cannot be neglected. Indeed, imposing a constant gap width during the gelation results in the strain hardening of the sample, as evidenced by the large negative normal force that develops. Such hardening leads to the slow drift in time of the gel elastic modulus $G'$ towards ever larger values, and thus to an erroneous estimate of $G'$. As an alternative, we show that imposing a constant normal force equals to zero during the gelation, instead of a constant gap width, suppresses the hardening as the decrease of the gap compensates for the sample contraction. Using normal force controlled rheology, we then investigate the impact of thermal history on 1.5\\% wt. agar gels. We show that neither the value of the cooling rate, nor the introduction of a constant temperature stage during the cooling process influence the gel elastic properties. Instead, $G'$ only depends on the terminal temperature reached at the end of the cooling ramp, as confirmed by direct imaging of the gel microstructure by cryoelectron microscopy. The present work offers an extensive review of the technical difficulties associated with the rheology of hydrogels and paves the way for a systematic use of normal force controlled rheology to monitor non-isochoric processes.

  20. 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.

  1. Rheology of Lignocellulose Suspensions and Impact of Hydrolysis: A Review.

    PubMed

    Nguyen, Tien Cuong; Anne-Archard, Dominique; Fillaudeau, Luc

    2015-01-01

    White biotechnologies have several challenges to overcome in order to become a viable industrial process. Achieving highly concentrated lignocellulose materials and releasing fermentable substrates, with controlled kinetics in order to regulate micro-organism activity, present major technical and scientific bottlenecks. The degradation of the main polymeric fractions of lignocellulose into simpler molecules is a prerequisite for an integrated utilisation of this resource in a biorefinery concept. The characterisation methods and the observations developed for rheology, morphology, etc., that are reviewed here are strongly dependent on the fibrous nature of lignocellulose, are thus similar or constitute a good approach to filamentous culture broths. This review focuses on scientific works related to the study of the rheological behaviour of lignocellulose suspensions and their evolution during biocatalysis. In order to produce the targeted molecules (synthon), the lignocellulose substrates are converted by enzymatic degradation and are then metabolised by micro-organisms. The dynamics of the mechanisms is limited by coupled phenomena between flow, heat and mass transfers in regard to diffusion (within solid and liquid phases), convection (mixing, transfer coefficients, homogeneity) and specific inhibitors (concentration gradients). As lignocellulose suspensions consist of long entangled fibres for the matrix of industrial interest, they exhibit diverse and complex properties linked to this fibrous character (rheological, morphological, thermal, mechanical and biochemical parameters). Among the main variables to be studied, the rheological behaviour of such suspensions appears to be determinant for process efficiency. It is this behaviour that will determine the equipment to be used and the strategies applied (substrate and biocatalysis feed, mixing, etc.). This review provides an overview of (i) the rheological behaviour of fibrous materials in suspension, (ii) the

  2. Rheological evolution of planetary basalts during cooling and crystallization

    NASA Astrophysics Data System (ADS)

    Sehlke, Alexander

    Basaltic lavas cover large portions of the surface of the Earth and other planets and moons. Planetary basalts are compositionally different from terrestrial basalts, and show a variety of unique large-scale lava flow morphologies unobserved on Earth. They are usually assumed to be much more fluid than basalts on Earth, such as Hawaiian basalt, but their rheology is largely unknown. I synthesized several synthetic silicate melts representing igneous rock compositions of Mars, Mercury, the Moon, Io and Vesta. I measured their viscosity, as well as several terrestrial lavas including Hawaiian basalt, by concentric cylinder and parallel plate viscometry. Planetary melts cover a wide range of viscosity at their liquidus, overlapping with terrestrial basaltic melts. I derived a new viscosity model that is based on the Adam-Gibbs theory of structural relaxation, predicting these viscosities much more accurately than previously published viscosity models. During crystallization, the rheological behavior changes from Newtonian to pseudoplastic. Combining rheology experiments with field observations, the rheological conditions of the pahoehoe to `a`a morphological transition for Hawaiian basalt were determined in strain rate-viscosity space. This transition occurs at temperatures around 1185+/-15°C. For Mercurian lavas, this transition is predicted to occur at higher temperatures around 1250+/-30°C. We find that the rheology of these lavas is broadly similar to terrestrial ones, suggesting that the large smooth volcanic plains observed on Mercury's northern hemisphere are due to flood basalt volcanism rather than unusually fluid lavas. We also show that KREEP lavas, a type of basalt associated with sinuous rilles on the lunar surface, is more likely to form rilles through levee construction, as the high and rapidly increasing viscosity prohibits sufficient thermo-mechanical erosion.

  3. 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.

  4. Nonlocal rheological properties of granular flows near a jamming limit

    NASA Astrophysics Data System (ADS)

    Aranson, Igor S.; Tsimring, Lev S.; Malloggi, Florent; Clément, Eric

    2008-09-01

    We study the rheology of sheared granular flows close to a jamming transition. We use the approach of partially fluidized theory (PFT) with a full set of equations extending the thin layer approximation derived previously for the description of the granular avalanches phenomenology. This theory provides a picture compatible with a local rheology at large shear rates [G. D. R. Midi, Eur. Phys. J. E 14, 341 (2004)] and it works in the vicinity of the jamming transition, where a description in terms of a simple local rheology comes short. We investigate two situations displaying important deviations from local rheology. The first one is based on a set of numerical simulations of sheared soft two-dimensional circular grains. The next case describes previous experimental results obtained on avalanches of sandy material flowing down an incline. Both cases display, close to jamming, significant deviations from the now standard Pouliquen’s flow rule [O. Pouliquen, Phys. Fluids 11, 542 (1999); 11, 1956 (1999)]. This discrepancy is the hallmark of a strongly nonlocal rheology and in both cases, we relate the empirical results and the outcomes of PFT. The numerical simulations show a characteristic constitutive structure for the fluid part of the stress involving the confining pressure and the material stiffness that appear in the form of an additional dimensionless parameter. This constitutive relation is then used to describe the case of sandy flows. We show a quantitative agreement as far as the effective flow rules are concerned. A fundamental feature is identified in PFT as the existence of a jammed layer developing in the vicinity of the flow arrest that corroborates the experimental findings. Finally, we study the case of solitary erosive granular avalanches and relate the outcome with the PFT analysis.

  5. 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…

  6. 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…

  7. Effects of cellulose derivative hydrocolloids on pasting, viscoelastic, and morphological characteristics of rice starch gel.

    PubMed

    Sun, Jing; Zuo, Xiao-Bo; Fang, Sheng; Xu, Hua-Neng; Chen, Jie; Meng, Yue-Cheng; Chen, Tao

    2017-06-01

    Effects of sodium carboxymethyl cellulose (CMC) and hydroxypropyl methyl cellulose (HPMC) on the pasting, viscoelastic, and morphological properties of rice starch gel were studied. The addition of CMC increased the peak and trough viscosities, while decreased the final and setback viscosities of rice starch. The peak and trough viscosities of rice starch gel were only little affected by the addition of HPMC. The dynamic viscoelastic result showed that the addition of CMC significantly increased the values of storage modulus (G') and loss modulus (G″), while reduced the value of tanδ as compared to the control sample. Only a small increase in values of G' and G″ was observed in the case of HPMC. The rice starch gel with CMC addition exhibited higher resistances to the stress and produced a stronger gel network. The creep recovery data were well fitted by a four-element Burger's model. Furthermore, the morphological characteristics were in agreement with the finding of rheological results. It was concluded that the addition of CMC and HPMC modified the rheology of rice starch gel in different ways and interacted under different models based on their molecular structures. Gluten-free foods such as rice cake are essential for people who suffer from celiac disease which is a digestive disorder caused by the consumption of grains containing gluten. The use of CMC and HPMC represents the most widespread approach used to mimic gluten in the manufacture of gluten-free breads based on rice starch, due to their structure-building and water-binding properties. Therefore, it is necessary and crucial to investigate the physical-chemical properties such as pasting and rheological properties of the rice starch with these hydrocolloids. In addition, a better understanding of the interactions of CMC and HPMC on the rice starch could provide additional tools for selection of gluten free recipes with improved rheological and textural properties. © 2016 Wiley Periodicals, Inc.

  8. 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

  9. Forward to the past

    PubMed Central

    Carlini, Alessandro; Actis-Grosso, Rossana; Stucchi, Natale; Pozzo, Thierry

    2012-01-01

    Our daily experience shows that the CNS is a highly efficient machine to predict the effect of actions into the future; are we so efficient also in reconstructing the past of an action? Previous studies demonstrated we are more effective in extrapolating the final position of a stimulus moving according to biological kinematic laws. Here we address the complementary question: are we more effective in extrapolating the starting position (SP) of a motion following a biological velocity profile? We presented a dot moving upward and corresponding to vertical arm movements that were masked in the first part of the trajectory. The stimulus could either move according to biological or non-biological kinematic laws of motion. Results show a better efficacy in reconstructing the SP of a natural motion: participants demonstrate to reconstruct coherently only the SP of the biological condition. When the motion violates the biological kinematic law, responses are scattered and show a tendency toward larger errors. Instead, in a control experiment where the full motions were displayed, no-difference between biological and non-biological motions is found. Results are discussed in light of potential mechanisms involved in visual inference. We propose that as soon as the target appears the cortical motor area would generate an internal representation of reaching movement. When the visual input and the stored kinematic template match, the SP is traced back on the basis of this memory template, making more effective the SP reconstruction. PMID:22712012

  10. Forward to the past.

    PubMed

    Carlini, Alessandro; Actis-Grosso, Rossana; Stucchi, Natale; Pozzo, Thierry

    2012-01-01

    Our daily experience shows that the CNS is a highly efficient machine to predict the effect of actions into the future; are we so efficient also in reconstructing the past of an action? Previous studies demonstrated we are more effective in extrapolating the final position of a stimulus moving according to biological kinematic laws. Here we address the complementary question: are we more effective in extrapolating the starting position (SP) of a motion following a biological velocity profile? We presented a dot moving upward and corresponding to vertical arm movements that were masked in the first part of the trajectory. The stimulus could either move according to biological or non-biological kinematic laws of motion. Results show a better efficacy in reconstructing the SP of a natural motion: participants demonstrate to reconstruct coherently only the SP of the biological condition. When the motion violates the biological kinematic law, responses are scattered and show a tendency toward larger errors. Instead, in a control experiment where the full motions were displayed, no-difference between biological and non-biological motions is found. Results are discussed in light of potential mechanisms involved in visual inference. We propose that as soon as the target appears the cortical motor area would generate an internal representation of reaching movement. When the visual input and the stored kinematic template match, the SP is traced back on the basis of this memory template, making more effective the SP reconstruction.

  11. 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

  12. Limitations of the rheological mucoadhesion method: the effect of the choice of conditions and the rheological synergism parameter.

    PubMed

    Hägerström, Helene; Edsman, Katarina

    2003-04-01

    This work demonstrates several limitations of the simple rheological method that is widely used to investigate mucoadhesion of polymer gels. We establish the importance of the choice of conditions and the synergism parameter for the results obtained in comparative studies. Dynamic rheological measurements were performed on gels based on four slightly different poly(acrylic acid) (Carbopol) polymers and their corresponding mixtures with porcine stomach mucin and bovine submaxillary gland mucin. The rationale for the comparison of the polymers had a large influence on the results obtained. The method does not give the same ranking order when two different comparison strategies are used. Moreover, we show that the results obtained are also sensitive to where in the 'rheological range' the comparison is made, e.g., at which value of G'. Positive values of the synergism parameters are, for example, only seen with weak gels. The choice of synergism parameter also has a bearing on the results obtained, and here we suggest a new refined relative parameter, the log ratio (log(G'(mix)/G'(p))). We also investigated the adhesion of the gel preparations to porcine nasal mucosa, using tensile strength measurements. Increased gel strength resulted in stronger adhesion, which is in contrast to the results from the rheological method, where the positive values of the synergism parameters were seen only with weak gels. On the basis of the limitations demonstrated and discussed, we recommend that the rheological method should not be used as a stand-alone method for the studying of mucoadhesive properties of polymer gels.

  13. 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.

  14. 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

  15. Textural, rheological and sensory properties and oxidative stability of nut spreads—a review.

    PubMed

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

    2013-02-20

    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.

  16. 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.

  17. 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

  18. 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

  19. 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

  20. Structural and rheological properties of chitosan semi-interpenetrated networks.

    PubMed

    Payet, L; Ponton, A; Grossiord, J-L; Agnely, F

    2010-06-01

    The local structure and the viscoelastic properties of semi-interpenetrated biopolymer networks based on cross-linked chitosan and poly(ethylene oxide) (PEO) were investigated by Small Angle Neutron Scattering and rheological measurements. The specific viscosity and the entanglement concentration of chitosan were first determined, respectively, by capillary viscosimetry and steady-state shear rheology experiments performed at different polymer concentrations. Mechanical spectroscopy was then used to study the gelation process of chitosan/PEO semi-interpenetrated networks. By fitting the frequency dependence of the elastic and loss moduli with extended relations of relaxation shear modulus around the sol-gel transition, it was shown that the addition of PEO chains had a significant effect on the viscoelastic properties of aqueous chitosan networks but no effect on the gelation time. The improvement of mechanical properties was in accordance with the correlation length decrease deduced from Small Angle Neutron Scattering experiments.

  1. 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].

  2. Scaling of Rheology Near the Colloidal Jamming Transition

    NASA Astrophysics Data System (ADS)

    Zhang, Zexin; Basu, Anindita; Haxton, Thomas; Liu, Andrea; Yodh, Arjun

    2009-03-01

    Recent simulations have proposed that the zero-temperature, zero-shear-stress jamming transition can be understood in the framework of critical phenomena, and thus can be described by various asymptotic scaling laws. We carry out rheology experiments in the vicinity of the jamming transition to study the scaling of flow properties of a bidisperse colloidal soft sphere system. We find, both below and above the jamming transition, a scaling collapse of the rheological data when the shear stress and shear rate are rescaled by proximity to the jamming transition. We extract critical scaling exponents and compared with simulations. C. S. O'Hern et al. Phys. Rev. E 68, 011306 (2003). P. Olsson, S. Teitel, Phys. Rev. Lett., 99, 178001 (2007). T. Hatano, arXiv:0803.2296v4 (2008), arXiv:0804.0477v2 (2008)

  3. Rheological investigation of thermal transitions in vesicular dispersion.

    PubMed

    Coppola, Luigi; Youssry, Mohamed; Nicotera, Isabella; Gentile, Luigi

    2009-10-15

    The thermal behavior of unsonicated dispersions of a double-chained surfactant, Dioctadecyldimethylammonium bromide (DODAB), has been studied over a wide concentration range using DSC and dynamic rheology. All dispersions are characterized by the pre- and main transition peaks at 35 degrees C and 43 degrees C, respectively. But, only above 10 mM DODAB, a third endotherm at 52 degrees C appears which may correspond to the (ULVs+Lalpha fragments)-->MLVs transition. The thermal-induced MLV's size is proportionally dependent on the concentration. In addition, and in agreement with DSC data, dynamic rheology has proven to be an indirect way to elucidate the structural transitions in these DODAB vesicular dispersions.

  4. 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.

  5. Characterization of protein rheology and delivery forces for combination products.

    PubMed

    Rathore, Nitin; Pranay, Pratik; Bernacki, Joseph; Eu, Bruce; Ji, Wenchang; Walls, Ed

    2012-12-01

    Characterization of a protein-device combination product over a wide range of operating parameters defined by end-user requirements is critical for developing a product presentation that is convenient for patient use. In addition to the device components, several product attributes, such as product rheology and product-container interactions, govern the functionality of a delivery system. This article presents results from a characterization study conducted for a high-concentration antibody product in a prefilled syringe. Analytical models are used to study the rheological behavior and to estimate delivery forces over a broad design space comprising temperature, concentration, and shear stress. Data suggest that high-viscosity products may exhibit significant shear thinning under the shear rates encountered under desired injection times.

  6. 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.

  7. Power-law rheology controls aftershock triggering and decay

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoming; Shcherbakov, Robert

    2016-11-01

    The occurrence of aftershocks is a signature of physical systems exhibiting relaxation phenomena. They are observed in various natural or experimental systems and usually obey several non-trivial empirical laws. Here we consider a cellular automaton realization of a nonlinear viscoelastic slider-block model in order to infer the physical mechanisms of triggering responsible for the occurrence of aftershocks. We show that nonlinear viscoelasticity plays a critical role in the occurrence of aftershocks. The model reproduces several empirical laws describing the statistics of aftershocks. In case of earthquakes, the proposed model suggests that the power-law rheology of the fault gauge, underlying lower crust, and upper mantle controls the decay rate of aftershocks. This is verified by analysing several prominent aftershock sequences for which the rheological properties of the underlying crust and upper mantle were established.

  8. 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).

  9. Power-law rheology controls aftershock triggering and decay

    PubMed Central

    Zhang, Xiaoming; Shcherbakov, Robert

    2016-01-01

    The occurrence of aftershocks is a signature of physical systems exhibiting relaxation phenomena. They are observed in various natural or experimental systems and usually obey several non-trivial empirical laws. Here we consider a cellular automaton realization of a nonlinear viscoelastic slider-block model in order to infer the physical mechanisms of triggering responsible for the occurrence of aftershocks. We show that nonlinear viscoelasticity plays a critical role in the occurrence of aftershocks. The model reproduces several empirical laws describing the statistics of aftershocks. In case of earthquakes, the proposed model suggests that the power-law rheology of the fault gauge, underlying lower crust, and upper mantle controls the decay rate of aftershocks. This is verified by analysing several prominent aftershock sequences for which the rheological properties of the underlying crust and upper mantle were established. PMID:27819355

  10. Rheological characterization of petrolatum using a controlled stress rheometer.

    PubMed

    Pandey, Preetanshu; Ewing, Gary D

    2008-02-01

    The current study focuses on characterizing the rheological characteristics of different petrolatum grades using a controlled stress rheometer. Both steady-state flow and dynamic oscillatory tests were conducted on the petrolatums. The thermorheological scans were found to be the most informative and reproducible for this study. Significant differences in the structure were observed between the petrolatum grades. The structural differences were found to be most significant in the temperature range 25-35 degrees C. The findings from this study will help in identifying the critical parameters (for e.g., temperature, mixing) during the processing and handling of such materials, which can have a direct impact on the product rheology and performance.

  11. 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.

  12. 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.

  13. Vibration Control of Sandwich Beams Using Electro-Rheological Fluids

    NASA Astrophysics Data System (ADS)

    Srikantha Phani, A.; Venkatraman, K.

    2003-09-01

    Electro-rheological (ER) fluids are a class of smart materials exhibiting significant reversible changes in their rheological and hence mechanical properties under the influence of an applied electric field. Efforts are in progress to embed ER fluids in various structural elements to mitigate vibration problems. The present work is an experimental investigation of the behaviour of a sandwich beam with ER fluid acting as the core material. A starch-silicone-oil-based ER fluid is used in the present study. Significant improvements in the damping properties are achieved in experiments and the damping contributions by viscous and non-viscous forces are estimated by force-state mapping (FSM) technique. With the increase in electric field across the ER fluid from 0 to 2 kV, an increase of 25-50% in equivalent viscous damping is observed. It is observed that as concentration of starch is increased, the ER effect grows stronger but eventually is overcome by applied stresses.

  14. 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.

  15. Optical twisting to monitor the rheology of single cells.

    PubMed

    de Saint Vincent, Matthieu Robert

    2016-05-26

    Biological cells exhibit complex mechanical properties which determine their responses to applied force. We developed an optical method to probe the temporal evolution of power-law rheology of single cells. The method consisted in applying optically a constant mechanical torque to a birefringent microparticle bound to the cell membrane, and observing dynamics of the particle's in-plane rotation. The deformation dynamics of the membrane followed a power law of time, which directly relates to cytoskeletal prestress as reported in the literature. The temporal evolution of this rheological behaviour, over time scales of several minutes, showed strong variations of the exponent on single adherent cells not subject to any specific treatment. The consistent observation of variations in the exponent suggests that, in their normal activity, living cells modulate their prestress by up to three orders of magnitude within minutes.

  16. Applications and limitations of a rheology for granular flows

    NASA Astrophysics Data System (ADS)

    Cawthorn, Chris; Hinch, John; Huppert, Herbert

    2007-11-01

    In order to assess the validity of the rheological law for granular flows proposed by Jop, Pouliquen and Forterre [Nature, vol. 441, pp.727-730], we present its application to a number of different problems. Whilst it works well for steady flow on a confined sandpile, or in an inclined channel, we will show that the law fails to qualitatively predict flow some simple geometries, such as annular Couette flow and vertical chute flow. In addition, we consider perturbations to 2D flow on an inclined plane and 3D flow in an inclined channel, where the effect of the confining vertical walls becomes important. Implications for the use of Jop's rheology for more complicated problems, particularly those involving dam-break or column collapse will also be addressed.

  17. 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.

  18. An apparatus for measuring the rheological properties of dental materials.

    PubMed

    Combe, E C; Moser, J B

    1976-01-01

    An indirect extrusion capillary viscometer has been developed. This has been tested for nonsetting Newtonian fluids and was found to give results close to, but slightly lower than the actual viscosity. The same apparatus has been successfully applied to a non-Newtonian fluid to determine the dependence of viscosity on shear rate. The technique described should meet the requirements for assessing the rheological characteristics important in the mixing and setting of dental materials. The developed viscometer must be coupled with a sensitive mechanical testing machine capable of an adequate range of crosshead speeds that can be changed rapidly. By obtaining force vs time curves at different shear rates for setting materials, viscosity can be calculated as a function of time. Also, the viscosity at any given time during the setting process can be calculated as a function of shear rate. This chould be of aid in the interpretation of changes in rheological properties during setting of dental materials.

  19. 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.

  20. Study of rheological properties of polypropylene/organoclay hybrid materials.

    PubMed

    Yu, Suzhu; Liu, Songlin; Zhao, Jianhong; Yong, Ming Shyan

    2006-12-01

    Polypropylene nanocomposites reinforced with organic modified montmorillonite clay have been fabricated by melt compounding using extrusion. The morphology of the composites is studied with transmission electron microscopy and X-ray diffraction. The melt-state rheological properties of the nanocomposites have been investigated as a function of temperature and organoclay loading. It is found that the organoclays are intercalated and dispersed evenly in the matrix. The storage and loss moduli of the hybrid composites decrease with temperature and increase with organoclay concentration. Both polypropylene and its composites demonstrate a melt-like rheological behavior, indicating the low degree of exfoliation of the organoclay. A shear thinning behavior is found for both polypropylene and its composites, but the onset of shear thinning for organoclay composites occurs at lower shear rates.

  1. 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.

  2. 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.

  3. 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. Copyright © 2014 Elsevier Ltd. All rights reserved.

  4. Rheology of red blood cell aggregation by computer simulation

    NASA Astrophysics Data System (ADS)

    Liu, Yaling; Liu, Wing Kam

    2006-12-01

    The aggregation of red blood cells (RBC) induced by the interactions between RBCs is a dominant factor of the in vitro rheological properties of blood, and existing models of blood do not contain full cellular information. In this work, we introduce a new three-dimensional model that couples Navier-Stokes equations with cell interactions to investigate RBC aggregation and its effect on blood rheology. It consists of a depletion mediated aggregation model to describe the interactions of RBCs and an immersed continuum model to track the deformation/motion of RBCs in blood plasma. To overcome the large deformation of RBCs, the meshfree method is used to model the RBCs. Three important phenomena in blood rheology are successfully captured and studied via this approach: the shear rate dependence of blood viscosity, the influence of cell rigidity on blood viscosity, and the Fahraeus-Lindqvist effect. As a microscopic illustration of the shear-rate dependence of the blood's viscoelasticity, the disaggregation of an RBC rouleau at shear rates varying between 0.125 and 24 s -1 is modeled. Lower RBC deformability and higher shear rates above 0.5 s -1 are found to facilitate disaggregation. The effective viscosities at different shear rates and for cells with different deformabilities are simulated. The numerical results are shown to agree with the reported experimental measurements. The Fahraeus-Lindqvist effect is, for the first time, studied through three-dimensional numerical simulations of blood flow through tubes with different diameters and is shown to be directly linked to axial-migration of deformable cells. This study shows that cell-cell interaction and cell deformability have significant effects on blood rheology in capillaries.

  5. 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.

  6. Relationship Between Seismic Velocity Anomalies and Rheological Anomalies

    NASA Astrophysics Data System (ADS)

    Karato, S.

    2001-05-01

    One of the ultimate goals of high-resolution Earth models is to reveal anomalies (lateral variations) in thermal and rheological structures. Although such a relationship has been well known at a qualitative level, no quantitative relationship has been established to allow estimate of anomalies in viscosity from seismological data. In this presentation, I formulate such a relationship for Earth's upper mantle, based on the latest mineral physics observations. The key in doing this is the quantitative analysis of the effects of water on seismic wave velocities. Earlier analysis indicated the importance of water on seismic wave velocities through enhanced attenuation (Karato, 1995). I have quantified this notion by combining laboratory observations on attenuation at limited conditions (Jackson et al., 1992) with the recent quantitative data on the effects of water on rheology at wider conditions (Karato and Jung, 2001). I show that both seismic wave velocities and rheology (viscosity) of Earth materials are controlled by "rheologically effective temperature (Teff)" that depends on temperature as well as water content. Such an analysis allows us to define the relationships between velocity anomalies and anomalies in Teff and hence anomalies in viscosity. The present formulation has been applied to the upper mantle beneath northeastern Japan where the high-resolution tomographic images are available. The results show that anomalies in effective temperatures of ~+400 K occur in these regions indicating that viscosity there could be lower than the average values by a factor of ~10 to ~1000. References Jackson, I. et al. (1992), Geophys. J. Int., 108: 517-534. Karato, S. (1995), Proc. Japan Academy, B71: 61-66. Karato, S. and Jung, H. (2001), submitted to Philos. Mag.

  7. Rheological evaluation of simulated neutralized current acid waste

    SciTech Connect

    Fow, C.L.; McCarthy, D.; Thornton, G.T.

    1986-06-01

    A byproduct of the Purex process is an aqueous waste stream that contains fission products. This waste stream, called current acid waste, is chemically neutralized and stored in double shell tanks on the Hanford Site. This neutralized current acid waste (NCAW) will be transported by pipe to B-Plant, a processing plant on the Hanford Site. Rheological and transport properties of NCAW slurry were evaluated. First, researchers conducted lab rheological evaluations of simulated NCAW. The results of these evaluations were then correlated with classical rheological models and scaled up to predict the performance that is likely to occur in the full-scale system. The NCAW in the tank will either be retrieved as is, i.e., no change in the concentration presently in the tank, or will be slightly concentrated before retrieval. Sluicing may be required to retrieve the solids. Three concentrations of simulated NCAW were evaluated that would simulate the different retrieval options: NCAW in the concentration that is presently in the tank; a slightly concentrated NCAW, called NCAW5.5; and equal parts of NCAW settled solids and water (simulating the sluicing stage), called NCAW1:1. The physical and rheological properties of three samples of each concentration at 25 and 100/sup 0/C were evaluated in the laboratory. The properties displayed by NCAW and NCAW5.5 at 25 and 100/sup 0/C allowed it to be classified as a pseudoplastic non-Newtonian fluid. NCAW1:1 at 25 and 100/sup 0/C displayed properties of a yield-pseudoplastic non-Newtonian fluid. The classical non-Newtonian models for pseudoplastic and yield-pseudoplastic fluids were used with the laboratory data to predict the full-scale pump-pipe network parameters.

  8. 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.

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

    PubMed

    Hermans, Eline; Vermant, Jan

    2014-01-07

    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.

  10. 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.

  11. Rheology of sediment transported by a laminar flow

    NASA Astrophysics Data System (ADS)

    Houssais, M.; Ortiz, C. P.; Durian, D. J.; Jerolmack, D. J.

    2016-12-01

    Understanding the dynamics of fluid-driven sediment transport remains challenging, as it occurs at the interface between a granular material and a fluid flow. Boyer, Guazzelli, and Pouliquen [Phys. Rev. Lett. 107, 188301 (2011)], 10.1103/PhysRevLett.107.188301 proposed a local rheology unifying dense dry-granular and viscous-suspension flows, but it has been validated only for neutrally buoyant particles in a confined and homogeneous system. Here we generalize the Boyer, Guazzelli, and Pouliquen model to account for the weight of a particle by addition of a pressure P0 and test the ability of this model to describe sediment transport in an idealized laboratory river. We subject a bed of settling plastic particles to a laminar-shear flow from above, and use refractive-index-matching to track particles' motion and determine local rheology—from the fluid-granular interface to deep in the granular bed. Data from all experiments collapse onto a single curve of friction μ as a function of the viscous number Iv over the range 3 ×10-5 ≤Iv≤2 , validating the local rheology model. For Iv<3 ×10-5 , however, data do not collapse. Instead of undergoing a jamming transition with μ →μs as expected, particles transition to a creeping regime where we observe a continuous decay of the friction coefficient μ ≤μs as Iv decreases. The rheology of this creep regime cannot be described by the local model, and more work is needed to determine whether a nonlocal rheology model can be modified to account for our findings.

  12. Factors Affecting the Rheologic Properties of Martian Polar Ice

    NASA Astrophysics Data System (ADS)

    Durham, W. B.

    1998-01-01

    The flow of the martian polar ice caps is influenced by the martian gravity field, the physical configuration of the caps and the underlying hard terrain, and the distribution and rheology of the material in the caps. This contribution speaks to the intrinsic theology of the material that comprises the polar caps. The polar caps are a mixture of phases of H2O, CO2, and rock. There is great uncertainty in the relative proportions of these components, and there are probably differences between compositions of the north and south polar caps. Frozen CO2 may exist as a shallow surface frost, especially on the south polar cap, but probably does not persist in rheologically important quantities. A good case can be made that CO2 is present as clathrate hydrate, and indeed, much of the material below a meter or so in the ice caps lies within the stability field Of CO2 hydrate. The amount of hydrate is difficult to predict, and the ratio of dust to ice in the layered deposits is not known to within several orders of magnitude. Finally, not only is the proportion of phases in the ice caps largely unknown, it is also likely to be nonuniform, as shown by layered deposits visible in sectional exposures at both poles. We assume for the purposes of discussion the simplest picture of the martian ice caps as void-free, predominantly water ice 1, with some clathuate hydrates and dust mixed in. The rheology of water ice is fairly well known, the rheology of hydrates is poorly known, and the dust can be safely assumed to be nondeformable in this mixture. To the extent the simple picture is incorrect (for example, if hydrates are present in very large quantities), the exercise here become less useful.

  13. Plate Interface Rheology, Mechanical Coupling and Accretion during Subduction Infancy

    NASA Astrophysics Data System (ADS)

    Agard, P.; Yamato, P.; Mathieu, S.; Prigent, C.; Guillot, S.; Plunder, A.; Dubacq, B.; Monie, P.; Chauvet, A.

    2015-12-01

    Understanding subduction rheology in both space and time has been a challenge since the advent of plate tectonics. We herein focus on "subduction infancy", that is the first ~1-5 My immediately following subduction nucleation, when a newly born slab penetrates into the upper plate mantle and heats up. The only remnants of this critical yet elusive geodynamic step are thin metamorphic soles, commonly found beneath pristine, 100-1000 km long portions of oceanic lithosphere emplaced on continents (i.e., ophiolites). Through the (i) worldwide compilation of pressure-temperature conditions of metamorphic sole formation augmented by pseudosection thermodynamic modeling, (ii) calculations of the viscosity of materials along the plate interface and (iii) generic numerical thermal models, we provide a conceptual model of dynamic plate interface processes during subduction infancy (and initiation s.l.). We show in particular how major rheological switches across the subduction interface control slab penetration, and the formation of metamorphic soles. Due to the downward progression of hydration and weakening of the mantle wedge with cooling, the lower plate (basalt, sediment) and the upper plate (mantle wedge) rheologies equalize and switch over a restricted temperature-time-depth interval (e.g., at ~800°C and ~1 GPa, during 0.1-2 My, for high-temperature metamorphic sole formation). These switches result in episodes of maximum interplate mechanical coupling, thereby slicing the top of the slab and welding pieces (basalt, sediment) to the base of the mantle wedge. Similar mechanical processes likely apply for the later, deeper accretion and exhumation of high-temperature oceanic eclogites in serpentinite mélanges, or for the accretion of larger tectonic slices. This model provides constraints on the effective rheologies of the crust and mantle and general understanding, at both rock and plate scale, for accretion processes and early slab dynamics.

  14. Factors affecting impairment of blood rheology in obese subjects.

    PubMed

    Hitsumoto, Takashi

    2012-11-01

    Impairment of blood rheology has been reported to be associated with cardiovascular diseases. Recently, visible micro channel methods [micro channel array flow analyzer (MC-FAN)] have been developed to clinically evaluate blood rheology. The aim of this cross-sectional study is to clarify the factors important for impairment of blood rheology in obese subjects using MC-FAN. One hundred and fifty-nine obese subjects and 100 non-obese subjects with no history of cardiovascular diseases were enrolled. Blood passage time (BPT) was measured using MC-FAN and relationships between BPT and various clinical parameters were examined. BPT was significantly higher in obese subjects than in non-obese subjects (obesity vs. non-obesity: 62.8 ± 17.9s vs. 54.1 ± 14.6s, p<0.001); however, there were no significant relationships between BPT and body mass index or waist circumference in obese subjects. BPT was significantly related to systolic blood pressure levels (r=0.21; p<0.001), high-sensitivity C-reactive protein concentrations (r=0.37; p<0.001), a marker of inflammation, and derivatives of reactive oxygen metabolites test (r=0.38; p<0.001), a marker of oxidative stress, smoking, and exercise habits in obese subjects. Furthermore, multivariate analysis revealed that derivatives of reactive oxygen metabolites test (t=5.2; p<0.001), high sensitivity C-reactive protein concentration (t=3.6; p<0.01), smoking (t=3.2; p<0.001), and exercise habits (t=-2.4; p<0.05) were independent variables for BPT. Data indicate that inflammation, oxidative stress, and lifestyle choices are more important factors for impairment of blood rheology, which is evaluated by MC-FAN, than the degree of adiposity in obese subjects. Copyright © 2012 Japanese College of Cardiology. Published by Elsevier Ltd. All rights reserved.

  15. Spectral rheology in a sphere. [for geological models

    NASA Technical Reports Server (NTRS)

    Caputo, M.

    1984-01-01

    An earth model is considered whose rheology is described by a stress train relation similar to that which seems to fit the laboratory data resulting from constant strain rate and creep experiments on polycrystalline halite and granite. The response of the model to a surface load is studied. It is found that the displacement and the creep are weakly dependent on the wavenumber and that the strain energy is concentrated in the low wavenumber and coherent over large regions.

  16. Rheological properties of erythrocytes in patients infected with Clostridium difficile.

    PubMed

    Czepiel, Jacek; Jurczyszyn, Artur; Biesiada, Grażyna; Sobczyk-Krupiarz, Iwona; Jałowiecka, Izabela; Świstek, Magdalena; Perucki, William; Teległów, Aneta; Marchewka, Jakub; Dąbrowski, Zbigniew; Mach, Tomasz; Garlicki, Aleksander

    2014-12-04

    Clostridium difficile infection (CDI) is a bacterial infection of the digestive tract. Acute infections are accompanied by increased risk for venous thromboembolism (VTE). To date, there have been no studies of the rheological properties of blood during the course of digestive tract infections. The aim of our study was to examine the effects of CDI on red blood cell (RBC) rheology, specifically RBC deformability, RBC aggregation, and plasma viscosity. In addition, the activity of glucose 6 phosphate dehydrogenase (G6PD) and acetylcholinesterase (AChE) in RBC was studied. Our study group included 20 patients with CDI, 20 healthy persons comprised the control group. We examined the effects of CDI on the rheology of RBCs, their deformability and aggregation, using a Laser-assisted Optical Rotational Cell Analyzer (LORCA). Plasma viscosity was determined using a capillary tube plasma viscosymeter. Moreover, we estimated the activity of AChE and G6PD in RBC using spectrophotometric method. A statistically significant increase was found in the aggregation index, viscosity and activity of G6PD whereas the amount of time to reach half of maximum aggregation (t½) and the amplitude of aggregation (AMP) both showed statistically significantly decreases among patients with CDI compared to the control group. We also observed that the Elongation Index (EI) was decreased when shear stress values were low, between 0.3 Pa and 0.58 Pa, whereas EI was increased for shear stress in the range of 1.13-59.97 Pa. These observations were statistically significant. We report for the first time that acute infection of the gastrointestinal tract with Clostridium difficile is associated with abnormalities in rheological properties of blood, increased serum viscosity as well as increased aggregation of RBCs, which correlated with severity of inflammation. These abnormalities may be an additional mechanism causing increased incidence of VTE in CDI.

  17. Rheology of magnesite and implications for subduction zone dynamics

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    We deformed two natural magnesite aggregates over a wide range of temperatures (400-1000oC) and strain rates (10-7 - 10-4/s) in order to determine the deformation mechanisms of magnesite and their respective rheologies. The two magnesite aggregates have similar compositions, but different grain sizes (1 vs. 100 μm). Experiments using fine-grained magnesite were performed in a Heard-type gas confining medium rock deformation apparatus at a constant effective pressure (= confining pressure - CO2 pressure) of 300 MPa. Experiments using coarse-grained magnesite were performed using molten salt or solid salt assemblies in a Griggs-type piston-cylinder rock deformation apparatus at a constant effective pressure of 900 MPa. At low temperatures (T≤600oC, strain rate = 10-5/s) both magnesite aggregates deform by crystal plastic mechanisms predominated by dislocation glide. However, at higher temperatures the coarse-grained magnesite aggregate deforms by dislocation creep and the fine-grained magnesite aggregate deforms by diffusion creep. The strain rate and temperature dependence of the low temperature plasticity, dislocation creep and diffusion creep rheologies can be described by power laws with stress exponents (n) of 19.7, 3.0 and 1.1 and activation enthalpies of 229, 410 and 209 kJ/mol, respectively. The rheology of the low temperature plasticity data can also be described using an exponential flow law with α = 0.022 MPa-1 with a best-fit activation enthalpy of 233 kJ/mol. Extrapolation of the experimentally determined rheological data to natural conditions indicates that magnesite is generally stronger than calcite and dolomite assuming similar grain sizes. However, its strength is orders of magnitude lower than olivine at all conditions in the Earth's mantle. Thus magnesite may act as a weak phase in altered lithosphere of subduction zones, and it may even promote deep-focus earthquakes through ductile instabilities.

  18. Membrane bioreactor sludge rheology at different solid retention times.

    PubMed

    Laera, G; Giordano, C; Pollice, A; Saturno, D; Mininni, G

    2007-10-01

    Rheological characterization is of crucial importance in sludge management both in terms of biomass dewatering and stabilization properties and in terms of design parameters for sludge handling operations. The sludge retention time (SRT) has a significant influence on biomass properties in biological wastewater treatment systems and in particular in membrane bioreactors (MBRs). The aim of this work is to compare the rheological behaviour of the biomass in a MBR operated under different SRTs. A bench-scale MBR was operated for 4 years under the same conditions except for the SRT, which ranged from 20 days to complete sludge retention. The rheological properties were measured over time and the apparent viscosity was correlated with the concentration of solid material when equilibrium conditions were reached and maintained. The three models most commonly adopted for rheological simulations were evaluated and compared in terms of their parameters. Then, steady-state average values of these parameters were related to the equilibrium biomass concentration (MLSS). The models were tested to select the one better fitting the experimental data in terms of mean root square error (MRSE). The relationship between the apparent viscosity and the shear rate, as a function of solid concentration, was determined and is proposed here. Statistical analysis showed that, in general, the Bingham model provided slightly better results than the Ostwald one. However, considering that a strong correlation between the two parameters of the Ostwald model was found for all the SRTs tested, both in the transient growth phases and under steady-state conditions, this model might be used more conveniently. This feature suggests that the latter model is easier to be used for the determination of the sludge apparent viscosity.

  19. 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…

  20. The evaluation of solder paste characteristics using AC impedance spectroscopy

    NASA Astrophysics Data System (ADS)

    Hirthe, Richard Walter

    One of the more critical aspects of engineering is often understanding the variety of complex materials that are employed in industry today. This encompasses knowledge of both the physical nature of materials, and how differences in composition and processing affect the properties and performance of the material (or combination of materials) to be utilized. The monitoring of solder paste characteristics during surface mount circuit assembly procedures is ultimately concerned with obtaining a high yield of reliable solder joints. The process control of solder paste systems under manufacturing conditions is, at present, not derived from on-line measurements of the paste. Because these tests are not performed in-process, they cannot detect critical changes in paste behavior caused by varying process conditions, environmental factors, or the loss of rheological characteristics induced by prolonged stress on a screen printer. AC impedance techniques can be a valuable tool in characterizing the properties of materials that possess measurable dielectric behavior. Recent advances in impedance measurement instrumentation (and the evolution of the personal computer) have yielded improved data acquisition and analysis capabilities. This has precipitated efforts to utilize this methodology for the study of more complex materials systems (such as solder paste). The primary focus of this investigation is the implementation of AC impedance techniques as a means of characterizing the behavior of a broad range of solder paste formulations. In the course of this work, it has been determined that it is possible to represent both the dielectric and the electro-chemical nature of these materials in the form of an electrical equivalent circuit model. This modeling yields significant detail concerning the microscopic attributes of these materials, unobtainable from other forms of study. As a process control tool in the manufacturing realm, the use of AC impedance techniques to monitor

  1. 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.

  2. 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.

  3. 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.

  4. Dielectric and rheological properties of polyaniline organic dispersions

    NASA Astrophysics Data System (ADS)

    Bohli, N.; Belhadj Mohamed, A.; Vignéras-Lefèbvre, V.; Miane, J.-L.

    2009-05-01

    This paper reports the examination of the evolution of polyaniline-organic solvent interactions in the temperature range of 294-353 K. For this purpose, rheological and dielectric investigations have been undertaken for dispersions of plast-doped polyaniline in two different solvents (dichloroacetic acid and formic acid/dichloroacetic acid mixture). Dielectric permittivity has been investigated using the open ended coaxial line method in the frequency range of [100 MHz, 10 GHz]. Dielectric loss spectra of both dispersions showed a relaxation peak which was well fitted by Havriliak-Negami function. The relaxation was attributed to a Maxwell Wagner Sillars relaxation within polyaniline clusters. The difference found between relaxation parameters of the pure solvent and polyaniline dispersions was attributed to the solvent/polyaniline interactions. The relaxation time relative to the PANI/DCAA dispersion followed an Arrhenius law. While a Vogel-Fulcher-Tammann law was found for the relaxation time of PANI/DCAA-FA dispersion. Above a certain temperature, 318 K for PANI/DCAA and 313 K for PANI/DCAA-FA, the rheological parameters of the dispersions changed, thus indicating a morphological change of polyaniline in the dispersion. In the same range of temperature, α and β relaxation parameters undergo significant changes. Those changes in dielectric and rheological parameters seem to be related to a structural change occurring in the polyaniline organic dispersion systems while increasing temperature. An interesting correlation between permittivity and viscosity was obtained.

  5. Comparison of the Rheology of Bauxite Residue Suspensions

    NASA Astrophysics Data System (ADS)

    Pashias, N.; Boger, D. V.; Summers, J.; Glenister, D. J.

    The paper presents an overview on the rheology of bauxite residue suspensions. Comparative viscosity and yield stress data are presented for bauxite residues generated in Australia, Jamaica, Surinam, and the USA. A yield stress for optimum dry disposal is specified as is the concentration for minimum energy consumption for the pumping of the four different materials. The data show that bauxite residues can be characterised at two structural states: the initial and the equilibrium or time-independent state. Data can be collected and reproduced for different muds providing there is an understanding of the time dependent nature of the material. The four red mud samples obtained from around the world have been characterised in both the initial and final equilibrium state. A comparison shows that after the course particle fraction has been removed the US, Surinam, and three samples from Western Australia all show similar rheological characteristics in the reduced structural state. A fundamental understanding of the basic rheology of bauxite residue is necessary for establishing an optimal waste disposal strategy.

  6. Rheological properties of polysaccharides from Dioscorea opposita Thunb.

    PubMed

    Ma, Fanyi; Zhang, Yun; Liu, Nanhua; Zhang, Jie; Tan, Gaixiu; Kannan, Balan; Liu, Xiuhua; Bell, Alan E

    2017-07-15

    This study investigated the chemical components and rheological properties of polysaccharides from Dioscorea opposita Thunb. Graded alcohol precipitation was used to extract Dioscorea opposita polysaccharide samples (S1, S2, S3 and S4). The monosaccharides, amino acid content and molecular weight of each sample were measured and compared. The rheological properties of the polysaccharide samples at different concentrations, temperatures and pH values were studied. The rheological properties of S1, S2 and S3 exhibited pseudoplastic properties and "gel-like" behaviour. The viscosity of S1 was improved with rising temperatures, especially temperatures higher than 80°C, which may be caused by the starch gelatinisation. The acidic and basic environments may break the structures of S3 and S4. However, the extreme conditions improved the viscosity of S1. This work was a basic investigation of the Dioscorea opposita polysaccharides, contributing to the function of yam products and applications of natural thickeners in the food industry. Copyright © 2017. Published by Elsevier Ltd.

  7. Rheology of Anhydrite during deformation in nature: a first look

    NASA Astrophysics Data System (ADS)

    Markus Schmalholz, Stefan; Urai, Janos

    2014-05-01

    The rheology of Anhydrite under conditions of natural deformation is largely unconstrained, although it has many important effects in salt tectonics and in long-tem predictions of engineering structures in salt. A review of laboratory triaxial experiments at low temperature indicate brittle, pressure dependent behavior. At temperatures above 400 C experimental deformation shows power law creep, with contributions of dislocation creep and diffusional creep. In naturally deformed Anhydrite rocks microstructures indicate recrystallization, solution - precipitation processes and pressure solution producing stylolites. Analysis of Anhydrite layers embedded in rock salt shows complex behavior. Bedding-parallel stretching leads to boudinage, with variable amounts of pinch-and-swell before rupture and precipitation of Halite in the boudin-neck. Bedding-parallel shortening of single layers embedded in salt leads to folding of the Anhydrite layers, with the fold shapes suggesting an effective viscosity contrast between 10 and 100. This is also in agreement with the absence of extension fracture in the outer arcs of the folds. Although much remains to be done in accurately constraining Anhydrite rheology in nature, and for example its dependence on pore fluid pressure and chemistry, these results provide a first order estimate of Anhydrite rheology in nature, to be used in numerical simulations. A challenging task is to find a unified flow law which describes power law creep and fracturing dependent on effective stress.

  8. 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.

  9. Maximum bubble pressure rheology of low molecular mass organogels.

    PubMed

    Fei, Pengzhan; Wood, Steven J; Chen, Yan; Cavicchi, Kevin A

    2015-01-13

    Maximum bubble pressure rheology is used to characterize organogels of 0.25 wt % 12-hydroxystearic acid (12-HSA) in mineral oil, 3 wt % (1,3:2,4) dibenzylidene sorbitol (DBS) in poly(ethylene glycol), and 1 wt % 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol (DMDBS) in poly(ethylene glycol). The maximum pressure required to inflate a bubble at the end of capillary inserted in a gel is measured. This pressure is related to the gel modulus in the case of elastic cavitation and the gel modulus and toughness in the case of irreversible fracture. The 12-HSA/mineral oil gels are used to demonstrate that this is a facile technique useful for studying time-dependent gel formation and aging and the thermal transition from a gel to a solution. Comparison is made to both qualitative gel tilting measurements and quantitative oscillatory shear rheology to highlight the utility of this measurement and its complementary nature to oscillatory shear rheology. The DBS and DMDBS demonstrate the generality of this measurement to measure gel transition temperatures.

  10. 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.

  11. Synthesis and rheological behavior of atactic polypropylene molecular bottlebrushes

    NASA Astrophysics Data System (ADS)

    Dalsin, Samuel; Bates, Frank; Hillmyer, Marc

    2014-03-01

    Molecular bottlebrushes are branched polymer structures characterized by an extremely high density of polymeric side chains emanating from a central backbone. Due to unique conformational and rheological properties, molecular bottlebrushes have become attractive candidates for developing new photonic bandgap materials, nanotubes and nanowires, and rheological modifiers. In this study, bottlebrushes comprised of atactic polypropylene (aPP) side chains were synthesized via ring-opening metathesis polymerization of norbornenyl-terminated aPP macromonomers. A series of bottlebrush polymers with fixed side chain length and variable backbone length was prepared using Grubbs' third-generation catalyst, yielding products with low dispersity in less than five minutes reaction time. Small-amplitude oscillatory shear measurements were performed to examine linear viscoelastic properties. Master curves of all bottlebrush polymers exhibited relaxation spectra devoid of any entanglement plateau, despite high molecular weights (up to 892 kg/mol). Lack of entanglement was further confirmed by zero shear viscosity experiments, which displayed a nearly linear dependence on molecular weight. These rheological properties are compared directly with a linear aPP control sample. Supported by ExxonMobil Chemical Company.

  12. 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.

  13. Rheology of water-silicate mixtures at low temperatures

    NASA Technical Reports Server (NTRS)

    Durham, William B.

    1992-01-01

    Lab studies of the effects of hard particulates on the rheology of ice have been mainly directed at the evolution of the Galilean satellites, but yield results that may be applicable to the rheology of the Martian polar caps. The experiments have explored the ductile rheology as well as brittle behavior of water + particulate (mainly quartz) mixtures in particulate volume fractions ranging from 0.001 to 0.56, particulate sizes 1 to 150 microns, temperatures 77 to 224 K, and deformation rates 3.5 x 10(exp -7) to 3.5 x 10(exp -4)/s, under confining pressures of 50 to 100 MPa. Particulates act mainly to strengthen the material in the ductile field, although work by others has shown that very close to the melting temperature hard particulates can actually cause softening. So called dispersion hardening by the Orowan mechanism of pinning glide dislocations, often exploited in metallurgy for strengthening materials, appears not to be an issue in ice except at very low temperatures, less than approx. 135 K.

  14. 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

    2016-02-06

    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.

  15. Rheological study of polypropylene irradiated with polyfunctional monomers

    NASA Astrophysics Data System (ADS)

    Otaguro, H.; Rogero, S. O.; Yoshiga, A.; Lima, L. F. C. P.; Parra, D. F.; Artel, B. W. H.; Lugão, A. B.

    2007-12-01

    The aim of this paper is to investigate the rheological properties of polypropylene (PP) modified by ionization radiation (gamma rays) in the presence of two different monomers. The samples were mixed in a twin-screw extruder with ethylene glycol dimethacrylate (EGDMA) or trimethylolpropane trimethacrylate (TMPTMA) with concentration in the range of 0.5-5.0 mmol. After that, they were irradiated with 20 kGy dose of gamma radiation. The structural modification of polypropylene was analyzed in the melt state by measuring melt flow rate (MFR), η* (complex viscosity) and G' (storage modulus) in the angular frequency range of 10 -1 to 3 × 10 2 rad s -1. From the oscillatory rheology data, one could obtain the values of η0 (zero shear viscosity) that would be related to the molar mass. All results were discussed with respect to the crosslinking and degradation process that occur in the post-reactor treatment to produce controlled rheology polypropylene. The resulting polymeric materials were submitted the cytotoxicity in vitro test by neutral red uptake methodology with NCTC L 929 cell line from American Type Culture Collection bank. All modified PP samples presented no cytotoxicity.

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

    PubMed

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

    2016-01-01

    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). 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. 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*). EndoREZ exhibited better rheological properties compared to the other two test sealers.

  17. 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

  18. 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

  19. Rheology of cellulose nanofibrils in the presence of surfactants.

    PubMed

    Quennouz, Nawal; Hashmi, Sara M; Choi, Hong Sung; Kim, Jin Woong; Osuji, Chinedum O

    2016-01-07

    Cellulose nanofibrils (CNFs) present unique opportunities for rheology modification in complex fluids. Here we systematically consider the effect of ionic and non-ionic surfactants on the rheology of dilute CNF suspensions. Neat suspensions are transparent yield-stress fluids which display strong shear thinning and power-law dependence of modulus on concentration, G' ∼ c(2.1). Surfactant addition below a critical mass concentration cc produces an increase in the gel modulus with retention of optical clarity. Larger than critical concentrations induce significant fibril aggregation leading to the loss of suspension stability and optical clarity, and to aggregate sedimentation. The critical concentration was the lowest for a cationic surfactant (DTAB), cc ≈ 0.08%, while suspension stability was retained for non-ionic surfactants (Pluronic F68, TX100) at concentrations up to 8%. The anionic surfactant SDS led to a loss of stability at cc ≈ 1.6% whereas suspension stability was not compromised by anionic SLES up to 8%. Dynamic light scattering data are consistent with a scenario in which gel formation is driven by micelle-nanofibril bridging mediated by associative interactions of ethoxylated surfactant headgroups with the cellulose fibrils. This may explain the strong difference between the properties of SDS and SLES-modified suspensions. These results have implications for the use of CNFs as a rheology modifier in surfactant-containing systems.

  20. Rheological behavior of silver nanowire conductive inks during screen printing

    NASA Astrophysics Data System (ADS)

    Hemmati, Shohreh; Barkey, Dale P.; Gupta, Nivedita

    2016-08-01

    The rheological behavior of silver nanowire (AgNW) suspensions adapted for screen printing inks was investigated. Aqueous silver nanowire inks consisting of AgNW (length of 30 μm, and diameter of 40 and 90 nm), dispersant and binder were formulated. The effect of AgNW content on the rheological behavior of the ink and the build-up of ink structure after screen printing were examined as they depend on applied shear and temperature. Rheological measurements under conditions that mimic the screen printing process were done to assess viscoelastic properties induced by flow alignment of the wires and the subsequent recovery of the low shear structure. The Stretched Exponential model (SEmo) was used to model the recovery process after screen printing to obtain the characteristic time of the recovery or build-up process. The characteristic time was determined at several temperatures to obtain the activation energy of recovery. The domination of Brownian motion or non-Brownian motion behavior can be characterized by a Peclet number, which is the ratio of shear rate to the rotational diffusion coefficient. The Peclet number and the dimensionless concentration of wires were used to assess the recovery mechanism. The steady viscosity at low and high shear rates was also treated by an activation energy analysis.

  1. Thermal and rheological properties of nixtamalized maize starch.

    PubMed

    Mendez-Montealvo, G; Sánchez-Rivera, M M; Paredes-López, O; Bello-Pérez, L A

    2006-12-15

    The effect of nixtamalization process on thermal and rheological characteristics of corn starch was studied. Starch of raw sample had higher gelatinization temperature than its raw counterpart, because, the Ca(2+) ions stabilize starch structure of nixtamalized sample; however, the enthalpy values were not different in both samples. The temperature of the phase transition of the retrograded starches (raw and nixtamalized) were not different at the storage times assessed, but the enthalpy values of the above mentioned transition was different, indicating a lower reorganization of the starch structure in the nixtamalized sample. The viscoamylographic profile showed differences between both starches, since raw starch had higher peak viscosity than the nixtamalized sample due to partial gelatinization of some granules during this heat treatment. Rheological test showed that at low temperature (25 degrees C) the raw and nixtamalized starches presented different behaviour; however, the elastic characteristic was more important in the starch gel structure. The nixtamalization process produced changes in thermal and rheological characteristics becoming important in those products elaborated from nixtamalized maize.

  2. Long-Lived Neighbors Determine the Rheological Response of Glasses

    NASA Astrophysics Data System (ADS)

    Laurati, M.; Maßhoff, P.; Mutch, K. J.; Egelhaaf, S. U.; Zaccone, A.

    2017-01-01

    Glasses exhibit a liquidlike structure but a solidlike rheological response with plastic deformations only occurring beyond yielding. Thus, predicting the rheological behavior from the microscopic structure is difficult, but important for materials science. Here, we consider colloidal suspensions and propose to supplement the static structural information with the local dynamics, namely, the rearrangement and breaking of the cage of neighbors. This is quantified by the mean squared nonaffine displacement and the number of particles that remain nearest neighbors for a long time, i.e., long-lived neighbors, respectively. Both quantities are followed under shear using confocal microscopy and are the basis to calculate the affine and nonaffine contributions to the elastic stress, which is complemented by the viscoelastic stress to give the total stress. During start-up of shear, the model predicts three transient regimes that result from the interplay of affine, nonaffine, and viscoelastic contributions. Our prediction quantitatively agrees with rheological data and their dependencies on volume fraction and shear rate.

  3. Complex fluid-fluid interfaces: rheology and structure.

    PubMed

    Fuller, Gerald G; Vermant, Jan

    2012-01-01

    Complex fluid-fluid interfaces are common to living systems, foods, personal products, and the environment. They occur wherever surface-active molecules and particles collect at fluid interfaces and render them nonlinear in their response to flow and deformation. When this occurs, the interfaces acquire a complex microstructure that must be interrogated. Interfacial rheological material properties must be measured to appreciate their role in such varied processes as lung function, cell division, and foam and emulsion stability. This review presents the methods that have been devised to determine the microstructure of complex fluid-fluid interfaces. Complex interfacial microstructure leads to rheological complexity. This behavior is often responsible for stabilizing interfacial systems such as foams and emulsions, and it can also have a profound influence on wetting/dewetting dynamics. Interfacial rheological characterization relies on the development of tools with the sensitivity to respond to small surface stresses in a way that isolates them from bulk stresses. This development is relatively recent, and reviews of methods for both shear and dilatational measurements are offered here.

  4. 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.

  5. Clay-cement suspensions - rheological and functional properties

    NASA Astrophysics Data System (ADS)

    Wojcik, L.; Izak, P.; Mastalska-Poplawska, J.; Gajek, M.

    2017-01-01

    The piping erosion in soil is highly unexpected in civil engineering. Elimination of such damages is difficult, expensive and time-consuming. One of the possibility is the grouting method. This method is still developed into direction of process automation as well as other useful properties of suspensions. Main way of modernization of the grouting method is connected it with rheology of injection and eventuality of fitting them to specific problems conditions. Very popular and useful became binders based on modified clays (clay-cement suspensions). Important principle of efficiency of the grouting method is using of time-dependent pseudothixotropic properties of the clay-cement suspensions. The pseudo-rheounstability aspect of the suspensions properties should be dedicated and fitted to dynamic changes of soil conditions destructions. Whole process of the modification of the suspension rheology is stimulated by the specific agents. This article contains a description of practical aspects of the rheological parameters managing of the clay-cement suspensions, dedicated to the building damages, hydrotechnic constructions etc.

  6. 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.

  7. Rheology of water-silicate mixtures at low temperatures

    NASA Technical Reports Server (NTRS)

    Durham, William B.

    1992-01-01

    Lab studies of the effects of hard particulates on the rheology of ice have been mainly directed at the evolution of the Galilean satellites, but yield results that may be applicable to the rheology of the Martian polar caps. The experiments have explored the ductile rheology as well as brittle behavior of water + particulate (mainly quartz) mixtures in particulate volume fractions ranging from 0.001 to 0.56, particulate sizes 1 to 150 microns, temperatures 77 to 224 K, and deformation rates 3.5 x 10(exp -7) to 3.5 x 10(exp -4)/s, under confining pressures of 50 to 100 MPa. Particulates act mainly to strengthen the material in the ductile field, although work by others has shown that very close to the melting temperature hard particulates can actually cause softening. So called dispersion hardening by the Orowan mechanism of pinning glide dislocations, often exploited in metallurgy for strengthening materials, appears not to be an issue in ice except at very low temperatures, less than approx. 135 K.

  8. Investigating the rheological properties of native plant latex.

    PubMed

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

    2014-01-06

    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).

  9. Rheological Fluids under Perturbation: Reconstruction and Relaxation Processes

    NASA Astrophysics Data System (ADS)

    de La Calleja, Elsa Maria; Carrillo, Jose Luis

    2006-03-01

    We study the evolution of the structure of electro rheological as well as magneto rheological fluids in the presence of perturbation fields. We have previously shown that the fibrous structure acquired by these dispersions in the presence of a static, electric or magnetic, field has multifractal characteristics[1]. If in addition to the static field a perpendicular pulsed field is applied, under certain conditions it is possible to rearrange the structure into an ordered one[2]. Based on the measured mass fractal dimension and the radial distribution of mass, we discuss these processes and other structural characteristics of the system approaching these phenomena as a glass transition. [1] J. L. Carrillo, F. Donado, and M. E. Mendoza: Fractal patterns, cluster dynamics, and elastic properties. Phys. Rev. E 68, 061509 (2003); J. L. Carrillo, M. E. Mendoza, and F. Donado: Fractal patterns and aggregation processes in rheological dispersions. J. Stat. Mech. P06001 (2005). [2] J. L. Carrillo, E. M. De la Calleja, M. E. Mendoza, and F. Donado, Ferroelectrics (in press).

  10. Rheological characterization of nuclear waste using falling-ball rheometry

    SciTech Connect

    Abbott, J.R.; Unal, C.; Stephens, T.; Pasamehmetoglu, K.O.; Graham, A.L.; Edwards, J.N.

    1994-07-01

    Knowledge of the rheological properties of saturated solutions containing solid particles is very important in nuclear waste management technology. For example, the nuclear waste in the Hanford Site high-level radioactive waste tanks contains strong electrolyte solutions with a high concentration of solids. Previous attempt using rotational viscometers to determine the rheology has shown unusual thixotropic and shear thinning behaviors with a lack of reproducibility. Using falling-ball rheometry, the rheology of the undisturbed simulant may be determined with much better reproducibility. In this study, a well-mixed simulant which has similar chemical composition to the actual waste will be tested. Falling-ball size and density will be varied to get data in a wide range of shear rates. To determine the rheogram, several methods will be tried to match the observed data. Based on these tests, a rheogram can be determined from the model and its best-fit parameters. The simulant shows shear-thinning behavior and a yield stress. This would suggest a H-B model. But when fitting to one of the simulants which showed a very low yield stress, the predictions assuming no yield and assuming yield resulted in no improvement in the fit when assuming yield.

  11. 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).

  12. Modeling of rheological properties for entangled polymer systems

    NASA Astrophysics Data System (ADS)

    Banerjee, Nilanjana

    The study of entangled polymer rheology both in the field of medicine and polymer processing has their major importance. Mechanical properties of biomolecules are studied in order to better understand cellular behavior. Similarly, industrial processing of polymers needs thorough understanding of rheology so as to improve process techniques. Work in this dissertation has been organized into three major sections. Firstly, numerical/analytical models are reviewed for describing rheological properties and mechanical behaviors of cytoskeleton. The cytoskeleton models are classified into categories according to the length scales of the phenomena of interest. The main principles and characteristics of each model are summarized and discussed by comparison with each other, thus providing a systematic understanding of biopolymer network modeling. Secondly, a new constitutive "toy" Mead-Banerjee-Park (MBP) model is developed for monodisperse entangled polymer systems, by introducing the idea of a configuration dependent friction coefficient (CDFC) and entanglement dynamics (ED) into the MLD "toy" model. The model is tested against experimental data in steady and transient extensional and shear flows. The model simultaneously captures the monotonic thinning of the extensional flow curve of polystyrene (PS) melts and the extension hardening found in PS solutions. Thirdly, the monodisperse MBP model is accordingly modified into polydisperse MBP "toy" constitutive model to predict the nonlinear viscoelastic material properties of model polydisperse systems. The polydisperse MBP toy model accurately predicts the material properties in the forward direction for transient uniaxial extension and transient shear flow.

  13. Identification of rheological properties of human body surface tissue.

    PubMed

    Benevicius, Vincas; Gaidys, Rimvydas; Ostasevicius, Vytautas; Marozas, Vaidotas

    2014-04-11

    According to World Health Organization obesity is one of the greatest public health challenges of the 21st century. It has tripled since the 1980s and the numbers of those affected continue to rise at an alarming rate, especially among children. There are number of devices that act as a prevention measure to boost person's motivation for physical activity and its levels. The placement of these devices is not restricted thus the measurement errors that appear because of the body rheology, clothes, etc. cannot be eliminated. The main objective of this work is to introduce a tool that can be applied directly to process measured accelerations so human body surface tissue induced errors can be reduced. Both the modeling and experimental techniques are proposed to identify body tissue rheological properties and prelate them to body mass index. Multi-level computational model composed from measurement device model and human body surface tissue rheological model is developed. Human body surface tissue induced inaccuracies can increase the magnitude of measured accelerations up to 34% when accelerations of the magnitude of up to 27 m/s(2) are measured. Although the timeframe of those disruptions are short - up to 0.2 s - they still result in increased overall measurement error.

  14. Factors Affecting the Rheological Measurement of Hyaluronic Acid Gel Fillers.

    PubMed

    Lorenc, Z Paul; Öhrlund, Åke; Edsman, Katarina

    2017-09-01

    With the number of available dermal fillers increasing, so is the demand for scientifically based comparisons, often with rheological properties in focus. Since analytical results are always influenced by instrument settings, consensus on settings is essential to make comparison of results from different investigators more useful. Preferred measurement settings for rheological analysis of hyaluronic acid (HA) fillers are suggested, and the reasoning behind the choices is presented by demonstrating the effect of different measurement settings on select commercial HA fillers. Rheological properties of 8 HA fillers were measured in a frequency sweep from 10 to 0.01 Hz at 0.1% strain, using an Anton Paar MCR 301, a PP-25 measuring system with a gap of 1 mm at 25°C. A 30-min period was used for relaxation of the sample between loading and measuring. The data presented here, together with previously published data, demonstrate differences in G' from 1.6 to 7.4 times for the same product. A large part of the differences were concluded to be due to differences in rheometry measurement settings. The confusion from the many parameters involved in rheometry can be avoided by simply using the elastic modulus (G') to differentiate products.

    J Drugs Dermatol. 2017;16(9):876-882.

    .

  15. 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.

  16. Numerical analysis of rheological and tribological behavior influence on 16MnCr5 forging fibering

    NASA Astrophysics Data System (ADS)

    Gavrus, A.; Pintilie, D.; Nedelcu, R.

    2016-10-01

    The present research work is focus on the influence of the rheological constitutive equation and friction law formulation on 16MnCr5 forging fibering. Numerical analysis using FE Forge® and Abaqus code show the importance of the rheological softening terms on the metals fibers morphology and position coordinate. Calibration of friction law and sensitivity of softening parameters corresponding to a Hansel-Spittel rheological equation have been studied.

  17. Clay particles as binder for earth buildings materials: a fresh look into rheology of dense clay suspensions

    NASA Astrophysics Data System (ADS)

    Landrou, Gnanli; Brumaud, Coralie; Habert, Guillaume

    2017-06-01

    In the ceramic industry and in many sectors, clay minerals are widely used. In earthen construction technique, clay plays a crucial role in the processing. The purpose of this research is to understand and modify the clay properties in earth material to propose an innovative strategy to develop a castable earth-based material. To do so, we focused on the modification of clay properties at fresh state with inorganic additives. As the rheological behaviour of clays is controlled by their surface charge, the addition of phosphate anion allows discussing deep the rheology of concentrated clay suspensions. We highlighted the thixotropic and shear thickening behaviour of a dispersed kaolinite clay suspensions. Indeed, by adding sodium hexametaphosphate the workability of clay paste increases and the behaviour is stable during time after a certain shear is applied. Moreover, we stress that the aging and the shift in critical strain in clay system are due to the re-arrangement of clay suspension and a decrease of deformation during time. The understanding of both effect: thixotropy and aging are crucial for better processing of clay-based material and for self-compacting clay concrete. Yet, studies need to pursue to better understand the mechanism.

  18. In situ rheological measurements at extreme pressure and temperature using synchrotron X-ray diffraction and radiography.

    PubMed

    Raterron, Paul; Merkel, Sébastien

    2009-11-01

    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.

  19. 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

  20. Impact of the overriding plate rheology on convergence zone dynamics.

    NASA Astrophysics Data System (ADS)

    Hertgen, Solenn; Yamato, Philippe; Guillaume, Benjamin; van Hunen, Jeroen

    2017-04-01

    Most of deformation at the Earth's surface is localized at plate boundaries. This deformation can be accommodated in very different ways depending on the tectonic setting. In the case of convergence zones, the deformation is typically simplified and classified as follows: - intra-oceanic convergence, when convergence involves two oceanic lithospheres, which generally leads to the subduction/obduction initiation and to the formation of an island arc; - convergence between an oceanic and a continental lithosphere, which is mainly accommodated by subduction and can lead to the formation of a mountain range at the plate boundary; - convergence involving two continental lithospheres, which is accommodated by collision and leads to the formation of a mountain range produced by the stacking of crustal slices. Different materials are thus involved (i.e., oceanic crust, continental crust, sediments). Depending on the context (oceanic or continental subduction), they can form contrasted structures in terms of units size, morphology and metamorphism (e.g., Alps vs. Andes/Altiplano-Puna). Moreover, some convergent zones with apparently similar tectonic settings (e.g., continent/continent convergence) show very different patterns of deformation with either very localized deformation (e.g., the Alps) or, at the opposite, deformation distributed over thousands of kilometers (e.g, Himalayas/Tibet). Finally, other convergent zones from different tectonic settings seem to show similar structures (e.g., Tibet plateau and Altiplano-Puna plateaus). Although the mechanism of plate convergence appears to be the same in each case, the structures obtained at the surface seem to be unique. Rheology of both the subducting plate and of the plate interface is known to influence the convergence zones dynamics. However, very few studies have addressed the role of the overriding plate rheology in details, while it may also exert a large control on the deformation style at plate boundaries. In

  1. Transient rheology of stimuli responsive hydrogels: Integrating microrheology and microfluidics

    NASA Astrophysics Data System (ADS)

    Sato, Jun

    Stimuli-responsive hydrogels have diverse potential applications in the field of drug delivery, tissue engineering, agriculture, cosmetics, gene therapy, and as sensors and actuators due to their unique responsiveness to external signals, such as pH, temperature, and ionic strength. Understanding the responsiveness of hydrogel structure and rheology to these stimuli is essential for designing materials with desirable performance. However, no instrumentation and well-defined methodology are available to characterize the structural and rheological responses to rapid solvent changes. In this thesis, a new microrheology set-up is described, which allows us to quantitatively measure the transient rheological properties and microstructure of a variety of solvent-responsive complex fluids. The device was constructed by integrating particle tracking microrheology and microfluidics and offers unique experimental capabilities for performing solvent-reponse measurements on soft fragile materials without applying external shear forces. Transient analysis methods to quantitatively obtain rheological properties were also constructed, and guidelines for the trade-off between statistical validity and temporal resolution were developed to accurately capture physical transitions. Employing the new device and methodology, we successfully quantified the transient rheological and microstructural responses during gel formation and break-up, and viscosity changes of solvent-responsive complex fluids. The analysis method was expanded for heterogeneous samples, incorporating methods to quantify the microrheology of samples with broad distributions of individual particle dynamics. Transient microrheology measurements of fragile, heterogeneous, self-assembled block copolypeptide hydrogels revealed that solvent exchange via convective mixing and dialysis can lead to significantly different gel properties and that commonly applied sample preparation protocols for the characterization of soft

  2. 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

  3. Interparticle interactions in concentrated suspensions and their bulk (rheological) properties.

    PubMed

    Tadros, Tharwat

    2011-10-14

    The interparticle interactions in concentrated suspensions are described. Four main types of interactions can be distinguished: (i) "Hard-sphere" interactions whereby repulsive and attractive forces are screened. (ii) "Soft" or electrostatic interactions determined by double layer repulsion. (iii) Steric repulsion produced by interaction between adsorbed or grafted surfactant and polymer layers. (iv)and van der Waals attraction mainly due to London dispersion forces. Combination of these interaction energies results in three main energy-distance curves: (i) A DLVO type energy-distance curves produced by combination of double layer repulsion and van der Waals attraction. For a stable suspension the energy-distance curve shows a "barrier" (energy maximum) whose height must exceed 25kT (where k is the Boltzmann constant and T is the absolute temperature). (ii) An energy-distance curve characterized by a shallow attractive minimum at twice the adsorbed layer thickness 2δ and when the interparticle-distance h becomes smaller than 2δ the energy shows a sharp increase with further decrease of h and this is the origin of steric stabilization. (iii) an energy-distance curve characterized by a shallow attractive minimum, an energy maximum of the DLVO type and a sharp increase in energy with further decrease of h due to steric repulsion. This is referred to as electrosteric repulsion. The flocculation of electrostatically and sterically stabilized suspensions is briefly described. A section is devoted to charge neutralization by polyelectrolytes and bridging flocculation by polymers. A distinction could be made between "dilute", "concentrated" and "solid suspensions" in terms of the balance between the Brownian motion and interparticle interaction. The states of suspension on standing are described in terms of interaction forces and the effect of gravity. The bulk properties (rheology) of concentrated suspensions are described starting with the case of very dilute

  4. Rheology of the 2006 Eruption at Tungurahua Volcano, Ecuador

    NASA Astrophysics Data System (ADS)

    Hanson, J. B.; Goldstein, F.; Lavallee, Y.; Kueppers, U.; von Aulock, F. W.; Mothes, P. A.; Bustillos, J.; Douillet, G.; Hess, K.; Dingwell, D. B.

    2009-12-01

    The current eruptive activity at Tungurahua commenced in 1999 and has seen several episodes of explosive volcanism during the intervening years. Important eruptions generating pyroclastic flows occurred in July 2006, August 2006 and February 2008. The August 2006 eruption climaxed in a VEI 3 explosion with 10s of pyroclastic flows and notably terminated with the extrusion of a 3-km long lava flow. This variability of eruptive scenarios represents an excellent opportunity to study the occurrence of multiple pulses of pyroclastic activity associated with near contemporaneous extrusion of lava flow from a single, central vent. Here we present results from an extensive field campaign in August 2009 and ongoing parameterization of the rheology of the cogenetic magmas involved during this most recent eruptive cycle at Tungurahua. We observe that in the July deposits, the pyroclastic flows were rich in dense exotic lithics and contained approximately ca. 50 % lapili to bomb size juvenile pyroclasts. In contrast, the August deposits are richer in porous, juvenile material (ca. 90%) and often host pancake-shaped bread-crust bombs. Evidence of pre-eruption magma mingling textures is found occasionally within the August activity. The August a’a lava flow is characterized by dense flow-banded blocks. Magma rheology is considered a chief determinant of eruptive style. While the rheology of single-phase silicate melts is well understood, the description of magma such as that at Tungurahua (i.e., bearing 30-50 % crystals and 10-35% bubbles) is relatively unknown. During sub-Plinian-type eruptions, the transition from ductile to brittle behaviour is largely strain rate, and temperature, dependent. Using a dilatometer, we measure softening temperatures (at a heating rate of 10 °C/min) of ca. 976 °C for the dense clasts and 1060 °C for the bread-crust bombs (with 35 % pores). Complementary deformation experiments in a uniaxial press reveal a variable strain rate

  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. 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…

  7. ACES's Challenges: Past Presidents Comment.

    ERIC Educational Resources Information Center

    Sheeley, Vernon Lee

    1990-01-01

    Recognizes the golden anniversary of the Association for Counselor Education and Supervision (ACES) and presents the statements of 15 past presidents of the association. Presidential leaders briefly review the association's past and suggest opportunities to help create a promising future for ACES. Outlines nine challenges which confront members of…

  8. 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…

  9. Past of a quantum particle

    NASA Astrophysics Data System (ADS)

    Vaidman, L.

    2013-05-01

    Although there is no consensus regarding the “reality” of the past of a quantum particle, in situations where there is only one trajectory with a nonvanishing quantum wave of the particle between its emission and detection points, it seems “safe” to associate the past of the particle with this trajectory. A method for analyzing the past of a quantum particle according to the weak trace it leaves is proposed. Such a trace can be observed via measurements performed on an ensemble of identically pre- and postselected particles. Examples in which this method contradicts the above common sense description of the past of the particle are presented. It is argued that it is possible to describe the past of a quantum particle, but the naive approach has to be replaced by both forward- and backward-evolving quantum states.

  10. The role of protein content on the steady and oscillatory shear rheology of model synovial fluids.

    PubMed

    Zhang, Z; Barman, S; Christopher, G F

    2014-08-28

    Recent studies have debated the role of protein content on the bulk rheology of synovial fluid; in particular, it has been questioned if proteins aggregate or interact with hyaluronic acid in synovial fluid to enhance bulk rheology, or if observed effects were due to systematic measurement error caused by interfacial rheology, stemming from protein adsorption to the interface. Utilizing several techniques to ensure results reflect only bulk rheology, an examination of the role of bovine serum albumin and γ-globulin on model synovial fluid rheology has been undertaken. When interfacial rheology caused by protein adsorption to the interface is abrogated, the bulk rheology of a model synovial fluid composed of bovine serum albumin, γ-globulin, and hyaluronic acid is found to be dominated solely by the hyaluronic acid over a wide range of shear rates, strains and frequencies. These results show that the previously reported enhanced rheological properties of model synovial fluids are solely due to interfacial rheology and not from any type of protein aggregation/interaction in bulk solution.

  11. Renovation and Strengthening of Wooden Beams With CFRP Bands Including the Rheological Effects

    NASA Astrophysics Data System (ADS)

    Kula, Krzysztof; Socha, Tomasz

    2016-09-01

    The paper presents a work analysis of wooden beams reinforced with glued composite bands from the top and resin inclusions, taking into account the rheology of materials. The paper presents numerical model of the multimaterial beam work including rheological phenomena described by linear equations of viscoelasticity. For the construction of this model one used MES SIMULIA ABAQUS environment in which were prepared its own procedures containing rheological models. The calculation results were compared with the literature data. One has done an analysis of the advisability of the use of CFRP reinforcements bands in terms of rheological phenomena.

  12. Rheological behaviour of egg white and egg yolk from different poultry specimen

    NASA Astrophysics Data System (ADS)

    Kumbár, V.; Nedomová, Š.; Votava, J.; Buchar, J.

    2017-01-01

    The main goal of this study is differences in rheological behaviour of hen (ISA BROWN), goose (Anser anser f. domestica) and Japanese quail (Coturnix japonica) egg white and egg yolk. The rheological behaviour of egg white and egg yolk was studied using a concentric cylinder viscometer. Rheological behaviour was pseudoplastic and flow curves were fitted by the Herschel-Bulkley model and Ostwald-de Waele model with high values of coeficients of determination R2. The meaning of rheological parameters on friction factors during flow of egg white and egg yolk in real tube has been shown. Preliminary information on time-dependent behaviour of tested liquids has been also obtained.

  13. 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

  14. 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

  15. 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

  16. A simplified model to evaluate the effect of fluid rheology on non-Newtonian flow in variable aperture fractures

    NASA Astrophysics Data System (ADS)

    Felisa, Giada; Ciriello, Valentina; Longo, Sandro; Di Federico, Vittorio

    2017-04-01

    Modeling of non-Newtonian flow in fractured media is essential in hydraulic fracturing operations, largely used for optimal exploitation of oil, gas and thermal reservoirs. Complex fluids interact with pre-existing rock fractures also during drilling operations, enhanced oil recovery, environmental remediation, and other natural phenomena such as magma and sand intrusions, and mud volcanoes. A first step in the modeling effort is a detailed understanding of flow in a single fracture, as the fracture aperture is typically spatially variable. A large bibliography exists on Newtonian flow in single, variable aperture fractures. Ultimately, stochastic modeling of aperture variability at the single fracture scale leads to determination of the flowrate under a given pressure gradient as a function of the parameters describing the variability of the aperture field and the fluid rheological behaviour. From the flowrate, a flow, or 'hydraulic', aperture can then be derived. The equivalent flow aperture for non-Newtonian fluids of power-law nature in single, variable aperture fractures has been obtained in the past both for deterministic and stochastic variations. Detailed numerical modeling of power-law fluid flow in a variable aperture fracture demonstrated that pronounced channelization effects are associated to a nonlinear fluid rheology. The availability of an equivalent flow aperture as a function of the parameters describing the fluid rheology and the aperture variability is enticing, as it allows taking their interaction into account when modeling flow in fracture networks at a larger scale. A relevant issue in non-Newtonian fracture flow is the rheological nature of the fluid. The constitutive model routinely used for hydro-fracturing modeling is the simple, two-parameter power-law. Yet this model does not characterize real fluids at low and high shear rates, as it implies, for shear-thinning fluids, an apparent viscosity which becomes unbounded for zero shear rate

  17. Relationships between debris fan morphology and flow rheology for wet and dry flows on Earth and Mars: A numerical modeling investigation

    NASA Astrophysics Data System (ADS)

    McGuire, Luke A.; Pelletier, Jon D.

    2013-09-01

    Liquid water may have flowed on the Martian surface in the recent geologic past. Arguments for and against liquid water flows have been made, in part, using interpretations of the morphology of Martian gullies and their associated debris fans. On Earth, sediment transport on steep, debris-flow-dominated hillslopes is often assumed to be a nonlinear function of hillslope gradient. In detail, however, sediment transport on such slopes must also depend on the rheology of the mass movements that drive the majority of transport, both in magnitude and frequency. In this study, we attempt to provide a firmer basis for (1) interpreting flow constituents and/or rheology from debris-fan morphology on Mars and (2) modeling debris-flow-dominated hillslopes on Earth by developing a mass-conservative numerical model that links the rheology of wet and dry granular flows on steep slopes to the morphology of debris fans deposited at their base. Individual flows are routed from initiation points on a slope to stopping points at the base of the hillslope. Model predictions for the shape and average slope of the fans depend on flow rheology. Model results indicate that debris fans associated with dry granular flows may develop average slopes below the kinetic angle of friction. In both the dry and wet cases, the model results suggest that fan morphology depends on the mean properties of the flows involved in fan formation as well as the amount of variation in flow behavior between individual mass movement events. These results provide an improved basis for interpreting the morphology of debris fans on both Earth and Mars.

  18. 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

    2016-09-05

    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.

  19. Astronautics: Past, present and future

    NASA Astrophysics Data System (ADS)

    Maksimov, A. I.

    2016-10-01

    The article deals with the beginning and evolution of astronautics in XX-XXI centuries. The great attention is paid to the contribution of private companies to the further expansion of the mankind space activities in the past few decades.

  20. Perspective: lessons from the past.

    PubMed

    Holland, Walter W

    2016-01-01

    A considered analysis of some factors used in the past 50-70 years in medical education, care on a hospital ward, organisation of health services, medical research and the attitudes of media and politics to health services is described. The possible reasons for changes in these areas over time are considered, and recommendations are made in each area on how current practice could be improved in the light of past experience. Copyright © 2014 John Wiley & Sons, Ltd.

  1. Microstructural Analysis and Rheological Modeling of Asphalt Mixtures Containing Recycled Asphalt Materials

    PubMed Central

    Cannone Falchetto, Augusto; Moon, Ki Hoon; Wistuba, Michael P.

    2014-01-01

    The use of recycled materials in pavement construction has seen, over the years, a significant increase closely associated with substantial economic and environmental benefits. During the past decades, many transportation agencies have evaluated the effect of adding Reclaimed Asphalt Pavement (RAP), and, more recently, Recycled Asphalt Shingles (RAS) on the performance of asphalt pavement, while limits were proposed on the amount of recycled materials which can be used. In this paper, the effect of adding RAP and RAS on the microstructural and low temperature properties of asphalt mixtures is investigated using digital image processing (DIP) and modeling of rheological data obtained with the Bending Beam Rheometer (BBR). Detailed information on the internal microstructure of asphalt mixtures is acquired based on digital images of small beam specimens and numerical estimations of spatial correlation functions. It is found that RAP increases the autocorrelation length (ACL) of the spatial distribution of aggregates, asphalt mastic and air voids phases, while an opposite trend is observed when RAS is included. Analogical and semi empirical models are used to back-calculate binder creep stiffness from mixture experimental data. Differences between back-calculated results and experimental data suggest limited or partial blending between new and aged binder. PMID:28788190

  2. Morphological, Thermal, and Rheological Properties of Starches from Maize Mutants Deficient in Starch Synthase III.

    PubMed

    Zhu, Fan; Bertoft, Eric; Li, Guantian

    2016-08-31

    Morphological, thermal, and rheological properties of starches from maize mutants deficient in starch synthase III (SSIII) with a common genetic background (W64A) were studied and compared with the wild type. SSIII deficiency reduced granule size of the starches from 16.7 to ∼11 μm (volume-weighted mean). Thermal analysis showed that SSIII deficiency decreased the enthalpy change of starch during gelatinization. Steady shear analysis showed that SSIII deficiency decreased the consistency coefficient and yield stress during steady shearing, whereas additional deficiency in granule-bound starch synthase (GBSS) increased these values. Dynamic oscillatory analysis showed that SSIII deficiency decreased G' at 90 °C during heating and increased it when the paste was cooled to 25 °C at 40 Hz during a frequency sweep. Additional GBSS deficiency further decreased the G'. Structural and compositional bases responsible for these changes in physical properties of the starches are discussed. This study highlighted the relationship between SSIII and some physicochemical properties of maize starch.

  3. 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.

  4. Microstructural Analysis and Rheological Modeling of Asphalt Mixtures Containing Recycled Asphalt Materials.

    PubMed

    Falchetto, Augusto Cannone; Moon, Ki Hoon; Wistuba, Michael P

    2014-09-02

    The use of recycled materials in pavement construction has seen, over the years, a significant increase closely associated with substantial economic and environmental benefits. During the past decades, many transportation agencies have evaluated the effect of adding Reclaimed Asphalt Pavement (RAP), and, more recently, Recycled Asphalt Shingles (RAS) on the performance of asphalt pavement, while limits were proposed on the amount of recycled materials which can be used. In this paper, the effect of adding RAP and RAS on the microstructural and low temperature properties of asphalt mixtures is investigated using digital image processing (DIP) and modeling of rheological data obtained with the Bending Beam Rheometer (BBR). Detailed information on the internal microstructure of asphalt mixtures is acquired based on digital images of small beam specimens and numerical estimations of spatial correlation functions. It is found that RAP increases the autocorrelation length (ACL) of the spatial distribution of aggregates, asphalt mastic and air voids phases, while an opposite trend is observed when RAS is included. Analogical and semi empirical models are used to back-calculate binder creep stiffness from mixture experimental data. Differences between back-calculated results and experimental data suggest limited or partial blending between new and aged binder.

  5. 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.

  6. 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.

  7. Physical, rheological, functional and film properties of a novel emulsifier: Frost grape polysaccharide (FGP) from Vitis riparia Michx

    USDA-ARS?s Scientific Manuscript database

    A novel emulsifier, Frost grape polysaccharide (FGP), isolated from natural exudate of the species Vitis riparia Michx, was physically and rheologically characterized. The determination of the physical, structural, thermodynamic, emulsification, film, and rheological properties of FGP provide essent...

  8. Rheological properties of concentrated aqueous injectable calcium phosphate cement slurry.

    PubMed

    Liu, Changsheng; Shao, Huifang; Chen, Feiyue; Zheng, Haiyan

    2006-10-01

    In this paper, the steady and dynamic rheological properties of concentrated aqueous injectable calcium phosphate cement (CPC) slurry were investigated. The results indicate that the concentrated aqueous injectable CPC showed both plastic and thixotropic behavior. As the setting process progressed, the yield stress of CPC slurry was raised, the area of the thixotropic hysteresis loop was enlarged, indicating that the strength of the net structure of the slurry had increased. The results of dynamic rheological behavior indicate that the slurry presented the structure similar to viscoelastic body and the property of shear thinning at the beginning. During the setting process, the slurry was transformed from a flocculent structure to a net structure, and the strength increased. Different factors had diverse effects on the rheological properties of the CPC slurry in the setting process, a reflection of the flowing properties (or injection), and the microstructure development of this concentrated suspension. Raising the powder-to-liquid ratio decreased the distance among the particles, increased the initial strength, and shortened the setting time. In addition, raising the temperature improved the initial strength, increased the order of reaction, and shortened the setting time, which was favorable to the setting process. The particle size of the raw material had much to do with the strength of original structure and setting time. The storage module G' of CPC slurry during the setting process followed the rule of power law function G'=A exp(Bt), which could be applied to forecast the setting time, and the calculated results thereafter are in agreement with the experimental data.

  9. Constraining the rheology of mantle and slabs from geodynamic modeling

    NASA Astrophysics Data System (ADS)

    Liu, L.; Stegman, D. R.

    2012-12-01

    The rheologic profiles of the ambient mantle and the viscous strength of oceanic plates after subduction are critical parameters governing the convection pattern of the solid Earth. Recent advancements in laboratory experiment provide useful constraints on rock rheology. However, both the extrapolation of lab-derived values to Earth-like dimensions on geological time scales and the imperfect knowledge of mantle compositions raise cautions on extending laboratory results into numerical modeling of mantle convection. Geodynamic inversions, on the other hand, provide an alternative measure on mantle rheology, although the resulting viscosity profiles differ significantly when different observational constraints are involved. We present a result from simulating the history of the Cenozoic Farallon subduction and from comparison with recent high-resolution seismic tomography of western US. The radial viscosity profile of the mantle, fundamental to our understanding of mantle dynamics, has only been constrained in relative or depth-averaged terms by models of the dynamic geoid, post-glacial rebound, or inversions of plate motions. Here we employ an alternative method to constrain this important property by comparing the locations and geometries of several individual slab segments across a range of depths in geodynamic models with seismic tomographic models. This method is critically dependent on matching sinking trajectories of slabs through absolute viscosity profiles. The exact match to the shape, angle, and depth of fast seismic anomalies critically depends on the integrated time-history of each segment's sinking trajectory and deformation which is controlled by absolute values of viscosity for several essential components in the system, including the slab, mantle wedge, plate boundaries, and radial profile of the upper mantle. Our study also provides a tight constraint on the viscous strength the subducting slabs, by matching the resulting slab curvature and position

  10. Physics of rheologically enhanced propulsion: Different strokes in generalized Stokes

    NASA Astrophysics Data System (ADS)

    Montenegro-Johnson, Thomas D.; Smith, David J.; Loghin, Daniel

    2013-08-01

    Shear-thinning is an important rheological property of many biological fluids, such as mucus, whereby the apparent viscosity of the fluid decreases with shear. Certain microscopic swimmers have been shown to progress more rapidly through shear-thinning fluids, but is this behavior generic to all microscopic swimmers, and what are the physics through which shear-thinning rheology affects a swimmer's propulsion? We examine swimmers employing prescribed stroke kinematics in two-dimensional, inertialess Carreau fluid: shear-thinning "generalized Stokes" flow. Swimmers are modeled, using the method of femlets, by a set of immersed, regularized forces. The equations governing the fluid dynamics are then discretized over a body-fitted mesh and solved with the finite element method. We analyze the locomotion of three distinct classes of microswimmer: (1) conceptual swimmers comprising sliding spheres employing both one- and two-dimensional strokes, (2) slip-velocity envelope models of ciliates commonly referred to as "squirmers," and (3) monoflagellate pushers, such as sperm. We find that morphologically identical swimmers with different strokes may swim either faster or slower in shear-thinning fluids than in Newtonian fluids. We explain this kinematic sensitivity by considering differences in the viscosity of the fluid surrounding propulsive and payload elements of the swimmer, and using this insight suggest two reciprocal sliding sphere swimmers which violate Purcell's Scallop theorem in shear-thinning fluids. We also show that an increased flow decay rate arising from shear-thinning rheology is associated with a reduction in the swimming speed of slip-velocity squirmers. For sperm-like swimmers, a gradient of thick to thin fluid along the flagellum alters the force it exerts upon the fluid, flattening trajectories and increasing instantaneous swimming speed.

  11. Linear and nonlinear rheology of architecturally complex polymers

    NASA Astrophysics Data System (ADS)

    Kapnistos, Michail

    We investigated the linear and nonlinear rheology of several model polymeric materials ranging from combs with linear or star-like backbone to third generation dendrimers and cyclic polymers (with no free ends or branches). These systems are governed by topological interactions, which influence their mechanical properties. We combined experiments with theoretical models in order to identify the factors that affect the mechanical response of polymers of various architectures. All polymeric materials exhibited some universal features that were assigned to their microscopic motions. The tube model and the concept of hierarchy of motions along with the dynamic tube dilation (DTD) were the key elements to understand the rheology of branched polymer melts and solutions. We also performed nonlinear experiments in solutions of branched polymers obtaining an extensive dataset of damping functions in combs. We found evidence that the above ideas and mainly DTD, are also present during nonlinear deformations. Apart for the experiments, we modified the existent tube model, improving several shortcomings. The topological free ends of combs were treated simultaneously with the branches and included the effect of polydispersity in a direct manner. The equations were integrated with a user-friendly computer interface for modeling the linear viscoelastic data of several polymer architectures. We explored the role of polymer topology in rheology with the use of model polymers. We found universal principles that govern the mechanical response and linked the microstructure with macroscopic experiments. The extended experimental data have revealed some issues not explained by current theoretical model that need to be addressed in the future.

  12. Polymer mediated surface interactions in pulp fiber suspension rheology

    NASA Astrophysics Data System (ADS)

    Zauscher, Stefan

    2000-08-01

    Small amounts (<3 wt.%/wt. dry fiber) of high molecular weight polyelectrolytes added to concentrated aqueous pulp fiber suspensions (>30 wt.% fiber) dramatically decrease the suspension's apparent viscosity, alter its flocculation state, and render the suspension extrudable. Macroscopic rheological measurements show that sufficient amounts of added polyelectrolyte reduce fiber network strength. Precisely how the reduction occurs is not clear. The results are consistent with the hypothesis that polymers alter interactions at the fiber contact points, but polymers may also affect the network structure; the resulting change in the macroscopic rheological properties is a convolution of both. To better understand how polymers affect surface interactions, we use colloidal probe microscopy, modified to represent the interactions between idealized fiber surfaces. Long range interactions between cellulose surfaces are governed by double layer forces, and once surfaces contact, by repulsive osmotic forces and viscoelasticity. Increasing the ionic strength decreases surface potentials and increases adhesive forces. High molecular weight polyelectrolytes cause strong steric repulsion at high surface coverage, where interactions are sensitive to probe velocity. Polymer bridging occurs at low coverage. Regardless of scan size, friction exhibits irregular stick-slip behavior related to surface roughness. At small scan sizes (˜10 nm) the coefficient of friction decreases with increasing load. Above a critical scan size of about 100 nm---corresponding to the average size of asperities on one of the model surfaces---friction forces are independent of scan size, but depend on the load. Small amounts [˜ O (100 ppm)] of high molecular weight polyelectrolytes significantly decrease sliding friction between cellulose surfaces. Hydrodynamic forces contribute little to friction. Our results lend support to the hypothesis that the rheology of concentrated pulp fiber suspensions can be

  13. 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.

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

    NASA Astrophysics Data System (ADS)

    Kraynik, Andrew M.; Reinelt, Douglas A.

    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.

  15. 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

  16. 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.

  17. 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.

  18. The rheology and stability of concentrated coal water slurries

    SciTech Connect

    Slaczka, A.; Piszczynski, Z.

    1995-12-31

    An experimental study was undertaken to investigate the rheological properties of coal-water slurries (CWS). Slurries were prepared from coal of different rank, different particle size distribution, additives and solid content. Viscosity at different shear rate were measured using a capillary viscometer specially constructed by the authors for this purpose. The stability of investigated CWS was performed too. The study has revealed a correlation between the rank of coal used for slurry preparation and its viscosity in all ranges of slurry concentration. The addition of some reagents causes a considerable decrease in the slurry viscosity. The stability of the slurry was improved too.

  19. Two-dimensional foam rheology with viscous drag.

    PubMed

    Janiaud, E; Weaire, D; Hutzler, S

    2006-07-21

    We formulate and apply a continuum model that incorporates elasticity, yield stress, plasticity, and viscous drag. It is motivated by the two-dimensional foam rheology experiments of Debregeas et al. [Phys. Rev. Lett. 87, 178305 (2001)10.1103/PhysRevLett.87.178305] and Wang et al. [Phys. Rev. E 73, 031401 (2006)10.1103/PhysRevE.73.031401], and is successful in exhibiting their principal features, which are an exponentially decaying velocity profile and strain localization. Transient effects are also identified.

  20. Coupling electrokinetics and rheology: Electrophoresis in non-Newtonian fluids.

    PubMed

    Khair, Aditya S; Posluszny, Denise E; Walker, Lynn M

    2012-01-01

    We present a theoretical scheme to calculate the electrophoretic motion of charged colloidal particles immersed in complex (non-Newtonian) fluids possessing shear-rate-dependent viscosities. We demonstrate that this non-Newtonian rheology leads to an explicit shape and size dependence of the electrophoretic velocity of a uniformly charged particle in the thin-Debye-layer regime, in contrast to electrophoresis in Newtonian fluids. This dependence is caused by non-Newtonian stresses in the bulk (electroneutral) fluid outside the Debye layer, whose magnitude is naturally characterized in an electrophoretic Deborah number.