Evolution Of Viscosity Research Articles

Viscoelasticity evolution in protein layers during binding reactions evaluated using high-frequency wireless and electrodeless quartz crystal microbalance biosensor without dissipation

In this study, we demonstrate the effectiveness of a resonance acoustic microbalance with a naked embedded quartz (RAMNE-Q) biosensor for evaluating viscoelastic property changes in thin protein layers during protein deposition reactions without dissipation measurement. Quartz crystal microbalance (QCM) biosensors have conventionally been adopted for the viscoelasticity evaluation of adsorbed protein layers by measuring dissipation as well as resonance frequency. However, dissipation, or the vibrational energy loss, is easily affected by many factors and is rarely measured with sufficiently high accuracy. To evaluate viscoelasticity only from a reliable frequency response, one needs to perform an ultrahigh-frequency measurement, which is here achieved using the RAMNE-Q biosensor. Simultaneous frequency measurement is performed for fundamental and overtone modes up to 406 MHz of a 58 MHz RAMNE-Q biosensor during various binding reactions, and evolutions of viscosity, shear modulus, and thickness of adsorbed protein layers are inversely evaluated. A marked difference is observed in the viscosity evolution between specific and nonspecific binding reactions. Furthermore, the reversed frequency response appears, which indicates the modification of the protein structure into a rigid structure.

Evaluation of the viscosity profile obtained for dispersions containing different proportions of milk protein concentrate / whey protein concentrate during simulated conditions of thermal processing

Denaturation and interaction of different proteins occur in different forms and intensity when the pH value varies in accordance with the medium in which they are located. This study aimed to verify the influence of whey protein/casein interaction in the evolution of viscosity at different pH values, using the Rapid Viscosity Analyzer (RVA) as the thermal processing simulator. Samples of commercial whey protein concentrate (WPC) and milk protein concentrate (MPC) have been analyzed. The results of this study can be applied in the development of products obtained from dairy powders such as processed cheeses and yoghurt.

Relationship between viscosity change and specificity in protein binding reaction studied by high-frequency wireless and electrodeless MEMS biosensor

This study proposes a methodology for evaluating specific binding behavior between proteins using a resonance acoustic microbalance with a naked-embedded quartz (RAMNE-Q) biosensor. We simultaneously measured the frequency responses of fundamental (58 MHz) and third-order (174 MHz) modes during multi step injections of proteins and deduced the thickness and viscosity evolutions of the protein layer. The viscosity increases with the progress of the binding reaction in nonspecific binding, but it markedly decreases in specific-binding cases. Thus, the high-frequency RAMNE-Q biosensor can be a powerful tool for evaluating specificity between proteins without measuring dissipation.

Equibiaxial extension of a viscoelastic partially extending strand convection model with large relaxation time

A combined numerical and asymptotic study is presented for a viscoelastic fluid, which behaves as a thixotropic yield stress fluid in the limit of large relaxation time. Homogeneous biaxial extension under a prescribed stress is addressed. The constitutive model is a viscoelastic partially extending strand convection model for the microstructure embedded in a Newtonian solvent. There are two important parameters: the ratio of yield stress to stress modulus and the ratio of retardation to relaxation times. The transient change that takes place if a configuration is stressed biaxially is investigated. Distinct asymptotic regimes are identified and governed by fast and slow time scales. Steady flow curves may be monotone or non-monotone, depending on the ratio of yield stress to stress modulus. In either case, a slow evolution of the apparent viscosity is found upon cessation of the applied stress. A regime where steady solutions exhibit extensional thickening in uniaxial extension, but not in biaxial extension, is consistent with prior observations. The von Mises criterion, which relates yield stresses in extension and shear, is retrieved for the special case of immediate yielding at low strain.

Sintering Kinetics Across Pore Closure Transition Accounting for Continuous Increase in Grain Coordination with Density

The influence of dihedral angle and particle coordination on the evolution of densification rate is investigated throughout the intermediate and final stages of sintering. From a review of literature data, heuristic expressions are proposed for representing different trajectories of evolution of coordination from the onset of skeleton formation up to full density. The influence of dihedral angle and coordination on the threshold density for pore closure is established by revisiting the Plateau–Rayleigh instability criterion. The intermediate and final stages are modeled using representative volume elements that do not restrict coordination to integer values. Computational results enlighten the interplay between coordination and dihedral angle on the evolution of sintering stress, bulk viscosity, and sintering rate. The results allow quantifying the amplitude of the drop of densification rate at pore closure transition. The monotonous increase of coordination with relative density brings about a monotonous increase of sintering rate at constant particle size. Simulations emphasize the beneficial effect of higher initial density and coordination in the green part.

Modeling the rheological behavior of waxy crude oils as a function of flow and temperature history

The solidification of waxy components during the cool down of waxy crude oils in pipelines may provide complex yield stress fluid behavior with time-dependent characteristics, which has a critical impact for predicting flow restart after pipeline shut-in. Here, from a previous set of data at a local scale with the help of Magnetic Resonance Imaging and a new full set of data for various flow and temperature histories, we give a general picture of the rheological behavior of waxy crude oils. The tests include start flow tests at different velocities or creep tests at different stress levels, abrupt changes of velocity level, steady flow, after cooling under static or flowing conditions. We show that when the fluid has been cooled at rest it forms a structure that irreversibly collapses during the startup flow. Under these conditions, the evolution of the apparent viscosity mainly depends on the deformation undergone by the fluid for low or moderate deformation and starts to significantly depend on the shear rate for larger values. Even the (apparent) flow curve of statically cooled waxy crude oils was observed to be dependent on the flow history, more specifically on the maximum shear rate experienced by the material. After being sufficiently sheared, i.e., achieving an equilibrium state, the rheological behavior is that of a simple liquid for shear rates lower than the maximum historical one. A model is proposed to represent those trends experimentally observed. In contrast with most previous works in that field, the model is built without any a priori assumption based on classical behavior of a class of fluids. Finally, it is shown that this model predicts the flow characteristics of these materials under more complex flow histories (sweep tests, sudden shear rate decrease) much better than the so far most often used (Houska) model.

Influence of Dihedral Angle and Grain Coordination on Densification Rate During Intermediate and Final Sintering Stages

The evolution of sintering stress, bulk viscosity, and densification rate during the intermediate stage and the final stage of sintering of random aggregates of particles is simulated using a new model able to account for the monotonous increase in the coordination number during sintering. For the intermediate stage, the representative volume element is a cone of revolution whereas, for the final stage, it is volume centered on a closed pore located at quadruple point. Care is taken to warrant the continuity between the two models at the transition between the two stages. Computations allow tracing the variation in sintering stress and bulk viscosity with relative density, coordination, and dihedral angle during the two stages, as well as at the transition between them. They show how, as a result, densification rate is enhanced by the increase in coordination. The model is assessed via comparison of the computed curves with the predictions of previous models based on periodic 3D arrangements, in which grain coordination number is constrained to jump between integer values. The agreement is generally very good in spite of the different approximations involved.

In vitro digestion of short-dough biscuits enriched in proteins and/or fibres, using a multi-compartmental and dynamic system (1): Viscosity measurement and prediction

The effects of biscuit composition on the viscosity generated during digestion were investigated. A control biscuit, one with proteins, one with fibres, and one with both proteins and fibres were digested under the same conditions, using the TNO intestinal model (TIM-1). The TIM-1 is a multi-compartmental and dynamic in vitro system, simulating digestion in the upper tract (stomach and small intestine) of healthy adult humans. Digesta were collected at different times, in the different compartments of the TIM-1 (stomach, duodenum, jejunum and ileum) and viscosity was measured with a dynamic rheometer. Results showed a marked effect of biscuit composition on chyme viscosity. Highest viscosity was obtained with biscuits containing viscous soluble fibres, followed by those enriched in both proteins and fibres, then by protein-enriched and control biscuits. The viscosity was maintained throughout the gut up to the ileal compartment. A prediction of the evolution of the chyme viscosity in each compartment of the TIM-1 was built, based on model curves describing the evolution of the viscosity as a function of biscuit concentration, and on dilution factors measured by spectrophotometry on a blank digestion.

Effect of hydrophobic monomer on the aqueous dispersion polymerization of acrylamide with quaternary ammonium cationic monomer

Aqueous dispersion polymerization has been considered as a promising green technology for preparing water-soluble polymers such as cationic polyacrylamide (CPAM). Dispersion copolymerization of acrylamide and 2-methylacryloylxyethyl trimethyl ammonium chloride was generally carried out in aqueous ammonium sulfate solution with poly(2-methylacryloylxyethyl trimethyl ammonium chloride) as the stabilizer. In this study, we reported the potential influence of a small amount of hydrophobic monomer, methyl methacrylate (MMA), on the above-mentioned aqueous dispersion polymerization system. It was found that MMA could play an important role in the polymerization process by significantly affecting the particle formation and stabilization, as well as the viscosity evolution of the reaction mixture during polymerization. With the addition of a small amount of MMA, the particle formation was accelerated and the viscosity of the polymerization system decreased significantly. With the increase in MMA addition, the final copolymer particle size was reduced and its size distribution became narrower; meanwhile, the particle morphology tended to be spherical. Moreover, it was found that the addition of MMA could favor the production of CPAM with high charge density. The flocculation performance of the resulting CPAM dispersion was also examined in detail and it was found that the introduction of MMA unit into CPAM molecular chain could improve its flocculation efficiency.

Rheological Behavior of Al-7Si-0.3Mg Alloy at Mushy State

In recent years, semisolid manufacturing has emerged as an attractive option for near net shape forming of components with aluminum alloys. In this class of processes, the key to success lies mainly in the understanding of rheological behavior of the semi-solid slurry in the temperature range between liquidus and solidus. The present study focuses on the non-Newtonian flow behavior of the pseudo plastic slurry of Al-7Si-0.3Mg alloy for a wide shear range using a high-temperature Searle-type rheometer. The rheological behavior of the slurry is studied with respect to relevant process variables and microstructural features such as shear rate, shear duration, temperature history, primary particle size, shape, and their distribution. The experiments performed are isothermal tests, continuous cooling tests, shear jump tests, and shear time tests. The continuous cooling experiments are aimed toward studying the viscosity and shear stress evolution within the slurry matrix with increasing solid fraction at a constant shear rate. Three different cooling rates are considered and their effect on flow behavior of the slurry was studied under iso-shear condition. Descending shear jump experiments are performed to understand the viscous instability of the slurry.

Study of Thermal Behaviour of Milk Protein Products Using a Chemometric Approach

This study deals with the evaluation of the behavior of viscosity evolution of the Milk Protein Products (MPPs) solutions in different concentrations used in different conditions of thermal processing by means of Rapid Visco Analyzer (RVA). Skimmed milk powder (SMP), whey protein Original Research Article Stephani et al.; BJAST, 7(1): 62-83, 2015; Article no.BJAST.2015.126 63 concentrate (WPC), milk protein concentrate (MPC), whey powder (WP) and demineralized whey powder (DWP) were analyzed; the evaluated solid-liquid ratio solutions were 0.1 g∙g -1 to 0.45 g∙g -1 of dry solids in water (DSW) for the MPC, 0.1 g∙g -1 to 0.4 g∙g -1 of DSW for the WPC and 0.5 g∙g -1 to 0.8 g∙g -1 of DSW for SMP, WP and DWP. Brazilian industrial heat treatment set ups were used, with temperatures ranging from 65°C to 95°C and retention time from 5 to 30 minutes. The results were interpreted according to the viscosities during heating and cooling, being possible to optimize the MPPs different parameters conditions with the interpretations of the viscographic profiles based on the thermal behavior of proteins, especially for the SMP, MPC and WPC. The data showed similarity in viscographic characteristics of the solutions when evaluated at 65°C for 30 minutes, at 85°C for 15 minutes and 95°C for 5 minutes, for the MPC and WPC at 95°C for 5 minutes, all of them for different concentrations of proteins in water.

Rheological Behaviour, Synthesis and Performance of Smart Thermal Barrier Coating Systems Based on Hollow Alumina

The stability of three water-based slurries containing different loads of Al microparticles was measured by laser scattering. The slurries displayed a Newtonian behaviour and the evolution of viscosity over nine days was found to be constant. Ground surfaces of nickel were also wetted similarly irrespective of the Al content in the slurries (30, 40 or 50 wt%) thereby demonstrating that the 1/10 PVA/H2O water based slurries are adequate for spraying. After deposition and annealing of the as-sprayed coatings, a thermal barrier coating system was formed with a top coat of hollow alumina spheres, an intermediate thermally grown oxide and a bottom aluminized bond coat. The coating system is shown to display very low thermal conductivity and remarkable oxidation resistance at high temperatures.

Viscosity and Thermal Evolution of Density and Wetting Angle of a Commercial Glaze by Means of Hot Stage Microscopy

In the present work we attempt to describe the results of the thermal behavior analysis of a commercial glaze obtained in a thermal microscope developed by the research group. At the same time, the density and the wetting angle of the glaze with an alumina surface was evaluated. Particularly the sintering temperature, the sphere, semi-sphere and fusion temperatures were also determined. These present characteristic viscosities. Afterward, by means of the de Vogel-Fulcher-Tammann equation, the viscosity as a function of temperature was estimated.In the first part the developed equipment is described together with the image analysis carried out for the in-situ cylindrical samples (2,5mm of height and diameter). The thermal cycle was up to 1200°C with a heating rate of 5°C/min. The developed equipment presents the following characteristics: some problems with the temperature evaluation, it was slightly affected by air currents and difficulties for achieving an adequate parallelism. On the other hand, the potentialities of the equipment for development and study of the thermal behavior of glasses was established.

Calorimetric and Rheological Studies on Cyclopentane Hydrate-Forming Water-in-Kerosene Emulsions

The effect of salt, a thermodynamic inhibitor of hydrate, on a density-matched cyclopentane hydrate-forming water-in-kerosene emulsion with a fixed aqueous phase mass fraction of 0.4 is presented, based on studies by microdifferential scanning calorimetry (μDSC) and rheometry. Kerosene is a candidate material for flow loop studies. Microdifferential scanning calorimetry data are presented on the equilibrium temperature (liquidus line); water-to-hydrate conversions are computed using the liquidus line. Mechanical properties obtained using a stress controlled rheometer are correlated to thermodynamic properties. Effects of subcooling, salt concentration, and shear rate dependence are studied and presented along with oscillatory rheometric and yield stress measurements. Critical time is defined as the onset of a viscosity jump, and the viscosity evolution time is the time from the initial jump to 90 % attainment of the final viscosity; both times are shortened by higher subcooling. The final viscosity, storage modulus and yield stress achieve a peak between 0.85 to 0.95 (mass fraction) water-to-hydrate conversion indicating a mechanical influence of capillary bridge formation. The hydrate slurry exhibits a shear thinning behavior when cycled up and down in shear rate, showing negligible hysteresis in the rate dependence.

The evolution of velocity profiles and turbulent viscosity in a system of currents with wind-induced and density flows

The results of an in-situ study and mathematical modeling of a system of currents with wind-induced and density flows are presented. The model is based on the obtained dependences of its key parameters on the density-field characteristics, changes in the water level, and the water-reservoir topography. The revealed features of the of shear-velocity profile are indicated and a function of its distribution from the bottom to the open surface of the water is given. The model that was developed is verified by the data from measuring the parameters of currents and composition of water in the Petrozavodsk Bay of Onega Lake in September 2007. The regularities for the evolution of distributions of the coefficient of the turbulent exchange and current velocity over depth and in time are revealed.

Curing Viscosity of HTPB‐Based Binder Embedding Micro‐ and Nano‐Aluminum Particles

AbstractAluminum is used as a metal fuel in energetic materials for the improvement of propulsion performance and density. Both nano‐sized and micrometer‐sized activated powders represent valuable options in order to improve metal combustion properties, each possessing advantages and drawbacks. These ingredients bear peculiar properties (namely, higher specific surface, coatings, or surface characteristics) which generate high mixing viscosity once suspended in a polymer as well as altered mechanical properties of the final product. Four different powders dispersed in a polymer binder are taken into consideration and the evolution of viscosity in time during the curing process is investigated. The suspending medium is represented by a mixture of hydroxyl‐terminated polybutadiene (HTPB), isophorone diisocyanate (IPDI) and dioctyl adipate (DOA). Viscosity was measured for 5 h on samples under isothermal curing at 60 °C. Non‐isothermal DSC kinetic analyses were also performed using the Kissinger method. It was found that, for the test conditions, a size reduction of metal particles slowed down the increment rate of curing viscosity while some peculiar coatings, such as fatty acids, introduced opposite trends.

Influence of formulation method and related processes on structural, electrical and electrochemical properties of LMS/NCA-blend electrodes

Abstract The impact of different formulation methods, involving related process technologies, as well as the influence of dispersing intensity on the structural and electrical coating layer properties of LiMn2O4/LiNi0,80Co0,15Al0,05O2 (LMS/NCA) blends are studied. Findings are finally correlated with the electrochemical rate-capability in order to derive process-structure–property functions to facilitate systematical electrode development. LMS was found to be sensitive according mechanical stress but by processing LMS/NCA blend electrodes this problem can be avoided. In general carbon black (CB) agglomerate size and its distribution in the binder network were identified to be significant factors influencing rate-capability. Both were found to influence pore structure by utilizing representative low and high energy methods for the formulation of the suspensions. The specific pore volume in the pore size region of 10 μm ≥ dp ≥ 0.5 μm was discovered to strongly influence rate-capability. These highways for lithium-ion transport allow for higher mass of lithium-ions per unit time penetrating into the inner surface of the coating layer. Specific volume and thus rate-performance can either be increased by a binder solution based formulation method or by decreasing the specific energy input during dispersing process. Hence no superior formulation method exists. The adjustment of mixing intensity and therewith the achieved CB agglomerate size, referring to the formulation method used, is essential. Thus comparable electrochemical rate performance was found for the same specific volume of approximately 0.25 cc g−1 but for different dispersing intensities. Further, the pore size region of 1.5 μm > dp > 0.03 μm was identified to be characteristic for the CB agglomerate size and the corresponding CB treatment method used. Peakedness of the pore size distribution was found to follow electrode conductivity which was the largest for a distributive dry mixing method. For electrodes showing a good CB agglomerate distribution in the binder network rate-capability was found to be limited by the pore structure of the coating layer and, thus, preliminarily by the corresponding ion transport kinetic. Based on the findings a model concept on processes occurring during dispersing was proposed and discussed to describe viscosity evolution over dispersing time.

Dielectric analysis of depth dependent curing behavior of dental resin composites

ObjectivesThe aim of this study is to investigate depth dependent changes of polymerization process and kinetics of visible light-curing (VLC) dental composites in real-time. The measured quantity – “ion viscosity” determined by dielectric analysis (DEA) – provides the depth dependent reaction rate which is correlated to the light intensity available in the corresponding depths derived from light transmission measurements. MethodsThe ion viscosity curves of two composites (VOCO Arabesk Top and Grandio) were determined during irradiation of 40s with a light-curing unit (LCU) in specimen depths of 0.5/0.75/1.0/1.25/1.5/1.75 and 2.0mm using a dielectric cure analyzer (NETZSCH DEA 231 with Mini IDEX sensors). The thickness dependent light transmission was measured by irradiation composite specimens of various thicknesses on top of a radiometer setup. ResultsThe shape of the ion viscosity curves depends strongly on the specimen thickness above the sensor. All curves exhibit a range of linear time dependency of the ion viscosity after a certain initiation time. The determined initiation times, the slopes of the linear part of the curves, and the ion viscosities at the end of the irradiation differ significantly with depth within the specimen. The slopes of the ion viscosity curves as well as the light intensity values decrease with depth and fit to the Lambert–Beer law. The corresponding attenuation coefficients are determined for Arabesk Top OA2 to 1.39mm−1 and 1.48mm−1, respectively, and for Grandio OA2 with 1.17 and 1.39mm−1, respectively. For thicknesses exceeding 1.5mm a change in polymerization behavior is observed as the ion viscosity increases subsequent to the linear range indicating some kind of reaction acceleration. SignificanceThe two VLC composites and different specimen thicknesses discriminate significantly in their ion viscosity evolution allowing for a precise characterization of the curing process even with respect to the polymerization mechanism.

Lithium/Sulfur Batteries upon Cycling: Application of Electrochemical Impedance Spectroscopy and in Situ X-Ray Diffraction

Lithium/Sulfur batteries, due to their high theoretical values of gravimetric (2500 Wh kg-1) and volumetric (2800 Wh L-1) energy densities, became one of the most popular candidates for next-generation energy storage system. However, the practical discharge capacity and cycle life of Li/S cells are still below expectation despite of many efforts which has been done during last two decades. Therefore, it is necessary to better understand the working mechanism of this system, in order to help to improve the electrochemical performances. Several different techniques can be used to analyze the components of Li/S batteries. Nevertheless, very often characterization methods are applied via an ex situ methodology, where post treatments of the samples are required. Ideal case is, when there is a possibility to “observe” the battery under operating conditions, via an in situ methods. X-ray diffraction (XRD) has proven to be a powerful technique to follow the lithium insertion mechanism in Li-ion batteries. It is also well known that structural and morphological changes occur inside the Li/S cell upon cycling, since the red-ox reaction is accompanied by phase transformation of active material (solid/liquid phases). Here we present synchrotron based, operando and in situ XRD studies performed on few independent cells. The Li/S batteries were monitored during several complete cycles and at two different rates (C/20 and C/8). Special pouch cell design allowed us to monitor the evolution of complete cell as well as each electrode separately. Our results show that all elemental sulfur present at the beginning in the electrode is getting reduced into soluble lithium polysulfides during initial discharge and the moment of sulfur disappearance corresponds nicely to the end of first discharge plateau. Well defined peaks of crystalline lithium sulfide (Li2S) start to appear just at the beginning of lower discharge plateau and reach the maximum intensity at the very end of discharge (1.5V). During following charge crystalline Li2S got oxidized back to the soluble polysulfides, which are further oxidized back to the elemental sulfur (end of charge, 3V). Moreover, the crystal structure of sulfur formed after recrystallization was found to be different from the orthorombic α-sulfur used in electrode preparation. Here, for the first time, we report appearance of another sulfur allotrope in Li/S system: monoclinic β-S. Another powerful technique which can be used to investigate the physical and electrochemical processes appearing inside the battery upon cycling is Electrochemical Impedance Spectroscopy. By applying EIS in Li/S system, important information concerning: electrolyte viscosity evolution, electrode morphology and passivation layer formation (Li2S and/or S8) can be obtained. Here we present the impedance of complete Li/S cell as a function of both: state of charge and cycle number. In order to separate the contribution of each electrode or phase (liquid polysulfides) to the impedance spectrum of complete two-electrode Li/S battery, symmetrical cells at different state of charge were also prepared.

Numerical–experimental method to study the viscous behaviour of ceramic materials

The aim of the work deals with the development of a numerical–experimental method to study the viscous behaviour of ceramic materials and to estimate the viscosity evolution as a function of temperature. The current state of the art regarding the study of viscous behaviour of ceramic materials is carried out by using optical methods able to perform measurements without contact with the sample to be analyzed. The two point bending configuration is the conventional test currently used. Despite the use of the optical technology, the test specimen, because of its viscous behaviour, interferes with the measuring device. The experimental test results are inevitably compromised. The developed numerical–experimental method aims at overcoming the drawbacks of the conventional experimental test configuration and at determining the material viscosity. This method consists of an ad hoc developed experimental test configuration and of a numeric simulation of the experimental test.