Reduced Shear Viscosity Research Articles

Invariant dynamics in a united-atom model of an ionic liquid.

We study a united-atom model of the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethyl)sulfonylamide to determine to what extent there exist curves in the phase diagram along which the microscopic dynamics are invariant when expressed in dimensionless, or reduced, form. The initial identification of these curves, termed isodynes, is made by noting that contours of reduced shear viscosity and reduced self-diffusion coefficient coincide to a good approximation. Choosing specifically the contours of reduced viscosity as nominal isodynes, further simulations were carried out for state points on these, and other aspects of dynamics were investigated to study their degree of invariance. These include the mean-squared displacement, shear-stress autocorrelation function, and various rotational correlation functions. These were invariant to a good approximation, with the main exception being rotations of the anion about its long axis. The dynamical features that are invariant have in common that they are aspects that would be relevant for a coarse-grained description of the system; specifically, removing the most microscopic degrees of freedom in principle leads to a simplification of the potential energy landscape, which allows for the existence of isodynes.

Diffusion and viscosity coefficient in Lennard-Jones fluids: excess entropy scaling law

We investigated the proportional relationship between the diffusion coefficient and the viscosity coefficient and excess entropy in Lennard-Jones fluids. Based on the theoretical basis of Dzugutov and Bell et al., we came up with a new expression. Using molecular dynamics simulation to calculate the radial distribution function (RDF), the reduced diffusion coefficient D* and the reduced shear viscosity coefficient η* in the state of reduced density ρ* = 0.5 and the reduced temperature range of 1 ≤ T* ≤ 2.8. The two body excess entropy S2 was calculated from RDF. The results showed that the reduced diffusion coefficient and the reduced viscosity coefficient and the excess entropy present the exponential scaling behaviour. Our results supported the notion put forth by Dzugutov and Bell et al. but had different adjust parameters. The dependence of the reduced diffusion coefficient on the reduced temperature are also explored, they qualitatively exhibited a 2/3 power function relationship. In addition, we have quantitatively calculated the relation schema of ln(η*)-ln(D*/T*) in Lennard-Jones fluids that with LJ potential (n = 12) without considering the influence of the packing fraction and found that the reduced diffusion coefficient and reduced viscosity satisfy the new Stokes–Einstein relationship proposed by Ohtori et al.

Cationic Polymerized Epoxy and Radiation Cured Acrylate Blend Nanocomposites Based on WS2 Nanoparticles—Part A: Curing Processes and Kinetics

Cationic photo-initiated and polymerized epoxies are characterized by good adhesion, high modulus, zero volatiles, low shrinkage and living polymerization characteristics. Radiation—cured acrylate resins are characterized by rapid initial curing with increased initial strength. The combination of radiation-cured acrylates and epoxies may present advantageous attributes. Thus, the system investigated is a hybrid epoxy/methyl acrylate and three different initiators for cationic polymerization of epoxies, the radical reaction of acrylates and the thermal initiator. When incorporating additives like opaque WS2 nanoparticles (NPs), absorption of the photo radiation takes place, which may lead to low photo activity. Curing kinetics measurements revealed that the absorbing/masking effect of WS2 was insignificant, and surprisingly, the level of curing was enhanced when the WS2 NPs were incorporated. FTIR results demonstrated that covalent bonds were formed between the inorganic fullerenes (IF-WS2) and the crosslinked matrix. Viscosity measurements showed a surprising reduction of five to ten times in the low-shear viscosity upon NPs incorporation compared to neat resins. It was concluded that the decrease of viscosity by the inorganic NPs, in addition to the enhanced level of conversion, has profound advantages for structural adhesives and 3D printing resins. To the best of our knowledge, this investigation is the first to report on a radiation-induced curing system containing opaque WS2 NPs that leads to an enhanced degree of curing and reduced shear viscosity.

Encapsulation of Lactobacillus rhamnosus GG in edible electrospun mats from calcium and sodium caseinates with pullulan blends

Electrospinning has been proposed as a method to encapsulate and preserve bioactive compounds in nanofibrous mats to ensure their delivery and associated health benefits when consumed directly or added to a food formulation. In previous work, we demonstrated the production of edible fibers to form mats of both calcium (CaCAS) and sodium (NaCAS) caseinate-pullulan (PUL), with the polysaccharide PUL added as a carrier to facilitate molecular entanglement for fiber formation. In this study, we determined the viability of the probiotic bacteria, Lactobacillus rhamnosus GG (LGG), used as a model bacterium, in mats of CaCAS-PUL and NaCAS-PUL. Electrospinning of aqueous solutions at room temperature (21 ± 1°C) of 15% (wt/wt) CaCAS and NaCAS mixed with 15% (wt/wt) PUL, with a 1:1 ratio of CAS:PUL, resulted in fibrous mats with average fiber diameter sizes of 233 ± 20 and 244 ± 21 nm, respectively, as determined by scanning electron microscopy. Addition of LGG in the amounts of 9.3 and 9.0 log10 cfu/mL to the CaCAS-PUL and NaCAS-PUL solutions before electrospinning resulted in average fiber diameter sizes of 212 ± 14 and 286 ± 16 nm, respectively. The LGG was found to be distributed within the CaCAS-PUL and NaCAS-PUL fibers. The addition of LGG increased the shear viscosity and conductivity of the CaCAS-PUL solution, enhancing molecular entanglement and resulting in thinner fibers. For NaCAS, LGG increased the conductivity but reduced shear viscosity. Adjustment of the NaCAS-PUL composition would be needed to optimize conditions for thinner fibers. The numbers of viable LGG recovered from the CaCAS-PUL and NaCAS-PUL nanofibrous mats after electrospinning were 9.5 and 9.6 log10 cfu/g, respectively, proving that the electrospinning conditions used were capable of supporting probiotic encapsulation. These results demonstrate that food-grade electrospun fibrous mats can be used to develop functional foods with delivery of probiotics to improve human or animal health.

Liquefaction of granular materials in constant-volume cyclic shearing: Transition between solid-like and fluid-like states

By means of 3D-DEM cyclic simple shear simulations at constant volume, this paper analyzes the evolution of the internal structure during cyclic liquefaction of dense granular media. Upon liquefaction, the granular system undergoes a fast transition to a regime where the fluid-like shear strain develops. This regime is characterized by low shear modulus, decreasing dilatancy, and reduced shear viscosity. We analyze the internal structure by means of several micro- and meso-scale descriptors, including coordination number, fabric anisotropy, number of clusters, a fraction of maximum cluster size, and a percolation index. We select a typical post-liquefaction cycle in which we highlight several particular states that naturally divide the cycle into different periods. During liquefaction, the system deforms significantly with an enhanced number of binary collisions initially and particle clusters subsequently. Both the coordination number and percolation index increase while fabric anisotropy oscillates. The fluid-like to solid-like transition is characterized by a well-defined value of the coordination number (3.6) when the particles percolate across the system. From the analysis of the micro- and meso-scale behaviors, we further discuss two possible criteria for exiting the fluid-like state based on the excess pore pressure.

Fibrillated Cellulose via High Pressure Homogenization: Analysis and Application for Orodispersible Films.

Powdered cellulose (PC) and microcrystalline cellulose (MCC) are common excipients in pharmaceuticals. Recent investigations imply that particle size is the most critical parameter for the different performance in many processes. High-pressure homogenization (HPH) was used to reduce fiber size of both grades. The effect of the homogenization parameters on suspension viscosity, particle size, and mechanical properties of casted films was investigated. PC suspensions showed higher apparent viscosities and yield stresses under the same process conditions than MCC. SLS reduced shear viscosity and thixotropic behavior of both cellulose grades probably due to increased electrostatic repulsion. Homogenization reduced cellulose particle sizes, but re-agglomeration was too strong to analyze the particle size correctly. MCC films showed a tensile strength of up to 16.0MPa and PC films up to 4.1MPa. PC films disintegrated within 30s whereas MCC films did not. Mixtures of MCC and PC led to more stable films than PC alone, but these films did not disintegrate anymore. Diclofenac sodium was incorporated in therapeutic dose with drug load of 47% into orodispersible PC films. The content uniformity of these films fulfilled requirements of Ph.Eur and the films disintegrated in 12s. In summary, PC and MCC showed comparable results after HPH and most differences could be explained by the smaller particle size of MCC suspensions. These results confirm the hypothesis that mainly the fiber size during processing is responsible for the existing differences of MCC and PC in pharmaceutical process, e.g., wet-extrusion/spheronization.

Characterization of the Fluidity of the Ultrasonic Plasticized Polymer Melt by Spiral Flow Testing under Micro-Scale.

The fluidity of a molten polymer plasticized by ultrasonic vibration was characterized by spiral flow testing based on an Archimedes spiral mold with microchannels. Mold inserts with various channel depths from 250 to 750 µm were designed and fabricated to represent the size effect under micro-scale. The effect of ultrasonic plasticizing parameters and the mold temperature on the flow length was studied to determine the rheological nature of polymers and control parameters. The results showed that the flow length decreased with reduced channel depth due to the size effect. By increasing ultrasonic amplitude, ultrasonic action time, plasticizing pressure, and mold temperature, the flow length could be significantly increased for both the amorphous polymer polymethyl methacrylate (PMMA) and the semi-crystalline polymers polypropylene (PP) and polyamide 66 (PA66). The enhanced fluidity of the ultrasonic plasticized polymer melt could be attributed to the significantly reduced shear viscosity.

Carbon fibers derived from wet‐spinning of equi‐component lignin/polyacrylonitrile blends

ABSTRACTEqui‐component blends of polyacrylonitrile (PAN) and lignin, i.e., with a lignin content as large as 50 wt %, were successfully used as precursors to produce carbon fibers. Rheological measurements demonstrated that increasing lignin content in spinning solution reduced shear viscosity and normal stress, indicating a decrease of viscoelastic behavior. This was confirmed by Fourier transform infrared results that show no discernable chemical reaction or crosslinking between PAN and lignin in the solution. However, the resulting carbon fibers display a large ID/IG ratio (by Raman spectroscopy) indicating a larger disordered as compared to that from pure PAN. The macro‐voids in the lignin/PAN blend fibers typically generated during wet‐spinning were eliminated by adding lignin in the coagulant bath to counter‐balance the out‐diffusion of lignin. Carbon fibers resulting from lignin/PAN blends with 50 wt % lignin content displayed a tensile strength and modulus of 1.2 ± 0.1 and 130 ± 3 GPa, respectively, establishing that the equi‐component wet‐spun L/P‐based carbon fibers possessed tensile strength and modulus higher than 1 and 100 GPa. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45903.

Rheology, curing temperature and mechanical performance of oil well cement: Combined effect of cellulose nanofibers and graphene nano-platelets

Cellulose nanofibers (CNFs) were prepared through acid hydrolysis and used in combination with graphene nano-platelets (GNPs) as modifiers for oil well cement (OWC). The rheology behavior of CNF/GNP-OWC slurries at three temperatures (i.e., 20, 40, and 60°C) was measured and modeled using four different rheological models. Thermal properties, surface functional groups, morphology, and mechanical performance of the composites were characterized. CNF/GNP-OWC slurry exhibited a typical shear-thinning behavior with reduced shear viscosity at higher shear rates. The use of CNFs and GNPs led to increased yield stresses of fresh CNF/GNP-OWC slurry and temperature significantly influenced the yield stress values. Among these rheology models, the Vom Berg model exhibits the best fitting result of the slurry rheology data (R2=0.999). The addition of CNFs and GNPs increased degree of hydration (DOH) value of CNF/GNP-OWC composites. Both flexural and compressive strengths of the CNF/GNP-OWC composites were enhanced with added CNFs and GNPs. The reinforcing mechanism was attributed to the increased DOH, reduced pores, and bridging effect of CNFs and GNPs in the composites.

Capillary rise dynamics of liquid hydrocarbons in mesoporous silica as explored by gravimetry, optical and neutron imaging: Nano-rheology and determination of pore size distributions from the shape of imbibition fronts

We present gravimetrical, optical, and neutron imaging measurements of the capillarity-driven infiltration of mesoporous silica glass by hydrocarbons. Square-root-of-time Lucas-Washburn invasion kinetics are found for linear alkanes from n-decane (C10) to n-hexacontane (C60) and for squalane, a branched alkane, in porous Vycor with 6.5 nm or 10 nm pore diameter, respectively. Humidity-dependent experiments allow us to study the influence on the imbibition kinetics of water layers adsorbed on the pore walls. Except for the longest molecule studied, C60, the invasion kinetics can be described by bulk fluidity and bulk capillarity, provided we assume a sticking, pore-wall adsorbed boundary layer, i.e. a monolayer of water covered by a monolayer of flat-laying hydrocarbons. For C60, however, an enhanced imbibition speed compared to the value expected in the bulk is found. This suggests the onset of velocity slippage at the silica walls or a reduced shear viscosity due to the transition towards a polymer-like flow in confined geometries. Both, light scattering and neutron imaging indicate a pronounced roughening of the imbibition fronts. Their overall shape and width can be resolved by neutron imaging. The fronts can be described by a superposition of independent wetting fronts moving with pore size-dependent square-root-of-time laws and weighted according to the pore size distributions obtained from nitrogen gas sorption isotherms. This finding indicates that the shape of the imbibition front in a porous medium, such as Vycor glass, with interconnected, elongated pores, is solely determined by independent movements of liquid menisci. These are dictated by the Laplace pressure and hydraulic permeability variations and thus the pore size variation at the invasion front. Our results suggest that pore size distributions can be derived from the broadening of imbibition fronts.

Rheological Investigation of the Effects of Introducing Diethylene Glycol on the Physical Properties of PVA Solutions and PVA Films

AbstractThe effects of diethyl glycol (DEG) on the rheolgical properties of polyvinyl alcohol(PVA) solutions in dimethyl sulfoxide and on the physical properties of PVA films were investigated. DEG seemed to change the state of hydrogen bonding in the solutions and in the films. In the case of 6 wt% PVA solutions, incorporating DEG abruptly reduced shear viscosity if DEG content exceeded 30 wt% to PVA whereas a little decrease of them was observed in 12 wt% PVA solutions over the DEG content observed. Further, at the same DEG content 6 wt% PVA solutions showed a more notable increase of viscosity with time at a constant shear rate than 12 wt% solutions. Dynamic mechanical thermal analysis revealed that introducing DEG broadened the peak of tan δ curve and lowered the glass transition temperature of PVA. DEG imparted toughening effects to PVA film preferably in the range of 10 to 20 wt% to PVA.

Lamellar Orientation and Corresponding Rheological Properties of Symmetric Diblock Copolymers under Steady Shear Flow

The kinetics of lamellar orientation and rheological properties of symmetric diblock copolymers under steady shear flow using the time-dependent Ginzburg−Landau (TDGL) approach were studied. The simulation results show that a high shear rate can induce a perpendicular alignment for temperatures just below the order−disorder transition (ODT). On the other hand, a low shear rate induces initially mixed morphologies composed primarily of perpendicular and parallel orientations; eventually, the perpendicular alignment is transformed into a parallel alignment via undulation instability. On the contrary, with decreasing temperature, the high shear rate produces a parallel alignment, and the low shear rate induces a perpendicular alignment. The results also show that the reduced shear viscosity rapidly reaches a maximum at a reduced shear strain near one and then decreases. The first and second normal stress differences N1 and N2 are related to the lamellar alignment.

Molecular dynamics calculation of the thermal conductivity and shear viscosity of the classical one-component plasma

The thermal conductivity λ and shear viscosity η of the three-dimensional classical one-component plasma (OCP) were determined by molecular dynamics experiments. In the simulations the velocity of the particles was spatially modulated, and the transport coefficients were calculated from the relaxation time of the modulation profile. The results are given for the 2⩽Γ⩽125 range of the plasma coupling parameter Γ. The reduced shear viscosity η* was found to exhibit a minimum at Γ=20 in agreement with previous calculations. In the 2⩽Γ⩽10 range our method yields η* values 20%–50% higher compared to some of the previously obtained data, while very good agreement was found at the position of the minimum of η*. The reduced thermal conductivity λ* exhibits a minimum (similarly to η*) at Γ between 15 and 20. The calculations presented here result in 30%–40% lower thermal conductivity compared to previously available data.

Rheological behavior and stability of concentrated silica suspensions

In the present article, the rheological behavior and phase stability of concentrated silica suspensions were investigated experimentally by examining the effects of particle size and temperature. The silica particles were stabilized by adsorption of a silane coupling agent, γ-methacryloxypropyl triethoxy silane (MPTES). The MPTES-coated silica particles behaved like hard spheres and exhibited the dispersion stability in tetrahydrofurfuryl alcohol which was used as a refractive-index matching solvent. For a monodisperse suspension, the limiting viscosities at high shear rates were correlated satisfactorily with the Krieger–Dougherty equation until the particle volume fraction φ reached 0.45 above which the limiting high-shear-rate viscosities did not exist. The highly concentrated monodisperse suspensions above φ=0.50 displayed the rapidly shear thinning viscosity at low shear rates and underwent the shear thickening at high shear rates. Specifically, the onset of shear thickening shifted to a higher shear rate either as temperature rose or as the suspension became stable. The dichroism from light passed in the flow-gradient direction probed the most effectively the order–disorder transition such as disappearance of hexagonally ordered layered structure and formation of particle clustering, which caused shear thickening at high shear rates. The abrupt change in dichroism caused by the breakdown of hexagonally layered structure occurred almost 1 decade before the onset of shear thickening. Finally, the bimodal suspensions prepared here possessed the reduced shear viscosity and stress in comparison with the monodisperse suspensions of identical volume fraction. The degree of the viscosity reduction became conspicuous for concentrated suspensions usually above φ=0.40.

Shear viscosity of the B phase of superfluid3He. III

We report the calculation of the shear viscosity in superfluid3He-B at 6, 21, and 30 bar. We have used the variational solution of the Boltzmann equation for quasiparticles. The transition probabilities are obtained within thes-p-d-wave approximation by fitting the normal state transport coefficients. The old and new Landau parameters are used to estimate the scattering amplitudes. The reduced shear viscosity does not depend very much on the choice of Landau parameters and agrees very well with experiment in the temperature range 0.5<t (=T/T c )≤1.0, whereT c is the transition temperature. We have also investigated the strong coupling corrections to the shear viscosity. Although the strong coupling corrections reduce the value of shear viscosity, the overall feature does not change from the weak coupling result. The pressure dependence of the reduced shear viscosity is found to be very small.

Viscometric properties of poly(dimethylsiloxane) filled with spherical silica particles

AbstractThe shear viscosity and primary normal stress coefficient were measured for colloidal dispersions of monodisperse silica spheres in poly(dimethylsiloxane). The viscometric properties of the dispersions were a function of the shear rate, particle diameter, and the volume fraction of particles. Dimensional analysis of rheological properties of colloidal dispersions of spherical particles in a second‐order fluid was performed, and the experimental data were analyzed in terms of the appropriate dimensionless groups. The reduced shear viscosity of the colloidal dispersions was a function of the volume fraction of particles and the reduced shear stress (or reduced shear rate). The reduced primary normal stress coefficient was a function of the volume fraction of particles, the reduced shear rate, and the Weissenberg number.

The rheology and mold flow of polyester sheet molding compound

AbstractFlow properties of sheet molding compounds (SMC) were measured by several rhemeters. Shear viscosities of SMC paste can be fitted by the Carreau viscosity equation and reduced to a single master curve by plotting the reduced shear viscosity (η/η0) against reduced shear rate (\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} η0/T). The deformation fo glass filled compounds under extensional forces. When the shear forced was applied, the compound defomed like a deck of cards being slid. It behaved essentially like a laminate of many layers. On the other hand, SMC compounds elongated much less before sample failure occurred under the extensional flow. The extensional viscosity was much higher than the shear viscosity. This phenomenon was explained by a solid composite theory and theories developed from local shear flows between adjacent fibers. The flow of SMC compounds during molding showed that the surface layers flowed further than the inner layers when the mold surfaces were hot. This casued inner plies to show through at the surface and resulting in some wavy glass orientation. This phenomenon was explained equalitatively by a heat penetration model.

Shear viscosity of the superfluid 3HeB

The shear viscosity η of superfluid 3 HeB is calculated in the s-p-d-wave approximation for the collision integral of the Boltzmann equation for quasiparticles. The new and old Landau parameters are used to estimate the scattering amplitude. We have estimated the possible range of values for the reduced shear viscosity. Also the strong-coupling corrections to η at 20 bar are obtained and the pressure dependence of η is calculated. The agreement between theory and experiment is good.

Possible range of values for the reduced shear viscosity of superfluid 3HeB

A possible range of values for the shear viscosity of superfluid 3He-B is obtained in the spd-wave approximation for the collision integral of the Boltzmann equation for quasiparticles. The reduced viscosity is in good agreement with experiments at 20 bar.

Shear viscosity of the B phase of superfluid 3He. II. s-p-d-wave approximation

The shear viscosity η(T) of superfluid 3He-B is studied throughout the temperature region 0⩽t⩽1 (t=T/T c). The Boltzmann equation for Bogoliubov-Valatin quasiparticles is solved by a variational method. In the calculation of the collision integral, the scattering amplitude is estimated in the s-p-d-wave approximation by taking into account the spin-dependent part as well as the spin-independent part. The reduced shear viscosity % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-qqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xHapdbiqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaacaaeaacq% aH3oaAaiaawoWaaiabg2da9iabeE7aOHqaciaa-HcaieaacaGFubGa% a8xkaGGaciab99caViabeE7aOjaa-HcacaGFubWaaSbaaKqaGgaaca% WFJbaaleqaaOGaa8xkaaaa!440E!\[\widetilde\eta = \eta (T)/\eta (T_c )\] in this approximation is smaller than those in the s-wave and s-p-wave approximations at all temperatures. The numerical result for \~η in the s-p-d- wave approximation is in good agreement with the recent experimental data of Parpia et al. and of Alvesalo et al. in the temperature range 0.5.⩽t⩽1.0.