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BackgroundThe changes in blood viscosity can influence the shear stress at the vessel wall, but there is limited evidence regarding the impact on thrombogenesis and acute stroke. We aimed to investigate the effect of blood viscosity on stroke and the clinical utility of blood viscosity measurements obtained immediately upon hospital arrival.MethodsPatients with suspected stroke visiting the hospital within 24 h of the last known well time were enrolled. Point-of-care testing was used to obtain blood viscosity measurements before intravenous fluid infusion. Blood viscosity was measured as the reactive torque generated at three oscillatory frequencies (1, 5, and 10 rad/sec). Blood viscosity results were compared among patients with ischemic stroke, hemorrhagic stroke, and stroke mimics diagnosed as other than stroke.ResultsAmong 112 enrolled patients, blood viscosity measurements were accomplished within 2.4 ± 1.3 min of vessel puncture. At an oscillatory frequency of 10 rad/sec, blood viscosity differed significantly between the ischemic stroke (24.2 ± 4.9 centipoise, cP) and stroke mimic groups (17.8 ± 6.5 cP, p

Two-dimensional steady thermocapillary flows in a liquid layer over a substrate, which has a uniform temperature and sinusoidal topography, are investigated by asymptotic theory. Here, the buoyancy effect is negligible and the interface is not significantly disturbed under low Marangoni number and low capillary number. A temperature gradient along the gas/liquid interface causes recirculating flows. For a small aspect ratio, which yields a sinusoidal topography with a long wavelength relative to the mean depth of the liquid layer, the second-order solutions are obtained analytically. The basic solutions show vertical diffusion of heat and vorticity from the substrate and interface, respectively. In the second corrections, the horizontal diffusion of heat weakens the overall flow and the convection of heat intensifies it. [ABSTRACT FROM AUTHOR]

Silica nanoparticle (SiNP)-poly(vinyl alcohol) (PVOH) coating is an important material system in paper coating applications, where particle distribution critically affects coating performance. In the present study, the authors investigated a role of physicochemical interaction between SiNP surface and PVOH chain in SiNP distribution in the coating layer, with a comparison of the suspension at pH 3 (good interaction) and pH 10 (poor interaction) as PVOH concentration was varied. Rheological properties and sedimentation behavior of the suspensions showed the dispersion stability of SiNP at pH 3 was improved by the addition of PVOH, whereas it was independent of the PVOH concentration at pH 10. Scanning electron microscopy and small angle x-ray scattering intensity of dried coating layer showed the uniform and dense structure with homogeneous distribution of SiNPs at pH 3, where spatial arrangement of SiNPs depended on the addition of PVOH. However, non-uniform and porous structures with SiNP aggregates were observed at pH 10, where the spatial arrangement of SiNPs was independent to the addition of PVOH. The stress development during drying of the coating suggested that the mechanical property was related to the spatial arrangement of individual SiNPs at pH 3, whereas to the distribution of SiNPs aggregates at pH 10. [ABSTRACT FROM AUTHOR]

ABSTRACT The homogeneous polycarbonate/poly(acrylonitrile-butadiene-styrene) (PC/ABS) nanocomposite thin films were prepared by a facile solvent casting method using phenylene modified-mesoporous silica materials as additives and dichloromethane as a solvent. The physicochemical analyses using small-angle X-ray scattering, nitrogen adsorption-desorption, solid-state 13C and 29Si nuclear magnetic resonance, and scanning electron microscope were investigated to provide clear physical and chemical properties for modified-mesoporous materials and nanocomposite films. Tensile tests were performed at room temperature according to ASTM D638. Rheological properties were also analyzed to observe any variance of solid-liquid property. As a compatibilizer and a reinforcing filler, mesoporous (organo-)silicas showed enhanced features in rheological and mechanical properties. The sound absorption coefficient was measured by the impedance tube up to 6400 Hz according to ISO 10534-2. It was found that the PC/ABS nanocomposites containing mesoporous materials can be used as a sound-proofing support material depending on fabrication process. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45777. [ABSTRACT FROM AUTHOR]

For melt-compounded poly(lactic acid) composites containing graphene nanoplatelets (GNPs) at low volume fractions, ΦGNP≤0.34 vol.%, this study focused on correlation between the composite properties and a large-scale structure of GNPs formed by a strong alternating current electric field (with the frequency and intensity of 60Hz and 1.75kV/mm, respectively). The electric field was applied to the composite in a rheometer through the parallel plate fixture, so that the parallel plates served as the rheological measurement fixture as well as the electrodes. Optical microscopy, transmission electron microscopy, and two-dimensional wide-angle X-ray diffraction measurements revealed that almost randomly oriented, thin stacks of GNPs in the as-fabricated composites were aligned by the electric field in the field direction and further organized into an extended chain (or column) of stacks. This chained-stack structure bridged two parallel plate electrodes when ΦGNP was above a threshold value, ΦGNP*≅0.17vol.%. Corresponding to this structural change, the liquidlike rheological response of the as-fabricated composites, characterized by the storage modulus G' almost proportional to ω2 at intermediate-to-low angular frequencies ω, became the solidlike response, G'~ω0 at low ω (for the composites having ΦGNP≥ΦGNP*), after application of the electric field. In contrast, the loss modulus G" was insensitive to the electric field and remained almost proportional to ω at low ω, suggesting that the chained-stack structure formed by the electric field was an elastic structure bridging the parallel plates. This bridge also served as an electrically conductive path between the plates so that an insulator-conductor transition occurred when the composites with ΦGNP≥ΦGNP* were subjected to the electric field. Quantitative analysis of the equilibrium modulus and conductivity of the composites suggested that the chained-stack structure formed by the electric field was not a rigid single slab but included junctions being much softer and less conductive compared to the body of GNP (each graphene nanoplate). Moreover, analysis of the ΦGNP dependence on the equilibrium modulus and static electrical conductance after the transition (ΦGNP≥0.17vol.%) suggested that an elastically inert secondary structure was formed by the GNP stacks remaining out of the chained-stack structure (primary structure). This secondary structure appeared to be in soft contact with the primary structure to provide an extra conducting path. [ABSTRACT FROM AUTHOR]

The structural anisotropy and shear rheology of colloidal gels under startup of shear flow are calculated by Brownian dynamics simulations modified to include particle surface-mediated attractions, which is a model for thermoreversible colloidal gels. Shear-induced structural changes are analyzed in both real and reciprocal space through computation of the pair distribution function and structure factor. A distinct structural anisotropy is evident as alignment along the compressional and vorticity axes. A spherical harmonics expansion of pair distribution function is calculated to analyze structural anisotropy. In reciprocal space, structural anisotropy is quantified through an alignment factor, which shows overshoot behavior similar to the stresses. Based on the microstructure analysis, the evolution of the structural anisotropy is explained by the anisotropic rupture of the colloidal gel microstructure. This result provides evidence for how shearing creates structural anisotropy. The structural anisotropy during flow startup is quantitatively related to rheological behavior via a stress-small angle neutron scattering (SANS) rule that is modified to consider the influence of the rupture of the colloidal gel structure. A simple structure kinetic equation accounting for bond creation and rupture provides a unifying view of the results. This new, modified stress-SANS rule quantitatively links the shear-induced structural anisotropy to the nonlinear rheology. [ABSTRACT FROM AUTHOR]

The formation of Taylor cone jet is a key process in electrohydrodynamic printing that is used to produce high resolution patterns. Even though the inks are complex fluids composed of particles, binder, and solvent, most of previous researches have assumed the ink as a Newtonian fluid. In this study, we investigate the effect of viscoelasticity of the ink on Taylor cone jet using two model systems designed to control the elasticity and viscosity of the ink independently. The elasticity and viscosity improve the stability by expanding the operating windows for Taylor cone jet. The results can be summarized in terms of two parameters: elasticity parameter, ξ, and viscosity parameter, χ. The increase in elasticity widens the range of voltage for Taylor cone jet zone, while the range of flow rate remains independent of elasticity. The effect of elasticity is dominant for ξ > 1while it is nearly negligible for ξ < 1. When the viscosity is increased, the Taylor cone jet zone is widened mainly by the flow rate whenχ < 1, while the voltage stabilizes the Taylor cone jet for χ > 1. This study will contribute to the optimal design of EHD printing ink by providing the operating window maps in terms of material properties. [ABSTRACT FROM AUTHOR]

Preheating of dental composites improves their flowability, facilitating successful restorations. However, the fiowability of dental composites is affected not only by temperature but also by the deformation conditions. In the present work, the effects of various deformation conditions upon the viscoelastic properties of a preheated dental composite were studied. The rheological properties of Z350 dental composites at 25, 45, and 60°C were measured by a strain-controlled rheometer. When a low strain (0.03%) was applied, the preheated composite exhibited greater shear storage modulus (G') and complex viscosity (p*) than a room-temperature composite. Oppositely, when a high strain (50%) was applied, G' and n* of a preheated composite were lower than those of a room-temperature composite. Preheating of dental composites might be helpful in clinical practice both to increase the slumping resistance when minimal manipulation is used (e.g., during the build-up of a missing cusp tip) and to increase flowability when manipulation entailing high shear strain is applied (e.g'., when uncured composite resin is spread on a dentin surface). [ABSTRACT FROM AUTHOR]

The microchannel flow of complex fluids has drawn wide attention due to possible applications to high end technologies. But its physics has rarely been understood due to the difficulties in getting the microstructural change of the complex fluids during the flow in confined complex geometries. To understand the characteristics of these complex flows, we studied the dynamics of aggregating particle suspensions in three dimensional 4:1 contraction flow using the self-consistent particle simulation method. It combines both Brownian dynamics and finite element methods self-consistently, which enables to consider long-range hydrodynamic interaction effectively. We observed heterogeneous cluster formation and analyzed it in terms of the competition between flow and interparticle forces. In addition, spatio-temporal fluctuation which originates from the microstructural change and its interaction with the flow was observed. The fluctuation was complex with no characteristic periodicity or pattern. Heterogeneous structure formation and spatio-temporal fluctuation were found to be the main factors that characterize the complex flow of the particulate suspensions in the micro-contraction channel flow. [ABSTRACT FROM AUTHOR]

The flow of viscoelastic fluids in a micro-fabricated 4:1 planar contraction channel was studied through flow visualization. As the Weissenberg number (Wi) increased, the flow developed from a Newtonian-like to vortex growth, and the transient start-up flow at high Wi was found to experience all the steady patterns at lower Wi flows. The flow sequence was different depending on the fluids and channel dimensions, however, in all the cases we could reach, the steady patterns at a low Wi flow could be matched 1:1 with the transient patterns at a high Wi flow. The plot of Wi and time when the two sets (transient and steady) were matched showed a clear functional relationship, from which the time-Weissenberg number superposition could be confirmed. [ABSTRACT FROM AUTHOR]

The first normal stress difference (N1) in large amplitude oscillatory shear (LAOS) consists of two contributions: one from non-oscillating nonzero mean value and the other from oscillating even harmonics, while the nonlinear shear stress can be expressed as a sum of odd harmonics. In this study, the two nonlinear contributions of N1 in entangled polymer solutions have been analyzed by systematical comparison with their shear stress counterparts (storage modulus and odd harmonics, respectively) as a function of strain amplitude and of Deborah number (De). The contributions of N1 were greater than those of the shear stress in the LAOS region. The nonzero mean value of N1 decreased with an increase in Deborah number, but conversely, the second harmonic of N1 increased. The relative intensity (the second harmonic over the fourth harmonic of N1) as an indicator of the nonlinearity of N1 decreased with the Deborah number. We also compared experimental results to model predictions from the eight-mode Giesekus constitutive equation. For the model, we obtained two sets of nonlinear parameters from the best fit of model predictions with both steady shear viscosity and the first normal stress difference coefficient. The model could not quantitatively predict the first normal stress difference behavior in LAOS even with these nonlinear parameter sets, which fit the steady data very well. This study shows that the contribution of the first normal stress difference in LAOS is as vital as that of shear stress, and it can be used as a good estimate of the performance of the constitutive equation. [ABSTRACT FROM AUTHOR]

The article presents a one-dimensional (1D) model for particle distribution using coating thickness at different drying times and conditions, which includes sedimentation, evaporation, and Brownian diffusion. The model system is made up of monodisperse silica particles in water, and the transient particulate distributions were imaged during its drying using cryogenic scanning electron microscopy (cryoSEM). It is concluded that certain limiting cases of the drying regime maps can be computed analytically.

The phase morphology, rheology, mechanical properties, and free volume of poly(trimethylene terephthalate)/polycarbonate (PTT/PC) blends have been investigated as a function of composition. The morphology indicated a two-phase structure, and the blends showed co continuous phase morphology between 30−60 wt % of poly carbonate. Due to the high viscosity of PC, PTT is more finely dispersed in the PC matrix than PC in the PTT matrix. The rheological measurements of the blends revealed that the complex viscosity increased with increase in PC content. Relatively low interfacial tension values of the blends determined using Palierne and Choi−Schowalter methods indicated that there is considerable interaction between the blend components (PTT and PC) due to the transesterification reactions. A random copolyester formed as a result of the transesterification acted as a compatibilizer in the initial stages of reactions which is the main factor for the change in miscibility. The phase morphology and the interfacial adhesion influence the mechanical properties such that addition of the PC phase decreases the tensile strength and Young’s modulus of the system. The free volume data from PALS results showed a slight positive deviation from the known linear additivity rule with increase in PC content, suggesting the blends are partially miscible. Our results show a good correlation among the phase morphology, rheology, mechanical, and free volume parameters. [ABSTRACT FROM AUTHOR]

Nonlinear response of linear and branched polymers has been investigated under medium strain amplitude oscillatory shear (strain amplitude range from 10% to 100%) with Fourier-transform rheology. A power law relationship was found between the relative third intensity (I3/I1), which is an indicator of nonlinearity, and the strain amplitude at low and medium strain amplitudes. On a log-log plot, the intercept and slope of I3/I1 were investigated at different excitation frequencies and temperatures. Simulation results with three different constitutive equations [Giesekus, exponential Phan-Thien Tanner (E-PTT), pom-pom model] were also compared. Experimental results show that the intercept was affected by the excitation frequency and temperature, and the slope of I3/I1 for linear polymer remained constant regardless of molecular weight, molecular weight distribution, and excitation frequency in accordance with the predictions of the constitutive equations (Giesekus and E-PTT). It should be noted that the slope of I3/I1 for branched polymer was lower than that of linear polymer, unlike the prediction of the pom-pom model. Among the molecular architecture and processing parameters (e.g., molecular weight, molecular weight distribution, frequency, and temperature), the slope of I3/I1 under medium amplitude oscillatory shear was found to depend only on the long chain branching, which means that it can be used as a measure of the degree of branching. The failure of the pom-pom model in predicting the nonlinear shear behavior was also pointed out. [ABSTRACT FROM AUTHOR]

In this study, polypropylene (PP)/clay nanocomposites containing different concentrations of ethylene‐methacrylic acid ionomer (i.e. Surlyn®) were prepared, and the effect of ionomer on clay dispersion was studied via WAXD, rheology, SEM, and TEM. The role of the ionomer in the nanocomposites was compared with that of maleic anhydride grafted PP (PP‐g‐MA), which has been widely used as a compatibilizer in making PP/clay nanocomposites. With an increase in the concentration of compatibilizer, the position of d001 peak of OMMT shifted toward a lower angle for PP‐g‐MA system, while the position remained almost unchanged for Surlyn system, in which a larger interlayer spacing (d001) was found with respect to the former. In rheology, the addition of the ionomer led to a gradual increase in both moduli and complex viscosity, and the nonterminal behavior at low frequency was observed in both systems. In addition, the ternary hybrid containing 20 wt % Surlyn achieved the largest enhancement in relative viscosity, which was more than that of the nanocomposite prepared from pure Surlyn or pure PP, presumably indicative of the existence of strong interaction between the components. Finally, SEM and TEM micrographs demonstrated that exfoliated structure was preferred for PP/Surlyn/OMMT hybrids, while intercalated morphology for PP/PP‐g‐MA/OMMT. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4024–4034, 2007 [ABSTRACT FROM AUTHOR]

Examines the effect of graft ratio on the dynamic moduli of acrylonitrile-butadiene-styrene copolymer. Complication on the dependence of rheological properties on the graft ratio; Mechanism of maximum storage modulus; Occurrence of morphological change.

Discusses a study which developed a numerical algorithm based on finite element method (FEM) for solving non-Newtonian fluid flow with the moving free surface problem encountered in polymer processing. FEM formulation of governing equations; Verification of the numerical algorithm in a fountain flow; Simulation of the two-dimensional/full three-dimensional viscous fluid buckling problem using the algorithm.

We suggest a numerical method to describe particle dynamics at the fluid interface. We adopt a coupling strategy by combining the color gradient lattice Boltzmann method (CGLBM) and smoothed profile method (SPM). The proposed scheme correctly resolves the momentum transfer among the solid particles and fluid phases while effectively controlling the wetting condition. To validate the present algorithm (CGLBM-SPM), we perform several simulation tests like wetting a single solid particle and capillary interactions in two solid particles floating at the fluid interface. Simulation results show a good agreement with the analytical solutions available and look qualitatively reasonable. From these analyses, we conclude that the key features of the particle dynamics at the fluid interface are correctly resolved in our simulation method. In addition, we apply the present method for spinodal decomposition of a ternary mixture, which contains two-immiscible fluids with solid particles. By adding solid particles, fluid segregation is much suppressed than in the binary liquid mixture case. Furthermore, it has different morphology, such as with the jamming structure of the particles at the fluid interface, and captured images are similar to bicontinuous interfacially jammed emulsion gels in literature. From these results, we confirm the feasibility of the present method to describe soft matters; in particular, emulsion systems that contain solid particles at the interface. [ABSTRACT FROM AUTHOR]

The local shear stress of non-Brownian suspensions was investigated using the lattice Boltzmann method coupled with the smoothed profile method. Previous studies have only focused on the bulk rheology of complex fluids because the local rheology of complex fluids was not accessible due to technical limitations. In this study, the local shear stress of two-dimensional solid particle suspensions in Couette flow was investigated with the method of planes to correlate non-Newtonian fluid behavior with the structural evolution of concentrated particle suspensions. Shear thickening was successfully captured for highly concentrated suspensions at high particle Reynolds number, and both the local rheology and local structure of the suspensions were analyzed. It was also found that the linear correlation between the local particle stress and local particle volume fraction was dramatically reduced during shear thickening. These results clearly show how the change in local structure of suspensions influences the local and bulk rheology of the suspensions. [ABSTRACT FROM AUTHOR]

We report a type of colloidal gel, induced by a minute incremental addition of mutually attractive small particles (size ~12 mil) to a suspension of highly charged large particles (size ~500 nm). The gel's morphological behavior does not follow the typical power-law scaling for fractal clusters. Its unique scaling behavior has two distinct power-law indices, based on particle volume fraction. We show the unique scaling behavior arises when nonfractal networks of large particles are bridged by small-particle clusters, which occurs between a lower and upper critical boundary of small particle volume fraction. [ABSTRACT FROM AUTHOR]