Search results for "Viscosity."

Dense Solid-Liquid Off-Bottom Suspension Dynamics: Simulation and Experiment

2009

Dense solid-liquid off-bottom suspension inside a baffled mechanically agitated stirred tank equipped with a standard Rushton turbine is investigated. Dynamic evolution of the suspension from start up to steady state conditions has been inspected by both visual experiments and computational fluid dynamics. A classical Eulerian-Eulerian Multi Fluid Model along with the “homogeneous” k-epsilon turbulence model is adopted to simulate suspension dynamics. In these systems the drag inter-phase force affects both solids suspension and distribution. Therefore, different computational approaches are tested in order to compute this term. Simulation results are compared with images acquired on the re…

Inverse Spin Fractionation:  a Tool to Fractionate Sodium Hyaluronate

2006

Kinetic interpretation of influence of sodium chloride concentration and temperature on xanthan gum dispersion flow model

2001

The present study derives a fixed-concentration (0.4%) xanthan gum dispersion flow model for different molar concentrations of sodium chloride (0–0.25M) and different temperatures (20–70°C). The Ostwald–de Waele model is used in all cases. A temperature rise reduces the shear-thinning characteristics of the systems, although the power law index is much less sensitive to changes in temperature when NaCl is added, even in very small amounts. The lowest consistency values correspond to the dispersions formulated in the absence of salt, the highest values are observed for molar values of ≥0.15, and there are decreases in consistency upon raising the temperature in all cases. The viscous behavio…

Molecular characterization of α,β-poly[( N -hydroxyethyl)- dl –aspartamide] by light scattering and viscometry studies

2000

Abstract α,β-poly[(N-hydroxyethyl)- dl -aspartamide] (PHEA) is a new synthetic polymer which is of interest in biomedical applications. In this paper, the molecular characterization of PHEA by multi-angle laser light scattering and viscometry off-line and on-line to a size exclusion chromatography system is reported. These techniques furnish an exhaustive and consistent characterization of the PHEA polymer. The fractionation of the PHEA macromolecules was relatively simple. Using an aqueous mobile phase of medium ionic strength, the elution was substantially regular and the macromolecules were not aggregate. The molar mass M of four PHEA samples approximately ranges from 46 to 53 K g/mol, t…

Intrinsic Viscosity of Aqueous Solutions of Carboxymethyl Guar in the Presence and in the Absence of Salt

2008

Intrinsic viscosities were determined for solutions of CMG in pure water and 0.9 wt.-% aqueous NaCl. To avoid the 0/0-type extrapolation typical for Huggins plots, a new procedure was used. For CMG and pure water, this requires only two adjustable parameters: the specific hydrodynamic volume of the polymer in the limit of infinite dilution and a hydrodynamic interaction parameter. The intrinsic viscosity of CMG (no salt) at room temperature is 6 050 mL · g -1 ; approximately half as large as that of Na-PSS of comparable molar mass. The ratio of the intrinsic viscosities with and without salt is ≈7 for CMG, as compared to >100 for Na-PSS. The reasons for the different behaviors of the two ty…

Hyperbranched Poly(ethylene glycol) Copolymers: Absolute Values of the Molar Mass, Properties in Dilute Solution, and Hydrodynamic Homology

2015

Hyperbranched poly(ethylene glycol) copolymers were synthesized by random anionic ring-opening multibranching copolymerization of ethylene oxide with glycidol as a branching agent, leading to poly(ethylene glycol) structure with glycerol branching points. Extending the available range of molar masses by novel synthesis strategies, a limited extent of control over the degree of polymerization was achieved by variation of the solvent in this copolymerization. Generally, absolute molar mass characterization of hyperbranched polymers still represents an unresolved challenge. A series of the hyperbranched poly(ethylene glycol)-co-(glycerol) copolymers (hbPEGs) of a wide range of molar masses (14…

Continuous polymer fractionation of poly(methyl vinyl ether) and a new Kuhn-Mark-Houwink relation

1995

Continuous polymer fractionation (CPF) — a new large-scale method — was applied to the technical poly(methyl vinyl ether) (PVME) using toluence as solvent and petroleum ether as non-solvent. Two different devices served as fractionation apparatus, namely a column packed with glass beads and a set of mixer-settler extractors. Advantages and draw-backs of these devices are discussed. The experiments yielded numerous PVME fractions, varying in molar mass from 22 to 87 kg/mol and in molecular non-uniformity U = (M¯w/Mn) – 1 from 0,25 to 0,41 according to gel-permeation chromatography as compared with ca. U = 1,30 for the starting material. The following Kuhn-Mark-Houwink relation was establishe…

A study of the refractive index and surface tension synergy of the binary water/ethanol: influence of concentration

2005

Pure alcohols or alcohols mixed with water are the most widely used solvents in a great variety of industrial applications, including the formulation of pharmaceutical and cosmetic products. As a result of water/alcohol molecular associations, variations result in the physico-chemical characteristics of the system, such as density, viscosity, refractive index and surface tension. The present study investigates the refractive index and the surface tension of ethanol and water mixtures at a temperature of 25°C, for different molar fractions. The data obtained allow us to study the corresponding refractive index and the surface tension synergies; in this sense, an absolute maximum refractive i…

Shear viscosity of polybutyleneterephthalate/liquid crystal polymer blends

1989

Viscosity measurements have been carried out on blends of polybuty-leneterephthalate (PBT) and a liquid crystalline copolyesteramide (LCP). The flow curves of the blends with LCP content larger than 20%, show a behavior similar to that of the pure LCP, with a rapid rise of the viscosity at low shear rates. The viscosity-composition curves exhibit a deep minimum at low LCP content which may be mainly attributed to the lack of interactions between the two phases.

On the definition of viscosity solutions for parabolic equations

2001

In this short note we suggest a refinement for the definition of viscosity solutions for parabolic equations. The new version of the definition is equivalent to the usual one and it better adapts to the properties of parabolic equations. The basic idea is to determine the admissibility of a test function based on its behavior prior to the given moment of time and ignore what happens at times after that.