Search results for "VISCOSITY"
showing 10 items of 542 documents
Complex singularities and PDEs
2015
In this paper we give a review on the computational methods used to capture and characterize the complex singularities developed by some relevant PDEs. We begin by reviewing the classical singularity tracking method and give an example of application using the Burgers equation as a case study. This method is based on the analysis of the Fourier spectrum of the solution and it allows to determine and characterize the complex singularity closest to the real domain. We then introduce other methods generally used to detect the hidden singularities. In particular we show some applications of the Padé approximation, of the Kida method, and of Borel-Polya method. We apply these techniques to the s…
Bistability and “Negative” Viscosity for a Suspension of Insulating Particles in an Electric Field
2003
It is shown that a suspension of insulating particles in a liquid with low conductivity possesses bistability and has a "negative" effective viscosity effect in the electric field due to internal rotations. By Brownian dynamics simulation it has been found that thermal fluctuations of the angular velocity of particles in this bistable system can have a large effect on the viscosity of the suspension.
Temperature and pressure dependence of the viscosities of perfluoropolyether fluids
1987
The viscosities of two structurally different perfluoropolyether fluids were determined at a series of temperatures and pressures, from 25 to 100°C and from 1 to 1000 bars. Flow activation energies and volumes as well as their temperature and pressure coefficients were derived. An attempt was made to relate measured and derived quantities to the compound structures.
The evolution of the meaning of blood hyperviscosity in cardiovascular physiopathology: Should we reinterpret Poiseuille?
2009
In the 1960s and 1970s, a number of researchers (including ourselves) involved in the study of cardiovascular pathophysiology and particularly in the development of techniques to quantify blood flow, came across the observation that, along with vessel diameter, also blood viscosity plays an important role not only in theory but also in practice. Until then, viscosity was thought to play only a marginal role in determining blood flow, a concept which was based on the 1828 theories of Jean Louis Marie Poiseuille (Fig. 1, and [1]).1 In his well-known formula, named after its fathers Hagen2 and Poiseuille,
Effect of adding new phosphazene compounds to poly(butylene terephthalate)/polyamide blends. I: Preliminary study in a batch mixer
2005
Abstract Poly(butylene terephthalate) (PBT) and a sample of polyamide have been melt processed in the presence of two new phosphazene compounds, namely 2,2-dichloro-4,4,6,6-bis[spiro(2′,2″dioxy-1′,1″biphenyl)]cyclotriphosphazene (2Cl-CP) and 2,2-bis-(2-methoxy-4-methyleneoxy-phenoxy)-4,4,6,6,-bis[spiro(2′,2″dioxy-1′,1″biphenyl)]cyclophosphazene (CP-2EPOX). The blends were prepared by using polyamide 6 (PA6) at 25/75 w/w and 75/25 w/w composition. In order to perform a preliminary analysis on the behaviour of the blends, the materials were prepared in a batch mixer. The materials have been completely characterized from a rheological, morphological, mechanical point of view. The results indic…
Damage accumulation in a carbon/epoxy composite : Comparison between a multiscale model and computed tomography experimental results
2012
International audience; High-resolution computed tomography has been carried out for carbon/epoxy laminates loaded in situ to failure. The experimental data allows major damage mechanisms to be quantified in 3D, in an unambiguous and mechanically representative way, where previous experimental analysis is limited. A multi-scale model that predicts damage accumulation in tensile loaded composites is compared to the experimental analysis, to validate the underpinning assumptions within the model and overall performance. The model considers the random nature of fibre-strengths, stress transfer resulting from fibre breaks, fibre/matrix debonding and viscosity of the matrix. Assumptions within t…
A simple method to interpret the rheological behaviour of intercalated polymer nanocomposites
2016
Abstract Nanocomposites are a new class of polymer composites that exhibit an interesting combination of chemical, physical, thermal and mechanical properties. Only small amounts of nanofiller are sufficient to generate great variations of many properties. This work focuses on the rheological behaviour of the intercalated polymer nanocomposites in shear flow. The increase of the viscosity and the more pronounced non-Newtonian behaviour is interpreted simply considering the increase of volume of the inert phase caused by the intercalation of the macromolecules. Indeed, the volume of the intercalated tactoids increases with increasing the interlayer distance. On the other hand, the interlayer…
On the factors governing the pressure dependence of the viscosity of moderately concentrated polymer solutions
1982
Viscosity measurements were carried out as a function of pressure and temperature with solutions of polystyrene in eight (endothermal) θ-solvents at the respective critical composition by means of a Searle-type apparatus. A rolling-ball viscometer was used for the investigation of the pure solvents. In all cases the viscosity coefficient increases in a more or less exponential manner when the pressure is raised. For θ-conditions, the volumes of activation of the solutions exceed that of the pure solvent by typically 10–15%. The exact amount of this extra efffect stemming from the presence of the polymer and its variation with temperature can be qualitatively correlated with the heats of mix…
UV-photometrisch bestimmte relative molare massen von anionisch erzeugten polyäthylenoxiden mit unterschiedlichen endgruppen
1976
Athylenoxid wurde mit Kalium-4-(phenylazo)benzylalkoholat (1f) polymerisiert, die gereinigten Produkte fraktioniert und anschliesend acyliert. Die UV-photometrische Bestimmung der Endgruppen ergab, das HO-Endgruppen, verglichen mit den Starterendgruppen, in grosem Uberschus vorhanden waren. Aus den Endgruppenwerten liesen sich Zahlenmittel des Molekulargewichts (Mn) ableiten. Sie wurden mit osmotisch bestimmten Mn-Werten und Viskositatsmittel (Mη)-verglichen und bestatigten die angenommene Struktur der Polyathylenoxide. Ethylene oxide was polymerized with potassium 4-(phenylazo)benzylalcoholate (1f). The purified and fractionated products were acylated. The ultra-violet measurement of the e…
Rigid Hyperbranched Polycarbonate Polyols from CO2 and Cyclohexene-Based Epoxides
2017
Hyperbranched, multifunctional polycarbonate polyols based on CO2, cyclohexene oxide (CHO), and the “inimer” (initiator–monomer) (4-hydroxymethyl)cyclohexene oxide (HCHO) were prepared in one-pot syntheses. The related linear poly(hydroxymethyl cyclohexene carbonate) structures based on protected HCHO and postpolymerization deprotection were also synthesized as model compounds. The content of hydroxyl functionalities was adjustable for both linear and hyperbranched terpolymer systems. All CO2/epoxide polymerizations were catalyzed by the (R,R)-(salcy)-Co(III)Cl complex. The polycarbonates obtained were comprehensively investigated using various 1D and 2D NMR techniques, SEC, FT-IR, UV–vis s…