Search results for "VISCOSITY"

Improving the rheometry of rubberized bitumen: experimental and computation fluid dynamics studies

2017

Abstract Multi-phase materials are common in several fields of engineering and rheological measurements are intensively adopted for their development and quality control. Unfortunately, due to the complexity of these materials, accurate measurements can be challenging. This is the case of bitumen-rubber blends used in civil engineering as binders for several applications such as asphalt concrete for road pavements but recently also for roofing membranes. These materials can be considered as heterogeneous blends of fluid and particles with different densities. Due to this nature the two components tends to separate and this phenomenon can be enhanced with inappropriate design and mixing. Thi…

Acyclovir Delivery Matrices Based on Poly(Ethylene Glycol)/Chitosan Semi-Interpenetrating Networks

2007

Abstract Chitosan matrix systems have been studied as potential vehicles for the prolonged release of acyclovir (ACV). The influence of chitosan concentration (from 0.83% to 1.67%) on viscoelastic properties of formulations with and without glyoxal was analyzed. For chitosan‐poly(ethylene glycol) 400 formulations loss modulus ( G ″) are greater than storage modulus ( G ′). This corresponds to the characteristic behavior of nonstructured systems. When glyoxal was added to the chitosan‐poly(ethylene glycol) 400 formulations, gelled matrix was obtained (i.e., G ′ is higher than G ″), except for the lowest chitosan concentration. ACV release rates for the both types of systems, with and without…

Release of isoamyl acetate from starch pastes of various structures : thermodynamic and kinetic parameters

2004

The release of isoamyl acetate from starch-based matrices was studied on the basis of a cumulative dynamic headspace analysis. Two corn starches were compared, which are known to yield pastes and gels differing in their structures and properties. These properties were assessed by viscometry and viscoelastic measurements. Aroma release was discussed as a function of the structure and texture parameters of the matrix. The release curves obtained from water and from the various starch-based matrices at 25 degrees C showed similar patterns but differed in their initial slopes and in the final plateau values. The lowest initial slopes were obtained for the normal starch dispersions that formed g…

1953

Sur une serie de palymethacrylates de methyl fractionnes des mesures de la diffusion lumineuse (en fonction de I'angle et de la longeur d'onde) on ete faites, puis la constante de diffusion, la constante de sedimentation dans I'ultrazentrifugeuse et la viscosite intrinshque [η] ont ete determines. Les poids moleculaires et les diametres des chaines souples sont en concordance d'apres ces methodes. La dependance des diametres des chaines sonples d,l du poids molkculaire est un peu plus forte que d'aprh la loi de Kuhn (dst ≃ M0.6). L'influence de cette decouverte sur la fonction de la diffusion lumineuse de mihe que sur l'equation de la viscosite de Kirkwood et Riseman est etudiee. Light-scat…

Dynamic anomalies at the glass transition of organic van der Waals liquids

1993

Abstract The paper discusses the question of whether there is a characteristic temperature T c above the calorimetric glass transition temperature T g . Mode-coupling theory (MCT) predicts a crossover from liquid- to solid-like dynamics at T c . Neutron scattering and gradient NMR experiments have been carried out to test MCT using the molecular van der Waals liquid ortho -terphenyl as a model system. A significant anomaly of the Debye—Waller factor and a “decoupling” of self-diffusion from viscosity support the MCT predictions. A critical discussion of the relevance of such tests and of the limitations of neutron scattering is presented.

Gelation of smectic liquid crystal phases with photosensitive gel forming agents.

2020

This paper studies the potential of 3 newly synthesized low molecular weight gelling agents (2 of them with azo groups) with the semicarbazide group as a H-bonding motif to gel the smectic phase of a commercial chiral smectic C material. To detect gelation two methods were used: the stabilization of the director pattern, which measures the interaction of the physical gel network with the LC-director, and the suppression of the onset of electrohydrodynamic instabilities, which measures the increase of viscosity. Special emphasis was put on the influence of the photochemical - isomerization of the gelling agents on gelation.From the stabilization of the director pattern an elastic component c…

Power Consumption in Uncovered Unbaffled Stirred Tanks: Influence of the Viscosity and Flow Regime

2013

Notwithstanding the increasing industrial interest toward unbaffled tanks, available experimental information on their behavior is still scant, even for basic quantities such as the mechanical power drawn. In this work, the influence of the Reynolds and Froude numbers on the power consumption characteristics is presented for unbaffled stirred tanks operating both in nonaerated conditions (subcritical regime) and in aerated conditions (supercritical regime), i.e., when the free surface vortex has reached the impeller and the gas phase is ingested and dispersed inside the reactor. Experimental results obtained at various liquid viscosities show that power numbers obtained in subcritical condi…

MR2410211 (2009b:47107) Păcurar, Mădălina Viscosity approximation of fixed points with $\phi$-contractions. Carpathian J. Math. 24 (2008), no. 1, 88-…

2009

Let T be a nonexpansive self-mapping of a closed bounded convex subset Y of a Hilbert space. For l in (0, 1), the author considers the iteration xl = lf(xl)+(1−l)Txl, where f from Y to Y is a $\phi$-contraction. Then, the author proves that (xl)l converges strongly as l goes to 0 to the unique fixed point of the $\phi$-contraction Pof, where P is the metric projection of Y onto the set FT of fixed points of T. The viscosity approximation method of the paper is obtained from the method proposed by A. Moudafi [J. Math. Anal. Appl. 241 (2000), no. 1, 46–55; MR1738332 (2000k:47085)] for mappings in Hilbert spaces, and by H. K. Xu [J. Math. Anal. Appl. 298 (2004), no. 1, 279–291; MR2086546 (2005…

Techniques to evaluate erythrocyte deformability in diabetes mellitus

2005

Using several rheological techniques, we examined the erythrocyte deformability in different groups of diabetic subjects. The macrorheological techniques used for this evaluation were respectively whole-blood filtration, filtration of erythrocyte suspensions, polyviscosimetry and diffractometry. Whole-blood filterability, at a negative pressure of 20 cm water, was decreased in type 2 diabetics; no difference was evident at a negative pressure of 10 cm water. The filtration of erythrocyte suspensions at low haematocrit (5%) did not show differences between normal and diabetic subjects. The polyviscosimetry, which explores the filterability of erythrocyte suspensions at high haematocrit (80%)…

Healon®5: A New Viscoadaptive Formulation

2000

To relate the practical relevance of our study results, specific requirement profiles for individual procedures have been correlated to the desired physicochemical characteristics. Healon®5 demonstrated the statistically significant highest zero shear viscosity of all OVD and a long relaxation time (Dick et al., 2000). It therefore most effectively creates and maintains a deep anterior chamber in order to facilitate safe surgical maneuvers (e.g., in case of vitreous pressure). Additionally, the high viscosity of Healon®5 exhibits a dynamic frequency dependence, which has not been observed in any pure hyaluronic acid formulation before. Healon®5’s properties change in response to surgical ma…