Search results for "VISCOSITY"
showing 10 items of 542 documents
Data from: Coping with the climate: cuticular hydrocarbon acclimation of ants under constant and fluctuating conditions
2018
Terrestrial arthropods achieve waterproofing by a layer of cuticular hydrocarbons (CHCs). At the same time, CHCs also serve as communication signals. To maintain waterproofing under different climate conditions, insects adjust the chemical composition of their CHC layer, but this may affect the communication via CHC. The detailed acclimatory changes of CHCs and how these influence their physical properties are still unknown. Here, we studied acclimation in two closely related ant species with distinct CHC profiles, Myrmica rubra and Myrmica ruginodis, in response to constant or fluctuating temperature and humidity regimes. We measured how acclimation affected CHC composition and viscosity, …
Relaxation phenomena in mixed isomeric alcohols by Mandelstam-Brillouin scattering
1991
Mandelstam-Brillouin scattering data in mixed isomeric alcohols n-pentanol (nPe-OH) and 2-methyl-2-butanol (2Me-2BuOH) are presented. The hypersonic velocity and normalized absorption are measured as a function of the scattering angle, in the temperature range from - 15-degrees-C to + 45-degrees-C, and as a function of n-PeOH molar fraction going from the pure n-PeOH to the pure 2Me-2BuOH. The experimental results confirm the existence of a shear relaxation phenomenon in the GHz region, that has been previously detected in pure liquids. The temperature dependence of the relaxation time tau-s and of the shear modulus G-infinity evaluated within viscoelastic liquid models, support the existen…
Recent advances on ionic liquid uses in separation techniques
2018
International audience; The molten organic salts with melting point below 100°C, commonly called ionic liquids (ILs) have found numerous uses in separation sciences due to their exceptional properties as non molecular solvents, namely, a negligible vapor pressure, a high thermal stability, and unique solvating properties due to polarity and their ionic character of molten salts. Other properties, such as viscosity, boiling point, water solubility, and electrochemical window, are adjustable playing with which anion is associated with which cation. This review focuses on recent development of the uses of ILs in separation techniques actualizing our 2008 article (same authors, J. Chromatogr. A…
Über den einfluß des substitutionsgrads auf die viskositätszahl (staudinger index) von cellulosenitraten
1962
Es wurden Untersuchungen uber die Abhangigkeit des STAUDINGER-Index vom Stickstoffgehalt in einem [η]-Bereich von 700 bis 4000 (ml·g−1) durchgefuhrt. Dabei wurde gegenuber den bisher in der Literatur vorliegenden Arbeiten eine verbesserte Praparations- und Mestechnik angewandt. Es wurde festgestellt, das der Gang des STAUDINGER-Index mit dem Substitutionsgrad swischen 13,0 und 13,8% geradlinig verlauft und durch folgende Gleichung wiedergegeben werden kann (vgl. Abb. 1): Hierin bezeichnet N den Stickstoffgehalt in %; x ist ein Faktor, der vom Polymerisationsgrad bzw. STAUDINGER-Index bei 13,8% in folgender Weise abhangt (vgl. Abb. 2): Bei Stickstoffgehalten uber 13,8% konnte keine Abhangigk…
Efficiency range of the Belousov-Zhabotinsky reaction to induce the self-organization of transient bonds in metallo-supramolecular polymeric systems.
2020
The periodic change of the oxidation state of the metal catalyst in the oscillating Belousov-Zhabotinsky (BZ) reaction has been reported to establish a periodic organization of metallo-supramolecular bonds in polymeric systems, which results in autonomous viscosity oscillations. To appraise the possible extent of quantitative control on the viscosity oscillation features, we assess how the kinetics of the BZ reaction affects the periodic self-organization of the metal-ligand coordination, and vice versa. Our model system includes mono-, bis-, and tetra-functional polyethyleneglycol (PEG) precursors end grafted with terpyridine ligands that are complexed with ruthenium ions, which oscillate …
On the existence of weak solution to the coupled fluid-structure interaction problem for non-Newtonian shear-dependent fluid
2016
We study the existence of weak solution for unsteady fluid-structure interaction problem for shear-thickening flow. The time dependent domain has at one part a flexible elastic wall. The evolution of fluid domain is governed by the generalized string equation with action of the fluid forces. The power-law viscosity model is applied to describe shear-dependent non-Newtonian fluids.
Theory of heterogeneous viscoelasticity
2015
We review a new theory of viscoelasticity of a glass-forming viscous liquid near and below the glass transition. In our model we assume that each point in the material has a specific viscosity, which varies randomly in space according to a fluctuating activation free energy. We include a Maxwellian elastic term and assume that the corresponding shear modulus fluctuates as well with the same distribution as that of the activation barriers. The model is solved in coherent-potential approximation (CPA), for which a derivation is given. The theory predicts an Arrhenius-type temperature dependence of the viscosity in the vanishing-frequency limit, independent of the distribution of the activatio…
Effect of thickener on disintegration, dissolution and permeability of common drug products for elderly patients
2019
Dysphagia is a very common problem suffered by elderly patients. The use of thickeners during administration in these patients helps to prevent difficulties with swallowing larger solid dosage forms. However, there are several indications when the thickeners may influence disintegration and dissolution processes of solid dosage forms, potentially affecting therapeutic efficacy. In this paper the effects of a commonly used thickener on tablet disintegration, dissolution and subsequent absorption of 6 formulated drugs frequently used in elderly patients (Aspirin, Atenolol, Acenocumarol, Candesartan, Ramipril and Valsartan) in two different administration conditions (intact tablet and crushed …
Do viscosity and wettability of fluoride varnishes affect their fluoride release?
2020
BACKGROUND: There are several brands of fluoride varnishes in the market, but the dynamics of fluoride release from each one might be different. The purpose of this study was to evaluate in vitro the release of fluorides by fluoride varnishes and to determine the correlation with viscosity and wettability. MATERIAL AND METHODS: Forty four enamel blocks 5x5 mm were randomly divided into 4 groups (n=11) ((Duraphat®, Clinpro™ White Varnish, Flúor Protector® and control). We applied 30 milligrams of fluoride varnish to each specimen. The specimens were immersed in a Calcium Phosphate solution at a pH= 6.0. We evaluated the release of fluoride, by using a selective fluoride electrode, during 6 w…
A comprehensive experimental study of the rheological behaviour of HDPE.
1986
Extensional properties of four high density polyethylenes with different molecular weights and molecular weight distributions are presented. The samples have already been well characterized in shear and non-isothermal extensional flow. The data were collected at 180 °C for elongational rates between 3 · 10−1 and 10−4s−1. Some qualitative and quantitative generalizations of the results are given.