Temperature Coefficient Of Viscosity Research Articles

Relationship between Viscosity Coefficients and Volumetric Properties Using a Scaling Concept for Molecular and Ionic Liquids

In this work, a scaling concept based on relaxation theories of the liquid state was combined with a relation previously proposed by the authors to provide a general framework describing the dependency of viscosity on pressure and temperature. Namely, the viscosity-pressure coefficient (partial differentialeta/partial differentialp)T was expressed in terms of a state-independent scaling exponent, gamma. This scaling factor was determined empirically from viscosity versus Tvgamma curves. New equations for the pressure- and temperature-viscosity coefficients were derived, which are of considerable technological interest when searching for appropriate lubricants for elastohydrodynamic lubrication. These relations can be applied over a broad range of thermodynamic conditions. The fluids considered in the present study are linear alkanes, pentaerythritol ester lubricants, polar liquids, associated fluids, and several ionic liquids, compounds selected to represent molecules of different sizes and with diverse intermolecular interactions. The values of the gamma exponent determined for the fluids analyzed in this work range from 1.45 for ethanol to 13 for n-hexane. In general, the pressure-viscosity derivative is well-reproduced with the values obtained for the scaling coefficient. Furthermore, the effects of volume and temperature on viscosity can be quantified from the ratio of the isochoric activation energy to the isobaric activation energy, Ev/Ep. The values of gamma and of the ratio Ev/Ep allow a classification of the compounds according to the effects of density and temperature on the behavior of the viscosity.

Water assisted injection moulding: development of insights and predictive capabilities through experiments on instrumented process in parallel with computer simulations

An idealised model of core-out in water assisted injection moulding (WAIM) is set up to isolate the effect of cooling by the water on the deposited layer thickness. Based on simulations, this is investigated for a specific case as a function of Pearson number and power law index. It is found that cooling significantly reduces the layer thickness to the extent that a change in the flow regime ahead of the bubble, from bypass to recirculating flow, is possible. For shear thinning melts with high temperature coefficient of viscosity, the simulations show very low layer thickness, which may indicate unfavourable conditions for WAIM. Although in the real moulding situation, other effects will be superimposed on those found here, the results provide new insights into the fundamentals of WAIM. Investigation of other effects characterised by Fourier and Reynolds numbers will be reported subsequently. Some early process measurement results from an experimental WAIM mould are presented. Reductions in residual wall thickness are observed as the water injection set pressure is increased and the duration of water bubble penetration through the melt is determined experimentally. The formation of voids within the residual wall is noted and observed to reduce in severity with increasing water injection pressure. The presence of such voids can be detected by the signature from an infrared temperatures sensor.

Synthesis and comparative properties of poly(dimethylsiloxane) grafted alkyl acrylate

AbstractLow hydrogen‐containing siloxane (l‐PDMS) material was prepared by H2SO4‐catalyzed equilibration of octa‐methyl cyclo tetra siloxane (D4), hexamethyl disiloxane (MM) and high hydrogen‐containing siloxane (h‐PDMS). Poly(dimethylsiloxane) (PDMS) grafted methyl acrylate (MA), ethyl acrylate (EA), and butyl acrylate (BA) were prepared by Pt‐catalyzed hydrosilylation reaction of l‐PDMS and three acrylates, respectively. PDMS grafted alkyl acrylate not only preserves the properties of PDMS, but also adds new ones. Viscosity, viscosity–temperature coefficient (VTC), viscosity‐index (VI), and TGA experiments indicate that the grafted copolymers have outstanding thermal stability as PDMS. The measurement of surface tension (ST) shows the grafted copolymers have low surface energy as PDMS. However, emulsifiability, lubricity, and solubility in organic solvent, such as acetone, isopropanol, of PDMS grafted alkyl acrylate were better than the properties of PDMS, which can be very useful for fine chemical industry. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Transport Coefficients of Nuclear Matter at High Temperatures

High temperature coefficients of viscosity and heat conductivity of nuclear matter are calculated on the basis of Chapman-Enskong approximation in the dilute gas limit. It is observed that increasing temperatures produce significant changes in coefficients.

Performance of synthetic oils in the hydrodynamic regime ‐ II. Generalisation

AbstractIn Parti I the results of an extensive experimental investigation of the performance of environmentally adapted oils in the hydrodynamic regime were reported. Four oils were tested in a tilting‐pad thrust bearing for different combinations of load, shaft speed, and supply oil temperature. In this second part, details of a generalisation procedure are described. A number of parameters representing the physical properties of an oil, such as viscosity and viscosity‐temperature coefficient, are adopted. The influence of each of these parameters on minimum oil film thickness, maximum temperature rise, and bearing power loss is then analysed. It is shown that viscosity measured at the supply oil temperature is the most important parameter. The effects of the viscosity‐temperature coefficient and oil thermal conductivity are less pronounced and yet significant. It is also shown that it is not possible to select an optimum oil that yields maximised oil film thickness, minimised temperature rise, and minimised power loss at the same time.

Base fluid parameters for elastohydrodynamic lubrication and friction calculations and their influence on lubrication capability

AbstractIn this study, base fluid parameters for elastohydrodynamic lubrication (EHL) and friction analyses have been determined experimentally. The viscosity at atmospheric pressure, η0, the pressure‐viscosity index, α, and the EHL friction coefficient, γ, are important parameters in EHL theory and they are crucial in the selection of efficient lubricants for different applications. This investigation focuses on three important lubrication mechanisms: the capability of forming a separating lubricant film, the friction generated in a lubricated contact, and the height of pressure peaks, such as the outlet pressure spike and pressure ripple caused by surface roughness. The influence of different lubricant parameters on these three mechanisms is discussed. The value of α is measured in a Couette high‐pressure viscometer, and the value of γ is obtained from a jumping‐ball device. Other parameters discussed are temperature‐viscosity coefficient, β, bulk modulus, B0, thermal conductivity at atmospheric pressure, λ0, and heat capacity unit volume, ρcp0.A comparison between traditional mineral base oils and environmentally adapted oil based on rapeseed oil and synthetic esters contributes to the further understanding of the performance of these new materials in lubrication applications. It is shown that rapeseed oil and synthetic esters have good lubricating properties and are, in most cases, better than mineral oils.

Temperature effects in hydrodynamic properties of comb-like polymer with laterally attached mesogenic units

The specific temperature effects in hydrodynamic properties (intrinsic viscosity, sedimentation velocity and translational diffusion) of side-on comb-like polymers with molecular weights from 5.70×10 5 to 3.02×10 6 were observed in dilute solution in two different solvents, benzene and chloroform, over a temperature range from 2 to 73°C. The viscosity temperature coefficient dln[ η]/d T was found to be negative in sign in chloroform (−0.007 K −1) and positive in benzene (+0.005 K −1). Increase in temperature leads to intensification of the excluded volume effects in real benzene solution of the polymer and to weakening of those in chloroform. Simultaneously, increase in temperature leads to decreasing unperturbed dimensions of the macromolecule chain in both the solvents. This effect is more pronounced in benzene (dln〈 h 2〉/d T=−0.005 K −1, where 〈 h 2〉 is the mean-square end-to-end distance) than in chloroform (−0.001 K −1). Origins of the temperature effects are discussed with relation to the lateral structure of the macromolecule where every monomer unit contains the threecyclic mesogenic moiety which is laterally (with the middle part) attached to a side chain consisting of 11 carbon atoms.

Simulated Non-Newtonian Lubricant Behaviour under Extreme Conditions

Equilibrium and non-equilibrium molecular dynamics techniques are used to simulate a molecular liquid (n-hexadecane) at extreme physical conditions (high temperatures, pressures and shear rates), typical of those encountered in many elastohydrodynamic lubrication applications, and to study the effects of pressure and temperature on the calculated theological properties. Pressure and temperature effects are found to be more pronounced at low shear rates than at high shear rates, where the non-Newtonian behaviour is dominated by the strong external kinematic effects. The observed non-Newtonian behaviour of the pressure and temperature coefficients of viscosity and the variation of certain molecular geometric functions calculated to assist the microscopic understanding are combined to provide a possible explanation for the phenomenon of limiting shear stress under elastohydrodynamic lubrication conditions. Further implications for the behaviour of lubricant-like molecules in practical applications are also discussed.

On the viscosity-temperature behavior of polymer melts

Based on the free volume concept and the equation by Doolittle, an empirical equation is offered for the flow activation energy, E*, for polymer melts for the range of over 150°C above glass transition temperature, Tg. This E* represents the temperature coefficient of viscosity for the Newtonian region which is also equal to the value measured at constant shear stress for non-Newtonian flow. Data show that the E* of linear polymers approaches a constant value for a temperature range above Tg+150°C. Data on 17 polymers are correlated. The proposed equation for this region predicts the E* of polymer melts from the volume expansion coefficient, αl, above Tg and also from the Tg.

Viscosity of NaI Solutions in Water-tert-Butanol Mixtures at 35 And 40°C

Abstract Viscosity of water-tert-butanol mixtures and of NaI solutions in those mixtures at 35 and 40°C have been measured. Results are discussed in terms of the effect of alcohol on the water structure and of NaI on the structure of water-alcohol mixtures. Temperature coefficients of viscosity have been calculated for several water-alcohol and water-amide mixtures. We conclude that it is precarious to describe structures basing on Δn/Δt values. It can be only presumed that whatever structure of solution arises, it is unstable when its temperature coefficient of viscosity is large. Plots of relative viscosities of NaI solutions (at various concentration of NaI) in water-tert-butanol mixtures have minima at about 6 mol% alcohol i.e. the composition range in which water structure exhibits the maximum ordering effect by tert-butanol molecules. A comparison of viscosities and standard solutions enthalpies for NaI solutions in water-alcohol and water-amide systems is made.

The temperature dependence of the doolittle equation parameter for polymer liquids

AbstractThe Doolittle equation parameter for polymer liquids is a function of temperature. Its dependence on temperature can be expressed by a quadratic equation. The constants in the equation are determined for four vinyl‐type polymer liquids: polystyrene (PS), poly(vinyl acetate) (PVAc), polydimethylsiloxane (PDMS), and polyisobutylene (PIB). It was found that the Doolittle parameter decreases with increasing temperature. Equations are presented for the pressure and temperature coefficients of viscosity, isoviscous temperature coefficient of volume, and the constant Km in the Miller equation. Comparisons of the predictions of the equations, with those in the literature, are favorable. © 1993 John Wiley & Sons, Inc.

Analytical and numerical calculations for thermal elastohydrodynamic lubrication problems of helical W-N gears

By adopting the pressure-viscosity coefficient perturbation method, the numerical calculations required to solve elastohydrodynamic lubrication (EHL) problems are greatly reduced. In addition, the initial gaps between tooth flanks and the instantaneous velocities of tooth profiles are deduced. The inlet and outlet boundaries of the lubricant are also discussed. The finite difference method (FDM) is used to determine perturbation solutions. It can be seen during the setting up of the difference equation, that higher grades of solution can be achieved with no iteration on the basis of the α 0 grade of solution, i.e. the isoviscosity solution, which is easier to obtain owing to its small non-linearity of pressure and film thickness. In addition, all matrices of coefficients of higher grades of the difference equation are the same except for the constant item of the equation, which will obviously make programming and calculation very convenient. Solutions to thermal EHL problems are converted into a superposition of the solution of isothermal EHL and higher grades of solution by the temperature-viscosity coefficient perturbation method. This greatly reduces the amount of numerical calculation because solutions of isothermal EHL will have already been obtained. The FDM is adopted to determine the perturbation solutions to thermal EHL problems. During the setting up of the difference equation it can be seen that higher grades of solution can be solved much more easily on the basis of the β 0 grade of solution, i.e. the solution of the isothermal EHL problem. In addition, the numerical calculation pattern of the Reynolds equations is the same as that of isothermal EHL. All matrices of coefficients of higher grades of difference equation (both Reynolds and energy equations) are the same except for the constant item of the equations. Groups of thermal EHL problems (totalling 1536) of helical W-N gears under different conditions are calculated analytically and numerically. Results are given in the form of figures and formulae from which many useful conclusions can be obtained. From a group of non-dimensional formulae calculating the maximum hydrodynamic lubrication pressures between tooth flanks under different conditions, the ratios of maximum oil film pressure under the condition of testing the limit contact stresses of tooth flanks and under different working conditions have been obtained. The ratios are taken as the coefficients modifying the limit contact stresses of tooth flanks considering the influence of thermal EHL because experimental determination of limit stresses is difficult. According to the traditional concepts, the coefficients are separated into coefficients of lubrication and velocity, which have been compared with relative coefficients of involute gears.

Hydrodynamic properties of molecules of polyvinylpyrrolidone as shown by sedimentation-diffusion analysis and viscometry

The authors have measured the coefficient of translational diffusion D 0, the sedimentation coefficient S 0 and the intrinsic viscosity [η] of samples and fractions of polyvinylpyrrolidone in 0.1 M sodium acetate solution in the interval MW 2 ⩽ M × 10 −3 ⩽ 2200. In the region M > 4 × 10 4 they obtained the relation: [ η] = 8.86 × 10 −5 M 0.74; D 0 = 2.42 × 10 −4 M −0.58 and S 0 = 2.14 × 10 −15 M 0.42. In the region M⩽4 × 10 4: [ η] = 5.0 × 10 −4 M 0.56, D 0 = 1.29 × 10 −4 M −0.52 and S 0 = 1.15 × 10 −15 M 0.48. The values of the hydrodynamic invariant A 0 = (3.2 ± 0.25) × 10 −10 erg degree −1 mole 1 3 , sedimentation parameter β s = (1.3 ± 0.17) × 10 7 mole 1 3 , temperature viscosity coefficient negative: Δ ln [ η]/ ΔT = −6.3 × 10 −3 degree −1. From the theory of the hydrodynamic properties of a worm-like necklace taking into account the influence of the effects of excluded volume an evaluation is made of the equilibrium rigidity A and the hydrodynamic diameter d of the chains modelling the macromolecules in solution. The evaluations of A agree with the values obtained from the Burchardt-Stockmayer-Fixman and Cowie-Bywater constructions: A = (2.1 ± 0.3) nm, d = (0.5 ± 0.13) nm.

A Thermodynamic Approach to Viscosity

For use in elastohydrodynamic systems, the ideal lubricant is generally one which forms a thick separating film between the rubbing surfaces over a wide range of operating conditions. This implies a fluid with a low temperature-viscosity coefficient and a high pressure-viscosity coefficient. Unfortunately, there is a braod correlation between these two values for liquids. This paper derives and then verifies, using experimental data, an expression for this correlation based upon the assumption that viscosity is a thermodynamic property of state. From the resultant expression, the factors that contribute to a high ratio of pressure- to temperature-viscosity coefficient are identified and discussed by reference to a range of lubricant structures. Other implications of viscosity being a property of state are also considered. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference In Baltimore, Maryland, October 16–19, 1988

Dependence of the intrinsic viscosity on temperature for solutions of some aromatic polyamides

The dependence of the intrinsic viscosity of a number of aromatic polyamides and poly- p-phenylene oxadiazole in sulphuric acid on temperature has been investigated. Characteristic of all the polyamides is a high negative value of the temperature viscosity coefficient which is interpreted as the result of increase in equilibrium flexibility due to deformation of the amide groups during thermal motion. It is shown that the temperature viscosity coefficient rises with increase in the MW of the polymers studied.

Temperature and solvent effects on the intrinsic viscosities of a star-shaped polystyrene

The excluded-volume effect on the solution behaviour of a star-shaped polystyrene has been studied by measuring intrinsic viscosities over the temperature range 25–55°C. Two good solvents (benzene, dioxane) were selected together with two poor solvents (cyclohexane, 71.4% dioxane-28.6% methanol). The viscosity-temperature coefficients and apparent activation energies were compared. Other parameters investigated were: α (the expansion factor), θ (the theta or Flory temperature), ψ 1 (the entropy parameter of the solvent) and κ 1 (the enthalpy parameter of the solvent). Since measurements were carried out in dilute solutions, the Kirkwood approximation was assumed, namely that polymers behave hydrodynamically like spheres. The classical method developed by Flory and Fox was used for analysis. The theory of Flory and Fox modified by Benoit and coworkers is discussed.

Water-Soluble Copolymers. XX. Copolymers of Acrylamide with Sodium 3-(N-Propyl)Acrylamido-3-Methylbutanoate: Solution Properties

Abstract Dilute solution properties of copolymers of acrylamide (AM) with sodium 3-(N-propyl)acrylamido-3-methylbutanoate (NaPAMB) of known molecular weight have been studied as a function of composition, temperature, time, pH, and added electrolytes. Phase separation and potentiometric studies have also been performed. The AM-NaPAMB copolymers possess lower molecular weights and solution viscosities than the AM-NaAMB copolymers. In addition, the AM-NaPAMB polymers exhibit moderate viscosity-temperature coefficients and poor salt tolerance. These polymers undergo phase separation in the presence of divalent cations as a function of temperature. The observed properties can be related to the steric and hydrophobic effects caused by the presence of the n-propyl substituent at the amide nitrogen.

Anomalous Temperature Dependence of Viscosity of Thermotropic Polyesters

A rheological study of a series of thermotropic liquid crystalline copolyesters containing varying proportions of hydroxybenzoic acid, isophthalic acid, and hydroquinone has shown unexpected behavior. Certain compositions were observed to exhibit a POSITIVE temperature coefficient of viscosity (viscosity increasing with shear rate) over the entire shear rate range. Other compositions showed flow curves which intersected at critical shear rates. This behavior is explained by a variation in chain stiffness with composition (high hydroxybenzoic acid content resulting in stiffer chains) which results in a biphasic melt. The unusual rheological behavior is a manifestation of the competition between isotropic and anisotropic phases, which is influenced by composition, temperature, and shear.

FLOW AND DIELECTRIC BEHAVIOUR OF BUTOXYSILOXANES

Butoxysiloxanes are prepared by reacting SiCl4 with 1-butanol and 1-butanol-water mixtures in the liquid phase at atmospheric pressure. Some of their physical properties such as density, refractive index, viscosity, viscosity-temperature-coefficient (VTC) viscosity index (VI) dielectric constant (e) dielectric loss (ϵ”) molar polarization (Pm) induced polarization (Pi) orientation polarization (Po), molar polarizability (α0) relaxation time (τ)and Batschinsky's constant (ω)are evaluated. Some of the values are compared with those of commercial grade linear polydimethylsiloxanes, cyclic polydimethylsiloxanes and petroleum oils. Viscosity-temperature and viscosity-pressure characteristics, thermal and oxidation stability of butaoxysiloxanes indicate that these could be useful substitutes for commercial grade silicones in some engineering applications.

Some aspects of current techniques for the preparation of capillary columns for gas chromatography

Desirable column properties and their relation to different steps in column preparation are discussed. The properties of different capillary materials are compared, the different methods for high-temperature silylation, which are being used to achieve deactivation and wettability, are considered and the advantages of immobilized silicone stationary phases are described. Immobilization leads primarily to improved stationary phase film stability and this is of particular utility in connection with polar columns; some polar silicone gums have a high temperature coefficient of viscosity and may therefore be redistributed on a capillary surface at elevated temperatures, leading to deterioration in column performance. Immobilization very efficiently counteracts such an effect. Silicones containing cyanopropyl and phenyl substitution cannot readily be cross-linked. It is demonstrated that a convenient way to solve this problem is to include some tolyl substitution in the gum that is to be cross-linked.