Showing papers in "Rheologica Acta in 1971"

Dehnungsverhalten von Polyäthylen-Schmelzen

Abstract: In einem Dehnungsrheometer werden Spannungs-Dehnungs-Diagramme von Polyathylen-Schmelzen bei 150 °C und bei konstanter Dehnungsgeschwindigkeit\(\dot \varepsilon _0\) gemessen (\(\dot \varepsilon _0\) zwischen 0,001 und 1 sec−1). Weiterhin wird der reversible (elastische) Dehnungsanteil bestimmt. Messungen mit einem „Dehnungstester fur Kunststoff-Schmelzen“ erganzen die Ausfuhrungen.

Particle motions in non-Newtonian media

Abstract: An experimental study of the behaviour of rigid and deformable particles suspended in pseudoplastic and elasticoviscous liquids undergoing slowCouette flow was undertaken. The velocity profiles deviated slightly from those obtained forNewtonian fluids, but the measured angular velocities of rigid spheres showed that the rotation of the field was equal to half the velocity gradient. While the measured angular velocities of rods and discs were in accord with theory applicable toNewtonian liquids, in both non-Newtonian media there was a steady drift in the orbit towards an asymptotic value corresponding to minimum energy dissipation in the flow. Furthermore, discs in elasticoviscous solutions of polyacrylamide at higher shear stresses aligned themselves in the direction of the flow and ceased to rotate. Migration of rigid particles across the planes of shear in the annul us of theCouette was also observed. In pseudoplastic liquids, the migration was towards the region of higher shear, whereas the opposite was true in elasticoviscous liquids. The deformation, orientation and burst of pseudoplastic drops inNewtonian liquids and that ofNewtonian drops in pseudoplastic fluids were similar to those previously in completelyNewtonian systems. With elasticoviscous drops, however, the deformation was smaller than given by theory. As in elasticoviscous fluids, two-body collisions of rigid uniform spheres in the pseudoplastic liquids were unsymmetrical and irreversible, thus differing from collisions inNewtonian systems where complete reversibility is observed. While some of the observed phenomena in elasticoviscous suspensions could be qualitatively interpreted, particle behaviour in the pseudoplastic liquids could not be explained in terms of the known rheological properties of the fluids.

Constitutive equations for polymer solutions derived from the bead/spring model of Rouse and Zimm

Abstract: The theory of dilute polymer solutions based on the bead/spring model in the form given by Zimm is reformulated for arbitrary homogeneous flow histories. It is shown that the center of resistance of a polymer molecule moves with the solvent. By a preliminary transformation [3.4], the equations for the center-of- resistance motion are separated from those for the motion of the N spring vectors. The spring-vector equations involve a symmetric non-singular matrix B [3.14] whose characteristic values equal the non-zero characteristic values of Zimms singular matrix HA. A further transformation [4.2] which diagonalizes B yields separate differential eq. [5.4] for pq*, the polymer contribution to the stress tensor associated with the q normal mode. Transformation to an embedded basis enables one to integrate these equations so as to obtain pq* in terms of the flow history ([5.6], [5.9]), and summation over q then gives the required constitutive eq. [5.17] for the polymer solution. These are of the same form as the “rubber-like liquid” constitutive equations (with addition of a solvent-contribution term) derived from the network theory of Lodge, but the memory function is determined to within three constants (e. g. N, h*, τ1). Peterlina solution for the normal-coordinate distribution function in steady shear flow is generalized for an arbitrary homogeneous (time-dependent or steady) flow and expressed in terms of pq* which can be evaluated when the flow history is given.

On pulsatile flow of non-Newtonian liquids

Abstract: We consider the behaviour of non-Newtonian liquids as they are made to flow through straight pipes of circular cross section under the action of a pressure -gradient which oscillates sinusoidally about a non-zero mean. The theory for such a situation is developed in detail and certain predictions, some quantitative some qualitative, are made. Quite a substantial increase in mean flow rate due to the fluctuation in the pressure-gradient is predicted under some conditions. The theoretical predictions are shown to be in good agreement with experimental results and a method for locating the “optimum conditions” is outlined which makes use of the experimentally determined apparent viscosity of the fluids only. The possible relevance of the work to blood flow in the human body is discussed.

Hydrodynamically induced crystallization of polymers from solution

Abstract: This paper deals with a study on the melting behaviour of polyethylene crystals showing a fibrillar morphology. These crystals were prepared by hydrodynamically induced crystallization from xylene solutions. Use was made of several techniques, such as differential scanning calorimetry, polarizing microscopy and infrared dichroism. The experimental observations indicate that the melting process of the fibrous crystals can only partly be related to morphological structures. The infrared dichroism and persistent birefringence up to temperatures of 200 °C are due mainly to the molecular orientation in the melt. The shrinkage on melting was found to depend on the thickness of and fibre orientation in the sample, as well as on the molecular weight of the polyethylene. A maximum shrinkage value of 93% was measured on fibrillar crystals of Marlex (M w =90 · 103). Calorimetric studies on the fusion of fibrillar crystals of high molecular weight polyethylene (M w =1.5 · 106) revealed that extendedchain backbones melt at 150 °C and even at 180 °C. The melt of these crystal structures remains partly oriented, as could be inferred from the constant temperature position of the melting peak on repeated crystallizing and melting.

Numerical calculation of storage and loss modulus from stress relaxation data for linear viscoelastic materials

Abstract: Numerical formulae are given for calculation of storage and loss modulus from the known course of the stress relaxation modulus for linear viscoelastic materials. These formulae involve values of the relaxation modulus at times which are equally spaced on a logarithmic time scale. The ratio between succeeding times corresponds to a factor of two. Bounds for the relative error of those formulae were derived. These bounds depend on the value of the damping, tanδ, at the angular frequency,ω. The lower the damping values, the easier is the calculation of the storage modulus. This calculation involves the value of the relaxation modulus at timet 0=1/ω, and that of its derivative with respect to the logarithm of time in a rather narrow region aroundt 0. By contrast, the calculation of the loss modulus is difficult. This calculation involves the value of the derivative of the relaxation modulus with respect to the logarithm of time in a broad interval aroundt 0. Especially the behaviour of the relaxation modulus at timest

A general method for the determination of approximations to the spectral distributions from the dynamic response functions

Abstract: A method, based on the logarithmic differentiation of the dynamic response functions with respect to frequency, is presented which is more general than the Stieltjes transform inversion method and yields approximations of both even and odd order from the storage functions and the loss functions. More than one approximation exists if the order, Jc, of the approximation (i.e. the order of the highest derivative) is ≥ 2 for approximations from the storage functions, or ≥ 1 for those from the loss functions. Of particular practical interest are the two first-order approximations from the loss functions and the two second-order approximations from the storage functions. The approximations are found by requiring that (1) the intensity function associated with a given approximation be normalized, and that (2) it have a single maximum only. If the maximum is not located at ωτ = 1, the time scale of the spectrum is adjusted accordingly. The choice of the most suitable approximation is discussed.

Heat-conducting micropolar fluids

Abstract: In this paper heat-conducting micropolar fluids are introduced as an extension of the theory of micropolar fluids. Constitutive equations appropriate to describe the thermal and mechanical response of micropolar fluids are constructed. The heat conduction equation is derived and the field equations are obtained. The solution to the problem ofPoiseuille flow through a channel with flat walls is given.

On the orthogonal superposition of simple shearing and small-strain oscillatory motions

Abstract: Certain limiting high-and low-frequency relations peculiar to the general Kaye-Bernstein-Kearsley-Zapas single integral constitutive equation are developed for orthogonally superposed simple shearing and small-strain time-sinusoidal shearing. The relations do not hold for a general simple fluid nor for single-integral constitutive equations in which arbitrary dependence of the kernel function on the rates of deformation is allowed. It is shown that solutions of polyisobutylene in cetane (4.4%, 6.8%) and solutions of polyethylene-oxide (0.7%) and J-100 (0.1%) in water obey the relations quite closely.

The rheological properties of saliva

Abstract: Saliva is a complex biological fluid that cannot be effectively studied by conventional methods such as theFerranti-Shirley Viscometer. Testing with theWeissenberg Rheogoniometer shows that saliva is viscoelastic and that the dynamic viscosity falls from 400-0.1 Poise over the frequency range 2.5×10−3 to 10 Hertz. The calculated elastic contribution can be correlated with dry weight content. Dynamic viscosity and shear modulus are both reduced in storage, by proteolytic enzymes. The mucolytic agent Ascoxal also brings about a reduction in these parameters but by a different mechanism. A comparison of the results with those obtained previously for sputum, shows, that saliva may be a suitable model system for assessing mucolytic agentsin vitro.

Extensional primary field approximations for viscoelastic media

Abstract: TheTrouton ratio, defined as the ratio of the extensional to the shear viscosity, may reach very high levels in viscoelastic media. Consequently the diagonal components of the deformation rate tensor, often of negligible importance in the analysis of flows ofNewtonian fluids, may be of primary interest here. Several significant phenomena unknown inNewtonian fluid mechanics are seen to have their origin in the tensile normal stresses generated by these extensional deformations of viscoelastic fluid media; they include the separation of particles or bubbles in accelerating flows (the „Uebler” effect), the operability of ductless siphons („Spinnbarkeit“) and, probably, turbulent drag reduction. A class of problems which may be treated by neglecting the usual shearing deformation rates and shearing stresses, and considering only the extensional behaviour of the medium, is identified. These problems are characterized by high values of the dimensionless elongation rate, defined as the product of the local extension rate and the natural time of the fluid. As this dimensionless group frequently reaches its highest levels in the primary fluid stream outside a boundary layer this approximation is termed an “Extensional Primary Field” or EPF approximation to focus attention on the primary or “outer” flow, as distinguished from flows in the vicinity of solid surfaces. The EPF approximation appears to provide a sufficient basis for analysis of several problems: converging flows into an orifice or duet from a larger reservoir, flows through porous solids and elongational flows with free surfaces as in textile fiber-spinning operations and flow in ductless siphons. In several other problems — lubricant squeeze films, turbulent flows under drag reducing conditions and flows about submerged objects — EPF considerations appear to be of importance but may not control the entire problem. The potential importance of EPF considerations in treating fluid mechanically controlled crystallization processes is noted.

Continuum theory of liquid crystals

Abstract: Eine Kontinuumstheorie ist kurzlich entwickelt worden, die erwarten last, die Eigenschaften der flussigen Kristalle zu beschreiben. Der Zweck dieser Arbeit ist es, erstens, diese Theorie vorzustellen, und, zweitens, ihre Anwendung auf die Viskosimetrie der nematischen flussigen Kristalle zu diskutieren. Oftmals benutzt man magnetische Felder in den umfangreichen Experimenten, um die Orientierung der bevorzugten Richtung zu kontrollieren, und daher ist eine Diskussion dieses Falles eingeschlossen.

Some investigations of melt fracture

Abstract: During melt fracture shear stresses and velocity profiles were measured in capillaries and slits. Different polymers show large differences in flow behaviour during melt fracture. The type of melt fracture can be predicted from the shape of the velocity profile in front of the entrance of the capillary or slit. Particular attention was paid to the behaviour of high-density polyethylene during instable flow accompanied by pressure and output variations.

Determination of normal-stress differences in steady shear flow

Abstract: Using the cone- and-plate apparatus ofAdams andLodge, values of pressure gradient,r-d¯p/dr in a range 300 to 3000 dyn/cm2, have been measured to an accuracy of 1% at shear rates near 10 sec−1 in liquids of viscosity less than 200 poise. Using the constancy of pressure gradient at a given shear rate as an indicator of liquid stability, it was found that a polyisobutene liquid containing 2% of ‘Oppanol B 200’ in ‘Oppanol B I’, when stored at rest at 25 °C, was stable during a certain 7-day period after dissolution and unstable during the subsequent 30 days.

Studies on the nature and significance of macromolecular complexes in the rheology of synovial fluid from normal and diseased human joints

Abstract: The rheological characteristics of synovial fluid have been examined with aWeissenberg Rheogoniometer.

A possible mechanism for stabilizing elongational flow in certain polymeric liquids at constant temperature and composition

Abstract: A new calculation of the stability of elongational flow of a liquid filament is based on an idealized treatment of the effects of non-uniformity of filament diameter. Two uniform cylindrical filaments of different initial cross-sectional areas are connected by a fictitious deformable clamp which transmits tensile force without interfering with the assumed homogeneous elongational flow of each filament. A uniform tensile force is suddenly applied and kept constant. For a Newtonian liquid, the area ratio rapidly tends to infinity. For a “rubberlike liquid”, the area ratio at first increases but then becomes constant; this suggests that finite deformation of a “Gaussian” molecular network may provide a possible mechanism for “spinnability” at constant temperature and composition.

The rheology of synovial fluid

Abstract: A review has been undertaken of the rheological properties of synovial fluid in which the viscosity of synovial fluid under single-shear and multi-shear rate conditions, and the visco-elastic behaviour in conditions of oscillatory shear rate have been described. Synovial fluid is a pseudo-plastic (shear-thinning) fluid, both in normal and pathological conditions. The fluid exhibits elasticity and a normal-force effect. The low friction in joints is associated with a full film of lubricant which separates the surfaces and high friction results from thin films of localised boundary friction due to asperity contacts. A series of experiments with varying types of cartilage and synovial fluid have suggested that the nature of the lubricating fluid and the articular surfaces are important in determining shear stress during reciprocating motion. Scanning electron microscopy has confirmed the suggestion that surface aggregation of hyaluronic acid-protein complex can give enhanced lubrication.

The viscosity of human blood plasma: its change in disease and on the exhibition of drugs

Abstract: Mit einem sehr genau arbeitenden Viskosimeter ist gefunden worden, das wenn die Art und die Konzentration des gerinnungshemmenden Mittels, die Temperatur der Bestimmung usw. aufs genaueste kontrolliert waren, das dann die Viskositat von menschlichem Blutplasma von normalen Tragern, unabhangig von Alter und Geschlecht, innerhalb eines sehr engen Bereiches liegt; auserdem hat jedes Individuum einen eigenen charakteristischen Wert innerhalb dieses Bereiches, der nur sehr wenig variiert (±1–2%). Die physiologischen Stimulantien des gewohnlichen Lebens-Nahrungsmittelaufnahme, Schlaf, korperliche Ubungen — verschieben die Viskositat nicht auserhalb des Normalbereiches.

Structure and rheology of emulsions stabilised by mixed emulsifiers

Abstract: The formulation of oil-in-water emulsions which have the mechanical properties of semi-solids, i. e. creams, involves both theoretical and practical problems. One solution is to use combinations of ionic or non-ionic surfactants with a fatty alcohol, as in Emulsifying Wax B. P., Cetrimide Emulsifying Wax B. P. C. and Cetomacrogol Emulsifying Wax B. P. C. By altering the total amount of such a mixed emulsifier in a formulation, the consistency may be varied from liquid to semi-solid. The rheological properties of such emulsions have been explained on the assumption that a viscoelastie network exists in the continuous phase, linking disperse phase globules. The nature, extent and strength of this network controls the flow properties of the system. This theory is discussed with particular reference to the anionic surfactant sodium dodecyl sulphate, the cationic surfactant cetrimide, and the long chain alcohols cetyl and stearyl and their mixtures. The importance of testing at small strains is emphasised e. g. creep and oscillatory testing, and it is shown that continuous shear methods, although theoretically less satisfactory, may also provide useful information.

Rheological properties of sputum

Abstract: Sputum is a mixture of saliva with bronchial secretion which, in its turn, is a mixture of tissue fluid transudate through surface epithelium as well as acid glycoproteins from the specialised secretory cells, the goblet cells of surface epithelium, the serous and mucous cells of the submucosal glands. It has recently been shown (Lamb andReid, 1969) that the acid glycoproteins include several types of sialic acid and sulphate. Since sputum has a low dry weight yield its viscosity probably arises from the nature and interaction of its chemical constituents. Sputum is a non-Newtonian fluid. We have recently studied it over a wide shear rate range using aWeissenberg rheogoniometer with oscillation for lower rates and aFerranti-Shirley viscometer for higher levels. This combination has enabled the pattern of sputum viscosity and elasticity to be established. At very low shear rate a feature has been described for the first time for any biological fluid: it has been found in all sputum samples studied and at the same shear rate, regardless of the disease or of the absolute level of viscosity. It would seem, therefore, to arise from some essential feature of the physico-chemical arrangement of sputum. Elasticity over the same shear rates has also been calculated. The following additional features will be discussed: repeatability of results from different aliquots of the same specimen, time-dependent increase in viscosity, variation between certain diseases and the effect of dehydration.

Der Einfluß von Molekulargewicht und Molekulargewichtsverteilung auf die viskoelastischen Eigenschaften von Polystyrolschmelzen

Abstract: Mit einem Schwingungsviskosimeter wird der komplexe Schubmodul von 11 Polystyrolschmelzen mit verschiedenen Molekulargewichten und Molekulargewichtsverteilungen bestimmt. Die bei mehreren Temperaturen zwischen 130 und 230 °C gemessenen Modulkurven werden in eine reduzierte Darstellung nachFerry bei 190 °C als Bezugstemperatur uberfuhrt, aus der drei Theologische Parameter abgeleitet werden.

On the flow of Newtonian and non-Newtonian liquids through corrugated pipes

Abstract: Consideration is given to the flow of Newtonian and non-Newtonian liquids through a “corrugated” pipe of circular cross section whose radius sinusoidally along its longitudinal axis. The flow is produced by a constant pressure gradient. The theory predicts that in the Newtonian case, the corrugated wall of the pipe causes a reduction in flow rate when compared with the value expected on the basis of a straight pipe of the same mean radius. This prediction is confirmed by experiment. In the case of elastico-viscous liquids, the theoretical analysis for a certain fluid model indicates that the reduction in flow rate may be amplified or reduced by the non-Newtonian properties of the liquid depending on the precise flow conditions. The qualitative predictions are again confirmed by experiment. The possible practical implications of the work are outlined.

On the stability of viscoelastic fluid flow

Abstract: This paper supplements the earlier ones of this series, which dealt withstationary instabilities of cellular type and generalizes the case of planeCouette flow foroscillatory cellular disturbances, usually termed as “over-stability”. Using the well-known scheme of linearization the disturbance equations are derived and the analytical solutions have been given. By numerical evaluation of these, the curves of neutral stability are calculated explicitely for certain typical cases. It is found that, in general, the overstability mode is higher than the stationary mode but that both can come close to each other if certain conditions are satisfied.

Kriechverformung des Betons unter statischer und unter dynamischer Belastung

Abstract: In einer fruheren Arbeit wurde gezeigt, das sich die Kriechverformung einer Betonprobe unter konstanter Last befriedigend mit den Mitteln der Reaktionskinetik beschreiben last. Es wird gezeigt, wie diese Uberlegungen erweitert werden mussen, um auf den Fall dynamischer Belastung ubertragen werden zu konnen. Eine Gleichung wird abgeleitet, die die Kriechverformung als Funktion der mittleren Spannung und der Spannungsamplitude angibt. Versuchsergebnisse mehrerer Autoren wurden ausgewertet und mit der Theorie verglichen. Die Ubereinstimmung ist im Rahmen der Mesgenauigkeit befriedigend.

A versatile surface rheometer

Abstract: In the study of the physical properties of hydrocolloid films at the aqueous-air interface and aqueousoil interface it is necessary to be able to look at the whole range of rheological properties from low viscosity liquid to viscoelastic solid. It is desirable to follow all these stages, in succession, sometimes, with one piece of apparatus.

Cohesion and tensile strength of bulk solids

Abstract: For both cohesion and tensile strength it is apparent that a correlation exists between the strength of the bed; whether this is due to surface tension forces or other, and its state of packing i. e. eq. [5] and [6]. Further more it has been established both in this and other work (24), (32) that the state of packing may be correlated with the imposed normal stress i. e. eq. [4]. It is possible therefore, that a simple consolidation test will give an estimation of the comparative ease of flow of powders. If more precise information is required the tensile strength determinations can be carried out and approximations of cohesion calculated. For a complete description of powder properties however it is advisable to determine the shear strength in addition to the tensile strength in that the shear index and yield loci can be more accurately determined. More variables need to be studied before an expression of the form of eq. [2] can be used universally. One approach is to start with a simple system (32) and build into it known variables such as moisture, as in these experiments, particle size (23) shape, density, chemical constitution etc.

Secondary flow in a parallel-disk viscometer

Abstract: A numerical solution of theNavier-Stokes equations is obtained for flow in a parallel-disk viscometer. The inertial secondary flow consists of a single eddy which is well represented away from the free surface by the approximate analytical solution for infinite disks.

Rheological properties of white soft paraffin

Abstract: Rheological properties of a sample of white soft paraffin B. P., determined using continuous shear and creep viscometry, are reported for temperatures from 5 °C to 50 °C. The material is linear viscoelastic up to 45 °C but non linear viscoelastic at 50 °C. Activation energies are derived fromArrhenius type curves of both continuous shear and creep viscosity data. A discontinuity in rheological properties between 25 °C and 30 °C is due to a structural transition within the material.

Experiments on the flow of newtonian and non-newtonian liquids through corrugated pipes

Abstract: Experiments on the flow of Newtonian and non-Newtonian liquids through corrugated pipes confirmed the theoretically derived prediction that the corrugated wall of the pipe causes a reduction in Newtonian flow rate compared with the value expected on the basis of a straight pipe of the same mean radius. In the case of elastico-viscous liquids, the theoretical analysis for a certain fluid model indicates that the reduction in flow rate may be either amplified or reduced by the non-Newtonian properties of the liquid, depending on the precise flow conditions. In the experiments, the Newtonian fluids used were water and glycerol-water mixtures and the non-Newtonian fluids were aqueous solutions of polyacrylamide. Implications of the results of this study for the effects of wax deposition in crude oil pipelines, for the effects of pipe coated internally with bitumen, and for "drag reduction" by the addition of small amounts of high-molecular-weight polymer to Newtonian solvents in turbulent pipe flow are discussed briefly.