This provides an assessment of the surface viscosity of a biological membrane at the macroscopic i. A rheometer is a laboratory device used to measure the way in which a liquid, suspension or slurry flows in response to applied forces. Abstract the characterization of the extensional rheology of polymeric solutions is important in several applications and industrial processes. A filament stretching technique for measuring the extensional viscosity of polymer solutions at constant stretch rate is presented. A filament stretching device for measuring the extensional viscosity of low. Extensional viscosity for polymer melts measured in the filament stretching rheometer. Extensional viscosity a linear combination of shear and bulk viscosity, describes the reaction to elongation, widely used for characterizing polymers. Measurement of extensional viscosity using the falling. Can extensional viscosity be measured with opposednozzle. Extensional rheology of concentrated polyethylene oxide. Kinematic viscosity is the dynamic viscosity divided by the density typical units m2s, stokes, st. Measurement of extensional viscosity by the stretching of.
In general, there are three methods used to determine the socalled apparent extensional viscosity, namely. Extensional rheometry of polymeric fluids and the uniaxial. Extensional rheology experiments conducted on polymer solutions were carried out with a filament stretching rheometer designed and constructed in our laboratory. Measurement of extensional viscosity by stretching large liquid bridges in microgravity, j. Extensional rheological properties are important in characterization and processing of polymeric liquids. Extensional viscosity also known as elongational viscosity is a viscosity coefficient when applied stress is extensional stress this parameter is often used for characterizing polymer solutions. Pdf methodology and measurements of extensional rheology by. Shearing is the motion of a fluid, layerbylayer, like a deck of cards. Up to now there is no measurement technique which would allow determination of the equilibrium extensional viscosity of low viscosity fluids i. Extensional viscosity for polymer melts measured in the. The apparent extensional viscosity measurements were carried out with the use of a customized rheometer which utilizes stagnation flow between two opposing. Ldpe the extensional viscosity shows a steady increase with increasing strain rate, the maximum can thus be found. The obtained results have been compared with the corresponding uniaxial extensional viscosity data and different strain hardening level in both viscosities has.
Filament breakup studies using a capillary breakup extensional rheometer a ber provide a low c cost approach to the measurement of effective extensional properties, and such tests can be performed with low viscosity polymer solutions. Inherent viscosity the effect of nylon on the viscosity of a solution of nylon and a solvent. Filament stretching and capillary breakup rheometers have been developed to characterize the extensional properties of polymeric solutions, mostly for highviscosity fluids. For example, at room temperature, water has a dynamic shear viscosity of about 1. Journal of nonnewtonian fluid mechanics, 40 1991 271280 271 elsevier science publishers b. It is interesting to note that at higher strain rates, the difference between the viscosity in simple extensional flow and in.
Extensional viscosity, a linear combination of shear and bulk viscosity, describes the reaction to elongation, widely used for characterizing polymers. The behaviour of nonnewtonian fluids in extensional flow is of both theoretical and practical importance. The sample is then stretched either at constant rate or under constant stress. For a polymer melt, the initial growth in the force can be retarded due to the absence of a solvent instantaneous viscosity, and experiments show that the filament fails i. The extensional flow capillary as a new method for. Pdf a technique based on contraction flow through a nozzle for extensional viscosity measurements has been evaluated for semi solid materials. Red cell extensional recovery and the determination of. Extensional flow resistance of 3d fiber networks in. Extensional viscosity may be determined by measuring the dimensions of the fiber as it extends.
A subsequent companion paper will discuss interpretation of. Commercial equipment for the measurement of elongational viscosities include the rheotens for highly viscous polymers. Planar extensional viscosity measurements for ldpe. Figure 6 compares the rheological responses of a long chain branched ldpe and a linear lldpe in.
A variety of pitch which gave by traction method a viscosity of 4. Actually, technically speaking, we should say resistance to shearing. The liquid sample is held between two coaxial discs and stretched by moving the bottom disc downwards with a speed that increases exponentially with time. The use of entrance pressure drop to obtain extensional viscosity is particularly attractive because it can be applied to both low and high viscosity liquids using the bagley correction obtained from a conventional capillary rheometer. Acierno d, titomanlino g, greco r 1974 differences in behavior between dilute and concentrated polymer solutions in elongational flow. Some of these techniques can be employed to measure the extensional viscosity of foods. Viscosity 5 viscosity coefficients viscosity coefficients can be defined in two ways. Extensional viscosity has been measured in various ways15. This strain hardening is mainly dominated by longchain branches, more branches lead to a more pronounced viscosity increase. The flow of fluid in a falling drop has been modeled in order to determine. The drop eventually falls, and fluid adheres to both the tube and the drop, creating a distinct extending fiber. The presence of a threedimensional network of highaspectratio co2philic fibers increases the extensional viscosity of melts but decreases the shear viscosity under a co2 atmosphere. Pdf measurement of extensional viscosity of polymer.
The lmi and lcr cannot output an inherent viscosity. An assessment of cogswells method for measurement of extensional viscosity article pdf available in polymer engineering and science 3114. Despite these early experiments, the developments in extensional rheometry were few until the end of the sixties. Characterizing longchain branding in polyethylene with. The role of extensional rheology in polymer processing koreaaustralia rheology journaldecember 1999 vol. It may be seen that the viscosity is a monotonically decreasing function of the strain rate. The rheosense viscometer enabled us to quickly and accurately measure small aliqouts of sample which was necessary due to limited amounts of biological material. Pdf a comparison of extensional viscosity measurements from. Apn002 v2aresevf to measure elongation viscosity of polymer. Consistent sample viscosity will enable cytovale to develop robust cellular assays for our core applications involving the high throughput mechanical measurement of cells. Much effort been put into the design and manufacturing of extensional rheometers, despite rheological measurements in shear using rotational rheometers being much easier to perform. In this paper, two techniques for the measurement of extensional forces are discussed.
In steady shear flow, the semidilute solutions exhibit shear thinning, and the highfrequency complex modulus measured in small amplitude oscillatory shear flow exhibits the characteristic scaling expected for. Because these materials are so entangled, the viscosity is very high, on the order of 10 610 8 times the viscosity of water. This paper describes a simple, portable apparatus that can detect and quantify a relative extensional viscosity screen factor that is useful in evaluating the properties of. Extensional viscosity can be measured using rheometers that apply extensional stress. This method for measurement of a screen factor, gives a relative value for extensional viscosity, which may be used. Gupta b department of chemical engineering, monash university, clayton, victoria, 3168 australia b department of chemical engineering, state university of new york at. Measurement of extensional viscosity of polymer solutions. Extensional viscosity for polymer melts measured in the filament stretching rheometer bach, anders. Apparent extensional viscosity measured in various devices. Measurement technique and data analysis of extensional viscosity for polymer melts by sentmanat extensional rheometer ser article pdf available in rheologica acta 494. Comparisons are made between extensional viscosity values introduced in finite element calculations as input data and predictions based on the calculated entry pressure losses for polymer melts. The role of extensional rheology in polymer processing. In the present work, we combine experimental measurements on polymer. Extensional viscosity and melt strength and their role in film blowing vol.
Extensional viscosity from entrance pressure drop measurements. Trouton 19061 despite these early experiments, the developments in elongational rheometry were few until the end of the sixties. In this study, we characterize the shear and extensional rheology of dilute to semidilute solutions of cellulose in the ionic liquid 1ethyl3methylimidazolium acetate emiac. Viscosity is a tensorial quantity that can be decomposed in different ways into two independent components.
The generation of such a rheological response is rare in literature because the addition of solidstate fibers typically increases both extensional and shear viscosities. The fluid sample is held between two disks which move apart at an increasing velocity so that the extension rate, based on the filament midpoint diameter, is constant. Extensional viscosity and melt strength and their role in. It is used for those fluids which cannot be defined by a single value of viscosity and therefore require more parameters to be set and measured than is the case for a viscometer. Cogswells method for measurement of extensional viscosity by determining the entry pressure loss in capillary viscometry is critically examined. Pdf an assessment of cogswells method for measurement. The results are useful in checking theoretical predictions and are also relevant to cases of stretching flow which occur in.
Our work extends the experimental studies that have been performed on cnt extensional rheology33,34 by determining cnt aspect ratio from. A comprehensive study of the extensional rheology of complex. From lab to production, providing a window into the process. A low cost extensional viscometer for small relaxation times. An assessment of cogswells method for measurement of. Apparatus for extensional viscosity measurements journal. Measurement of relaxation times in extensional flow of. Standard test method for relative extensional viscosity of. The main reason for this is that extensional deformations play a. In the falling drop technique, a drop is formed by slowly extruding a liquid downward through a small tube. Development of an astm method for measurement of the. The resistance of a fluid to an imposed extensional strain rate is a measure of the fluids extensional viscosity. The phrase \extensional viscosity, without further quali.
Dynamic viscosity, also absolute viscosity, the more usual one typical units pas, poise, p. The molecular viscosity is a property of the material that depends microscopically on bond strengths. The transient extensional behavior of polystyrenebased boger fluids of varying solvent quality and molecular weight, j. The result provides a measure of the molecular weight of the nylon.
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