rheology graph interpretation

12. Definition: G = / with shear modulus G, shear stress (in Pa), and shear strain or shear deformation (with the unit 1). Shear thinning will appear as a steep decline in the viscosity of the polymer as the shear rate increases. Flow behavior can be presented in two types of diagrams (Figure 5.1): Ideally viscous flow behavior (or: Newtonian flow behavior) means that the measured viscosity is independent of the shear rate (Figure 5.2, line 1). This mixture of viscous flow behavior and elastic deformation behavior is known as viscoelastic behavior. Particle to particle interactions affect low shear viscosity. The law of elasticity can be compared with the law of springs: F / s = C, with spring force F, deflection path s, and spring constant C, which describes the stiffness of a spring. For evaluating time-dependent viscoelastic behavior, oscillatory tests are performed with shearing under constant dynamic-mechanical conditions. At constant rotational speed, the model operates at a correspondingly constant oscillating frequency. This means: Both amplitude and frequency are kept constant for each individual test interval. Your yield stress is the interpolated stress value at which your curve crosses this threshold.Figure 2: Dotted line shows "Threshold" valueMethod Two: Extrapolated onsetThis method works best with Viscosity vs Shear Rate curves where you want to identify the onset of shear-thinning or Power Law behaviour. This rheological behavior is unique to polymers and is called 'shear thinning'. If, for example, you have a product that relies on its yield stress to keep it in a certain position or shape for a long period of time then even the first stirrings of yield may be a problem. Typical tests in this field are used for investigating temperature-dependent behavior without chemical modifications, e.g. Figure 9.5: With ideally elastic behavior, the sine curves of shear strain and shear stress do not show any phase shift; the two curve functions reach the amplitude values and the zero crossings at the same time[1]. A previously used unit for the kinematic viscosity was 1 cSt = mm2/s (centistokes), but cSt is not an SI unit and should not be used any longer. Graph for dilatant flow is like this In which curve is passing from . Most graphs will have a clearly labeled x-element, spaced along the graph's horizontal axis, and a clearly labeled y-element, spaced along the graph's vertical axis. 0.5 nm, polymers approx. Many materials display a mixture of viscous and elastic behavior when sheared (Figure 7.1). This force is required as a counter force to keep the lower plate in position. Anton Paar GmbH: e-learning course Basics of Rheometry, The International System of Units (SI), Bureau International des Poids et Mesures, ISBN 92-822-2213-6, 2006 (, Barnes, H.A., Hutton, J.F., Walters, K.: An introduction to rheology. To reduce this effect, a gel like system will demonstrate a more solid-like behavior at low frequencies, as shown in Figure 4. The storage modulus G' (G prime, in Pa) represents the elastic portion of the viscoelastic behavior, which quasi describes the solid-state behavior of the sample. In paints and coatings, rheology examines the behavior of flow and deformation properties during: Manufacturing ( pigment dispersion, mill base preparation ) Storage ( pigment/particle settling, in-can properties ) Application (brush, spray, roller ), and. (tangent delta), unit: dimensionless or 1. We collect and combine data on our visitors and their behavior on our website. The oscillation frequency is the reciprocal of the oscillation period (Figure 9.3). It is also a sensitive indicator of changes in a product resulting from ageing or changes in the formulation or process. Many of the materials in such processes are subject to large and rapid deformations before they reach steady flowif they ever do. The deflection path of the upper, movable plate is measured and rheologically evaluated as strain or deformation $\gamma$. The material properties that govern the specific way in which these deformation or flow behaviors occur are called rheological properties. temperature (e.g. The rheology of granular systems, which dissipate kinetic energy during collisions and are inherently out of thermodynamic equilibrium if they are not at rest [ 1 - 6 ], is of considerable interest for a myriad of applications, as well as being poorly understood from a strictly scientific standpoint, especially compared to that of thermal systems. Typical materials that show this behavior are coatings, glues, shampoos, polymer solutions and polymer melts. Most materials are normally moved from one place to another. This information has been sourced, reviewed and adapted from materials provided by Malvern Panalytical. the preset as well as the response curve, oscillate with the same frequency. The main tools to investigate mechanical properties are rheology and microrheology. Extensibility (E) is indicated by the length of the curve. an amplitude sweep from 0.1% to 10000% (0.001 to 100) strain at 1 Hz. Figure 9.11: Viewed through a magnifying glass: Viscoelastic solids predominantly consist of chemically bonded molecules, or structures with other strong interaction forces. The part of the G* value that runs along the x-axis is the elastic portion of the viscoelastic behavior presented as G' while the part of the G* vector that is projected onto the y-axis is the viscous portion G''. softening or melting behavior of samples when heated; or solidification, crystallization, or cold gelation when cooled (Figure 6.3). Lower temperatures: In both cases, the molecular networks will be less flexible and stiffer. Cure characteristics are attained through instruments like a Moving Die Rheometer (MDR). Storage modulus G' represents the stored deformation energy and loss modulus G'' characterizes the deformation energy lost (dissipated) through internal friction when flowing. A viscosity-temperature profile can be obtained under defined imposed shear conditions relevant to the process.Viscosity temperature profiles of oils. Using this test to apply a small force is a highly sensitive measure of how the material will withstand the gravitational force. Most samples show viscoelastic behavior. The rheology data we generate and the insight we can bring to your development process can help ensure that the polymer's properties meet specifications for the end use (texture, product pour) and product quality: surface distortions, anisotropy, strength, structure development. Please use one of the following formats to cite this article in your essay, paper or report: Malvern Panalytical. Two excellent methods are the viscometric 3-step thixotropy test and the oscillatory 3-step thixotropy test.The graphic below shows the Viscometric 3-step Thixotropy Test:In this test shear rate is stepped from low (1 1/s) to high (100 1/s) and back to low (1 1/s) whilst changes in viscosity are recorded throughout. Figure 1.3: Visualization of the size ratio of 1:1000, which is similar to the size ratio of molecules and particles in a fluid. We're moving! This is due to links inside the material, for example chemical bonds or physical-chemical interactions (Figure 9.11). The software should guide you through it but, in essence, you fit a straight line to both the lower Newtonian plateau and the shear thinning regions of the curves and hit the "identify onset" or similar button. Figure 6.3: Typical temperature-dependent behavior of a sample, here honey, which becomes softer and thinner when heated[1]. Since rheology and viscometry are closely related, why not also have a look at our page dedicated to everything about viscosity and viscometry. 2001, ISO 3219: Plastics (polymers/resins in the liquid state or as emulsions or dispersions): Viscosity using a rotational viscometer with a defined shear rate. flow cups [a,b,c] or falling/rolling ball viscometers[d,e]). Kinematic viscosity is always determined if gravitational force or the weight of the sample is the driving force. These include misinterpreting graphs as pictures, slope/height confusion, problems finding the slopes of lines not passing through the origin, and the inability to interpret the meaning of the area under various graph curves. The second way is to preset the driving force via torque or shear stress (controlled shear stress, CSS or CS). They develop a flow resistance caused by internal friction. Figure 2. Plot the gradient curve and identify the stress value at which the gradient curve shows a negative peak (see fig 4.). Materials that typically display such behavior include highly filled dispersions, such as ceramic suspensions (casting slurries), starch dispersions, plastisol pastes that lack a sufficient amount of plasticizer, dental filling masses (dental composites) as well as special composite materials for protective clothing. Figure 2 General guidelines for interpreting graphs (see area . A single-point viscosity reading at this part of the profile - typical for a simple viscometer test - would completely miss the highly-significant differences in zero-shear viscosity between the coatings.Zero-shear viscosity measurement necessitates the use of a highly sensitive instrument that can impart very small stresses and measure incredibly low shear rates. Rheology and zeta potential analyses were systematically used to evaluate the quality of the slurries and powders produced. Figure 9.14: Preset of an amplitude sweep: Here, with controlled strain and an increase in the amplitude in five steps. Figure 9.15: Preset of a frequency sweep, here with controlled shear strain and an increase or decrease in frequency in five steps. This comprehensive resource in Applied Rheology is great for beginners and experienced users alike, and includes insights as well as practical tips for making meaningful measurements from rheology expert Thomas G. Mezger, author of The Rheology Handbook. Usually, the value is stated as a percentage. The term cohesive energy (Figure 3) refers to a measure of the materials elastic strength. For the fluid state, the following holds: The phase shift is between 45 and 90, thus 90 > 45. A product that exhibits a long, slow viscosity build to a highly-structured state after shearing is termed thixotropic. Changing the PMMA concentration from 1 to Acknowledgements Other common tests investigate the temperature-dependent behavior during gel formation or chemical curing. When a yield stress is introduced to a material, it will make the material to behave like a solid at rest and resist any suspended material from settling. The size of the shear gap is also known for the measuring system used. Wiley, New York, 1994. Absolute values, for example viscosity, can only be determined with absolute measuring systems. (, Pharmaceutical instrument qualification service, Rheology- and rheometry-related information, Rotational viscometers, oscillatory rheometers, and measuring geometries, Definition of terms: Shear stress, shear rate, law of viscosity, kinematic viscosity, Flow behavior, flow curve, and viscosity curve, Definition of terms: Shear strain or shear deformation, shear modulus, law of elasticity, Approaches to measuring viscoelastic behavior, Evaluation of the time-dependent flow behavior, Examples of a flow curve and viscosity curve, Examples of the calculation of shear rates, Flow curve and yield point determination with rotational viscometry, Internal structures of samples and shear-thinning behavior, Methods and devices for controlling the temperature, Structural Decomposition and Regeneration, Temperature-dependent behavior (oscillation), Temperature-dependent behavior with gel formation or curing, Temperature-dependent behavior without chemical modifications, Time-dependent behavior with gel formation or curing, Yield point, evaluation using the flow curve, Dynamic Mechanical Analyzer: MCR 702 MultiDrive, Find examples for calculation of shear rates here, methods and devices available for controlling the temperature, temperature-dependent behavior without chemical modifications, temperature-dependent behavior during gel formation or chemical curing, temperature-dependent viscoelastic behavior, Bitumen at T = +80 C/ +60 C/ +40 C/ +20 C/ 0 C, 200 Pas / 1 kPas / 20 kPas / 0.5 MPas / 1 MPas, Preset rotational speed or shear-rate ramp, usually ascending or descending in steps, Preset torque or shear-stress ramp, usually ascending or descending in steps, Flow curves with shear stress $\tau$ and shear rate $\dot \gamma$, usually with the latter plotted on the x-axis, Viscosity curves with viscosity and shear rate $\dot \gamma$ (or shear stress $\tau$), usually with the latter plotted on the x-axis. Another type of viscosity is the kinematic viscosity $\nu$ (pronounced: nu). Rheology is a general term referring to the science of studying flow and deformation of materials. Establishing quality control measures to properly . To simulate situations and explore product behaviour where low stresses are maintained for a period of time, for example in draining, sedimentation, sagging or leveling scenarios. 2010 (2014), (DIN 53211) Paints, varnishes and similar coatings; flow time using the DIN flow cup. It is only the temperature that changes according to a preset profile. Like to learn more?If you would like some advice on how these test methods could be applied to your products please don't hesitate to ask us a question. Shear thinning properties can provide desirable attributes to a product, such as suspension stability or drip resistance when at rest but ease of application or pouring when a stress is applied. Also, a time-dependent temperature profile is preset. Definition: $\tau$ = F / A with shear stress $\tau$ (pronounced: tau), shear force F (in N) and shear area A (in m2), see Figures 8.2 and 8.3. It is measured in millimeters or centimeters. In practice, therefore, rheology stands for viscosity measurements, characterisation of flow behaviour and determination of material structure. There are different methods and devices available for controlling the temperature. https://www.azom.com/article.aspx?ArticleID=10219. Studying the effect of flour improvers dough handling properties. This lag is called the phase shift (pronounced: delta, Figures 9.6 and 9.7). This signifies the point of inflection on the viscosity profile.As for your choice of method, this should be governed by:CorrelationThe quality of the correlation of the obtained value to the observed flow behaviour. : Rheology, principles, measurements, and applications. When put into motion, molecules and particles are forced to slide along each other. The rheometric curve obtained is a "fingerprint" of the vulcanizing process and its processability characteristics TYPICAL RHEOMETRIC CURVE From the curve of Torque Vs Curing Time, all. The first significant peak in first compression. The International Academy of Rheology by Anton Paar offers you the opportunity to broaden your knowledge and improve your skills in the field of rheology. For more information on this source, please visit Malvern Panalytical. Figure 9.12: Viewed through a magnifying glass: Viscoelastic liquids are typically composed of mainly unlinked individual molecules, which may show some entanglement as, for example, uncrosslinked polymers. Polymer rheological testing and analysis: 2 Then afew chapters follow on the explanation of the different kinds deformation (chapter 2);the use of graphs in general (chapter 3), and rheology graphs in particular (chapter 4).A consideration of the simplest kind of liquid that we will meet comes next theNewtonian liquid (chapter 5), and we then show how we can calculate its flowbehaviour i. You can also withdraw your consent at a later time by accessing the Cookie Settings. Figure 9.3: A sine curve is described by its amplitude (maximum deflection) and its oscillation period or frequency. Key features: A uniquely practical approach to the often difficult science of food rheology Includes chapters introducing the basics of food rheology before moving on to how data can be usefully and easily interpreted by the food scientist Can be used as a teaching aid on academic or industry-based courses Product Identifiers Publisher Figure 3. Rheologists describe the deformation and flow behavior of all kinds of material. Shear-thickening (or: dilatant flow behavior) means increasing viscosity with increasing shear rates (Figure 5.2, line 3). We're moving! Rheometers are able to determine many more rheological parameters. May also be called torsion. A low phase angle signifies that the material behaves like a solid. This article describes the general techniques of designing and interpreting rheological tests to improve the stability of samples. of Non-Newt. This friction always goes along with the development of frictional heat in the sample, and consequently, with the transformation of deformation energy into heat energy. Figure 9.4: Oscillatory test with the two-plates model, here for ideally elastic behavior. You will also find everything there is to know about flow and viscosity curves and examples of calculations and test types. Figure 3.3: Preset profiles for flow curves as time-dependent step-like ramps, here with 15 steps corresponding to 15 measuring points, with controlled shear rate CSR (left) and controlled shear stress CSS (right). Take a look at the curve below which shows a typical viscosity vs shear stress profile where a significant yield is occurring. Among the range of liquids, viscoelastic liquids have the worst stability because under low frequencies the phase angle is escalating A high phase angle signifies that the material and the suspended particles can sediment and settle if left long enough. It can be compared with the size difference between small fish and large ships. Are you ready for a journey of discovery down Rheology Road with Joe Flow? Definition of the law of elasticity for oscillatory shear tests: with complex shear modulus G* (G star, in Pa), shear-stress amplitude A (in Pa), and strain amplitude A (dimensionless, or expressed in %). [1] The graph's title should also tell you exactly what it's about. The Basics of Capillary Rheometry Rheology studies the deformation and flow of fluids. The signal is rheologically evaluated as shear stress $\tau$. Nevertheless, the real yield stress value itself can have a variety of values. This information is used to improve the website. "How to Design and Interpret Rheological Tests". Rheological testing refers to the measuring of the deformation of matter under the influence of imposed stress and analyzing the internal response of materials to forces. Shear-thinning behavior is related to theinternal structures of samples. 5 m = 5000 nm. Consistency (K) and Power Law Index (n) parameters are then reported. The unit for shear modulus is Pa (pascal). 18 January 2023. For calculations, please note: The units for density are kg/m3 and g/cm3, where 1000 kg/m3 = 1 g/cm3. This is just a clever way of saying that the product is more of a solid than a liquid, and then if you deform it, as long as you don't push it beyond what we call the 'yield point' it's going to bounce back again to its original shape. To millers and bakers, farinographs are essential for: Adjusting dough mixing parameters: absorption, time, pre-hydration ratio. Often, it is also interesting to characterize behavior that occurs if this upper limit is exceeded with increasing deformation, when the inner structure gets softer, starts to flow, or breaks down in a brittle way. Traditionally, capillary rheometers have been used to measure the shear viscosity and elasticity of viscous materials at high shear rates. Three parameters characterize this relationship: the consistency k, the flow index n, and the yield shear stress . . The results obtained are always dependent on the used device and cannot be compared with each other (e.g.