Rheology (; ) is the study of the flow of
matter, primarily in a
fluid (
liquid or
gas) state, but also as "soft
solid
Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structur ...
s" or solids under conditions in which they respond with
plastic
Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adapta ...
flow rather than deforming
elastically in response to an applied force. Rheology is a branch of
physics
Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which ...
, and it is the science that deals with the
deformation and flow of materials, both solids and liquids.
[W. R. Schowalter (1978) Mechanics of Non-Newtonian Fluids Pergamon ]
The term ''
rheology'' was coined by
Eugene C. Bingham
Eugene Cook Bingham (8 December 1878 – 6 November 1945) was a professor and head of the department of chemistry at Lafayette College. Bingham made many contributions to rheology, a term he is credited (along with Markus Reiner) with introducing. ...
, a professor at
Lafayette College, in 1920, from a suggestion by a colleague,
Markus Reiner.
[The Deborah Number](_blank)
The term was inspired by the
aphorism of
Heraclitus
Heraclitus of Ephesus (; grc-gre, Ἡράκλειτος , "Glory of Hera"; ) was an ancient Greek pre-Socratic philosopher from the city of Ephesus, which was then part of the Persian Empire.
Little is known of Heraclitus's life. He wrot ...
(often mistakenly attributed to
Simplicius), (, 'everything flows'
) and was first used to describe the flow of liquids and the deformation of solids. It applies to substances that have a complex microstructure, such as
muds,
sludges,
suspensions,
polymer
A polymer (; Greek '' poly-'', "many" + '' -mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
s and other
glass formers (e.g., silicates), as well as many foods and additives,
bodily fluids (e.g., blood) and other
biological materials, and to other materials that belong to the class of
soft matter such as food.
Newtonian fluids can be characterized by a single coefficient of
viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the int ...
for a specific temperature. Although this
viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the int ...
will change with temperature, it does not change with the
strain rate. Only a small group of fluids exhibit such constant viscosity. The large class of fluids whose viscosity changes with the strain rate (the relative
flow velocity) are called
non-Newtonian fluids.
Rheology generally accounts for the behavior of non-Newtonian fluids, by characterizing the minimum number of functions that are needed to relate stresses with rate of change of strain or strain rates. For example,
ketchup can have its viscosity reduced by shaking (or other forms of mechanical agitation, where the relative movement of different layers in the material actually causes the reduction in viscosity) but water cannot. Ketchup is a shear-thinning material, like
yogurt and
emulsion
An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Alth ...
paint (US terminology
latex paint or
acrylic paint
Acrylic paint is a fast-drying paint made of pigment suspended in acrylic polymer emulsion and plasticizers, silicone oils, defoamers, stabilizers, or metal soaps. Most acrylic paints are water-based, but become water-resistant when dry. ...
), exhibiting
thixotropy, where an increase in relative flow velocity will cause a reduction in viscosity, for example, by stirring. Some other non-Newtonian materials show the opposite behavior,
rheopecty: viscosity increasing with relative deformation, and are called shear-thickening or
dilatant materials. Since Sir
Isaac Newton
Sir Isaac Newton (25 December 1642 – 20 March 1726/27) was an English mathematician, physicist, astronomer, alchemist, Theology, theologian, and author (described in his time as a "natural philosophy, natural philosopher"), widely ...
originated the concept of viscosity, the study of liquids with strain-rate-dependent viscosity is also often called ''
Non-Newtonian fluid mechanics''.
The experimental characterisation of a material's rheological behaviour is known as ''
rheometry'', although the term ''rheology'' is frequently used synonymously with rheometry, particularly by experimentalists. Theoretical aspects of rheology are the relation of the flow/deformation behaviour of material and its internal structure (e.g., the orientation and elongation of polymer molecules), and the flow/deformation behaviour of materials that cannot be described by classical fluid mechanics or elasticity.
Scope
In practice, rheology is principally concerned with extending
continuum mechanics to characterize the flow of materials that exhibit a combination of
elastic
Elastic is a word often used to describe or identify certain types of elastomer, elastic used in garments or stretchable fabrics.
Elastic may also refer to:
Alternative name
* Rubber band, ring-shaped band of rubber used to hold objects togethe ...
,
viscous
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the in ...
and
plastic
Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adapta ...
behavior by properly combining
elasticity and (
Newtonian)
fluid mechanics. It is also concerned with predicting mechanical behavior (on the continuum mechanical scale) based on the micro- or nanostructure of the material, e.g. the
molecular size and architecture of
polymer
A polymer (; Greek '' poly-'', "many" + '' -mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
s in solution or the particle size distribution in a solid suspension.
Materials with the characteristics of a fluid will flow when subjected to a
stress, which is defined as the force per area. There are different sorts of stress (e.g. shear, torsional, etc.), and materials can respond differently under different stresses. Much of theoretical rheology is concerned with associating external forces and torques with internal stresses, internal strain gradients, and flow velocities.
[R. B. Bird, W. E. Stewart, E. N. Lightfoot (1960), Transport Phenomena, John Wiley & Sons, ][R. Byrin Bird, Charles F. Curtiss, Robert C. Armstrong (1989), Dynamics of Polymeric Liquids, Vol 1 & 2, Wiley Interscience, and 978-0471518440][Faith A. Morrison (2001), Understanding Rheology, Oxford University Press, and 978-0195141665]
Rheology unites the seemingly unrelated fields of
plasticity and
non-Newtonian fluid dynamics by recognizing that materials undergoing these types of deformation are unable to support a stress (particularly a
shear stress
Shear stress, often denoted by ( Greek: tau), is the component of stress coplanar with a material cross section. It arises from the shear force, the component of force vector parallel to the material cross section. '' Normal stress'', on ...
, since it is easier to analyze shear deformation) in static
equilibrium. In this sense, a solid undergoing plastic
deformation is a
fluid, although no viscosity coefficient is associated with this flow. Granular rheology refers to the continuum mechanical description of
granular material
A granular material is a conglomeration of discrete solid, macroscopic particles characterized by a loss of energy whenever the particles interact (the most common example would be friction when grains collide). The constituents that compose ...
s.
One of the major tasks of rheology is to establish by measurement the relationships between
strains (or rates of strain) and stresses, although a number of theoretical developments (such as assuring frame invariants) are also required before using the empirical data. These experimental techniques are known as
rheometry and are concerned with the determination of well-defined ''rheological material functions''. Such relationships are then amenable to mathematical treatment by the established methods of
continuum mechanics.
The characterization of flow or deformation originating from a simple shear stress field is called shear rheometry (or shear rheology). The study of extensional flows is called extensional rheology. Shear flows are much easier to study and thus much more experimental data are available for shear flows than for extensional flows.
Viscoelasticity
* Fluid and solid character are relevant at long times:
We consider the application of a constant stress (a so-called ''creep experiment''):
** if the material, after some deformation, eventually resists further deformation, it is considered a solid
** if, by contrast, the material flows indefinitely, it is considered a fluid
* By contrast, ''elastic and viscous'' (or intermediate,
viscoelastic) behaviour is relevant at short times (''transient behaviour''):
We again consider the application of a constant stress:
[William N. Findley, James S. Lai, Kasif Onaran (1989), Creep and Relaxation of Nonlinear Viscoelastic Materials, Dover Publications]
** if the material deformation strain increases linearly with increasing applied stress, then the material is linear elastic within the range it shows recoverable strains. Elasticity is essentially a time independent processes, as the strains appear the moment the stress is applied, without any time delay.
** if the material deformation strain rate increases linearly with increasing applied stress, then the material is viscous in the Newtonian sense. These materials are characterized due to the time delay between the applied constant stress and the maximum strain.
** if the materials behaves as a combination of viscous and elastic components, then the material is viscoelastic. Theoretically such materials can show both instantaneous deformation as elastic material and a delayed time dependent deformation as in fluids.
*
Plasticity is the behavior observed after the material is subjected to a ''yield stress'':
A material that behaves as a solid under low applied stresses may start to flow above a certain level of stress, called the ''
yield stress
In materials science and engineering, the yield point is the point on a stress-strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Below the yield point, a material will deform elastically and wi ...
'' of the material. The term ''plastic solid'' is often used when this plasticity threshold is rather high, while ''yield stress fluid'' is used when the threshold stress is rather low. However, there is no fundamental difference between the two concepts.
Dimensionless numbers
Deborah number
On one end of the spectrum we have an
inviscid or a simple Newtonian fluid and on the other end, a rigid solid; thus the behavior of all materials fall somewhere in between these two ends. The difference in material behavior is characterized by the level and nature of elasticity present in the material when it deforms, which takes the material behavior to the non-Newtonian regime. The non-dimensional Deborah number is designed to account for the degree of non-Newtonian behavior in a flow. The Deborah number is defined as the ratio of the characteristic time of relaxation (which purely depends on the material and other conditions like the temperature) to the characteristic time of experiment or observation.
Small Deborah numbers represent Newtonian flow, while non-Newtonian (with both viscous and elastic effects present) behavior occurs for intermediate range Deborah numbers, and high Deborah numbers indicate an elastic/rigid solid. Since Deborah number is a relative quantity, the numerator or the denominator can alter the number. A very small Deborah number can be obtained for a fluid with extremely small relaxation time or a very large experimental time, for example.
Reynolds number
In
fluid mechanics, the
Reynolds number is a measure of the
ratio
In mathematics, a ratio shows how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lemons is eight to six (that is, 8:6, which is equivalent to the ...
of
inertial
forces (
) to
viscous
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the in ...
forces (
) and consequently it quantifies the relative importance of these two types of effect for given flow conditions. Under low Reynolds numbers viscous effects dominate and the flow is
laminar, whereas at high Reynolds numbers inertia predominates and the flow may be
turbulent. However, since rheology is concerned with fluids which do not have a fixed viscosity, but one which can vary with flow and time, calculation of the Reynolds number can be complicated.
It is one of the most important
dimensionless numbers in
fluid dynamics and is used, usually along with other dimensionless numbers, to provide a criterion for determining
dynamic similitude
Similitude is a concept applicable to the testing of engineering models. A model is said to have similitude with the real application if the two share geometric similarity, kinematic similarity and dynamic similarity. ''Similarity'' and ''simil ...
. When two geometrically similar flow patterns, in perhaps different fluids with possibly different flow rates, have the same values for the relevant dimensionless numbers, they are said to be dynamically similar.
Typically it is given as follows:
:
where:
* ''u''
s – mean
flow velocity,
−1"> s−1* ''L'' – characteristic length,
* ''μ'' – (absolute) dynamic
fluid viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the int ...
,
−2"> s m−2or
a s
A, or a, is the first letter and the first vowel of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''a'' (pronounced ), plural ''aes ...
* ''ν'' – kinematic fluid viscosity:
,
2 s−1">2 s−1* ''ρ'' – fluid
density
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematicall ...
,
−3">g m−3
Measurement
Rheometers are instruments used to characterize the rheological properties of materials, typically fluids that are melts or solution. These instruments impose a specific stress field or deformation to the fluid, and monitor the resultant deformation or stress. Instruments can be run in steady flow or oscillatory flow, in both shear and extension.
Applications
Rheology has applications in
materials science,
engineering
Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad range of more speciali ...
,
geophysics,
physiology
Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemic ...
, human
biology
Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary ...
and
pharmaceutics.
Materials science is utilized in the production of many industrially important substances, such as
cement,
paint, and
chocolate
Chocolate is a food made from roasted and ground cacao seed kernels that is available as a liquid, solid, or paste, either on its own or as a flavoring agent in other foods. Cacao has been consumed in some form since at least the Olmec ci ...
, which have complex flow characteristics. In addition,
plasticity theory has been similarly important for the design of metal forming processes. The science of rheology and the characterization of viscoelastic properties in the production and use of
polymer
A polymer (; Greek '' poly-'', "many" + '' -mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
ic materials has been critical for the production of many products for use in both the industrial and military sectors.
Study of flow properties of liquids is important for pharmacists working in the manufacture of several dosage forms, such as simple liquids, ointments, creams, pastes etc. The flow behavior of liquids under applied stress is of great relevance in the field of pharmacy. Flow properties are used as important quality control tools to maintain the superiority of the product and reduce batch to batch variations.
Materials science
Polymers
Examples may be given to illustrate the potential applications of these principles to practical problems in the processing and use of
rubbers,
plastics, and
fiber
Fiber or fibre (from la, fibra, links=no) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often incorporate ...
s.
Polymers
A polymer (; Greek '' poly-'', "many" + '' -mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
constitute the basic materials of the rubber and plastic industries and are of vital importance to the textile,
petroleum
Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...
,
automobile
A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people instead of goods.
The year 1886 is regarded ...
,
paper
Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, rags, grasses or other vegetable sources in water, draining the water through fine mesh leaving the fibre evenly distribu ...
, and
pharmaceutical industries. Their viscoelastic properties determine the mechanical performance of the final products of these industries, and also the success of processing methods at intermediate stages of production.
In
viscoelastic materials, such as most polymers and plastics, the presence of liquid-like behaviour depends on the properties of and so varies with rate of applied load, i.e., how quickly a force is applied. The
silicone toy '
Silly Putty' behaves quite differently depending on the time rate of applying a force. Pull on it slowly and it exhibits continuous flow, similar to that evidenced in a highly viscous liquid. Alternatively, when hit hard and directly, it shatters like a
silicate glass.
In addition, conventional rubber undergoes a
glass transition (often called a ''rubber-glass transition''). E.g. The
Space Shuttle ''Challenger'' disaster was caused by rubber O-rings that were being used well below their glass transition temperature on an unusually cold Florida morning, and thus could not flex adequately to form proper seals between sections of the two
solid-fuel rocket boosters.
Biopolymers
Sol-gel
With the
viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the int ...
of a
sol
Sol or SOL may refer to:
Astronomy
* The Sun
Currency
* SOL Project, a currency project in France
* French sol, or sou
* Argentine sol
* Bolivian sol, the currency of Bolivia from 1827 to 1864
* Peruvian sol, introduced in 1991
* Peruvian sol ...
adjusted into a proper range, both
optical quality glass fiber and
refractory
In materials science, a refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycrystalline, polyphase, ...
ceramic fiber can be drawn which are used for
fiber-optic sensors and
thermal insulation
Thermal insulation is the reduction of heat transfer (i.e., the transfer of thermal energy between objects of differing temperature) between objects in thermal contact or in range of radiative influence. Thermal insulation can be achieved with ...
, respectively. The mechanisms of
hydrolysis
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile.
Biological hydrolysi ...
and
condensation, and the rheological factors that bias the structure toward linear or branched structures are the most critical issues of
sol-gel science and technology.
Geophysics
The scientific discipline of
geophysics includes study of the flow of molten
lava and study of debris flows (fluid mudslides). This disciplinary branch also deals with solid Earth materials which only exhibit flow over extended time-scales. Those that display viscous behaviour are known as
rheid
In geology, a rheid is a substance whose temperature is below its melting point and whose deformation by viscous flow during the time of observation is at least three orders of magnitude (1,000×) greater than the elastic deformation under the ...
s. For example,
granite
Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies un ...
can flow plastically with a negligible yield stress at room temperatures (i.e. a viscous flow). Long-term creep experiments (~10 years) indicate that the viscosity of granite and glass under ambient conditions are on the order of 10
20 poises.
Physiology
Physiology includes the study of many bodily fluids that have complex structure and composition, and thus exhibit a wide range of viscoelastic flow characteristics. In particular there is a specialist study of blood flow called
hemorheology. This is the study of flow properties of blood and its elements (
plasma and formed elements, including
red blood cell
Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "hol ...
s,
white blood cells and
platelets).
Blood viscosity
Hemorheology, also spelled haemorheology (from Greek ‘αἷμα, ''haima'' ' blood' and rheology, from Greek ῥέω ''rhéō'', 'flow' and -λoγία, ''-logia'' 'study of'), or blood rheology, is the study of flow properties of blood and its ...
is determined by plasma viscosity,
hematocrit (volume fraction of red blood cell, which constitute 99.9% of the cellular elements) and mechanical behaviour of red blood cells. Therefore, red blood cell mechanics is the major determinant of flow properties of blood.
The leading characteristic for hemorheology has been
shear thinning in steady shear flow. Other non-Newtonian rheological characteristics that blood can demonstrate includes
pseudoplasticity
In rheology, shear thinning is the non-Newtonian behavior of fluids whose viscosity decreases under shear strain. It is sometimes considered synonymous for pseudo-plastic behaviour, and is usually defined as excluding time-dependent viscosity, ti ...
,
viscoelasticity, and
thixotropy.
Red Blood Cell Aggregation
There are two current major hypotheses to explain blood flow predictions and shear thinning responses. The two models also attempt to demonstrate the drive for reversible red blood cell aggregation, although the mechanism is still being debated. There is a direct effect of red blood cell aggregation on blood viscosity and circulation.
The foundation of hemorheology can also provide information for modeling of other biofluids.
The bridging or "cross-bridging" hypothesis suggests that macromolecules physically crosslink adjacent red blood cells into rouleaux structures. This occurs through adsorption of macromolecules onto the red blood cell surfaces.
The depletion layer hypothesis suggests the opposite mechanism. The surfaces of the red blood cells are bound together by an osmotic pressure gradient that is created by depletion layers overlapping.
The effect of rouleaux aggregation tendency can be explained by hematocrit and fibrinogen concentration in whole blood rheology.
Some techniques researchers use are optical trapping and microfluidics to measure cell interaction in vitro.
Disease and Diagnostics
Changes to viscosity has been shown to be linked with diseases like hyperviscosity, hypertension, sickle cell anemia, and diabetes.
Hemorheological measurements and genomic testing technologies that act as preventative measures and diagnostic tools.
Hemorheology has also been correlated with aging effects, especially with impaired blood fluidity, and studies have shown that physical activity may improve the thickening of blood rheology.
Zoology
Many animals make use of rheological phenomena, for example
sandfish that exploit the granular rheology of dry sand to "swim" in it or
land gastropods that use
snail slime for adhesive
locomotion. Certain animals produce specialized
endogenous complex fluids, such as the sticky slime produced by
velvet worms to immobilize prey or the fast-gelling underwater slime secreted by
hagfish to deter predators.
Food rheology
Food rheology is important in the manufacture and processing of food products, such as cheese and
gelato. An adequate rheology is important for the indulgence of many common foods, particularly in the case of sauces, dressings,
yogurt, or
fondue.
Thickening agents
A thickening agent or thickener is a substance which can increase the viscosity of a liquid without substantially changing its other properties. Edible thickeners are commonly used to thicken sauces, soups, and puddings without altering their ta ...
, or
thickeners, are substances which, when added to an aqueous mixture, increase its
viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the int ...
without substantially modifying its other properties, such as taste. They provide body, increase
stability, and improve
suspension of added ingredients. Thickening agents are often used as
food additives and in
cosmetics
Cosmetics are constituted mixtures of chemical compounds derived from either natural sources, or synthetically created ones. Cosmetics have various purposes. Those designed for personal care and skin care can be used to cleanse or protec ...
and
personal hygiene product
Personal care or toiletries are consumer products used in personal hygiene, personal grooming or for beautification.
Products
Personal care includes products as diverse as cleansing pads, colognes, cotton swabs, cotton pads, deodorant, eye li ...
s. Some thickening agents are gelling agents, forming a
gel
A gel is a semi-solid that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady-state, although the liquid phase may still di ...
. The agents are materials used to thicken and stabilize liquid solutions,
emulsion
An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Alth ...
s, and
suspensions. They dissolve in the liquid phase as a
colloid mixture that forms a weakly cohesive internal structure.
Food thickeners
A thickening agent or thickener is a substance which can increase the viscosity of a liquid without substantially changing its other properties. Edible thickeners are commonly used to thicken sauces, soups, and puddings without altering the ...
frequently are based on either
polysaccharides (
starch
Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human die ...
es,
vegetable gums, and
pectin), or
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s.
Concrete rheology
Concrete's and
mortar's workability is related to the rheological properties of the fresh
cement paste. The mechanical properties of hardened concrete increase if less water is used in the concrete mix design, however reducing the water-to-cement ratio may decrease the ease of mixing and application. To avoid these undesired effects,
superplasticizers are typically added to decrease the apparent yield stress and the viscosity of the fresh paste. Their addition highly improves concrete and mortar properties.
Filled polymer rheology
The incorporation of various types of
fillers
In processed animal foods, a filler is an ingredient added to provide dietary fiber, bulk or some other non-nutritive purpose.
Products like corncobs, feathers, soy, cottonseed hulls, peanut hulls, citrus pulp, screening, weeds, straw, and cere ...
into
polymer
A polymer (; Greek '' poly-'', "many" + '' -mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
s is a common means of reducing cost and to impart certain desirable mechanical, thermal, electrical and magnetic properties to the resulting material. The advantages that filled polymer systems have to offer come with an increased complexity in the rheological behavior.
Usually when the use of fillers is considered, a compromise has to be made between the improved mechanical properties in the solid state on one side and the increased difficulty in melt processing, the problem of achieving uniform
dispersion
Dispersion may refer to:
Economics and finance
*Dispersion (finance), a measure for the statistical distribution of portfolio returns
*Price dispersion, a variation in prices across sellers of the same item
*Wage dispersion, the amount of variatio ...
of the filler in the polymer matrix and the economics of the process due to the added step of compounding on the other. The rheological properties of filled polymers are determined not only by the type and amount of filler, but also by the shape, size and size distribution of its particles. The viscosity of filled systems generally increases with increasing filler fraction. This can be partially ameliorated via broad particle size distributions via the
Farris effect. An additional factor is the
stress transfer at the filler-polymer interface. The interfacial adhesion can be substantially enhanced via a coupling agent that adheres well to both the polymer and the filler particles. The type and amount of
surface treatment
Surface finishing is a broad range of industrial processes that alter the surface of a manufactured item to achieve a certain property. Finishing processes may be employed to: improve appearance, adhesion or wettability, solderability, corrosion re ...
on the filler are thus additional parameters affecting the rheological and material properties of filled polymeric systems.
It is important to take into consideration wall slip when performing the rheological characterization of highly filled materials, as there can be a large difference between the actual strain and the measured strain.
[C. Feger, M. McGlashan-Powell, I. Nnebe, D.M. Kalyon, Rheology and Stability of Highly Filled Thermal Pastes, IBM Research Report, RC23869 (W0602-065) 2006. http://domino.research.ibm.com/library/cyberdig.nsf/papers/7AAC28E89CA36CC785257116005F824E/$File/rc23869.pdf]
Rheologist
A rheologist is an
interdisciplinary scientist or engineer who studies the flow of complex liquids or the deformation of soft solids. It is not a primary degree subject; there is no qualification of rheologist as such. Most rheologists have a qualification in mathematics, the physical sciences (e.g.
chemistry
Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, proper ...
,
physics
Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which ...
,
geology
Geology () is a branch of natural science concerned with Earth and other Astronomical object, astronomical objects, the features or rock (geology), rocks of which it is composed, and the processes by which they change over time. Modern geology ...
,
biology
Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary ...
), engineering (e.g.
mechanical
Mechanical may refer to:
Machine
* Machine (mechanical), a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement
* Mechanical calculator, a device used to perform the basic operations ...
,
chemical,
materials science, plastics engineering and engineering or
civil engineering),
medicine
Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care pr ...
, or certain technologies, notably
materials or
food. Typically, a small amount of rheology may be studied when obtaining a degree, but a person working in rheology will extend this knowledge during postgraduate research or by attending short courses and by joining a professional association.
See also
*
Bingham plastic
*
Die swell
*
Fluid dynamics
*
Glass transition
*
Liquid
*
List of rheologists
This is a list of notable rheologists.
Rheologists
* Eugene C. Bingham
* Robert Byron Bird
* Mosto Bousmina
* Percy Williams Bridgman
* Pierre Carreau
* Alfred L. Copley
* Maurice Couette
* Armand de Waele
* Jerald Ericksen
* Denis Ev ...
*
Microrheology
*
Rheological weldability for thermoplastics
*
Rheopectic
*
Solid
Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structur ...
*
Thixotropy
*
Transport phenomena
*
Viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the int ...
*
Interfacial rheology
References
External links
"The Origins of Rheology: A short historical excursion" by Deepak Doraiswamy, DuPont iTechnologies
RHEOTEST Medingen GmbH– Short history and collection of rheological instruments from the time of Fritz Höppler
- On the Rheology of Cats
; Societies
American Society of RheologyAustralian Society of RheologyBritish Society of RheologyEuropean Society of RheologyFrench Society of RheologyNordic Rheology SocietyRomanian Society of RheologyKorean Society of Rheology
; Journals
*
Applied Rheology'
*
Journal of Non-Newtonian Fluid Mechanics'
*
Journal of Rheology'
*
Rheologica Acta'
{{Authority control
Rheology,
Tribology