Thixotropy
Encyclopedia
Thixotropy is the property of certain gels or fluids that are thick (viscous) under normal conditions, but flow (become thin, less viscous) over time when shaken, agitated, or otherwise stressed. They then take a fixed time to return to a more viscous state.
In more technical language:
some non-Newtonian
pseudoplastic
fluids show a time-dependent change in viscosity
; the longer the fluid undergoes shear stress
, the lower its viscosity. A thixotropic fluid is a fluid which takes a finite time to attain equilibrium viscosity when introduced to a step change in shear rate. Some thixotropic fluids return to a gel state almost instantly, such as ketchup, and are called pseudoplastic fluids. Others such as yoghurt take much longer and can become nearly solid. Many gel
s and colloids are thixotropic materials, exhibiting a stable form at rest but becoming fluid when agitated.
Some fluids are anti-thixotropic: constant shear stress for a time causes an increase in viscosity or even solidification. Constant shear stress can be applied by shaking or mixing. Fluids which exhibit this property are usually called rheopectic
. They are much less common.
s are thixotropic, with their behavior of great importance in structural
and geotechnical engineering
. Landslide
s, such as those common in the cliff
s around Lyme Regis
, Dorset
and in the Aberfan spoil tip disaster in Wales
are evidence of this phenomenon. Similarly, a lahar
is a mass of earth liquefied by a volcanic
event, which rapidly solidifies once coming to rest.
Drilling muds used in geotechnical applications can be thixotropic. Honey from honey bees may also exhibit this property under certain conditions.(Heather honey).
Another example of a thixotropic fluid is the synovial fluid
found in joints between some bones. The ground substance
in the human body is thixotropic, as is semen
.
Some clay deposits found in the process of exploring caves exhibit thixotropism: an initially solid-seeming mudbank will turn soupy and yield up moisture when dug into or otherwise disturbed. These clays were deposited in the past by low-velocity streams which tend to deposit fine-grained sediment.
is a thixotropic adhesive that cures anaerobically.
Thixotropy has been proposed as a scientific explanation of blood liquification miracles such as that of Saint Januarius in Naples
.
Semi-solid casting processes such as thixomoulding use the thixotropic property of some alloys (mostly light metal
s) (bismuth
). Within certain temperature ranges, with appropriate preparation, an alloy can be put into a semi-solid state, which can be injected with less shrinkage and better overall properties than by normal injection molding
.
Solder paste
s used in electronics manufacturing printing processes are thixotropic materials.
Many kinds of inks—used in silkscreen textile printing
—made from plastisol
, exhibit thixotropic qualities. Some, such as those used in CMYK-type process printing, are designed to quickly regain viscosity once they are applied to protect the structure of the dots for accurate color reproduction. This is a sort of reverse thixotropy.
The ink developed for the Fisher space pen
is a visco-elastic, thixotropic ink, with a consistency similar to that of very thick rubber cement, flows as a result of the shearing action of the rolling ball in its socket. This shearing action liquefies the solid gel thixotropic ink, allowing the pen to write smoothly and dependably on most surfaces and even underwater.
thixis, touch (from thinganein, to touch) + -tropy, -tropous, from Greek -tropos, of turning, from tropos, changeable, from trepein, to turn.
In more technical language:
some non-Newtonian
Non-Newtonian fluid
A non-Newtonian fluid is a fluid whose flow properties differ in any way from those of Newtonian fluids. Most commonly the viscosity of non-Newtonian fluids is not independent of shear rate or shear rate history...
pseudoplastic
Power-law fluid
A Power-law fluid, or the Ostwald–de Waele relationship, is a type of generalized Newtonian fluid for which the shear stress, τ, is given by\tau = K \left^n where:...
fluids show a time-dependent change in viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
; the longer the fluid undergoes shear stress
Shear stress
A shear stress, denoted \tau\, , is defined as the component of stress coplanar with a material cross section. Shear stress arises from the force vector component parallel to the cross section...
, the lower its viscosity. A thixotropic fluid is a fluid which takes a finite time to attain equilibrium viscosity when introduced to a step change in shear rate. Some thixotropic fluids return to a gel state almost instantly, such as ketchup, and are called pseudoplastic fluids. Others such as yoghurt take much longer and can become nearly solid. Many gel
Gel
A gel is a solid, jelly-like material 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...
s and colloids are thixotropic materials, exhibiting a stable form at rest but becoming fluid when agitated.
Some fluids are anti-thixotropic: constant shear stress for a time causes an increase in viscosity or even solidification. Constant shear stress can be applied by shaking or mixing. Fluids which exhibit this property are usually called rheopectic
Rheopecty
Rheopecty or rheopexy is the rare property of some non-Newtonian fluids to show a time-dependent change in viscosity; the longer the fluid undergoes shearing force, the higher its viscosity. Rheopectic fluids, such as some lubricants, thicken or solidify when shaken...
. They are much less common.
Natural examples
Some clayClay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
s are thixotropic, with their behavior of great importance in structural
Structural engineering
Structural engineering is a field of engineering dealing with the analysis and design of structures that support or resist loads. Structural engineering is usually considered a specialty within civil engineering, but it can also be studied in its own right....
and geotechnical engineering
Geotechnical engineering
Geotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. Geotechnical engineering is important in civil engineering, but is also used by military, mining, petroleum, or any other engineering concerned with construction on or in the ground...
. Landslide
Landslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
s, such as those common in the cliff
Cliff
In geography and geology, a cliff is a significant vertical, or near vertical, rock exposure. Cliffs are formed as erosion landforms due to the processes of erosion and weathering that produce them. Cliffs are common on coasts, in mountainous areas, escarpments and along rivers. Cliffs are usually...
s around Lyme Regis
Lyme Regis
Lyme Regis is a coastal town in West Dorset, England, situated 25 miles west of Dorchester and east of Exeter. The town lies in Lyme Bay, on the English Channel coast at the Dorset-Devon border...
, Dorset
Dorset
Dorset , is a county in South West England on the English Channel coast. The county town is Dorchester which is situated in the south. The Hampshire towns of Bournemouth and Christchurch joined the county with the reorganisation of local government in 1974...
and in the Aberfan spoil tip disaster in Wales
Wales
Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...
are evidence of this phenomenon. Similarly, a lahar
Lahar
A lahar is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water. The material flows down from a volcano, typically along a river valley. The term is a shortened version of "berlahar" which originated in the Javanese language of...
is a mass of earth liquefied by a volcanic
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
event, which rapidly solidifies once coming to rest.
Drilling muds used in geotechnical applications can be thixotropic. Honey from honey bees may also exhibit this property under certain conditions.(Heather honey).
Another example of a thixotropic fluid is the synovial fluid
Synovial fluid
Synovial fluid is a viscous, non-Newtonian fluid found in the cavities of synovial joints. With its yolk-like consistency , the principal role of synovial fluid is to reduce friction between the articular cartilage of synovial joints during movement.-Overview:The inner membrane of synovial joints...
found in joints between some bones. The ground substance
Ground substance
Ground substance is a term for the non-cellular components of extracellular matrix which contain the fibers.It is usually not visible on slides, because it is removed during the preparation process....
in the human body is thixotropic, as is semen
Semen
Semen is an organic fluid, also known as seminal fluid, that may contain spermatozoa. It is secreted by the gonads and other sexual organs of male or hermaphroditic animals and can fertilize female ova...
.
Some clay deposits found in the process of exploring caves exhibit thixotropism: an initially solid-seeming mudbank will turn soupy and yield up moisture when dug into or otherwise disturbed. These clays were deposited in the past by low-velocity streams which tend to deposit fine-grained sediment.
Applications
Thread-locking fluidThread-locking fluid
Thread-locking fluid is a thin, single-component adhesive, applied to the threads of fasteners such as screws and bolts to prevent loosening, leakage, and corrosion. Typically, thread-locking fluids are methacrylate-based, and cure anaerobically...
is a thixotropic adhesive that cures anaerobically.
Thixotropy has been proposed as a scientific explanation of blood liquification miracles such as that of Saint Januarius in Naples
Naples
Naples is a city in Southern Italy, situated on the country's west coast by the Gulf of Naples. Lying between two notable volcanic regions, Mount Vesuvius and the Phlegraean Fields, it is the capital of the region of Campania and of the province of Naples...
.
Semi-solid casting processes such as thixomoulding use the thixotropic property of some alloys (mostly light metal
Light metal
Light metals are metals of low atomic weight. The cut off between light metals and heavy metals varies. Lithium, beryllium, sodium, magnesium and aluminium are almost always included. Additional metals up to nickel are often included as well. Metals heavier than nickel are usually called heavy...
s) (bismuth
Bismuth
Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent poor metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead...
). Within certain temperature ranges, with appropriate preparation, an alloy can be put into a semi-solid state, which can be injected with less shrinkage and better overall properties than by normal injection molding
Injection molding
Injection molding is a manufacturing process for producing parts from both thermoplastic and thermosetting plastic materials. Material is fed into a heated barrel, mixed, and forced into a mold cavity where it cools and hardens to the configuration of the cavity...
.
Solder paste
Solder paste
Solder paste sometimes refers to soldering flux that does not contain solder.Solder paste is used to connect the leads of integrated chip packages to attachment points in the circuit patterns on a printed circuit board...
s used in electronics manufacturing printing processes are thixotropic materials.
Many kinds of inks—used in silkscreen textile printing
Textile printing
Textile printing is the process of applying colour to fabric in definite patterns or designs. In properly printed fabrics the colour is bonded with the fiber, so as to resist washing and friction...
—made from plastisol
Plastisol
Plastisol is a suspension of PVC particles in a plasticizer; it flows as a liquid and can be poured into a heated mold. When heated to around 177 degrees Celsius, the plastic and plasticizer mutually dissolve each other. On cooling the mold below 60 degrees C, a flexible, permanently plasticized...
, exhibit thixotropic qualities. Some, such as those used in CMYK-type process printing, are designed to quickly regain viscosity once they are applied to protect the structure of the dots for accurate color reproduction. This is a sort of reverse thixotropy.
The ink developed for the Fisher space pen
Space Pen
The Space Pen , marketed by Fisher Space Pen Company, is a pen that uses pressurized ink cartridges and is claimed to write in zero gravity, underwater, over wet and greasy paper, at any angle, and in very wide temperature range.The Fisher Space Pen was invented by American industrialist and pen...
is a visco-elastic, thixotropic ink, with a consistency similar to that of very thick rubber cement, flows as a result of the shearing action of the rolling ball in its socket. This shearing action liquefies the solid gel thixotropic ink, allowing the pen to write smoothly and dependably on most surfaces and even underwater.
Etymology
The word comes from GreekGreek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
thixis, touch (from thinganein, to touch) + -tropy, -tropous, from Greek -tropos, of turning, from tropos, changeable, from trepein, to turn.
See also
- Aberfan disaster
- Calcium SulfateCalcium sulfateCalcium sulfate is a common laboratory and industrial chemical. In the form of γ-anhydrite , it is used as a desiccant. It is also used as a coagulant in products like tofu. In the natural state, unrefined calcium sulfate is a translucent, crystalline white rock...
- dilatantDilatantA dilatant material is one in which viscosity increases with the rate of shear strain. Such a shear thickening fluid, also known by the acronym STF, is an example of a non-Newtonian fluid....
(antonym) - Fumed silicaFumed silicaFumed silica, also known as pyrogenic silica because it is produced in a flame, consists of microscopic droplets of amorphous silica fused into branched, chainlike, three-dimensional secondary particles which then agglomerate into tertiary particles. The resulting powder has an extremely low bulk...
- Kaye effectKaye EffectThe Kaye Effect is a property of complex liquids which was first described by the British engineer Alan Kaye in 1963.While pouring one viscous mixture of an organic liquid onto a surface, the surface suddenly spouted an upcoming jet of liquid which merged with the downgoing one.This phenomenon has...
- NanocelluloseNanocelluloseNanocellulose or microfibrillated cellulose , is a material composed of nanosized cellulose fibrils with a high aspect ratio . Typical dimensions are 5–20 nanometers width and length up to 2000 nanometers. It is pseudo-plastic...
- polymerPolymerA polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
- Pseudoplastic
- Rheopexy (antonym)
- Shear thinningShear thinningShear thinning is an effect where a fluid's viscosity—the measure of a fluid's resistance to flow—decreases with an increasing rate of shear stress. Another name for a shear thinning fluid is a pseudoplastic. This property is found in certain complex solutions, such as lava, ketchup, whipped cream,...
- Silly puttySilly PuttySilly Putty , is the Crayola-owned trademark name for a class of silicone polymers. It is marketed today as a toy for children, but was originally created by accident during research into potential rubber substitutes for use by the United States in World War II...
- Solder paste#Composition find "thixotropic index"
- viscosityViscosityViscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...