Thermophoresis
Encyclopedia
Thermophoresis, thermodiffusion, or Soret effect (or Ludwig-Soret effect), is a phenomenon observed when a mixture of two or more types of motile particles (particles able to move) are subjected to the force of a temperature gradient
and the different types of particles respond to it differently. The term "Soret effect" normally means thermophoresis in liquids only. The term "thermophoresis" is most often intended to mean the behavior in aerosols, not liquids, but the broader meaning is also common. The mechanisms of thermophoresis in liquid mixtures differ from those in gas mixtures, and are generally not as well understood.
The phenomenon is observed at the scale of one millimeter or less. An example that may be observed by the naked eye with good lighting is when the hot rod of an electric heater is surrounded by tobacco smoke: the smoke goes away from the immediate vicinity of the hot rod. As the small particles of air nearest the hot rod are heated, they create a fast flow away from the rod, down the temperature gradient. They have acquired higher kinetic energy with their higher temperature. When they collide with the large, slower-moving particles of the tobacco smoke they push the latter away from the rod. The force that has pushed the smoke particles away from the rod is an example of a thermophoretic force. For illustration see aerosols.wustl.edu.
Thermodiffusion is labeled "positive" when particles move from a hot to cold region and "negative" when the reverse is true. Typically the heavier/larger species in a mixture exhibits positive thermophoretic behavior while the lighter/smaller species exhibit negative behavior. In addition to the sizes of the various types of particles and the steepness of the temperature gradient, the heat conductivity and heat absorption of the particles play a role. Recently, Braun and coworkers have suggested that the charge and entropy of the hydration shell of molecules play a major role for the thermophoresis of biomolecule
s in aqueous solutions.
The thermophoretic force has a number of practical applications. The basis for applications is that, because different particle types move differently under the force of the temperature gradient, the particle types can be separated by that force after they've been mixed together, or prevented from mixing if they're already separated.
towards the hot side, since the higher temperature makes the transition
structure required for atomic jumps more achievable. The diffusive flux may occur in either direction (either up or down the temperature gradient), dependent on the materials involved. Thermophoretic force has been used in commercial precipitators for applications similar to electrostatic precipitators. It is exploited in the manufacturing of optical fiber in vapor deposition
processes. It can be important as a transport mechanism in fouling
. Thermophoresis has also been shown to have potential in facilitating drug discovery
by allowing the detection of aptamer
binding by comparison of the bound versus unbound motion of the target molecule. This approach has been termed microscale thermophoresis
. Furthermore, thermophoresis has been demonstrated as a versatile technique for manipulating single biological macromolecules, such as genomic-length DNA
, in micro- and nanochannels by means of light-induced local heating. Thermophoresis is one of the methods used to separate different polymer particles in field flow fractionation
.
in 1870 and further understood by John Strutt
in 1882. Thermophoresis in liquid mixtures was first observed and reported by Carl Ludwig
in 1856 and further understood by Charles Soret
in 1879.
It has been analyzed theoretically by Sydney Chapman
.
Temperature gradient
A temperature gradient is a physical quantity that describes in which direction and at what rate the temperature changes the most rapidly around a particular location. The temperature gradient is a dimensional quantity expressed in units of degrees per unit length...
and the different types of particles respond to it differently. The term "Soret effect" normally means thermophoresis in liquids only. The term "thermophoresis" is most often intended to mean the behavior in aerosols, not liquids, but the broader meaning is also common. The mechanisms of thermophoresis in liquid mixtures differ from those in gas mixtures, and are generally not as well understood.
The phenomenon is observed at the scale of one millimeter or less. An example that may be observed by the naked eye with good lighting is when the hot rod of an electric heater is surrounded by tobacco smoke: the smoke goes away from the immediate vicinity of the hot rod. As the small particles of air nearest the hot rod are heated, they create a fast flow away from the rod, down the temperature gradient. They have acquired higher kinetic energy with their higher temperature. When they collide with the large, slower-moving particles of the tobacco smoke they push the latter away from the rod. The force that has pushed the smoke particles away from the rod is an example of a thermophoretic force. For illustration see aerosols.wustl.edu.
Thermodiffusion is labeled "positive" when particles move from a hot to cold region and "negative" when the reverse is true. Typically the heavier/larger species in a mixture exhibits positive thermophoretic behavior while the lighter/smaller species exhibit negative behavior. In addition to the sizes of the various types of particles and the steepness of the temperature gradient, the heat conductivity and heat absorption of the particles play a role. Recently, Braun and coworkers have suggested that the charge and entropy of the hydration shell of molecules play a major role for the thermophoresis of biomolecule
Biomolecule
A biomolecule is any molecule that is produced by a living organism, including large polymeric molecules such as proteins, polysaccharides, lipids, and nucleic acids as well as small molecules such as primary metabolites, secondary metabolites, and natural products...
s in aqueous solutions.
The thermophoretic force has a number of practical applications. The basis for applications is that, because different particle types move differently under the force of the temperature gradient, the particle types can be separated by that force after they've been mixed together, or prevented from mixing if they're already separated.
Applications
Impurity ions may move from the cold side of a semiconductor waferWafer (electronics)
A wafer is a thin slice of semiconductor material, such as a silicon crystal, used in the fabrication of integrated circuits and other microdevices...
towards the hot side, since the higher temperature makes the transition
Transition state
The transition state of a chemical reaction is a particular configuration along the reaction coordinate. It is defined as the state corresponding to the highest energy along this reaction coordinate. At this point, assuming a perfectly irreversible reaction, colliding reactant molecules will always...
structure required for atomic jumps more achievable. The diffusive flux may occur in either direction (either up or down the temperature gradient), dependent on the materials involved. Thermophoretic force has been used in commercial precipitators for applications similar to electrostatic precipitators. It is exploited in the manufacturing of optical fiber in vapor deposition
Vapor deposition
Vapor deposition can refer to:* Chemical vapor deposition* Physical vapor deposition...
processes. It can be important as a transport mechanism in fouling
Fouling
Fouling refers to the accumulation of unwanted material on solid surfaces, most often in an aquatic environment. The fouling material can consist of either living organisms or a non-living substance...
. Thermophoresis has also been shown to have potential in facilitating drug discovery
Drug discovery
In the fields of medicine, biotechnology and pharmacology, drug discovery is the process by which drugs are discovered or designed.In the past most drugs have been discovered either by identifying the active ingredient from traditional remedies or by serendipitous discovery...
by allowing the detection of aptamer
Aptamer
Aptamers are oligonucleic acid or peptide molecules that bind to a specific target molecule. Aptamers are usually created by selecting them from a large random sequence pool, but natural aptamers also exist in riboswitches. Aptamers can be used for both basic research and clinical purposes as...
binding by comparison of the bound versus unbound motion of the target molecule. This approach has been termed microscale thermophoresis
Microscale Thermophoresis
Microscale Thermophoresis is a technology for the analysis of biomolecules. Microscale Thermophoresis is the directed movement of particles in a microscopic temperature gradient...
. Furthermore, thermophoresis has been demonstrated as a versatile technique for manipulating single biological macromolecules, such as genomic-length DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
, in micro- and nanochannels by means of light-induced local heating. Thermophoresis is one of the methods used to separate different polymer particles in field flow fractionation
Field Flow Fractionation
Field-flow fractionation, abbreviated FFF, is a separation technique where a field is applied to a fluid suspension or solution pumped through a long and narrow channel, perpendicular to the direction of flow, in order to cause separation of the particles present in the fluid, dependent on their...
.
History
Thermophoresis in gas mixtures was first observed and reported by John TyndallJohn Tyndall
John Tyndall FRS was a prominent Irish 19th century physicist. His initial scientific fame arose in the 1850s from his study of diamagnetism. Later he studied thermal radiation, and produced a number of discoveries about processes in the atmosphere...
in 1870 and further understood by John Strutt
John Strutt, 3rd Baron Rayleigh
John William Strutt, 3rd Baron Rayleigh, OM was an English physicist who, with William Ramsay, discovered the element argon, an achievement for which he earned the Nobel Prize for Physics in 1904...
in 1882. Thermophoresis in liquid mixtures was first observed and reported by Carl Ludwig
Carl Ludwig
----Carl Friedrich Wilhelm Ludwig was a German physician and physiologist.In 1842 Ludwig became a professor of physiology and in 1846 of comparative anatomy...
in 1856 and further understood by Charles Soret
Charles Soret
Charles Soret was a Swiss physicist and chemist. He is universally known for his work on thermodiffusion .-Life:...
in 1879.
It has been analyzed theoretically by Sydney Chapman
Sydney Chapman
Sydney Chapman may refer to:*Sir Sydney Chapman , , British economist and civil servant*Sydney Chapman FRS , British mathematician...
.
See also
- Microscale ThermophoresisMicroscale ThermophoresisMicroscale Thermophoresis is a technology for the analysis of biomolecules. Microscale Thermophoresis is the directed movement of particles in a microscopic temperature gradient...
- Deposition (Aerosol physics)Deposition (Aerosol physics)In aerosol physics, Deposition is the process by which aerosol particles collect or deposit themselves on solid surfaces, decreasing the concentration of the particles in the air. It can be divided into two sub-processes: dry and wet deposition. The rate of deposition, or the deposition velocity,...
- Dufour effectDufour effectThe Dufour effect is the energy flux due to a mass concentration gradient occurring as a coupled effect of irreversible processes. It is the reciprocal phenomenen to the Soret effect....
- Maxwell Stefan diffusion