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This article refers to the scientific phenomenon of sedimentation. For sedimentation in the treatment of water and wastewater, see Sedimentation (water treatment).
Sedimentation describes the motion of molecules in
solutions or
particle (ecology)s in
a solution (chemistry) in response to an external force such as
gravitation, centrifugal force or electromagnetism. Sedimentation may pertain to objects of various sizes, ranging from
suspension (chemistry) of dust and pollen
particle (ecology) to
cell (biology)ular suspensions to
solutions of single
molecules such as proteins and
peptides. Even small molecules such as
aspirin can be sedimented, although it can be difficult to apply a sufficiently strong force to produce significant sedimentation.
In a sedimentation experiment, the applied force accelerates the particles to a terminal velocity v_{term} at which the applied force is exactly canceled by an opposing drag force. In general, the drag force varies linearly with the terminal velocity, i.e., F_{drag} = f v_{term} where
f depends only on the properties of the particle and the surrounding fluid. Similarly, the applied force generally varies linearly with some coupling constant (denoted here as
q) that depends only on the properties of the particle, F_{app} = q E_{app}. Hence, it is generally possible to define a
sedimentation coefficient s \ \stackrel{\mathrm{def-->{=}\ q/f that depends only on the properties of the particle and the surrounding fluid. Thus, measuring
s can reveal underlying properties of the particle.
In many cases, the motion of the particles is blocked by a hard boundary; the resulting accumulation of particles at the boundary is called a
sediment. The concentration of particles at the boundary is opposed by the
diffusion of the particles.
The sedimentation of particles under gravity is described by the Mason-Weaver equation, which has a simple exactsolution. The sedimentation coefficient
s in this case equals m_{b}/f, where m_{b} is the
buoyant mass.
The sedimentation of particles under the
centrifugal force is described by the Lamm equation, which likewise hasan exact solution. The sedimentation coefficient
s also equals m_{b}/f, where m_{b} is thebuoyant mass. However, the Lamm equation differs from the Mason-Weaver equation because the centrifugal force depends on radius from the origin of rotation, whereas gravity is presumed constant. The Lamm equation also has extra terms, since it pertains to
Circular sector-shaped cells, whereas the Mason-Weaver equation pertainsto
cuboid cells (i.e., cells whose walls are aligned with the three
Cartesian coordinate system).
Particles with a charge or dipole moment can be sedimented by an electric field or
electric field gradient, respectively. These processes are called electrophoresis and dielectrophoresis, respectively. For electrophoresis, the sedimentation coefficient corresponds to the particle charge divided by its drag (physics) (the
electrophoresis). Similarly, for dielectrophoresis, the sedimentation coefficient equals the particle's electric dipole moment divided by its
drag (physics).
See also
This article refers to the scientific phenomenon of sedimentation. For sedimentation in the treatment of water and wastewater, see Sedimentation (water treatment).
Sedimentation describes the motion of
molecules in solutions or particle (ecology)s in a solution (chemistry) in response to an external force such as gravitation,
centrifugal force or electromagnetism. Sedimentation may pertain to objects of various sizes, ranging from
suspension (chemistry) of dust and pollen
particle (ecology) to
cell (biology)ular suspensions to solutions of single
molecules such as proteins and
peptides. Even small molecules such as
aspirin can be sedimented, although it can be difficult to apply a sufficiently strong force to produce significant sedimentation.
In a sedimentation experiment, the applied force accelerates the particles to a
terminal velocity v_{term} at which the applied force is exactly canceled by an opposing drag force. In general, the drag force varies linearly with the terminal velocity, i.e., F_{drag} = f v_{term} where
f depends only on the properties of the particle and the surrounding fluid. Similarly, the applied force generally varies linearly with some coupling constant (denoted here as
q) that depends only on the properties of the particle, F_{app} = q E_{app}. Hence, it is generally possible to define a sedimentation coefficient s \ \stackrel{\mathrm{def-->{=}\ q/f that depends only on the properties of the particle and the surrounding fluid. Thus, measuring
s can reveal underlying properties of the particle.
In many cases, the motion of the particles is blocked by a hard boundary; the resulting accumulation of particles at the boundary is called a sediment. The concentration of particles at the boundary is opposed by the
diffusion of the particles.
The sedimentation of particles under gravity is described by the
Mason-Weaver equation, which has a simple exactsolution. The sedimentation coefficient
s in this case equals m_{b}/f, where m_{b} is the
buoyant mass.
The sedimentation of particles under the
centrifugal force is described by the
Lamm equation, which likewise hasan exact solution. The sedimentation coefficient
s also equals m_{b}/f, where m_{b} is thebuoyant mass. However, the Lamm equation differs from the Mason-Weaver equation because the centrifugal force depends on radius from the origin of rotation, whereas gravity is presumed constant. The Lamm equation also has extra terms, since it pertains to Circular sector-shaped cells, whereas the Mason-Weaver equation pertainsto cuboid cells (i.e., cells whose walls are aligned with the three
Cartesian coordinate system).
Particles with a charge or dipole moment can be sedimented by an
electric field or
electric field gradient, respectively. These processes are called electrophoresis and dielectrophoresis, respectively. For electrophoresis, the sedimentation coefficient corresponds to the particle charge divided by its
drag (physics) (the
electrophoresis). Similarly, for dielectrophoresis, the sedimentation coefficient equals the particle's electric dipole moment divided by its
drag (physics).
See also
- Coagulation (disambiguation)
- Flocculation
Definition: sedimentation from Online Medical Dictionary
The Online Medical Dictionary is a searchable dictionary of definitions from medicine, science and technology.
Definition: sedimentation coefficient from Online Medical Dictionary
The Online Medical Dictionary is a searchable dictionary of definitions from medicine, science and technology.
Sedimentation - Wikipedia, the free encyclopedia
Sedimentation describes the motion of molecules in solutions or particles in suspensions in response to an external force such as gravity, centrifugal force or electric force.
Erythrocyte sedimentation rate - Wikipedia, the free encyclopedia
The erythrocyte sedimentation rate (ESR), also called a sedimentation rate, sed rate, or Biernacki Reaction, is the rate at which red blood cells precipitate in a period of 1 hour.
sedimentation - definition of sedimentation by the Free Online ...
The act or process of depositing sediment.
sedimentation definition of sedimentation in the Free Online ...
sedimentation. In geology, the process of deposition of a solid material from a state of suspension or solution in a fluid (usually air or water).
sedimentation constant - definition of sedimentation constant in the ...
sedimentation constant
sedimentation - definition of sedimentation in the Medical dictionary ...
sedimentation /sed·i·men·ta·tion/ (sed?i-men-ta´shun) the settling out of sediment.
Blood sedimentation - Hutchinson encyclopedia article about Blood ...
In medicine, measure of the rate at which red blood cells (erythrocytes) settle out of suspension in blood plasma. This is affected by the amount of protein in the plasma which, in ...
sedimentation - Hutchinson encyclopedia article about sedimentation
sediment. Any loose material that has ‘settled’ after deposition from suspension in water, ice, or air, generally as the water current or wind speed decreases.
