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Sedimentation

 

 
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Sedimentation
 
 
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Sedimentation describes the motion of molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
s in solution
Solution

In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent....
s or particle
Particle (ecology)

In marine and freshwater ecology, a particle is a small object. Particles can remain in suspension in the ocean or freshwater, however they eventually settle and accumulate as sediment....
s in suspensions
Suspension (chemistry)

In chemistry, a suspension is a heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometre....
 in response to an external force such as gravity
Gravitation

Gravitation is a natural phenomenon that gives weight to objects. In everyday life, attraction due to gravity is the result of the presence of relatively large bodies, such as the Earth and the Moon....
, centrifugal force
Centrifugal force

In classical mechanics, centrifugal force is an outward force associated with rotation. Centrifugal force is one of several so-called pseudo-forces , so named because, unlike Fundamental interaction, they do not originate in interactions with other bodies situated in the environment of the particle upon which they act....
 or electric force
Electromagnetism

Electromagnetism is the physics of the electromagnetic field, a field which exerts a force on Elementary particles with the property of electric charge and which is reciprocally affected by the presence and motion of such particles....
. Sedimentation may pertain to objects of various sizes, ranging from suspensions
Suspension (chemistry)

In chemistry, a suspension is a heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometre....
 of dust and pollen particles
Particle (ecology)

In marine and freshwater ecology, a particle is a small object. Particles can remain in suspension in the ocean or freshwater, however they eventually settle and accumulate as sediment....
 to cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
ular suspensions to solution
Solution

In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent....
s of single molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
s such as protein
Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
s and peptide
Peptide

Peptides are short polymers formed from the linking, in a defined order, of a-amino acids. The link between one amino acid residue and the next is known as an amide chemical bond or a peptide bond....
s. Even small molecules such as aspirin
Aspirin

Aspirin , also known as acetylsalicylic acid , is a salicylate medication, often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, and as an anti-inflammatory medication....
 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
Terminal velocity

File:Terminal velocity.svgIn fluid dynamics an object is moving at its terminal velocity if its speed is constant due to the restraining force exerted by the air, water or other fluid in which it is moving....
  at which the applied force is exactly canceled by an opposing drag force.






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Sedimentation describes the motion of molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
s in solution
Solution

In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent....
s or particle
Particle (ecology)

In marine and freshwater ecology, a particle is a small object. Particles can remain in suspension in the ocean or freshwater, however they eventually settle and accumulate as sediment....
s in suspensions
Suspension (chemistry)

In chemistry, a suspension is a heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometre....
 in response to an external force such as gravity
Gravitation

Gravitation is a natural phenomenon that gives weight to objects. In everyday life, attraction due to gravity is the result of the presence of relatively large bodies, such as the Earth and the Moon....
, centrifugal force
Centrifugal force

In classical mechanics, centrifugal force is an outward force associated with rotation. Centrifugal force is one of several so-called pseudo-forces , so named because, unlike Fundamental interaction, they do not originate in interactions with other bodies situated in the environment of the particle upon which they act....
 or electric force
Electromagnetism

Electromagnetism is the physics of the electromagnetic field, a field which exerts a force on Elementary particles with the property of electric charge and which is reciprocally affected by the presence and motion of such particles....
. Sedimentation may pertain to objects of various sizes, ranging from suspensions
Suspension (chemistry)

In chemistry, a suspension is a heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometre....
 of dust and pollen particles
Particle (ecology)

In marine and freshwater ecology, a particle is a small object. Particles can remain in suspension in the ocean or freshwater, however they eventually settle and accumulate as sediment....
 to cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
ular suspensions to solution
Solution

In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent....
s of single molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
s such as protein
Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
s and peptide
Peptide

Peptides are short polymers formed from the linking, in a defined order, of a-amino acids. The link between one amino acid residue and the next is known as an amide chemical bond or a peptide bond....
s. Even small molecules such as aspirin
Aspirin

Aspirin , also known as acetylsalicylic acid , is a salicylate medication, often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, and as an anti-inflammatory medication....
 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
Terminal velocity

File:Terminal velocity.svgIn fluid dynamics an object is moving at its terminal velocity if its speed is constant due to the restraining force exerted by the air, water or other fluid in which it is moving....
  at which the applied force is exactly canceled by an opposing drag force. For small enough particles (low Reynolds number
Reynolds number

In fluid mechanics and heat transfer, the Reynolds number is a dimensionless number that gives a measure of the ratio of inertial forces to viscosity forces and, consequently, it quantifies the relative importance of these two types of forces for given flow conditions....
), the drag force varies linearly with the terminal velocity
Terminal velocity

File:Terminal velocity.svgIn fluid dynamics an object is moving at its terminal velocity if its speed is constant due to the restraining force exerted by the air, water or other fluid in which it is moving....
, i.e., (Stokes flow
Stokes flow

Stokes flow is a type of fluid flow where advection inertia forces are small compared with Viscosity forces. The Reynolds number is low, i.e. ....
) 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, . Hence, it is generally possible to define a sedimentation coefficient
Sedimentation coefficient

The sedimentation coefficient s of a particle is used to characterize its behaviour in sedimentation processes, notably centrifugation. It is defined as the ratio of a particle's sedimentation velocity to the acceleration that is applied to it ....
  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
Sediment

Sediment is any particulate matter that can be sediment transport by fluid dynamics, and which eventually is deposited.Sediments are most often transported by water transported by wind and glaciers....
. The concentration of particles at the boundary is opposed by the diffusion
Diffusion

Molecular diffusion, often called simply diffusion, is a net transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion....
 of the particles.

The sedimentation of particles under gravity is described by the Mason-Weaver equation
Mason-Weaver equation

The Mason-Weaver equation describes the sedimentation and diffusion of solutes under a uniform force, usually a gravitational field. Assuming that the gravitational field is aligned in the z direction , the Mason-Weaver equation may be written...
, which has a simple exact solution. The sedimentation coefficient s in this case equals , where is the buoyant mass.

The sedimentation of particles under the centrifugal force
Centrifugal force

In classical mechanics, centrifugal force is an outward force associated with rotation. Centrifugal force is one of several so-called pseudo-forces , so named because, unlike Fundamental interaction, they do not originate in interactions with other bodies situated in the environment of the particle upon which they act....
 is described by the Lamm equation
Lamm equation

The Lamm equation describes the sedimentation and diffusion of a solute under ultracentrifuge in traditional Circular sector-shaped cells. The Lamm equation can be written:...
, which likewise has an exact solution. The sedimentation coefficient s also equals , where is the buoyant 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 sector
Circular sector

A circular sector or circle sector, is the portion of a circle enclosed by two radius and an Arc , where the smaller area is known as the minor sector and the larger being the major sector....
-shaped cells, whereas the Mason-Weaver equation pertains to box-shaped
Cuboid

In geometry, a cuboid is a solid figure bounded by six faces, forming a convex polyhedron. There are two competing and incompatible definitions of a cuboid in the mathematical literature....
 cells (i.e., cells whose walls are aligned with the three Cartesian axes
Cartesian coordinate system

In mathematics, the Cartesian coordinate system is used to determine each Point uniquely in a Plane through two numbers, usually called the x-coordinate or abscissa and the y-coordinate or ordinate of the point....
).

Particles with a charge or dipole moment can be sedimented by an electric field
Electric field

In physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field ....
 or electric field gradient
Electric field gradient

Mathematically, the electric field gradient is the hessian matrix of the electrical potential V:It is an important structural property of a crystalline solid, where it is defined at the location of a atomic nucleus....
, respectively. These processes are called electrophoresis
Electrophoresis

Electrophoresis is the best-known electrokinetic phenomena. It was discovered by Reuss in 1807. He observed that clay particles dispersed in water migrate under influence of an applied electric field....
 and dielectrophoresis
Dielectrophoresis

Dielectrophoresis is a phenomenon in which a force is exerted on a dielectric particle when it is subjected to a non-uniform electric field. This force does not require the particle to be electric charge....
, respectively. For electrophoresis, the sedimentation coefficient corresponds to the particle charge divided by its drag
Drag (physics)

The term drag is widely used in Physics and Engineering and is central to the field of fluid dynamics. "Drag" refers to forces that oppose the motion of a solid object through a fluid ....
 (the electrophoretic mobility
Electrophoresis

Electrophoresis is the best-known electrokinetic phenomena. It was discovered by Reuss in 1807. He observed that clay particles dispersed in water migrate under influence of an applied electric field....
). Similarly, for dielectrophoresis
Dielectrophoresis

Dielectrophoresis is a phenomenon in which a force is exerted on a dielectric particle when it is subjected to a non-uniform electric field. This force does not require the particle to be electric charge....
, the sedimentation coefficient equals the particle's electric dipole moment divided by its drag
Drag (physics)

The term drag is widely used in Physics and Engineering and is central to the field of fluid dynamics. "Drag" refers to forces that oppose the motion of a solid object through a fluid ....
. ,

See also

  • Coagulation (disambiguation)
    Coagulation (disambiguation)

    Coagulation may refer to:* Coagulation, in colloid chemistry, a process in which dispersed colloidal particles agglomerate. See flocculation* Coagulation of blood...
  • Flocculation
    Flocculation

    Flocculation is a process where a solute comes out of solution in the form of floc or flakes. The action differs from Precipitation in that the solute coming out of solution does so at a concentration generally below its solubility limit in the liquid....