Centrifuge is a machine that uses centrifugal force to separate the components of liquid and solid particles or a mixture of liquid and liquid. Centrifuges are mainly used to separate solid particles from liquid in suspension, or to separate two liquids in emulsion that have different densities and are not compatible with each other, such as separating cream from milk.
When the suspension containing fine particles stands still, the suspended particles gradually sink due to the action of gravity field. The heavier the particle, the faster it sinks, whereas particles less dense than liquid rise. The velocity of the particle moving in the gravitational field is related to the size, shape and density of the particle, and also to the strength of the gravitational field and the viscosity of the liquid. Particles the size of red blood cells, a few micrometers in diameter, can be observed under normal gravity.
In addition, when the substance settles in the medium, there is also a diffusion phenomenon. Diffusion is unconditional and absolute. Diffusion is inversely proportional to the mass of the material, and the smaller the particles, the more serious the diffusion. Subsidence is relative, conditional, and requires external forces to move. The sedimentation is proportional to the weight of the object, and the larger the particle, the faster the sedimentation. For particles smaller than a few microns, such as viruses or proteins, they form colloidal or semi-colloidal states in solution, and it is impossible to observe the sedimentation process using gravity alone. Because the smaller the particles, the slower the settlement, and the more serious the diffusion phenomenon. So you need to use the centrifuge to produce a strong centrifugal force, in order to force these particles to overcome the diffusion of sedimentation motion.
Centrifugation is to use the powerful centrifugal force generated by the high-speed rotation of the centrifuge rotor to accelerate the settling speed of the particles in the liquid and separate the materials with different settling coefficients and buoyancy densities in the sample.
