Colloid
A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others extend ...
al particles in a
sol are continuously bombarded by the molecules of the
dispersion medium
Interface and colloid science is an interdisciplinary intersection of branches of chemistry, physics, nanoscience and other fields dealing with colloids, heterogeneous systems consisting of a mechanical mixture of particles between 1 nm ...
on all sides. The impacts are however not equal in every direction. As a result, the sol particles show random or zig-zag movements. This random or zig-zag motion of the colloidal particles in a sol is called
Brownian motion
Brownian motion, or pedesis (from grc, πήδησις "leaping"), is the random motion of particles suspended in a medium (a liquid or a gas).
This pattern of motion typically consists of random fluctuations in a particle's position insi ...
or Brownian movement.
The phenomenon of Brownian motion was observed by
Robert Brown in the form of random zig-zag motion of pollen grains suspended in water. This kind of movement is found in all colloidal systems. Such random motion is visible under
ultramicroscope
An ultramicroscope is a microscope with a system that lights the object in a way that allows viewing of tiny particles via light scattering, and not light reflection or absorption. When the diameter of a particle is below or near the wavelength of ...
s and for bigger particles even under ordinary microscopes.
The Brownian motion becomes progressively less prominent, as the particles grow in size or the
viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the inte ...
of the medium increases.
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Colloidal chemistry
Random dynamical systems