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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, [1] while others extend the definition to include substances like aerosols and gels.
In chemistry, a suspension is a heterogeneous mixture of a fluid that contains solid particles sufficiently large for sedimentation. The particles may be visible to the naked eye , usually must be larger than one micrometer , and will eventually settle , although the mixture is only classified as a suspension when and while the particles have ...
A colloid is a heterogeneous mixture where the dispersed particles have at least in one direction a dimension roughly between 1 nm and 1 μm or that in a system discontinuities are found at distances of that order. [8] A suspension is a heterogeneous dispersion of larger particles in a medium. Unlike solutions and colloids, if left undisturbed ...
In addition, a heterogeneous mixture may have a uniform (e.g. a colloid) or non-uniform (e.g. a pencil) composition. Several solid substances, such as salt and sugar , dissolve in water to form homogeneous mixtures or " solutions ", in which there are both a solute (dissolved substance) and a solvent (dissolving medium) present.
The overlap between the diffuse layers of two approaching particles results in a repulsive double layer interaction potential, which leads to particle stabilization. When salt is added to the suspension, the electrical double layer repulsion is screened, and van der Waals attraction become dominant and induce fast aggregation.
The difference in mass density between the colloidal particles of mass density and the medium of suspension of mass density , and the diameter of the particles, have an influence on the value of . As an example, consider a colloidal suspension of polyethylene particles in water, and three different values for the diameter of the particles: 0.1 ...
An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation.Emulsions are part of a more general class of two-phase systems of matter called colloids.
Colloids are formed by phase separation, though not all phase separations forms colloids - for example oil and water can form separated layers under gravity rather than remaining as microscopic droplets in suspension. A common form of spontaneous phase separation is termed spinodal decomposition; it is described by the Cahn–Hilliard equation.