Nano Technology and Graphene Research Centre
PUSAT RISET PENGEMBANGAN INSTITUSI NANO TEKNOLOGI DAN GRAPHENE

Nanotechnology Synthesis and Dispersion


Dispersion

A dispersion is a system in which particles are dispersed in a continuous phase of a different composition (or state). See also emulsion. A dispersion is classified in a number of different ways, including how large the particles are in relation to the particles of the continuous phase, whether or not precipitation occurs, and the presence of Brownian motion.

In chemistry, a suspension is a heterogeneous mixture that contains solid particles sufficiently large for sedimentation. The particles may be visible to the naked eye, usually must be larger than 1 micrometer, and will eventually settle. A suspension is a heterogeneous mixture in which the solute particles do not dissolve, but get suspended throughout the bulk of the solvent, left floating around freely in the medium.[1] The internal phase (solid) is dispersed throughout the external phase (fluid) through mechanical agitation, with the use of certain excipients or suspending agents. An example of a suspension would be sand in water. The suspended particles are visible under a microscope and will settle over time if left undisturbed. This distinguishes a suspension from a colloid, in which the suspended particles are smaller and do not settle.[2] Colloids and suspensions are different from solution, in which the dissolved substance (solute) does not exist as a solid, and solvent and solute are homogeneously mixed.

A suspension of liquid droplets or fine solid particles in a gas is called an aerosol or particulate. In the atmosphere, these consist of fine dust and soot particles, sea salt, biogenic and volcanogenic sulfates, nitrates, and cloud droplets.

Suspensions are classified on the basis of the dispersed phase and the dispersion medium, where the former is essentially solid while the latter may either be a solid, a liquid, or a gas.

In modern chemical process industries, high-shear mixing technology has been used to create many novel suspensions.

Suspensions are unstable from the thermodynamic point of view; however, they can be kinetically stable over a large period of time, which determines their shelf life. This time span needs to be measured to ensure the best product quality to the final consumer. "Dispersion stability refers to the ability of a dispersion to resist change in its properties over time."[3]

 

Bead Milling Process

In the milling vessel, the grinding medium is kept moving by the agitator, which itself is driven by a motor. The dispersion process takes place between the grinding beads sliding on each other and between the rotor and/or the vessel sides and the grinding beads.

 

 

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