Colloid

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Cranberry glass [5]
Milk [3]
Whipped cream [4]

A colloid is a substance composed of extremely small particles of one material (the dispersed phase) evenly and stably distributed in another material (the continuous phase) [1]. The size of the dispersed particles (1–1000 nanometres across) is larger than in a solution - small enough to be dispersed evenly and maintain a homogeneous appearance, but large enough to scatter light and not dissolve [2]. A colloidal system can be solid, liquid, or gaseous. The following examples of colloids common seen in our daily lives are shown as continuous phase / dispersed phases.

Examples

Liquid/Liquid: milk, mayonnaise

Liquid/Gas: whipped cream

Liquid/Solid: ink, blood

Solid/Gas: aerogel, styrofoam

Solid/Liquid: jelly, agar, gelatin

Solid/Solid: cranberry glass

Gas/Liquid: fog, mist, hair sprays

GAs/Solid: smoke, cloud

Research

Colloids are a major area of ongoing research in soft matter. In particular, many groups try to understand the interactions between colloidal particles, their natural phases and dynamics, and the factors that affect their self-assembly.

Aizenberg et al. recently investigated patterned colloidal deposition controlled by electrostatic and capillary forces [6]. They showed that electrostatic interactions and capillary forces could be used to control the self-assembly of colloidal particles. When colloidal particles are charged, they will prefer to attach to oppositely charged interfaces. The salt content of the solution affects the screened length in Coulomb interactions, so this parameter can be used to control how densely they cluster in this scenario. As such a template dries, capillary forces act to focus the microspheres in denser clusters.

References

[1] http://encyclopedia.farlex.com/Colloidal+system

[2] http://en.wikipedia.org/wiki/Colloid

[3] http://en.wikipedia.org/wiki/File:Milk.jpg

[4] http://en.wikipedia.org/wiki/File:Kakao_mit_Sahne_281104.jpg

[5] http://en.wikipedia.org/wiki/File:Vintage_cranberry_glass.jpg

[6] J. Aizenberg et al. Patterned Colloidal Deposition Controlled by Electrostatic and Capillary Forces. Physical Review Letters vol. 84, no. 13, 2997-3000.