softmatter:Colloid
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Dispersions or suspensions of colloidal particles have been studied from as early as the 17th Century. Inorganic particles such or gold were suspended in solvents by alchemists [1]. In the 19th century, rubber was developed using the sap of certain plants and tress. 'Rubber' is a stable suspension of small polymeric beads which do not disolve in the suspending medium. Nowadays, colloidal suspensions are found in many fields from food products like yoghurt and jelly, to manufactured goods like paints and coatings.
Colloidal particles have a range of shapes, interaction potentials, and sizes which make for very interesting scientific properties [2]. Here we introduce different types of colloidal particles and describe some of their interesting behaviours.
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Spherical particles
Anisotropic particles
Anisometric particles
- Gels
Rheological properties of colloidal suspensions
- Shear thinning and shear thickening
- Gels
Sedimentation of colloidal particles
Sedimentation of colloidal particles is one form of self-assembly of colloidal structures. These structures can either be amorphous or crystalline. Sedimentation is achieved by preparing a dilute suspension of particles and allowing the particles to sediment under the influence of gravity. Typically, these particles are density mismatched so they are heavier than the solvent. The rate of sedimentation can be altered by varying the density of the solvent. The process of sedimentation is usually divided into four regimes: the clear liquid on top, a part where colloids are freely settling at the initial volume fraction, the "fan" in which there is a gradient in particle concentration from the initial volume fraction to the volume fraction at which particles accumulate at the bottom, and the sediment [3].
Experimental techniques used to study colloids
- Dynamic light scattering
- ConfocalMicroscopy
- Rheology
References
[1] The Structure and Rheology of Complex Fluids
[2] Vermant and Solomon, J. Phys.:Condens. Matter 17 (2005)
[3] Hoogenboom, Derks, Vergeer, and van Blaaderen, J. Chem Phys 117(24) (2002)
