Other colloids may be opaque or have a slight color. State of subdivision such that the molecules optical properties of colloids pdf polymolecular particles dispersed in a medium have at least one dimension between approximately 1 nm and 1 μm, or that in a system discontinuities are found at distances of that order. Because of the size exclusion, the colloidal particles are unable to pass through the pores of an ultrafiltration membrane with a size smaller than their own dimension. The smaller the size of the pore of the ultrafiltration membrane, the lower the concentration of the dispersed colloidal particles remaining in the ultrafiltered liquid.
The measured value of the concentration of a truly dissolved species will thus depend on the experimental conditions applied to separate it from the colloidal particles also dispersed in the liquid. The colloid particles are attracted toward water. They are also called reversible sols. These are opposite in nature to hydrophilic colloids. The colloid particles are repelled by water. They are also called irreversible sols.
In some cases, a colloid suspension can be considered a homogeneous mixture. This is because the distinction between “dissolved” and “particulate” matter can be sometimes a matter of approach, which affects whether or not it is homogeneous or heterogeneous. This refers to the impossibility of any overlap between hard particles. Colloidal particles often carry an electrical charge and therefore attract or repel each other. The charge of both the continuous and the dispersed phase, as well as the mobility of the phases are factors affecting this interaction.