Colloid
This field of study began in 1845 by Francesco Selmi,[4][5][6][7] who called them pseudosolutions, and expanded by Michael Faraday[8] and Thomas Graham, who coined the term colloid in 1861.
[10][11] Colloidal: State of subdivision such that the molecules or 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.
Some hydrocolloids like starch and casein are useful foods as well as rheology modifiers, others have limited nutritive value, usually providing a source of fiber.
Because colloid is multiple phases, it has very different properties compared to fully mixed, continuous solution.
Therefore, if the colloidal particles are denser than the medium of suspension, they will sediment (fall to the bottom), or if they are less dense, they will cream (float to the top).
Larger particles also have a greater tendency to sediment because they have smaller Brownian motion to counteract this movement.
These include electrostatic interactions and van der Waals forces, because they both contribute to the overall free energy of the system.
If the interaction energy is greater than kT, the attractive forces will prevail, and the colloidal particles will begin to clump together.
A method called gel network stabilization represents the principal way to produce colloids stable to both aggregation and sedimentation.
The most widely used technique to monitor the dispersion state of a product, and to identify and quantify destabilization phenomena, is multiple light scattering coupled with vertical scanning.
[28][29][30][31] This method, known as turbidimetry, is based on measuring the fraction of light that, after being sent through the sample, it backscattered by the colloidal particles.
The backscattering intensity is directly proportional to the average particle size and volume fraction of the dispersed phase.
Dynamic light scattering can be used to detect the size of a colloidal particle by measuring how fast they diffuse.
If the apparent size of the particles increases due to them clumping together via aggregation, it will result in slower Brownian motion.
Temperature affects not only viscosity, but also interfacial tension in the case of non-ionic surfactants or more generally interactions forces inside the system.
Storing a dispersion at high temperatures enables to simulate real life conditions for a product (e.g. tube of sunscreen cream in a car in the summer), but also to accelerate destabilisation processes up to 200 times.
[38] One of the finest natural examples of this ordering phenomenon can be found in precious opal, in which brilliant regions of pure spectral color result from close-packed domains of amorphous colloidal spheres of silicon dioxide (or silica, SiO2).
[41][42] Thus, it has been known for many years that, due to repulsive Coulombic interactions, electrically charged macromolecules in an aqueous environment can exhibit long-range crystal-like correlations with interparticle separation distances, often being considerably greater than the individual particle diameter.
In all of these cases in nature, the same brilliant iridescence (or play of colors) can be attributed to the diffraction and constructive interference of visible lightwaves that satisfy Bragg’s law, in a matter analogous to the scattering of X-rays in crystalline solids.
The large number of experiments exploring the physics and chemistry of these so-called "colloidal crystals" has emerged as a result of the relatively simple methods that have evolved in the last 20 years for preparing synthetic monodisperse colloids (both polymer and mineral) and, through various mechanisms, implementing and preserving their long-range order formation.
The term biomolecular condensate has been used to refer to clusters of macromolecules that arise via liquid-liquid or liquid-solid phase separation within cells.
Macromolecular crowding strongly enhances colloidal phase separation and formation of biomolecular condensates.
