Colloids

By the way, what are colloids and what are they for?
Colloids are small particles of any nature substantially larger than ordinary molecules but too small to be visible to the unaided eye. Broadly, colloids are substances, including thin films and fibres, having at least one dimension in this general size range of about 10−7 to 10−3 cm is a colloid. Colloidal systems may exist as dispersions of one substance in another, for example, smoke particles in air, or as single materials, such as rubber or the membrane of a biological cell.
The scientific study of colloids dates from the early 19th century. Among the first notable investigations was that of the British botanist Robert Brown. During the late 1820s Brown discovered, with the aid of a microscope, that minute particles suspended in a liquid are in continual, random motion. This phenomenon, which was later designated Brownian motion, was found to result from the irregular bombardment of colloidal particles by the molecules of the surrounding fluid. Francesco Selmi, an Italian chemist, published the first systematic study of inorganic colloids. Selmi demonstrated that salts would coagulate such colloidal materials as silver chloride and Prussian blue and that they differed in their precipitating power. The Scottish chemist Thomas Graham, who is generally regarded as the founder of modern colloid science, delineated the colloidal state and its distinguishing properties. In several works published during the 1860s, Graham observed that low diffusivity, the absence of crystallinity, and the lack of ordinary chemical relations were some of the most salient characteristics of colloids and that they resulted from the large size of the constituent particles.
The early years of the 20th century witnessed various key developments in physics and chemistry, a number of which bore directly on colloids. These included advances in the knowledge of the electronic structure of atoms, in the concepts of molecular size and shape, and in insights into the nature of solutions. Moreover, efficient methods for studying the size and configuration of colloidal particles were developed —for example, ultracentrifugal analysis, electrophoresis, diffusion, calorimetry and the scattering of visible light, X-rays and neutron. More recently, biological and industrial research on colloidal systems has yielded much information on dyes, detergents, lipids, polymers, nucleic acid, proteins, and other substances important to everyday life.

Source: Britannica Academic Edition: Colloids.

Examples of colloids: milk is a souce of colloids. Nanocapsules made of polyelectrolyte multilayers (Figure below).


 Kapseln2 The Two Classifications of a Colloid thumbnail                    Milk                                                     Nanocapsules made of polyelectrolyte multilayers                                                                                  Fog

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