colloid
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What is a colloid in physics?
In physics, a colloid is any substance with particles larger than atoms or ordinary molecules but still too small to be seen without aid, typically ranging from 10^-7 to 10^-3 cm. These systems can be dispersions of one substance within another, like smoke in air, or exist as single materials such as rubber. Colloids are classified as either reversible, where original components can be reproduced, or irreversible, including sols (dilute suspensions), pastes, emulsions, foams, and certain gels.
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How is a colloid different from a solution or a suspension?
Colloids, solutions, and suspensions differ in particle size and stability. A colloid consists of particles substantially larger than atoms or ordinary molecules, ranging from 10^-7 to 10^-3 cm. Solutions are more stable and closely resemble true solutions, while suspensions are irreversible systems with particles that settle over time. The Tyndall effect, the scattering of light by suspended particles, is exhibited by colloids and suspensions but not by solutions.
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What are some common examples of colloids?
Colloids are substances with particles larger than atoms/molecules but too small to see with the naked eye, ranging from 10^-7 to 10^-3 cm. They can be dispersions like smoke in air or single materials like rubber.
Examples of irreversible systems include sols, pastes, emulsions, foams, and certain types of gels.
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How do the particles in a colloid behave differently from those in a solution?
In a solution, the mixture is homogenous, meaning the substances are uniformly distributed and can vary continuously up to the limit of solubility. In contrast, a colloid consists of particles substantially larger than atoms or ordinary molecules, but still too small to be seen unaided.
The movement of colloidally suspended particles is known as Brownian motion, resulting from irregular bombardment by the molecules of the surrounding fluid.
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What is the Tyndall effect and how does it relate to colloids?
The Tyndall effect is the scattering of a beam of light by small particles in a medium, such as smoke or dust, making the light beam visible. It occurs when particles are roughly the same size as the wavelength of light.
A colloid is any substance with particles larger than atoms or ordinary molecules but too small to be seen with the naked eye. Colloidal systems can be dispersions of one substance in another, like smoke particles in the air. The Tyndall effect is a characteristic property of colloids, as the particles in a colloidal solution are large enough to scatter light.
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How do colloids play a role in everyday products and technologies?
Colloids are substances with particles larger than atoms or molecules but too small to be seen without aid, typically ranging from 10^-7 to 10^-3 cm. They appear in many forms, such as smoke in the air or as single materials like rubber.
Colloids are used and occur in nature, living organisms, and industrial processes. For example, dispersing agents containing colloids ensure that pigment particles act independently in coating films during manufacturing, storage, application, and film formation.
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colloid, any substance consisting of particles substantially larger than atoms or ordinary molecules but too small to be visible to the unaided eye; more broadly, any substance, including thin films and fibres, having at least one dimension in this general size range, which encompasses about 10−7 to 10−3 cm. 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.
Colloids are generally classified into two systems, reversible and irreversible. In a reversible system the products of a physical or chemical reaction may be induced to interact so as to reproduce the original components. In a system of this kind, the colloidal material may have a high molecular weight, with single molecules of colloidal size, as in polymers, polyelectrolytes, and proteins, or substances with small molecular weights may associate spontaneously to form particles (e.g., micelles, microemulsion droplets, and liposomes) of colloidal size, as in soaps, detergents, some dyes, and aqueous mixtures of lipids. An irreversible system is one in which the products of a reaction are so stable or are removed so effectively from the system that its original components cannot be reproduced. Examples of irreversible systems include sols (dilute suspensions), pastes (concentrated suspensions), emulsions, foams, and certain varieties of gels. The size of the particles of these colloids is greatly dependent on the method of preparation employed.
All colloidal systems can be either generated or eliminated by nature as well as by industrial and technological processes. The colloids prepared in living organisms by biological processes are vital to the existence of the organism. Those produced with inorganic compounds in Earth and its waters and atmosphere are also of crucial importance to the well-being of life-forms.
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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 soon developed—for example, ultracentrifugal analysis, electrophoresis, diffusion, and the scattering of visible light and X-rays. More recently, biological and industrial research on colloidal systems has yielded much information on dyes, detergents, polymers, proteins, and other substances important to everyday life.