Colloids


Also found in: Dictionary, Thesaurus, Medical.
Related to Colloids: Types of Colloids

Colloids

 

the traditional term for maximally disperse (microheterogeneous) systems. The particles in the dispersed phase in colloidal systems, colloid particles, usually have dimensions of 10-7 to 10-5 cm. In a gas or liquid, these particles freely and independently experience intense Brownian movement, uniformly occupying the entire volume of the disperse medium. Such freely disperse colloids as smoke or sols are resistant to sedimentation—that is, their particles do not precipitate. Colloid particles collide in the process of Brownian movement or upon mixing. If upon collision there is no particle enlargement resulting from conglomeration (coagulation) or fusion (coalescence), then the colloid is resistant to aggregation (for example, lyophilic and stabilized lyophobic colloids).

Colloids form upon condensation of substances in a homogeneous medium (such as supersaturated solutions, vapor, or supercooled fluids) if the nucleation centers of a new dispersed phase that have formed in the medium—that is, tiny drops or crystals—are not able to grow to dimensions exceeding 10-5–10-4 cm. Condensation is often accompanied by chemical reactions that result in the formation of poorly soluble compounds. Another means of producing colloids is dispersion, which is spontaneous in the case of lyophilic systems and forced in the case of lyophobic systems. The existence of aggregation-resistant liquid lyophobic colloids is always brought about by the presence of surface-active agents (stabilizers) in the disperse medium. These substances produce an adsorption-solvate protective layer on the particle surfaces and prevent the close approach and coagulation of particles under the action of short-range forces of molecular attraction. The close approach of particles may be impeded by the disjoining pressure of the liquid dispersion medium, which is solvated by molecules or ions of the stabilizer in the adsorption layer; by electrostatic repulsion of like-charged ions adsorbed on the particle surfaces; or by enhanced structural viscosity of the surface protective layer, the “structural-mechanical barrier.”

Nonstructured liquid colloids, or sols, have a number of properties that are intermediate between those of coarsely disperse systems and solutions. When the protective action of the stabilizer is reduced in lyophobic sols (astabilization, or destabilization, of the system), structured colloids called gels form. Solid microheterogeneous systems are also considered colloids; they consist of fine-grained bodies (such as some minerals, alloys, and crystallized glasses) in which the size of the structural elements or inclusions does not exceed the limits of colloidal dimensions.

L. A. SHITS

References in periodicals archive ?
At Knowsley, the latest enhancements include a one million Euro investment in a complete twin-screw extrusion line, which features high torque and high volume extrusion, with multiple loss-in weight feeders in addition to an underwater strand pelletising technology (particularly suited to high temperature crystalline polymers) for more uniform geometry - which Colloids states provides greater stability in the customer's process.
Through the alliance, Grace Dearborn and Allied Colloids will leverage their global resources in technologies, expertise and service to meet increasing customer needs in a more cost-effective, added-value approach.
This volume describes the role of colloids in agrochemicals, highlighting the importance of fundamental research in practical applications.
One of Colloids most recent successes has been working with a large film producer to provide a fully compostable system for use in the manufacture of mulch film.
Participants will be provided with a review of surface and colloid science and the principles of wetting/dispersing pigments as they relate to dispersion processes.
ANH is a procedure of withdrawing a unit of blood from a patient and replacing the volume with colloid solutions that replace the withdrawn volume, but do not carry oxygen.
Based on BioPAL's proprietary "Proton Cascade(TM)" technology, these colloids have a strong T1 signal leading to brightening of the administered stem cells.
By delivering our materials with particle sizes that are 80% smaller and delivered in a high concentration water based colloid, manufacturers no longer have to worry about how to disperse or suspend their nanomaterials for production.
Hercules acquired the Limeira plant as part of its bolt-on acquisition of Citrus Colloids in 1998 and now ranks as the world's largest producer of pectin, a natural food additive derived from citrus and apple peels.
The combination of the textile dyes and pigments businesses into the Colors division, the restructuring of the polymers business and the rapid integration of Allied Colloids will lead to cost savings of CHF 150 million in 1999.
TEHRAN (FNA)- Iranian researchers produced nanoparticles in forms of colloids which have very good optical properties and conserve their stability for a long time.
Objective: "Recent progress in colloid physics has led to fundamental understanding of so-called `patchy~ colloids which undergo highly directional interactions with well-defined spots on their surface.