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Colloidal gold is a sol or colloidal suspension of nanoparticles of gold in a fluid, usually water. [1] The colloid is coloured usually either wine red (for spherical particles less than 100 nm ) or blue-purple (for larger spherical particles or nanorods ). [ 2 ]
Nanoparticles can also be functionalized with polymers or oligomers to sterically stabilize the nanoparticles by providing a protective layer that prevents the nanoparticles from interacting with each other. [8] Alloys of two metals, called bimetallic nanoparticles, are used to create synergistic effects on catalysis between the two metals. [9]
Nanoparticles are distinguished from microparticles (1-1000 μm), "fine particles" (sized between 100 and 2500 nm), and "coarse particles" (ranging from 2500 to 10,000 nm), because their smaller size drives very different physical or chemical properties, like colloidal properties and ultrafast optical effects [3] or electric properties.
The decrease in total free energy for microscopic particles is much larger than that of thermal energy, resulting in an effective confinement of large colloids to the interface. Nanoparticles are restricted to the interface by an energy reduction comparable to thermal energy. Thus, nanoparticles are easily displaced from the interface.
A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, [1] while others extend the definition to include substances like aerosols and gels.
Particle agglomeration refers to the formation of assemblages in a suspension and represents a mechanism leading to the functional destabilization of colloidal systems. . During this process, particles dispersed in the liquid phase stick to each other, and spontaneously form irregular particle assemblages, flocs, or agglom
The physical processes responsible for upconversion in nanoparticles are the same as those in bulk crystals on the microscopic level, although total efficiency and other ensemble effects will have unique considerations in the nanoparticle case. The processes contributing to upconversion may be grouped according to the number of ions involved.
A nanofluid is a fluid containing nanometer-sized particles, called nanoparticles. These fluids are engineered colloidal suspensions of nanoparticles in a base fluid. [1] [2] The nanoparticles used in nanofluids are typically made of metals, oxides, carbides, or carbon nanotubes. Common base fluids include water, ethylene glycol, [3] and oil.