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Retroreflective Microspheres
Retroreflective Microspheres incorporate a hemispherically coated aluminum shell which provides maximum retroreflection. In bulk, these metallized glass spheres appear as a grey powder. Under an optical microscope, each individual microsphere displays a partial aluminum coating. Aluminum (Al) coatings on microspheres offer advantages in developing retroreflective surfaces for high visibility materials and applications. The hemispherical (half-shell) aluminum coating creates the mechanism for retroreflectivity as the light passes through the clear half of the glass bead and “bounces” off the reflective aluminum-coated back surface, directing the light back to the source or the viewer. Additional surface coatings (silane or fluorochemical) ensure that the spheres remain on the surface of the formulation, thereby enhancing the effect of retroreflectivity.
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Density Marker Beads
Density marker beads are small colored microspheres of known mass density that are used for calibrating density gradients and determining density in gradient columns. Density gradients are often used for separations and purification of cells, viruses and sub-cellular particles. Generally a set of several density marker beads covering a range of densities is used. The gradient is calibrated with beads that float at different heights within the column. When a test sample is added to the column, it drops until the point of neutral buoyancy, and the density is determined from the calibration chart. Density gradient columns can be used to measure the density of any sample.
Fluorescent & Phoshorescent Microspheres
Polyethylene microspheres of high sphericity and narrowly graded particle size distribution are used in industrial and scientific applications for process control, diagnostics, and medical device technology. It is often advantageous to color code the particles by size to better understand which part of the process the spheres of the specific size were able to pass through, or where the contamination in the process is coming from. Polyethylene is inert to most solvents. Polyethylene microspheres are hydrophobic and need to be coated with surfactant prior to suspending in water or aqueous media.
Hollow Glass Microspheres
Hollow Glass Microspheres, also called bubbles, microbubbles, or microballoons, are typically made out of borosilicate- sodalime glass blend formulation and provide the benefits of low density, high heat and chemical resistance. The walls of glass microspheres are rigid and typically have the thickness of 10% of the diameter of the sphere. The crush strength of the hollow spheres is determined by the thickness of the walls and, as expected, the higher the sphere density the higher the crush strength. The lightweight hollow glass spheres are chemically stable, noncombustible, nonporous, and have excellent water resistance.
Amorphous Silica Microspheres & Nanospheres
Silica microspheres are inherently hydrophillic and negatively charged. These particles provide higher opacity than glass microspheres and are often used as contrast particles. Aqueous suspensions of silica microspheres rarely require the use of surfactants or stabilizers. Silane coatings enable silica microspheres to be modified to generate functional groups or alter surface properties. Additional advantage of silica microspheres is glass transition temperature of over 1000 degrees Celsius, which makes them suitable for high temperature applications. Silica microspheres and nanospheres are composed of synthetic amorphous silica made in a laboratory batch environment.
