Custom Janus Particles, Microspheres, Microbeads – Bichromal Particles

Custom Janus Particles Manufacturing

Bichromal (half-white half-black or any other color) Microspheres

What are Custom Janus Particles?

Janus particle is anisotropic and refers to a particle, typically of spherical shape, with two hemispheres which may vary in color, optical properties, surface tension, electrostatic charge, magnetic response, conductivity, fluorescence, reflectivity and more.

Custom Janus Particles Manufacturing

Cospheric LLC uses a patented process to offer a unique capability of manufacturing custom Janus particles with partial coatings and dual functionality.

Currently half-shell or hemispherical coatings can be applied to any sphere (glass, polymer, ceramic) in sizes 45 micron in diameter and higher. For best uniformity of coating, the core material needs to be available in spherical form and with high particle size uniformity (high monodispersity).

Options for Custom Janus Particles Coating

Custom Janus Particles - Half-coated glass microspheres - Partial coating on glass particles

Half-coated glass microspheres – Partial coating on glass particles

Coatings can be customized for any color and coverage of between 20% to 60% of the sphere. Each coating is custom formulated for color, charge, magnetic, electric, and surface properties, and solvent resistance per customers’ needs.

Hemispherical coatings of less than 1 micron with tolerances as low as 0.25 micron have been routinely demonstrated. Color combinations are truly unlimited. White, black, silver, blue, green, red, yellow, brown, purple as well as transparent microspheres have been made. Sphericity of greater than 90% and custom particle size ranges are offered.

Cospheric has successfully produced custom Janus particles from solid and hollow glass microspheres, including soda-lime, borosilicate, and barium titanate glass .

Applications of Custom Janus Particles

Custom Janus Particles

Red Coating on Metal Surface Microspheres

Rotation in Electromagnetic Field

Optically anisotropic spheres and custom janus particles with magnetic half-shells have been originally developed for applications in electronic displays, such as e-paper due to their ability to orient themselves in response to electromagnetic field and show a visual response. This is achieved by making spheres both bipolar and bichromal, with dipole precisely aligned with two differently colored hemispheres.

As the spheres align themselves, the viewer will observe the color of one hemisphere, while the other hemisphere will be hidden from view, providing an obvious strong visible indication of the presence of the field or other stimuli. In alternating electromagnetic field, these janus microspheres have been proven to spin at hundreds of times per second.

Visual Indication of Rotation

Due to the anisotropic nature of the particles, they provide additional benefits in visualizing the movement of the particles in a fluid. Specifically, the bichromality of the sphere provides a contrast and a reference point in observing not only the translational but also the rotational movement of the particles in the fluid stream.

Janus particles are now widely used in numerous applications in diagnostics, medical research, microscopy and biotechnology, as well as electronics.


This video demonstrates the microstructure consisting of one channel filled with dielectric fluid and placed between two electrodes under a microscope. A janus sphere moves in response to direction and strength of electric field, which is observed and recorded under the microscope. Polarity of the sphere is immediately obvious by direction of its movement. Electrostatic charge is calculated from strength of electric field, dielectric constant of surrounding materials, and sphere velocity.

Every application is unique and requires different sizes, colors, densities, fluorescent properties, environmental stability, or surface properties.