Everything about Microspheres
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  • Bichromal Janus Particles, Microspheres, Microbeads – Stock selection or Custom-made

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

    Bichromal (half-white half-black or any other color) Microspheres, Janus Particles. In this picture - Paramagnetic black microspheres with partial white coating - Magnification 40x.

    Cospheric offers unique capability to manufacture Janus microspheres and microparticles with partial coatings and dual functionality. Currently half-shell or hemispherical coatings can be applied to any sphere (glass, polymer, ceramic) in sizes 45micron in diameter and higher. 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.

    Half-coated glass microspheres - Partial coating on glass particles

    Half-coated glass microspheres - Partial coating on glass particles. In this picture - Soda lime glass microspheres with partial red coating - Magnification 40x.

    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.

    We have successfully coated solid and hollow glass microsphere, including soda-lime, borosilicate, and barium titanate glass microspheres. We have also coated on silver.

    Half-coated Microspheres

    Half-coated Microspheres

    Optically anisotropic spheres and janus particles with magnetic half-shells have been originally developed for applications in electronic displays, such as e-paper, but are now widely used in numerous applications in diagnostics, medical research, microscopy and biotechnology, as well as electronics, 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 microspheres have been proven to spin at hundreds of times per second.

  • Negatively-charged Yellow Microparticles – Back in Stock

    Highly Negative Charged Microspheres - Polyethylene, Selection of Sizes 5 to 500um

    Highly Negative Charged Microspheres - Polyethylene, Selection of Sizes 5 to 500um, 1.0g/cc

    Cospheric’s neutrally-buoyant highly charged yellow microspheres have a strong negative charge and are used by scientists in medical technology, biotechnology, applied physics and research. Precise particles with known density of 1.0g/cc that behave in a known way are useful as a model particles in simulation experiments.  Particles in a range of diameters from 5micron to 500micron(0.5mm) are currently back in stock.

    Bright yellow polymer microparticles of high sphericity are spherical polyethylene beads that are specifically designed with density ~1.0g/cc for suspension in fresh water,  serving as seed or tracer particles and enabling flow visualization and Particle Image Velocimetry PIV analysis of fluid flow in a device. 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. Microspheres are supplied in dry powder form and are color stable in solution. No solvents are used in the manufacturing process. Polyethylene is inert to most solvents.

    Cospheric also offers unique capability to manufacture Bichromal janus microspheres and microparticles with partial coatings and potentially dual functionality. Currently half-shell or hemispherical coatings can be applied to any sphere (glass, polymer, ceramic) in sizes 45micron in diameter and higher. 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.

    It would be interesting to combine these highly charged yellow microspheres with a partial paramagnetic black coating and investigate the behavior of these spheres in electromagnetic field.

  • PIV Seeding – Microparticle Recommendations

    Flow Visualization can best be accomplished with colored or fluorescent tracing particles of the same density as the fluid being studied.Particle image velocimetry (PIV) is the term used for imaging the fluid flow using colored tracer particles.  Through high speed particle imaging the velocity of the particles can be obtained and mapped.

    Photo Courtesy of Wiki-CommonsFor PIV experiments in water there are a wide variety of 1g/ml microspheres available as seeding particles, Cospheric offers polyethylene seeding particles in a variety of colors (fluorescent and non-fluorescent) and sizes from 10-20um, on up to 1mm.

    Particle size selection is important to ensure that observations can be accurately made.  For imaging systems without any magnification or unaided human observation it is recommended to use micro-spheres that are larger than 200um.   Human eyes can resolve features down to about 75um, at 200um+ the particles will be large enough to be discernible.

    Correctly seeding the system is also important.  For most applications loadings of 0.1-0.3% are sufficient.  This is the equivalent of about 1 gram of particles per gallon of fluid in systems of 10-50 gallons (40-200 liters) .  Exact loading levels will depend on the individual experiment requirements.

    For aqueous systems, polyethylene micro-particles will require a surfactant to wet properly.  For general flow studies pre-wetting the PE microspheres with Simple Green concentrated cleaner works well.  For biological systems a bio-compatable surfactant such as Tween 20 or Tween 80 is recommended.

    Seeding particle color selection is important to ensure that sufficient contrast is achieved during testing.  Very bright fluorescent micro-particles are available in densities of 1g/cc  these offer not only bright testing under daylight conditions, but also the option of illumination with lasers or uv lights for increased system contrast.

    The recommended PIV seeding particles are available from Cospheric.

    For green lasers (530nm)  we recommend UVPMS-BR
    For dark backgrounds: UVPMS-BY, UVPMS-BG, BLPMS, ORGPMS, BSPMS, or WPMS
    For light backgrounds: GRYPMS, VIOPMS, UVPMS-BR, UVPMS-BO

  • Density Marker Beads

    Cospheric recently added density marker beads in aqueous solution to their range of products.   Available in densities from 1.02 g/ml to 1.13 g/ml.

    The beads come in a variety of colors and densities and ship within one business day.   These beads are small microspheres of very specific particle density that are used to visualize density gradients.  Commonly used in Percoll gradients these beads offer a fast visual indicator for scientists.

    Density Markers Beads are:
    DMB-FGRN-1.02 Fluorescent Green at 1.02g/cc
    DMB-FORG-1.04 Fluorescent Orange at 1.04g/cc
    DMB-RBLU-1.08 Blue at 1.08g/cc
    DMB-FRED-1.09 Fluorescent Red at 1.09g/cc
    DMB-FBLU-1.13 Fluorescent Blue at 1.13g/cc

    Cospheric Density Marker Beads are provided at a 20% concentration in an aqueous solution in 2.5ml vials. Unlike density marker kits which used to be manufactured by GE Healthcare and have been discontinued, the Cospheric’s colored microspheres are ready for use right out of the vial, don’t need to be swollen, will work with any media, do not expire, and do not change density over time.

    Resources on Creating Density Gradients:

    Biotechnology: Theory and Techniques, Volume I (Jones and Bartlett Series in Biology) by Jack Chirikjian and Chirikjian (Jan 1, 1995)
    Pages 45-50 on Density Gradient Centrifugation.

  • Calculating microspheres per gram

    During scientific experiment design and analysis it is common to need to know the number of spheres per gram of dry material.  We have put together the table below to help speed up the process.

    If you have material of a density different from those listed in the table, divide the number of spheres per gram in the density ~1.0 g/cc column by the true particle density of your material to get an estimate of the number of spheres per gram.

    Product Size Polyethylene
    Density ~1.0 (g/cc)
    Soda Lime Glass
    Density ~2.5 (g/cc)
    Lower (um) Upper (um) Spheres per Gram Spheres Per Gram
    20 27 147,162,715 58,630,564
    27 32 74,393,558 29,638,868
    32 45 33,467,185 13,333,540
    45 53 16,233,536 6,467,544
    53 63 9,788,528 3,899,812
    63 75 5,813,720 2,316,223
    75 90 3,401,258 1,355,083
    90 106 2,029,192 808,443
    106 125 1,239,525 493,835
    125 150 734,672 292,698
    150 180 425,157 169,385
    180 212 253,649 101,055
    212 250 154,941 61,729
    250 300 91,834 36,587
    300 355 54,371 21,662
    355 425 32,196 12,827
    425 500 19,305 7,691
    500 600 11,479 4,573
    600 710 6,796 2,708
    710 850 4,025 1,603
    850 1000 2,413 961
    1180 1400 890 354
    1400 1700 513 204
    1700 2000 302 120
    2000 2360 184 73
    2360 2800 111 44
    2800 3350 66 26

    Note: This table assumes the mean diameter is half way between the upper and lower size.