Everything about Microspheres
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  • Particle Image Velocimetry and Tracer Particle Visibility

    Particle Image Velocimetry (PIV) expresses a vast field with varying techniques and data acquisition methods. However, the main goal is providing an optical method of flow visualization. The exact information obtained depends on which method is used, with new algorithms and approaches being discovered constantly.

    There are generally two ways data is obtained PIV and Particle Tracking Velocimetry (PTV) which can then be broken down into many other methods based on how exactly the data was obtained and the processing done to said data. PIV measures the velocity field of a fluid based on a Eulerian method where stated locations are observed over time to determine the flow. While PTV tracks the movement of singular particles over time, a Lagrangian approach. This provides a plot of the particles movement and by relation information about the fluid flow. They each use the same tracer particles however they look at them in different senses. If logs in a river are representations of our seed particles then PIV looks at the river and sees the logs moving through it determining how the river flows based on this information. While PTV watches the movement of individual logs to obtain similar information. Which leads to the assumption that tracking particles must be easily visualized.

    Visibility being an important aspect of tracer particles is a given but how those particles are visible is where differences can come about. Tracers can be visible if they block light from reaching the visualization mechanism (eye, camera, etc.) essentially being visible as a shadow. This method is known as backlit shadowgraphy where the flow is placed between an illumination source and a camera allowing for the absence of light (shadow) caused by tracer particles to be tracked.

    Reflective Silver Coated Hollow Glass

    Another approach to assuring particle visibility is using highly reflective spheres that will reflect in the direction of your camera set-up allowing them to appear as dots of high intensity light, of the illumination source used. Lasers are most commonly used as the illumination source for this form of particle visibility. As lasers have high power, high collimation, and a relatively tight emission bandwidth. Recently LED’s are also being used as the illumination source for reflectivity visualization methods as well as backlit shadowgraphy. LED’s may not currently have the power or collimation abilities of lasers but are consistently growing in power. LED’s also have a very limited emission spectrum as well as their ease of use and low cost compared to lasers.

    Fluorescent Tracer Particles

    Finally, some tracer particles can emit their own light which allows them to be an easily distinguishable wavelength from the illumination source which can often flood the visualization area. One of the most common examples of this would be fluorescent spheres. Which when excited by the illumination source will emit a different wavelength of light. This allows the wavelength of light used as your illumination source to be filtered out providing an image with just the light from tracers. Phosphorescent spheres fall into a category similar to fluorescent particles as phosphorescence emits light similarly to fluorescence. However, phosphorescence emits over longer periods of time. Another significant difference of phosphorescent materials is their unique temperature variance which allows for them to be used as a form of temperature sensor.

    With both PIV and PTV having their strengths and weaknesses there is no clear superior method. However, with advances in technology PTV is becoming more feasible and thus may overtake PIV methods due to its ability to provide greater data varieties. Visibility options also have their unique aspects that ensure their necessity in specific cases. Shadowgraphy is gaining traction in areas due to its reduced cost requirement and ease of use. While, fluorescent tracers remain as an ideal option for applications where shadowgraphy can not quite meet the necessary criteria.

  • Fluorescent Glass Microspheres

    Fluorescent Red Coated Soda Lime Glass MicrospheresSolid glass microspheres hemispherically coated with fluorescent coatings,  a fluorescent coating is precisely applied to half of the core sphere,  making the glass spheres appear colorful and fluorescent at daylight and exhibit bright fluorescent response under UV light.  Fluorescent coatings are available in seven standard colors, with three options for glass cores available for customers who require a fluorescent tracer of a specific emission spectra and density.  Fluorescent coatings can also be applied to other microsphere cores on special request, exact size range options vary by material.  For PIV applications that typically use green lasers (530nm) as excitation sources, we recommend utilizing our fluorescent red coating in conjunction with a 570-580nm high pass filter so only the fluorescent particles will be visible during imaging.

    Three standard core densities are:

    Borosilicate Glass Core – Density ~2.2g/cc
    Soda Lime Glass Core – Density ~2.5g/cc
    Barium Titanate Glass Core – Density ~4.5g/cc

    Seven standard fluorescent color coating options on glass with broad spectrum responses:

    Fluorescent Blue Glass (445nm peak emission) at 407nm excitation
    Fluorescent Green Glass (515nm peak emission) at 414nm excitation
    Fluorescent Yellow Glass (525nm peak emission) at 485nm excitation
    Fluorescent Orange-Yellow Glass (594nm peak emission) at 460nm excitation
    Fluorescent Orange Glass (606nm peak emission) at 577nm excitation
    Fluorescent Red Glass (607nm peak emission) at 585nm excitation
    Fluorescent Violet Glass (636nm peak emission) at 584nm excitation

  • Janus (Micro) Particles – From 45um to 1mm+

    Black and White Jansum particles (1mm diameter)Cospheric offers unique capability to manufacture Janus microspheres and micro-particles 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 on up to 1mm and higher. 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 in both fluorescent and non-fluorescent have been made. Sphericity of greater than 90% and custom particle size ranges are offered.

    Fluorescent Red on Silver Coated Glass 50um

    Fluorescent Red on Silver Coated Glass 50um

    The custom coating capability offers customers the ability to create fluorescent glass micro-spheres of the specific size and emission/excitation needed. As the micro spheres and coating are solvent resistant

    they work ideally as fluorescent tracers or highly visible targets. We can overcoat clear glass or silver coated glass for the effect needed.

    For those needing very large Spheres Cospheric can coat spheres of 1mm and larger.

    Janus microparticles are now available as either dry powder or in a diellectric oil.

  • Density Marker Beads Kit Now Available from Cospheric LLC

    Santa Barbara, CA, December 6, 2013 – Cospheric LLC, a microsphere manufacturing and distributing company, expanded their line of density marker beads which now offers six different densities including 1.02 g/cc (fluorescent green), 1.04g/cc (fluorescent orange), 1.06g/cc (fluorescent violet), 1.08 g/cc (dark blue), 1.09 g/cc (fluorescent red), and 1.13g/cc (fluorescent blue). Cospheric Density Marker Beads are now provided at a 20% concentration in an aqueous solution in 2.5ml vials, which makes the spheres easier to work with for the customers. Microspheres of different densities can be purchased individually or as a density marker beads kit.

    Microspheres of accurately known mass density are generally used as an external marker to facilitate the monitoring of the density gradient shape and range. Density marker beads enable excellent stratification and bright coloration for high visibility with the unaided eye. Historically density calibration beads in the size ranges of 212-250um or 250-300um are used. Unlike the discontinued density marker kits which used to be manufactured by GE Healthcare and sold by Sigma-Aldrich, Cospheric’s DMB density marker beads are ready for use right out of the vial, don’t need to be swollen, do not expire, and do not change density over time. Cospheric’s DMB microspheres will create Percoll gradients but will also work with any other centrifugation media. The colored microbeads may be recovered and stored for future use.

    The density marker beads provide a rapid, simple, and accurate method for measuring the density. Generally a set of several such beads, covering a range of densities, is used. In the biomedical industry researchers are sometimes looking for cells having targeted specific gravities. In order to locate these cells in test tubes it is useful to have colored marker beads which will show where the delineation between specific densities occurs. Density marker beads are also used for calibrating particles in other industries, such as agriculture, microbiology and others.

    About Cospheric LLC:
    Cospheric LLC develops, manufactures, and distributes high-quality microspheres in sizes from 10 micron to 1000 micron (1mm). Cospheric specializes in polyethylene microspheres and carries a large stock of polyethylene microspheres in many colors, fluorescent, phosphorescent, neutrally-buoyant, and paramagnetic properties. Cospheric also offers a selection of soda-lime and borosilicate glass, silica, metal-coated, and titanium dioxide-coated spheres, some available in spacer grades with very tight particle size distributions. Cospheric LLC welcomes inquiries for custom manufacturing of microspheres tuned to each customer’s unique specifications. Cospheric is an eco-friendly company that uses only recyclable materials and no solvents in the manufacturing process. For more information, pricing and sample requests visit www.cospheric.com.

    About Microspheres:
    Microspheres or beads are spherical particles usually between 1 to 1000 microns in diameter and are manufactured for wide variety of uses in research, medicine, consumer goods, paints and coatings, adhesives, personal care, household products, cosmetics, skin care, and other industries.

  • 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.