Everything about Microspheres
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  • Suspension of Hydrophobic Particles in Aqueous Solution – Density Gradients

    Fluid Flow Visualization using Microspheres, Spherical Particles

    Fluorescent polyethylene microspheres for flow visualization in aqueous systems. Suspension of beads in aqueous solutions.

    Background Information

    Many materials are hydrophobic (water-fearing) in nature. Due to their non-polar chemical structure, hydrophobic particles want to minimize contact with polar (water) molecules and, as a result, tend to aggregate on the surface of the water and resist going into suspension. This presents a challenge to scientists and engineers who would like to be able to work with hydrophobic particles suspended in aqueous solution.

    Examples of the applications are using fluorescent polyethylene microspheres for flow visualization in aqueous systems, creating density gradients, filtration and contamination control studies.

    Fortunately, there is a simple way to overcome the hydrophobic effect. It is called a surfactant, a detergent, or simply “soap.” Surfactant is a magical molecule that has both hydrophobic and hydrophilic properties, which coats the particles and helps them mix into water. The same mechanism applies when we use soap to wash greasy dishes or stained clothes.

    Selection of the surfactant depends purely on your process and product requirements. Dishwashing liquid works great, so does Simple Green. For scientists working on biological applications we recommend the use of Tween surfactants. Tween is the commercial name for Polysorbate non-ionic surfactants, which are stable, nontoxic, and often used in pharmacological, cosmetic, and food applications. Non-ionic detergents are considered to be “mild” detergents because they are less likely than ionic detergents to denature proteins. By not separating protein-protein bonds, non-ionic detergents allow the protein to retain its native structure and functionality.

    Tween 20 and Tween 80 are frequently used. Both surfactants are yellowish, water-soluble viscous liquids. Primary difference between the two is viscosity. Tween 20 has lower viscosity and is easier to work with.

    Suspension Process

    There are many ways to suspend the particles (e.g. put a few drops of dish detergent into water and shake with the particles).

    The process below is specific for using the minimum amount of Tween for biologically sensitive applications.


    • Gloves and eye protection are to be worn at all times during solution preparation and use.
    • Care should be taken when handling hot objects/liquids and immersion blender.
    • Centrifuge should be properly balanced and allowed to come to a full stop before opening.


    • We recommend using distilled water to minimize impurities.
    • We recommend boiling the water to sterilize and to make it easier to disperse a small amount of surfactant uniformly. This also increases shelf-life of prepared solutions and suspensions.
    • We use an immersion blender to disperse the surfactant in water quickly and effectively.


    Preparing Tween Solution:
    • Fill a heatproof container with distilled water.
    • Ensure the water level is high enough to cover the immersion blender.
    • Heat water to boiling and leave boiling for 5 minutes.
    • Weigh out 0.1g of Tween per 100ml of water used (creating 0.1% solution).
    • Slowly add Tween to boiled water while mixing with immersion mixer (~30 seconds).
    • Some bubbles will form during mixing.
    • Bubbles will dissipate on cooling and solution will appear clear.
    Suspending particles in Tween solution.
    • Place the desired amount of particles into a container.
    • Dispense prepared Tween solution on top of particles.
    • We recommend at least five times greater volume of solution to the volume of particles.
    • Cover tightly and place containers into a centrifuge.
    • Centrifuge on highest setting for at least 5 minutes.
    • If some particles are still floating on the surface of water, more centrifuging may be necessary.
    • A small quantity of particles may accumulate on the top surface and not enter solution despite additional centrifugation. Typically, these particles will go into suspension over time (hours).
    Other Considerations
    • A greater length of centrifuging or larger volume of Tween solution may be necessary to suspend certain materials and particle sizes.
    • As a 0.1% Tween solution is sufficient for most applications, concentration levels could be raised to support particles that are more resistant to entering solution.
    • Once the particles are suspended, solution can may be diluted further to increase the volume.
    • Particles can be recycled and reused as necessary. The suspension might need to be repeated.
    • If no centrifuge is available, it is possible to shake the container by hand (up and down, upside down) to achieve the same result.

    Here is an example of Cospheric fluorescent beads 150 to 180micron in diameter being dispersed in a pilot bioreactor.

    About Cospheric

    Our extensive product line consists of more than two thousand unique spherical microparticle and nanoparticle products, all developed based on customer demand. We work with each individual customer to find a creative solution for their unique needs ­– tight particle size ranges, wide selection of colors, densities, properties and formulations. We are the sole global supplier for the majority of our products. We developed a disruptive technology which is redefining the microsphere market and creating a new category of precision spherical particles. Our research department is always excited to tackle new challenging projects. Explore at www.Cospheric.com.

    Other Information

    The information contained in this document is correct to the best of our knowledge at the date of publication. It should not be viewed as all inclusive, but as a guide only. It does not represent any guarantee of the properties of the product. Cospheric LLC shall not be held liable for any damage resulting from handling of or from contact with the above product. For these reasons, it is important that product users carry out their own tests to satisfy themselves as to the suitability of the safety precautions for their own intended applications.

  • Particle Image Velocimetry – Intro to Tracer Particle Parameters

    PIV is a vast field with varying techniques and differing areas of research. Techniques vary from 2D PIV, only viewing velocity in a plane of the fluid system, to high speed TOMO PIV which views a 3D area of fluid and can be time resolved allowing for acceleration data to also be obtained. Another difference is that the size of liquid PIV set-ups can range from micron sized micro channels to multi thousand-gallon tanks. While the area being imaged may not vary as much as the

    Barium Sulfate Tracer for X-ray imaging

    systems themselves, it can still differ from units of micro meters to potentially meters. With viewing windows growing as new advancements in science and technology progress, the need for seed particles to match them will grow. One example of this is the rise of helium filled soap bubble seeders that provide an easily visualized 300um bubble for air systems allowing for large areas to be seeded and visualized. Or barium sulfate polyethylene microspheres which are useful due to being a radio contrast agent allowing for visualization via x-ray imaging.

    Therefore, a one solution fits all approach is not feasible when it comes to seed particle selection. As each experiment will have differing size, density, light intensity/visibility, particle material, and seeding concentration needs based on desired results.

  • 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.

  • Glass Microspheres Used in Studying Self-Cleaning Gecko-Inspired Adhesives

    Image of Self-cleaning Adhesive of Gecko's Toes

    Image of Self-cleaning Adhesive of Gecko's Toes Source: wikipedia.com

    Researchers from Carnegie Melon University and Karlsruhe Institute of Technology have recently published an article in Journal of the Royal Society titled Staying Sticky: Contact Self-Cleaning of Gecko-Inspired Adhesives that presents the first gecko-inspired adhesive that matches both the attachment and self-cleaning properties of gecko’s foot on a smooth surface.

    Using glass microspheres to simulate contamination the scientists created a synthetic gecko adhesive that could self-clean and recover lost adhesion. Real world applications of self-cleaning adhesives are reusable adhesive tapes, clothing, medical adhesives (bandages) and pick-and-place robots, among others.

    Everyday challenge with traditional adhesives is that they loose their stickiness once contaminated. Geckos have been intriguing researchers for decades because of their unique and striking capability to maintain the stickiness of their toes through contact self-cleaning. They can travel up the walls and ceilings in a wide variety of “dirty” settings retaining adhesion.

    Upon experimentation, scientists discovered that the critical variable is the relative size of microfibers that make up the adhesive compared to the diameter of contaminant particles. Glass microspheres were used in diameters from 3 to 215microns. Glass microspheres were packed in air and used as supplied. Contamination of the samples was achieved by brining each sample in contact with a monolayer of glass microspheres with specific speeds under predetermined compressive loads. The cleaning process involved a load-drag-unload procedure.

    Best self-cleaning results were obtained with the largest contaminants (glass microspheres), with the size of the adhesive fiber much smaller than the contaminating particle. This information is important to know when designing self-cleaning adhesives—make the adhesive fibers much smaller for improved adhesion recovery. This cleaning mechanism requires unloading particles by dragging. The other extreme of contaminating microspheres being much smaller than the adhesive fibers has advantages in some situations, even though it works by a different mechanism. Smaller microspheres tended to become embedded into the adhesive material. Particle embedding is a temporary cleaning process but might be sufficient in some applications.

  • Black Paramagnetic Spheres and Micropsheres 10micron to 1.4mm

    Black polyethylene paramagnetic microspheres are now available in wide selection of particle sizes ranging from 10 micron to 1.4 millimeters. The particles are supplied in dry powder form. No solvents are used in the manufacturing process. Black paramagnetic polymer microspheres have a strong response to magnetic fields and can be manipulated with a magnet. Highly opaque particles with maximum hiding power.

    Paramagnetic microspheres have the ability to increase in magnetization with an applied magnetic field and loose their magnetism when the field is removed. Neither hysteresis nor residual magnetization is observed and that provides the end use two very practical advantages:

    • When the filed is removed, the microspheres demagnetize and re-disperse easily. This property allows efficient washing steps, low background and good reproducibility.
    • The behavior of the microspheres is always the same whatever the magnetization cycles may be. Such behavior is a key point for automated instrument.

    According to Wikipedia, paramagnetic materials have a small, positive susceptibility to magnetic fields. These materials are slightly attracted by a magnetic field and the material does not retain the magnetic properties when the external field is removed. Paramagnetic properties are due to the presence of some unpaired electrons, and from the realignment of the electron paths caused by the external magnetic field.

    Encyclopedia Britanica defines paramagnetism as a kind of magnetism characteristic of materials weakly attracted by a strong magnet, named and extensively investigated by the British scientist Michael Faraday beginning in 1845. Most elements and some compounds are paramagnetic. Strong paramagnetism (not to be confused with the ferromagnetism of the elements iron, cobalt, nickel, and other alloys) is exhibited by compounds containing iron, palladium, platinum, and the rare-earth elements.

    Paramagnetic microparticles are used in numerous applications where they can be manipulated with a magnet, observed and cleaned-up for reuse.

    • Solid Phase Immunoassays
    • Bacteria Detection
    • High Throughput screening
    • Rapid Tests
    • Cell Sorting
    • Biosensors
    • Nucleic Acids Technology
    • Microfluidics