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January 15th, 2020
Featured Technical Article


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 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 .

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Brightly colored and fluorescent polymer microspheres are specifically designed for use as precision flow tracers and seed particles for water flow visualization and particle image velocimetry (PIV) experiments. Highly spherical microparticles have tight size distribution and density of 1g/cc, matching to properties of fresh water.

Suspension of microspheres enables the visualization and characterization of fluid flow and simulating the capability of a device to withstand certain size particles.

Ask a Scientist:

 Q: I followed Cospheric's protocol for suspending particles , but not all particles got suspended. Some particles have floated to the surface or sunk to the bottom over time. Did I do something wrong?

A: This scenario is common if the researcher does not carefully select the right particle to match specific properties of the fluid at specified environmental conditions. The behavior of spherical particles in solution is best characterized by Stoke's law. Stokes’s law is a mathematical equation that calculates the settling velocities of small spherical particles in a fluid medium. The law is derived by consideration of the forces acting on a particular particle as it sinks through a liquid column under the influence of gravity. The critical variables are diameter of the particle, viscosity of the fluid, and density delta between the particle and the fluid at specified temperature.


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Cospheric LLC
Manufacturer and worldwide distributor of NIST-traceable precision spheres, microspheres, beads and microparticles for R&D and industrial applications . Variety of materials, densities, colors, coatings, sizes and properties. Custom products developed to meet customer specifications. Most products are in-stock and ship within 1 business day.