[nanoPost] Coating of hollow glass microspheres

Company UK

The company has developed a variety of techniques that allow the surface of the microspheres to be coated with a range of materials such as metals, metal oxides, pigments and dyes.

These low density composite materials have the potential to act as replacements for conventional materials offering significant weight savings and performance advantage in areas as diverse as water purification, defence, aerospace, marine and automotive coatings, diagnostics and cosmetics.

Hollow glass microspheres coated with photocatalytic titanium dioxide

In the presence of light in the near UV region, titanium dioxide generates reactive oxygen species and hydroxyl radicals capable of breaking down many organic and inorganic pollutants in wastewater, as well as destroying micro-organisms. However, titania nanopowders used for this purpose are extremely difficult to recover from treated wastewater by conventional, high throughput filtration techniques.

The microspheres provide a buoyant, filterable and reusable alternative to solid titania nanoparticles for the photocatalytic remediation of wastewater. The microspheres against a range of water industry relevant organic pollutants and have also been demonstrated to be effective in reducing gaseous pollutants.

The material is available in the size range 10 to 50 microns and has a robust, continuous, smooth surface coating of titania which does not shed into the treated water.

Fluorescent Microspheres

Fluorescent hollow glass microspheres allow enhanced visualisation in certain applications such as diagnostics and fluid dynamics.

The company have developed techniques to incorporate fluorescent dyes into microsphere coating materials. The dyes are covalently bound into the coating so that there is no possibility of dye leaching from the microspheres. Furthermore, the coating stabilises the fluorescent dye, greatly increasing the fluorescent lifetime of the microspheres.

The company currently produce microspheres incorporating fluorescein and rhodamine B fluorophores. Other customer specified fluorescent dyes can be added to cater for specific applications.

The fluorescent coating can also be layered over other coatings, where it will be transparent and colourless until viewed under the correct illumination.

Magnetic Microspheres

The company produce magnetic hollow glass microspheres by coating with superparamagnetic iron oxide or a paramagnetic nickel/phosphorus alloy. The iron oxide microspheres are additionally coated with a thin layer of silica to make them more robust.

The microspheres are available with an amine functionalised surface ready for conjugating antibodies to create a buoyant immunocapture particle. The advantage of hollow glass microspheres over other immunodiagnostic particles is that they are easy to recover from the sample matrix. On standing they will simply float to the surface or, in a sample containing lots of particulate matter, they can be cleanly separated from debris by centrifugation.

The company have developed a magnetic pen that allows the microspheres to be easily manipulated. They can be cleanly retrieved from the surface of the sample and then released into a another solution.

Metal Coated Microspheres

The company can produce hollow glass microspheres coated with nickel, copper, gold or silver.

The metal is applied by deposition processes which result in a robust, continuous coating. The thickness of the metal coating can be varied over the range of a few nanometers to several microns.

Metal coated hollow microspheres exhibit the properties of solid metal particles, but with a substantial weight saving. Some of these properties include high thermal conductivity, high electrical conductivity, mechanical strength, electromagnetic absorption and ferromagnetism.

If necessary, a protective or functional coating can be applied to the surface of the metal coated microsphere.

Silver coated hollow glass microspheres are used in flow visualisation studies because of their high reflectivity. The company  can produce material where all the microspheres have densities within a given range to maximise the time they remain in suspension.

Some metal coated microspheres become hydrophobic when a thick coating of metal is applied. The company  can apply a hydrophilic polymer coating when required to allow the microspheres to disperse freely as aqueous suspensions.

Titania Coated Microspheres

Coating hollow glass microspheres with titanium dioxide results in a lightweight pigment with applications in areas such as aerospace and automotive paints.

The company titania coated microspheres can be made to a client-specified size and density in either rutile or anatase form, rutile being the most thermodynamically stable crystalline form of titania. A photocatalytically inactive form of our titania coated microspheres is also available, for applications where this property would be undesirable.