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

  • Silica Nanospheres as Photonic Nanostructure Found in the ‘Disco’ Clam Ctennoides Ales

    Scientists from UC Berkeley have recently discovered that a strange naturally occurring bright display of the ‘disco’ or ‘electric’ clam Ctenoides ales is actually a photonic display created by a layer of silica nanospheres. The display functions solely by reflecting light.

    An article was published in the Journal of The Royal Society titled “A Dynamic Broadband Reflector Built from Microscopic Silica Spheres in the ‘Disco’ Clam Ctenoides Ales“, where the researchers shared their findings.

    Laboratory elemental analysis of the reflective nanospheres showed that they are indeed composed of amorphous silica. Both the outer shells and the cores are composed of silica. Silica nanospheres are secreted by the animal and used as a light scattering structure in a behavior modulated reflective photonic display.

    The measurements show that the diameter of the silica nanospheres is at around 300nanometers, an optimal particle size for scattering visible light, especially the shorter blue-green wavelengths of 400-500nm that predominate at 3-50m underwater, which is typically the clam’s habitat. In addition to the diameter, the highly organized packing structure of the nanospheres aid in the scattering of the visible light at the shorter wavelengths.

    The display is so bright that it has been mistakenly thought of as bioluminescent, but the findings show that it is actually based on light scattered by photonic nanostructures.

    Silica has a high index of refraction at n=1.43 at 589nm.

    Silica Nanospheres - 300nm in diameter

    Silica Nanospheres - 300nm in diameter - available from CosphericNano

    This study is extremely interesting to scientists in many different fields because it opens their minds up to many creative uses of silica nanospheres that have not been known before. The findings show a practical way to manipulate light in low light situations. Among its other advantages, silica, similar to glass, is a very durable material, with high melt point. Using silica nanospheres in tightly packed arrays to create photonic nanostructures seems like a great idea.

    Highly precise and spherical silica nanospheres with narrow size distribution, diameters around 300nm and sphericity of greater than 99% in dry powder from can be purchased from CosphericNano—a new website specializing in precise silica nanospheres.

  • Reflective Billboard – Creative Outdoor Billboard for McDonald’s

    What a creative alternative to power-hungry digital displays. This large outdoor billboard is totally environmentally friendly because compared to LCD and LED displays that run on electricity, this display takes no energy to run. This creative outdoor billboard is made with reflective tape, visible only when illuminated by headlights in the darkness, created by ad agency Cossette.  To promote a local 24-hour McDonald’s in Canada, Cossette Vancouver designed this reflective billboard that’s only visible at night when cars pass by. By day, the billboard appears blank with no message, but at night, motorists driving along the highway reveal Mickey-D’s clever advertisement with their car headlights. Not only does this display save energy, it can be put anywhere, even in cities with strict requirements on flashing and lit displays.

    Even though this particular display was made using reflective tape, many types of retroreflective media can be made by incorporating retroreflective microspheres in a variety of substances. Retroreflective Microspheres are made by applying a half-shell aluminum coating on solid barium titanate glass microspheres. The spheres hemispherically coated with a thin aluminum shell produce a bright retroreflective response directed back to the light source.