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.

  • Use of Polyethylene Spheres for Analyzing Microplastic Transport in Correlation with Earthworm Presence

    Work by Matthias C. Rillig, Lisa Ziersch, and Stefan Hempel at Freie Universität and Brandenburg Institute of Advanced Biodiversity Research in Berlin has been published in an article titled Microplastic transport in soil by earthworms. This article investigates earthworms effect on microplastic movement into subsurface soil layers.

    Polyethylene Microplastic

    With the increase in plastic usage in recent decades the issue of how this discarded plastic will affect marine environments has been studied extensively. However, effects of microplastics on soil environments have not been tested to the same extent. Scientists have begun testing microplastic movement into lower soil layers by analyzing how differing sized polyethylene beads moved in a 21-day period with and without earthworm facilitation.

    The experiment was designed to confirm the assumption that earthworms would aid in particle movement. Results found earthworms to have a significant positive effect on transporting polyethylene particles from the soil surface. While particle size was also an important factor on the level of transportation into subsurface environments. With polyethylene spheres in the size range 710-850um being significantly more likely to move into the lowest layer when earthworms were present.

    With this experiment showing the ability of earthworms to transport microplastics into subsurface layers more research needs to be done to determine the effects this may have on the soil environment and the worms themselves. Including the multitude of other organisms that could also facilitate similar transportation. As well as the possibilities of microplastics reaching ground water where problems similar to those realized in marine systems could occur.

  • 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

  • Stainless Steel Microspheres

    300 Series stainless steel is well known for its corrosion resistant properties. Now Scientists are demanding high quality spherical stainless steel microspheres which offer high density (7.8g/cc), high sphericity (>90% round) and corrosion resistance (300 series stainless steel).

    A full range of precision sizes are now available from 1-22um on up to 1.0-1.2mm.

    Stainless Steel 250um (0.25mm) Spheres

    Stainless Steel 250um (0.25mm) Spheres

    Applications for Stainless steel spheres include.
    1) Conductive Spacers
    2) High Density Projectiles
    3) Charge Transport
    4) Shock Absorbtion

    Research vial quantities are listed, many sizes have kg quantities in stock for larger project needs.

  • 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.