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Metal Coated Microspheres – Conductive Silver Coating
From early days engineers have been looking for ways to shield circuits from electromagnetic interference (EMI). One of the most effective methods of shielding is by creating an electrically conductive enclosure around the circuit or device. This can be accomplished by using any electrically conductive material. Advances in coated microspheres have enabled the creation of light weight electrically conductive coatings that provide excellent EMI shielding.
Electrically conductive microspheres are produced by applying a metallic silver coating to the surface of the microspheres, thus giving the advantages of a metal particle with the additional properties of the core microsphere. Typically hollow glass microspheres are silver coated as this offers the combination of a low density filler and a conductive particle. Coatings with EMI shielding of greater than 45db have been produced by adding as little as 20% by weight of M-18 silver coated microspheres.Cospheric offers metal coated (silver) electrically conductive microspheres in a variety of sizes and densities as shown in the table below, custom particle size ranges are also available:
Product Average particle size (μm) Particle size range (μm) True particle density (g/cm3) Bulk density (g/cm3) Crush strength (psi) M-18 17 5–30 (std) 0.72 0.34 28000 M-30 27 10–45(std) 0.62 0.37 18000 M-40 36 15–70 (std) 0.49 0.35 6000 M-45 43 15–80 (std) 0.32 0.20 2000 M-60 74 25–120(std) 0.16 0.10 300 -
Technical Characteristics of PMMA Microspheres
PMMA microspheres - Cospheric LLC
PMMA micropsheres or polymethylmethacrylate microspheres are often referred as acrylic microspheres. PMMA polymer is an amorphous, transparent and colorless thermoplastic that is hard and stiff. It has good abrasion and UV resistance and excellent optical clarity. It has somewhat poor solvent resistance. PMMA spheres are soluble in organic solvents such as acetone, benzene, or halogenated hydrocarbons. Though flammable, PMMA material has low smoke emission.
Poly(methyl methacrylate) or PMMA is less hydrophobic than polystyrene and reported to show reduced nonspecific protein and peptide binding. The density of these beads, 1.19 g/cc, is considerably heavier than polystyrene particles, allowing more rapid separation and making them easier to concentrate by centrifugation. The particles typically have a hydrophilic anionic surface with refractive index of 1.48.
PMMA micropsheres have good biocompatibility which allows the particles to be used in many medical and biochemical applications. Diameter and monodispersity specifications for the micropsheres are dictated by the requirements of each application.
PMMA micropsheres are used in such a wide variety of industries as investigations in the colloidal crystal field, toners for copying machines, biomedical devices and injectable dermal fillers.
Research quantities of PMMA microspheres can be obtained from several suppliers depending on the desired particle size.
Bangs Labs offers PMMA microspheres 0.5 micron – 5 micron in diameter. Cospheric LLC sells research samples of PMMA spheres in several tight size ranges from 10 micron to 150 micron. Goodfellow offers polymethylmethacrylate spheres in two diameters of 1.5mm and 3.18mm.
Below is some detailed technical information on material properties of PMMA:
(source: Goodfellow)Electrical Properties
Dielectric constant @1MHz 2.6
Dielectric strength ( kV mm-1 ) 15
Dissipation factor @ 1MHz 0.014
Surface resistivity ( Ohm/sq ) 1014
Volume resistivity ( Ohmcm ) 2-14 x 1015Mechanical Properties
Elongation at break ( % ) 2.5-4
Hardness – Rockwell M 92-100
Izod impact strength ( J m-1 ) 16-32
Poisson’s ratio 0.35 – 0.4
Tensile modulus ( GPa ) 2.4-3.3
Tensile strength ( MPa ) 80Physical Properties
Abbe number 57.2
Density ( g cm-3 ) 1.19
Flammability HB
Limiting oxygen index ( % ) 17-20
Radiation resistance Fair
Refractive index 1.49
Resistance to Ultra-violet Good
Water absorption – over 24 hours ( % ) 0.2Thermal Properties
Coefficient of thermal expansion ( x10-6 K-1 ) 70-77
Heat-deflection temperature – 0.45MPa ( C ) 105
Heat-deflection temperature – 1.8MPa ( C ) 95
Lower working temperature ( C ) -40
Specific heat ( J K-1 kg-1 ) 1400 – 1500
Thermal conductivity @23C ( W m-1 K-1 ) 0.17-0.19
Upper working temperature ( C ) 50 to 90 -
Solid Red Polyethylene Microspheres Announced
Santa Barbara, CA - May 28, 2010 - Cospheric LLC is now offering a product line of solid red polyethylene microspheres in particle size ranges from 10um to 1000um (1mm).Offering a bright red color. These microspheres can be used as additives in personal care products, or in fluid flow visualization experiments. Samples are in stock and ready to ship to customers for R&D use of product evaluation. These high quality microspheres are specified to be greater than 90% spherical, and greater than 90% in the specified size range.
Sample Density is 0.98g/cc (Custom densities are available)
Spherical Particle sizes include:
10-27um, 27-32um (30 micron), 32-38um (35 micron), 38-45um (40 micron), 45-53um (50 micron), 53-63um (60 micron), 63-75um (70 micron), 75-90um (80 micron), 90-106um (0.1mm), 106-125um, 125-150um, 150-180um, 180-212um (0.2mm), 212-250um (0.25mm), 250-300um (0.3mm), 300-355um (0.35mm), 355-400um (0.4mm), 400-500um (0.5mm), 500-600um (0.6mm), 600-710um (0.7mm), 710-850um (0.8mm), 850-1000um (0.9mm).
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Fluorochromes – Excitation and Emission Wavelengths
Below is a very useful table of various Fluorochromes that can be used in research requiring precise responses. For more information about Fluorescent Microspheres that utilize fluorochromes check out this related article. “Fluorescent Microspheres – Properties and Applications”
The fluorochrome table is also available for download as a pdf.
Table of Excitation and Emission Wavelengths FLUOROCHROME
EXCITATION(nm)
EMISSION (nm)
3-Hydroxypyrene 5,8,10-Tri Sulfonic acid 403 513 5-Hydroxy Tryptamine 380-415 520-530 5-Hydroxy Tryptamine (5-HT) 400 530 Acid Fuchsin 540 630 Acridine Orange (bound to DNA) 502 526 Acridine Red 455-600 560-680 Acridine Yellow 470 550 Acriflavin 436 520 AFA (Acriflavin Feulgen SITSA) 355-425 460 Alizarin Complexon 530-560 580 Alizarin Red 530-560 580 Allophycocyanin 650 661 ACMA 430 474 Aminoactinomycin D 555 655 Aminocoumarin 350 445 Anthroyl Stearate 361-381 446 Astrazon Brilliant Red 4G 500 585 Astrazon Orange R 470 540 Astrazon Red 6B 520 595 Astrazon Yellow 7 GLL 450 480 Atabrine 436 490 Auramine 460 550 Aurophosphine 450-490 515 Aurophosphine G Continue reading “Fluorochromes – Excitation and Emission Wavelengths” »
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Solid Polyethylene Microspheres for Effects in Color Cosmetics
A recent article in Cosmetics & Toiletries magazine describes the use Solid Polyethylene Mirospheres for Effects in Color Cosmetics.
Flesh Tone Microspheres - Color Matched to Skin Sample
Micropsheres have been used in cosmetics for some time, primarily as fillers and exfoliators. Most recently scientists started to utilize light reflecting properties of microspheres for creating unique optical effects, such as optical blurring and wrinkle filling. Due to light scattering effects of the spherical surface, formulating with appropriate microspheres can minimize the appearance of fine lines and uneven skin tone, due to optically reducing contrast on the skin.
The spherical shape and smooth surface of microspheres creates a low friction ball-bearing effect that gives formulations an elegant, silky feel. This ball-bearing effect promotes better blending on the skin and a more natural finish due to the enhanced slip, glide and omnidirectional spreadability, imparting a cream to powder texture. Outstanding roundness also provides lubrication during application, which enhances the tactile experience of a cosmetic product. Continue reading “Solid Polyethylene Microspheres for Effects in Color Cosmetics” »
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