Everything about Microspheres
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  • Deformable Silver Coated PMMA Microsphere Spacers

    Silver Coated Glass Microspheres work well for increasing the conductivity of bond lines, but they lack the capability to deform when compressed to give increased conductive contact between the surfaces of the bond line.  These newly released Silver Coated PMMA Microspheres offer the low weight deformable pmma cores, and 250nm thick silver coating for high conductivity.

    Conductivity of this product has been measured at <0.5ohm per square with a 30% by volume preparation.  Sizes available cover both the common 50 micron (45-53um)  and 100 micron (90-106um) sizes and many others.

    These spheres are perfect for producing anisotropic (only conductive in one direction) conductive bond lines.

    Actual bond line thickness achieved will be a function of the assembly pressure and the size spheres selected.

    In addition to being high conductive these silver coated PMMA is bio-compatible.

  • Calculating microspheres per gram

    During scientific experiment design and analysis it is common to need to know the number of spheres per gram of dry material.  We have put together the table below to help speed up the process.

    If you have material of a density different from those listed in the table, divide the number of spheres per gram in the density ~1.0 g/cc column by the true particle density of your material to get an estimate of the number of spheres per gram.

    Product Size Polyethylene
    Density ~1.0 (g/cc)
    Soda Lime Glass
    Density ~2.5 (g/cc)
    Lower (um) Upper (um) Spheres per Gram Spheres Per Gram
    20 27 147,162,715 58,630,564
    27 32 74,393,558 29,638,868
    32 45 33,467,185 13,333,540
    45 53 16,233,536 6,467,544
    53 63 9,788,528 3,899,812
    63 75 5,813,720 2,316,223
    75 90 3,401,258 1,355,083
    90 106 2,029,192 808,443
    106 125 1,239,525 493,835
    125 150 734,672 292,698
    150 180 425,157 169,385
    180 212 253,649 101,055
    212 250 154,941 61,729
    250 300 91,834 36,587
    300 355 54,371 21,662
    355 425 32,196 12,827
    425 500 19,305 7,691
    500 600 11,479 4,573
    600 710 6,796 2,708
    710 850 4,025 1,603
    850 1000 2,413 961
    1180 1400 890 354
    1400 1700 513 204
    1700 2000 302 120
    2000 2360 184 73
    2360 2800 111 44
    2800 3350 66 26

    Note: This table assumes the mean diameter is half way between the upper and lower size.

  • Technical Characteristics of PMMA Microspheres

    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 5 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 1015

    Mechanical 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 )      80

    Physical 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 ( % )      0.2

    Thermal 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