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.

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

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 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