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| Appearance of the pores in the SPI-Pore™ PCTE membrane filters | Corrosion cast of a typical SPI-Pore™ PCTE membrane filter showing the spatial arrangement of the pores. |
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In contrast, polycarbonate filters contain uniform, cylindrical pores, preferentially etched into the membrane, thus allowing for an even distribution of a collected sample in one plane across the entire exposed membrane surface.
Hence all samples are captured on a flat, smooth, featureless surface. The precisely sized pores in a very narrow distribution ensure accurate separation, or fractionation, of samples by size.
Contaminant-free, these microporous screens are biologically inert, offer
excellent chemical resistance and thermal stability, provide superior
strength and negligible adsorption of filtrate. These factors combined
with the unique filtration capabilities of the polycarbonate membrane,
make it a clear preference for a number of EM and LM applications,
including:
Airborne Particulate Analysis including asbestos, Chemotaxis, Cytology,
Histology, Paleontology, Parenterals, and Water Analysis for asbestos
and other suspended inorganics.
The color of the most commonly purchased form of the product is white, but in some situations, the
black form of the product is preferred.
The filtration and physical properties of PC membrane filters
make them fairly unique and set them apart from membrane filters of other
compositions, giving them in many instance, unique performance
advantages. Consequently, in many general laboratory situations, many
users of membrane filters elect to include an assortment of PC membranes
on standby for when one of those unique kinds of situations arise and
filtration must be done immediately.
Chemical Compatibility of PCTE membranes:
The membranes are surprisingly resistant to a number of organic solvents and inorganic liquids.
But we must caution that some solvents will instantly dissolve PCTE membranes and you should
consult our solvent resistance information.
Fluorescence characteristics
All PCTE membrane filters, irrespective of the manufacturer, so far as we
know, are made from a polycarbonate that contains fluorescent pigmentation
in the raw material. Again, to the best of our knowledge, this most
important and unique raw material is not available without this pigmentation
system. We have not studied exactly what wavelengths the fluorescence occurs,
but we are pretty sure that a laser will light them up like a Christmas tree.
Birefringence:
All polycarbonate membrane filters, to our knowledge, exhibit some amount of birefringence
and that is because polycarbonate crystallizes and therefore has a crystalline texture. In
a polarizing microscope, the individual crystallites show up as a fine, barely resolvable
"pepper" like appearance.
Maximum use temperature:
The polymer starts to soften at around 150°C and will actually melt at
around 240°C. Should your requirements involve work at higher
temperatures, we would recommend you consider either A) Anopore®
aluminum oxide membrane filters or
B) the SPI-Pore™
Silver Membrane Filters.
Do the membranes have a charge?
The polycarbonate track etch membranes do not have an inherent charge,
either positive or negative. They do, however, act in the same way as the
dielectric film in a capacitor, and static electricity will build up on it.
This static charge will cause the membrane to act as if it has a charge, but
that charge is not actually a property of the membrane; it is the result of
the environment which the membrane has experienced. The Zerostat®
antistatic gun has proved effective in terms of neutralizing any charge that
might build up on a membrane.
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