Over the years, we have received a number of questions about the optical clarity of our polycarbonate (PCTE) membrane filters. Optically clear membranes are of importance when viewing plankton from the Antarctic under a microscope, manufacturing porous PDMS chambers, epifluorescent microscopy, and numerous other applications studies or even unmanned biology missions into space! All of our polycarbonate membrane filters are made by the same process, track-etching, but the clarity of our filters varies based on both the use of the base film (amorphous or crystalline– we use both) as well as the pore size and density. To shed some light on (or through) the matter of our filters' optical clarity we put together a handy infographic that you can check out at the bottom of this page.
Amorphous polycarbonate has no defined molecular arrangement within the film, and as such tends to show greater clarity (in an otherwise untreated film) when compared to crystalline PCTE. Crystalline films have been treated to align a large percentage of PCTE molecules. This tends to create a more opaque membrane with more limited optical clarity. You might think then, that an amorphous film is preferred over a crystalline film to gain better clarity, but base film chemistry is not the only contributor to clarity. Pores within a track-etch membrane are clean cylindrical holes that transverse straight from one side of the membrane to the other; as such light can freely pass right through these holes. But when you mix “clean” light from the holes with the naturally birefringent properties of PCTE film (see our FAQ on PCTE membranes for more information on this) you will get a “fuzzy” mix of light coming through, with the fuzziness being somewhat proportional to the pore size. So what’s the clearest membrane to use? Well, that depends on your application. If you’re filtering particulates within a dry air stream, the attached chart should give you a pretty good idea of the range of clarity. If you’re filtering in liquids, water will greatly enhance the optical clarity of all PCTE membranes as it mitigates the effect of light moving through the pores.
To learn more about Sterlitech's polycarbonate filters, check out some of our other blog articles below:
- Totally Tubular: Polycarbonate Membranes as Templates for Nanotubes
- Etching the Tracks in a Track-etched Membrane Filter
Polycarbonate membranes can range from almost entirely opaque to virtually transparent. Contact us to request transparent membranes. To browse our complete selection of polycarbonate membrane filters, click here.