The polycarbonate track-etch (PCTE) membrane filters are precision, two-dimensional microporous screens. As in the case of other screens, particle capture takes place on the surface. Compare this to ordinary cast membrane filters which depend upon particle capture by random entrapment within the filter's tortuous pores.
PCTE membranes are manufactured in a two-step process. In the first step, thin polycarbonate film is exposed to collimated (directionally-controlled) fission particles in a nuclear reactor. As these particles pass through the polycarbonate material, they leave sensitized tracks. The number of tracks per square centimeter depends primarily upon the amount of time that the film is in the reactor. Thus, there is direct control over the pore density.
In the second step of the manufacturing process, the tracks left by the particles are preferentially etched, or dissolved, into uniform cylindrical pores. By varying the time of exposure of the irradiated film, the temperature, and the strength of the etching solution, a precisely controlled pore size and shape is produced.