Fig. 4.

Fabrication process of nanoporous membranes with the track-UV technique. a Schematic of the nanopore formation process in a thin slice of the polymer film irradiated with energetic heavy ions and subsequent UV radiation. Each ion projectile produces a nanometric cylindrical track (in atomic representation) inside the polymer film (light blue). Given the collimated ion beam (blue arrows), the tracks are oriented parallel and stochastically distributed. Tracks are amorphous cylinders and consist of broken polymer chains and decreased density due to the release of small volatile degradation molecules such as C₂H₄ and CO during ion irradiation and UV-induced photochemical reactions⁵⁶. The charged fragments such as terephthalic acids are further cleaned when an electric field is applied across the membrane immersed in water. Finally, uniform nanopores form inside the core of the track. b UV absorption (at 365 nm) as a function of ion fluence of PET Lumirror® (blue square) and Hostaphan® (red circle) films. Dashed lines are linear fits