Formation of nanoscale protrusions on polymer films after atomic oxygen exposure; Observations with positron annihilation lifetime spectroscopy

Goto, Aki*; Michishio, Koji*; Oka, Toshitaka   ; Tagawa, Masahito*; Yamashita, Shinichi*

Atomic oxygen (AO) is one of the dominant components of the residual atmosphere in low Earth orbit. AO collides with spacecraft with translational energy of 5 eV, forming nanoscale protrusions on polymeric materials. This study investigated the size of free-volume holes and the layer thickness that interacted with AO for polyethylene (PE), polypropylene (PP), and polystyrene (PS) by positron annihilation lifetime spectroscopy. By the AO irradiation, oxidized layer formed in the surface, and the maximum depth of the oxidized layer for PE and PP were deeper than for PS. The different sizes of free-volume holes would affect the injection depths of AO, resulting in the oxidized layers' thicknesses and surface morphologies.