Surface texture on polymers

"WRINKLED SKINS" gives the impression that formation of surface texture on polymers via ion bombardment has just been discovered (C&EN, Jan. 22, page 8). This phenomenon was studied extensively at NASA's Lewis Research Center in the Terrestrial Applications of Ion Thruster Technology program under the direction of Bruce Banks in the early 1980s.

In the materials department at Virginia Tech, I had a small contract with NASA to characterize both the targets and sputter deposits of many polymers using scanning electron microscopy and X-ray photoelectron spectroscopy, briefly reported in Polymeric Materials: Science & Engineering Preprints (1984, 50, 459). In general, the topography that developed on the targets depended on the distribution of sputter-resistant regions (for example, spherulites, variable cross-link density); preexisting topography (for example, molding marks); and the increase in sputter rate as the angle of ion impact deviated from perpendicular. Thus the centers of spherulites became the apex of cones, and fine scratches on polished molding plates produced wrinkles or channels. The surface composition of both targets and sputter-deposits was always depleted of electronegative elements, presumably due to formation of volatile species.

David W. Dwight
State College, Pa.