Force Microscopy of Ion-Containing Polymer Surfaces: Morphology and Charge Structure

Abstract

A force microscope is used to detect charge structure on the surfaces of films of the insulating polymers polystyrene and poly(styrene-co-butyl methacrylate). In contrast, films of the ionomer styrene-co-N-methyl-4-vinylpyridinium toluenesulfonate with 6% ionic monomer (520 μmol/g ions) do not show such a charge structure by force microscopy, and charge deposited on the surface decays rapidly. The film of a copolymer/ionomer blend, with 26 μmol/g ions, shows intermediate behavior where the surface charge decays over a period of ca. 1 h. Annealing the films does not change the observed behavior of the insulating polymer films or the ionomer films but does affect the behavior of the blend. In the latter case, annealing makes the surface of the film sufficiently conductive that the film does not hold a charge. X-ray photoelectron spectroscopy results reveal that the change in the behavior corresponds to a change in the surface composition where the surface is enriched with ions from the ionomer. © 1992, American Chemical Society. All rights reserved.