Percolation Effects on the Surface of a Polyimide Film Modified with Aqueous Solutions of an Alkali and Acid

摘要

A cluster structure of the surface of a polypyromellitimide film was studied by the electron microscopy and ATR IR spectroscopy methods at different steps of consecutive treatment with aqueous solutions of an alkali and acid. The effective size and fractal dimension D of polyamidoacid clusters, as well as the degree ρ_s of the filling of the surface with the latter were calculated from the data of the electron microscopy as a function of the degree of imide group conversion into amidoacid units on the film surface. The ρ_s and D parameters were shown to increase with a rise in β: ρ_s = 0.1–0.3 and D = 1.3–1.4 at β < β_(cr) and ρ_s ≈0.6 and D ≈ 1.7 at β > β_(cr), where β_(cr) is a critical degree of conversion, which corresponds to the formation of a continuous physical network of polyamidoacid macromolecules or a percolation cluster. In a region close to β_(cr) (at β< β_(cr)), the correlation length l and the concentration C of the clusters vary according to the laws of the percolation theory for two-dimensional lattices: l ～ (β_(cr)–β)~(-v) and C ～ (β(cr)–β)~α, where = 1.3 ± 0.1 and α = 0.67 ± 0.05.