Wettability of Polyacetylene: Surface Energetics and Determination of Material Properties

The critical surface tension for wetting, γ_c, of predominantly cis-polyacetylene has been found from contact angle measurements to be 40.1 mN m^-1. This is the largest γ_c found to date for a purely hydrocarbon polymeric solid. When polyacetylene is iodine-doped to (CHI_0.20)_x, γ_c increases modestly to 44.2 mN m^-1. Changes in the limiting slope in the vicinity γ₁→ γ_c of the Zisman plot suggest that the doped polymer is better wetted by polar liquids. Using γ_c found for cis-(CH)_x and empirical correlations established with the solubility parameter, δ, produced a value of δ = 9.94 (cal cm^-3)¹/². This is in good agreement with the value of 9.7 (cal cm^-3)^1/2 calculated from group contributions. From established empirical correlations between γ_C and the Lorentz-Lorentz function, the dielectric constant of cis-(CH)_x was found to be 3.6. This value is in excellent agreement with previously reported direct measurements. The dispersion component of the substrate surface energy, γ_s^d, has been found, by using the method of Fowkes, to be 58 mN m^-1 for cis-(CH)_x and 90 mN m^-1 for (CHI_0.20)_x.