Mutual diffusion studies of polystyrene and poly(xylenyl ether) using Rutherford backscattering spectrometry

Abstract

The concentration versus depth profile in diffusion couples initially consisting of layers of pure polystyrene (PS) and poly(xylenyl ether) (PXE) were measured. To reveal the profile, the PXE molecules (after diffusion) were preferentially stained in the glass by exposing the couple to a solution of 2 mol % Br in methanol; the covalently bound Br nuclei serve as heavy nuclear tags which permit a sensitive determination of the PXE depth profile by Rutherford backscattering spectrometry (RBS). The samples were annealed at temperatures,T, ranging from 177–210 °C that are above the glass transition temperature,T _g, of the pure PS (105 °C) but below theT _g of pure PXE (216 °C). The measured concentration versus depth profile is markedly asymmetric, with a low slope at low values of the volume fraction of PXE, φ_PXE, but with a much greater slope at high values of φ_PXE. These results are in qualitative agreement with the variation in the mutual diffusion coefficient,D, expected as φ_PXE increases, causing theT _g of the blend to increase towards, and finally exceed, the diffusion temperature. Values ofD extracted from these concentration versus depth profiles at low values of φ_PXE using the Boltzmann-Matano analysis are in good agreement with those measured by forward recoil spectrometry (FRES) in deuterated-PS: PXE couples with only small composition differences.