True chemical composition profiles at polymer interphases: Recovery from measurements distorted by instrumental broadening

Abstract

The determination of chemical composition profiles at polymer interphases is an important issue at the moment of elucidating the physical mechanisms that operate in polymer diffusion processes and for calculating diffusion parameters. Several techniques are available to measure these profiles, the most common being forward recoil spectroscopy, Rutherford backscattering spectrometry, nuclear reaction analysis, confocal Raman microspectroscopy (CRM), and scanning infrared microscopy. However, all these techniques are affected by the limited resolution of the experimental setup, which in practice produces a rounding effect on the sharp corners of the composition profile; this may lead to incorrect conclusions regarding the measurements. In this work an inverse technique is proposed to correct this undesirable effect in the profiles. The inversion is performed on a model of the measuring process, which includes the instrumental broadening function, a quantitative representation of the limited resolution. The proposed methodology was tested using numerically generated experiments and genuine experimental runs obtained from CRM measurements at interphases of polymer bilayers. In all cases, the recovered profiles were close to the expected ones. In the truly experimental results diffusion tails are observed behind and ahead of the diffusion front before the numerical treatment of the data. These tails may be caused by a genuine mass diffusion or by an artifact. After the numerical treatment the tails disappear and a sharp interphase is recovered, a result one expects for the polymer pairs under study.