ABSTRACT
Self-diffusion in polymer melts has been modeled using the reputation model. Polymer-polymer binary diffusion in miscible blends of polymers with different repeat units in their chains during miscibilization and phase separation is very important. In such blends, attractive interactions between the monomers, when summed over a polymer chain, may lead to large enthalpic driving forces favoring mixing. This in turn results in a mutual diffusion rate that is rapid compared with entropically driven self-diffusion. This phenomenon is dependent on composition. Binary diffusion coef™cients between miscible blends of PVC (polyvinyl chloride) and PCL (polycaprolactone) were measured by Jones et al. [1]. Diffusion coef™cients were obtained from measurements of transient concentration pro™le from an initial step change in concentration. A sharp interface was set up between blends of PVC and PCL, differing in concentration by 10%. The sample was then held at a temperature of 91.5 ± 0.5°C in a vacuum oven for known times of 8 h to 7 days. The ™nal distribution of the two polymer species after diffusion broadening across the interface was then determined using x-ray microanalysis in a scanning electron microscope in which x-rays from inner-shell transitions excited by the electron beam and characteristic of the element producing them were counted by a detector. The concentration of chlorine atoms in PVC was measured across the sample. The spatial resolution of this technique was 3 µm. With care during sample preparation, a concentration resolution of 1% is possible.
