Interdiffusion at polymer-polymer interfaces
There is not an extensive understanding of diffusion behaviour between chemically different polymers, especially where polymers are partially compatible. Nuclear reaction analysis has been used to observe the diffusion of molten DPEO into glassy PMMA where both polymers are above their entanglement molecular weight. The observed slowing down of diffusion of DPEO may be due to concentration dependent changes m interaction parameter or blend glass transition temperature, Tg. Small angle neutron scattering was used to find the interaction parameter χ, at the temperatures above the melting temperature (Tm) of DPEO but below the Tg of PMMA. The blend exhibited upper critical solution temperature behaviour, enthalpic interactions were dominant and/was found to be concentration dependent. Elastic recoil detection showed that glassy PMMA was quickly dissolved into molten DPEO and subsequently into the evolving DPEO/PMMA blend. The rate of increase of blend PMMA volume fraction (ψPMMA) decreases with increasing volume fraction. DPEO/PMMA diffusion couples can be described by both Fickean and limited supply case II diffusion. PMMA was substituted with a block copolymer polystyrene-b-poly(methylmethacrylate) (PS-PMMA). Polystyrene is immiscible with DPEO and PMMA, however diffusion behaviour was similar to that of pure PMMA with DPEO. PS-PMMA flux into the growing blend was similar to a higher molecular weight than the PMMA block present. Neutron reflectivity was employed to analyse interfacial concentration profiles with better resolution than is possible with ion beam analysis. For the anneal times utilized the diffusion was limited to movement of only a portion of the polymer chain. Bilayers were fitted by a model which included a growing precursor layer with ΨDΡΕΟ- 0.1 and a developing broadening between this layer and DPEO. The copolymer did not diffuse to a distance greater than the radius of gyration of the polymer components.