We investigate the morphological development of polystyrene (PS)-C ₆₀ nanocomposites along the length of a prototype co-rotating twin-screw extruder with sampling capabilities. The effects of C ₆₀ concentration and output on the morphological evolution along the extruder are studied employing a suite of characterization techniques covering a wide range of length-scales, thereby shedding new light on the dispersion mechanism in this model system. We show that the relatively new spin-echo small-angle neutron scattering (SESANS) technique is well suited to probe both the distribution and the dispersion of C ₆₀ . SESANS complements optical microscopy (OM) data as it covers sampling areas several orders of magnitude larger than OM. The multi-scale morphological information conveyed by OM, SESANS, SANS and rheological data shows that for larger outputs, C ₆₀ agglomerates are eroded as they travel along the extruder, resulting in C ₆₀ dispersion and distribution at both molecular and micrometric levels. The picture is more complex when smaller feed rates are used, as the evolution of C ₆₀ dispersion depends on the C ₆₀ loading. For larger C ₆₀ contents, agglomeration develops along the extruder, whereas dispersion is improved for smaller C ₆₀ contents. Overall, it is concluded that an over-high feed rate in extrusion does not necessarily result in a bigger size of the nanoparticle agglomerates because of the complex interplay between stresses and residence time. ... Read more

We investigated the effect of the feeding formulation (premixed powders of pure components versus solvent-blended mixture) of polystyrene–C60 composites on the dispersion and reagglomeration phenomena developing along the barrel of a twin-screw extruder. The dispersion of C60 in the PS matrix is studied over different length scales using a combination of optical microscopy, spin-echo small-angle neutron scattering (SESANS), small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), and wide-angle X-ray scattering (WAXS). When a solvent-blended mixture is used as the feeding formulation, the inlet material contains essentially molecularly dispersed C60 as revealed by the nanodomains with very small phase contrast. However, C60 reagglomeration occurs along the extruder, creating a morphology still containing only nanodomains but with much higher phase contrast. In the case of mixed powders, the material evolves from the initial macroscopic mixture of pure polystyrene and C60 into a composite simultaneously containing micro- and nanoaggregates of C60 as well as C60 molecularly dispersed in the matrix. Our results show that the two different initial feeding formulations with widely different initial morphologies converge along the extruder, through opposite morphological pathways, into a similar final nanomorphology which is dictated by the interplay between the thermodynamics of the system and the flow. Correlations between the morphological evolution along the extruder and the thermorheological properties of the composites are identified. ... Read more