A Journey along the Extruder with Polystyrene:C₆₀ Nanocomposites: Convergence of Feeding Formulations into a Similar Nanomorphology

Abstract

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.

Different agglomeration properties of PC61BM and PC71BM in photovoltaic inks – a spin-echo SANS study

“…Full details are presented in ESI † along with the relevant theory. SESANS has found some recent practical applications in materials science, for instance in the study of fullerene agglomerates in polymer composites 58,59 and the porosity of silica Stöber particles. 60 In this work, we describe the rst application of SESANS to the study of the agglomeration behaviour of the functionalized fullerenes PC 61 BM and PC 71 BM in different organic solvents, with relevance to organic photovoltaics.…”

Evolution of dispersion in the melt compounding of a model polymer nanocomposite system: A multi-scale study

“…S1(a) in supporting information). Details about this apparatus can be found in the supporting information and elsewhere [36,39,40].…”

“…The details of the experimental apparatuses and procedures were previously described [36] and so are not repeated here (see supporting information).…”

“…In recent years, polystyrene nanocomposites (PSNCs) containing fullerene nanoparticles have been the subject of a number of studies reporting improvements in properties such as electrical conductivity [23,24], thermal stability [25][26][27][28] and permeability [29,30]. The impact of C 60 loading and sample preparation conditions on the corresponding degree of distribution/dispersion, glass transition temperature (T g ) and melt viscosity have also been the focus of several studies [17,20,35,36].…”

“…In our previous work [36], we studied the impact of feeding conditions (premixed powders of pure components versus a solventblended mixture) of C 60 PSNCs on the dispersion and re-agglomeration phenomena that develop along the axis of a prototype small scale twinscrew extruder. With this device, which allows for the on-line sampling of material at different locations along the barrel without disturbing the extrusion process, we demonstrated that two feeding formulations with widely different initial morphologies converged along the extruder into a similar final nano-morphology.…”