For the neat phenoxy (Fig. 3a) as well as for the phenoxy filled with organoclay (Fig. 3b), the dissolution is rapid as evidenced in the image sequence through the decrease of the spacing between the visible interfaces delineating the filament. The interfaces detected optically correspond to the diffusion fronts of the epoxy resin precursors and delimit the thermoplastic or nanocomposite layer still unaffected by the resin. In both cases, the residual glassy layer of the filament completely disappears before 20 min, i.e. much before gelation of the RTM6, as a result of interdiffusion between the low molar mass resin precursors and the polymer chains [36]. In contrast to organoclay, the black MWCNT prevent optical detection of the interface between the inner core of the filament and its gel layer containing swollen nanocomposite (Fig. 3c). Nevertheless, for MWCNT nanocomposite filaments, apparent migration of the nanotubes can be still observed. The MWCNT-free epoxy resin front can be easily followed thanks to the clear contrast between the MWCNT and the polymer matrix. The motion of the nanofillers in this situation is passive as they are definitely not Brownian particles. The chemical potential gradient generated at the interface between the TP and the epoxy precursors acts as the thermodynamic driving force for the interdiffusion between the two while the NF are passively transported.