Crystallization of Polycaprolactone within Nanopapers Based on Graphene-Related Materials

The crystallization of polymers in nanopapers based on graphene-related materials (GRMs) influences both elastic deformability and heat transfer within the nanostructure. Polycaprolactone (PCL) crystallizes in nanopapers, producing different crystalline fractions. We relate their formation to the interactions between polymer chains and the surface of GRM. In addition to conventional PCL crystals, we observe higher melting point crystals that result from strong heterogeneous nucleation, as well as crystals that melt above PCL's equilibrium melting temperature, seemingly linked to the prewetting of crystalline layers. The relative intensity of various melting peaks depends on the structural features and defects of GRM and the nanopaper preparation process. The molecular weight of PCL affects the thermal stability of crystals that melt above PCL's equilibrium melting temperature. Notably, these high-stability crystals cannot be thermally fractionated by successive self-nucleation and annealing (SSA), nor can they be dissolved in a conventional solvent for PCL, indicating a particularly strong interaction between PCL and GRM in nanopapers, which might be utilized in other hybrid organic-inorganic nanostructures.