Coarse-Grained Simulations of Model Polymer Nanofibres

We describe the development of a coarse-grained (CG) force field for nylon-6 (polycaprolactam) and its application to the simulation of the structure and macromolecular dynamics within cylindrical fibres formed by this polymer, having diameters in the 14-28 nm range. Our CG model is based on the MARTINI force field for the non-bonded interactions and on Boltzmann-inverted gas-phase atomistic simulations for intramolecular stretching and bending energies. The simulations are carried out on infinite, isolated nanofibres at temperatures of 300, 400 and 500 K, with different starting configurations. Starting from ordered chain-extended configurations, we simulate the melting of the polymer in the nanofibres and, after cooling back to room temperature, its re-crystallization in a chain-folded lamellar configuration. This agrees with experimental observations on electrospun nylon-6 nanofibres and demonstrated the suitability of the approach for the simulation of these systems. The effect of nanoscale confinement on the structure and dynamics of the polymer chains is extensively discussed.