Structure of nylon 46 lamellar crystals:: An investigation including adjacent chain folding

The structure of nylon 46 lamellar crystals was investigated by molecular dynamics simulations taking into account the occurrence of chain folding. Fold arrangements compatible with adjacent chain reentry were simulated and comparatively analyzed. The C-14 fold consisting of a 14-membered loop with one amide group included in the fold was found to be the most stable arrangement. Computer simulation of crystal models including the folds revealed that the packing preferences of the nylon in the lamellar crystals were not altered by changes in the chain-folding mechanism. Results confirmed the energy similitude between the alpha and beta forms of nylon 46 and supported the occurrence of a statistical lattice composed of these two forms as the most probable structure for nylon 46 chain-folded crystals. Monte Carlo simulations were also carried out to confirm the suitability of such statistical structure and to account for certain thermal effects observed by experimentation.