Layer-by-layer crystallization from surface-induced nematic layers: a new mechanism of secondary nucleation revealed by molecular dynamic simulations

Molecular dynamic simulations were conducted to study the surface nucleation of n-pentacontane (C50) near the surface of a crystal slab of stretched periodic chains.  Order parameters identifying nematic and crystalline order showed that, even above the melting point of C50, a nematic layer with thickness around 0.9 nm (equivalent to about two layers of crystal) is induced on the crystal slab surface and grew as two-dimensional patches instead of stem-by-stem. When quenched below the melting point, the nematic layer transforms into a crystalline phase, following a classical nucleation theory in two dimensions, similar to that developed by Bourque and coworkers (Macromolecules, 2016, 49(9), 3619–3629). As the new crystalline layer approaches completion, a new nematic over-layer forms, which then, in turn, propagates the crystalline front another step forward. These novel results suggest a new mechanism of secondary nucleation of oligomers and polymers.