Flow-induced inhomogeneity and enhanced nucleation in a long alkane melt

Flow-enhanced crystal nucleation in a lightly entangled melt of n-pentacontahectane (C150H302, or C150) is examined by nonequilibrium molecular dynamics simulation under steady shear and uniaxial extension. Under sufficiently strong flow fields above the melting temperature, strong fluctuations give rise to domains with high local alignment on the Kuhn length-scale. Upon quenching, the nucleation of small crystallites was found to occur preferentially within these domains. This behavior is at odds with classical nucleation theory, wherein it is typically assumed that nucleation occurs uniformly throughout the melt with equal rate. Comparisons are drawn between the simulation results and theories involving the formation of precursors that precede the formation of crystals.