Solidification of a supercooled liquid in a narrow channel.

We simulate solidification in a narrow channel through the use of a phase-field model with an adaptive grid. In different regimes, we find that the solid can grow in fingerlike steady-state shapes, or become unstable, exhibiting unsteady growth. At low melt undercoolings, we find good agreement between our results, theoretical predictions, and experiment. For high undercoolings, we report evidence for a new stable steady-state finger shape which exists in experimentally accessible ranges for typical materials.

Molecular weight effects on chain pull-out fracture of reinforced polymeric interfaces.

Using Brownian dynamics, we simulate the fracture of polymer interfaces reinforced by diblock connector chains. We consider the mushroom regime, where connector chains are grafted with low surface density, for the case of large pulling velocities. We find that for short chains the interface fracture toughness depends linearly on the degree of polymerization N of the connector chains, while for longer chains the dependence becomes N(3/2). Based on the geometry of the initial chain configuration, we propose a scaling argument that accounts for both short and long chain limits and the crossover between them.