"plunger" Method for Simulating Crystal-Melt Interfacial Free Energies

Crystal-melt interfacial free energies are important ingredients in predicting the nucleation barrier for polymers to crystallize. Experimental measurement of polymer crystal-melt interfacial tensions is challenging, particularly for crystal facets other than the lamellar surfaces. We propose a simple way to obtain the interfacial free energy for any polymer crystal surface and melt using molecular dynamics simulation. We measure the force on a simulated nanoscale "plunger", that restrains a melt from flowing into the gap between two crystals cleaved along the (100) plane. This gives the difference between the crystal-vacuum and crystal-melt interfacial free energies. Separately, the crystal-vacuum interfacial free energy is obtained by measuring the force required to hold two crystals apart and integrating the force with respect to distance. We obtain the crystal-melt interfacial free energy by subtracting the above values. Results from this method applied to n-alkanes can be compared to measurements of the homogeneous nucleation barrier.