A Monte Carlo study of the pattern formation during transitions in n-alkane crystals

Abstract

The rotator phase transition in n-alkane was recently found to show a characteristic pattern of preferred growth along the b-axis (shorter axis) of the unit cell. In order to investigate the origin of this anisotropic growth, a pattern formation in n-alkane crystal is studied during the transition between the low temperature orthorhombic (LO) phase and the rotator (R) phase by use of the Monte Carlo method. Of possible factors that will influence the growth pattern, we here concentrate on the mode of chain packing by assuming that the chains have rigid planar zigzag conformation and are placed in a regular orthohexagonal lattice. The herringbone order in the LO phase is found to develop rather quickly resulting characteristic domains with the (100) and (110) boundaries. The domain boundaries run preferentially along the b-axis at lower temperatures and are considered as a stacking fault or antiphase boundary. The transition between the LO phase and the R phase is found to exhibit a characteristic pattern, where the R phase domains grow preferentially along the b-axis. All these behaviors are shown to originate from different energies of the (100) and (110) boundaries.