Influence of Surface Property on the Crystallization of Hentetracontane under Nanoscopic Cylindrical Confinement

The crystallization behavior and the orientation of linear alkane hentetracontane (C41) confined in cylindrical nanoporous alumina templates with different surface energies were investigated by nonisothermal crystallization and X-ray diffraction. The surface of pristine nanoporous alumina was modified to have low surface energy by grafting with polydimethylsiloxane. In the pristine nanoporous alumina, C41 crystallized at two crystallization temperature ranges, lower than bulk, and exhibited the decreased Avrami exponents. C41 in the surface-modified nanoporous alumina showed the inhibition of crystallization at higher temperature range among the two crystallization temperature ranges but the enhancement of crystallization at much lower temperature ranges than in the pristine nanoporous alumina. It was clearly shown that those variations of crystallization behavior imply the surface effect on crystallization. The crystal orientation was also affected by surface modification of the alumina template. The a-axis of orthorhombic C41 crystals in the pristine nanoporous alumina was preferentially oriented parallel to the pore axis, while b- and c-axes were perpendicular to the pore axis. C41 crystals in the surface-modified nanoporous alumina showed two types of orientation. One was identical to that in the pristine nanoporous alumina, and the other was the orientation that the crystals were tilted with respect to the c-axis as the (110) plane parallel to the pore axis.