Dynamics and packing mode of long-chained n-alkane molecules in the nano-channel of MCM-41

High-resolution solid-state 13C NMR spectra of long-chained n-alkanes included in the nano-channel of MCM-41 have been observed. Each spectrum has two sets of peaks: one from very flexible molecules and the other from molecules with no significant flexibility. These molecules are characterized by carbon spin lattice relaxation times, T1, of < 1 s and > 10 s, respectively. This phenomenon is ascribed to phase separation of the alkanes in the nano-channel, i.e., the amorphous and crystalline phases, respectively. The mechanism of this phase separation and the dynamics of these molecules in the nano-channel are discussed.