Molecular dynamics and structural phase transition in C60 nanowhiskers

Abstract

Nanowhiskers of C60 (C60 NWs) have been formed by a liquid-liquid interfacial precipitation method which uses an interface of the concentrated toluene solution of C60/2-propanol. In order to study the motion of C60 molecules in nanowhiskers, we have performed measurements of low-temperature X-ray diffraction, magnetic susceptibility, specific heat and 13C-NMR for C60 NWs. The temperature dependence of lattice constant for C60 NWs is in good agreement with that for pristine C60 powder, which demonstrates the large discontinuity at Tc ∼ 265 K caused by the structural phase transition. However, the temperature dependence of magnetic susceptibility for C60 NWs exhibits a faint anomaly at Tc. The temperature dependence of specific heat for C60 NWs shows two small anomalies at 232 K and 254 K. High resolution 13C-NMR measurements of the C60 NWs indicate that both of toluene and 2-propanol molecules interact with the C60 NW molecules in the suspension and the precipitate states obtained from the LLIP method. The broader linewidth of 13C-NMR in the dried C60 NWs compared with that in the pristine C60 powder indicates that the slower molecular reorientation in the dried C60 NWs compared with that in the pristine C60 powder. Since a rapid rotation of C60 molecules could be directly detected by 13C-NMR, polymer formation between C60 molecules is unlikely in C60 NWs at room temperature.