Nanoconfinement Effects on the Glass-Liquid Transition of Vapor-Deposited 1-Pentene

The glass-transition temperature, T-g, of supported thin films is modified by the presence of free surface and substrate interface. To clarify the properties of nanoconfined liquids, the interactions of 1-pentene films with various substrates were investigated as a function of temperature using time-of-flight secondary ion mass spectrometry (TOP-SIMS) and time-of-flight ion scattering spectroscopy (TOF-ISS). A monolayer of 1-pentene wets a Si substrate; surface mobility occurs in the sub-T-g region (50-60 K), as revealed by the uptake of molecules into a porous Si substrate. The enhanced surface mobility induces sub-T-g dewetting of monolayer and multilayer films formed on a perfluoroalkyl-modified substrate. When a multilayer of 1-pentene is deposited on Ni(111), the topmost layer exhibits a liquidlike nature in the sub-T-g region, but mobility in the film interior is not induced up to T-g = 70 K. The adhesive interaction at the interface of Ni(111) is thought to play a role in the propagation of solidity in the film interior, thereby quenching surface-induced processes in the glass liquid transition of thin films. The enhanced surface mobility is also associated with the structural transformation of porous 1-pentene films in the sub-T-g region.