Frozen Local Conformation of Interfacial Polyisoprene Chains at Room Temperature

The performance of a polymer composite material, in which inorganic fillers are dispersed, is closely related to the aggregation states and dynamics of polymer chains at the filler interface. In this study, the local conformation of polyisoprene (PI) at a quartz substrate interface was studied as a model system for the rubber/filler composite material. Films of PI were prepared from a toluene solution onto quartz substrates by a spin-coating method. Sum-frequency generation vibrational spectroscopy revealed that the local conformation of interfacial PI chains at the quartz interface depended on the spinning rate. The tilt angle of methyl groups increased with the rotational speed probably due to the centrifugal force applied to chains during the solidification process. This result indicates that the interfacial orientation of PI chains can remain even at room temperature, which is approximately 90 K higher than the bulk glass transition temperature (T_g^b). The interfacial orientation disappeared at a temperature approximately 120 K higher than T_g^b.