Direct observation of mobility of thin polymer layers via asymmetric interdiffusion using neutron reflectivity measurements

摘要

In this study, we investigated the diffusion dynamics at the interface between deuterated poly(methyl methacrylate) (d-PMMA) and protonated poly(methyl methacrylate) (h-PMMA) in two-layered thin films of d- and h-PMMA layers via neutron reflectivity (NR) measurements during isothermal annealing above the glass transition temperature T-g. When T-g of d-PMMA was higher than that of h-PMMA, the d-PMMA layer thickness increased with increasing annealing time t(a) and, simult(a)neously, the h-PMMA layer thickness decreased. However, the opposite t(a) dependence of the layer thicknesses was observed, if the T-g of d-PMMA was decreased by the increase in the fraction of the low-molecular weight d-PMMA: With increasing t(a), the d-PMMA layer thickness decreased and the h-PMMA layer thickness increased when T-g of d-PMMA was lower than that of h-PMMA. This change in the t(a) dependence of the layer thickness was related to the change in the mobility of the d-PMMA layer accompanied by the change in the T-g value of d-PMMA. With the decrease in the d-PMMA layer thickness from 49 nm to 13 nm, when the h-PMMA layer thickness was maint(a)ined, the t(a) dependence of the layer thickness changed and the mobility of the d-PMMA layer dramatically increased. These results suggest that the mobility of thin polymer films can be determined by the observation of interfacial dynamics via NR measurements.