Direct measurement of chain diffusion at interfaces of PPO/PS bilayer films by nano-thermal analysis and time-of-flight secondary ion mass spectrometry

Chain diffusion at the polyphenylene oxide/polystyrene (PPO/PS) interface of bilayer films were investigated using nanothermal analysis (nano-TA) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). An ultralow-angle slicing technique by the surface and interfacial cutting analysis system (SAICAS) was used to expand the size of the interfacial region effectively. The glass-transition temperature (T_g) at the interface was directly evaluated by nano-TA. The gradient of T_g at the PPO/PS interface became broad after annealing. An increase in annealing time caused an increase in the T_g of the initial PS layer, indicating that the PPO diffused across the interface. Since PPO/PS is a compatible blend system, the local chemical compositions were evaluated by Fox equation. The methodology presented here is useful for interfacial analyses of various polymer composite systems and is beneficial because the isotope labeling is not necessary.