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Method to Probe Glass Transition Temperatures of Polymer Thin Films

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journal contribution
posted on 19.05.2015 by Bolin Li, Xiaolin Lu, Yonghao Ma, Xiaofeng Han, Zhan Chen
A new methodology was developed to probe glass transition temperatures (Tgs) of polymer thin films supported on gold (Au) substrates and confined between two solid (silica and silver) surfaces based on the surface plasmon polariton (SFPP) signals generated by sum frequency generation (SFG) spectroscopy. The measured Tgs for polymer (poly­(methyl methacrylate), poly­(benzyl methacrylate) and poly­(ethyl methacrylate)) thin films supported on Au substrates showed similar thickness-dependent trend, that is, the Tg decreased as the thin film thickness decreased due to the free surface effect. However, the measured Tg of the (poly­(methyl methacrylate)) thin films confined between two solid surfaces increased significantly with respect to the bulk value, indicating the strong interfacial effect when the free surface was replaced by a buried interface. This method to measure the Tg can be applied to study different polymer thin films supported on metal surfaces or confined between two solid surfaces with different surface chemistries. More importantly, SFG has the unique selectivity and sensitivity to study surfaces and interfaces, providing the feasibility to develop SFG into a powerful tool to detect surface, interfacial, and bulk Tgs of a polymer thin film simultaneously in the future.