Raising glass transition temperature of polymer nanofilms as a function of negative interface energy

Abstract

Based on a thermodynamic approach, glass transition temperature (T_g) of substrate-supported polymer nanofilms (s-PNFs) is investigated for carbon-chain polymers, taking the role of the interface energy into consideration. Relative to the T_g depression, originating from the positive interface energy due to the weak interfacial van der Waals interactions, the T_g raise is reversely induced by the negative interface energy, induced by the hydrogen bonds formed between the side-chains of polymers and the surface hydroxyl groups of substrates. Moreover, the T_g raise can be reinforced for s-PNFs with simple side-chains. The model predictions agree well with available experimental or simulation results.