Interfacial Effect in Supported Thin PET Films Covered with a Thin PPO Layer

• Published in: Macromolecules Vol. 53; no. 19; pp. 8683 - 8692
• Main Authors: Wu, Xiaoling, Xu, Jianquan, Sun, Weihan, Hong, Yongming, Zhang, Cuiyun, Zhang, Li, Wang, Xinping
• Format: Journal Article
• Language: English
• Published: American Chemical Society 13.10.2020
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.0c00575

The thickness dependent chain mobility in polymer films influenced by the interfacial effect was investigated by the cold crystallization behavior of thin poly­(ethylene terephthalate) (PET) films covered by a thin poly­(2,6-dimethyl-1,4-phenyleneoxide) (PPO) layer to eliminate the free surface effect. Two characteristic film thicknesses were observed, which were related to the long-range perturbations of the interfacial effect. Below the first thickness (h s*), the bulk-like crystallization temperature of PET films begins to shift upward, and below the second thickness (h n*), crystallization of PET films is completely suppressed. These two characteristic thicknesses are proportional to the adsorbed layer thickness. We found that h s* is much greater than the thickness of the PET film with a free surface, while h n* is independent of the free surface. This result indicated that the thickness for the suppression of polymer film dynamics can be increased by removing the contribution of the free surface. The value of h n * independent of the free surface may be attributed to the fact that the chain conformation within this thickness adopts the chain conformation at the interface, causing the “free surface” to vanish. The chain conformations affected by the substrate are another cause of long-range perturbations.