The study of nanoconfinement of PEO-PPO-PEO triblock copolymer in nanoporous ultrahigh molecular weight polyethylene membrane and their interactions

Abstract

This project was aimed to investigate the confinement of micelle-forming triblock copolymer of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) in high-strength ultrahigh molecular weight polyethylene membrane (UHMWPE), and the resultant composite membrane of PEO-PPO-PEO/UHMWPE. Poor mechanical strength of PEO-PPO-PEO was improved by impregnating the copolymer into the UHMWPE membrane. At the same time, the inherent hydrophobicity of UHMWPE membrane was altered to become amphiphilic membrane rendering broader applications particularly in biomedical area. The change in hydrophobicity was evidenced by the contact angle which significantly reduced from 129.0° to 31.8° in the presence of PEO-PPO-PEO. The composite membrane of UHMWPE/PEO-PPO-PEO showed intriguing confinement crystallization behavior where PEO under confinement in UHMWPE membrane changes from crystalline to amorphous as evidenced by the presence of the absorption band at 1349 cm^-1 as well as the broad peak in the FTIR spectra, and the lack of the melting and crystallization transitions in DSC thermograms above room temperature. The confinement led to a significant shift of the crystallization temperature of PEO from 32.8 °C to a significantly lower temperature at around -19 °C because the crystallization mechanism changed from heterogeneous nucleation to homogeneous nucleation‒similar to those reported in anodic aluminum oxide (AAO) nano-templates. In addition, a substantial reduction in crystallinity was observed when the copolymer was under confinement of the membrane. The disordered PEO or amorphization of PEO under confinement of porous UHMWPE membrane has potential application in solid-state battery application as a membrane separator. The confinement of PEO in UHMWPE membrane distinguishes itself from that in the AAO system in a way that the system reported in this study allows accurate crystallinity determination which leads to better understanding in crystallization process under confinement. In addition, the membrane provides cleaner specimen leaving no trace of non-confined PEO, larger DSC signal, and it can be directly applied as a separator in the solid-state battery application.

Date of Award	2021
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Ping GAO (Supervisor)