PhD Thesis Presentation - The Study of Nanoconfinement of PEO-PPO-PEO Triblock Copolymer in Nanoporous Ultrahigh Molecular Weight Polyethylene Membrane and their Interactions

Poor mechanical integrity of micelle-forming copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) is overcome by impregnating the copolymer into ultrahigh molecular weight polyethylene membrane (UHMWPE). At the same time, the inherent hydrophobicity of UHMWPE membrane is altered to become amphiphilic membrane rendering broader applications particularly in biomedical area. The change in hydrophobicity is evidenced by the contact angle which significantly reduces in the presence of PEO-PPO-PEO. The composite membrane of UHMWPE/PEO-PPO-PEO shows intriguing confinement crystallization behavior where PEO under confinement in UHMWPE membrane changes from crystalline to amorphous as evidenced by FTIR and DSC results. The confinement leads to a significant shift of the crystallization temperature of PEO to much lower temperatures because the crystallization mechanism changes 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 is 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. In addition to FTIR and DSC, other material characterizations include rheology, XRD, ToF-SIMS, SEM/ESEM, single-crystal XRD, BET, AFM, tensile testing, and contact angle measurement. The confinement effect is also investigated in other classes of UHMWPE membranes possessing different thicknesses. The confinement of PEO in UHMWPE membrane distinguishes itself from that in the AAO system in a sense that 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 solid-state battery application.