New insight into PEO modified inner surface of HNTs and its nano-confinement within nanotube

In this study, we demonstrate the use of poly (ethylene oxide) (PEO) for in-situ modification of the inner surface of halloysite nanotubes (HNTs) with water molecules as the hydrogen bond forming medium, as well as the nano-confinement of PEO molecular chains within the nanotube. Before testing, the Soxhlet experiment of PEO/HNTs powder is applied in order to remove the physical adsorption of PEO molecules onto the outmost surface of HNTs. The crystal temperature of PEO changes sharply from 36.9 °C of neat PEO to −25 °C of PEO in the PEO/HNTs powder and the decomposed temperature of PEO in the PEO/HNTs powder is about 13.1 °C higher than that of neat PEO, which is mainly owing to the nano-confinement effect of PEO within the HNTs with a diameter of about 10 nm. From thermo-gravimetric (TG) analysis, about 7.71 % by weight of PEO has been chemically bonded to HNTs. The hydrogen bonds among PEO, HNTs, and water molecules are evidenced by FTIR and XPS performances. Meanwhile, the binding energy of Al_2p in the innermost surface of HNTs shifts from 74.7 eV in the neat HNTs to 74.5 eV in the PEO/HNTs powder, while that of Si_2p on the outmost surface of HNTs keeps almost constant, indicating that the hydrogen bonds only exists inner the nanotube and PEO molecular chains have been trapped in nano-scale within HNTs, which is in accordance with the DSC and TG observation.