NH2-Terminated Poly(ethylene oxide) Containing Nanosized NiO Particles:  Synthesis, Characterization, and Structural Considerations

Highly concentrated nanosized NiO particles have been prepared by means of vacuum evaporation of Ni on NH2-terminated poly(ethylene oxide) matrix film and subsequent purification by removal of a part of the matrix which was soluble in ethanol. TEM observation revealed that the purified composites contain uniformly dispersed NiO particles with an average diameter of less than 5 nm and fairly narrow size distribution. From the analyses including high-resolution TEM, electron diffraction pattern, and X-ray diffraction (XRD), the resultant particles were found to be fcc NiO, and significant lattice expansion was observed. The chemical bonding of amine end groups of the matrix molecules to NiO particle surfaces was suggested by XPS measurements. XRD and differential scanning calorimetry measurements indicate that the matrix structure in the composite is amorphous. This amorphous nature of the matrix could be caused by the restriction of molecular chain mobility through the chemical interaction between NiO particles and matrix molecules, leading to the insoluble nature of the composite in ethanol. On the other hand, the composite is soluble in propionic acid with no evidence for significant aggregation of NiO particles. The maximum content of NiO reaches ca. 50 wt % after purification, which is due to the localization of NiO particles into some parts of the matrix film during formation of NiO particles. The particle growth mechanism is discussed from the effect of initial amount of deposited Ni on the average particle diameter, its standard deviation, and the content of NiO in the composite.