In this project, we studied the morphology of SiO2/TiO2 hollow nanoparticles (HNPs), the morphology of polymer-embedded HNPs and diffusion of solvents into polymer-embedded HNPs, mainly based on small angle scattering methods.
The average outer diameter, average inner diameter and polydispersity of HNPs were characterized by a combination of experimental methods, including light, X-ray and neutron scattering, electron microscopy and N2 adsorption-desorption isotherms. Furthermore, the porosity of the shells of HNPs and the size of intrawall pores were determined by a new method proposed with the combination of the above techniques.
Three kinds of polymer-embedded HNP systems were prepared by freeze drying technique, i.e. poly(ethylene oxide) (PEO)-embedded HNPs, poly(methyl methacrylate) (PMMA)-embedded HNPs and polyethylene (PE)-embedded HNPs. The morphology of polymer-embedded HNP systems was investigated by SAXS and electron microscopy. A multi-shell sphere model was proposed to analyze the experimental SAXS data. For PEO-embedded HNPs, HNPs were observed to be supported on porous PEO scaffold. Moreover, it was found that nearly 96% of HNPs were buried uniformly in the PEO matrix, with a thin porous PEO layer deposited on the inner surface of HNP. However, the analysis for the morphology of PMMA-embedded HNPs and PE-embedded HNPs with current SAXS model was hindered due to the aggregation of HNPs.
Diffusion of solvents into polymer-embedded HNP systems was monitored by in-situ SAXS. Complex SAXS models were further proposed to obtain the diffusion kinetics. Diffusion of liquid low molecular PEO in PEO-embedded HNPs was found to consist of three stages, i.e. induction stage, steady state stage and depletion stage. It was further found that the filling rate of HNPs by solvent in the steady state stage was about 3 times faster than that in the induction stage and about 90 times faster than that in the depletion stage. Diffusion of water in PMMA-embedded HNPs and diffusion of oleyl alcohol and tetrafluorobenzene in PE-embedded HNPs were found to consist of a fast process and a slow process, which correspond to the relatively fast wetting of the polymer surface and the slow diffusion of solvents in the polymer matrix, respectively.
