The impact of nanoconfinement introduced by nanoparticles on polymer crystallization has attracted extensive attention because it plays an important role in the ultimate properties of polymer nanocomposites. In this study, interfacial and spatial confinement effects of silica (SiO2) nanoparticles on the crystallization behaviors of poly(ethylene oxide) (PEO)/SiO2 composites were systematically investigated by changing the size and concentration of SiO2 in PEO matrix. The composites with high silica loadings exhibit two crystallization peaks of PEO as determined by differential scanning calorimetry. The first peak at 7-43 degrees C is related to the bulk PEO, while the second peak at -20 to -30 degrees C is attributed to the restricted PEO segments. Three-layer (amorphous, interfacial, and bulk) model is proposed to interpret the confined crystallization of PEO/SiO2 composites, which is supported by the results of thermogravimetric analysis and solid-state H-1 nuclear magnetic resonance. In amorphous layer, most PEO segments are directly adsorbed on SiO2 surface via hydrogen bonding. The interfacial PEO layer, which is nonuniform, is composed of crystallizable loops and tails extending from amorphous layer. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 414-423