The role of TiO2 nanoparticle surfaces in affecting the crystalline structure of low-density polyethylene (LDPE) has been investigated by varying the nanoparticle surface from hydrophilic (as-received) to less hydrophilic (dried) or more hydrophilic (polar silane treated). Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WXRD) were used to determine the degree of crystallinity and crystalline structure. The impact of nanoparticle aggregates on the nanometer to micrometer organization of LDPE crystals was studied with atomic force microscopy (AFM) and small-angle light scattering (SALS). This characterization showed that the presence of the TiO2 nanoparticles, with the various different surface conditions investigated, did not alter the degree of LDPE crystallinity, the unit cell dimensions, the average lamellar thickness, or the average spherulite size. However, the nanoparticles did affect the internal arrangement of intraspherulitic crystalline aggregates by decreasing the relative optic axis orientation of these crystals, usually referred to as internal spherulite disorder. The LDPE filled with the nanoparticles treated with a polar silane (N-(2-aminoethyl) 3-aminopropyl-trimethoxysilane (AEAPS)) showed the highest internal spherulitic disorder and exhibited the most poorly developed spherulite structure. The combination of SALS with AFM has allowed a detailed characterization of the morphology of the semicrystalline polymer nanocomposites. Information on the internal organization of the spherulites, the size of the nanoparticle aggregates, and the location of the nanoparticle aggregates can be uniquely obtained when both techniques are used. (C) 2005 Wiley Periodicals, Inc.