3D Hierarchical orientation in polymer–clay nanocomposite films

Abstract

Organically modified clay was used as reinforcement for HDPE using maleated polyethylene (PEMA) as a compatibilizer. The effect of compatibilizer concentration on the orientation of various structural features in the polymer-layered silicate nanocomposite (PLSN) system was studied using two-dimensional (2D) small angle X-ray scattering (SAXS) and 2D wide-angle X-ray scattering (WAXS). The dispersion (repeat period) and three-dimensional (3D) orientations of six different structural features were easily identified: (a) clay clusters/tactoids (0.12 μm), (b) modified clay (002) (24–31 Å), (c) unmodified clay (002) (13 Å), (d) clay (110) and (020) planes normal to (b) and (c), (e) polymer crystalline lamellae (001) (190–260 Å), and (f) polymer unit cell (110) and (200) planes. A 3D study of the relative orientation of this hierarchical morphology was carried out by measuring three scattering projections for each sample. Quantitative data on the orientation of these structural units in the nanocomposite film is determined through calculation of the major axis direction cosines and through a ternary, direction-cosine plot. Surprisingly, it is the unmodified clay which shows the most intimate relationship with the polymer crystalline lamellae in terms of orientation. Association between clay and polymer lamellae may be related to an observed increase in lamellar thickness in the composite films. Orientation relationships also reveal that the modified clay is associated with large-scale tactoid structures.