Polyamide 66 (PA66) was chosen as the representative of hydrophilic polymers, to investigate the influence of epitaxial crystals in semi-crystalline polymers/reduced graphene oxide nanocomposite injection-molding bars. A differential scanning calorimeter was used, and the two-dimensional wide-angle X-ray diffraction technique, as well as the two-dimensional small angle X-ray scattering technique, were used to research the crystallization behavior in PA66/RGO nanocomposites. The results indicated that RGO was an effective nucleation agent for PA66. The presence of RGO could enhance the orientation degree of the PA66 crystals and did not influence the crystal structure of the PA66. The non-epitaxial crystals and the epitaxial crystals existed in PA66/RGO nanocomposites. The size of epitaxial crystals was much greater than that of the non-epitaxial crystals. Tensile test results showed that the presence of fewer epitaxial crystals can improve the mechanical properties of a polymer.

Epitaxial crystallization between Polyamide 66 (PA66) and reduced graphene oxide (RGO) can enhance the interfacial interaction and the mechanical properties of PA66/RGO nanocomposites. In situ two-dimensional synchrotron radiation wide angle X-ray diffraction and small angle X-ray scattering were used to track the structural evolution of the PA66/RGO nanocomposites with an epitaxial crystal during uniaxial deformation. In the PA66/RGO nanocomposites, the structural evolution of non-epitaxial and epitaxial crystals could be clearly analyzed. The non-epitaxial crystal, whose crystal plane can slip, shows the rearrangement and the Brill transition during uniaxial deformation. While the PA66 chains of an epitaxial crystal are held by RGO, the crystal plane could therefore not slip. The epitaxial crystal also constrains the deformation of the amorphous phase and the crystal form transition of non-epitaxial crystals around them. With the content increase of epitaxial crystals, the constraint effect becomes more obvious. Therefore, the rigid epitaxial crystals in the PA66/RGO nanocomposites promote mechanical properties. The present findings can deepen the understanding of structural evolution during the tensile deformation of PA66/RGO nanocomposites and the influence of the epitaxial crystals on the mechanical property in semicrystalline polymers with a H-bond.

Crystalline block copolymers have been used to prepare plate-like colloidal systems with well-controlled size, shape, and size distribution. The isotropic-to-nematic (I–N) phase transition of the novel plate-like colloidal particle suspensions has been reported previously. In this work, we focus on the characterization of the solution structure of the crystals and the N-phase using small- and ultrasmall-angle X-ray scattering techniques (SAXS/USAXS). The system has polystyrene-block-poly­(l-lactide) (PS-b-PLLA) block copolymer single crystals (BCSCs) with different sizes dispersed in p-xylene. These crystals are truncated lozenge in shape and have effective diameters ranging from 550 to 4000 nm with a uniform dry thickness of 18.0 nm. Scattering of the individual crystal in solution can be simplified using a disc model with a core layer of 9–10 nm due to the lower contrast of the tethered PS layer. BCSC suspensions filled in thin quartz capillaries are prepared for monitoring the structural information. SAXS measurements of the isotropic phase show a strong face-to-face correlation, indicating that platelets form small stacked clusters in solutions. The isotropic phase is thus a coexistence of single crystals and the stacked multiple-layered clusters. The face-to-face spacing, d, in the N phases is around 75–90 nm, which increases slightly upon increasing the size of crystals. For a given system, the spacing does not change with increasing concentration under the current experimental conditions. Finally, the possible formation of lamellar domains within the N phase is also discussed due to the lateral attraction of this system. These results demonstrate the importance of the lateral attraction between the polar crystalline PLLA blocks on the formation of the N phase: the BCSCs self-assemble into larger sheets via the lateral attraction, which further enhances the I–N transition.

It has been reported that the introduction of reduced graphene oxide (RGO) can enhance the crystallization and orientation of high-density polyethylene (HDPE) matrix and thus improve the mechanical properties of HDPE/RGO nanocomposites. In this study, the local microstructures and orientations in different regions of HDPE/RGO bars with varied RGO contents were further explored by two-dimensional small-angle X-ray scattering using a microbeam technique. It is unveiled that the orientation orderings of each position is intensified with increasing RGO amount, and of particular interest is the observation of the slight change of the ordering degrees in diverse zones of HDPE/RGO nanocomposite bars, indicating that RGO imposes a uniform enhancing effect upon HDPE matrix within different areas and consequently induces an effective increase of the mechanical properties of HDPE/RGO nanocomposites.