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The recently developed tough and self-healing hydrogels, containing a large number of physical bonds, have found widespread applications in bioengineering and soft electronics. Owing to the sophisticated physical interactions and organization, these hydrogels often demonstrate structural heterogeneities, which strongly influence their mechanical performances. Using poly­(N,N-dimethyl acrylamide-co-methacrylic acid) hydrogels (P­(DMAA-co-MAAc)) with dynamic hydrogen bonds (H-bonds) as a model system, the structural characterization has been carried out in this study using small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) analyses, along with exploring the influence of the structure on the mechanical properties. By systematically tuning the polymer composition, including the monomer fraction and chemical cross-linking density, two different hydrogel regions with distinct mechanical properties were observed: the swollen regions and shrunk regions. The former was mechanically weak, whereas the latter exhibited a tough behavior. Both types of hydrogels were noted to be highly heterogeneous, which results from the nanoscale spatial polymer concentration fluctuations at ∼100 nm scale. Combined with the contrast variation utilizing SANS, the structure parameters, including the polymer volume fraction of the dense and sparse regions, volume fraction occupied in the space, and average correlation length of the long-range and short-range heterogeneous structures, were explored using a scaling model based on a two-phase system composed of the densely and sparsely cross-linked regions. Using in situ SAXS, the microscopic deformation of the tough and shrunk hydrogels was noted to follow the affine deformation, while a significantly non-affine deformation was observed in the swollen hydrogels, which might have led to the different mechanical performances of these materials.

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With coal gangue and high alumina refractory solid wastes as raw materials, needle-like mullite powder, with an average diameter of about 1 μm, was synthesized at 1300°C by using the conventional solid-state reaction method. Mullite ceramics were derived from the inexpensive needle-like powder. Phase composition was examined by using X-ray diffraction (XRD), while morphologies of the ceramics were observed by using scanning electron microscopy. The content and distribution of elements in the sintered samples were characterized with energy dispersive spectrometer and X-ray fluorescence spectroscopy. Mechanical properties of the mullite ceramics were studied by using the three-point bending method. The aspect ratio of the needle-like mullite particles was up to 6. The mullite sample sintered at 1500°C for 3 hours had a density of 2.515 g•cm −3 , which was slightly lower than the theoretical density. Maximum fracture toughness and bending strength of the mullite ceramics were 1.82 MPa•m 1/2 and 71.76 MPa, respectively. This study realizes the resource utilization of gangue and high alumina refractory solid wastes, and the prepared mullite ceramics have good application prospect.

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