Systematic study of the nanostructures of exfoliated polymer nanocomposites

Abstract

High-performance bioinspired materials have shown rapid development over the last decade. Examples are brick-and-mortar hierarchical structures, which are often achieved via solvent evaporation. Although good properties are claimed, most systems are composed of stacked or intercalated platelets. Exfoliation is a crucial step to give ultimate anisotropic properties, e.g. thermal, mechanical and barrier properties. We propose a general framework for all the various types of micro-scale structures that should be distinguished for 2D-filler nanocomposites. In particular, the exfoliated state is systematically explored by the immobilization of montmorillonite platelets via (gelatin) hydrogelation. Scattering techniques were used to evaluate this strategy at the level of the particle dispersion and the regularity of spatial arrangement. The gelatin/montmorillonite exfoliated nanostructures are fully controlled by the filler volume fraction since the observed gallery d-spacings perfectly fall onto the predicted values. Surprisingly, X-ray analysis also revealed short- and quasi long-range arrangement of the MMT at high loading.

Affine Deformation and Self-Assembly Alignment in Hydrogel Nanocomposites

“…This has been observed before in fiber reinforcement, for example, in aramid fibers, E f goes range from 240 to ∼80 GPa due to the pleated sheet structure, even when there is a high ⟨P 2 ⟩. 51,52 Therefore, particularly at low dspacings, such as from 33MMT, 39 the Halpin−Tsai model couples the effects of high filler concentrations with aspect ratios.…”

“…In addition, our previous wide-angle X-ray scattering (WAXS) and focused ion beam scanning electron microscopy (FIB-SEM) analyses show that the polymer is homogeneously distributed within the lamellae, resulting in exfoliated nanostructures. 39 A flame resistance test was performed for a few nanocomposites after 50% RH equilibration; see Figures 2e and S12. This test provides a rapid way to assess nanocomposite flame retardancy.…”

“…We have indirectly measured, via FIB-SEM, the average length of 212 ± 97 nm of dispersed nanoparticles in composite cross-section. 39 All chemicals used were of analytical grade.…”

“…One advantage of such a mechanism comes from nanoparticle immobilization with the aid of an appropriate matrix solvent, thus initially preventing loss of filler aspect ratio. This translates to nanostructures that are effectively exfoliated/ intercalated and well-aligned, 39 which is crucial for final material properties, for example, gas transport and mechanical properties. Even though this mechanism serves as a separate nacre-inspired strategy, many studies have resulted in a similar composite preparation method via trial and error.…”

“…This cannot be attributed to a lowered aspect ratio due to particle stacking, which would have been present in WAXS and SEM data. 39 Since all the composites were exfoliated, the main contribution to the modulus should have been the orientational order.…”