Supramolecular exfoliation of layer silicate clay by novel cationic pillar[5]arene intercalants

Abstract

Clays are multi-layered inorganic materials that can be used to prepare nanocomposite fillers. Because the multi-layered structure is thermodynamically stable, it is difficult to change a multi-layered material into single layers to improve its dispersity. Previously, clays were modified with dodecylammonium cations to promote complexation with nylon 6, nylon 66, polypropylene, polyethylene, polystyrene, and polycaprolactone to increase the mechanical strength (and/or thermal stability) of the composite material; however, complete exfoliation could not be achieved in these composites. In this study, pillar[5]arenes are synthesized and functionalized with ten cationic substituents as novel intercalants for modifying bentonite clay, which is a multi-layered metal-cation-containing silicate. The pillar[5]arenes exfoliate the clay by forming polyrotaxanes with poly(ethylene glycol) through host–guest interactions.

Giant single-crystal-to-single-crystal transformations associated with chiral interconversion induced by elimination of chelating ligands

“…Reports of reversible SCSC transformations associated with large volume and mass changes are rare in the literature (Supplementary Table 2 ). The 50% total volumetric shrinkage and 36% total weight loss observed for the present material, which are reminiscent of the expansion of clay structures by adding ethylene glycol 39 , 40 , are larger than those observed for other typical single-crystal materials that undergo reversible SCSC transformations, and they are even comparable to those of two recently discovered porous crystalline materials that contain biomolecules, i.e., ferritin and tripeptide, that demonstrate giant expandability in response to guest sorption 31 , 32 . Although detailed atomic level structural information is important for understanding these super-adaptive crystal lattices, such information is difficult to obtain for these biomolecules because of the disordered nature of the guests in their pores and the disruption of the single-crystal lattice that occurs upon giant expansion.…”

Systematic study of the nanostructures of exfoliated polymer nanocomposites

“…This is encouraging because examples of perfect exfoliation are limited, with often high temperature and pressure required. 26 In comparison, other successful 2D silicate bionanocomposites have been reported, usually at lower loadings, and, even so, fall inside the intercalated regime (Figure 2c). 18,31 The WAXS diffraction patterns were also obtained at higher q scattering vectors by moving the detection setup (Figure 3a).…”

“…Restacking into aggregates, or tactoids, is one of the most frequently addressed issues in nanocomposite preparation and processing. [23][24][25][26] When platelets are stacked (S) they are phase separated from the polymer matrix, indicating chains do not diffuse in between the individual layers, which remain immiscible. In X-ray diffraction, the gallery d-spacing, d001, corresponds to the initial bulk material.…”

“…In fact, to the best of our knowledge, positional order has been only reported in silicates modified by quaternary ammonium cations and host-guest additives. 26 Our exfoliation strategy depends on the formation of a continuous network to immobilize the 2D material and develop yield stress. However, the extent of gelation or network density seemed to decrease with higher MMT loadings.…”

Fast and Clean Synthesis of Nylon-6/Synthetic Saponite Nanocomposites

“…In many cases, the inclusion of a highly dispersed, single-layered, delaminated clay in the polymer matrix can enhance the properties of the polymer [ 16 ]. Kakuta et al [ 17 ] recently synthesized and functionalized organic compounds, such as pillar [ 5 ] arenes, with several cationic substituents and used them as intercalants to modify bentonite. They proved that the pillararenes exfoliate the clay by forming polyrotaxanes with poly(ethylene glycol) through host–guest interactions.…”