Giant Multistep Crystalline vs. Osmotic Swelling of Synthetic Hectorite in Aqueous Acetonitrile

Abstract

Intercalation of large organocations into 2:1 clay minerals may be hampered by two problems: on one hand, the solubility of organocations in water is limited and the resulting high selectivity for adsorption in the polar solvent may lead to non-equilibrium structures. On the other hand, the large expansion of the interlayer space will slow down kinetics of ion exchange considerably. The best workaround for these obstacles is to suspend the clay minerals in mixtures of water with more hydrophobic organic solvents that nevertheless trigger a considerable expansion of the interlayer space by swelling. This in turn fosters ion exchange. The current study, therefore, revisited pioneering work by Bradley (1945) and investigated the swelling behavior of synthetic sodium hectorite (Na-hec) as a function of the composition of the swelling solvent, a mixture of acetonitrile and water. Up to a maximum acetonitrile content of 65 vol.%, delamination by osmotic swelling occurred. At even higher acetonitrile concentrations, swelling was limited to the crystalline swelling regime where a step-like adjustment of the d value was observed. Several mixtures were identified yielding a well defined and uniform interlayer height as evidenced by rational 00l-series with the d spacing decreasing with increasing acetonitrile content. Surprisingly, for a specific acetonitrile:water ratio even an ordered interstratification of two strictly alternating interlayer heights with distinctly different solvent compositions was observed.

Swelling properties of graphite oxides and graphene oxide multilayered materials

“…The crystalline and osmotic swelling are commonly found in clay minerals. 157,[212][213][214][215] Remarkably, crystalline swelling is found for Brodie GO in all so far studied solvents except for water, while for Hummers GO only osmotic swelling has so far been reported. Crystalline swelling provides an opportunity to evaluate the thickness of solvent layers confined between GO sheets.…”

Sandwich‐Like Encapsulation of a Highly Luminescent Copper(I) Complex

“…For fast kinetics of the intercalation of [Cu(dppb) 2 ] + the one‐layer hydrate of Na + ‐hec was first swollen in acetonitrile: water mixture (75:25 vol%) (Figure 1a). Swelling in this solvent mixture is limited to the crystalline regime and the basal spacing [ 17 ] expanded in this mixture from d 001 = 12.3 Å for the one‐layer hydrate [ 11 ] to 30.7 Å for the crystalline swollen Na + ‐hec (Figure S1b, Supporting Information), as determined by means of small‐angle X‐ray scattering (SAXS). Enlarging the gap opening between adjacent silicate layers to ≈21 Å (subtracting the layer thickness of hectorite, 10 from 30.7 Å) facilitates the intercalation of the bulky metal‐complex ions [Cu(dppb) 2 ] + of ≈10 Å.…”

“…Only the latter are capably to swell osmotically. [ 9c,17 ] When immersing the alternating heterostructure into deionized, pure water, the crystal forceless and spontaneously delaminates into double‐stacks, where a hydrophobic monolayer of [Cu(dppb) 2 ] + is encapsulated between the two thin silicate layers (Figure 1c).…”

Swelling Pressures of Graphite Oxide and Graphene Oxide Membranes in Water and Ethanol

“…Osmotic swelling is controlled by the relatively easy flow of solvent in and out of structure regulated by osmotic effects. [29][30][31][32][33] Remarkably, crystalline swelling is found for Brodie GO in all so far studied solvents except water [34][35][36][37][38] while for Hummers GO only osmotic-like swelling was so far reported. [37,39,40] Adding water to clays under conditions of confinement is known to produce pressures in the range of tens or even hundreds of bar.…”

“…Osmotic swelling is controlled by the relatively easy flow of solvent in and out of structure regulated by osmotic effects. [ 29–33 ] Remarkably, crystalline swelling is found for Brodie GO in all so far studied solvents except water [ 34–38 ] while for Hummers GO only osmotic‐like swelling was so far reported. [ 37,39,40 ]…”