Unmodified Clay Nanosheets at the Air–Water Interface

Abstract

Quasi-two-dimensional (2D) nanolayers, such as graphene oxide or clay layers, adhere to gas–liquid or liquid–liquid interfaces. Particularly, clays are of wide general interest in this context because of their extensive and crucial use as Pickering emulsion stabilizers, as well as for their ability to provide colloidosome capsules. So far, clays could only be localized at oil–water or air–saline-water interfaces in aggregated states, while our results now show that clay nanosheets without any modification can be located at air–deionized-water interfaces. The clay mineral used in the present work is synthetic fluorohectorite with a very high aspect ratio and superior quality in homogeneity and charge distribution compared to other clay minerals. This clay mineral is more suitable for achieving unmodified clay anchoring to fluid interfaces compared to other clay minerals used in previous works. In this context, we studied clay nanosheet organization at the air–water interface by combining different experimental methods: Langmuir–Blodgett trough studies, scanning electron microscopy (SEM) studies of film deposits, grazing-incidence X-ray off-specular scattering (GIXOS), and Brewster angle microscopy (BAM). Clay films formed at the air–water interface could be transferred to solid substrates by the Langmuir–Schaefer method. The BAM results indicate a dynamic equilibrium between clay sheets on the interface and in the subphase. Because of this dynamic equilibrium, the Langmuir monolayer surface pressure does not change significantly when pure clay sheets are spread on the liquid surface. However, also, GIXOS results confirm that there are clay nanosheets at the air–water interface. In addition, we find that clay sheets modified by a branched polymer are much more likely to be confined to the interface.

Bright, noniridescent structural coloration from clay mineral nanosheet suspensions

“…Clay nanosheets are strong in-plane but rather soft cross-plane, allowing them to curve or undulate ( 46 , 51 ). Adjacent layers of clay nanosheets in the Bragg stacks that can be turbostratically stacked with random displacement ( 43 ). This will result in local variations of separations, while the moment of inertia of the clay layers is evenly spaced.…”

“…Na-fluorohectorite (Na-FHt) is a synthetic clay mineral with superior quality regarding structural homogeneity, narrow charge distribution, and especially large aspect ratio (≈20,000) compared to most other clay minerals (41)(42)(43). Na-FHt when immersed in water forms nematic suspensions where single nanosheets are separated to uniform distances defined by the amount of water added (39,(43)(44)(45)(46), as evidenced by small-angle x-ray scattering (SAXS), birefringence (BF), or other methods (36,37,39,45,(47)(48)(49)(50).…”

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

“…They reported that high temperature and pressure were required as high-energy sources to separate the layers. Additionally, Akita and co-workers 22 and Brito et al 23 found that centrifugation and annealing processes were necessary to achieve a single-layered clay. Clearly, perfect exfoliation methods are poorly understood, although several mechanisms have been proposed.…”

Water Dynamics in Composite Aqueous Suspensions of Cellulose Nanocrystals and a Clay Mineral Studied through Magnetic Resonance Relaxometry

“…The properties of a polymer nanocomposite largely depend on the properties of incorporated nanoparticles, namely, their shape, size, aspect ratio, specific surface area, and so on . Among all kinds of nanoparticles, clays have been found to be effective because of their wide availability, cost-effectiveness, and easy processability . In particular, the smectite-type clays are known to form nematic liquid-crystalline phases in aqueous suspensions. , Clay-based nanocomposites have been exceedingly studied and explored to find a wide range of applications, such as adsorbents of organic pollutants in water, soils, and air, rheological modifiers in paints, inks, and grease, and drug delivery carriers .…”