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.
Highlights
Self-assembly processes are essential and important in biology, materials science, and technology,[1−5] for instance, at liquid− liquid interfaces[6−8] for the design of emulsions
Various methods have been employed for studies of selfassembly of graphene oxide (GO) at the air−liquid interface such as Langmuir− Blodgett methods for single-layer film assembly, evaporationinduced assembly for free-standing membranes, or threedimensional (3D) interfaces for crumpled shells.[15]
This was done in three steps: First, the double layer (DBL) suspension was spread on the surface, followed by spreading of the dipalmitoyl phosphatidylcholine (DPPC) lipid solution on top of the clay films while continuously monitoring the pressure to keep it around 30 mN/m
Summary
Self-assembly processes are essential and important in biology, materials science, and technology,[1−5] for instance, at liquid− liquid interfaces[6−8] for the design of emulsions. We have monitored the structural organization of synthetic fluorohectorite clay nanolayer colloids, modified and unmodified, confined at the air−water interface using surface-sensitive techniques such as grazing-incidence Xray off-specular scattering (GIXOS),[74] scanning electron microscopy (SEM), and Brewster angle microscopy (BAM).[75] Both the film thickness and in-plane organization were studied. Na-FHt (Na0.5[Mg2.5 Li0.5]⟨Si4⟩O10F2) was synthesized from the melt following a published procedure,[38] resulting in clay with high aspect ratio and unique homogeneous charge density. This clay mineral has been demonstrated to have superior quality compared to other clay minerals.[38]. Si wafers’ specifications are as follows: grade, prime; CZ growth; B dopant, orientation, 100; resistivity, 1−5 Ω/m
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