Michels-Brito Paulo H, Malfatti-Gasperini Antonio, Mayr Lina, Puentes-Martinez Ximena, Tenório Rômulo P, Wagner Daniel R, Knudsen Kenneth D, Araki Koiti, Oliveira Rafael G, Breu Josef, Cavalcanti Leide P, Fossum Jon Otto
Department of Physics, Norwegian University of Science and Technology, NTNU, 7491 Trondheim, Norway.
Brazilian Synchrotron Light Laboratory, LNLS, Brazilian Center for Research in Energy and Materials, CNPEM, Campinas 13083-970, Brazil.
Langmuir. 2021 Jan 12;37(1):160-170. doi: 10.1021/acs.langmuir.0c02670. Epub 2020 Dec 29.
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.
准二维（2D）纳米层，如氧化石墨烯或粘土层，会附着在气-液或液-液界面上。特别地，在这种情况下，粘土因其作为Pickering乳液稳定剂的广泛且关键的用途以及提供胶体囊泡的能力而受到广泛关注。到目前为止，粘土只能以聚集状态定位在油水或空气-盐水界面处，而我们现在的结果表明，未经任何修饰的粘土纳米片可以定位在空气-去离子水界面处。本工作中使用的粘土矿物是合成氟代锂蒙脱石，与其他粘土矿物相比，其具有非常高的纵横比，并且在均匀性和电荷分布方面具有卓越的品质。与先前工作中使用的其他粘土矿物相比，这种粘土矿物更适合实现未修饰的粘土在流体界面上的锚固。在这种情况下，我们通过结合不同的实验方法研究了空气-水界面处的粘土纳米片组织：Langmuir-Blodgett槽研究、薄膜沉积物的扫描电子显微镜（SEM）研究、掠入射X射线非镜面散射（GIXOS）和布鲁斯特角显微镜（BAM）。在空气-水界面形成的粘土薄膜可以通过Langmuir-Schaefer方法转移到固体基板上。BAM结果表明界面上和亚相中粘土片之间存在动态平衡。由于这种动态平衡，当纯粘土片铺展在液体表面时，Langmuir单层表面压力不会显著变化。然而，GIXOS结果也证实了空气-水界面处存在粘土纳米片。此外，我们发现由支化聚合物修饰的粘土片更有可能局限于界面。
