Atomic Force Microscopy Study of Self-Assembled Sodium Chloride Nanocrystallites and Their Morphology Transitions

Interfacial liquid layers play a central role in a variety of phenomena ranging from friction to molecular recognition. Liquids near a solid surface form an interfacial layer where the molecular structure is different from that of the bulk. Here we report atomic resolution three-dimensional images of electrolyte solutions near a mica surface that demonstrate the existence of three types of interfacial structures. At low concentrations (0.01–1 M), cations are adsorbed onto the mica. The cation layer is topped by a few hydration layers. At higher concentrations, the interfacial layer extends several nanometres into the liquid. It involves the alternation of cation and anion planes. Fluid Density Functional calculations show that water molecules are a critical factor for stabilizing the structure of the interfacial layer. The interfacial layer stabilizes a crystal-like structure compatible with liquid-like ion and solvent mobilities. At saturation, some ions precipitate and small crystals are formed on the mica.

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“…5 ). The morphology of the nano and microcrystals follows some of the crystalline orientations of the mica 40 .…”

Section: Resultsmentioning

confidence: 97%

Atomically resolved three-dimensional structures of electrolyte aqueous solutions near a solid surface

et al. 2016

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“…For salt surfaces in the presence of water vapor below the DRH, the water layer thickness varies from submonolayer to multilayer, nanometer thin films. , The effects of thin-film water on the mobility and structure of salt ions at the interface have been characterized by conductivity, spectroscopy, and microscopy − studies. Prior to deliquescence, but above some critical RH where there is sufficient adsorbed water, ions become mobile and migrate along the surface.…”

Section: Introductionmentioning

confidence: 99%

Reaction of Bromide with Bromate in Thin-Film Water

2010

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Thin-film water is ubiquitous in nature, occurring on virtually all surfaces exposed to the ambient environment. In particular, alkali halide salts below their deliquescence point are expected to be coated with water films from one molecular layer to a few nanometers thick. While salt ion mobility in thin-film water has been characterized in the literature, little is known about the chemistry occurring within these films. Here we investigate the surface chemistry change of a mixed bromine salt (KBr/KBrO(3)) using X-ray photoelectron spectroscopy, secondary electron microscopy, and energy-dispersive X-ray spectroscopy. At 68% relative humidity, the Br(-) surface concentration was observed to deplete with increasing water vapor exposure time. Known bulk solution kinetics for the reaction of Br(-) + BrO(3)(-) has a second-order dependence on H(+) concentrations. However, in the present experiments there was no addition of an external acid. These results suggest that the pH and chemical reactions within thin-film water are uniquely differently from bulk solution. Because bromine chemistry in the atmosphere is strongly influenced by pH, these results have implications for the cycling of bromine where thin-film water is present.

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“…Less work has been done on dewetting of homogeneous surfaces by pure liquids and salt solutions, although features like those found with polymer films (hole nucleation, rim instabilities, fingering, regular droplet arrays, and spinodal dewetting) have been seen with water films dewetting on muscovite mica. Evaporating salt solutions on mica have been used to study epitaxy and morphology − of crystals depositing from thicker films and array-like crystal growth at a receding three-phase line . Intriguing patterns have been produced by evaporation of Ba(NO 3 ) 2 solution on polymer films, and the formation of unusual polymorphs has been found to occur by evaporation at the contact line of glycine and mannitol solutions …”

Section: Introductionmentioning

confidence: 99%

Crystal Patterns Created by Rupture of a Thin Film

Harrington

Campbell

Christenson

2013

Crystal Growth & Design

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We describe a method of generating remarkable crystal patterns on smooth surfaces such as mica, glass, or calcite. Very dilute droplets of aqueous salt solution (0.1 wt % NaCl) are deposited on the chosen substrate, and if the perimeter of these droplets becomes pinned by crystal deposition, they thin and concentrate by evaporation rather than shrink laterally. When thin enough, the liquid film ruptures by one of two mechanisms. In the first, crystals nucleate on the substrate and puncture the film, and as the holes grow radially from the rupturing crystal, the receding liquid rim deposits two-dimensional crystal dendrites. A second mechanism of rupture can occur with more dilute solutions (0.025 wt % NaCl), where attractive forces across the liquid film lead to rupture before crystals nucleate. This results in a pattern of bare patches surrounded by crystals, because supersaturation is only reached when the neighboring holes in the film are close to coalescence. The method is applicable to any solute in a volatile solvent on any smooth substrate, and the interplay of dewetting, crystal deposition, and symmetry of crystal and substrate leads to complex, system-specific patterns. The technique may be developed into methods of surface patterning with technologically important crystals.

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Atomic Force Microscopy Study of Self-Assembled Sodium Chloride Nanocrystallites and Their Morphology Transitions

Cited by 11 publications

References 45 publications

Atomically resolved three-dimensional structures of electrolyte aqueous solutions near a solid surface

Atomically resolved three-dimensional structures of electrolyte aqueous solutions near a solid surface

Reaction of Bromide with Bromate in Thin-Film Water

Crystal Patterns Created by Rupture of a Thin Film

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