Dynamic study of [Emim]Ac ionic liquid droplet impact on mildly heated solid surfaces

We investigate the interfacial properties of the non-halogenated ionic liquid (IL), trihexyl(tetradecyl)phosphonium bis(mandelato)borate, [P6,6,6,14][BMB], in proximity to solid surfaces, by means of surface force measurement. The system consists of sharp atomic force microscopy (AFM) tips interacting with solid surfaces of mica, silica, and gold. We find that the force response has a monotonic form, from which a characteristic steric decay length can be extracted. The decay length is comparable with the size of the ions, suggesting that a layer is formed on the surface, but that it is diffuse. The long alkyl chains of the cation, the large size of the anion, as well as crowding of the cations at the surface of negatively charged mica, are all factors which are likely to oppose the interfacial stratification which has, hitherto, been considered a characteristic of ionic liquids. The variation in the decay length also reveals differences in the layer composition at different surfaces, which can be related to their surface charge. This, in turn, allows the conclusion that silica has a low surface charge in this aprotic ionic liquid. Furthermore, the effect of temperature has been investigated. Elevating the temperature to 40 °C causes negligible changes in the interaction. At 80 °C and 120 °C, we observe a layering artefact which precludes further analysis, and we present the underlying instrumental origin of this rather universal artefact.

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Pressure generated at the instant of impact between a liquid droplet and solid surface

Royal Society Open Science ◽

10.1098/rsos.181101 ◽

2018 ◽

Vol 5 (12) ◽

pp. 181101 ◽

Cited By ~ 7

Author(s):

Y. Tatekura ◽

M. Watanabe ◽

K. Kobayashi ◽

T. Sanada

Keyword(s):

Solid Surface ◽

Shape Factor ◽

Liquid Droplet ◽

Pressure Rise ◽

Propagation Speed ◽

Spherical Shape ◽

Water Hammer ◽

Droplet Impact ◽

Maximum Pressure ◽

The Impact

The prime objective of this study is to answer the question: How large is the pressure developed at the instant of a spherical liquid droplet impact on a solid surface? Engel first proposed that the maximum pressure rise generated by a spherical liquid droplet impact on a solid surface is different from the one-dimensional water-hammer pressure by a spherical shape factor (Engel 1955 J. Res. Natl Bur. Stand. 55 (5), 281–298). Many researchers have since proposed various factors to accurately predict the maximum pressure rise. We numerically found that the maximum pressure rise can be predicted by the combination of water-hammer theory and the shock relation; then, we analytically extended Engel’s elastic impact model, by realizing that the progression speed of the contact between the gas–liquid interface and the solid surface is much faster than the compression wavefront propagation speed at the instant of the impact. We successfully correct Engel’s theory so that it can accurately provide the maximum pressure rise at the instant of impact between a spherical liquid droplet and solid surface, that is, no shape factor appears in the theory.

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Diameter-dependent wetting of tungsten disulfide nanotubes

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1607202113 ◽

2016 ◽

Vol 113 (48) ◽

pp. 13624-13629 ◽

Cited By ~ 9

Author(s):

Ohad Goldbart ◽

Sidney R. Cohen ◽

Ifat Kaplan-Ashiri ◽

Polina Glazyrina ◽

H. Daniel Wagner ◽

...

Keyword(s):

Composite Materials ◽

Molecular Basis ◽

Liquid Droplet ◽

Outer Wall ◽

Tungsten Disulfide ◽

Solid Surfaces ◽

Hollow Core ◽

Experimental Paradigm ◽

Simple Process ◽

Unique Shape

The simple process of a liquid wetting a solid surface is controlled by a plethora of factors—surface texture, liquid droplet size and shape, energetics of both liquid and solid surfaces, as well as their interface. Studying these events at the nanoscale provides insights into the molecular basis of wetting. Nanotube wetting studies are particularly challenging due to their unique shape and small size. Nonetheless, the success of nanotubes, particularly inorganic ones, as fillers in composite materials makes it essential to understand how common liquids wet them. Here, we present a comprehensive wetting study of individual tungsten disulfide nanotubes by water. We reveal the nature of interaction at the inert outer wall and show that remarkably high wetting forces are attained on small, open-ended nanotubes due to capillary aspiration into the hollow core. This study provides a theoretical and experimental paradigm for this intricate problem.

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