Discrete Electrolytes Research

Liquid ionics beyond Poisson-Boltzmann

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Publications: 2012

25.

S. Karpitschka, E. Dietrich, J.R.T. Seddon, H.J.W. Zandvliet, D. Lohse, & H. Riegler
"Nonintrusive optical visualization of surface nanobubbles"
Phys. Rev. Lett. 109, 066102 (2012)

Individual surface nanobubbles are visualized with nonintrusive optical interference-enhanced reflection microscopy, demonstrating that their formation is not a consequence of the hitherto used intrusive atomic force microscopy technique. We then use this new and fast technique to demonstrate that surface nanobubbles form in less than a few seconds after ethanol-water exchange, which is the standard procedure for their preparation, and examine how they react to temperature variations.

24.

J.R.T. Seddon, M.P. Kok, E.C. Linnartz, & D. Lohse
"Bubble puzzles in liquid squeeze: Cavitation during compression"
EPL 97, 24004 (2012)

We let a steel ball fall on a thin liquid layer. Thereby the liquid was squeezed out from between the falling sphere and the solid boundary, which was made of thick glass, allowing for direct high-speed visualisation of the liquid layer at the point of closest approach. Surprisingly, vapour cavities were created during squeeze, with the liquid forced to change phase to vapour as the sphere approached the boundary and the pressure thus increased. This is a direct contradiction to common preconceptions, where classical theory expects the phase transition from liquid to vapour to occur during depressurisation. We believe that our result is the first direct experimental evidence of the shear-induced cavitation model of Joseph (J. Fluid Mech., 366 (1998) 367).

23.

R.P. Berkelaar, J.R.T. Seddon, H.J.W. Zandvliet, & D. Lohse
"Temperature dependence of surface nanobubbles"
ChemPhysChem 13, 2213 (2012)

The temperature dependence of nanobubbles was investigated experimentally using atomic force microscopy. By scanning the same area of the surface at temperatures from 51oC to 25oC it was possible to track geometrical changes of individual nanobubbles as the temperature was decreased. Interestingly, nanobubbles of the same size react differently to this temperature change; some grow whilst others shrink. This effect cannot be attributed to Ostwald ripening, since the growth and shrinkage of nanobubbles appears to occur in distinct patches on the substrate. The total nanobubble volume per unit area shows a maximum around 33oC, which is comparable with literature where experiments were carried out with increasing temperature. This underlines the stability of surface nanobubbles.

22.

J.H. Weijs, J.R.T. Seddon, & D. Lohse
"Diffusive shielding stabilizes bulk nanobubble clusters"
ChemPhysChem 13, 2197 (2012)
→ Cover Issue

Using molecular dynamics, we study the nucleation and stability of bulk nanobubble clusters. We study the formation, growth, and final size of bulk nanobubbles. We find that, as long as the bubble-bubble interspacing is small enough, bulk nanobubbles are stable against dissolution. Simple diffusion calculations provide an excellent match with the simulation results, giving insight into the reason for the stability: nanobubbles in a cluster of bulk nanobubbles protect each other from diffusion by a shielding effect.

21.

J.R.T. Seddon, D. Lohse, W.A. Ducker, & V.S.J. Craig
"A deliberation on nanobubbles at surfaces and in bulk"
ChemPhysChem 13, 2179 (2012)
→ Invited Review

Surface and bulk nanobubbles are two types of nanoscopic gaseous domain that have recently been discovered in interfacial physics. Both are expected to be unstable to dissolution because of the high internal pressure driving diffusion and the surface tension which squeezes the gas out, but there is a rapidly growing body of experimental evidence that demonstrates both bubble types to be stable. However, the two types of bubbles also differ in many respects: surface nanobubble stability is most probably assisted by the nearby wall, which can repel the water (in the case of hydrophobicity), accept physisorbed gas molecules, and reduce the surface area through which outfluxing can occur; bulk nanobubbles, on the other hand, must stabilise themselves. This is perhaps through ionic shielding, perhaps through diffusive shielding, or perhaps through both. Herein, the features of both bubble types are described individually, their common and disparate features are discussed, and emerging applications are examined.

20.

D. Fernandez-Rivas, B. Verhaagen, J.R.T. Seddon, A.G. Zijlstra, L.-M. Jiang, L.W.M. van der Sluis, M. Versluis, D. Lohse, & H.J.G.E. Gardeniers
"Localized removal of layers of metal, polymer, or biomaterial by ultrasound cavitation bubbles"
Biomicrofluidics 6, 034114 (2012)

We present an ultrasonic device with the ability to locally remove deposited layers from a glass slide in a controlled and rapid manner. The cleaning takes place as the result of cavitating bubbles near the deposited layers and not due to acoustic streaming. The bubbles are ejected from air-filled cavities micromachined in a silicon surface, which, when vibrated ultrasonically at a frequency of 200 kHz, generate a stream of bubbles that travel to the layer deposited on an opposing glass slide. Depending on the pressure amplitude, the bubble clouds ejected from the micropits attain different shapes as a result of complex bubble interaction forces, leading to distinct shapes of the cleaned areas. We have determined the removal rates for several inorganic and organic materials and obtained an improved efficiency in cleaning when compared to conventional cleaning equipment. We also provide values of the force the bubbles are able to exert on an atomic force microscope tip.

19.

O. Bliznyuk, J.R.T. Seddon, V. Veligura, E.S. Kooij, H.J.W. Zandvliet, & B. Poelsema
"Directional liquid spreading over chemically defined radial wettability gradients"
ACS Appl. Mater. Interfaces 4, 4141 (2012)

We investigate the motion of liquid droplets on chemically defined radial wettability gradients. The patterns consist of hydrophobic fluorinated self-assembled monolayers (SAMs) on oxidized silicon substrates. The design comprises a central hydrophobic circle of unpatterned SAMs surrounded by annular regions of radially oriented stripes of alternating wettability, i.e., hydrophilic and hydrophobic. Variation in the relative width of the stripes allows control over the macroscopic wettability. When a droplet is deposited in the middle, it will start to move over to the radially defined wettability gradient, away from the center because of the increasing relative surface area of hydrophilic matter for larger radii in the pattern. The focus of this article is on a qualitative description of the characteristic motion on such types of anisotropic patterns. The influence of design parameters such as pattern dimensions, steepness of the gradient, and connection between different areas on the behavior of the liquid are analyzed and discussed in terms of advancing and receding contact lines, contact angles, spatial extent, and overall velocity of the motion.