Experimental setup for measuring the dispersion forces by the adhered cantilever method.

Dispersion forces start to play role in modern micro/nanoelectromechanical devices, but the methods to measure these forces at distances close to contact (<50 nm) suffer from pull-in instability. The method of adhered cantilever proposed recently has no instability and is able to make measurements at short separations. To measure the force at the average distance between surfaces in contact, one has to know the shape of an elastic beam with one end fixed at a height of 1-10 μm and the other end adhered to the substrate.

Nanoreactors in action for a durable microactuator using spontaneous combustion of gases in nanobubbles.

A number of recent studies report enhancement of chemical reactions on water microdroplets or inside nanobubbles in water. This finding promises exciting applications, although the mechanism of the reaction acceleration is still not clear. Specifically, the spontaneous combustion of hydrogen and oxygen in nanobubbles opens the way to fabricate truly microscopic engines.

Fast Electrochemical Actuator with Ti Electrodes in the Current Stabilization Regime.

The actuators needed for autonomous microfluidic devices have to be compact, low-power-consuming, and compatible with microtechnology. The electrochemical actuators could be good candidates, but they suffer from a long response time due to slow gas termination. An actuator in which the gas is terminated orders of magnitude faster has been demonstrated recently.

Wetting of surfaces decorated by gas-phase synthesized silver nanoparticles: Effects of Ag adatoms, nanoparticle aging, and surface mobility.

The wetting state of surfaces can be rendered to a highly hydrophobic state by the deposition of hydrophilic gas phase synthesized Ag nanoparticles (NPs). The aging of Ag NPs leads to an increase in their size, which is also associated with the presence of Ag adatoms on the surface between the NPs that have a strong effect on the wetting processes. Furthermore, surface airborne hydrocarbons were removed by UV-ozone treatment, providing deeper insight into the apparent mobility of the NPs on different surfaces and their subsequent ripening and aging.

Highly energetic impact of H and O nanobubbles on Pt surface.

Hypothesis Water electrolysis performed by short (≲5μs) voltage pulses of alternating polarity generates a dense cloud of H and O nanobubbles. Platinum electrodes turn black in this process, while they behave differently when the polarity is not altered. We prove that the modification of Pt is associated with highly energetic impact of nanobubbles rather than with any electrochemical process.

Effect of Airborne Hydrocarbons on the Wettability of Phase Change Nanoparticle Decorated Surfaces.

We present here a detailed study of the wettability of surfaces nanostructured with amorphous and crystalline nanoparticles (NPs) derived from the phase-change material GeSbTe (GST). Particular attention was devoted to the effect of airborne surface hydrocarbons on surface wetting. Our analysis illustrates that a reversible hydrophilic-hydrophobic wettability switch is revealed by combined ultraviolet-ozone (UV-O) treatments and exposure to hydrocarbon atmospheres.

Collective behavior of bulk nanobubbles produced by alternating polarity electrolysis.

Nanobubbles in liquids are mysterious gaseous objects with exceptional stability. They promise a wide range of applications, but their production is not well controlled and localized. Alternating polarity electrolysis of water is a tool that can control the production of bulk nanobubbles in space and time without generating larger bubbles.

Electrically controlled cloud of bulk nanobubbles in water solutions.

Using different experimental techniques we visualize a cloud of gas in water that is produced electrochemically by the alternating polarity process. Liquid enriched with gas does not contain bubbles strongly scattering visible light but its refractive index changes significantly near the electrodes. The change of the refractive index is a collective effect of bulk nanobubbles with a diameter smaller than 200 nm.

Highly energetic phenomena in water electrolysis.

Water electrolysis performed in microsystems with a fast change of voltage polarity produces optically invisible nanobubbles containing H and O gases. In this form the gases are able to the reverse reaction of water formation. Here we report extreme phenomena observed in a millimeter-sized open system.

Effect of Disjoining Pressure on Surface Nanobubbles.

In gas-oversaturated solutions, stable surface nanobubbles can exist thanks to a balance between the Laplace pressure and the gas overpressure, provided the contact line of the bubble is pinned. In this article, we analyze how the disjoining pressure originating from the van der Waals interactions of the liquid and the gas with the surface affects the properties of the surface nanobubbles. From a functional minimization of the Gibbs free energy in the sharp-interface approximation, we find the bubble shape that takes into account the attracting van der Waals potential and gas compressibility effects.

Capillary-force measurement on SiC surfaces.

Capillary forces have been measured by atomic force microscopy in the sphere-plate geometry, in a controlled humidity environment, between smooth silicon carbide and borosilicate glass spheres. The force measurements were performed as a function of the rms surface roughness ∼4-14 nm mainly due to sphere morphology, the relative humidity (RH) ∼0%-40%, the applied load on the cantilever, and the contact time. The pull-off force was found to decrease by nearly two orders of magnitude with increasing rms roughness from 8 to 14 nm due to formation of a few capillary menisci for the roughest surfaces, while it remained unchanged for rms roughness <8 nm implying fully wetted surface features leading to a single meniscus.

Influence of materials' optical response on actuation dynamics by Casimir forces.

The dependence of the Casimir force on the frequency-dependent dielectric functions of interacting materials makes it possible to tailor the actuation dynamics of microactuators. The Casimir force is largest for metallic interacting systems due to the high absorption of conduction electrons in the far-infrared range. For less conductive systems, such as phase change materials or conductive silicon carbide, the reduced force offers the advantage of increased stable operation of MEMS devices against pull-in instabilities that lead to unwanted stiction.

Influence of surface roughness on dispersion forces.

Surface roughness occurs in a wide variety of processes where it is both difficult to avoid and control. When two bodies are separated by a small distance the roughness starts to play an important role in the interaction between the bodies, their adhesion, and friction. Control of this short-distance interaction is crucial for micro and nanoelectromechanical devices, microfluidics, and for micro and nanotechnology.

New type of microengine using internal combustion of hydrogen and oxygen.

Microsystems become part of everyday life but their application is restricted by lack of strong and fast motors (actuators) converting energy into motion. For example, widespread internal combustion engines cannot be scaled down because combustion reactions are quenched in a small space. Here we present an actuator with the dimensions 100 × 100 × 5 μm(3) that is using internal combustion of hydrogen and oxygen as part of its working cycle.

Transient nanobubbles in short-time electrolysis.

Water electrolysis in a microsystem is observed and analyzed on a short-time scale of ∼10 μs. The very unusual properties of the process are stressed. An extremely high current density is observed because the process is not limited by the diffusion of electroactive species.

Combustion of hydrogen-oxygen mixture in electrochemically generated nanobubbles.

Ignition of exothermic chemical reactions in small volumes is considered as difficult or impossible due to the large surface-to-volume ratio. Here observation of the spontaneous reaction is reported between hydrogen and oxygen in bubbles whose diameter is smaller than a threshold value around 150 nm. The effect is attributed to high Laplace pressure and to fast dynamics in nanobubbles and is the first indication on combustion in the nanoscale.

Application of the Lifshitz theory to poor conductors.

The Lifshitz formula for dispersive forces is generalized to the materials, which cannot be described with the local dielectric response. The principal nonlocality of poor conductors is related to the finite screening length of the penetrating field and collisional relaxation; at low temperatures the role of collisions plays the Landau damping. Spatial dispersion makes the theory self-consistent.

Analysis of the performance of a particle velocity sensor between two cylindrical obstructions.

The performance of an acoustic particle velocity sensor that is placed between two cylindrical objects has been analyzed both analytically and by means of finite volume simulations on fluid dynamics. The results are compared with acoustic experiments that show a large magnification of the output signal of the particle velocity sensor due to the mounting of the sensor between two cylinders. The influences of this construction consist of an attenuation of particle velocities at frequencies below a few hertz, whereas signals in the higher frequency range are amplified, up to approximately three times (10 dB) in a frequency range between 50 and 1000 Hz.

Casimir-lifshitz force out of thermal equilibrium and asymptotic nonadditivity.

We investigate the force acting between two parallel plates held at different temperatures. The force reproduces, as limiting cases, the well-known Casimir-Lifshitz surface-surface force at thermal equilibrium and the surface-atom force out of thermal equilibrium recently derived by M. Antezza et al.

Nonlocal impedances and the Casimir entropy at low temperatures.

The problem with the temperature dependence of the Casimir force is investigated. Specifically, the entropy behavior in the low temperature limit, which caused debates in the literature, is analyzed. It is stressed that the behavior of the relaxation frequency in the T-->0 limit does not play a physical role since the anomalous skin effect dominates in this range.