Local Oversaturation Research Articles

Refractive Index of Single Surface Nanobubbles.

Here, we report a label-free optical relative refractive index (RI) sensing technique based on the image contrast of surface plasmon resonance microscopy (SPRM). The positive or negative contrast of a SPRM pattern reflects the relative RI of a nanosized object to the medium. Through directly imaging the relative RI, we classified two kinds of surface nanobubbles generated by varied pathways. The former type of nanobubbles nucleated from local oversaturation of gas molecules had a RI lower than that of water and a transient lifetime. The second type of nanobubbles formed by a methanol-water exchange process had a RI higher than that of water and a long lifetime. The relative RI of surface nanobubbles indicated that the gas state is sparse for transient nanobubbles and compressed inside the stable nanobubbles.

Micro-droplet nucleation through solvent exchange in a turbulent buoyant jet

Solvent exchange is a process involving mixing between a good solvent with dissolved solute and a poor solvent. The process creates local oversaturation which causes the nucleation of minute solute droplets. Such ternary systems on a macro-scale have remained unexplored in the turbulent regime. We experimentally study the solvent exchange process by injecting mixtures of ethanol and trans-anethole into water, forming a turbulent buoyant jet in the upward direction. Locally, turbulent mixing causes oversaturation of the trans-anethole following turbulent entrainment. We optically measure the concentration of the nucleated droplets using a light attenuation technique and find that the radial concentration profile has a sub-Gaussian kurtosis. In contrast to the entrainment-based models, the spatial evolution of the oversaturation reveals continuous droplet nucleation downstream and radially across the jet, which we attribute to the limited mixing capacity of the jet. Although we are far from a full quantitative understanding, this work extends the knowledge on solvent exchange into the turbulent regime, and brings in a novel type of flow, broadening the scope of multicomponent, multiphase turbulent jets with phase transition.

Hydrogen-Bonding-Induced H-Aggregation of Charge-Transfer Complexes for Ultra-Efficient Second Near-Infrared Region Photothermal Conversion

Hydrogen-Bonding-Induced H-Aggregation of Charge-Transfer Complexes for Ultra-Efficient Second Near-Infrared Region Photothermal Conversion

Investigation of Electrochemical and Chemical Processes Occurring at Positive Potentials in “Water-in-Salt” Electrolytes

Lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) based water-in-salt electrolytes (WiSEs) has recently emerged as a new promising class of electrolytes, primarily owing to their wide electrochemical stability windows (∼3–4 V), that by far exceed the thermodynamic stability window of water (1.23 V). Upon increasing the salt concentration towards superconcentration the onset of the oxygen evolution reaction (OER) shifts more significantly than the hydrogen evolution reaction (HER) does. The OER shift has been explained by the accumulation of hydrophobic anions blocking water access to the electrode surface, hence by double layer theory. Here we demonstrate that the processes during oxidation are much more complex, involving OER, carbon and salt decomposition by OER intermediates, and salt precipitation upon local oversaturation. The positive shift in the onset potential of oxidation currents was elucidated by combining several advanced analysis techniques: rotating ring-disk electrode voltammetry, online electrochemical mass spectrometry, and X-ray photoelectron spectroscopy, using both dilute and superconcentrated electrolytes. The results demonstrate the importance of reactive OER intermediates and surface films for electrolyte and electrode stability and motivate further studies of the nature of the electrode.

A Bubble-STORM Approach for Super-Resolved Imaging of Nucleation Sites in Hydrogen Evolution Reactions.

Stochastic optical reconstruction microscopy (STORM) is a powerful strategy to achieve super-resolved imaging of biological structures by virtue of the stochastic photoactivation of fluorophores and superlocalization algorithm. Herein, we report a fluorophore-free bubble-STORM approach for super-resolved imaging of nucleation sites in hydrogen evolution reactions (HER). When applying an appropriate pulse potential to the electrode, rapid electro-reduction of protons created a local oversaturation of hydrogen molecules and thus the nucleation of sparsely distributed hydrogen nanobubbles. A surface plasmon resonance microscopy was employed to monitor the process and report the localization of each nanobubble via superlocalization fitting. The withdrawal of electrode potential, or the microconvection, led to the immediate disappearance of nanobubbles and recovered the electrode surface before the next pulse. By repeating the procedures for thousands of cycles, one was able to reconstruct a map of nucleation sites with a spatial resolution beyond the optical diffraction limit. This approach does not require a model fluorogenic reaction or fluorescent labeling to the nanobubbles, thus revealing the intrinsic nucleation sites in the natural states. Our results further indicated the fast growth, coalescence, and detachment behaviors of nanobubbles on a time scale of sub-milliseconds, underscoring the significance of high temporal resolution for studying nanobubble nucleation.

Non-spherical oscillations drive the ultrasound-mediated release from targeted microbubbles

Ultrasound-driven microbubbles are attractive for a variety of applications in medicine, including real-time organ perfusion imaging and targeted molecular imaging. In ultrasound-mediated drug delivery, bubbles decorated with a functional payload become convenient transport vehicles and offer highly localized release. How to efficiently release and transport these nanomedicines to the target site remains unclear owing to the microscopic length scales and nanoseconds timescales of the process. Here, we show theoretically how non-spherical bubble oscillations lead first to local oversaturation, thereby inducing payload release, and then to microstreaming generation that initiates transport. Experimental validation is achieved through ultra-high-speed imaging in an unconventional side-view at tens of nanoseconds timescales combined with high-speed fluorescence imaging to track the release of the payload. Transport distance and intrinsic bubble behavior are quantified and agree well with the model. These results will allow for optimizing the therapeutic use of targeted microbubbles for precision medicine.

Importance of non-intrinsic platinum dissolution in Pt/C composite fuel cell catalysts.

The dissolution of different platinum-based nanoparticles deposited on a commercial high-surface area carbon (HSAC) support in thin catalyst films is investigated using a highly sensitive electrochemical flow cell (EFC) coupled to an inductively coupled plasma mass spectrometer (ICP-MS). The previously reported particle-size-dependent dissolution of Pt is confirmed on selected industrial samples with a mean Pt particle size ranging from 1 to 4.8 nm. This trend is significantly altered when a catalyst is diluted by the addition of HSAC. This indicates that the intrinsic dissolution properties are masked by local oversaturation phenomena, the so-called confinement effect. Furthermore, by replacing the standard HSAC support with a support having an order of magnitude higher specific surface area (a micro- and mesoporous nitrogen-doped high surface area carbon, HSANDC), Pt dissolution is reduced even further. This is due to the so-called non-intrinsic confinement and entrapment effects of the (large amount of) micropores and small mesopores doped with N atoms. The observed more effective Pt re-deposition is presumably induced by local Pt oversaturation and the presence of nitrogen nucleation sites. Overall, our study demonstrates the high importance and beneficial effects of porosity, loading and N doping of the carbon support on the Pt stability in the catalyst layer.

The oxygen reduction reaction at the three-phase boundary: nanoelectrodes modified with Ag nanoclusters.

Silver nanoclusters are deposited on bifunctional Θ-shaped nanoelectrodes consisting of a carbon nanoelectrode combined with a hollow nanopipette. The Θ-nanoelectrodes are used as model systems to study interfacial mass transport in gas diffusion electrodes and in particular oxygen-depolarized cathodes (ODC) for the oxygen reduction reaction (ORR) in chlor-alkali electrolysers. By local delivery of O2 gas to the electroactive Ag nanoclusters through the adjacent nanopipette, enhanced currents for the ORR at the Ag nanoparticles are recorded which are not accountable when considering the low solubility and slow diffusion of O2 in highly alkaline media. Instead, local oversaturation of O2 leads to current enhancement at the Ag nanoclusters. Due to the intrinsic high mass transport rates at the nanometric electrodes accompanied by local delivery of reactants, the method generally allows to study electrochemical reactions at single nanoparticles beyond the limitations induced by slow diffusion and low reactant concentration. Kinetic and mechanistic information, for instance derived from Tafel slopes, can be obtained from kinetic regimes not accessible to standard techniques.

Surface nanobubbles and nanodroplets

Surface nanobubbles are nanoscopic gaseous domains on immersed substrates which can survive for days. They were first speculated to exist about 20 years ago, based on stepwise features in force curves between two hydrophobic surfaces, eventually leading to the first atomic force microscopy (AFM) image in 2000. While in the early years it was suspected that they may be an artifact caused by AFM, meanwhile their existence has been confirmed with various other methods, including through direct optical observation. Their existence seems to be paradoxical, as a simple classical estimate suggests that they should dissolve in microseconds, due to the large Laplace pressure inside these nanoscopic spherical-cap-shaped objects. Moreover, their contact angle (on the gas side) is much smaller than one would expect from macroscopic counterparts. This review will not only give an overview on surface nanobubbles, but also on surface nanodroplets, which are nanoscopic droplets (e.g., of oil) on (hydrophobic) substrates immersed in water, as they show similar properties and can easily be confused with surface nanobubbles and as they are produced in a similar way, namely, by a solvent exchange process, leading to local oversaturation of the water with gas or oil, respectively, and thus to nucleation. The review starts with how surface nanobubbles and nanodroplets can be made, how they can be observed (both individually and collectively), and what their properties are. Molecular dynamic simulations and theories to account for the long lifetime of the surface nanobubbles are then reported on. The crucial element contributing to the long lifetime of surface nanobubbles and nanodroplets is pinning of the three-phase contact line at chemical or geometric surface heterogeneities. The dynamical evolution of the surface nanobubbles then follows from the diffusion equation, Laplace’s equation, and Henry’s law. In particular, one obtains stable surface nanobubbles when the gas influx from the gas-oversaturated water and the outflux due to Laplace pressure balance. This is only possible for small enough surface bubbles. It is therefore the gas or oil oversaturation ζ that determines the contact angle of the surface nanobubble or nanodroplet and not the Young equation. The review also covers the potential technological relevance of surface nanobubbles and nanodroplets, namely, in flotation, in (photo)catalysis and electrolysis, in nanomaterial engineering, for transport in and out of nanofluidic devices, and for plasmonic bubbles, vapor nanobubbles, and energy conversion. Also given is a discussion on surface nanobubbles and nanodroplets in a nutshell, including theoretical predictions resulting from it and future directions. Studying the nucleation, growth, and dissolution dynamics of surface nanobubbles and nanodroplets will shed new light on the problems of contact line pinning and contact angle hysteresis on the submicron scale.

High dynamic range image acquisition method using proportion integration differentiation controller

The extensive application of surface mount technology requires various measurement methods to evaluate the printed circuit board (PCB), and visual inspection is one critical method. The local oversaturation, arising from the nonconsistent reflectivity of the PCB surface, will lead to an erroneous result. This paper presents a study on a high dynamic range image (HDRI) acquisition system which can capture HDRIs with less local oversaturation. The HDRI system is composed of the liquid crystal on silicon (LCoS) and charge-coupled diode (CCD) sensor. In this system, the LCoS uses a negative feedback to extend the dynamic range of the system, and the proportion integration differentiation (PID) theory is used to control the system for its rapidity. The input of the PID controller is images captured by the CCD sensor and the output is the LCoS mask, which controls the LCoS’s reflectivity. The significant characteristics of our method are that the PID control can adjust the image brightness pixel to pixel and the feedback procedure is accomplished by the computer in less time than the traditional method. Experimental results demonstrate that the system could capture HDRIs with less local oversaturation.

The image adaptive method for solder paste 3D measurement system

The extensive application of Surface Mount Technology (SMT) requires various measurement methods to evaluate the circuit board. The solder paste 3D measurement system utilizing laser light projecting on the printed circuit board (PCB) surface is one of the critical methods. The local oversaturation, arising from the non-consistent reflectivity of the PCB surface, will lead to inaccurate measurement. The paper reports a novel optical image adaptive method of remedying the local oversaturation for solder paste measurement. The liquid crystal on silicon (LCoS) and image sensor (CCD or CMOS) are combined as the high dynamic range image (HDRI) acquisition system. The significant characteristic of the new method is that the image after adjustment is captured by specially designed HDRI acquisition system programmed by the LCoS mask. The formation of the LCoS mask, depending on a HDRI combined with the image fusion algorithm, is based on separating the laser light from the local oversaturated region. Experimental results demonstrate that the method can significantly improve the accuracy for the solder paste 3D measurement system with local oversaturation.

Preparing Polyaluminum Chloride Coagulants Using Ultrasonic-Assisted NaOH Dosing

This study elucidates an ultrasonic vibration system to promote in alkalinity dosing, which is a new method for preparing polyaluminum chloride (PACl). The ultrasonic vibrating system breaks up the NaOH solution into a fine mist, which may be more evenly dispersed into the aluminum solution than preventing local oversaturation in polymerization. The coagulant was subjected to the Al-Ferron test to determine its composition, and jar tests to investigate its long-term stability. The results indicated that this ultrasonic-assisted NaOH dosing leads to a more stable polymerization of aluminum and OH− ions, increasing the proportion of Al13 in the final product. After 2 months of aging, the PACl that had been prepared with ultrasonic-aided NaOH dosing at 0.25 mL/min, and also exhibited the best turbidity removal results.

On the possibility for local oversaturation of deuterium in palladium

The aim of the present paper is to give just an idea of how a deuterium overconcentration can be reached in domains of few micrometres of a palladium electrode, by considering the key role both of the electrode internal structure and the non-equilibrium conditions imposed by the electrolytic process

Silicon amorphization model in the process of ion implantation

When bombarded with light ions, the region of primary collision is not considered as amorphous, and the attained amorphous state in the irradiated layer is the result of the diffusion-coagulation processes with participation of vacancies originating in different collision cascades. From our viewpoint, however, the phenomenon of amorphization has the same nature for ions of different masses. It starts with decay of oversaturated solid state solution of vacancies. Note that, as a result of the interaction of the bombarding particle with the silicon atoms and subsequent spatial separation of vacancies and interstitials, the collision cascade region can be considered as the region of local vacancy oversaturation