Controllable Nucleation of Nanobubbles at a Modified Graphene Surface

The properties of nanoscale gas bubbles at the solid/water interface have been investigated for more than 20 years. However, the stability of nanobubbles remains far from being understood. How to control the formation of nanobubbles is the key issue for understanding their long lifetime. In this work, using molecular dynamics simulations we modify the substrate （graphene） with charge dipoles in which the local properties of the surface could be changed. Nanobubbles could be stabilized on the local hydrophobic area and modified area with the hydrophilic boundary where gas nuclei are deposited beforehand. Those results provide two methods to control the nucleation of gas nanobubbles and fix them on a target area.

Experimental Study on the Dependency of Ice Nucleation Active Surface Site Density on ATD Aerosol Size

In light of the percentage of Earth’s cloud coverage, heterogeneous ice nucleation in clouds is the most important global-scale pathway. More recent parameterizations of ice nucleation processes in the atmosphere are based on the concept of ice nucleation active surface site density (ns). It is usually assumed that ns is independent of time and aerosol size distribution, i.e. that the surface properties of aerosols of the same species do not vary with size. However, the independence of ns on aerosol size for every species has been questioned. This study presents the results of ice nucleation processes of ATD laboratory-generated aerosol (particle diameters of 0 - 3 μm). Ice nucleation in the condensation mode was performed in a Dynamic Filter Processing Cham- ber at temperatures of -18°C and -22°C, with a saturation ratio with respect to water of 1.02. Results show that ns increased by lowering the nucleation temperature, and was also dependent on the particle size. The ns of particles collected on the filters, after a 0.5 μm D50 cut-off cyclone, resulted statistically higher with respect to the values obtained from the particles collected on total filters. The results obtained suggest the need for further investigation of ns dependence of same composition aerosol particles with a view to support weather and climate predictions.

Investigation of the Heterogeneous Nucleation on Fractal Surfaces

Classical theory of heterogeneous nucleation has been developed with an implied hypothesis of smooth substrate surfaces; however, morphologies of any real substrate surfaces are generally complicated and demonstrate fractal characteristics. In this paper, the wettability between the embryo and the fractal substrate surface was discussed, and heterogeneous nucleation behaviors were theoretically analyzed. The result shows that the roughness factor of a fractal surface varies with the scale of the embryo. As a result, the fractal character of the substrate surface has important effects on heterogeneous nucleation behaviors. It has been shown that the energy barrier for heterogeneous nucleation of a non-wetting phase on a fractal rough surface increases with increasing fractal dimensions, and both the critical nucleus radius and the nucleation energy barrier decrease with increasing fractal dimensions for heterogeneous nucleation of a wetting phase on the fractal rough surface. For a non-wetting system, the critical nucleus radius shows a slight shift with changes of the intrinsic wetting angle, but for a wetting system, the critical nucleus radius shows an obvious change with decreasing intrinsic wetting angle, thus imposes a stronger effect on the heterogeneous nucleation behaviors.

Surface nucleation and independent growth of Ce（OH）4 within confinement space on modified carbon black surface to prepare nano-CeO2 without agglomeration

Highly dispersed negative carboxyl groups can be formed on carbon black （CB） surface modified with strong nitric acid. Therefore positive cations can be uniformly absorbed by carboxyl groups and precipitated within a confinement space on modified CB surface to prepare highly dispersed nanomaterials. In this paper, the formation and dispersion status of surface negative carboxyl groups, adsorption status of Ce^3＋, surface confinement nucleation, crystallization and calcination process were studied by EDS, SEM, and laser particle size analysis. The results show that the carboxyl groups formed on modified CB surface are highly dispersed, and Ce^3＋ cations can be uniformly anchored by carboxyl groups. Therefore, highly dispersed Ce^3＋ can react with OH^- within a confinement surface region to form positive nano-Ce（OH）4 nuclei which also can be adsorbed by electrostatic attraction. After independent growth of Ce（OH）4 without agglomeration, highly dispersed CeO2 nanoparticles without agglomeration can be prepared together with the help of effectively isolates by CO2 released in the combustion of CB.

Formation mechanism of micro-flows in aqueous poly(ethylene oxide) droplets on a substrate at different temperatures

The drying of aqueous poly（ethylene oxide） （PEO） droplet on a substrate at different temperatures was studied. It was found that the contact line receded when the substrate was at a temperature above 60 ℃. Different nucleation behavior and surface profiles of PEO films were found in different droplets drying processes. The rheological properties of aqueous PEO solutions were studied to understand the mechanism of contact line recession and micro-flow in drying aqueous PEO droplets. It was found that at low temperature, the contact line was static because of great viscous stress; while at high temperature, it receded because of great Marangoni force and the decrease of viscous stress. It was indicated that Marangoni convection was inhibited by the outward capillary flow and viscous stress at low temperature, whereas it became dominant at high temperature. Two types of mechanism for surface profiles and nucleation of PEO film from drying droplets are proposed, providing a theoretical guide for polymer solution application in oil and gas foam flooding technology.

Comments on "Reexamination of Correlations for Nucleate Site Distribution on Boiling Surface by Fractal Theory

In recently published paper by Yang Chunxin[1], I reexamined the paper. On page 128, the paper 'pointed out that the size and spatial distribution density of nucleation sites presented on real boiling surface can be described by the normalized fractal distribution function, and the physical meaning of parameters involved in some experimental correlations proposed by early investigations are identified according to fractal distribution'. However, the definition on fractal dimension given by Yang[1] is highly questionable, and the results obtained by Yang are contradictory to the basic fractal theory. Here are my comments: