Critical size of iron nanoparticles on liquid substrates

We study the iron atomic aggregates deposited on silicone oil surfaces by using atomic force microscopy. The aggregates are composed of disk-shaped nanoparticles with the mean diameter Φc≈31.7 nm and height Hc≈4.5 nm, which are nearly independent of the nominal film thickness. The experiment shows that a material condensation process must occur in the nanoparticles during the growth period. The anomalous phenomenon is explained.

Growth and aggregation of Cu nanocrystals on ionic liquid surfaces

We report a catalyst-free growth of Cu nanocrystals on ionic liquid surfaces by thermal evaporation method at room temperature.After deposition of Cu on ionic liquid surfaces,ramified Cu aggregates form.It is found that the aggregates are composed of both granules and nanocrystals with triangular or hexagonal appearances.The sizes of the nanocrystals are in the range of tens to hundreds of nanometers and increase with the nominal deposition thickness.The growth mechanism of the Cu aggregates and nanocrystals is presented.

Microstructure evolution of Cu atomic islands on liquid surfaces in the ambient atmosphere

We report the microstructure evolution of copper（Cu） nm-sized atomic islands on silicone oil surfaces in the ambient atmosphere. The origin of these nearly free sustaining atomic islands is explained by a three-stage growth model. The first stage is the nucleation and growth of atomic granules. Subsequently, the compact atomic islands grow by the aggregation of the atomic granules. Finally, they adhere to each other and form branched atomic islands. During the characteristic evolution, the atomic granules reconstruct and the average height of the atomic islands increases from 7.0±1.0 nm to13.0±1.0 nm. The detailed evolution mechanism of the Cu atomic islands is presented.

Structural evolution of silicone oil liquid exposed to Ar plasma

Structure properties of silicone oil serving as a liquid substrate exposed to Ar plasma axe investigated in this paper. Under the action of energetic Ar ions, the surface of silicone oil liquid substrate exhibits a branch-like fractal aggregation structure, which is related to the structure evolution of silicone oil liquid from Si-O chain to Silo network. The radicals from the dissociation of silicone oil molecule into the Ar plasma turns the plasma into a reactive environment. Therefore, the structural evolution of silicone oil liquid substrate and the reactive radicals in the plasma space become possible factors to affect the aggregation of nanopaxticles and also the structures and the compositions of nanopaxticles.

The Disintegration of a Floating Ferrofluid Layer into an Ordered Drop System in a Vertical Magnetic Field

Magnetic fluids,also known as ferrofluids,are versatile functional materials with a wide range of applications.These applications span from industrial uses such as vacuum seals,actuators,and acoustic devices to medical uses,including serving as contrast agents for magnetic resonance imaging(MRI),delivering medications to specific locations within the body,and magnetic hyperthermia for cancer treatment.The use of a non-wettable immiscible liquid substrate to support a layer of magnetic fluid opens up new possibilities for studying various fluid flows and related instabilities in multi-phase systems with both a free surface and an interface.The presence of two deformable boundaries within a ferrofluid layer significantly reduces the critical magnetic field strength required to transform the layer into an organized system of drops or polygonal figures evolving according to the intensity,frequency and direction of the considered magnetic field.This paper experimentally investigates this problem by assuming a uniform magnetic field perpendicular to the surface.This specific subject has not been previously explored experimentally.The critical magnetic field intensity required to destabilize the ferrofluid layer is determined based on the layer’s thickness and the fluid’s initial magnetic susceptibility.It is demonstrated that the critical magnetic field strength needed to disrupt the initially continuous ferrofluid layer increases with the layer’s thickness.Conversely,an increase in the ferrofluid’s magnetic susceptibility results in a decrease in the critical magnetic field strength.The emerging droplet structures are analyzed in terms of the number of drops,their size,and the periodicity of their arrangement.The number of droplets formed depends on the initial thickness of the layer,the presence or absence of a stable rupture in the upper layer,and the rate at which the magnetic field strength is increased to the critical value.A characteristic viscous time is proposed to evaluate the decomposition of the ferrofluid layer,which depends on the duration of the magnetic field’s application.The experimental data on the instability of a ferrofluid layer on a liquid substrate are compared with the theoretical results from the study of“magnetic fluid sandwich structures”conducted by Rannacher and Engel.This comparison highlights the similarities and differences between experimental observations and theoretical predictions,providing a deeper understanding of the behavior of ferrofluid layers under the influence of magnetic fields.

Morphology and microstructure of Ag islands of aggregated atoms on oil surfaces

The morphology evolution of silver islands on silicone oil surfaces is measured and the microstructure of the islands is studied. The deposited Ag atoms diffuse and aggregate on the oil surface and then Ag islands with the width of the order of 10^2-nm form. After the samples are removed from the vacuum chamber, the immediate measurement shows that the apparent Ag coverage of the total area decays with the magnitude up to （23.0±3.8）% in few minutes. In the following two hours, the samples are kept in the ambient atmosphere and several unexpected results are detected： 1） as the topological structure of the islands evolves, the total area of each island decreases gradually and the maximum decrement measured is around 20%; 2） if an island breaks and becomes two small pieces, the total area decreases obviously; 3） however, if two small islands meet and stick together, a sudden increment of the total area is observed. These phenomena, mirroring the evolution process of the island microstructure, are resulted from both the diffusion of the atoms and the combination of the defects inside the islands.

Surface effects of liquid metal amoeba

Liquid metals(LM) such as eutectic gallium-indium and gallium-indium-tin are important functional liquid-state metal materials with many unique properties, which have attracted wide attentions especially from soft robot area. Recently the amoeba-like transformations of LM on the graphite surface are discovered, which present a promising future for the design and assemble of self-fueled actuators with dendritically deformable body. It appears that the surface tension of the LM can be significantly reduced when it contacts graphite surface in alkaline solution. Clearly, the specific surface should play a vital role in inducing these intriguing behaviors, which is valuable and inspiring in soft robot design. However, the information regarding varied materials functions underlying these behaviors remains unknown. To explore the generalized effects of surface materials in those intriguing behavior, several materials including glass, graphite, nickel and copper oxides(CuO) were comparatively investigated as substrate surfaces.Important results were obtained that only LM amoeba transformations were observed on graphite and CuO surfaces. In order to identify the proper surface condition for LM transformation, the intrinsic properties of substrate surfaces, such as the surface charge and roughness, as well as the specific interaction with LM like wetting behavior and mutual locomotion etc., were characterized. The integrated results revealed that LM droplet appears more likely to deform on surfaces with higher positive surface charge density, higher roughness and less bubble generation on them. In addition, another surface material,CuOx, is identified to own similar ability to graphite, which is valuable in achieving amoeba-like transformation. Moreover, this study offers a fundamental understanding of the surface properties in realizing LM amoeba transformations, which would shed light on packing and structure design of liquid metal-based soft device within multi-material system.