Silicone Oil Surfaces Research Articles

One-dimensional Growth of Zinc Crystals on a Liquid Surface.

The catalyst-free growth of nanocrystals on various substrates at room temperature has been a long-standing goal in the development of material science. We report the growth of one-dimensional zinc nanocrystals on silicone oil surfaces by thermal evaporation method at room temperature (20 ± 2 °C). Uniform zinc nanorods with tunable size can be obtained. The typical length and width of the nanorods are 250–500 nm and 20–40 nm, respectively. The growth mechanism can be attributed to the effect of the liquid substrate and the preferential growth direction of the crystals. This result provides a novel and simple way to fabricate the precursors (zinc crystals) for preparation of Zn-based semiconductors and other metallic crystals on liquid substrates.

MICROSTRUCTURE EVOLUTION OF GOLD ATOMIC AGGREGATES FABRICATED ON SILICONE OIL SURFACE

Gold atomic aggregates are fabricated by vapor-depositing Au atoms onto a silicone oil surface and the microstructure evolution is investigated by atomic force microscopy (AFM) observation. It is found that the Au aggregates are composed of Au circular nanoparticles with diameter around 45 nm, which is independent with the nominal film thickness d. As d increases from 1 nm to 15 nm, the height of the nanoparticles increases from 15 nm to 25 nm, indicating the geometric shape of the Au nanoparticles evolves from plateau to spherical. Furthermore, the roughness analysis shows that the mean surface roughness increases linearly with d in the range of 1 nm–15 nm, which is quite different from the findings in Ag system. The anomalous microstructure evolution of Au aggregates suggests that the growth of Au aggregates may be dominated by the shadowing effect.

Fabrication of Size-Controlled Gold Nanoparticles on Silicone Oil Surface and Mechanism for Size-Controllability

By thermal evaporation method, size-controlled gold (Au) nanoparticles were fabricated on silicone oil surface and the growth mechanism was investigated. Atomic force microscopy (AFM) study showed that quasi-circular granules with height of 10.0 nm and diameter of 60.0 nm were formed on the oil surface, which was independent with substrate temperature Ts. Transmission electron microscopy (TEM) observation revealed that the granules were further composed of Au nanoparticles. By changing Ts from 285 to 343 K, the mean diameter of nanoparticles can be well manipulated from 7.2 ± 0.7 to 10.1 ± 1.0 nm. The one dimensional power spectra density analysis and high resolution TEM study demonstrated that the origin of the size-controllability of the Au nanoparticles were dominated by the simple aggregation of small nanoparticles. Subsequently, a sequential growth model for Au nanoparticle was presented.

Microstructure evolution of Cu atomic islands on liquid surfaces in the ambient atmosphere**Project supported by the National Natural Science Foundation of China (Grant Nos. 11204283 and 11304298), the Natural Science Foundation of Zhejiang Province, China (Grant No. LQ13A040002), and the Scientific Research Project Funds of Talent Introduction of China Jiliang University (Grant No. 01101-000406).

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 to 13.0±1.0 nm. The detailed evolution mechanism of the Cu atomic islands is presented.

Temperature dependence of the aggregation behavior of aluminum nanoparticles on liquid substrate

Aluminum (Al) nanoparticle aggregates have been fabricated by thermal evaporation method on silicone oil surfaces at different substrate temperatures. The average diameter and height of the Al nanoparticles, namely Φavg and Havg, are of the order of 101 and 100 nm, respectively. As the substrate temperature Ts increases from 293 to 393 K, to the first order of approximation, Φavg increases exponentially and Havg increases quickly between 333 and 373 K. By transmission electron microscopy measurement, we find that the Al nanoparticles and their aggregates exhibit amorphous structure over the whole temperature range. A simple theoretical model is established to explain the coalescence process of the nanoparticles with Ts.

Evaporation enhancement effect of TiO2 nanoparticles on silicone oil in electrorheological fluid suspension

Electrorheological (ER) fluids are suspensions which consist of dielectric particles and insulation fluid. The ER fluids can change from liquid-like to solid-like state under the applied electric field. For traditional ER fluids, the maximum yield/shear stress is only several kPa and the size of dielectric particles is generally of micron. Since 2003, a series of new type ER fluids have been discovered, of which the yield/shear stress is as high as several hundred kPa. Such a type of ER fluid is called giant ER fluid or polar molecule-dominated ER fluid (PM-ER fluid), in which the size of dispersed particles is of nanoscale. Dimethyl silicone oil is the most commonly used dispersing agent in ER fluids, because of its stable physical and chemical behaviors. There is no obvious evaporation in traditional ER fluids when it is mixed with micron grade particles. However, when it is mixed with nanoparticles to prepare giant ER fluids, the silicone oil volatilizes easily in atmosphere. If time is long enough, the silicone oil in ER suspension can even be evaporated completely. In this paper, the existence of TiO2 nanoparticles in ER suspensions enhances the volatilization phenomenon has been studied through experiment. Analysis shows that the nanoparticles caused convex nanoscale curved surfaces on the gas-solid interface makes the vapor pressure increase greatly at the silicone oil surface, and leads to the enhancement of its volatilization. Influence of particle concentration, environmental temperature and viscosity of silicone oil on the evaporation enhancement effect is also studied and analysed systematically. Results show that the increase of the fraction of nanoparticles, viscosity of silicone oil as well as the temperature would promote the effect of evaporation enhancement of silicone oil in the suspensions.

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.

Kinetic Roughening with Surface Diffusion: Crossover from Ramified Aggregates to Continuous Films on Liquid Surfaces

Ramified iron aggregates are fabricated on silicone oil surface by thermal evaporation method at room temperature and the crossover from ramified aggregates to continuous films is studied by atomic force microscopy. It is shown that the aggregates are composed of numerous granules with the average diameter around 34 nm. The dynamic scaling analysis shows that the growth exponent β= 0.23 ±0.02 and the roughness exponent α evolves from 0.65 to 0.42 with the nominal film thickness, indicating a roughening behavior transfer may exist during the growth process. The physical interpretation for the scaling behavior is presented.

Aggregation behavior of Au atoms and atomic islands on liquid surfaces

The aggregation behavior of Au atoms and atomic islands on silicone oil surfaces has been systematically investigated by analyzing the evolution of surface coverage. The apparent Au surface coverage increases linearly with the nominal film thickness at low thicknesses and the rate of increase is almost independent of deposition flux. However, as the deposition flux increases, the surface coverage goes up linearly. Further analysis reveals that the deposition flux strongly affects the system free-energy of the island-oil system and therefore the aggregation behavior of the Au atoms and islands.

Anomalous Kinetic Roughening of Nanostructured Ag Islands on Liquid Surfaces

By atomic force microscopy, the surface evolution and kinetic roughening of nanostructured Ag islands on silicone oil surfaces are studied. It is found that the islands are composed of quasi-circular granules with planar size around 50.0 nm, which is approximately independent of nominal thickness d . Our measurement indicates that the geometrical shape of the granules changes from plateau to sphere as d goes up. The dynamic scaling analysis reveal that the roughness exponent α varies between 0.80 and 0.90 as d increases. The average roughness w rms shows power-law relationship with d and the growth exponent β= 0.53 ±0.03 when d ≤4.0 nm. However, w rms deviates obviously from the power-law relationship for the samples with d > 4.0 nm. This anomalous behavior of β is explained by the competition between the shadowing and reemission processes, and then the kinetic evolution and formation mechanism of the islands are presented.

Aggregation Mechanism of Ag Atoms Deposited on Liquid Surfaces

We study the aggregation of silver (Ag) atoms deposited on silicone oil surfaces. It is observed that the apparent Ag coverage of the total area, � , increases linearly with the nominal film thickness h for h< 0:9 nm and its slope k decreases clearly as the deposition flux f increases. Our atomic force microscopy (AFM) observation shows that the average thickness of the atomic aggregates first increases with f , and then approaches a saturation value. Then, the aggregation mechanism of Ag atoms is presented.

Preferred structures of the atomic Ag islands on silicone oil surfaces

Varying the substrate temperature Ts from 285 to 353 K, both the aggregation behavior of Ag atoms and the preferred structures of the atomic Ag islands on silicone oil surfaces are investigated. After deposition, the deposited Ag atoms form isolated islands with a preferred height. Our observations reveal that, as Ts increases, the preferred island height increases from 20.0 to 33.0 nm, which results in the decrease of the Ag apparent coverage, from 9.6 ± 0.1% to 6.5 ± 0.3%. Further, the crystal structure of the Ag islands changes from amorphous to polycrystalline as the substrate temperature Ts goes up. Subsequently a 3D aggregation mechanism of the Ag atoms on the liquid substrates is proposed.

Plasma-treated carbonyl iron particles as a dispersed phase in magnetorheological fluids

The aim of this paper is to document suitability of plasma-treated carbonyl iron particles as a dispersed phase in magnetorheological fluids. Surface-modified carbonyl iron particles were prepared via their exposure to 50% argon and 50% octafluorocyclobutane plasma. The X-ray photoelectron spectroscopy was used for analysis of chemical bonding states in the surface layer. Plasma-treated particles were adopted for a dispersed phase in magnetorheological (MR) fluids, and the MR behaviour was investigated using rotational rheometer equipped with magnetic field generator. Viscoelasticity changes of MR fluids were measured in the small-strain oscillatory shear flow as a function of the strain amplitude, frequency and the magnetic flux density. The MR fluids based on plasma-treated particles exhibit promoted suspension stability, which is attributed to the interactions between fluorine bonded on particle surface and methyl groups of silicone oil.

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 102-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.

Application of quartz crystal microbalance to study the impact of pH and ionic strength on protein–silicone oil interactions

In this study, we have used quartz crystal microbalance (QCM) to quantitate the adsorption of a protein on silicone oil coated surfaces as a function of protein concentration, pH and ionic strength using a 5 MHz quartz crystal. Protein adsorption isotherms were generated at different solution pH and ionic strengths. Surface saturation concentrations were selected from adsorption isotherms and used to generate adsorption profiles from pH 3.0 to 9.0, and at ionic strengths of 10 mM and 150 mM. At low ionic strength (10 mM) and pH 5.0 (close to the isoelectric point of the protein), maximum adsorption of protein to the silicone oil surface was observed. At higher ionic strength (150 mM), no significant pH influence on adsorption was observed. QCM could be used as a reliable technique to study the binding of proteins to silicone oil coated surfaces.

Condensation Behavior of Ag Aggregates on Liquid Surfaces

We report a condensation behavior of silver aggregates on silicone oil surfaces. The deposited Ag atoms diffuse and aggregate on the oil surface, and then form granular clusters and ramified islands. The apparent Ag coverage of the total area increases linearly with the nominal film thickness h for h < 0.9 nm. However, the coverage exhibits a fluctuation behavior for 1.0 nm < h < 2.5 nm. it is found that the anomalous behavior of the coverage is resulted from a characteristic material condensation process in the aggregates.

AFM study of forces between silicon oil and hydrophobic–hydrophilic surfaces in aqueous solutions

An investigation has been made of the interactions between silicone oil and various solid substrates immersed in aqueous solutions. Measurements were made using an atomic force microscope (AFM) using the colloid-probe method. The silicone oil drop is simulated by coating a small silica sphere with the oil, and measuring the force as this coated sphere is brought close to contact with a flat solid surface. It is found that the silicone oil surface is negatively charged, which causes a double-layer repulsion between the oil drop and another negatively charged surface such as mica. With hydrophilic solids, this repulsion is strong enough to prevent attachment of the drop to the solid. However, with hydrophobic surfaces there is an additional attractive force which overcomes the double-layer repulsion, and the silicone oil drop attaches to the solid. There is circumstantial evidence that linear and nonlinear effect take part in force results from compression of the silicone oil film coated on the glass sphere.

COMPARISON OF STRESS RELIEF MECHANISMS OF METAL FILMS DEPOSITED ON LIQUID SUBSTRATES BY THERMAL EVAPORATING AND SPUTTERING

Various metal film systems, deposited on liquid (silicone oil) substrates by thermal evaporating and DC-magnetron sputtering methods, have been successfully fabricated and the stress relief mechanisms are systematically studied by analyzing the characteristic surface morphologies. The experiment shows that the evaporating metal films can move on silicone oil surfaces freely due to the nearly zero adhesion of solid–liquid interface, which results in spontaneous formation of ordered surface patterns with a characteristic sandwiched structure driven by the internal stress. For the sputtering metal film system, however, the top surface of silicone oil can be modified to form an elastomeric polymer layer on the liquid substrate during deposition. Subsequent cooling of the system creates a higher compressive stress in the film, which is relieved by buckling of the film to form periodic wavy structures because the adhesion of solid–elastomer interface is quite strong.

Transient regimes and crossover for epitaxial surfaces

We apply a formalism for deriving stochastic continuum equations associated with lattice models to obtain equations governing the transient regimes of epitaxial growth for various experimental scenarios and growth conditions. The first step of our methodology is the systematic transformation of the lattice model into a regularized stochastic equation of motion that provides initial conditions for differential renormalization-group (RG) equations for the coefficients in the regularized equation. The solutions of the RG equations then yield trajectories that describe the original model from the transient regimes, which are of primary experimental interest, to the eventual crossover to the asymptotically stable fixed point. We first consider regimes defined by the relative magnitude of deposition noise and diffusion noise. If the diffusion noise dominates, then the early stages of growth are described by the Mullins-Herring (MH) equation with conservative noise. This is the classic regime of molecular-beam epitaxy. If the diffusion and deposition noise are of comparable magnitude, the transient equation is the MH equation with nonconservative noise. This behavior has been observed in a recent report on the growth of aluminum on silicone oil surfaces [Z.-N. Fang, Thin Solid Films 517, 3408 (2009)]. Finally, the regime where deposition noise dominates over diffusion noise has been observed in computer simulations, but does not appear to have any direct experimental relevance. For initial conditions that consist of a flat surface, the Villain-Lai-Das Sarma (VLDS) equation with nonconservative noise is not appropriate for any transient regime. If, however, the initial surface is corrugated, the relative magnitudes of terms can be altered to the point where the VLDS equation with conservative noise does indeed describe transient growth. This is consistent with the experimental analysis of growth on patterned surfaces [H.-C. Kan, Phys. Rev. Lett. 92, 146101 (2004); T. Tadayyon-Eslami, Phys. Rev. Lett. 97, 126101 (2006)].

Generation of metal-nanoparticle colloidal solution by means of magnetron deposition on a liquid surface

A new method for generating a metal-nanoparticle colloidal solution by means of magnetron deposition on a chemically neutral metal on the surface of a flowing liquid in a high-cycle mixing scheme is proposed. The properties of the Au nanoparticle colloidal solution produced by Au magnetron deposition on the surface of vacuum silicone oil were investigated experimentally. The density and kinematical viscosity of the solution have been measured. The gold nanoparticle mean size and concentration are specified, and nanoparticle growth model is considered.