Fundamental study of adhesion of ice to cooling solid surface (Discussion on influence of copper oxide layer on ice adhesion force)

In many situations, ice often adheres to a cooling solid surface, frequently causing serious accidents. It is critical to clarify the mechanism of ice adhesion to the cooling surface in order to prevent ice adhesion. In a past study, the shearing stresses of two kinds of test plates with a copper surface having the higher thermal conductivity were measured. The shearing stress corresponds to ice adhesion force. Both shearing stresses were significantly different; however, the cause remains unclear.Therefore, the present study focuses on an oxide layer as the main factor causing the difference of both shearing stresses; the influence of the oxide layer formed on shearing stress was discussed. And in the removal and reformation processes of the oxide layer, the time variation of the shearing stress was clarified. Moreover, the relationship between the state of the copper surface and the shearing stress was also clarified by surface analysis.     

Investigation on adhesion force of TBAB hydrate to cooling copper surface

When ice slurry is employed for air conditioning, there is gap of 5–7 °C between the melting point of the ice and the cooling water temperature. However, TBAB hydrate slurry made from an aqueous TBAB solution can remove the gap because it has a more suitable melting point. Furthermore, the slurry is relatively a high latent heat of fusion and good fluidity. So, the slurry is the most promising material for air conditioning. However, it is expected that TBAB hydrate in the slurry strongly adheres to surface of a metal such as copper. However, to date, there have been no quantitative studies of the adhesion forces, so in the present work adhesion forces of TBAB hydrates to copper surface at 3 and 5 °C were measured varying TBAB solution concentrations. And the adhesion force and its surface temperature-dependency were investigated based on surface energies and observations of hydrates crystals.     

Suppression of ice adhesion force to cooling wall due to voltage application

For ice storage, one of the authors has previously reported on the ice slurry formed by cooling water–silicone oil mixture with stirring. When the mixture is stirred in a vessel, the oil is charged due to static electricity. If the vessel can attract the charged oil, suppression of ice adhesion force to a cooling wall may be possible. In this study, therefore, a certain voltage was applied to the vessel filled with the mixture with cooling and stirring simultaneously, and water was frozen in the vessel. Then, the ice adhesion force to the cooling vessel wall was measured under a constant apparent adhesion area between the ice and cooling vessel wall. From the measurement results, optimal conditions of the oil viscosity, rotation speed and applied voltage to suppress the ice adhesion force effectively were clarified. Moreover, the factors governing suppression of the ice adhesion force were clarified.     

Influences of number of hydroxyl groups and cooling solid surface temperature on ice adhesion force

It is important to quantitatively clarify factors governing ice adhesion force to a cooling solid surface. Thus, one of the authors considered hydrogen bonding between hydroxyl groups of the ice and solid surface. Several additives with different numbers of hydroxyl groups were selected. The ice adhesion force of ice which is made from an additive–pure water mixture to a cooling hard glass surface was measured at a fixed surface temperature. Similar measurements were conducted with various molar-concentrations of several additives and with surface temperatures. Since the hydrogen bonding on the surface occurs after adsorption of the additive and ice adhesion force depends on surface energy of ice, measurements of the amounts of additives adsorbed to the SiO₂ and the surface energy were similarly conducted. And influences of the number of hydroxyl groups in the adsorbed additive and the surface on ice adhesion force to the glass surface were quantitatively clarified.     

Fundamental study on adhesion of ice to cooling solid surface

Many technological troubles are caused by ice adhesion to a cooling solid wall (surface). Therefore, it is urgent to clarify a mechanism of ice adhesion.It is thought that ice adhesion to the cooling wall is governed by heat transfer and interfacial phenomena between ice and the wall. In this study, shearing stress corresponding to adhesion force per unit area to remove ice from the wall surface and some reagents' contact angles on the wall and ice were measured, varying the wall material and its surface state. Moreover, shearing work to remove ice from the wall surface and surface energies of the wall and ice were calculated by the shearing stress and contact angles, respectively. And adhesion energy at an interface between ice and the wall was also calculated by the calculated surface energies. And then, influence of heat transfer and interfacial phenomena on ice adhesion was discussed to clarify the mechanism of ice adhesion.     

Measurement on nano scale by scanning probe microscope for obtaining real ice adhesion force

It is important to know a real ice adhesion force on a cooling solid surface. When an ice adhesion force is measured by giving a shearing force at the interface between the solid surface and ice, there is a possibility that a measured ice adhesion force is an apparent value including a force that destroys ice due to unevenness of the surface. Thus, to measure the ice adhesion force without influence of the surface unevenness, one of the authors developed a method for measuring the ice adhesion force on the nano scale by using a scanning probe microscope. In this paper, ice adhesion forces to copper oxide and hard glass test plates were measured at −5 °C on the nano scale by this method, and the real ice adhesion forces could be measured. Moreover, the representative value of proper shearing stresses obtained by real ice adhesion forces divided each ice adhesion area was given.     

Efficiency of surface modified Ti coated with copper nanoparticles to control marine bacterial adhesion under laboratory simulated conditions

Titanium (Ti) used as condenser material in nuclear power plants encounter severe biofouling in marine environment which in turn affects the efficiency of the metal. To reduce the biofouling by marine microorganisms, surface modification of the Ti was carried out by anodization process to obtain nanotubes (TiO₂-NTs). The electrolyte solution containing 1% of ammonium fluoride resulted in uniform growth of TiO₂-NTs. TiO₂-NTs were further coated with chemically synthesized copper nanoparticles (NT-CuNP) using 3-amino propyl triethoxy silane as a coupling agent. NT-CuNP was characterized by field-emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy and X-ray diffraction. The stability of the coating was determined by the amount of Cu⁺ ions released into the surrounding using AAS. The microbial adhesion on the surface of Ti, TiO₂-NTs and NT-CuNP coupons were evaluated by sea water exposure studies using total viable count method and also characterized by FE-SEM for any morphological changes. The NT-CuNP coupons show a 60% reduction in microbial adhesion when compared to control Ti coupons.     

Investigation of method for measuring adhesion force of ice in nano/micro scale by using SPM

Ice adhesion to a cooling solid surface occurs in many situations, and it causes many serious problems that can lead to economic losses. Therefore, it is necessary to clarify the mechanism of ice adhesion to a cooling surface. In past studies, the adhesion force of ice was reported to be strongly governed by the surface energy of the cooling solid surface. In consideration of this surface energy, it is essential to investigate the ice adhesion force on a nano/micro scale. However, very little research has been conducted in nano/micro scale. Thus, in this paper, by using a scanning probe microscope (SPM), the methods for measuring the ice adhesion force and contact area between the cooling solid surface and formed ice are proposed, and the optimal measurement conditions of the SPM are determined. Then, the validity and effectiveness of the method are clarified.     

Polyaniline/Vanadium oxide composites: An effective control in morphology by varying reactant concentrations

A one pot synthesis protocol is presented for the realization of organic/inorganic hybrid nanostructures comprised of polyaniline and vanadium oxide. The polyaniline/vanadium oxide hybrid morphology is tailored by controlling the relative concentration of reactants which resulted in diverse morphologies ranging from nanorods, combined nano/microrods to porous nano/microspheres. Temporal evolution of morphology is investigated to elucidate the formation mechanism in detail. The prepared composites exhibit enhanced thermal stability in comparison to pure polyaniline which may be attributed to the strong chemical combination of vanadium oxide and polyaniline within the composites as prevailed by FTIR and TGA analysis of the products. This simple and controllable approach for synthesizing the organic/inorganic hybrid material should have future applications in energy storage devices, sensors and many more.     

Fundamental study on adhesion of ice to solid surface: Discussion on coupling of nano-scale field with macro-scale field

In a previous study, it was reported that the removal process (behavior) of ice from a cooling solid surface depended on the characteristic of the solid surface, and that the ice adhesion force to the cooling surface was mainly governed by the surface energy of the surface. In the present study, using the method of surface analysis, the ice removal process and the ice adhesion force clarified in a macro-scale field were also discussed in a nano-scale field to couple these scale fields. Simultaneously, another surface analysis of the solid surface was carried out to identify the distributions of hydrophilic and hydrophobic groups on a solid surface. Attempts to couple the nano-scale field with the macro-scale field revealed that the results for both scale fields were in approximate qualitative agreement.     

Measurements of correct ice adhesion forces to metal test plates in nano-scale by using SPM

To prevent many problems caused by ice adhesion, its control technology is required. To settle this technology, obtaining the correct ice adhesion force is a key point. However, ice adhesion forces obtained by current conventional methods are apparent values including a force breaking ice. Thus, authors developed a method to measure correct ice adhesion force and accurate ice diameter in a nano-scale by SPM and both for copper were measured. To construct a database to store the correct ice adhesion forces and diameters for various metals, first, the ice adhesion forces and the ice diameters for aluminum, titanium, carbon steel, and stainless steel are measured at −5°C by the SPM. Additionally, to easily compare our results with other works, shearing stresses of the metals are also given by the ice adhesion forces and ice adhesion areas. Validities of our results are proven by comparing them with the surface energies and other works.     

Numerical simulation of local ice loads in uniform and randomly varying ice conditions

The ice loading process has a clear stochastic nature due to variations in the ice conditions and in the icebreaking processes of ships. The statistical characteristics of local ice loads are typically studied on the basis of field measurements. In this paper, a numerical method was applied to simulate a ship moving forward in either uniform or randomly varying ice conditions, where the thickness and strength properties of the ice encountered by the ship were assumed to be constant or randomly generated using the Monte Carlo method. The purpose of this simulation is to show the origin of the statistical variation in ice loading, which is difficult to identify in field measurements. To validate the numerical results, an icebreaking tanker, MT Uikku, was then modeled in a simulation program, the ice loading process was stochastically reproduced and the calculated amplitude values of the ice-induced frame loads were compared with the field measurements.     

Characterization of surfactant coatings in capillary electrophoresis by atomic force microscopy

This paper describes the adsorption mechanisms and aggregation properties of cetyltrimethylammonium bromide (CTAB) and didodecyldimethylammonium bromide (DDAB) surfactants that are used for dynamic coatings in capillary electrophoresis (CE). Atomic force microscopy is used to directly visualize surfactant adsorption on fused silica. It was found that the single-chained surfactant CTAB forms spherical aggregates on silica while the double-chained surfactant DDAB forms a bilayer. Aggregation at the surface occurs at approximately the same surfactant concentration in which EOF reversal is observed in CE. The nearest-neighbor distance between CTAB aggregates varies inversely with buffer pH and becomes constant at the point when the silanol groups are fully ionized. DDAB forms a flat, uniform coating independent of pH. Increasing the buffer ionic strength changes the morphology of the CTAB aggregates from spherical to cylindrical. The change in morphology can alter the surface coverage, which is related to the "normalized" EOF measured in identical buffers. The morphology of a surfactant coating is also shown to affect its ability to inhibit protein adsorption to the capillary wall. Specifically, the full surface coverage provided by DDAB proved superior in a head-to-head comparison with CTAB.     

Preparation of CNFs surface to coat with copper by electroless process

In the present work, the effects of oxidative pretreatments of carbon nanofibers in different mineral acids were studied. It has been found that the pretreatment of carbon nanofibers was very important to obtain the different grain size copper nanoparticles on the CNF. This material was pretreated with three different oxidative solutions, in order to increase their specific surface: HNO₃, KMnO₄ + HNO₃ and K₂Cr₂O₇ + H₂SO₄. The highest oxidative coarsening conditions imply the highest active surface, increasing possible copper nucleation points. Sensitized solution has been NiCl₂ instead of SnCl₂, which was used in conventional electroless process. In all cases, electroless process was carried out at room temperature and pH of the plating solution was maintained at the value of 12.5.     

利用表面活性剂量改变孔洞率制备的纳米多孔SiO2膜

采用表面活性剂十六烷基三甲基溴化氨(CTAB)为模板剂,在酸性条件下产生多孔结构,再经热处理去除CTAB。实验中使用溶胶?凝胶技术,正硅酸乙酯(TEOS)为硅源,以及二次去离子水,盐酸为催化剂等原料,利用表面活性剂与硅源水解后形成的聚集体相互作用,在溶液中形成分子自组装体,制备前驱体溶胶。通过简单提拉迅速蒸发溶剂制备纳米多孔或纳米介孔SiO2薄膜,分析和研究了表面活性剂浓度对纳米多孔SiO2薄膜的结构和孔洞率的影响,通过操纵表面活性剂的含量,能控制薄膜的纳米结构、孔洞率、孔大小和孔的形态以及膜的形貌。小角度射线衍射、场发射透射电子显微镜、原子力显微镜显示可以制得具有六方、立方和由三维六方和简单立方组成的新相结构以及比介孔大的纳米多孔结构的薄膜。椭偏仪测量得到所制备薄膜的孔洞率为51.8%-65.6%,借助此孔洞率能计算薄膜的折射率和介电常数。     

Enhanced adhesion of osteoblastic cells on polystyrene films by independent control of surface topography and wettability

We independently controlled surface topography and wettability of polystyrene (PS) films by CF₄ and oxygen plasma treatments, respectively, to evaluate the adhesion and proliferation of human fetal osteoblastic (hFOB) cells on the films. Among the CF₄ plasma-treated PS films with the average surface roughness ranging from 0.9 to 70 nm, the highest adhesion of hFOB cells was observed on a PS film with roughness of ~ 11 nm. When this film was additionally treated by oxygen plasma to provide a hydrophilic surface with a contact angle less than 10°, the proliferation of bone-forming cell was further enhanced. Thus, the plasma-based independent modification of PS film into an optimum nanotexture for human osteoblast cells could be appplied to materials used in bone tissue engineering.     

Evaluation of film adhesion to substrates by means of surface acoustic wave dispersion

For thin film structures acoustically classified as slow-on-fast systems, modeling and evaluation of their interfacial condition are known to be very complex and difficult due to dispersion and multi-mode excitation of acoustic waves. This paper presents a quantitative model and a reliable measurement procedure established for adhesion evaluation of such film structures. An effective interface model employing a virtual intermediate layer is utilized for the dispersion prediction of the surface acoustic wave, which is affected by various interfacial conditions. Through acoustic microscopy experiments, this model presents a potential method to classify the bonding condition. Comparisons with a destructive scratch test and an acoustic imaging verify the failure mode of the film structure.     

Constant chemical potential titration. Application to determination of nonionic surfactant concentrations

Titration is most often associated with the idea of a stoichiometric reaction. Generally, it is not considered possible to titrate a compound against a reagent unless the titration reaction is near total and if the result is not a product of well-defined stoichiometry. In this work, we illustrate that accurate titration is possible with compounds and reagents that interact to form an association of undefined stoichiometry. Our model is the potentiometric titration of nonionic surfactant with cationic surfactant using a cationic surfactant-selective electrode. The result of this reaction is mixed micelles, the composition of which depends on the concentrations of the two surfactants in solution.