超疏水涂膜的研究进展

超疏水涂膜以其独特的性能,在国防、工农业生产和日常生活中有着广泛的应用前景。但目前的制备技术制约了其在建筑外墙涂料等大型设施方面的应用。探索如何采用简单有效的方法构造和调控涂膜的双微观结构,从而获得性能持久优异的超疏水性涂膜,并有效应用于生产和生活的各个方面是这一领域研究的最终目标。本文就超疏水材料表面理论的发展和近几年来超疏水膜制备技术取得的新成果进行了概括,并指出制备超疏水涂膜存在的问题和发展方向。利用表面能极低的含氟材料,将溶胶－凝胶、相分离技术和自组装梯度功能等技术有机结合,获得适宜的表面粗糙度和微观构造,是实现超疏水涂膜工业化生产的可行途径。     

Wetting of heterogeneous surfaces of block copolymers containing fluorinated segments

 The wetting of well-characterized heterogeneous surfaces of block copolymers has been studied by low-rate dynamic contact angle measurements using axisymmetric drop-shape analysis. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to investigate the roughness, the heterogeneity and the chemical composition of the surfaces. By changing the block length of polysulfone and semifluorinated polyester segments in the block copolymers, the surface heterogeneity of thin films prepared on silicon wafers could be controlled. Tapping-mode AFM measurements showed that soft, hydrophobic domains of varying size on the submicrometer length scale were obtained on these surfaces (60–250 nm). The mean roughness was of the order of several nanometers. The results of the contact angle measurements showed that neither roughness nor heterogeneity had a significant effect on the advancing contact angle of water, at the scale of the features present; however, the contact angle hysteresis increased with increasing percentage of the soft domains. We assume that liquid retention by the solid upon retraction of the three-phase line is the main cause for the observed increase in contact angle hysteresis. Concerning the molecular composition of these block copolymer surfaces, angle-resolved XPS analysis showed a surface segregation of fluorine within the surface region. A direct correlation was found between the fluorine content of the block copolymer surfaces and the advancing contact angle of water. Received: 26 May 2000 Accepted: 3 January 2001     

Thermal Decomposition Studies of Organoplatinum Films

 This study examines the thermal decomposition of 1,5-cyclooctadiene platinum (II) chloride organometallic films, deposited by thermal evaporation. The thin film samples were annealed both in air and hydrogen with well-controlled temperature regimes. After annealing, the decomposed thin films were examined by AFM and STM scanning probe, XPS and TEM microbeam analytical techniques. The experimental results confirm that the thermal decomposition products on silicon substrates are composed predominantly of metallic platinum. Annealing in hydrogen can reduce substantially the decomposition temperature of the material from around 250 to 160 °C but the surface morphology of the decomposed films is significantly different to those annealed in air. The metallic nature of the thermally decomposed films was confirmed by bonding configuration recognition, electronic property probing and microstructure analysis.     

Potentiometric Studies on SomeCephalosporin Complexes

Summary.  The interaction of Ca(II), Cu(II), Zn(II), Pb(II), and La(III) ions with the antibiotics cephalexin, cefadroxil, cephaloridine, and cefoperazone as secondary ligands was investigated potentiometrically. The formation constants were determined for a ligand-to-metal ratio of 1:1 at 25°C and KNO₃. The protonation constants of the complexes were evaluated for the system . The order of stability of the binary and ternary complexes were examined. It was found that glycine adds preferably [M(II)-cephalosporin] rather than to the aqueous complexes of M(II). In all cases 1:1:1 complexes were formed. Received February 4, 2000. Accepted (revised) May 10, 2000     

Recent Advances in the Description of the Structure of Water, the Hydrophobic Effect, and the Like-Dissolves-Like Rule

Summary.   Following a critical survey of the vast recent literature, the state of the art may be summarized as follows: (A) Water structure. The key is appreciating the next-nearest neighbour aspect. Thus, liquid water may be conceived as a fluctuating mixture of broadly two groups of structure elements: (i) an open ice-I_h-type outer neighbour bonding at about 4.5 ? and (ii) a dense ice-II-type outer neighbour bonding at about 3.4 ?. On the other hand, the nearest neighbour distance of about 2.8 ? and the number of these neighbors (4) is very similar in the solid and liquid state. The characterization of the two states may be directed either by the geometry of the H-bonds (more linear H-bonds in (i) and more bent H-bonds in (ii) or by the bonding forces operating (H-bonding favours the ordered open state (i), oxygen–oxygen interactions favour the random dense state (ii). Basically, the nature of liquid water can be understood in terms of a competition between H-bond (Coulomb) and dispersion (van der Waals) forces. Since the bonding characteristics in crystalline phases carry over to the liquid state, any molecular dynamics (MD) model of the liquid would have first of all to reproduce well the ice polymorph structures under appropriate thermodynamic conditions. (B) Hydrophobic effect. The two classic approaches, i.e. the clathrate cage model and the cavity-based model, appear to be just different perspectives on the same physics. The particular features of water are (i) the small molecular size or, more specifically, the small size of the space between water molecules and the low expansibility, and (ii) the structure of the water molecule with the same number of donor and acceptor sites arranged tetrahedrally. Due to (i), cavity formation is particularly demanding, and this is the main contributor to the hydrophobic effect. This is mitigated by the capability of water, due to (ii), to form a cage around a nonpolar solute without sacrificing much of the H-bonding; rather, H-bonding networks are stabilized by the presence of guest molecules. In view of the tangential orientation of the first-sphere waters, such a cage can be compared with an elasticated net effecting strong solute–solvent dispersive interactions, rendering the solubility of nonpolar gases exothermic at room temperature. Furthermore, cavity formation largely determines the excess entropy, whereas dispersive forces determine the excess enthalpy. This gives rise to compensation behaviour when the solute size varies. Whereas an increase in solute size enhances the cavity formation energy, polarizability is also increased, and this leads to stronger solute–water interaction. Unfortunately, present models of cavity formation predict positional entropies that are far in excess of the experimental entropies so that orientational contributions due to cage formation are hard to accommodate. (C) Like-dissolves-like rule. The number of exceptions is dramatically reduced if the term polarity is given a broader meaning. Instead of identifying it solely with dipolarity, it should also include higher multipolar properties, in particular quadrupolarity. Quadrupolar solvent effects on solvation and reactivity are receiving increasing attention, particularly in low dielectric solvents. Received May 8, 2001. Accepted (revised) May 23, 2001     

Inferring wettability of heterogeneous surfaces by ToF-SIMS

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been examined as a possible predictive tool for surface wettability. Heterogeneous surfaces were prepared with hydrophilic and hydrophobic regions of known surface coverage using self-assembled monolayers. The surface coverage of each component was then correlated with ToF-SIMS fragmentation of the hydrophobic and hydrophilic surface groups and static contact angle measurements. From these measurements, a clear relationship between the surface wettability and relative intensity of characteristic secondary ions was identified. Moreover, our results for planar surfaces can be extrapolated to predict the wettability of particulate samples for which direct contact angle measurements are not straightforward. The ability to infer particle wettability by ToF-SIMS is well suited to mineral characterization and in particular, the prediction of mineral flotation efficiencies.     

Review of non-reactive and reactive wetting of liquids on surfaces

Wettability is a tendency for a liquid to spread on a solid substrate and is generally measured in terms of the angle (contact angle) between the tangent drawn at the triple point between the three phases (solid, liquid and vapour) and the substrate surface. A liquid spreading on a substrate with no reaction/absorption of the liquid by substrate material is known as non-reactive or inert wetting whereas the wetting process influenced by reaction between the spreading liquid and substrate material is known as reactive wetting. Young's equation gives the equilibrium contact angle in terms of interfacial tensions existing at the three-phase interface. The derivation of Young's equation is made under the assumptions of spreading of non-reactive liquid on an ideal (physically and chemically inert, smooth, homogeneous and rigid) solid, a condition that is rarely met in practical situations. Nevertheless Young's equation is the most fundamental starting point for understanding of the complex field of wetting. Reliable and reproducible measurements of contact angle from the experiments are important in order to analyze the wetting behaviour. Various methods have been developed over the years to evaluate wettability of a solid by a liquid. Among these, sessile drop and wetting balance techniques are versatile, popular and provide reliable data. Wetting is affected by large number of factors including liquid properties, substrate properties and system conditions. The effect of these factors on wettability is discussed. Thermodynamic treatment of wetting in inert systems is simple and based on free energy minimization where as that in reactive systems is quite complex. Surface energetics has to be considered while determining the driving force for spreading. Similar is the case of spreading kinetics. Inert systems follow definite flow pattern and in most cases a single function is sufficient to describe the whole kinetics. Theoretical models successfully describe the spreading in inert systems. However, it is difficult to determine the exact mechanism that controls the kinetics since reactive wetting is affected by a number of factors like interfacial reactions, diffusion of constituents, dissolution of the substrate, etc. The quantification of the effect of these interrelated factors on wettability would be useful to build a predictive model of wetting kinetics for reactive systems.     

Particle adsorption in evaporating droplets of polymer latex dispersions on hydrophilic and hydrophobic surfaces

Stain patterns formed by drying up of droplets of polymer latex dispersion on hydrophilic and hydrophobic surfaces were examined in light of the mechanism of particle adsorption in evaporating droplets. On hydrophilic surfaces, the volume of droplets decreased with time, keeping the initial outline of contact area, and circular stain patterns were formed after the dry-up of droplets. By the microscopic observation of particles in the droplets, it was found that a large portion of the particles were forced to adsorb on the outline of the contact area where a microscopic thin water layer was formed because of hydrophilicity of the surface. On hydrophobic surfaces, on the other hand, the contact area of droplets decreased as evaporation proceeded, while no particle was adsorbed on the surface at the early stages. The particles in the droplets started to aggregate when the concentration of particles reached a critical value, and the aggregates adsorbed on the surface forming tiny spots after the dry-up. Time evolutions of contact angle, contact area and volume of the droplets were analyzed in light of differences in the adsorption mechanisms between hydrophilic and hydrophobic surfaces. Received: 14 January 1998 Accepted: 1 May 1998     

Determination of Thiosemicarbazones by Means of the Induced Iodine-Azide Reaction

 The iodine-azide reaction induced by eight thiosemicarbazones was investigated. Inducing properties of thiosemicarbazones are different and depend on the parent carbonyl compound used for synthesis. The inductor coefficients of the examined thiosemicarbazones vary from 61 to 176. Optimum conditions for the determination of microamounts of thiosemicarbazones are given. The detection limit for the determination by the back-titration method depends on the inducing activity and is 0.9 μg for phenyl-thiosemicarbazones and 2 μg for diethyl-thiosemicarbazone in a 5-mL sample, and this corresponds to a concentration of 0.9 × 10⁻⁶ mol/L and , respectively. The automatic titration with the diluted iodine solution decreases the detection limit to about 50 ng in a 10-mL sample. Received October 28, 1998. Revision April 9, 1999.     

Vibrational Spectroscopy and Analytical Electron Microscopy Studies of Fe–V–O and In–V–O Thin Films

Summary.  Orthovanadate (M ³⁺VO₄; M = Fe, In) and vanadate (Fe₂V₄O₁₃) thin films were prepared using sol-gel synthesis and dip coating deposition. Using analytical electron microscopy (AEM), the chemical composition and the degree of crystallization of the phases present in the thin Fe–V–O films were investigated. TEM samples were prepared in both orientations: parallel (plan view) and perpendicular (cross section) to the substrate. In the first stages of crystallization, when the particle sizes were in the nanometer range, the classical identification of phases using electron diffraction was not possible. Instead of measuring d values, experimentally selected area electron diffraction (SAED) patterns were compared to calculated (simulated) patterns in order to determine the phase composition. The problems of evaluating the ratio of amorphous and crystalline phases in thin films are reported. Results of TEM and XRD as well as IR and Raman spectroscopy showed that the films made at lower temperatures (300°C) consisted of nanograins embedded in the dominating amorphous phase. Characteristic vibrational spectra allowed to distinguish between the different crystalline phases, since the IR and Raman bands showed broadening due to the decreasing particle size of the films thermally treated at lower temperatures. Vibrational analysis also showed that the electrochemical cycling of crystalline films led to spectra that were in close agreement with the spectra of the nanocrystalline films prepared at lower temperatures. The formation of a nanocrystalline structure is therefore a prerequisite for obtaining a higher charging/discharging stability of Fe–V–O and In–V–O films. Received October 4, 2001. Accepted (revised) November 23, 2001     

SIMS Profiling and TEM of CVD Films on Multi-Filament Samples

 A suitable fibre coating is essential to obtain optimal fibre-matrix interaction in fibre-strengthened composite materials. Thin films (∼100 nm) of silicon carbide, turbostratic carbon, and boron nitride were deposited by CVD as single or double layers on commercial multi-filament fibres in a continuous process. The fibre material itself may be carbon, alumina, silicon carbide, or a quaternary ceramic of SiCBN. The application of MCs⁺-SIMS enables one to determine the composition (including impurities of H and O) of various fibre coating materials with an accuracy of at least 20% relative. Due to the special geometry of the multi-filament samples the depth resolution of the SIMS depth profiles is limited, nevertheless, layered structures and some details of the interface between coating and fibre can be studied. The depth calibration of the SIMS depth profiles is derived from sputter rates established on flat samples with a composition similar to that of the fibre coating material. However, the obtained film thicknesses are not extremely different from the values derived from TEM on cross sections of coated fibres.     

A review of factors that affect contact angle and implications for flotation practice

Contact angle and the wetting behaviour of solid particles are influenced by many physical and chemical factors such as surface roughness and heterogeneity as well as particle shape and size. A significant amount of effort has been invested in order to probe the correlation between these factors and surface wettability. Some of the key investigations reported in the literature are reviewed here.It is clear from the papers reviewed that, depending on many experimental conditions such as the size of the surface heterogeneities and asperities, surface cleanliness, and the resolution of measuring equipment and data interpretation, obtaining meaningful contact angle values is extremely difficult and such values are reliant on careful experimental control. Surface wetting behaviour depends on not only surface texture (roughness and particle shape), and surface chemistry (heterogeneity) but also on hydrodynamic conditions in the preparation route. The inability to distinguish the effects of each factor may be due to the interplay and/or overlap of two or more factors in each system. From this review, it was concluded that:

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Surface geometry (and surface roughness of different scales) can be used to tune the contact angle; with increasing surface roughness the apparent contact angle decreases for hydrophilic materials and increases for hydrophobic materials.

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For non-ideal surfaces, such as mineral surfaces in the flotation process, kinetics plays a more important role than thermodynamics in dictating wettability.

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Particle size encountered in flotation (10-200 μm) showed no significant effect on contact angle but has a strong effect on flotation rate constant.

There is a lack of a rigid quantitative correlation between factors affecting wetting, wetting behaviour and contact angle on minerals; and hence their implication for flotation process. Specifically, universal correlation of contact angle to flotation recovery is still difficult to predict from first principles. Other advanced techniques and measures complementary to contact angle will be essential to establish the link between research and practice in flotation.     

Wettability of proteins adsorbed on silica glasses treated with fluorosurfactants

Generally, the apolar/polar surface is probed by water-wetting, which is measured using a method such as the sessile liquid drop method. However, when one tries to measure the wetting of a surface where biological macromolecules are adsorbed, there is the problem of a change in conformation due to drying the surface; hence, using this method in situ information cannot be obtained. We have developed a new method that can be used to measure the wettability of the adsorbed protein surface without drying. This method, the dropping time method, which is based on measuring the dropping time of a film of liquid along a protein-covered surface when this surface is instantaneously vertically removed from the protein solution. The adsorption behavior of four proteins (albumin, lysozyme, β-lactoglobulin, ovalbumin) on the surface of silica glass that has been treated with various fluorosurfactants is studied using this method. At a high concentration of protein, the surfaces of adsorbed proteins of any kind are fairly hydrophilic on glass treated with all fluorosurfactants. At a lower concentration of protein, the hydrophilicity of the protein layer depends on the kind of fluorosurfactant and also on the protein adsorption process. The apolar glass surface becomes more hydrophilic with increasing dipping time in the protein solution. On the other hand, the hydrophilic glass surface shows a complex change in the hydrophilicity with elapsed time after dipping it into a solution of albumin or lysozyme, i.e., the hydrophilicity decreases in the early stage of the adsorption and then increases with proceeding adsorption. Received: 19 March 1999 Accepted in revised form: 10 June 1999     

Studies on Hybrid Organic/Inorganic Nanocomposite Gels Using Photoluminescence Techniques

Summary.  Transparent nanocomposite gels made of hybrid organic/inorganic polymers, synthesized through the sol-gel method, composed of poly-(ethylene oxide) or poly-(propylene oxide) chains, and grafted on silica through urea bridges, have been studied by steady-state and time-resolved photoluminescence techniques. These nanocomposite materials consist of two distinguished subphases, an organic and an inorganic one. The volume fraction of the organic (polyether) subphase is larger than that of the inorganic (silica) subphase, and it increases with increasing polyether chain size. The condensation of the silica subphase provides luminescent entities emitting light by electron-hole recombination on delocalized states associated with the active chemical species of the urea bridges. Materials with smaller polyether chains are more luminescent than such with longer polyether chains. Divalent or trivalent cations introduced into these materials enhance the luminescence intensity by solubilization close to the silica cluster surface and thus by decreasing surface defects and the ensuing quenching mechanism. Received June 23, 2000. Accepted (revised) July 18, 2000     

Quantitative Analysis of Thin Aluminium-Oxynitride Films by EPMA

 Thin films of aluminium oxynitride with diverse composition were prepared by dc-magnetron sputtering of aluminium, utilising sputtering power as well as argon, oxygen and nitrogen gas flows to vary the composition. Since film properties depend mainly on the content of incorporated oxygen and nitrogen, a method for quantitative analysis of the main constituents based on electron probe micro analysis with energy dispersive detection was developed. The excellent precision of the quantitative results for aluminium as well as oxygen and nitrogen are shown. Furthermore, a film layer analysis program was applied for the quantification of several films deposited under the same deposition parameters on silicon wafers, from 520 nm down to 40 nm thickness, showing that electron probe micro analysis with energy dispersive detection is a reliable method for quantitative compositional analysis of thin aluminium oxynitride films down to approximately 20 nm thickness. Since this method of analysis provides only bulk information, expected inhomogeneities of the depth distribution of the film components were checked by secondary ion mass spectrometry depth profiles of two thin films and correlated to the EPMA results. The thickness of the films was determined by ellipsometry. Received September 1, 1998     

Analysis of Laser Irradiated Organo-Platinum Films

 A study of the surface electronic configuration and surface morphology of excimer laser irradiated organo-platinum films [cis-dichlorobis(triphenylphosphine)platinum(II)] is presented. The films were deposited by thermal evaporation to a thickness of approximately 1 μm. The organo-platinum films were irradiated in air with 248 nm UV light in order to produce metallic deposits. The irradiation source used was a krypton fluoride excimer laser with a pulse length of approximately 20 ns. After irradiation, the surface morphology of the films was studied by atomic force microscopy, which yielded information concerning the effect of exposure dose on the surface roughness. The composition of the deposits was investigated using X-ray photoelectron and Fourier-transform infrared spectroscopy. The effect of annealing the deposits has also been studied. XPS analysis of the annealed samples has provided evidence for the formation of platinum silicide (PtSi).     

Recent Developments in Conjugated Polymer Based Plastic Solar Cells

Summary.  Recent developments on photovoltaic elements based on solid state composites of conjugated, semiconducting polymers mixed with buckminsterfullerene are reviewed. The photoinduced charge transfer from donor-type semiconducting conjugated polymers onto acceptor-type conjugated polymers or acceptor molecules such as buckminsterfullerene is reversible, ultrafast (within 100 fs) with a quantum efficiency approaching unity, and the charge separated state is metastable (up to ms at 80 K). This phenomenon of photoinduced electron transfer leads to a number of potentially interesting applications which include, among others, sensitization of the photoconductivity, reverse saturable absorption (optical limiting), and photovoltaic phenomena. Recent studies on the realization of photovoltaic elements with 3% power conversion efficiency are reported. Received December 19, 2000. Accepted December 22, 2000     

Preparation of Nanostructured Magnetic Films by the Plasma Jet Technique

Summary.  Magnetic films were prepared by the plasma jet technique from Fe, mumetal, and Fe/Hf or Fe/Ta nozzles. Two different plasma jet systems with different vacuum pumps were used to compare the quality of the produced films. The films prepared from a Fe nozzle in the two different equipments shows that oxygen in the residual atmosphere of the low vacuum reactor leads mainly to the formation of iron oxides. The Fe and mumetal films prepared in the high vacuum system contain only a very small amount of oxygen, as proved by chemical analysis and ferromagnetic resonance. The mumetal film, moreover, shows good soft magnetic properties and low magnetic damping. For the reactive plasma jet deposition of nanogranular Fe–Hf–O and Fe–Ta–O films, the low vacuum system was used. The films with higher oxygen content exhibit tunneling-type conductivity. In some films, superparamagnetic behaviour and spin-dependent tunneling magnetoresistance were observed. Received October 5, 2001. Accepted November 22, 2001     

X-Ray Emission from Thin Films on a Substrate – Calculation and Experiments

 Monte Carlo simulation of electron transport in solids is widely used in electron microscopy, spectroscopy and microanalysis. The reliability of physical models incorporated in a Monte Carlo code is usually checked by comparing with experimental results. Elastic or inelastic collisions are usually considered as the basic interactions of electrons with atoms. In our Monte Carlo code the single scattering model is employed for simulation of X-ray emission from thin films of Au on the Si substrate. The electron beam energy was in the range 10–30 keV, the take-off-angle was 40°. The simulated values of X-ray production were calculated in our Monte Carlo code using several models of ionisation cross-sections. For the emitted intensities the depths of inelastic collision and X-ray absorption were taken into account, then the k-ratios were calculated. These data were compared with experimental values of k-ratios calculated from X-ray intensities of Au M and Au L characteristic lines. We followed mainly the dependence of the k-ratios of the film element on film thickness. The film thickness was in the range 0.05–1 μm. Reasonably good agreement was found for dependences of X-ray intensity on film thickness in the whole energy range and for both lines, especially for Powell’s model of the ionisation cross-section.     

Thin Films and Interfaces of Electroactive Organic Materials: The Surface Science Approach

Summary.  We highlight the importance of interfacial properties in determining the performance of devices based on electroactive organic materials. Investigations of the interfaces of benzene with Al(111) and In₂O₃ are presented as a model of interface properties for devices based on complex aromatic molecules. At both interfaces the binding is shown to be electrostatic, with the resulting interface dipole determining the band alignment. It is also argued that chemical modification of substrates can be used to tailor both electronic and structural properties. Received May 30, 2000. Accepted September 21, 2000