Analysis of wetting as an efficient method for studying the characteristics of coatings and surfaces and the processes that occur on them: A review

The use of a method of studying wetting both for the research of fundamental problems of surface physicochemistry, such as obtaining information on the structure and properties of the interface and the processes that occur with its participation, and for technological applications related to the preparation of new materials and coatings is analyzed. The fundamental relationships between the contact angle and the thermodynamic and geometric characteristics of the surface are discussed; the factors that have an effect on the contact angle value on nanocomposite surfaces are analyzed. It is shown that recent advances in digital processing of video images provide a qualitatively new level of measurement of contact angles and make the analysis of surface wetting one of the most efficient experimental methods for studying the processes that occur at interfaces. In some cases, the accumulated basic knowledge about the relationship between the measured contact angle and the properties of the surface under study makes it possible to rapidly and reliably obtain detailed information about the roughness, chemical composition, and topology of the surface without using expensive equipment; in other cases, it provides additional information that makes it possible to reveal the mechanisms of the surface phenomena under study. As a case in point, we describe the use of techniques of analysis of wetting for determining the surface porosity and surface topology, for estimating the pattern of interaction between polymer materials and aqueous media, and for revealing the efficiency of anticorrosion coatings on metal surfaces.     

Mikrowellen‐PECVD für kontinuierliche Großflächenbeschichtung bei Atmosphärendruck

Microwave PECVD for continuous wide area coating at atmospheric pressure Plasma processes are applied for a variety of surface modifications. Examples are coatings to achieve an improved corrosion and scratch protection, or surface cleaning. Normally, these processes are vacuum based and therefore suitable to only a limited extend for large area industrial applications. By use of atmospheric pressure plasma technology integration in continuously working manufacturing lines is advantageously combined with lower costs and higher throughput. Microwave plasma sources present powerful modules for plasma enhanced chemical vapour deposition at atmospheric pressure. At Fraunhofer IWS processes and equipment as well as application specific materials are developed. The coatings are suitable for scratch resistant surfaces, barrier and corrosion protective layers or anti‐reflex layers on solar cells. The film properties achieved are comparable with those produced by low pressure processes.     

镁合金表面功能涂层制备与界面表征技术的研究进展

随着低碳经济的发展,汽车轻量化的呼声愈来愈高。镁合金作为最有前景的轻量化材料之一,其表面防腐功能涂层的研究已经越来越受到人们的重视。简要介绍了物理方法和化学方法制备镁基表面防腐功能涂层的工艺技术特点,重点讨论了衡量涂层质量的现行标准以及现有的各种测量界面结合强度的方法,特别是界面应变能释放率定量分析的方法,文中结合自己的实验结果进行了分析。     

Measurement and Modeling of the Bidirectional Reflectance of SiO2 Coated Si Surfaces

An understanding of the variation of directional radiative properties of rough surfaces with dielectric coatings is important for temperature measurements and heat transfer analysis in many industrial processes. An experimental study has been conducted to investigate the effect of coating thickness on the bidirectional reflectance distribution function (BRDF) of rough silicon surfaces.Silicon dioxide films with thicknesses of 107.2, 216.5, and 324.6 nm were deposited using plasma-enhanced chemical vapor deposition onto the rough side of two Si wafers. The wafer surfaces exhibit distinct anisotropic characteristics as a result of chemical etching during the manufacturing process. A laser scatterometer measures the BRDF at a wavelength of 635 nm, after improvement of the signal-to-noise ratio. The slope distribution function obtained from the measured BRDF of uncoated Si surfaces was used in an analytical model based on geometric optics for rough surface scattering and thin-film optics for microfacet reflectance. The predicted BRDFs are in reasonable agreement with experimental results for a large range of coating thicknesses. The limitations of the geometric optics for modeling the BRDF of coated anisotropic rough surfaces in the specular direction are demonstrated. The results may benefit future radiative transfer analysis involving complicated surface microstructures with thin-film coatings.     

Functionalized superhydrophobic coatings with micro-/nanostructured ZnO particles in a sol–gel matrix

Among the methods to create superhydrophobic surfaces by wet chemistry, one of the strategies consists in coating the substrate with a hydrophobic polymer with specific morphology. Such elaborated surfaces are largely developed and can present complex architectures but are generally fragile. Ceramic-based coatings show better durability. In this work, a new route associating inorganic and polymeric parts is used. Surfaces with superhydrophobic properties are prepared with a mixture of zinc oxide (ZnO) particles in a hybrid organic inorganic matrix prepared via sol–gel route. ZnO particles were synthesized by the inorganic polycondensation route and exhibit an appropriate micro-/nanostructure for superhydrophobicity. Sol–gel matrix is obtained by the alkoxide route with aluminum-tri-sec-butoxide (ASB) and (3-glycidoxypropyl)trimethoxysilane (GPTMS). A step of octadecylphosphonic acid (ODP) functionalization on ZnO particles and on film surfaces was employed to considerably improve hydrophobic properties. This new route enables to obtain superhydrophobic coatings that exhibit water contact angles superior to 150°. These coatings show a homogeneous and smooth coverage on aluminum alloy substrate. Results attest the significance of the synergy for superhydrophobic coatings: a micro-/nanostructured surface and an intrinsic hydrophobic property of the material. The durability of the coatings has also been demonstrated with only a slight decrease in hydrophobicity after erosion.     

粉状纳米材料的表面研究进展与展望

粉状纳米材料表面是决定其性能的关键性因素之一。用热物理法,化学法和机械制造法都可制得纳米粉,但其表面却有所不同。热物理法能得到表面比较纯净的纳米粉。纳米粉表面与其成分、结构和形态有关,它对纳米粉的化学和物理性能有着决定性的影响。因此,粉状纳粉材料应用前景也决取于其表面研究的进展。     

Easy‐to‐clean Schichten – spezielle Anwendungen

Easy to clean surfaces – special applications Easy to clean surfaces can be made by wet‐chemical coating with subsequent heat‐treatment. Organically modified metal oxide films form the base reinforced by nano composite structures. The hydro‐ and oleophobic effect is obtained by perfluorinated organic molecule chains in the nano composite sol‐gel coatings. Application specific materials can be synthesized by the proper choice of suitable starting compounds and process parameters. The resulting coatings consist of a three‐dimensional cross‐linked inorganic part (such as a silica network) combined with an organic part. The organic material acts either as a surface modifier (example: alkyl, phenyl) or as crosslinker (example: acrylic, epoxy). The properties of such coating systems can be adjusted to obtain a wide range of glass‐ceramic or polymer‐like properties. The incorporation of nanoparticles into these materials significantly enhances the abrasion and the scratch resistance. Such coatings mainly on metal parts are used in diagnostics, analytical chemistry and medical technology.     

金属表面超疏水性的研究进展

超疏水金属表面在表面自清洁、抗腐蚀、流动减阻及微流体无损输送等方面有着潜在的应用价值.综述了金属表面巯水性在理论及实现方法上的新进展,介绍了目前国内外提高金属表面疏水性的途径,重点归纳了金属超疏水表面的制备方法及相关应用,展望了今后的研究方向.     

Bioactive Ca–P coating with self-sealing structure on pure magnesium

Bioactive coatings containing Ca and P with self-sealing structures were fabricated on the surface of pure magnesium using micro-arc oxidation technique (MAO) in a specific calcium hydroxide based electrolyte system. Coatings were prepared at three applied voltages, i.e. 360, 410 and 450 V, and the morphology, chemical composition, corrosion resistance and the degradation properties in Hank’s solution of the MAO-coated samples with three different applied voltages were investigated. It was found that all the three coatings showed similar surface morphologies that the majority of micro-pores were filled with compound particles. Both the porous structures and the compound particles were found to contain consistent chemical compositions which were mainly composed of O, Mg, F, Ca and P. Electrochemical tests showed a significant increase in corrosion resistance for the three coatings, meanwhile the coating obtained at 450 V exhibited the superior corrosion resistance owing to the largest coating thickness. The long term immersion tests in Hank’s solution also revealed an effective reduction in corrosion rate for the MAO coated samples, and the pH values of the coated samples always maintained a lower level. Besides, all the three coatings were subjected to a mild and uniform degradation, while the coating obtained at 360 V showed a relatively obvious degradation characteristic and appreciable Ca and P contents on the surfaces of the three coatings were observed after immersion in Hank’s solution. The results of the present study confirmed that the MAO coatings containing bioactive Ca and P elements with self-sealing structures could significantly enhance the corrosion resistance of magnesium substrate in Hanks’ solution with great potential for medical application.     

Biological evaluation of ultrananocrystalline and nanocrystalline diamond coatings

Nanostructured biomaterials have been investigated for achieving desirable tissue-material interactions in medical implants. Ultrananocrystalline diamond (UNCD) and nanocrystalline diamond (NCD) coatings are the two most studied classes of synthetic diamond coatings; these materials are grown using chemical vapor deposition and are classified based on their nanostructure, grain size, and sp³ content. UNCD and NCD are mechanically robust, chemically inert, biocompatible, and wear resistant, making them ideal implant coatings. UNCD and NCD have been recently investigated for ophthalmic, cardiovascular, dental, and orthopaedic device applications. The aim of this study was (a) to evaluate the in vitro biocompatibility of UNCD and NCD coatings and (b) to determine if variations in surface topography and sp³ content affect cellular response. Diamond coatings with various nanoscale topographies (grain sizes 5–400?nm) were deposited on silicon substrates using microwave plasma chemical vapor deposition. Scanning electron microscopy and atomic force microscopy revealed uniform coatings with different scales of surface topography; Raman spectroscopy confirmed the presence of carbon bonding typical of diamond coatings. Cell viability, proliferation, and morphology responses of human bone marrow-derived mesenchymal stem cells (hBMSCs) to UNCD and NCD surfaces were evaluated. The hBMSCs on UNCD and NCD coatings exhibited similar cell viability, proliferation, and morphology as those on the control material, tissue culture polystyrene. No significant differences in cellular response were observed on UNCD and NCD coatings with different nanoscale topographies. Our data shows that both UNCD and NCD coatings demonstrate in vitro biocompatibility irrespective of surface topography.     

Vibration-resistant direct-phase-detecting optical interferometers

Two dual-beam differential direct-phase-detecting optical interferometers for scanning moving surfaces are described. Two beams from these interferometers are focused ~42 mum apart on moving surfaces, and the difference in their reflected path lengths is measured to provide the surface roughness measurement. These interferometers are exceptionally insensitive to environmental vibrations and to surface physical and chemical factors. Applications discussed include the measurement of the surface roughness of a rotating cylinder and a moving web.     

Preparation of CdS coatings on the inner surface of silica aerogels by single-source metal-organic chemical vapor deposition at atmospheric pressure

CdS coatings are deposited on the external and inner surfaces of silica aerogels with a single-source metal-organic chemical vapor deposition method at atmospheric pressure. Thermogravimetry analysis and differential scanning calorimetry experiments are used to investigate the thermal behavior of silica aerogels, and the sample treated at 500 °C for 120 min has been found to possess the lowest density. The densities and morphologies of the silica aerogels under the different treatment temperatures are also studied. The CdS coatings are deposited on the inner surface of the silica aerogels with a 4 l/min flow of Ar gas. The procedure for the preparation of the CdS coatings on the inner surface is reported in details. The surface morphologies of the CdS-coated silica aerogels are analyzed by scanning electron microscopy. The results of the energy dispersive X-ray spectroscopy and X-ray diffraction analysis demonstrate that the CdS coatings are composed of cadmium and sulphur with an approximately atomic ratio of 1:1, and they are hexagonal structures.     

DNA Hairpin Stabilization on a Hydrophobic Surface

DNA hybridization in the vicinity of surfaces is a fundamental process for self‐assembled nanoarrays, nanocrystal superlattices, and biosensors. It is widely recognized that solid surfaces alter molecular forces governing hybridization relative to a bulk solution, and these effects can either favor or disfavor the hybridized state depending on the specific sequence and surface. Results presented here provide new insights into the dynamics of DNA hairpin‐coil conformational transitions in the vicinity of hydrophilic oligo(ethylene glycol) (OEG) and hydrophobic trimethylsilane (TMS) surfaces. Single‐molecule methods are used to observe the forward and reverse hybridization hairpin‐coil transition of adsorbed species while simultaneously measuring molecular surface diffusion in order to gain insight into surface interactions with individual DNA bases. At least 35 000 individual molecular trajectories are observed on each type of surface. It is found that unfolding slows and the folding rate increases on TMS relative to OEG, despite stronger attractions between TMS and unpaired nucleobases. These rate differences lead to near‐complete hairpin formation on hydrophobic TMS and significant unfolding on hydrophilic OEG, resulting in the surprising conclusion that hydrophobic surface coatings are preferable for nanotechnology applications that rely on DNA hybridization near surfaces.     

刻蚀处理对钛表面形貌的影响

发展电化学刻蚀和化学刻蚀技术,对钛表面进行处理,并应用扫描电镜、X射线衍射方法对其表面进行表征,探讨电化学刻蚀钛表面形成微观结构的机理.结果表明,经刻蚀后钛表面形成了纳米级微观结构,提高了表面粗糙度,可增强生物材料涂层与钛基底的结合强度.     

Formation of carbonate apatite on calcium phosphate coatings containing silver ions

The prerequisite for bioactive materials to bond to living bone is the formation of biologically equivalent carbonate apatite on their surfaces in the body. Calcium phosphate ceramic surfaces can be transformed to a biological apatite through a series of surface reactions including dissolution–precipitation and ion exchange. In the present work, apatite coatings with different crystallinity, compositions and crystal sizes, including a well-crystallized hydroxyapatite coating, were synthesized electrochemically and doped with silver ions in silver nitrate solution at room temperature. The formation of a new carbonate apatite on the surface of these coatings was investigated in an acellular simulated body fluid with ion concentrations comparable with those of human blood plasma, using scanning electron microscopy and Fourier transform-infrared spectroscopy. The results show that small quantities of silver ions incorporated into apatite coatings may have a strong stimulatory effect on the formation of carbonate apatite without adversely affecting the chemical stability of these coatings.     

Synthetic Fibers with Silver-Containing Coatings and Their Antimicrobial Properties

Chemical and electrochemical methods to deposit nanolayers of metallic silver and its low-solubility compounds on polymer fiber surfaces are presented. The morphology and phase composition of the coatings were studied and their antimicrobial activity compared. We find that the antimicrobial activity of the coatings increases substantially with increasing solubility. Their high surface area and high porosity make synthetic fibers with these coatings promising for application as antimicrobial filters in air purification and water treatment systems.     

Silicon etch with chromium ions generated by a filtered or non-filtered cathodic arc discharge

The pre-treatment of substrate surfaces prior to deposition is important for the adhesion of physical vapour deposition coatings. This work investigates Si surfaces after the bombardment by energetic Cr ions which are created in cathodic arc discharges. The effect of the pre-treatment is analysed by X-ray diffraction, Rutherford backscattering spectroscopy, scanning electron microscopy and in-depth X-ray photoemission spectroscopy and compared for Cr vapour produced from a filtered and non-filtered cathodic arc discharge. Cr coverage as a function of ion energy was also predicted by TRIDYN Monte Carlo calculations. Discrepancies between measured and simulated values in the transition regime between layer growth and surface removal can be explained by the chemical reactions between Cr ions and the Si substrate or between the substrate surface and the residual gases. Simulations help to find optimum and more stable parameters for specific film and substrate combinations faster than trial-and-error procedure.     

Osteoblast responses to as-deposited and heat treated sputtered CaP surfaces

The clinical success of dental implants is governed by implant surfaces and bone cell responses that promote rapid osseointegration. The objective of this study was to evaluate the in vitro osteoblast cell response to heat treated and non-heat treated CaP coatings. In this study, the heat treated surfaces exhibited a poorly crystallized HA-type structure whereas the non-heat treated surface exhibited an amorphous structure. The heat treated CaP surfaces were observed to have a mean contact angle measurement of 57.95±0.95 degrees, whereas the non-heat treated CaP surfaces were observed to have a mean contact angle measurement of 44.6±0.3 degrees. From the in vitro cell culture study, the ATTC CRL 1486 human embryonic palatal mesenchyme (HEPM) cells displayed a similar protein production and hexosaminidase activity on the heat treated and non-heat treated CaP surfaces throughout the nine day experiment. However, the HEPM cells cultured on non-heat treated CaP surfaces were observed to have higher specific ALP activity after nine days incubation compared to cells cultured on heat treated CaP surfaces. The higher specific ALP activity by cells on non-heat treated surfaces were suggested to be attributed to the lower degree of crystallinity and the lower contact angles observed in this study. © 2001 Kluwer Academic Publishers     

Analysis of the errors of automated coordinate methods for measuring step parameters of machined surfaces

Computer coordinate methods of measurement are now becoming the main methods for the metrology of surface quality. Nevertheless they lead to certain additional specific errors which are manifested to the greatest degree in the measurement of step parameters and the parameters of extremum values of surface coordinates. An estimate is given below of the errors of computer coordinate methods of measuring step parameters of the roughness profile of machined surfaces and practical recommendations are given concerning the choice of measurement regimes. Deceased Translated from Izmeritel’naya Tekhnika, No. 8, pp. 68–70, August, 1996.     

Solventless adhesive bonding using reactive polymer coatings

A novel solventless adhesive bonding (SAB) process is reported, which is applicable to a wide range of materials including, but not limited to, poly(dimethylsiloxane) (PDMS). The bonding is achieved through reactions between two complementary polymer coatings, poly(4-aminomethyl-p-xylylene-co-p-xylylene) and poly(4-formyl-p-xylylene-co-p-xylylene), which are prepared by chemical vapor deposition (CVD) polymerization of the corresponding [2.2]paracyclophanes and can be deposited on complementary microfluidic units to be bonded. These CVD-based polymer films form well-adherent coatings on a range of different substrate materials including polymers, glass, silicon, metals, or paper and can be stored for extended periods prior to bonding without losing their bonding capability. Tensile stress data are measured on PDMS with various substrates and compared favorably to current methods such as oxygen plasma and UV/ozone. Sum frequency generation (SFG) has been used to probe the presence of amine and aldehyde groups on the surface after CVD polymerization and their conversion during bonding. In addition to bonding, unreacted functional groups present on the luminal surface of microfluidic channels provide free chemical groups for further surface modification. Fluorescently labeled molecules including rhodamine-conjugated streptavidin and atto-655 NHS ester were used to verify the presence of active functional groups on the luminal surfaces after bonding.