Spreading of a water drop on a marble surface

Measurements of the wetting contact angle for a marble surface were carried out for two systems: dry marble plate-water drop-saturated water vapour and marble wetted by water-water drop-dry air (in the presence of molecular sieves). The marble plate was placed in a measuring chamber and contact angles were measured after different lengths of time; it was found that their values grew to a maximum which was reached after about 30 min. It was found that when the dry marble plate was placed in saturated water vapour for 24 h the contact angle decreased in comparison with its maximal value. To explain the results obtained, theoretical calculations were made. The theoretical calculations and measurements showed that it was possible to obtain a contact angle greater than zero on a marble surface, depending on the structure and thickness of the water film.     

Influence of n-alkanes on wettability and zeta potential of quartz

Contact angles were measured in the following systems: quartz/water droplet/saturated vapor of water + n-alkane and quartz/water droplet/saturated vapor of n-alkane. The alkanes tested were from hexane to pentadecane. In both systems non-smooth changes of contact angle as a function of the chain length were observed. These changes are similar to the zeta-potential changes measured previously for two different samples of quartz in the quartz/n-alkana/water system. On the basis of the results and calculations it is suggested that the observed non-smooth changes of contact angle are due to similar changes in film pressures of the water and n-alkanes.     

One-step production of superhydrophobic coatings on flat substrates via atmospheric Rf plasma process using non-fluorinated hydrocarbons

This paper describes the direct deposition of hydrocarbon coatings with a static water contact angle higher than 150 using simple C6 hydrocarbons as a reactive gas in helium plasma generated in ambient air without any preroughening of the silicon (100) substrate. The film morphology and hydrophobicity are found to strongly depend on the structure of the reagent hydrocarbon. The films deposited with n-hexane and cyclohexane exhibited relatively smooth morphology and the water contact angle was only ～95°, similar to polypropylene. When benzene was used as a main reactive gas, the deposited film surface showed nanoscale textured morphology and superhydrophobicity with a water contact angle as high as 167°. Because the plasma is generated in air, all films show some degree of oxygen incorporation. These results imply that the incorporation of a small amount of oxygenated species in hydrocarbon films due to excitation of ambient air is not detrimental for superhydrophobicity, which allows the atmospheric rf plasma with the benzene precursor to produce rough surface topography needed for superhydrophobicity.     

Asymmetric distribution of falling film solution flowing on hydrophilic horizontal round tube

A two-dimension two phase flow model was established to simulate the falling film flow of LiBr solution on a horizontal hydrophilic tube with different solution sprinkle density and tube surface wettability, and the latter has been an overlook factor. The transient characteristics of solution spreading as well as steady film thickness were analyzed. The results show that a continuous film can only be obtained at sufficiently greater sprinkle density with real surface wettability, the liquid coverage of tube surface increases with the increase of sprinkle density or the decrease of static contact angle. The obvious asymmetric distributions of film thickness and film velocity over the horizontal tube surface are demonstrated in a steady state. The thinnest film thickness or maximum film velocity takes place at circumferential angle around 120°. A modified Nusselt equation for predicting the film thickness is suggested and verified by available both simulation and experimental data.     

THE LINE/PSEUDO-LINE TENSION IN THREE-PHASE SYSTEMS

The effect of drop (bubble) size on contact angle was examined over a wide range of drop (bubble) sizes for the CCl₄-toluene solution/NaCl aqueous solution/quartz, ethylene gtycol/CCI₄-toluene solution/quartz, bitumen/ Na₅P₃O₁₀ aqueous solution/quartz, water/kerosene/quartz, heptane/water/quartz, and air bubble/water/polyethylene systems. For most systems, a nonlinear relationship between cosine of the contact angle and reciprocal of drop (bubble) base radius was obtained. All known factors affecting the contact angle/drop size relationship are discussed. It was found that the effect of gravitational forces as well as solid strain in the vicinity of the three-phase contact line are not responsible for the contact angle/drop size relationship for the systems examined. It appears that surface heterogeneities (contaminants) have the greatest effect on the contact angle/drop size relationship as is evident for these results from our laboratory. Also, surface roughness can contribute to the effect of drop size on contact angle. A theoretical background is presented and modifications of both the Cassie Equation and Wenzel Equation are derived.

A linear correlation of cosine of the contact angle vs. reciprocal of drop base radius was obtained for the heptane/waler/quartz systems, when high purity single-component liquids and a smooth, chemically cleaned, quartz plate were used. The line tension was determined for this system to be (5.1 ± 4.3) 10 ^- 9N.     

Experimental determination of the surface roughness parameter in metal films

New approximate equations for the conductivity of metal films are derived from the theoretical predictions of the surface roughness model previously proposed to describe the effect of the rms surface roughness on the film conductivity. Comparison between exact and approximate values of the film conductivity shows good agreement in well defined thickness and roughness parameters ranges. It is found that these approximate equations are convenient tools for a systematic study of the influence of annealing temperature or condensation conditions on the film surface properties. On the basis of the present model previously published data are reinterpreted giving experimental values for the fractional change in the surface roughness due to the nucleation of a metal overlayer.     

Study of layer-by-layer self-assembled viscoelastic films on thickness-shear mode resonator surfaces

We describe quartz crystal electroacoustic admittance studies in thickness shear mode resonators loaded with self-assembled multilayers composed of alternate layers of glucose oxidase (GOx) and poly(allylamine) covalently attached to [Os(bpy)2ClPyCOH]- , (PAH-Os), deposited on a 3-mercaptopropanesulfonic acid (MPS)-modified gold on the quartz crystal. The complex acoustic impedance parameters, R(S) and X(LS) of a lumped-element Butterworth-Van Dyke (BVD) resonator have been determined for organized thin films of different thickness obtained by varying the number of enzyme layers, n, in (PAH-Os)n(GOx)n structures. The ellipsometric film thickness and mass for dry enzyme multilayer films and films in contact with water were evaluated, and the average film density was estimated. By combination of the estimated film thickness and density, the expression for the surface mechanical impedance of the lumped-element modified resonator (Granstaff and Martin model), and the liquid density and viscosity, we simulate the layer-by-layer film growth on the basis of the measured electroacoustic impedance. The complex impedance X(LS) and R(S) increase with film thickness and the enzyme films can be regarded as acoustically thin in the reduced state for films thinner than 600 nm. We have also measured electroacoustic parameters for PAH-Os/GOx self-assembled multilayers under electrochemical perturbation in a buffer electrolytic solution. The electrostatically self-assembled multilayers behaved as lossy viscoelastic films at 10 MHz with G'f and G'f on the order of 10(6) Pa. The films became viscoelastic upon oxidation to Os(III), resulting in an increase of R(S) and X(LS) in the oxidized state with the number of (PAH-Os)(GOx) bilayers due to film swelling and an increase in the shear moduli during oxidation.     

Components of surface free energy of galena

Measurements of the contact angle for water, diiodomethane, bromoform and 1,1,2,2-tetrabromoethane on non-oxidized and oxidized surfaces of galena were made. Using the results obtained, the geometric mean approach, and the long-range and short-range interactions approaches, the dispersion and non-dispersion, and Lifshitz-van der Waals and acid-base components of the surface free energy of galena were determined and compared with those calculated from adsorption isotherms ofn-octane andn-propanol. On the basis of the measurements and calculations it was found that the surface free energy of galena depends on its degree of oxidation and arise mainly from London's and acid-base intermolecular interactions. It was also found that values of the dispersion and non-dispersion components of galena surface free energy determined from the contact angle assuming that a film is present around the water and diiodomethane drops, are close to those obtained from adsorption isotherms ofn-octane andn-propanol.     

Preparation and characterization of poly(N-isopropylacrylamide) films on a modified glass surface via surface initiated redox polymerization

A functionalization with 3-aminopropyltriethoxysilane (APTES) monolayer of a hydroxylated glass surface, followed by the surface initiated graft radical polymerization of N-isopropylacrylamide (NIPAm) using amino groups of APTES monolayer chemical bonded with glass surface and Ce⁴⁺ as a redox initiating system. The microstructure of poly(N-isopropylacrylamide) (PNIPAm) film obtained from the redox graft polymerization on the modified glass surfaces was examined by water contact angle, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM), and the results showed that about 60 nm thickness of thermosensitive polymer (PNIPAm) film successfully formed.     

A study on the components of surface free energy of quartz from contact angle measurements

Measurements of the contact angle for water, glycerol, formamide, diiodomethane and 1,1,2,2-tetrabromoethane on a quartz surface were made. Using the results obtained, the geometric mean approach and long-range and acid-base interaction approach, the dispersion, non-dispersion, Lifshitz-van der Waals and acid-base components of the surface free energy of quartz were determined and compared with those determined in different ways. On the basis of the measurements and calculations it was found that the surface free energy of quartz depends largely on the amounts of silanol groups and physically adsorbed water molecules on its surface. It was also found that the two tested approaches to surface free energy of solids and liquids gave similar results, and it is suggested that the surface free energy of quartz results mainly from dispersion and hydrogen-bond intermolecular interactions.     

Effects of film forming and hydrophobic properties of starches on surface sized packaging paper

The effect on mechanical and barrier properties upon addition of glycerol to temperature‐responsive hydrophobically modified (HM) potato starch was studied on free films. The addition of glycerol lowered the glass transition temperature, the storage modulus, and the water vapor permeability (WVP) for the HM starch films. The HM starch phase separates upon cooling below an upper critical temperature into a solid and a liquid phase. Adding glycerol to the warm starch solution had an inhibiting effect on the particulate precipitation. Substrates surface sized with HM starch with various amounts of glycerol were investigated with respect to barrier properties; WVP, contact angle and Cobb values. Hydroxypropylated starch was used as a reference. Cobb values and WVP results on surface‐sized substrates indicated that the film formation properties of the starches were of great importance for the final surface properties. Good film formation properties were essential for the gas barrier and water resistance while they were less important for high contact angles. The WVP decreased as the glycerol content of the sizes increased, but no sufficient water vapor barrier could be obtained. The HM starches investigated in this work provided good oxygen barrier and the contact angles indicated a hydrophobic character of the surface. The role of the precipitate was investigated, and surface sizing with the precipitate gave low WVP and high contact angles despite its poor film‐forming properties under the experimental conditions. Cobb60 values were slightly improved for HM starch with increasing glycerol content over glycerol‐free sizing. Copyright © 2007 John Wiley & Sons, Ltd.     

Preparation and characterization of amorphous manganese sulfide thin films by SILAR method

Manganese sulfide thin films were deposited by a simple and inexpensive successive ionic layer adsorption and reaction (SILAR) method using manganese acetate as a manganese and sodium sulfide as sulfide ion sources, respectively. Manganese sulfide films were characterized for their structural, surface morphological and optical properties by means of X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis and optical absorption measurement techniques. The as-deposited film on glass substrate was amorphous. The optical band gap of the film was found to be thickness dependent. As thickness increases optical band gap was found to be increase. The water angle contact was found to be 34°, suggesting hydrophilic nature of manganese sulfide thin films. The presence of Mn and S in thin film was confirmed by energy dispersive X-ray analysis.     

An experimental investigation of modes of flow under conditions of evaporation of liquid on a vertical heating surface

An experimental investigation is performed of the effect of temperature head on the flow of evaporating film of liquid, defined by the wetting line or by ribs, on a vertical heating surface. The experiments are performed under conditions of evaporation of R11 Freon in a medium of own vapor on a vertical copper plate, including the presence of ribbing. The visualization of flow is performed. Analysis is made of the effect of the evaporation intensity in the neighborhood of liquid-vapor-wall contact line on the conditions of film discontinuity and on the pattern of resultant streamer flow. It is demonstrated that, rather than spreading, the liquid in the case of streamer flow on the heating surface contracts downstream even for a close-to-zero equilibrium wetting angle. This is due to intense evaporation of liquid in the region of liquid-vapor-wall contact line, where the liquid film exhibits a minimal thickness, to the variation of curvature of the interface in this region, and to the emergence of thermal contact angle. The dependence of thermal contact angle on temperature head is determined. Dynamic measurements are performed of the local thickness of flowing films of liquid using a capacitance meter, and spectral analysis is performed of waves which arise because of instability of film flow on the evaporating film surface.     

Studies of the surface free energy of sulphur

From adsorption isotherms the water film pressure values on a sulphur surface were determined. An interpretation of the changes with film thickness and the value of the work of wetting processes is proposed. It is concluded that the characteristic film pressure values determined correspond to the work of immersional, adhesional and immersional-cohesional wetting. On the basis of water film pressure values, values of the dispersion component of sulphur surface free energy were determined.     

Study of thermocapillary film rupture using a fiber optical thickness probe

Rupture of a subcooled water film flowing down an inclined plate with a 150×150 mm heater is studied using a fiber optical thickness probe. The main governing parameters of the experiment and their respective values are: Reynolds number (3.2–30.2), plate inclination angle from the horizon (3–90 deg), heat flux (0–1.53 W/cm²). The effect of the heat flux on the film flow leads to the formation of periodically flowing rivulets and thin film between them. As the heat flux grows the film thickness between rivulets gradually decreases, but, upon reaching a certain critical thickness, the film spontaneously ruptures. The critical film thickness is practically independent on the film Reynolds number as well as on the plate inclination angle and lies in the neighborhood of 60 µm (initial film thickness varies from 93 to 368 µm). The heater surface temperature prior to rupture is also independent of Re and Θ, and is about 45°C (initial film temperature is 24°C). The process of rupture involves two stages: 1) abrupt film thinning down to a very thin residual film remaining on the heater; 2) rupture and dryout of the residual film. The threshold heat flux required for film rupture is scarcely affected by the plate inclination angle but grows with the Reynolds number.     

Effect of n-alkanes and n-alcohols on quartz surface hydration

The results are presented of investigations to determine the effect of the presence of two different liquids (polar and nonpolar) on the properties of hydration layers of a quartz surface. The thickness of the water layers and energy changes related to water adsorption are determined on the basis of the experimental results. The water structure type and the formation mechanism of these layers are suggested.     

有机硅对天然乳胶的改性研究

采用复合阳离子型乳液聚合制备出一种带正电荷的有机硅乳液,通过杂凝聚共混和接枝两种不同的改性方法对带负电荷的天然乳胶进行改性,并比较了两种改性方法对胶膜力学性能、耐溶剂性、耐水性、表面形貌等的改性效果。结果表明,与纯天然乳胶膜相比,改性后胶膜的断裂伸长率均有提高,在石油醚中的增重率降低,表面水接触角增大,改性后胶膜的表面更加平整致密,其中共混改性对水接触角影响较大,接枝改性对力学性能、耐溶剂性、表面形貌的改性效果更为显著。其在工业生产医疗制品,如医用胶管、医用手套及避孕套等领域具有广泛的应用前景。     

Aerosol assisted deposition of melamine-formaldehyde resin: Hydrophobic thin films from a hydrophilic material

An intrinsically hydrophilic melamine-formaldehyde thin film (water contact angle of 34° for a cast flat surface) was deposited on a glass substrate using aerosol assisted chemical vapour deposition. The resultant resin films showed a highly developed microstructure consisting of spherical structures that were agglomerated into towers. The surface wetted via a Cassie-Baxter mechanism with air trapped underneath the water droplets and resultant water contact angles as high as 135°. Film thickness and coverage were crucial in determining the wetting properties. Films with limited deposition gave hydrophilic results, whereas thicker films greater than 4 μm were superhydrophilic. This behaviour could be explained by the ease of trapping air under the coating. It is shown that the water wetting properties of a single material can be altered from superhydrophilic to near superhydrophobic by controlling the surface microstructure in a single-step aerosol route.     

金属锌表面超疏水薄膜的制备及其摩擦学性能

通过简单两步法在金属锌表面构筑超疏水薄膜, 锌片首先经N,N-二甲基甲酰胺(DMF)处理在表面构筑微纳结构薄膜, 然后在表面覆盖硬脂酸薄膜以实现超疏水. 采用扫描电子显微镜, 傅里叶红外光谱仪和接触角测量仪等手段表征了超疏水表面的形成机制和表面形貌, 并利用微纳米摩擦磨损试验机研究了超疏水薄膜的减摩耐磨特性. 研究结果发现, 在锌表面形成了一层纳米棒状结构的超疏水薄膜, 水的接触角可达155^o. 超疏水薄膜具有明显的减摩和耐磨特性, 这可归因于DMF处理导致的表面微织构化效应以及脂肪酸自组装薄膜的纳米润滑效应.     

Tailoring of the morphology and chemical composition of thin organosilane microwave plasma polymer layers on metal substrates

The growth of thin microwave organosilicon plasma polymers on model zinc surfaces was investigated as a function of the film thickness and the oxygen partial pressure during film deposition. The evolution of the topology of the film was studied by atomic force microscopy (AFM). The nano- and micro-roughness was investigated at the inner and the outer surfaces of the plasma polymers. A special etching procedure was developed to reveal the underside of the plasma polymer and thereby its inner surface. Rough films contained voids at the interface, which reduced the polymer/metal contact area. The increase in oxygen partial pressure led to a smoother film growth with a perfect imitation of the substrate topography at the interface. The chemical structure of the films was determined by infrared reflection absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). ToF-SIMS at the outer and the inner surface of the plasma polymers showed that the density of methylsilyl groups increases in the outer surface layer of the plasma polymer and depends on the oxygen partial pressure. The chemical composition of the films could be altered to pure SiO₂ without changing the morphology by using oxygen-plasma post-treatment. This was proved by means of IRRAS and AFM. Chemistry and topology of the films were correlated with the apparent water contact angle. It was found that a linear relationship exists between the nanoscopic roughness of the plasma polymer and the static contact angle of water. Superposition of a nanoscopic roughness of the metal surface and the nanoscopic roughness of methylsilyl-rich films led to ultra-hydrophobic films with water contact angles up to 160°.