Showing papers on "Sessile drop technique published in 2000"

Pattern formation in drying drops

Abstract: Ring formation in an evaporating sessile drop is a hydrodynamic process in which solids dispersed in the drop are advected to the contact line. After all the liquid evaporates, a ring-shaped deposit is left on the substrate that contains almost all the solute. Here I show that the drop itself can generate one of the essential conditions for ring formation to occur: contact line pinning. Furthermore, I show that when self-induced pinning is the only source of pinning an array of patterns---that include cellular and lamellar structures, sawtooth patterns, and Sierpinski gaskets---arises from the competition between dewetting and contact line pinning.

Long-wearable soft contact lens

Abstract: The present invention relates to a soft contact lens, and provides a contact lens which shows small and stable contact angle to water at its surface in water as well as in air, little deposition in wearing, high oxygen permeability, no adhesion of lens to a cornea and superior extended-wearing characteristics. The present invention provides a hydrogel soft contact lens which has contact angle at a lens surface in a range of 10-50° by the captive bubble method in water and 30-90° by the sessile drop method in air, oxygen permeability of not less than 30 and water content of not less than 5%, and also a hydrogel soft contact lens consisting of a polymer comprising a hydrophilic siloxanyl monomer shown by a specified general formula.

Modified sessile drop method for assessing initial soil-water contact angle of sandy soil

Abstract: Existing methods for determining the soil-water contact angle as a measure of water repellency are either indirect, cumbersome, or time-consuming. Our objective was to develop a method that is simpler than existing procedures and that still yields accurate results. The proposed method represents a modified sessile drop method for measuring the initial contact angle of powdered or granular material. The measurements are made by placing a layer of uniform soil particles onto adhesive tape, adding droplets of deionized water, and reading off the contact angle at the three-phase boundary line with a goniometerfitted microscope immediately after placing the drops on the soil sample. Sieved soil fractions <63 μm, 63 to 100 μm, and 100 to 200 pm were used to ensure particle layer uniformity. The method was tested on 10 samples from different depths of a sandy soil profile. The contact angles measured on these soil fractions were compared with the water drop penetration time (WDPT) test and the capillary-rise method. The contact angles of the fractions <63 μm and 63 to 100 μm compared reasonably well with those measured with the capillary-rise method and their rank order agreed in general with that of the WDPT test. We conclude thai the new method appears to he promising for the simple, rapid, and reproducible determination of the contact angle of sandy soils. The sessile drop method can he used in a wider range of water repellency conditions compared with either the capillary-rise or the WDPT method.

Evaluation of surface energy of solid polymers using different models

Abstract: In the present work, contact angles formed by drops of diethylene glycol, ethylene glycol, formamide, diiodomethane, water, and mercury on a film of polypropylene (PP), on plates of polystyrene (PS), and on plates of a liquid crystalline polymer (LCP) were measured at 20°C. Then the surface energies of those polymers were evaluated using the following three different methods: harmonic mean equation and geometric mean equation, using the values of the different pairs of contact angles obtained here; and Neumann's equation, using the different values of contact angles obtained here. It was shown that the values of surface energy generated by these three methods depend on the choice of liquids used for contact angle measurements, except when a pair of any liquid with diiodomethane was used. Most likely, this is due to the difference of polarity between diiodomethane and the other liquids at the temperature of 20°C. The critical surface tensions of those polymers were also evaluated at room temperature according to the methods of Zisman and Saito using the values of contact angles obtained here. The values of critical surface tension for each polymer obtained according to the method of Zisman and Saito corroborated the results of surface energy found using the geometric mean and Neumann's equations. The values of surface energy of polystyrene obtained at 20°C were also used to evaluate the surface tension of the same material at higher temperatures and compared to the experimental values obtained with a pendant drop apparatus. The calculated values of surface tension corroborated the experimental ones only if the pair of liquids used to evaluate the surface energy of the polymers at room temperature contained diiodomethane. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1831–1845, 2000

Nonstoichiometric Interfaces and Al 2 O 3 Adhesion with Al and Ag

Abstract: We have determined the relative stability of stoichiometric, oxygen-rich, and aluminum-rich $\mathrm{Al}/\mathrm{Al}{}_{2}\mathrm{O}{}_{3}$ and $\mathrm{Ag}/\mathrm{Al}{}_{2}\mathrm{O}{}_{3}$ interfaces from first principles. Stable structures vary significantly with oxygen chemical potentials. Computed works of adhesion agree reasonably well with sessile drop experimental values, including correlation with measured oxygen chemisorption effects on Ag. The ordering of predicted bond energies of the interfaces, ceramics, and metals seems consistent with monotonic and fatigue fracture experiments.

Surface Energy Determinations of Wood: Comparison of Methods and Wood Species

Abstract: The Lifshitz−van der Waals, acid−base, and total surface free energies of various wood species were calculated from contact angle measurements. For spruce (Picea abies) and meranti (Shorea spp.) the following three methods were compared: capillary rise in wood powder columns (based on the Washburn equation), dynamic contact angle measurements (according to the Wilhelmy-plate principle), and sessile drop measurements along and across the grain of the wood. The capillary rise method was limited to nonswelling solvents, which means that only the Lifshitz−van der Waals component could be measured. With the dynamic contact angle measurement, the wettability during the first immersion was decreased compared to that of the sessile drop. This was probably due to reduced capillary penetration, but with the second immersion the presence of an adsorbed solvent layer increased the wettability and hence affected the surface energy data. The sessile drop measurements were highly dependent on the direction of measureme...

Effect of alkalis, phosphorus, and water on the surface tension of haplogranite melt

Abstract: The sessile drop method has been used for measurements of the surface tension of haplogranite (HPG) melts containing an excess of alkalis and phosphorous (HPG8, HPG8 + 5 wt% Li 2 O, 5 wt% Na 2 O, 20 wt% Na 2 O, 5 wt% K 2 O, 5 wt% Rb 2 O, 5 wt% Cs 2 O, 10 wt% P 2 O 5 ) and of Armenian rhyolite in the temperature interval, 650–1665 °C, and at 1 bar pressure. Sessile drops were placed on graphite substrates in a Pyrox tube furnace purged with Ar. Drop shape was monitored with a videocamera and stored in a videorecorder. The surface tension was calculated by measuring the two principal radii of curvature of the drop shape in vertical cross section. The precision of the method was checked against the surface tension of water. The surface tension of HPG and rhyolite melt is ~280–300 ± 5 mN/m in the temperature interval 1200–1400 °C. Temperature dependence of the surface tension of haplogranite melts and rhyolite is weak and positive (dσ/d T = 0.06 to 0.09 mN/m/°C). Addition of 5 wt% of alkali oxides (except Li 2 O) results in a decrease of the surface tension of haplogranite melts. The HPG melts with 10 wt% P 2 O 5 have 30% higher surface tension than haplogranite melts with excess alkalis, and a negative temperature derivative (dσ/d T = −0.1 mN/m/°C). The HPG melts with 20 wt% Na 2 O and 5 wt% Li 2 O exhibit a decrease in surface tension with temperature (dσ/d T = −0.02 and −0.10 mN/m/°C, respectively). The surface tension of HPG8 melt saturated with water at 1–4 kbar was measured on sessile drops quenched at high pressure in an internally heated gas vessel at temperatures of 800–1200 °C. Water pressure significantly decreases the surface tension of melt from 270 mN/m at 1 bar (1000 °C) to 65 mN/m at 4 kbar. At 1 bar in “dry” conditions, dσ/d T = +0.056 mN/m/°C and at 3 kbar of water pressure, dσ/d T = +0.075 mN/m/°C. The decrease in the surface tension of HPG melt at a water pressure of several kbars is from −10 to −30 mN/m/wt% H 2 O. The increase of water content to more than 10 wt% in granite melts may not result in any significant decrease in the surface tension, which may be explained by formation of a surface sublayer having physical properties very distinct from those of the bulk.

Optimum parameters for wetting silicon carbide by aluminum alloys

Abstract: The effect of magnesium and silicon additions to aluminum, free silicon on the SiC substrate, nitrogen gas in the atmosphere, and process temperature on the wetting characteristics of SiC by aluminum alloys are investigated using the sessile drop technique The contribution of each of these parameters and their interactions to the contact angle, surface tension, and driving force for wetting are determined In addition, an optimized process for enhanced wetting is suggested and validated Results show that the presence of free silicon on the surface of SiC significantly reduces the contact angle between the molten alloy and the substrate The positive effect of silicon on the contact angle is attributed to a chemical reaction in which both SiC and aluminum are active participants The results also indicate that nitrogen gas in the atmosphere positively influences the liquid/vapor surface tension, and the presence of magnesium in the aluminum alloy favorably affects the overall driving force for wetting A mechanism is proposed to explain the beneficial role that the interaction of nitrogen with magnesium plays in enhancing wetting Magnesium significantly reduces the surface tension of aluminum melts but has a low vapor pressure Consequently, it readily volatilizes during holding at the processing temperature and is lost from the alloy It is proposed that a series of chemical reactions in the system Al-Mg-N are responsible for reintroducing magnesium into the melt, thus, maintaining a low melt surface tension Interactions between the aluminum alloy and the silicon carbide substrate that may lead to the dissolution of the substrate and the formation of undesirable reaction products, particularly Al4C3, are examined, and means for mitigating their formation are outlined

Measurements of Line Tension for Solid−Liquid−Vapor Systems Using Drop Size Dependence of Contact Angles and Its Correlation with Solid−Liquid Interfacial Tension

Abstract: According to the modified Young equation, one of the direct ways of measuring line tension for solid−liquid−vapor systems takes advantage of the dependence of the contact angle on the radius of curvature of the three-phase line. This approach was used to determine line tension measurements for six organic liquids on two different self-assembled monolayer (SAM) surfaces (mixed monolayers of methyl and carboxylic acid terminated alkanethiol on gold at two different composition levels). Low-rate advancing contact angles were measured using Axisymmetric Drop Shape Analysis-Profile (ADSA-P). The general trend observed for each system was that the contact angle decreases as the radius of the three-phase line for the sessile drop increases from approximately 1 to 5 mm. It was found that the drop size dependence of contact angles can be interpreted as being due to a positive line tension. The line tension values are all in the order of 10-6 J/m. Also a correlation was observed between the line tension and the sol...

The combined effect of roughness and heterogeneity on contact angles: the case of polymer coating for stone protection

Abstract: The individual effects of heterogeneity and roughness on contact angles have been repeatedly analysed in the literature, but the application of the accepted models to practical situations is often not correctly performed. In the present paper the combined effects of roughness and heterogeneity on the contact angles of water on stone surfaces protected by a hydrophobic polymer coating are considered. Two different kinds of calcareous stone with different surface roughnesses and porosities were protected against the effect of water absorption by two different polymer coatings. The contact angles of water on the protected stone surfaces were measured by the Wilhelmy and the sessile drop techniques. A comparison of the results obtained shows not only the limits of the static sessile drop technique, but also the combined effect of roughness and heterogeneity. Some considerations are developed on the application of commonly accepted models to surfaces with a combination of roughness and heterogeneity. Some othe...

Effect of the Oxygen Partial Pressure on the Surface Tension of Molten Silicon and Its Temperature Coefficient

Abstract: Dependence of the surface tension of molten silicon on temperature, the oxygen partial pressure in ambient argon atmosphere have been determined at temperatures ranging from 1693 to 1873K and in the range of PO2 from 10-25 to 10-14 MPa using a high purity BN substrate with the sessile drop method. Change of the surface tension with the oxygen partial pressure is very small in the range of PO2≤10-22 MPa. The surface tension decreases remarkably with increasing the oxygen partial pressure in the range of PO2 from 10-22 to 10-20 MPa, and increases slightly with increasing the oxygen partial pressure in the range of PO2>PO2, sat. The temperature coefficient of surface tension, δσ/δT, is minus and increases with increasing PO2, δσ/δT at PO2=10-25 MPa is equal to about -0.74 mN·m-1·K-1 and then δσ/δT gradually increase with increasing the oxygen partial pressure up to 10-22 MPa. δσ/δT steeply increases with increasing the oxygen partial pressure in the range of PO2 from 10-22 to 10-20 MPa. And again gradually increases with further increases of PO2 up to 10-15 MPa, where δσ/δT is equal to -0.15 mN·m-1·K-1. It is found that the surface tension of molten silicon and its temperature coefficient are sensitive to the oxygen partial pressure of argon atmosphere in the measuring system.

Surface Free Energy Analysis of Natural and Modified Natural Rubber Latex Films by Contact Angle Method

Abstract: The contact angles of soft latex dipped films of high-ammonia natural rubber (HA) latex concentrate, deproteinized natural rubber (DPNR) latex, and oil-incorporated natural rubber latex were determined by the sessile drop method. The surface free energies were calculated using different procedures available in the literature. For each type of latex film, the harmonic-mean treatment gives the highest polar component of the surface free energy, while those from the Lifshifz−van der Waals acid−base method were the lowest. This trend is the same for each type of latex films but the magnitude varies. Among the various latex types, the unleached NR latex film surface is the most hydrophilic; the deproteinized latex film, the least. All the NR film surfaces were found to be monopolar basic in nature, with the unleached NR film being the most basic and those of HA the least. The behavior of the various film surfaces is discussed in terms of the presence of non-rubbers and their removal by washing (leaching) of th...

Wettability of NiAl, NiAlN, TiBC, and TiB–CN films by glass at high temperatures

Abstract: The sticking/adhesion of glass to glass molding dies and forming tools is a critical problem which limits the quality of glass products and the performance and reliability of molding dies and forming tools. Depositing NiAl, NiAlN, TiBC, and TiBCN coatings and characterizing their wettability by glass at high temperature are part of an overall program that is being conducted to develop a non-sticking, oxidation resistant, and wear resistant coating system for glass molding dies and forming tools. The use of contact angle analysis for evaluation of wettability is described in this paper. The contact angles were measured by the sessile drop technique and analyzed by an image analyzer. The film microstructures were studied using cross-sectional TEM technique. Factors affecting the wettability are discussed. NiAl and NiAlN films seemed to offer more potential than TiBC and TiBCN films in terms of non-wettability by glass at high temperatures, they are promising ‘working’ layers for glass molding dies and forming tools.

Investigation of specific heat and thermal expansion in the glass-transition regime of Pd-based metallic glasses

Abstract: The alloys Pd–Ni–P and Pd–Ni–Cu–P have an outstanding glass-forming ability and stability against crystallisation in the undercooled liquid state at temperatures greater than the glass-transition temperatures. Samples of the copper containing alloys can be vitrified readily by cooling the liquid at rates ⩾0.1 K/s. This rate allows us to investigate the thermodynamic quantities of this alloy system in the liquid as well as in the glassy state during continuous cooling or heating without interference from crystallisation. In the present work, the specific heat and the volume expansion coefficient in the glassy and in the undercooled liquid state were determined at temperatures less than and greater than the glass-transition temperature by applying differential scanning calorimetry (DSC) and sessile drop (SD) technique, respectively. The glass temperatures of the samples resulting from the cooling rate were investigated during re-heating by both the methods. By comparing the results, a correlation between enthalpy and specific volume as a function of temperature could be demonstrated experimentally for these metallic alloys. We attribute the characteristic course of the enthalpy and the specific volume in the range of the glass-transition to structural relaxation processes and to the fraction of free volume in the glass as a function of temperature and time.

Influence of ash on mass transfer and interfacial reaction between natural graphite and liquid iron

Abstract: The interfacial reaction is a factor that plays an important role in governing the rate of many metallurgical processes. In the direct iron smelting process, interfacial reactions of carbonaceous materials, such as coals, with molten iron is one of the key factors that dictate the rate of carbon transfer from the carbonaceous materials into molten iron and establish a carbon concentrated melt to reduce iron oxide in the slag phase. In the current investigation, wetting of natural graphite, which contains 8.8 pct ash, by iron was studied in a horizontal tube furnace at 1600 °C using the sessile drop approach to establish a fundamental understanding of the influence of ash on interactions between graphite and iron. The mass-transfer phenomena between the solid substrate and the iron droplet were studied by withdrawing the assembly at different time intervals. After the wetting experiment, the contacting surface of the iron droplet was observed by a field emission scanning electron microscope (FESEM). The components of the interfacial layer formed during the experiment were examined by energy dispersive spectroscopy (EDS). The change in the carbon and sulfur contents of the droplet at different time intervals during the wetting experiment was analyzed by a LECO carbon and sulfur analyzer. It was found that the formation of an ash interfacial layer between the carbonaceous materials and the liquid iron has a strong influence on the mass transfer and interfacial reaction.

Interfacial phenomena in some slag-metal reactions

Abstract: In the present work, the change of the interfacial tension at the slag-metal interface for sulfur transfer between molten iron, slag, and gas phases was monitored by X-ray sessile drop method in dynamic mode in the temperature range of 1830 to 1891 K. The experiments were carried out with pure iron samples immersed partly or fully in the slag phase. The slag consisted of 30 wt pct CaO, 50 wt pct Al2O3, and 20 wt pct SiO2 (alumina saturated at the experimental temperatures) with additions of FeO. Metal and slag samples contained in alumina crucibles were exposed to a CO-CO2-SO2-Ar gas mixture with defined oxygen and sulfur partial pressures, and the change of the shape of the metal drop was determined as a function of time. The equipment and the technique were calibrated by measurements of the surface tensions of the pure Cu, Ni, and Fe containing two different amounts of dissolved oxygen. A theoretical model was developed to determine the sulfur content of the metal as a function of time on the basis of sulfur diffusion in the slag and metal phases as well as surface tension-induced flow on the metal drop surface. Attempts were made to compute the interfacial tensions on the basis of force balance.

Surface Tension Measurements on Ethene−Butene Random Copolymers and Different Polypropenes

Abstract: The pendant drop apparatus is used in order to study the surface tension of ethene−1-butene random copolymer melts over the whole range of compositions, including poly(1-butene) (P-1-B) and at different temperatures. Furthermore, the surface tensions of isotactic polypropene (i-PP) and syndiotactic polypropene (s-PP) are measured. The surface tension of the melt of random copolymers decreases as a function of copolymer composition from pure polyethene (PE) to pure P-1-B in a nearly exponential manner, and the surface tensions of copolymers with a P-1-B content in the range of approximately 40 wt % match the surface tension of i-PP and s-PP. This indicates the possible existence of a window of miscibility. This result is verified by the calculation of the solubility parameters from additional sessile drop measurements on solid copolymers at room temperature and from pressure−volume−temperature data of the melts applying the Flory−Orwoll−Vrij equation-of-state theory. Also, the theory of the conformational ...

Contact angle measurements and interpretation: wetting behavior and solid surface tensions for poly(alkyl methacrylate) polymers

Abstract: Low-rate dynamic contact angles of a large number of liquids were measured on a poly(ethyl methacrylate) (PEMA) polymer using an automated axisymmetric drop shape analysis profile (ADSA-P). The results suggested that not all experimental contact angles can be used for the interpretation in terms of solid surface tensions: eight liquids yielded non-constant contact angles and/or dissolved the polymer on contact. From the experimental contact angles of the remaining four liquids, we found that the liquid-vapor surface tension times the cosine of the contact angle changes smoothly with the liquid-vapor surface tension, i.e. γlv cos ζ depends only on γlv for a given solid surface (or solid surface tension). This contact angle pattern is again in harmony with those from other methacrylate polymer surfaces of different compositions and side-chains. The solid-vapor surface tension of PEMA calculated from the equation-of-state approach for solid-liquid interfacial tensions was found to be 33.6 ± 0.5 mJ/m2 from th...

Bonding and wetting in non-reactive metal/SiC systems: weak or strong interfaces?

Abstract: Wetting (contact angles) and bonding (work of adhesion) of Ag and binary Ag-Si alloys on basal planes of monocrystalline α-SiC are studied by the sessile drop technique under a static atmosphere of purified helium at 1200°C. The analysis of the experimental results allows the role of each component of the alloy on the interfacial energies of the system and on wetting to be determined. The conclusions drawn for the Ag/SiC couple are used to explain wetting and bonding in other metal/SiC systems.

Processing of Al–SiCp Metal Matrix Composites by Pressureless Infiltration of SiCp Preforms

Abstract: An optimum method for producing Al-SiCp metal matrix composites was developed by determining the optimum conditions for wetting SiC by aluminum and the optimum parameters for pressureless infiltration of SiCp preforms The quantitative effect of magnesium and silicon additions to aluminum, free silicon on the SiC substrate, nitrogen gas in the atmosphere, and process temperature on the wetting characteristics of SiC by aluminum alloys was investigated using the sessile drop technique The contribution of each of these parameters and their interactions, in terms of a relative power, to the contact angle, surface tension, and driving force for wetting were determined In addition, an optimized process for enhanced wetting was suggested and validated The optimum conditions for wetting SiC by aluminum that were arrived at were used to infiltrate SiCp preforms and the mechanical properties of the resulting metal matrix composites were measured The effect of SiC particle size, infiltration time, preform height, vol% SiC in the preform, and Si coating on the SiC particles on the pressureless infiltration of SiCp compacts with aluminum was investigated and quantified The contribution of each of these parameters and their interactions to the retained porosity in the composite, the modulus of elasticity, and the modulus of rupture were determined Under optimum infiltration conditions, metal matrix composites with less than 3% porosity, over 200 GPa modulus of elasticity, and about 300 MPa modulus of rupture were routinely produced

Characterization of the interface between the bulk glass forming alloy Zr41Ti14Cu12Ni10Be23 with pure metals and ceramics

Abstract: The reaction of the bulk glass forming alloy Zr_(41)Ti_(14)Cu_(12)Ni_(10)Be_(23) (Vit 1) with W, Ta, Mo, AlN, Al_2O_3, Si, graphite, and amorphous carbon was investigated. Vit 1 samples were melted and subsequently solidified after different processing times on discs of the different materials. Sessile drop examinations of the macroscopic wetting of Vit 1 on the discs as a function of temperature were carried out in situ with a digital optical camera. The reactions at the interfaces between the Vit 1 sample and the different disc materials were investigated with an electron microprobe. The structure and thermal stability of the processed Vit 1 samples were examined by x-ray diffraction and differential scanning calorimetry. The results are discussed in terms of possible applications for composite materials.