Determination Of Surface Tension Research Articles

Studies of infiltration by apparent thermogravimetry

A technique named ‘apparent thermogravimetry’ (ATG) has been developed for studying infiltration phenomena. It has been used for investigating of infiltration of copper, cast iron, and cobalt alloys into porous tungsten, sintered steel, and tungsten carbide. A description of ATG signal behaviour has been obtained, taking into account ‘internal’ (capillary, viscous, gravitational, end-drag) and ‘external’ (wetting, buoyancy, Archimedean) forces. Dependencies of Archimedean foroe and wetting angle on different parameters are described in relation to the infiltration mechanism. The ATG method can be used to determine surface tension or contact angle.

Application of freezing front technique and axisymmetric drop shape analysis-profile for the determination of surface tensions of adsorbed protein layers

The surface tensions of human albumin, immunoglobulin G, and fibrinogen were determined by using two different techniques: (1) the freezing front technique and (2) the pendant drop arrangement in conjunction with axisymmetric drop shape analysis-profile (ADSA-P). The changes in surface tension, resulting from the adsorption of proteins from solution, at various concentrations, onto polymer particles are reported by using the freezing front technique. Furthermore, the adsorption of proteins onto the solution—air interface is also reported by using the pendant drop arrangement. The large differences between the two types of measurements are discussed in terms of the different extents of conformational changes in response to different interfacial tensions driving these changes. A further qualitative difference between the two methods as used here is that the ADSA surface tension measurement registers only the properties of the top few ångströms of the layer whereas the solidification front technique registers the presence of much thicker layers.

Software package for determination of surface tension of liquid metals

The problems of the development of algorithms to process experimental results obtained by the sessile drop method are discussed. Algotithms are based on the numerical solution of the Young-Laplace equation and the regularization method for Dorsey formula. A software package for IBM PC AT has been developed. The results of calculations for droplets formed in a cup (liquid Fe) and on a plate (slag CaOB 2O 3) are given.

Surface tension measurements of refractory liquid metals by the pendant drop method under ultrahigh vacuum conditions: Extension and comments on Tate’s law

The pendant drop method, used in an ultrahigh vacuum drop tube, allowed new determinations of the liquid surface tension of the refractory metals. After a description of the melting apparatus, the amazing reproducibility in terms of droplets masses (≂0.6%) observed is discussed herein. Evidence is given of the harmful action of hydrogen bubbles contained in the commercial rods. Working with very thin wires (down to 0.3 mm), a variation curve for the Harkin’s correction factor of Tate’s law in its untabulated range is proposed. The validity of the representation of this factor is discussed via a dimensional analysis. Finally, new values of σLV for pure Re (2.510 J m−2), W (2.310 J m−2), Ta (2.010 J m−2), Nb (1.840 J m−2), Ir (2.140 J m−2), and Zr (1.435 J m−2) are proposed.

Design and performance of a dynamic interfacial tension spinning‐drop tensiometer

Two standard spinning‐drop tensiometers (SDT) have been modified by the addition of video equipment and an interface to a personal computer. (Since two tensiometers were available in our laboratory, both were modified. There is no reason why the system can’t be set up with only one tensiometer). The computer has been fitted with a special video board and a menu‐driven image enhancement and analysis program. A date‐time generator accurately measures the age of the aqueous‐organic interface. The operator can record droplet images for later analysis. Alternatively, the video board can “capture” a droplet image for immediate analysis. Analysis usually consists of measurement of drop length and drop width. However, interesting emulsification and solubilization phenomena can also be recorded for later study. These modifications greatly enhance the capabilities of the SDT. This new system is referred to as the tensiometer image analysis apparatus. Similar procedures can be used with air droplets to determine surface tension values. The operator can determine equilibrium interfacial tension (IFT) values with greater accuracy and in less time than is possible with the conventional SDT. Rapidly changing IFT values can be accurately determined at intervals of as little as one second. These capabilities have been used in studies of detergency, deresination of wood pulp, and deinking of waste paper. The video capture and analysis capabilities of this system are also useful in other applications.

Some properties of melts of A 2B 6 compounds

Devices for experimental determination of surface tension and viscosity of A 2B 6 compound melts have been developed. Surface tension, visocisity and volume effect of crystallization of melts of a few A 2B 6 compounds have been determined. These properties are important for practice of A 2B 6 single crystal growth from the melt.

Monitoring the surface tension of lipid membranes by a bubble method

A new method for the determination of lipid membrane surface tension was developed. Advantages of this method are that it allows for multiple measurements on a single membrane, is fast and direct not requiring empirical corrections, may be applied for dynamical surface-tension measurements and may be used with thin films and asymmetrical electrolytes. The pressure and radius of a bubble are measured. A piezoresistive sensor is used to minimize the transducer compliance. By moulding the sensor to a brass plate a resolution of 0.025 mm H2O (0.25 Pa) is obtained. The bubble is filmed using a videocamera and the radius of the bubble determined with the aid of a microcomputer. Data for monoolein/hexadecane in potassium chloride solutions and a cooling curve are presented and compared with previous results.

DESIGN OF A SENSITIVE AND PRACTICAL CONSTANT HEAD STALAGMOMETER

Surface tension of effluents may play an important role in salt and heavy metal accumulation, in soil profile, and in polluting groundwater. Various methods are available for measuring surface tension: capillary rise method, Terson method, film detachment method, and drop weight method. The stalagmometer is an instrument for determining surface tension by drops. The authors designed a two piece, constant head stalagmometer consisting of a capillary tube of 10-cm length connected with a 10-ml mariotte burrette. It measures volume of 10 drops of given and reference liquid to estimate surface tension from the drop-volume method. This paper reports the results of the laboratory tests in water at 5, 10, 20, 40, and 60% concentration for different numbers of drops. The maximum error percentage for 10 drops among all liquids was 5% in the DCH stalagmometer. The corresponding value for CVH stalagmometer was 45%.

Capillary characteristics of high temperature melts measured by sessile-drop method using computer-aided TV system

An automated TV system with a computer for measuring the capillary constant, surface tension, density, and wetting angles of melts by the sessile-drop method is described. Hardware and software support issues have been treated. Surface tension and density of a number of high temperature melts, including copper, CaF2, and alloys Pb+0.34 at %S, 5Cu+0.5Ge+94.5Sn (at%) were measured. The surface tension-concentration isotherm (1100 °C) obtained for the Cu-alloy Ga-Ge (1∶1) system was found to have a smooth run and show a sharp decrease of surface tension σlg on adding of Ga-Ge alloy to copper. The obtained results are in good agreement with the manual measurements data. The use of a standard TV camera (625 lines) as a data acquisition device with the subsequent statistical processing of data was found to provide the accuracy of surface tension determination within the range of 1% and an appreciable measurement time reduction.

A single-parameter method for the determination of surface tension and contact angle

The classical problem of determination of liquid surface tension from the shape of a sessile drop is reinterpreted. A non-dimensionalisation, first suggested by Smolders, is chosen in which the shape of the drop is characterized solely by the value of the Bond number in which the observed maximum radius of the drop appears as a characteristic length. The Bond number is defined as Bo = ϱgr2max/γ, where ϱ is the density, γ is the surface tension of the liquid, g is the acceleration due to gravity and rmax is the maximum half width of the drop. A graphical presentation of the results allows an immediate comparison with experimental drops, eliminating the use of iterative procedures. Graphs from which the contact angle can be read are also presented. A computer code is given for those cases where a refined approach is necessary. The power of the method is to be found in its simplicity and its diagnostic capabilities. Comparisons with experimental results are given.

Characterization of fillers and fibres by wetting and electrokinetic measurements

The surface chemical properties of organosilane-treated silica powders and oxidized carbon fibres were studied by means of wetting and electrokinetic measurements. A capillary flow technique was successfully applied to characterize the influence of the surface treatment on the wetting behaviour of silica powders. By measuring the time dependence of the liquid rise in a loosely packed column of powder the advancing contact angles with water and methylene iodide were calculated. Comparison of the measurements of the rise height of the liquid front, with the weight gain caused by the penetrating liquid, shows that the calculated contact angles agree well when surface-treated silica powders are investigated. Different approaches for the determination of the solid surface tension were applied and provide comparable results regarding the differences in the wetting properties of various fillers. The results of the wetting experiments correlate with zeta potential measurements (electrophoresis, streaming potential). This method is a useful experimental technique to determine the nature (polar, non-polar) and the amount of functional groups on surface treated silica fillers and carbon fibres. By measuring the zeta potential vs the pH of a 10 −3 N KCl solution varying amounts of acidic groups at the surface can be proved to exist. 1. 1. The content of acidic silanol groups is decreased when treating silica powders with organo-silanes. This correlates with a decrease in the solid surface tension. 2. 2. The surface oxidation of carbon fibres results in an increase in the number of acidic carboxylic groups which correlates with a higher solid surface tension. The decreased hydrophilicity of silane-treated fillers is also shown by a higher zeta potential maximum in KCl solutions and by lower Gutmann acceptors numbers ( AN). Combination of the methods applied provides a good understanding of the surface chemical properties of silica powders and carbon fibres.

The influence of droplet volume and contact angle on liquid surface tension measurements by axisymmetric drop shape analysis-profile (ADSA-P)

The axisymmetric drop shape analysis-profile (ADSA-P) technique was evaluated with respect to the influence of contact angle and droplet volume. The system was implemented on our standard contact angle measuring apparatus employing a Vidicon video camera and a 512 × 256 pixels framegrabber. For calibration of the x and y magnification factors a perfectly spherical ball was used of approximately the same dimensions as the liquid droplet under study. Droplets of water, formamide and hexadecane with volumes varying from 2–200 μl were put on FEP-Teflon and PMMA. Erroneous surface tensions were found by ADSA-P when too small or too large droplet volumes were employed. Ideal volumes to be used were dependent on the contact angle and amounted in our system to 5–10 μl for θ < 40°, 20–50 μl for 40° < θ < 90° and 50–100 μl for θ > 90°. Statistical evaluation of results obtained for the same droplet (i.e. water on Parafilm), digitized 16 times using two different sets of five calibration frames, indicated that digitization of the liquid profile is the largest source of variation. Typical standard deviations over 16 images of the same droplet are ± 0.9 mJ m −2 in surface tension and ± 1.5° in contact angle. However, in summary it is concluded that ADSA-P is a powerful tool for simultaneous determination of liquid surface tension and contact angle, even when implemented using a relatively simple image analyser.

Activated sludge foams: Effects of environmental variables on organism growth and foam formation

Actinomycetes that are implicated in foam formation in activated sludge sewage treatment plants were isolated from plants in Queensland, Australia. Foaming and surface tension determinations were carried out on mixed liquors from foaming and non‐foaming plants and on pure cultures of the isolated actinomycetes which were identified as Nocardia amarae. Foam stability of mixed liquors increased with increasing temperature and concentration of mixed liquor suspended solids. The results showed that a surfactant was released by the organisms and that the bacterial cells were responsible for stabilization of laboratory scale foams. The nitrogen source for growth did not affect the foam or surfactant production, however, the carbon source produced growth form‐dependent changes to the foam but did not affect surfactant production.

Containerless measurement of liquid-liquid surface tension of a demixing lead borate composition in space

A description is given of a method by which the liquid-liquid interfacial tension between the end member compositions of a phase-separating PbO–B2O3 composition can be directly measured. The technique is based upon the rotation of a compound droplet (consisting of the two end member compositions) in a containerless facility in a microgravity environment. A discussion is given of the theoretical basis for the determination of the liquid-liquid surface tension as well as the experimental procedure to be used. In addition, calculations are presented which illustrate some potential limitations of this method.

Surface tension by pendant drop: I. A fast standard instrument using computer image analysis

An improved method has been developed for the determination of surface and interfacial tensions from primary drop shape data. In addition, wetting angles of sessile drops may be determined. The method has been built around a commercial pendant drop instrument and an IBM-compatible PC with a frame grabber card. In order to differentiate the drop profile, a filter routine using a local threshold and interpolation technique has been developed that is combined with an edge-tracing algorithm. The program for calculation of surface tension is divided into two parts. The first part is based on the traditional optical method and uses inflection of the drop profile. By means of several polynomial interpolations and curve fitting of theoretical profiles, the form factor β and surface tension γ are determined. The second part of the calculation utilizes the above values as a first estimate and then performs a further optimalization of γ by comparison between experimental and theoretical Young—Laplace profiles. With a PC AT with a 80287 mathematical coprocessor the measurements take about 5 s and the reproducibility is typically 0.01–0.03 mN/m for a wide range of known liquids.

Surface tension and viscosity from damped free oscillations of viscous droplets

Damped oscillations of a viscous droplet in vacuum or in an inert gas of negligible density are considered. The dependence of the complex decay factor on the properties of the liquid is investigated for the first time, and numerical results are compared with earlier studies for special cases. A new method is developed to determine both surface tension and viscosity from a single experiment in which the damping rate and frequency of oscillations are measured. The procedure to determine surface tension and viscosity from oscillating levitated liquids is outlined, and results are presented for various modes of shape oscillations.

The Estimation of Some Properties of Surface Active Agents

The method of estimating surfactant properties for a homologue series only from the properties of two compounds from the investigated series of surfactants and from the properties of the standard series is proposed. Using the proposed method the HLB and the hydrophobicity index can be estimated with maximum errors not exceeding 0.5 and 0.06, while the relative errors of the determination of surface tension, wetting, foaming and biodegradation abilities are 1.2%, 11.5% 4.2% and 3.3% respectively

The determination of surface tension at elevated temperatures by drop image analysis

The advantages of image analysis as applied to surface tension measurements by the sessile drop technique are discussed. It is demonstrated that valuable effective improvements of dimensional resolution are obtained. Errors in surface tension arising from various unavoidable sources such as chemical reactions or optical distortions are shown to be the main difficulties in applying the sessile drop technique at high temperature. This suggests a limiting spatial resolution of the digitizer beyond which no further improvements to the accuracy of the surface tension results are possible.The technique has been applied to determine the surface tension of liquid Cu, Bi and Ag as well as a series of sodium borosilicate glasses.

Apparatus for the Determination of Surface Tension

A semiautomatic apparatus for the determination of surface and interfacial tensions by the drop volume method is described. Using this apparatus it is possible to form drops in different ways: with constant or changed speed, very slowly or quickly. The interfacial tensions measured are in agreement with literature values and with surface tensions determined on a stable drop

The suitability of nichrome for measurement of gas-liquid interfacial tension by the wilhelmy method

Determination of surface tension by the Wilhelmy method is facilitated by having a zero contact angle between the Wilhelmy plate and the liquid phase. Compared to filter paper or platinum, nichrome was shown to exhibit minimal hysteresis between advancing and receding contact angles under several experimental conditions. Calibration with a series of solvents of known surface tension indicates that the receding contact angle is zero. Comparison of equilibrium spreading pressures for several lipids measured by the Wilhelmy and Langmuir methods showed proportionality with a slope near 1.0. Thus, nichrome is superior to other commonly used materials for measurements of surface tension at the gas-liquid interface.