Drop Surface Tension Research Articles

Development of a new methodology to study drop shape and surface tension in electric fields.

Development of a new methodology for the study of both shape and surface tension of conducting drops in an electric field is presented. This methodology, called axisymmetric drop shape analysis-electric fields (ADSA-EF), generates numerical drop profiles in an electrostatic field, for a given surface tension. Then, it calculates the true value of the surface tension by matching theoretical profiles to the shape of experimental drops, using the surface tension as an adjustable parameter. ADSA-EF can be employed to simulate and study drop shapes in the electric field and to determine its effect on liquid surface tension. The method can also be used to measure surface tension in microgravity, where current drop-shape techniques are not applicable. The axisymmetric shape of the drop is the only assumption made in the development of ADSA-EF. The new scheme is applicable when both gravity and electrostatic forces are present. Preliminary measurements using ADSA-EF suggest that the surface tension of water increases by about 2% when an electric field with the magnitude of 10(6) V/m is applied.

Comparison of methods to detect biosurfactant production by diverse microorganisms

Three methods to detect biosurfactant production, drop collapse, oil spreading, and blood agar lysis, were compared for their ease of use and reliability in relation to the ability of the cultures to reduce surface tension. The three methods were used to test for biosurfactant production in 205 environmental strains with different phylogenetic affiliations. Surface tension of select strains that gave conflicting results with the above three methods was also measured. Sixteen percent of the strains that lysed blood agar tested negative for biosurfactant production with the other two methods and had little reduction in surface tension (values above 60 mN/m). Thirty eight percent of the strains that did not lyse blood agar tested positive for biosurfactant production with the other two methods and had surface tension values as low as 35 mN/m. There was a very strong, negative, linear correlation between the diameter of clear zone obtained with the oil spreading technique and surface tension ( r s=−0.959) and a weaker negative correlation between drop collapse method and surface tension ( r s=−0.82), suggesting that the oil spreading technique better predicted biosurfactant production than the drop collapse method. The use of the drop collapse method as a primary method to detect biosurfactant producers, followed by the determination of the biosurfactant concentration using the oil spreading technique, constitutes a quick and easy protocol to screen and quantify biosurfactant production. The large number of false negatives and positives obtained with the blood agar lysis method and its poor correlation to surface tension ( r s=−0.15) demonstrated that it is not a reliable method to detect biosurfactant production.

Two-dimensional simulation of drop deformation and breakup at around the critical Weber number

The breakup of two-dimensional liquid drops is numerically investigated at around the critical Weber number. The Moving Particle Semi-implicit (MPS) method is used to solve the unsteady Navier–Stokes equations for both the drops and the ambient fluid. The two dominant forces affecting drop breakup, pressure drag and surface tension force, are verified using the two benchmarks: pressure distribution on the surface of a cylinder in a uniform flow and oscillation of a square drop under surface tension force. The results show that the breakup process occurs in two stages. During the first stage, the drops become stretched and thinned normal to the flow direction of the ambient fluid. During the second stage, detached points appear on the surface of the drops, which are ascribed to the unstable growth of surface waves. The post-breakup topology of the drops is dependent on the value of the Weber number: the larger the Weber number is, the more detached points on the surface of the drops emerge. Another feature commonly shared in the two stages is that some fine fragmentations are stripped from the equatorial edges of the drops. The critical Weber number is predicted to be 13 for uranium dioxide drops in water, at which breakup regime is consistent with the so-called vibration regime.

Interaction decay of nonionic surfactants at water surfaces

For large ether molecule surfactants with an alkane tail as the hydrophobic moiety and an ethylene oxide head (C 2H 4O) (POE) as the hydrophilic moiety, water surface tension drop in their presence is triggered by the attraction of water molecules to hydrophilic POE heads of surfactants at the air–water interface, which can be related to interactions between POE chains. It was found that interactions between POE chains decayed exponentially with respect to separation distance and increased with increase in POE chain length.

Copolymers at Interfaces

We discuss the adsorption of multiblock copolymers at the interface between two selective solvents of the constituent monomers. We consider two cases, namely when the blocks are regular, and when the copolymer is made of random sequences. In both cases, we discuss the various surface regimes, and we compare the properties of the layers. We find that the saturation concentration and the drop in surface tension are larger for the random case, except when selectivity and the number of sequences of the regular chain are both large.

Surface supercooling and stability of n-alkane films

The surface tension of n-octadecane was studied in the vicinity of the bulk melting point using both the maximum bubble pressure and Wilhelmy plate methods. The bubble surfaces were found to be supercooled below the surface freezing point. The onset of surface freezing is indicated by a sharp drop in surface tension at a constant temperature. This transition is accompanied by an increased film stability resulting in longer bubble lifetimes at the liquid surface. Variations in bubble lifetime reflect changes in the interfacial mechanical properties of the film from liquidlike to solidlike.

Implementation and examination of a new drop shape analysis algorithm to measure contact angle and surface tension from the diameters of two sessile drops

The performance of a new algorithm developed to measure contact angle and surface tension of sessile drops is examined. To calculate the contact angle and surface tension, the new algorithm (ADSA-TD) requires the radius (contact or equatorial) and volume of two sessile drops of different sizes that are placed on the same surface. Initially, the algorithm was tested using synthetic drops (synthetic or theoretical drops are produced by numerical integration of the Laplace equation). The radii and volumes of synthetic drops were used as ADSA-TD inputs. The calculated contact angle ( θ) and surface tension ( γ) by ADSA-TD matched perfectly the assumed values of θ and γ used to produce the synthetic drops, confirming theoretically the validity of the new algorithm. In the next step, the sensitivity of the algorithm to input errors was examined. It was shown experimentally that both calculated contact angle and surface tension are affected by the errors in volume and radius. Besides the error in input values, it was shown that the size difference between the paired drops and the differences in their contact angles would affect the output of ADSA-TD. As it turns out, the calculated surface tension is so sensitive to the above factors that ADSA-TD does not appear to be promising as a surface tension measurement technique. However, ADSA-TD produced acceptable contact angle values as compared to measurements made by other proven techniques such as axisymmetric drop shape analysis-profile. Thus, ADSA-TD may be of interest as a contact angle measurement technique which does not require the liquid surface tension as input.

Spreading Dynamics of Surfactant Solutions

The spreading behavior of microdrops of surfactant solutions at solid surfaces has been studied. The influence on the spreading of different factors, such as the drop lifetime prior to surface contact, surface tension dynamics, surface energy, and surfactant properties, was systematically investigated. The results obtained suggest the existence of two spreading regimes exhibiting different spreading characteristics: In the first, nondiffusive regime, the spreading is very rapid and controlled to different extents by inertia, gravity, and capillarity, depending on the drop size, impact energy, and interfacial tension balance. It is shown in this study that the initial drop surface tension, which is set by the surface tension decay rate and the drop lifetime prior to the surface impact, strongly influences the maximum spreading distance in the nondiffusive spreading regime. The second, diffusion-controlled regime, is characterized by slower concentration-dependent spreading rates. The spreading rate is, here, mainly controlled by the diffusive transport of surfactant to the expanding liquid−vapor interface. In this regime, the drop base radius exhibits an approximate rb2 ∝ t dependence on time. The spreading kinetics at hydrophobic surfaces has been discussed in the framework of a simplified theory. Depending on the assumptions regarding the drop shape, rb5/2 ∝ t to rb2 ∝ t spreading laws are obtained. This agrees reasonably with the experimentally observed relationship.

How a fungus escapes the water to grow into the air

Fungi are well known to the casual observer for producing water-repelling aerial moulds and elaborate fruiting bodies such as mushrooms and polypores. Filamentous fungi colonize moist substrates (such as wood) and have to breach the water–air interface to grow into the air. Animals and plants breach this interface by mechanical force. Here, we show that a filamentous fungus such as Schizophyllum commune first has to reduce the water surface tension before its hyphae can escape the aqueous phase to form aerial structures such as aerial hyphae or fruiting bodies. The large drop in surface tension (from 72 to 24 mJ m−2) results from self-assembly of a secreted hydrophobin (SC3) into a stable amphipathic protein film at the water-air interface. Other, but not all, surface-active molecules (that is, other class I hydrophobins and streptofactin from Streptomyces tendae) can substitute for SC3 in the medium. This demonstrates that hydrophobins not only have a function at the hyphal surface but also at the medium–air interface, which explains why fungi secrete large amounts of hydrophobin into their aqueous surroundings.

In situ optical measurement of liquid drop surface tension in gas metal arc welding

The surface tension of detached liquid drops in pulsed gas metal arc welding was determined in situ from the period of the prolate-oblate oscillations initiated by the detachment event. The oscillating drops were imaged by an optical shadowgraph technique utilizing laser illumination. Images obtained during the welding process were recorded with a high-speed video camera and stored for subsequent analysis. For 4047 aluminium alloy wire, surface tension values in the range 0.54-0.7 were obtained for various droplet sizes.

The dependence of the surface tension of surfactant solutions on drop size

It is shown that when the surface area of a surfactant solution is greatly extended by creating a dispersion of small particles (e.g., drops), the surface tension of the solution of which the particles consist depends on the particle size. This stems from the fact that the amount of surfactant in each particle is finite. Consequently, the distribution of surfactant between the bulk and the interface of a small particle is different from its distribution in the original solution. Calculations for SDS solutions demonstrate that the surface tension of drops appreciably deviates from that of the original solution for drops smaller than about 10 μm in radius. This size range coincides with that typical of aerosols and emulsions. For surfactants of higher surface activity, the effect of size on the surface tension is appreciable even for much larger drops.

Surface tension effects of heparin coating on arterial line filters.

An investigation was conducted to determine the effects that heparin-coated screen arterial line filters have on the surface tension of cardiopulmonary bypass (CPB) priming solution. Five brands of non-heparin coated arterial line filters (Bard H625, Bentley AF1040, Intersept 40mum, Pall EC3840 and Pall SP3840) and four brands of heparin-coated filters (Bard H640, Bentley AF1040C and AF1040D and Intersept 40mum) were tested in a closed-loop circuit containing two litres of Plasma-Lyte A and pumped at a rate of five litres per minute. Samples were collected at 0.5, 20, 60 and 120 minutes to determine the surface tension of the recirculated solution. The non-heparin coated arterial line filters showed no significant changes in surface tension, either between the individual groups or over time. The benzalkonium-heparin coated filters (Bard H640, Bentley AF1040C and Intersept 40mum) all showed significant decreases in surface tension when compared to zero circulation time or to the noncoated groups. The largest drop in surface tension occurred within the first five minutes of recirculation. The circuit with a Bentley AF 1040D (a new nonbenzalkonium process) coated filter showed no significant change in surface tension.

Surface tension and contact angles of molten cadmium telluride

The surface tension and contact angle of molten cadmium telluride (CdTe) were measured as a function of temperature by the sessile drop technique. A FORTRAN code was developed to calculate the surface tension of sessile drops, with the contact angle ranging from O to 180°. The wetting of cadmium telluride melt was studied on different surfaces. The surface tension of cadmium telluride was about 160 ±5 dynes · cm−1[1.6 m−1] at the melting point of 1093°C. The contact angle of CdTe melt was about 65° on a quartz optical flat, 75° on commercial fused quartz, and 125° on boron nitride coated quartz.

A theoretical and experimental study on the oscillation of a hanging drop.

The damping oscillation of a hanging drop on a nozzle in the air was studied theoretically and experimentally. In the experiments, an elongated drop on a brass nozzle by electrostatic force was made to oscillate by removing the electric field instantaneously and the subsequent drop motion was recorded by a high-speed camera. In the theoretical study, the time-dependent drop shape and flow inside the drop were simulated numerically by use of the finite element method. It was found that the experimental results of oscillatory behavior for a hanging drop of aqueous glycerin solution were in good agreement with the calculated ones and that the frequency of oscillation was affected by drop volume, surface tension and nozzle size.

Niels Bohr

October seventh marks the hundredth anniversary of the birth of Niels Bohr. Bohr achieved international stature when he devised the first quantum model of the atom in 1913. He went on to contribute greatly to the emergence of the “new” quantum theory as it was developed in the late 1920s, generating ideas and theories, and providing much of the philosophical framework for the quantum theory as we now understand it. Later, he invented the liquid-drop model of the nucleus (perhaps reflecting his earliest interests in the surface tension of drops in a jet), and worked on the theory of nuclear fission. Bohr also created in Copenhagen an institute—initially for theoretical physics, but later expanded—to which many of the best young physicists flocked, and where they hammered out the answers to many pressing problems in physics. Bohr was always in the forefront, probing, questioning, reflecting, but above all, discussing physics with his guests.

High-temperature containerless calorimeter

A high-temperature (> 1500 K) containerless calorimeter is described and its usefulness demonstrated. The calorimeter uses the technique of omnidirectional electron bombardment of pendant drops to achieve an isothermal test environment. The small heat input into the sample (i.e., 15–50 W) can be controlled and measured. The apparatus can be used to determine the total hemispherical emissivity, specific heat, heat of fusion, surface tension, and equilibrium melting temperature of small molten drops in the temperature range of 1500 to 3500 K. The total hemispherical emissivity εT and specific heat Cp of pure niobium and two alloys of niobium–germanium have been measured in the temperature range of 1700 to 2400 K. As reported in the literature, εT varied as a function of temperature. However, Cp values for both the pure metal and alloys seem to be independent of temperature. Cp for the liquid alloy phase was also measured and compared to the solid phase.

Development of New Surfactant from Renewable Resources

With a view to develop an industrially viable and economically feasible process for the preparation of non-toxic, completely and easily biodegradable surface active agents, derived entirely from renewable resources of the country, a long range study has been undertaken in our laboratory. The title compounds have been prepared by the transesterification reaction between fatty acid esters and sucrose. The products obtained have been purified and tested for their performance as surface active agents. The different surface active properties determined are detergency, surface tension, foaming, wetting and emulsification. The present work shows that some of the compounds are as active as the standard compounds like sodium lauryl sulfate and sodium dodecyl benzene sulphonate. Most of these compounds exhibit large drop in surface tension. The cmc obtained by the surface tension versus log concentration curves is found to be in the range of 0.02 to .07 per cent. These compounds are very good detergents and emulsifiers with a moderate wetting property.

On the surface tension of liquid drops

Curvature corrections to the surface tension of spherical fluid-vapour interfaces are studied. A continuum Landau-Ginzburg free energy functional is used to derive a closed-form expression for δ, the first curvature correction to the surface tension of a liquid drop. In this model, capillary wave-like fluctuations produce the only non-zero contribution to δ. It is found that δ is positive and diverges as the correlation length near a critical point.

Physical chemical properties of solutions of bis‐quaternary ammonium bromides

AbstractThe physical chemical properties of a series of bisalkyldimethyldi‐ammonium polyoxyethylene bromides were studied by measuring the critical micelle concentrations as function of their molecular structure. The conductivity vs. concentration plots revealed the existence of two distinct discontinuities which were labeled CMC1 and CMC2. The CMC1 was always lower than the CMC2. The conventional surface tension vs. log concentration curve showed the classical sharp break which coincided with either the CMC1 or the CMC2, but failed to reveal the presence of both critical micelle concentrations in the same experiment. The existence of two CMC2 was attributed to the presence of the two charges localized in separated atoms. The CMC1 and CMC2 appear to follow an expression of the type CMC=A —Bn, where A and B are constants and n the number of carbon atoms present in the hydrocarbon long chain attached to the quaternary ammonium nitrogen. The CMCs appear to increase with the increasing number of oxyethylene residues up to a certain length of the polyoxyethylene chain. For most compounds there was a substantial drop in surface tension with the increasing concentration of the salt. However, some compounds containing only one oxyethylene residue showed practically no surface tension dependence on concentration although the critical micelle concentrations were apparent in the conductivity vs. concentration curve. The energy to transfer one methylene group from the aqueous to the micellar phase was found to vary from −0.57 kT to −0.84 kT. The alkylene oxylated bisquaternary bromides studied appear to have unusual physical chemical properties.

The thermodynamic potential for homogeneous nucleation in a two-dimensional lattice gas

The Bethe or quasichemical approximation, is applied to the two-dimensional, triangular lattice gas in order to compute the probability of liquid drop formation in a supersaturated vapor. Comparison is made with the classical theory of homogeneous nucleation of Becker and Doring. The probability is of the form ρl exp(−Δψ/kT), where ρl is the density of bulk liquid (instead of the density of supersaturated vapor, which appears in the classical theory) and Δψ is a potential which approaches the classical form in the large drop limit. The potential for well-characterized, compact drops does not exist for sufficiently small drops, which we interpret to mean that such drops do not exist in the supersaturated vapor. When the limiting compact drop size is smaller than the classically predicted critical drop, the classical theory holds; however, in the opposite case large discrepancies occur. The error increases with increasing degree of supersaturation. Surface tensions were calculated in the large drop limit, showing a significant drop in surface tension with increasing supersaturation.