A method for estimating interfacial tensions and contact angles from sessile and pendant drop shapes

We report definitive evidence for an effective interfacial tension between two types of miscible fluids using spinning-drop tensiometry (SDT). Isobutyric acid (IBA) and water have an upper critical solution temperature (UCST) of 26.3 °C. We created a drop of the IBA-rich phase in the water-rich phase below the UCST and then increased the temperature above it. Long after the fluids have reached thermal equilibrium, the drop persists. By plotting the inverse of the drop radius cubed (r-3) vs the rotation rate squared (ω2), we confirmed that an interfacial tension exists and estimated its value. The transition between the miscible fluids remained sharp instead of becoming more diffuse, and the drop volume decreased with time. We observed droplet breakup via the Rayleigh−Tomotika instability above the UCST when the rotation rate was decreased by 80%, again demonstrating the existence of an effective interfacial tension. When pure IBA was injected into water above the UCST, drops formed inside the main drop ev...

Evidence for the Existence of an Effective Interfacial Tension between Miscible Fluids: Isobutyric Acid−Water and 1-Butanol−Water in a Spinning-Drop Tensiometer

We studied the interfacial tension between coexisting colloid-rich and polymer-rich fluid phases in a phase-separated colloid−polymer mixture. First, the location of the fluid−fluid binodal and the tie lines between the coexisting phases were determined using a recently proposed method that only requires the volumes of the coexisting phases as input. The spinning drop method was used to determine the very low interfacial tension between the coexisting phases. We also used the dynamics of the breakup process of the droplet of one phase suspended in the other to determine the interfacial tension.

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Measurement of the interfacial tension of a phase-separated colloid-polymer suspension

Interfacial tension of polyethyleneglycol-dextran-water systems: influence of temperature and polymer molecular weight

The spinning drop method was used to measure the interfacial tension of Athabasca bitumen in contact with an aqueous phase (D2O); variables included temperature, salinity, alkalinity, surfactant type (TRS 10–80, Suntech 5, sodium dodecyl sulfate), surfactant concentration, isopropyl alcohol concentration, bitumen drop size and age of interface. In the absence of surfactant, the bitumen/aqueous interfacial tension decreased with increasing temperature and salinity. Bitumen drops contacting alkaline medium exhibited interfacial tension minima below a pOH of three. In the presence of surfactant, the interfacial tension behavior was often complex. The interfacial tension-concentration plot for Suntech 5 surfactant exhibited two CMC type discontinuities. Low interfacial tension (<0.01 mN m−1) was observed only in the presence of added electrolyte. Interfacial tension values were sensitive to the age of surfactant preparation and volume ratio of the oleic-to-aqueous phases. The interfacial tension of the bitumen/brine-TRS 10–80 system increased upon addition of isopropyl alcohol. An increase in temperature required an increase in salinity to maintain a constant low interfacial tension. The experimental results are discussed in terms of changes in the structure of the amphiphile at the bitumen/aqueous interface.



On a employe la methode de la goutte tournante pour mesurer la tension interfaciale du bitume d'Athabasca en contact avec une phase aqueuse (D2O); les variables comprenaient: (a) la temperature, (b) la salinite, (c) l'alcalinite, le type d'agent tensio-actif (TRS-1080, Suntech 5, dodecyl sulfate de sodium), (d) concentration de l'agent tensio-actif, (e) concentration de l'alcool isopropylique, (f) dimension de la goutte de bitume et (g) ǎge de l'interface. En l'absence de l'agent tensio-actif, la tension interfaciale entre le bitume et l'eau diminue avec l'accroissement de la temperature et de la salinite. Les gouttes de bitume en contact avec un milieu alcalin presentent des minima de tension interfaciale pour un pOH inferieur a trois. En presence d'un agent tensio-actif, le comportement de la tension interfaciale s'est avere souvent complexe. Le graphique de la tension interfaciale en fonction de la concentration, dans le cas de l'agent tensio-actif Suntech 5, a presente deux discontinuites du type CMC. On a observee une tension interfaciale faible (<0.01 mN m−1) seulement en presence d'un electrolyte additionnel. Les valeurs de la tension interfaciale se sont averees sensibles a l'ǎge de la preparation de l'agent tensio-actif et au rapport en volume des phases huile et eau. La tension superficielle du systeme bitume/melange saumure-agent tensio-actif TRS-10-80 croǐt avec l'addition d'alcool isopropylique. Une elevation de la temperature implique une augmentation de la salinite pour une faible tension superficielle constante. On discute les resultats experimentaux en fonction des changements de structure de “l'amphiphile” a l'interface bitume-eau.

Interfacial tension behavior of athabasca bitumen/aqueous surfactant systems

Depending on operating speed, gyrostatic equilibrium is not approached closely enough for reliable tension measurement. Flow visualization experiments show that virtually rigid rotation gives way to secondary flows around the drop as spin velocity is decreased. Flows are attributable to a gravity‐induced, internal, hydrodynamic shear layer, to a misalignment‐induced Taylor column, to externally excited inertial oscillations, and to mass transfer effects. Bizarre shapes of ultralow tension drops are probably caused by these effects, which should be avoided by design or operation of the instrument. Relevant criteria are given.

L. E. Scriven

Papers

On interfacial tension measurement with a spinning drop in gyrostatic equilibrium